JP2002141283A - Semiconductor substrate, its producing method, semiconductor device and method for patterning - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the patterning accuracy in photolithography process at the time of fabricating a semiconductor device using a nitride semiconductor substrate. SOLUTION: On the rear surface of a substrate comprising a GaN layer 100, protrusions and recesses 100a having a level difference of 1/10 or more of the wavelength of exposing light and being used in photolithography process are provided. Since the exposing light entering from the surface of the substrate is diffuse reflected on the rear surface of the substrate, reflectance of the exposing light is lowered on the rear surface of the substrate and the intensity of reflected light is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor substrate used as a substrate for a blue light emitting diode or a blue semiconductor laser device, a method for manufacturing the same, a semiconductor device using the nitride semiconductor substrate, and a method for manufacturing the semiconductor device. And a method for forming a pattern.

[0002]

2. Description of the Related Art Conventionally, GaN (gallium nitride), InN
(Indium nitride), AlN (aluminum nitride) or a semiconductor device using a Group III nitride semiconductor composed of a mixed crystal thereof, such as a blue light emitting diode (blue LED) or a blue semiconductor laser device, is mostly on a sapphire substrate. Was formed.

In the process of manufacturing a semiconductor device using a nitride semiconductor, particularly in the process of manufacturing a semiconductor laser device or the like,
Even if an alignment error of about 1 μm does not pose a practical problem, the mercury lamp can be used without using an expensive KrF stepper (about one billion yen) used in a photolithography process for Si (silicon). Sufficient alignment accuracy can be ensured by an inexpensive exposure apparatus (about 10 million yen per unit) using g-line (wavelength 436 nm) or i-line (wavelength 365 nm).

[0004]

However, when a nitride semiconductor substrate is used as a substrate of a semiconductor device, when a semiconductor device is formed, particularly, a pattern is formed by an exposure apparatus using a g-line or an i-line of a mercury lamp. During formation, there has been a problem that the accuracy of the resist pattern in the photolithography process (hereinafter, referred to as pattern accuracy) is degraded, and the yield of semiconductor devices is significantly reduced.

In view of the above, it is an object of the present invention to improve the pattern accuracy in a photolithography process in manufacturing a semiconductor device using a nitride semiconductor substrate.

[0006]

Means for Solving the Problems To achieve the above-mentioned object, the present inventors have proposed a method of forming a pattern using g-line or i-line when a conventional nitride semiconductor substrate is used. The cause of the deterioration in accuracy was examined, and as a result, the following was found.

FIG. 23 shows a conventional nitride semiconductor substrate, specifically a substrate made of GaN (hereinafter referred to as a GaN substrate).
This shows a state in which exposure is performed on the resist film formed thereon.

As shown in FIG. 23, for example, an i-line is irradiated as exposure light 4 onto a resist film 2 on a GaN substrate 1 via a photomask 3 having an opening 3a. Incidentally, the wavelength of light that can be absorbed by the nitride semiconductor is short, for example, the wavelength of light that can be absorbed by GaN is 360 nm or less. Therefore, when g-line or i-line is used as the exposure light 4, the light passes through the resist film 2. The exposure light 4 incident on the surface of the GaN substrate 1, that is, the incident light 4, propagates through the GaN substrate 1 without being absorbed. As a result, the incident light 4
Is the emission light 5 emitted from the back surface of the GaN substrate 1 and G
It is divided into reflected light 6 generated by being reflected on the back surface of the aN substrate 1. When the back surface of the GaN substrate 1 is a mirror surface, the reflectance of the incident light 4 on the back surface of the GaN substrate 1, that is, the GaN substrate 1
The reflectance of the incident light 4 at the interface between air and air reaches about 20%.

Here, the region 2a in the resist film 2 is the region that should be originally exposed by the incident light 4, but the resist film 2 is exposed from the back side by the reflected light 6, so that the resist film 2 is originally exposed. The area 2b that should not be exposed is exposed. As a result, it was found that when a conventional nitride semiconductor substrate was used, defects such as peeling of the resist film 2 or reduction in the size of the resist pattern occurred and pattern formation was not performed normally.

When the thickness of the GaN substrate 1 is reduced and the incident light 4 is easily transmitted through the GaN substrate 1, the intensity of the reflected light 6 is increased, or when the intensity of the reflected light 6 is increased. The incident light 4 which has passed through the opening 3a when the aperture width is several times or less the wavelength of the incident light 4, that is, the exposure light
Is diffracted to the outside of the opening 3a, whereby the reflected light 6 spreads further outside (see FIG. 23) and the like. It has been found that the above-described problem of the deterioration of the pattern accuracy occurs more remarkably.

In this specification, reflection means regular reflection (incident angle = reflection angle) and reflectance means regular reflectance, and reflection other than regular reflection is called irregular reflection.
The substrate surface means a surface on which a nitride semiconductor layer is grown when a semiconductor device is manufactured using the nitride semiconductor substrate.

The present invention has been made based on the above findings. Specifically, the first semiconductor substrate according to the present invention comprises a semiconductor layer containing a group III nitride as a main component,
A scattering portion that scatters light incident on the semiconductor layer from one surface of the semiconductor layer is provided on another surface or inside the semiconductor layer.

[0013] According to the first semiconductor substrate, the scatterer which forms the substrate and scatters incident light from one surface of the semiconductor layer containing a group III nitride as a main component is formed on the other surface of the semiconductor layer or on the other surface. Since it is provided inside, it is possible to reduce the intensity of the reflected light generated when the incident light is reflected on another surface. For this reason, in a photolithography process for manufacturing a semiconductor device using the first semiconductor substrate, that is, a nitride semiconductor substrate, exposure light incident from one surface (hereinafter, sometimes referred to as a substrate surface) is irradiated with another light. It is possible to avoid a situation in which light is reflected on a surface (hereinafter, also referred to as the back surface of the substrate) and is exposed to a region of the resist film that should not be exposed. Therefore, the pattern accuracy in the photolithography process can be improved, so that the production yield of the nitride semiconductor device can be improved. For example, when the first semiconductor substrate is a GaN substrate, in particular, it is possible to reliably prevent reflection of the g-line or i-line of the mercury lamp on the back surface of the substrate. Since the pattern accuracy in the lithography process is significantly improved, the production yield of the nitride semiconductor device is significantly improved.

In the first semiconductor substrate, it is preferable that the scattering portion is provided with unevenness having a level difference of about 1/10 or more of the wavelength of incident light on the other surface of the semiconductor layer.

With this configuration, the incident light can be efficiently diffusely reflected, that is, scattered, on the other surface.
The reflectance of the incident light on the other surface can be reduced, and the intensity of the reflected light can be reliably reduced.

At this time, the reflectance of the incident light on the other surface of the semiconductor layer is preferably 13% or less.
The wavelength of the incident light is 365 nm (i-line) or 436 nm (g
Line).

In the first semiconductor substrate, the scattering portion is provided inside the semiconductor layer, and is provided for incident light.
It is preferable to include a grain or a layer made of a material having a different refractive index from the group III nitride.

With this configuration, the incident light can be efficiently scattered inside the semiconductor layer, so that the intensity of the reflected light can be surely reduced.

At this time, the diameter of the particles made of the above-mentioned material,
It is preferable that the width of the layer made of the above-mentioned material along a direction parallel to one surface or the thickness of the layer made of the above-mentioned material is about 1/10 or more of the wavelength of the incident light.
In addition, the particles or layers made of the above-described materials are provided along a direction parallel to one surface, the scattering portions are provided along a direction parallel to one surface, and III. It is preferable that another semiconductor layer containing a group nitride as a main component and the above-described grains or layers are alternately stacked. Further, the thickness of the scattering portion is preferably about 1/10 or more of the wavelength of the incident light. The above-mentioned materials are Si, SiO ₂ , SiN
Alternatively, it is preferably Al ₂ O ₃ . Further, the transmittance of the scattering portion for incident light is preferably 80% or less, and the wavelength of the incident light is preferably 365 nm or 436 nm.

A second semiconductor substrate according to the present invention comprises a semiconductor layer containing a group III nitride as a main component, and a transmitting portion for transmitting incident light incident on the semiconductor layer from one surface of the semiconductor layer is provided. On the other side.

According to the second semiconductor substrate, a transmission portion which constitutes the substrate and transmits incident light incident from one surface of the semiconductor layer containing a group III nitride as a main component is formed on the other surface of the semiconductor layer. Since it is provided, the reflectance of the incident light on the other surface can be reduced, so that the intensity of the reflected light generated when the incident light is reflected on the other surface can be reduced. Therefore, in a photolithography process for manufacturing a semiconductor device using a second semiconductor substrate, that is, a nitride semiconductor substrate, exposure light incident from one surface (substrate front surface) is reflected by another surface (substrate rear surface). As a result, it is possible to avoid a situation where a region of the resist film that should not be exposed is exposed. Therefore,
Since the pattern accuracy in the photolithography process can be improved, the production yield of the nitride semiconductor device can be improved. For example, if the second semiconductor substrate is GaN
In the case of a substrate, in particular, it is possible to reliably prevent reflection of the g-line or i-line of the mercury lamp on the back surface of the substrate, and as a result, the pattern accuracy in the photolithography process using the g-line or i-line as exposure light is remarkable. As a result, the production yield of the nitride semiconductor device is significantly improved.

In the second semiconductor substrate, it is preferable that the transmission portion is formed by forming a layer made of a material having a refractive index different from that of the group III nitride on the other surface of the semiconductor layer.

With this configuration, it is possible to reliably reduce the reflectance of the other surface with respect to the incident light.

At this time, the layers made of the above-mentioned materials are a plurality of layers, and it is preferable that at least two of the plurality of layers have different refractive indices with respect to incident light. Further, the refractive index of the above-mentioned material with respect to incident light is III
It is preferable that the refractive index of the group nitride with respect to the incident light is about 9/10 or less. The above-mentioned materials are SiO ₂ , S
iN or Al ₂ O ₃ or a semiconductor layer II
A compound of a group I element and oxygen, or Al _x Ga ₁ -xN
(However, it is preferable that 0 <x ≦ 1). When the above-mentioned material is a compound of a group III element and oxygen constituting the semiconductor layer, the process can be simplified as compared with the case where a film serving as a new transparent portion is formed on the back surface of the substrate, and impurities are not mixed into the substrate. And the like can be prevented, and the production yield of the substrate can be improved.

In the second semiconductor substrate, it is preferable that the transmittance of the transmission portion with respect to the incident light is 80% or more.

In this way, it is possible to reliably reduce the reflectance of the other surface with respect to the incident light. At this time, the wavelength of the incident light is preferably 365 nm or 436 nm.

It is preferable that the second semiconductor substrate further includes a scattering portion provided between the other surface of the semiconductor layer and the transmission portion or inside the semiconductor layer and for scattering incident light.

With this configuration, after the incident light is scattered by the scattering portion, the scattered incident light is transmitted by the transmission portion, so that the intensity of the reflected light can be further reduced.

A third semiconductor substrate according to the present invention comprises a semiconductor layer containing a Group III nitride as a main component, and has an absorbing portion for absorbing incident light incident on the semiconductor layer from one surface of the semiconductor layer. At least in part.

According to the third semiconductor substrate, at least a portion of the semiconductor layer is provided with an absorbing portion that constitutes the substrate and absorbs incident light incident from one surface of the semiconductor layer containing a group III nitride as a main component. As a result, the intensity of the reflected light generated when the incident light is reflected by another surface can be reduced. For this reason, in a photolithography process for manufacturing a semiconductor device using a third semiconductor substrate, that is, a nitride semiconductor substrate, exposure light incident from one surface (substrate front surface) is reflected by another surface (substrate rear surface). As a result, it is possible to avoid a situation where a region of the resist film that should not be exposed is exposed. Therefore, the pattern accuracy in the photolithography process can be improved, so that the production yield of the nitride semiconductor device can be improved. For example, when the third semiconductor substrate is a GaN substrate, in particular, it is possible to reliably prevent the reflection of the g-line or i-line of the mercury lamp on the back surface of the substrate. Since the pattern accuracy in the lithography process is significantly improved,
The production yield of the nitride semiconductor device is significantly improved.

In the third semiconductor substrate, it is preferable that the transmittance of the absorbing portion with respect to the incident light is 80% or less.

With this configuration, even when the back surface of the substrate is a mirror surface, the reflectance of incident light on the back surface of the substrate can be substantially reduced to about 13% or less, so that the pattern accuracy in the photolithography process can be ensured. Can be improved. At this time, the wavelength of the incident light is preferably 365 nm or 436 nm.

In the third semiconductor substrate, the absorbing portion is preferably made of a material having an absorption coefficient larger than that of the group III nitride for incident light.

With this configuration, since the incident light is surely absorbed by the absorbing portion, the intensity of the reflected light can be surely reduced. At this time, it is preferable that the above-mentioned material is a plurality of materials having mutually different absorption coefficients for incident light, or contains at least one of Si and W.

In the third semiconductor substrate, it is preferable that the absorbing portion is formed by adding an impurity to the semiconductor layer so as to generate a level for absorbing incident light.

With this arrangement, since the incident light is reliably absorbed by the absorbing portion, the intensity of the reflected light can be reliably reduced, and the lowering of the crystallinity of the third semiconductor substrate, ie, the nitride semiconductor substrate can be prevented. . At this time, the impurities preferably include at least one of C, O, Si, S, Cl, P, and As. Further, when the absorption coefficient of the absorbing portion with respect to the incident light is α and the thickness of the absorbing portion is z0, it is preferable that the relationship z0 ≧ 0.223 / α holds.

In the third semiconductor substrate, it is preferable that the absorbing portion has a point defect formed in the semiconductor layer.

With this configuration, the incident light is reliably absorbed by the absorbing portion, so that the intensity of the reflected light can be reliably reduced, and a decrease in the crystallinity of the third semiconductor substrate, that is, the nitride semiconductor substrate can be prevented. . At this time, it is preferable that the point defect is formed by introducing protons into the semiconductor layer.

[0039] In the third semiconductor substrate, it is preferable that the absorbing portions are unevenly distributed along a direction parallel to one surface of the semiconductor layer.

In this case, not only the incident light is absorbed by the absorbing portion but also the incident light is scattered by the absorbing portion, so that the intensity of the reflected light can be further reduced. In the case of manufacturing a ridge-type laser device using a semiconductor substrate, for example, a photolithography process is performed without deteriorating the characteristics of the active layer on the substrate by not providing an absorption section below the ridge structure in the semiconductor substrate. And the effect of improving the pattern accuracy can be obtained.

According to the first method of manufacturing a semiconductor substrate of the present invention, a method of manufacturing a semiconductor device having a light refractive index different from that of a group III nitride on a first semiconductor layer containing a group III nitride as a main component. Partially forming a scattering portion, and crystal-growing a second semiconductor layer containing a group III nitride as a main component on the first semiconductor layer including the light scattering portion, thereby forming the first semiconductor layer. Forming a semiconductor substrate composed of a layer, a light scattering portion, and a second semiconductor layer.

According to the first method for manufacturing a semiconductor substrate, a light scattering portion is formed between the first semiconductor layer and the second semiconductor layer constituting the semiconductor substrate. , The intensity of the reflected light can be reduced. Therefore, in a photolithography process for manufacturing a nitride semiconductor device using this semiconductor substrate, it is possible to avoid a situation in which a region of the resist film that should not be exposed is exposed, thereby improving pattern accuracy. Therefore, the production yield of the nitride semiconductor device can be improved.

According to the first method of manufacturing a semiconductor substrate, a material having a refractive index different from that of the first semiconductor layer, that is, a light scattering portion made of a material different from that of the first semiconductor layer is partially formed. Since the second semiconductor layer is crystal-grown on the first semiconductor layer including the light scattering portion, light scattering is performed such that defects or the like generated in the first semiconductor layer are inherited by the second semiconductor layer. Part. Therefore, the crystallinity of the second semiconductor layer can be improved, so that the crystallinity of the semiconductor substrate having the light scattering portion can be improved.

In the first method for manufacturing a semiconductor substrate, the step of partially forming the light scattering portion includes the steps of forming a film to be a light scattering portion over the entire surface of the semiconductor layer; Forming a light scattering portion by partially forming a mask pattern and etching the film using the mask pattern to remove a portion of the film not covered by the mask pattern; and And removing the pattern.

In this manner, the light scattering portion formed partially on the first semiconductor layer can be realized reliably.

In the second method of manufacturing a semiconductor substrate according to the present invention, a step of forming irregularities having a step larger than a predetermined value on a back surface of a semiconductor layer containing a Group III nitride as a main component;
Forming a buried film made of a material having a different optical refractive index from the group III nitride on the back surface of the semiconductor layer having the unevenness, thereby forming a semiconductor substrate composed of the semiconductor layer and the buried film. Have.

According to the second method for manufacturing a semiconductor substrate, irregularities serving as light scattering portions are formed on the back surface of the semiconductor layer constituting the semiconductor substrate, that is, on the interface between the semiconductor layer and the buried film. After that, the intensity of light reflected on the back surface of the substrate, that is, the intensity of the reflected light can be reduced. Therefore, in a photolithography process for manufacturing a nitride semiconductor device using this semiconductor substrate, it is possible to avoid a situation in which a region of the resist film that should not be exposed is exposed, thereby improving pattern accuracy. Therefore, the production yield of the nitride semiconductor device can be improved.

In addition, according to the second method for manufacturing a semiconductor substrate, the back surface of the semiconductor layer which has been roughened by providing irregularities can be flattened by the buried film, so that the back surface of the substrate is flattened. Thereby, the manufacturing process of the semiconductor device can be simplified.

Further, according to the second method for manufacturing a semiconductor substrate, when another semiconductor layer mainly containing a group III nitride is to be crystal-grown as a buried film, it is formed on a convex portion of the unevenness. Since the crystallinity of the other semiconductor layer to be formed can be improved, the crystallinity of the semiconductor substrate having the light scattering portion can be improved.

According to a third method of manufacturing a semiconductor substrate of the present invention, a material having a larger light absorption coefficient than a group III nitride is formed on a first semiconductor layer containing a group III nitride as a main component. Forming a light absorbing portion partially, and crystal-growing a second semiconductor layer containing Group III nitride as a main component on the first semiconductor layer including the light absorbing portion.
Forming a semiconductor substrate composed of the semiconductor layer, the light absorbing portion, and the second semiconductor layer.

According to the third method for manufacturing a semiconductor substrate, a light absorbing portion is formed between the first semiconductor layer and the second semiconductor layer constituting the semiconductor substrate. , The intensity of the reflected light can be reduced. Therefore, in a photolithography process for manufacturing a nitride semiconductor device using this semiconductor substrate, it is possible to avoid a situation in which a region of the resist film that should not be exposed is exposed, thereby improving pattern accuracy. Therefore, the production yield of the nitride semiconductor device can be improved.

According to the third method of manufacturing a semiconductor substrate, a material having an absorption coefficient different from that of the first semiconductor layer, that is, a light absorbing portion made of a material different from that of the first semiconductor layer is partially formed. Since the second semiconductor layer is crystal-grown on the first semiconductor layer including the light-absorbing portion, light absorption that defects and the like generated in the first semiconductor layer are inherited by the second semiconductor layer is considered. Part. Accordingly, since the crystallinity of the second semiconductor layer can be improved, the crystallinity of the semiconductor substrate having the light absorbing portion can be improved.

According to the fourth method of manufacturing a semiconductor substrate of the present invention, a light absorbing portion is formed by injecting impurities into a semiconductor layer containing a group III nitride as a main component to generate a level for absorbing light. Forming a semiconductor substrate composed of a semiconductor layer and a light absorbing portion.

According to the fourth method for manufacturing a semiconductor substrate, since a light absorbing portion is formed in a semiconductor layer constituting the semiconductor substrate, light incident on the surface of the substrate and then reflected on the back surface of the substrate,
That is, the intensity of the reflected light can be reduced. Therefore, in a photolithography process for manufacturing a nitride semiconductor device using this semiconductor substrate, it is possible to avoid a situation in which a region of the resist film that should not be exposed is exposed, thereby improving pattern accuracy. Therefore, the production yield of the nitride semiconductor device can be improved.

According to the fourth method of manufacturing a semiconductor substrate, since a light absorbing portion is formed by injecting impurities into a semiconductor layer serving as a substrate, a decrease in crystallinity of a semiconductor substrate having a light absorbing portion can be prevented. .

In the fourth method of manufacturing a semiconductor substrate, the step of forming a light absorbing portion includes forming a mask pattern partially on the semiconductor layer, and using the mask pattern to add impurities to the semiconductor layer. It is preferable to include a step of partially forming a light absorbing portion in the semiconductor layer by implantation and a step of removing the mask pattern.

In this way, a light absorbing portion formed partially on the semiconductor layer can be reliably realized. In the case of manufacturing a ridge-type laser device using a semiconductor substrate, for example, the photolithography can be performed without deteriorating the characteristics of the active layer on the semiconductor substrate by not providing an absorption section below the ridge structure in the semiconductor substrate. The effect of improving the pattern accuracy in the process can be obtained.

In the first semiconductor device according to the present invention, a scattering portion for scattering light incident from one surface is provided on another surface or inside, and a semiconductor substrate mainly containing a group III nitride is provided. And a structure formed on one surface of a semiconductor substrate by using photolithography and etching for a semiconductor layer made of a group III nitride.

According to the first semiconductor device, since the semiconductor device uses the first semiconductor substrate according to the present invention, unnecessary exposure of the resist film does not occur in the photolithography process. Therefore, the dimensional accuracy of the structure formed on the substrate can be improved, so that the production yield of the semiconductor device can be improved.

A second semiconductor device according to the present invention is characterized in that a transmission portion for transmitting light incident from one surface is provided on another surface, and a semiconductor substrate mainly containing a group III nitride;
A structure formed on one surface of a semiconductor substrate by using photolithography and etching on a semiconductor layer made of a group III nitride.

According to the second semiconductor device, since the semiconductor device uses the second semiconductor substrate according to the present invention, unnecessary exposure of the resist film does not occur in the photolithography process. Therefore, the dimensional accuracy of the structure formed on the substrate can be improved, so that the production yield of the semiconductor device can be improved.

A third semiconductor device according to the present invention is provided with a semiconductor substrate having a group III nitride as a main component, wherein at least a portion for absorbing light incident from one surface is provided; A structure formed on one surface of the semiconductor substrate by using photolithography and etching for the semiconductor layer made of nitride.

According to the third semiconductor device, since the semiconductor device uses the third semiconductor substrate according to the present invention, unnecessary photosensitization does not occur in the resist film in the photolithography process. Therefore, the dimensional accuracy of the structure formed on the substrate can be improved, so that the production yield of the semiconductor device can be improved.

In any one of the first to third semiconductor devices, the above structure may have a ridge structure or a groove structure.

In the third semiconductor device, it is preferable that the above-described structure has a ridge structure, and that no absorption portion is provided below the ridge structure in the semiconductor substrate. In this case, the effect of improving the pattern accuracy in the photolithography process can be obtained without deteriorating the characteristics of the active layer on the substrate.

The first pattern forming method according to the present invention comprises:
A scattering portion for scattering light incident from one surface is provided on another surface or inside, and a semiconductor made of a group III nitride is provided on one surface of a semiconductor substrate containing a group III nitride as a main component. Forming a layer, forming a positive or negative resist film on the semiconductor layer, irradiating the resist film with exposure light through a photomask having openings, and developing the resist film. When the resist film is a positive type, the portion of the resist film irradiated with the exposure light is removed, and when the resist film is a negative type, the portion of the resist film which is not irradiated with the exposure light is removed. And a step of forming a resist pattern thereby, and a step of etching the semiconductor layer using the resist pattern as a mask.

According to the first pattern forming method, since it is a pattern forming method for manufacturing a semiconductor device using the first semiconductor substrate according to the present invention, even a region of the resist film which should not be exposed to light is required. Exposure can be avoided. For this reason, the precision of the resist pattern can be improved, so that the production yield of the semiconductor device can be improved.

The second pattern forming method according to the present invention comprises:
A transmission part for transmitting light incident from one surface is provided on the other surface, and a semiconductor layer made of a group III nitride is formed on one surface of the semiconductor substrate containing a group III nitride as a main component. Forming, and forming a positive or negative resist film on the semiconductor layer, and irradiating the resist film with exposure light through a photomask having an opening,
By developing the resist film, the exposed portion of the resist film was exposed to light when the resist film was positive, and the resist film was not exposed to light when the resist film was negative. The method includes a step of removing a portion to form a resist pattern thereby, and a step of etching the semiconductor layer using the resist pattern as a mask.

According to the second pattern forming method, since it is a pattern forming method for manufacturing a semiconductor device using the second semiconductor substrate according to the present invention, even a region which should not be exposed to light in the resist film Exposure can be avoided. For this reason, the precision of the resist pattern can be improved, so that the production yield of the semiconductor device can be improved.

The third pattern forming method according to the present invention comprises:
A semiconductor layer made of a group III nitride is formed on one surface of a semiconductor substrate containing a group III nitride as a main component, wherein an absorption part for absorbing light incident from one surface is provided at least in part. And forming a positive or negative resist film on the semiconductor layer, irradiating the resist film with exposure light through a photomask having an opening, and developing the resist film. If the resist film is of a positive type, the portion of the resist film irradiated with the exposure light is removed, and if the resist film is of the negative type, the portion of the resist film which is not irradiated with the exposure light is removed. The method includes a step of forming a resist pattern and a step of etching the semiconductor layer using the resist pattern as a mask.

According to the third pattern forming method, since it is a pattern forming method for manufacturing a semiconductor device using the third semiconductor substrate according to the present invention, even a region of the resist film which should not be exposed to light is used. Exposure can be avoided. For this reason, the precision of the resist pattern can be improved, so that the production yield of the semiconductor device can be improved.

[0072]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A semiconductor substrate according to a first embodiment, a method for manufacturing the same, and a pattern forming method for manufacturing a semiconductor device using the semiconductor substrate will be described with reference to the drawings. It will be described with reference to FIG.

FIG. 1 is a sectional view of a semiconductor substrate according to the first embodiment.

As shown in FIG. 1, the semiconductor substrate according to the first embodiment includes a group III nitride semiconductor layer, specifically, Ga
It is composed of an N layer 100. In addition, the GaN layer 100 (hereinafter, G
The surface of the (aN substrate 100) is (000
1) The Ga surface, and the back surface of the GaN substrate 100 is (000)
1) The N-plane and the thickness of the GaN substrate 100 is, for example, 20
0 μm.

The feature of the first embodiment is that the GaN substrate 10
0 is a rough surface having irregularities 100a. Here, assuming that the wavelength of exposure light used in a photolithography process for manufacturing a semiconductor device using the GaN substrate 100 is λ, the unevenness 100a preferably has a step of about λ / 10 or more.

FIGS. 2A to 2E are cross-sectional views showing each step of the method for manufacturing the semiconductor substrate according to the first embodiment shown in FIG.

First, as shown in FIG.
A silicon-on-sapphire substrate (hereinafter, referred to as an SOS substrate) including a 0 μm sapphire substrate 101 and a 80 μm thick silicon substrate 102 is prepared.

Next, MOVPE (metal organi) using trimethylaluminum and ammonia as source gases
c vapor phase epitaxy), as shown in FIG. 2B, an AlN layer 103 is formed on a silicon substrate 102 of the SOS substrate at a temperature of 1000 ° C. to a thickness of 200 nm.
Grow thickness.

FIG. 3 shows an example of a MOVPE apparatus used in the method for manufacturing a semiconductor substrate according to the first embodiment. As shown in FIG. 3, the MOVPE apparatus includes a reaction tube 150 made of quartz or stainless steel, and a reaction tube 15.
Susceptor 1 on which substrate 151 to be processed is placed
52 and a heating means 153 for heating the substrate 151 via the susceptor 152 in the reaction tube 150. The reaction tube 150 has a gas inlet 150a through which the raw material gas and the carrier gas are introduced, and a gas outlet 150b through which the used gas is exhausted. The susceptor 152 is made of, for example, graphite. Heating means 15
As 3, a resistance wire heater (resistance heater) or a lamp heater is used.

In the growth of the group III nitride semiconductor layer by the MOVPE method, the growth of the group III element surface is dominant because the growth rate of the group III element surface is high. Therefore, in the step of forming the AlN layer 103 shown in FIG.
3 is the Al surface, while the back surface of the AlN layer 103 is
That is, the surface of the AlN layer 103 on the silicon substrate 102 side is N
Surface.

Next, gallium chloride obtained by reacting HCl gas and Ga at a temperature of 800 ° C., and HVPE (hydrid) using ammonia as a source gas.
As shown in FIG. 2C, a GaN layer 100 is grown to a thickness of 250 μm on the AlN layer 103 at a temperature of 1000 ° C. by using an evapor phase epitaxy method. At this time, since the surface of the AlN layer 103 is an Al surface, Ga
The surface of the N layer 100 on the AlN layer 103 side, that is, the GaN layer 10
0 is the N-plane, while the surface of the GaN layer 100 is the G-plane.
The surface is a. In addition, since the GaN layer 100 is formed on the SOS substrate including the sapphire substrate 101 and the silicon substrate 102, the sapphire substrate 101 applies a compressive stress to the GaN layer 100 and the silicon substrate 102
Since the tensile stress given to zero is balanced, the thick GaN layer 100 can be grown without generating cracks.

FIG. 4 shows an example of an HVPE apparatus used in the method for manufacturing a semiconductor substrate according to the first embodiment. As shown in FIG. 4, the HVPE apparatus includes a reaction tube 160 made of quartz or the like, a susceptor 162 in which a substrate 161 to be processed is placed in the reaction tube 160, and a reaction tube 16.
Ga1 in molten state reacted with HCl gas in
A dish 164 in which 63 is placed and a heating means 165 for heating the inside of the reaction tube 160 from outside the reaction tube 160 are provided. The reaction tube 160 has a first gas inlet 160a into which ammonia gas and carrier gas are introduced, and a second gas inlet 160 into which HCl gas and carrier gas are introduced.
b and a gas outlet 160c from which used gas is exhausted
And The susceptor 162 is made of, for example, graphite or quartz, and the dish 164 is made of, for example, quartz. As the heating means 165, a tubular resistance wire heater or the like is used.

Next, as shown in FIG. 2D, the silicon substrate 10 was treated by using a mixed solution of hydrofluoric acid and nitric acid.
By removing only 2 sapphire substrate 101
And a GaN layer 100, ie, Ga
The N substrate 100 is separated. Here, the GaN substrate 100
Of the GaN substrate 10
The AlN layer 103 is formed on the back surface of the “0”.

Next, as shown in FIG. 2E, the back surface of the GaN substrate 100 is ground to form the AlN layer 103.
Is removed, and unevenness 10 is formed on the back surface of the GaN substrate 100.
0a is formed to roughen the back surface. Here, the method of roughening the back surface of the GaN substrate 100 is not particularly limited. For example, the back surface of the GaN substrate 100 is polished using an abrasive having a particle size of 10 to 50 μm.
The back surface of N substrate 100 can be roughened. Specifically, in the first embodiment, the thickness of the GaN substrate 100 is reduced until the thickness of the GaN substrate 100 finally becomes about 200 μm.
By polishing the back surface of No. 00, the semiconductor substrate according to the first embodiment shown in FIG. 1 was obtained.

FIG. 5 shows how the resist film formed on the semiconductor substrate, that is, the GaN substrate 100 according to the first embodiment shown in FIG. 1 is exposed.

As shown in FIG. 5, the resist film 171 on the GaN substrate 100 is irradiated with, for example, g-line as exposure light 173 through a photomask 172 having an opening 172a. At this time, the exposure light 173 transmitted through the resist film 171 and incident on the surface of the GaN substrate 100 (hereinafter, also referred to as the substrate surface), that is, the incident light 1
Reference numeral 73 is divided into outgoing light 174 emitted from the back surface of the GaN substrate 100 (hereinafter, also referred to as the back surface of the substrate) and reflected light 175 generated by irregular reflection by the unevenness 100a on the back surface of the substrate. The region 171a in the resist film 171 is a region that should be originally exposed by the incident light 173. As the exposure device, for example, a contact aligner using a g-line of a mercury lamp as a light source is used.

The present inventors formed a resist film on a GaN substrate having various back surfaces including the semiconductor substrate according to the first embodiment, and then exposed the resist film. A resist pattern was formed by developing the resist film, and its appearance was examined. Hereinafter, the results will be described with reference to FIG.

FIG. 6 shows that the width of the line portion and the space portion is 2
μm line and space resist pattern
The graph shows the relationship between the reflectance of the exposure light (g-line) on the back surface of the substrate and the non-defective appearance ratio of the resist pattern forming the line portion when formed on an aN substrate.

Here, “good appearance” means that the width of the resist pattern is in the range of 2 ± 0.2 μm.
Further, the reflectance of exposure light on the back surface of the substrate (hereinafter, referred to as back surface reflectance) is changed by changing the particle size or polishing time of the abrasive in polishing for roughening the back surface. . Note that the back surface reflectivity is defined as the output angle of 90 ° (approximately 90 °) from the substrate surface after being reflected on the back surface of the substrate with respect to the intensity of incident light incident on the substrate surface at an incident angle of 90 ° (including approximately 90 °). (Including measured values) of the intensities of the reflected light emitted in the above-described manner. For example, in the case where the back surface of the GaN substrate is a very flat surface in which steps on the order of an atomic layer can be seen with an atomic force microscope, the back surface reflectance is about 21%. Such a very flat surface can be formed using a very fine abrasive having a particle size of less than 1 μm.
It is obtained by polishing the back surface of the aN substrate and then heating the back surface to about 1000 ° C. in an ammonia atmosphere.

As shown in FIG. 6, when the back surface reflectance is 16% or more, since the resist film is exposed from the back side by the reflected light having a high intensity, the resist film is peeled off or the size of the resist pattern is reduced. As a result, the appearance non-defective rate decreases. On the other hand, as the backside reflectance decreases, the appearance goodness rate increases, and when the backside reflectance becomes 13% or less, the appearance goodness rate becomes almost 100%. That is,
When the back surface reflectance becomes 13% or less, a desired resist pattern can be formed with a yield of almost 100%.

Hereinafter, the reason why the result shown in FIG. 6 is obtained will be described. When the back surface of the GaN substrate is a mirror surface, the back surface reflectance is as high as about 20% or more as described above (see “Means for Solving the Problems” or FIG. 23), so that the reflection from the back surface of the substrate generated during exposure is large. Since the light exposes the resist film from the back side, defects such as peeling of the resist film or reduction in the size of the resist pattern occur. In particular, when the width of the opening of the photomask is about several times or less the wavelength of the exposure light, the reflected light slightly spreads outside the opening due to the diffraction of the exposure light in the photomask, so that the resist film is originally exposed. Areas that should not be exposed are more likely to be exposed. On the other hand, as in this embodiment, Ga
If the back surface of the N layer is roughened, irregular reflection occurs on the back surface of the substrate during exposure, in other words, regular reflection hardly occurs on the back surface of the substrate, and the back surface reflectance is reduced.
Since harmful exposure from the back side of the resist film hardly occurs, it is possible to form a resist pattern with no defective appearance.

That is, according to the first embodiment, Ga
Irregularities 100a are formed on the back surface of the N substrate 100,
As a result, since the rear surface is roughened, regular reflection of the incident light 173 does not easily occur on the rear surface of the GaN substrate 100, so that the rear surface reflectance can be reliably reduced. For this reason, it is possible to avoid a situation where the intensity of the reflected light 175 is reduced and the reflected light 175 exposes an area of the resist film 171 that should not be exposed (an area other than the area 171a). The accuracy of the resist pattern composed of the film 171 can be improved. Therefore,
Since the pattern accuracy in the photolithography process for manufacturing a semiconductor device using the GaN substrate 100 can be improved, the manufacturing yield of the nitride semiconductor device can be improved.

In the first embodiment, the back surface reflectance is reduced by forming the unevenness 100a on the back surface of the GaN substrate 100 and roughening the back surface. However, the method of reducing the back surface reflectance is as follows. There is no particular limitation, for example, a dielectric may be sprayed unevenly on the back surface of the substrate, a spherical or indefinite-shaped substance may be provided on the back surface of the substrate, or a low-reflectance film may be formed on the back surface of the substrate. . However, when the back surface reflectance is reduced by these methods, it is likely to cause impurities to be mixed into elements and the like in the subsequent semiconductor process. Therefore, if possible, the back surface reflectance is reduced by roughening the back surface of the GaN substrate 100. Is preferred.

In the first embodiment, polishing is used to roughen the back surface of the GaN substrate 100. Alternatively, the GaN substrate 100 may be polished by an arbitrary method such as sandblasting or etching. The back surface may be roughened.

In the first embodiment, the exposure light incident on the substrate surface at an incident angle of 90 ° (including approximately 90 °) is reflected by the back surface of the substrate and then emitted from the substrate surface at an angle of 90 °.
(Including approximately 90 °), which causes the resist film to be exposed, thereby reducing the reflectance of the exposure light incident on the substrate surface at an incident angle of 90 ° on the back surface of the substrate. The rough surface shape of the back surface of the substrate is not particularly limited as long as it is provided. However, in the case where the rough surface shape of the back surface of the substrate reflects the exposure light incident on the substrate surface at an incident angle of 90 ° in a specific angle direction with respect to the substrate surface, that is, the main surface of the substrate, a predetermined shape in the resist film is used. Since there is a possibility that a region other than the exposure region may be exposed, it is preferable that the back surface of the substrate has a rough surface shape that causes irregular reflection. Specifically, by providing unevenness having a step of about 1/10 or more of the wavelength of the exposure light on the back surface of the substrate, the exposure light incident on the substrate surface at an incident angle of 90 ° can be scattered or irregularly reflected in all directions. Can be. At this time, it is preferable to provide irregularities on the back surface of the substrate so that the back surface reflectance is about 13% or less.

In the first embodiment, the type of exposure light used in the photolithography step is not particularly limited, but light of a wavelength that propagates without being absorbed in the GaN substrate 100, for example, g-line Alternatively, when i-rays or the like are used as the exposure light, the pattern accuracy can be dramatically improved as compared with the related art.

In the first embodiment, the type of the resist film used in the photolithography process may be a positive type or a negative type.

In the first embodiment, GaN is used as a material for the nitride semiconductor substrate. However, the present invention is not limited to this. For example, a group III nitride semiconductor made of GaN, InN, AlN, or a mixed crystal thereof may be used. May be used. At this time, as long as these group III nitride semiconductors are the main components of the substrate, the substrate may contain other materials.

(Second Embodiment) A semiconductor substrate according to a second embodiment, a method for manufacturing the same, and a pattern forming method for manufacturing a semiconductor device using the semiconductor substrate will be described below with reference to the drawings. I do.

FIG. 7 is a sectional view of a semiconductor substrate according to the second embodiment.

As shown in FIG. 7, the semiconductor substrate according to the second embodiment includes a group III nitride semiconductor layer, specifically, Ga
An N layer 100 (hereinafter, also referred to as a GaN substrate 100). The surface of the GaN substrate 100 is (00
01) Ga surface and the back surface of the GaN substrate 100 is (00)
01) N-plane, and the thickness of the GaN substrate 100 is, for example, 3
00 μm.

The semiconductor substrate according to the second embodiment is characterized in that a 200 nm thick aluminum oxide (Al ₂ O 3) functioning as an anti-reflection film against exposure light such as g-line or i-line is formed on the back surface of the GaN substrate 100. O ₃ ) layer 104 is provided. Here, the aluminum oxide layer 104
Unlike sapphire and the like, it has a polycrystalline structure or an amorphous structure, while the refractive index of the aluminum oxide layer 104 is 1.68, which is about the same as sapphire. Also,
To function as an anti-reflection film means that, while preventing reflection of light incident from the front surface of the GaN substrate 100 on the back surface of the GaN substrate 100, the light is transmitted through the anti-reflection film and emitted from the back surface of the anti-reflection film. Means that. Therefore, the light transmittance of the antireflection film is preferably 80% or more.

The method for manufacturing the semiconductor substrate according to the second embodiment shown in FIG. 7 is as follows. The method for manufacturing a semiconductor substrate according to the second embodiment is the same as the method for manufacturing a semiconductor substrate according to the first embodiment shown in FIGS. 2A to 2E until the step shown in FIG. Is almost the same.

That is, first, as shown in FIG. 2A, an SOS substrate composed of a sapphire substrate 101 and a silicon substrate 102 is prepared, and then the MOVPE method using trimethylaluminum and ammonia as a source gas is performed as shown in FIG. As shown in (b), an AlN layer 103 is formed on a silicon substrate 102 of the SOS substrate to a thickness of 200 nm.
Grow thickness. Then, using the HVPE method using gallium chloride and ammonia as source gases, FIG.
As shown in (c), the GaN layer 1 is formed on the AlN layer 103.
00 is grown to a thickness of 300 μm. Then, FIG.
As shown in (d), by removing only the silicon substrate 102, the sapphire substrate 101 is separated from the GaN layer 100, which is to be a nitride semiconductor substrate, that is, the GaN substrate 100. Here, both surfaces of the GaN substrate 100 are mirror surfaces without irregularities, and
An 1N layer 103 is formed.

Next, in an atmosphere in which the partial pressures of water vapor and nitrogen were 10% and 90%, respectively, under normal pressure,
600 ° C. for the GaN substrate 100 including the N layer 103,
Perform a heat treatment for 10 minutes. Thereby, the AlN layer 1
03 is selectively oxidized to form an aluminum oxide layer 104 having a thickness of 200 nm, whereby the semiconductor substrate according to the second embodiment shown in FIG. 7 is completed.

The present inventors formed a line-and-space resist pattern similar to that of the first embodiment on a semiconductor substrate according to the second embodiment via a film to be processed by exposure using g-line. When the film to be processed was etched using the resist pattern as a mask, the dimension of the patterned film to be processed was almost 100% within a predetermined range. At this time, when the back surface reflectance of the semiconductor substrate according to the second embodiment was examined, it was a very low value of about 0.5% or less, which is the reason why the pattern formation was successfully performed. Was speculated.

That is, according to the second embodiment, Ga
Since the aluminum oxide layer 104 functioning as an anti-reflection film is formed on the back surface of the N substrate 100, the back surface reflectance can be reduced, thereby reducing the intensity of light reflected on the back surface of the substrate after entering from the front surface of the substrate. . For this reason,
In a photolithography process for manufacturing a semiconductor device using the GaN substrate 100, a situation in which exposure light incident from the surface of the substrate is reflected on the back surface of the substrate and is exposed to areas other than the predetermined exposure area in the resist film. Can be avoided. Therefore, the pattern accuracy in the photolithography process can be improved, so that the production yield of the nitride semiconductor device can be improved.

According to the second embodiment, the AlN layer 103 formed on the back surface of the GaN substrate 100 at the time of forming the GaN substrate 100 is oxidized to form the aluminum oxide layer 104. The process can be simplified as compared with the case where a new anti-reflection film is formed on the back surface of the GaN substrate 100, and the production yield of the GaN substrate 100 can be improved by preventing a problem such as impurity mixing into the GaN substrate 100.

In the second embodiment, aluminum oxide is used as the material of the antireflection film, but SiO ₂ or SiN may be used instead. Here, conditions for realizing a low-reflectance antireflection film using these materials will be described. First, it is preferable that the thickness of the antireflection film be an odd multiple of 1/4 wavelength of the wavelength of the exposure light in the antireflection film. Further, the refractive index of the antireflection film is a nitride semiconductor substrate (a GaN substrate in this embodiment).
It is preferable that the difference in the refractive index is as large as possible. In particular, the refractive index of the antireflection film is 9/10 of the refractive index of the nitride semiconductor substrate.
It is preferable that it is not more than about. For example, in this embodiment, the aluminum oxide layer 104 serving as an anti-reflection film is used.
Has a refractive index of 1.68 and the aluminum oxide layer 104
Has a thickness of 200 nm, which corresponds to ／ wavelength of the g-line wavelength (436 nm / 1.68) in the antireflection film. Further, since the difference between the refractive index (1.68) of the aluminum oxide layer 104 and the refractive index (about 2.5) of the GaN substrate 100 is relatively large, the allowable range of the thickness that can reduce the back surface reflectance to 13% or less. In other words, the allowable range of the thickness that can surely improve the pattern accuracy in the photolithography process becomes relatively wide. Specifically, the thickness of the aluminum oxide layer 104 is
1 of the wavelength of the exposure light in the aluminum oxide layer 104
When the target is set to 波長 wavelength, the backside reflectance is set to 13
% Is about 1/4 wavelength ± 1/8 wavelength. This is about 65 nm ± 40 nm in the case of g-line exposure.

Tables 1 and 2 show the characteristics of various antireflection films examined by the present inventors when the i-line and the g-line were used as exposure light, respectively. However, both characteristics were obtained when the thickness of the anti-reflection film was set to a target of 波長 wavelength of the exposure light in the anti-reflection film and a GaN substrate was used as the nitride semiconductor substrate. It is.

[0111]

[Table 1]

[0112]

[Table 2]

As shown in [Table 1] and [Table 2], unless the refractive index of the anti-reflection film is set to 2.32 or less, which is smaller than the refractive index (2.5) of GaN, the anti-reflection film cannot be sufficiently used. Effects cannot be obtained. The refractive index of the antireflection film is Ga
As the refractive index becomes smaller than the refractive index of N, the effect of reducing the reflectance (backside reflectance), that is, the antireflection effect increases, and the allowable range of the thickness that can reduce the backside reflectance to 13% or less increases. In Tables 1 and 2, Ti
The difference between the refractive index of the antireflection film made of O ₂ and ZrO ₂ between the case of using g-line and the case of using i-line is that TiO ₂ and ZrO ₂ near the wavelengths of g-line and i-line. Is caused by a large chromatic dispersion.

In the second embodiment, as the antireflection film, a laminate of a plurality of layers made of a material having a refractive index different from that of the group III nitride serving as the substrate may be used. At this time, it is preferable that at least two layers of the laminate have different refractive indexes.

In the second embodiment, the type of exposure light used in the photolithography step is not particularly limited, but light having a wavelength that propagates in the GaN substrate 100 without being absorbed, for example, g-line Alternatively, when i-rays or the like are used as the exposure light, the pattern accuracy can be dramatically improved as compared with the related art.

Further, in the second embodiment, the type of the resist film used in the photolithography process may be a positive type or a negative type.

In the second embodiment, GaN is used as the material of the nitride semiconductor substrate. However, the present invention is not limited to this, and is made of GaN, InN, AlN, or a mixed crystal thereof.
A group III nitride semiconductor may be used. At this time, if these group III nitride semiconductors are the main components of the substrate,
The substrate may include other materials.

(Modification of Second Embodiment) Hereinafter, a semiconductor substrate and a method of manufacturing the same according to a modification of the second embodiment will be described with reference to the drawings.

The modification of the second embodiment is different from the second embodiment in that gallium oxide (Ga ₂ O) is used instead of the aluminum oxide layer as an anti-reflection film for g-line or i-line exposure light. ₃ ) The use of layers.

FIGS. 8A to 8C are cross-sectional views showing steps of a method for manufacturing a semiconductor substrate according to a modification of the second embodiment. The method for manufacturing a semiconductor substrate according to the modification of the second embodiment is different from the method for manufacturing a semiconductor substrate according to the first embodiment shown in FIGS. 2A to 2E in FIG. The steps up to the shown steps are almost the same.

That is, first, as shown in FIG. 2A, an SOS substrate composed of a sapphire substrate 101 and a silicon substrate 102 is prepared, and then, the MOVPE method using trimethylaluminum and ammonia as source gases is performed as shown in FIG. As shown in (b), an AlN layer 103 is formed on a silicon substrate 102 of the SOS substrate to a thickness of 200 nm.
Grow thickness. Then, using the HVPE method using gallium chloride and ammonia as source gases, FIG.
As shown in (c), the GaN layer 1 is formed on the AlN layer 103.
00 is grown to a thickness of 300 μm. Then, FIG.
As shown in (d), by removing only the silicon substrate 102, the sapphire substrate 101 is separated from the GaN layer 100, which is to be a nitride semiconductor substrate, that is, the GaN substrate 100.

Next, as shown in FIG. 8A, the AlN layer 103 is removed by polishing, and the GaN substrate 100 is removed.
Is mirror-finished by polishing. Thereafter, in an atmosphere in which the partial pressures of oxygen and nitrogen are 10% and 90%, respectively, under normal pressure, the GaN substrate 100 is heated at 700 ° C.
A heat treatment for 0 minutes is performed. As a result, as shown in FIG. 8B, both surfaces of the GaN substrate 100 are oxidized, and a gallium oxide layer 105 having a thickness of 70 nm is formed on both surfaces.

By the way, if the gallium oxide layer 105 adheres to both surfaces of the GaN substrate 100, the subsequent device formation will be hindered. Therefore, the gallium oxide layer 105 on the front side of the GaN substrate 100 is removed by the following method. .
That is, GaN having gallium oxide layers 105 on both surfaces
The substrate 100 is introduced into a crystal growth apparatus such as a MOVPE apparatus as shown in FIG. At this time, the GaN substrate 1
00 is brought into close contact with the susceptor so that there is no gap between the back surface of the GaN substrate 100 and the susceptor.
Heat to ° C. As a result, the gallium oxide layer 105 on the surface side of the GaN substrate 100 is reduced and Ga is sublimated, so that a clean GaN surface is exposed on the surface of the GaN substrate 100. On the other hand, the gallium oxide layer 105 on the back surface side of the GaN substrate 100 is in close contact with the susceptor and hardly in contact with hydrogen, so that it is hardly reduced and is not sublimated. As a result, as shown in FIG. 8C, a GaN substrate 100 having a gallium oxide layer 105 on the back surface, that is, a semiconductor substrate according to a modification of the second embodiment is obtained.

According to a modification of the second embodiment, GaN
Since the gallium oxide layer 105 functioning as an anti-reflection film is formed on the back surface of the substrate 100, the reflectance of the back surface can be reduced, whereby the intensity of light reflected from the back surface of the substrate after entering from the front surface of the substrate can be reduced. Therefore, GaN
In a photolithography process for manufacturing a semiconductor device using the substrate 100, a situation in which exposure light incident from the front surface of the substrate is reflected on the back surface of the substrate and is exposed to an area other than a predetermined exposure area in the resist film. Can be avoided. Therefore, the pattern accuracy in the photolithography process can be improved, so that the production yield of the nitride semiconductor device can be improved.

According to a modification of the second embodiment,
Since the gallium oxide layer 105 is formed by oxidizing the GaN substrate 100, the process can be simplified as compared with the case where a new anti-reflection film is formed on the back surface of the GaN substrate 100, and
Prevent problems such as impurity mixing into the GaN substrate 100 and
The production yield of the aN substrate 100 can be improved.

According to a modification of the second embodiment,
Before the device formation using the GaN substrate 100, the gallium oxide layer 105 can also be formed on the front surface side of the GaN substrate 100.
5, the surface of the GaN substrate 100 can be protected. On the other hand, when device formation is performed using the GaN substrate 100, the gallium oxide layer 105 on the substrate surface side can be reduced and removed in the crystal growth apparatus to expose the clean GaN surface, thereby allowing the clean GaN surface to be exposed. For example, it becomes possible to sequentially form a device structure such as a clad layer or an active layer.

(Third Embodiment) Hereinafter, a semiconductor substrate according to a third embodiment, a method for manufacturing the same, and a pattern forming method for manufacturing a semiconductor device using the semiconductor substrate will be described with reference to the drawings. I do.

FIG. 9 is a sectional view of a semiconductor substrate according to the third embodiment.

As shown in FIG. 9, the semiconductor substrate according to the third embodiment includes a group III nitride semiconductor layer, specifically, Ga
It is composed of an N layer 100. In addition, the GaN layer 100 (hereinafter, G
The surface of the (aN substrate 100) is (000
1) The Ga surface, and the back surface of the GaN substrate 100 is (000)
1) N-plane, and the thickness of the GaN substrate 100 is, for example, 30
0 μm.

The feature of the third embodiment is that the GaN substrate 10
0 to 50 μm deep from its surface inside
A region, a material having a refractive index different from GaN, for example, a plurality of SiO ₂ grains 106a made of SiO ₂ is embedded discontinuously with respect to g-line or i-line, etc. of the exposure light,
The light scattering portion (the portion that scatters light incident from the substrate surface) 106 is formed by the plurality of SiO ₂ particles 106a. Here, the shape of each SiO ₂ particle 106a is not particularly limited, but in the third embodiment, the diameter of each SiO ₂ particle 106a (GaN substrate 100
Is a few tens of μm in a cross section parallel to the surface.
And the height (length along the direction perpendicular to the surface of the GaN substrate 100) of each SiO ₂ particle 106a is 10
It is about 0 nm.

FIGS. 10A to 10E are cross-sectional views showing each step of the method for manufacturing a semiconductor substrate according to the third embodiment, specifically, the method for manufacturing a semiconductor substrate shown in FIG. The method for manufacturing a semiconductor substrate according to the third embodiment is described in FIG.
The manufacturing method of the semiconductor substrate according to the first embodiment shown in FIGS. 2A to 2E is substantially the same up to the step shown in FIG.

That is, first, as shown in FIG. 2A, an SOS substrate including a sapphire substrate 101 and a silicon substrate 102 is prepared, and then, the MOVPE method using trimethylaluminum and ammonia as source gases is performed as shown in FIG. As shown in (b), an AlN layer 103 is formed on a silicon substrate 102 of the SOS substrate to a thickness of 200 nm.
Grow thickness. Then, using the HVPE method using gallium chloride and ammonia as source gases, FIG.
As shown in (c), the GaN layer 1 is formed on the AlN layer 103.
00 is grown to a thickness of 220 μm. At this time, GaN
The surface of the layer 100 is a (0001) Ga plane. afterwards,
As shown in FIG. 2D, by removing only the silicon substrate 102, the sapphire substrate 101 and the GaN layer 100 to be the nitride semiconductor substrate, that is, the GaN substrate 10
Separate from 0.

Next, as shown in FIG.
The layer 103 is removed by polishing, and the back surface of the GaN substrate 100 is mirror-finished by polishing using an abrasive having a very small particle size.

Next, as shown in FIG.
RF (high frequency) using argon gas on the substrate 100
A plurality of SiO ₂ particles 106a are deposited by a sputtering method. In the third embodiment, as the deposition conditions of the SiO ₂ particles 106a, the gas pressure is 0.2 Pa and the RF output is 2
It was set to 00W. Here, the deposition conditions of the SiO ₂ particles 106a vary depending on the sputtering apparatus used,
SiO In conditions such as SiO ₂ layer is uniformly deposited ₂
Since it is difficult to deposit the particles discontinuously, it is preferable to use conditions under which SiO ₂ particles having the largest possible particle size are deposited. In the RF sputtering method, generally, RF
It is preferable to increase the output to increase the diameter of the sputtered particles. However, when the RF output is increased, the discharge tends to be unstable. In this case, it is preferable to lower the gas pressure.

An important point in the third embodiment is that the configuration shown in FIG.
In the step shown in FIG._TwoThe accumulation of the grains 106a is represented by S
iO_TwoThe GaN substrate 100 is completely covered by the grains 106a.
Stop before it is overturned. Where SiO_Twograin
106a depending on the timing at which the deposition of 106a is stopped._Two
The arrangement state of the grains 106a differs. For example, SiO _Two
The GaN substrate 100 is completely covered by the grains 106a.
Just before_TwoIf the deposition of the grains 106a is stopped, Ga
SiO covering N substrate 100_TwoLayer-like opening
Condition arises. In addition, SiO_TwoGaN based on grain 106a
Before the coating of the plate 100 proceeds_TwoBank 106a
If the product is stopped, multiple SiO_TwoGrains 106a are in the shape of an island
A state of being scattered on the aN substrate 100 occurs. Third implementation
In the form, SiO_TwoThe arrangement state of the grains 106a is particularly limited.
Although not specified, both sides of the GaN substrate 100
A device in which a pole is provided and current flows in the thickness direction of the substrate.
When forming silicon or the like, SiO_TwoGaN with grains 106a
It is preferable that the coverage area of the substrate 100 is as small as possible.
Needless to say,

Next, the G having the SiO ₂ particles 106a is provided.
The aN substrate 100 is introduced into a GaN crystal growth apparatus such as a MOVPE apparatus, and as shown in FIG.
A GaN layer 107 is formed on an N substrate 100 by forming SiO ₂ particles 106a.
Grow so that the space between them is filled. Specifically, MO
In a VPE apparatus, by using trimethylgallium and ammonia as a source gas and using hydrogen as a carrier gas, GaN can be formed at a temperature of 1000 ° C.
The layer 107 is grown. The growth conditions of the GaN layer 107 are as follows:
Although it depends on the crystal growth method to be used, when the MOVPE method is used as in this embodiment, the crystal growth temperature is set to 9
By increasing the group V / III group feed ratio (the ratio of the supply flow rate of ammonia per minute to the flow rate of trimethylgallium per minute) to 1000 ° C. or higher, the group III source (Ga Since the migration is activated, the GaN layer 107 can be grown so that the space between the SiO ₂ grains 106a is filled. At this time, if the GaN layer 107 is grown to a thickness of about 10 μm, the surface of the GaN layer 107 becomes flat. However, in the third embodiment, the GaN layer 107 becomes flat before the surface of the GaN layer 107 becomes completely flat. The crystal growth of the layer 107 is completed.

Next, as shown in FIG.
On the layer 107 (the already deposited SiO ₂ grains 106a
), A new SiO 2 layer is formed using RF sputtering.
_Two grains 106a are deposited. After that, the GaN substrate 100 is introduced again into the GaN crystal growth apparatus, and the GaN layer 107 is further grown. Here, in the third embodiment, by the thickness of the GaN layer 107 is repeated and the crystal growth of the deposition and GaN layer 107 of SiO ₂ grains 106a to reach about 30 [mu] m, specifically, SiO ₂ grains 1
By performing RF sputtering for depositing 06a a total of six times, as shown in FIG.
The light scattering portion 106 in which the SiO ₂ particles 106a are embedded in 7 is formed. Thereafter, GaN was grown using HVPE using gallium chloride and ammonia as source gases.
The layer 107 is further subjected to crystal growth with a thickness of about 50 μm, thereby completing the semiconductor substrate according to the third embodiment shown in FIG. At this time, since the GaN layer 107 is finally integrated with the GaN substrate 100 made of the same material,
At 0 (e), the GaN layer 107 is not shown.

In the third embodiment, SiO ₂
When the space between the grains 106a is filled with the GaN layer 107, the G
Although the crystal growth of the aN layer 107 was interrupted, the GaN layer 10
When the GaN layer 107 is crystal-grown so as to completely fill the space between the SiO ₂ grains 106a so that the surface of the layer 7 is completely flat, the SiO ₂ grains 106a are distributed in a layered manner.

The present inventors formed a line-and-space resist pattern similar to that of the first embodiment on a semiconductor substrate according to the third embodiment via a film to be processed by exposure using g-line. When the film to be processed is etched using the resist pattern as a mask, the transmittance of the light scattering portion 106 is set to 80% or less, so that the dimension of the patterned film to be processed is almost 100%.
It was within the specified range. This is because the light that is reflected from the back surface of the substrate and returns to the front surface of the substrate after entering from the front surface of the substrate passes through the light scattering portion 106 twice, so that the transmittance of the light scattering portion 106 is 80% and the back surface of the substrate is Even when the mirror has a backside reflectance of about 20%, the substantial backside reflectance is 2%.
This is because 0% × 80% × 80% ≒ 13%, so that pattern formation can be performed well.

That is, according to the third embodiment, Ga
Since the light scattering portion 106 is formed inside the N substrate 100, the intensity of light reflected from the back surface of the substrate after entering from the front surface of the substrate can be reduced. For this reason, in a photolithography process for manufacturing a semiconductor device using the GaN substrate 100, the exposure light incident from the substrate surface is reflected on the back surface of the substrate and is exposed to areas other than the predetermined exposure area in the resist film. Situation can be avoided. Therefore,
Since the pattern accuracy in the photolithography process can be improved, the production yield of the nitride semiconductor device can be improved.

[0141] According to the third embodiment, after partially forming the GaN substrate 100 and the material is different SiO ₂ grains 106a in GaN substrate 100, SiO ₂ grains 106a
In order to grow a new GaN layer (GaN layer 107) that will be a part of the substrate on the GaN substrate 100 containing Si, it is required that the GaN layer carry over the defects and the like generated in the original GaN substrate 100 by SiO. _It can be suppressed by the _two grains 106a. Therefore, since the crystallinity of the GaN layer 107 can be improved, the crystallinity of the nitride semiconductor substrate having the light scattering portion can be improved.

In the third embodiment, the deposition of the SiO ₂ particles 106a and the crystal growth of the GaN layer 107 are repeated a plurality of times, respectively. As long as the transmittance becomes 80% or less, the deposition of the SiO ₂ particles 106a and the GaN layer 107
May be performed at least once.
In addition, since the transmittance of the light scattering portion 106 varies in a complicated manner depending on the shape or density of the SiO ₂ particles 106a, the shape or density is theoretically determined so that the light scattering portion 106 has a desired transmittance. It is difficult. Therefore, the light scattering unit 10
6, the number of depositions of the SiO ₂ particles 106 a or the SiO ₂ particles 10
It is preferable to experimentally determine the thickness and the like of the region where 6a is embedded.

Further, in the third embodiment, the SiO ₂ particles 106a naturally formed by the RF sputtering method are used as the light scattering portions 106, but the method of forming the light scattering portions is not particularly limited. for example, after forming a SiO ₂ layer over the entire surface of the GaN substrate, the mask pattern is formed on the SiO ₂ layer is partially formed for etching a SiO ₂ layer using the mask pattern Accordingly, by removing the portions not covered by the mask pattern in the SiO ₂ layer, SiO ₂ that is patterned
A light scattering portion composed of a layer may be formed, and then, the mask pattern may be removed. When SiO ₂ particles are used as the light scattering portion, the diameter of the SiO ₂ particles is 1/10 of the wavelength of the exposure light.
It is preferable that it is at least about the same. Further, as the light scattering portion, in the case of using the SiO ₂ layer is patterned, the width along the direction parallel to the substrate surface in the SiO ₂ layer, or the thickness of the SiO ₂ layer is the exposure light 1/1 of wavelength
It is preferably about 0 or more. Further, even when SiO ₂ particles are used as the light scattering portion, the patterned Si
Even when the O ₂ layer is used, the thickness of the light scattering portion is preferably about 1/10 or more of the wavelength of the exposure light.

In the third embodiment, SiO ₂ is used as the material of the light scattering portion.
The material is not particularly limited as long as it is a material on which a GaN layer can be crystal-grown and has a refractive index different from that of GaN. In addition to SiO ₂ , for example, Si, SiN or Al ₂
O ₃ or the like may be used. Further, the light scattering portion does not necessarily have to be a particle or layer made of a single material, and a GaN layer can be crystal-grown thereon, and a particle or layer made of a plurality of materials having a different refractive index from GaN is used. They may be combined or stacked. Alternatively, it may be a combination of a particle or layer made of at least one or more materials as described above and a hole or the like.

In the third embodiment, the type of exposure light used in the photolithography step is not particularly limited, but light having a wavelength that propagates in the GaN substrate 100 without being absorbed, for example, g-line Alternatively, when i-rays or the like are used as the exposure light, the pattern accuracy can be dramatically improved as compared with the related art.

In the third embodiment, the type of the resist film used in the photolithography process may be a positive type or a negative type.

In the third embodiment, GaN is used as the material of the nitride semiconductor substrate. However, the material is not limited to GaN, and may be made of GaN, InN, AlN, or a mixed crystal thereof.
A group III nitride semiconductor may be used. At this time, if these group III nitride semiconductors are the main components of the substrate,
The substrate may include other materials.

(Fourth Embodiment) Hereinafter, a semiconductor substrate according to a fourth embodiment, a method for manufacturing the same, and a pattern forming method for manufacturing a semiconductor device using the semiconductor substrate will be described with reference to the drawings. I do.

FIG. 11 is a sectional view of a semiconductor substrate according to the fourth embodiment.

As shown in FIG. 11, the semiconductor substrate according to the fourth embodiment has a 200 μm-thick GaN
Layer 100 and 15 μm thick Al _0.1 Ga _0.9 on the back side of the substrate
And an N layer 108. The back surface of the GaN layer 100, that is, the GaN layer 100 and the Al _0.1 Ga _0.9 N layer 10
8 is a rough surface having irregularities 100a. In other words, the semiconductor substrate according to the fourth embodiment is different from the semiconductor substrate (GaN substrate 100) according to the first embodiment shown in FIG.
_It has a structure in which a _0.1 Ga _0.9 N layer 108 is formed.
In addition, assuming that the wavelength of the exposure light used in the photolithography process for manufacturing the semiconductor device using the semiconductor substrate of the present embodiment is λ, the unevenness 100a preferably has a step of about λ / 10 or more.

The method for manufacturing the semiconductor substrate according to the fourth embodiment shown in FIG. 11 is as follows. The method for manufacturing a semiconductor substrate according to the fourth embodiment is described with reference to FIGS.
In the method for manufacturing a semiconductor substrate according to the first embodiment shown in FIG. 2, the steps up to the step shown in FIG.

That is, first, as shown in FIG. 2A, a sapphire substrate 101 having a thickness of 300 μm and a
After preparing an SOS substrate including a silicon substrate 102 having a thickness of μm, the MOVPE method using trimethylaluminum and ammonia as source gases is used to form a silicon substrate 102 on the silicon substrate 102 of the SOS substrate as shown in FIG. 200 nm at a temperature of 1000 ° C.
Grow thickness. Then, using the HVPE method using gallium chloride and ammonia as source gases, FIG.
As shown in (c), the GaN layer 1 is formed on the AlN layer 103.
00 is grown to a thickness of 250 μm. After that, as shown in FIG. 2D, only a silicon substrate 102 is removed by a process using a mixed solution of hydrofluoric acid and nitric acid, thereby forming a sapphire substrate 101 and a GaN layer 100 serving as a nitride semiconductor substrate. That is, the GaN substrate 100 is separated.
Next, as shown in FIG.
The AlN layer 103 is removed by polishing the back surface of the GaN substrate 100 using a polishing agent of μm until the thickness of the GaN substrate 100 finally becomes about 200 μm, and unevenness 100a is formed on the back surface of the GaN substrate 100. Forming and roughening the back surface. Thus, the GaN substrate 100 shown in FIG. 1 is obtained.

Next, an MO using trimethylaluminum, trimethylgallium and ammonia as source gases was used.
At a temperature of 1000 ° C., Al _0.1 Ga _0.9
The N layer 108 is grown to a thickness of 15 μm. This allows
The semiconductor substrate according to the fourth embodiment shown in FIG. 11 is obtained. The unevenness 100a on the back surface of the GaN substrate 100 is A
The GaN substrate 10 buried by the l _0.1 Ga _0.9 N layer 108 and thereby including the Al _0.1 Ga _0.9 N layer 108
0 (hereinafter, may be simply referred to as the substrate back surface) is flattened.

Here, the back surface of the substrate is not necessarily flat.
There is no need to convert. However, in the fourth embodiment, the back of the substrate
In a state where the surface does not cause light scattering,
To determine the light scattering effect (see the first embodiment)
Al under the condition that the back surface of the substrate is flattened_0.1Ga_0.9N layer
108 is grown. Flattening of the back surface of the substrate can be realized
Al_0.1Ga_0.9The crystal growth conditions for the N layer 108
Depends on the crystal growth method used, but as in the present embodiment,
When the MOVPE method is used, the crystal growth temperature is set to 900
℃ or higher and the feed ratio of group V / group III raw materials (ammonium
(A) The supply flow rate per minute of trimethyl aluminum
Or the supply flow rate of trimethylgallium per minute
Of the group III raw material
(Ga or Al) migration becomes active
Then, the unevenness 100a_0.1Ga_{0. 9}By the N layer 108
Buried in the substrate to flatten the back surface of the substrate.

The present inventors formed a line-and-space resist pattern similar to that of the first embodiment on a semiconductor substrate according to the fourth embodiment via a film to be processed by exposure using g-line. Then, when the film to be processed was etched using the resist pattern as a mask, the transmittance of the unevenness 100a, that is, the light scattering portion to the exposure light was 8%.
By setting it to 0% or less, the dimensions of the patterned film to be processed were almost 100% within a predetermined range.
This is because the light that is reflected from the back surface of the substrate and returns to the front surface of the substrate after being incident from the front surface of the substrate passes through the light scattering portion twice, so that the transmittance of the light scattering portion is 80% and the back surface of the substrate has a mirror surface. This is because, even when the back surface reflectance is about 20%, the substantial back surface reflectance is 20% × 80% × 80% ≒ 13%, so that pattern formation can be favorably performed.

That is, according to the fourth embodiment, Ga
Since the unevenness 100a provided at the interface between the N layer 100 and the Al _0.1 Ga _0.9 N layer 108 functions as a light scattering portion, the intensity of reflected light generated when incident light from the front surface of the substrate is reflected on the back surface of the substrate can be reduced. . For this reason, in the photolithography process for manufacturing a semiconductor device using the semiconductor substrate of the present embodiment, the exposure light incident from the substrate surface is reflected on the back surface of the substrate, and other regions other than the predetermined exposure region in the resist film are exposed. Can be avoided. Therefore, the pattern accuracy in the photolithography process can be improved, so that the production yield of the nitride semiconductor device can be improved.

According to the fourth embodiment, the unevenness 10
Since the back surface of the roughened GaN substrate 100 provided with Oa can be flattened by the Al _0.1 Ga _0.9 N layer 108, the manufacturing process of the semiconductor device can be simplified.

According to the fourth embodiment, the unevenness 10
On the back surface of the GaN substrate 100 0a is provided, for crystal growth of the Al _0.1 Ga _0.9 N layer, 108 is a group III nitride semiconductor layer, Al _0.1 Ga _0.9 N is formed on the convex portion of the concavo-convex 100a Since the crystallinity of the layer 108 can be improved, the crystallinity of the nitride semiconductor substrate having a light scattering portion can be improved.

In the fourth embodiment, the unevenness 100
a on the back surface of the GaN substrate 100 provided with_0.1Ga
_0.9Although the N layer 108 was formed,_0.1Ga_0.9N layer 10
8 has a different refractive index from that of the GaN substrate 100
Forming another material layer (which may not be a nitride semiconductor layer)
However, it is possible to realize the light scattering effect by the unevenness 100a.
it can. At this time, the GaN base provided with the irregularities 100a
An anti-reflection film (the second embodiment or the
When a material layer that functions as
Can further reduce the intensity of reflected light. By the way,
In the fourth embodiment, Al is used to bury the irregularities 100a.
_0.1Ga_0.9The thickness of the N layer 108 (15 μm)
Is very thick compared to the wavelength of the exposure light such as i-line
And Al_0.1Ga_0.9The N layer 108 is used as an anti-reflection film.
Hardly works. Therefore, in the fourth embodiment,
The reflected light is Al_0.1Ga_0.9Interface between N layer 108 and air
(Reflectance of about 21%) and the GaN substrate 10
0 and Al_0.1Ga_0.9Interface with N layer 108 (reflectance is uneven
100a depending on the shape or density)
It becomes superposition with light. That is, in the fourth embodiment,
Is a GaN substrate 100 and Al _0.1Ga_0.9With the N layer 108
The light scattered by the interface, that is, the unevenness 100a is Al
_0.1Ga_0.9Reflected at the interface between the N layer 108 and air
May return to the surface of the GaN substrate 100
You. As described above, the first embodiment is performed by exposure using g-line.
Line-and-space shape (line and space)
A resist pattern having a pace part width of 2 μm) was formed.
Sometimes the pattern formation was good, but
When the occupied area of the opening in the photomask is about 50%
It is thought that there was. That is, in the fourth embodiment,
Increases the area occupied by the openings in the photomask.
After being scattered by the irregularities 100a,
_0.1Ga_0.9The light reflected at the interface between the N layer 108 and air
The effect of light that exposes the dist film from behind cannot be ignored.
It is thought that.

In the fourth embodiment, the type of exposure light used in the photolithography step is not particularly limited, but light of a wavelength that propagates without being absorbed in the GaN substrate 100, for example, g-line Alternatively, when i-rays or the like are used as the exposure light, the pattern accuracy can be dramatically improved as compared with the related art.

In the fourth embodiment, the type of the resist film used in the photolithography process may be a positive type or a negative type.

In the fourth embodiment, GaN is used as the material of the nitride semiconductor substrate. However, the present invention is not limited to this, and is made of GaN, InN, AlN, or a mixed crystal thereof.
A group III nitride semiconductor may be used. At this time, if these group III nitride semiconductors are the main components of the substrate,
The substrate may include other materials.

(Fifth Embodiment) Hereinafter, a semiconductor substrate according to a fifth embodiment, a method for manufacturing the same, and a pattern forming method for manufacturing a semiconductor device using the semiconductor substrate will be described with reference to the drawings. I do.

FIG. 12 is a sectional view of a semiconductor substrate according to the fifth embodiment.

As shown in FIG. 12, the semiconductor substrate according to the fifth embodiment has a group III nitride semiconductor layer, specifically,
An aN layer 100 is formed. Further, the GaN layer 100 (hereinafter, referred to as GaN layer 100)
The surface of the GaN substrate 100 may be referred to as (00
01) Ga surface and the back surface of the GaN substrate 100 is (00)
01) N-plane, and the thickness of the GaN substrate 100 is, for example, 3
00 μm.

The feature of the fifth embodiment is that the GaN substrate 10
In a region having a depth of about 80 μm and a region of approximately 75 μm from the surface inside 0, a plurality of materials having a larger absorption coefficient than GaN for exposure light such as g-line or i-line, for example, Si Is discontinuously buried, and a plurality of Si layers 109a form light absorbing portions (portions for absorbing light incident from the substrate surface) 109. Where each S
The width of the i-layer 109a (the width along the direction parallel to the substrate surface) and the interval between the Si layers 109a are each 1
It is about μm. That is, the respective Si layers 109a are arranged in a periodic stripe shape. In addition, each Si layer 109a
(Height along a direction perpendicular to the substrate surface) is about 100 nm. Further, the Si layer 109a in a region (that is, the first layer) having a depth of about 80 μm from the surface inside the GaN substrate 100 and the GaN substrate 100
And the Si layer 109a in a region having a depth of about 75 μm from the surface inside (i.e., the second layer) is displaced by about 1 μm along a direction parallel to the substrate surface.

FIGS. 13A to 13E and FIGS.
(C) is sectional drawing which shows each process of the manufacturing method of the semiconductor substrate which concerns on 5th Embodiment. The method for manufacturing a semiconductor substrate according to the fifth embodiment is different from the method for manufacturing a semiconductor substrate according to the first embodiment shown in FIGS.
The steps up to the step (d) are substantially the same.

That is, first, as shown in FIG. 2A, an SOS substrate composed of a sapphire substrate 101 and a silicon substrate 102 is prepared, and then, the MOVPE method using trimethylaluminum and ammonia as a source gas is performed as shown in FIG. As shown in (b), an AlN layer 103 is formed on a silicon substrate 102 of the SOS substrate to a thickness of 200 nm.
Grow thickness. Then, using the HVPE method using gallium chloride and ammonia as source gases, FIG.
As shown in (c), the GaN layer 1 is formed on the AlN layer 103.
00 is grown to a thickness of 220 μm. At this time, GaN
The surface of the layer 100 is a (0001) Ga plane. afterwards,
As shown in FIG. 2D, by removing only the silicon substrate 102, the sapphire substrate 101 and the GaN layer 100 to be the nitride semiconductor substrate, that is, the GaN substrate 10
Separate from 0.

Next, as shown in FIG.
The layer 103 is removed by polishing, and the back surface of the GaN substrate 100 is mirror-finished by polishing using an abrasive having a very small particle size.

Next, as shown in FIG.
After a first Si layer 110 having a thickness of 100 nm is deposited on the substrate 100 by an RF sputtering method, as shown in FIG. 13C, the openings periodically arranged on the first Si layer 110 are formed. A first resist pattern 111 having a portion is formed by photolithography.

Next, as shown in FIG. 13D, the first Si layer 1 is formed using the first resist pattern 111 as a mask.
10 is subjected to wet etching using hydrofluoric nitric acid to pattern the first Si layer 110 in a periodic stripe shape, and then, as shown in FIG. The resist pattern 111 is removed.

Next, the GaN substrate 100 is, for example, MOVP
Introduced to GaN crystal growth equipment such as E equipment,
As shown in (a), the first Ga
The N layer 112 is grown so that the first Si layer 110 is buried. Specifically, in a MOVPE apparatus, trimethylgallium and ammonia are used as a source gas and hydrogen is used as a carrier gas, whereby
The first GaN layer 112 is grown at a temperature of 00 ° C.
The growth conditions of the first GaN layer 112 are different depending on the crystal growth method to be used. However, when the MOVPE method is used as in the present embodiment, the crystal growth temperature is set to 900 ° C. or higher and the group V / III material is used. By setting the supply ratio (the ratio of the supply flow rate of ammonia per minute to the supply flow rate of trimethylgallium per minute) to 1000 or more, the migration of the group III raw material (Ga) becomes active, so that the first First Ga so that Si layer 110 is buried.
An N layer 112 can be grown.

Next, as shown in FIG. 14B, a second Si layer 11 having a thickness of 100 nm is formed on the first GaN layer 112.
After depositing No. 3 by RF sputtering, a second resist pattern (not shown) is formed on the second Si layer 113 in the same manner as in the step shown in FIG. Then, FIG.
Similarly to the step shown in FIG. 3D, the second Si layer 113 is etched using the second resist pattern as a mask, and as shown in FIG. After patterning into a periodic stripe, the second resist pattern is removed. The first Si layer 110
And the second Si layer 113 are patterned by being shifted from each other by a predetermined distance.

Next, the GaN substrate 100 is, for example, MOVP
Introduced again to the GaN crystal growth apparatus such as the E apparatus, and FIG.
As shown in (c), a second GaN layer 114 is grown on the first GaN layer 112 so that the second Si layer 113 is buried. At this time, the growth conditions of the second GaN layer 114 are the same as the growth conditions of the first GaN layer 112. Further, the first GaN layer 112 and the second GaN layer 114 are finally integrated with the GaN substrate 100 made of the same material. Thereby, the first GaN layer 112 and the second Ga
In a GaN substrate 100 including an N layer 114, a patterned first Si layer 110 and a second Si layer 113 are formed.
(That is, the light absorbing portion 109 composed of the plurality of Si layers 109a shown in FIG. 12) is formed.

The present inventors formed a line-and-space resist pattern similar to that of the first embodiment on a semiconductor substrate according to the fifth embodiment via a film to be processed by exposure using g-line. Then, when the film to be processed is etched using the resist pattern as a mask, the dimension of the patterned film to be processed is almost 100% by setting the transmittance of the light absorbing portion 109 to 80% or less.
It was within the specified range. This is because the light that is reflected from the back surface of the substrate and then returns to the front surface of the substrate after entering from the front surface of the substrate passes through the light absorbing portion 109 twice, so that the transmittance of the light absorbing portion 109 is 80% and the back surface of the substrate is Even when the mirror has a backside reflectance of about 20%, the substantial backside reflectance is 2%.
This is because 0% × 80% × 80% ≒ 13%, so that pattern formation can be performed well.

That is, according to the fifth embodiment, Ga
Since the light absorbing portion 109 is formed inside the N substrate 100, the intensity of light reflected from the back surface of the substrate after entering from the front surface of the substrate can be reduced. For this reason, in a photolithography process for manufacturing a semiconductor device using the GaN substrate 100, the exposure light incident from the substrate surface is reflected on the back surface of the substrate and is exposed to areas other than the predetermined exposure area in the resist film. Situation can be avoided. Therefore,
Since the pattern accuracy in the photolithography process can be improved, the production yield of the nitride semiconductor device can be improved.

According to the fifth embodiment, the Si layer 109a made of a material different from that of the GaN substrate 100 is
After partially forming the G layer on the G layer including the Si layer 109a,
Since a GaN layer (the first GaN layer 112 and the second GaN layer 114) that newly becomes a part of the substrate is crystal-grown on the aN substrate 100, defects or the like generated in the original GaN substrate 100 The fact that the GaN layer is taken over by the Si layer 1
09a. Therefore, the crystallinity of the newly grown GaN layer can be improved, and the crystallinity of the nitride semiconductor substrate having the light absorbing portion can be improved.

According to the fifth embodiment, since the Si layer 109 constituting the light absorbing portion 109 is unevenly distributed along the direction parallel to the substrate surface, the light absorbing portion 1
09 not only absorbs light, but also absorbs light.
09 scatters light, so that the intensity of reflected light can be further reduced.

Further, according to the fifth embodiment, since the Si layer 109a constituting the light absorbing portion 109 is conductive,
By providing the light absorbing portion, the resistivity of the nitride semiconductor substrate does not decrease.

In the fifth embodiment, Si is used as the material of the light absorbing portion. However, the material of the light absorbing portion allows the crystal growth of a GaN layer thereon and has a light absorption coefficient higher than that of GaN. Is not particularly limited as long as it is a large material. However, as a material of the light absorbing portion, a material having conductivity as described above is more preferable. Examples of such a material include W (tungsten) in addition to Si. Tungsten is a metal, but tungsten deposited by a CVD method or the like has low luster and has a light absorbing property, and is effective as a material of a light absorbing portion.
In addition, the light absorbing portion does not necessarily have to be a grain or layer made of a single material, and a grain or layer made of a plurality of materials having a light absorption coefficient larger than that of GaN on which a GaN layer can be grown. Layers may be combined or laminated. Alternatively, it may be a combination of a particle or layer made of at least one or more materials as described above and a hole or the like.

Incidentally, the absorption coefficient of Si used as the material of the light absorbing portion of this embodiment is determined by the method of depositing the Si layer,
It changes greatly depending on the film quality or contained impurities. However,
When the thickness of the Si layer is 300 to 500 nm, its absorption coefficient reaches about 10 ⁵ / cm or more. In addition, Si
If the thickness of the layer is 100 nm, the intensity of light transmitted through the Si layer is reduced to at least 1 / e (e: the base of natural logarithm). 8
0% or less, and the Si layer sufficiently functions as a light absorbing portion. On the other hand, the thickness of the Si layer is less than 100 nm,
In particular, when the thickness is less than 50 nm, the transmittance may be 80% or more depending on the film quality of the Si layer, and the function as the light absorbing portion may be insufficient.

In the fifth embodiment, the type of exposure light used in the photolithography step is not particularly limited, but light having a wavelength that propagates in the GaN substrate 100 without being absorbed, for example, g-line Alternatively, when i-rays or the like are used as the exposure light, the pattern accuracy can be dramatically improved as compared with the related art.

In the fifth embodiment, the type of the resist film used in the photolithography process may be a positive type or a negative type.

In the fifth embodiment, GaN is used as the material of the nitride semiconductor substrate. However, the present invention is not limited to this, and is made of GaN, InN, AlN, or a mixed crystal thereof.
A group III nitride semiconductor may be used. At this time, if these group III nitride semiconductors are the main components of the substrate,
The substrate may include other materials.

(Sixth Embodiment) Hereinafter, a semiconductor substrate and a method for manufacturing the same according to a sixth embodiment, and a pattern forming method for manufacturing a semiconductor device using the semiconductor substrate will be described with reference to the drawings. I do.

FIG. 15 is a sectional view of a semiconductor substrate according to the sixth embodiment.

As shown in FIG. 15, the semiconductor substrate according to the sixth embodiment has a group III nitride semiconductor layer,
An aN layer 200 is formed. In addition, the GaN layer 200 (hereinafter, referred to as GaN layer 200)
The surface of the (GaN substrate 200) is (00
01) Ga surface and the back surface of the GaN substrate 200 is (00)
01) N-plane, and the thickness of the GaN substrate 200 is, for example, 3
00 μm.

A feature of the sixth embodiment is that an impurity such as As (arsenic) is formed in a region extending from the back surface of the GaN substrate 200 to a thickness of 150 μm so as to generate a level absorbing exposure light such as g-line or i-line. Light absorbing portion 201 introduced into
Is formed.

FIGS. 16A to 16F are cross-sectional views showing each step of the method for manufacturing the semiconductor substrate according to the sixth embodiment shown in FIG.

First, as shown in FIG.
An SOS substrate including a 00 μm sapphire substrate 202 and a 80 μm thick silicon substrate 203 is prepared.

Next, as shown in FIG. 16B, an AlN layer was formed on the silicon substrate 203 of the SOS substrate at a temperature of 1000 ° C. by MOVPE using trimethylaluminum and ammonia as source gases. 20
4 is grown to a thickness of 200 nm.

Next, as shown in FIG. 16 (c), the gallium chloride obtained by reacting HCl gas and Ga at a temperature of 800 ° C. and the HVPE method using ammonia as a raw material gas were used. A GaN layer 201 having a thickness of 150 μm on the AlN layer 204 at a temperature of 1000 ° C.
Grow thickness. At this time, by introducing a gas containing As as a constituent element such as arsine into the crystal growth apparatus at a supply flow rate of 0.1% of the supply flow rate of ammonia, for example, the GaN layer 201 into which As is introduced, The absorbing part 201 can be formed. Note that As can be introduced into the GaN layer by installing a GaAs crystal near the region where the HCl gas reacts with Ga in the crystal growth apparatus, instead of introducing a gas such as arsine. 201 can be formed.

Next, by stopping only the supply of arsine and continuing the crystal growth by the above-described HVPE method, as shown in FIG. The GaN layer 200 is grown under the thickness of 150 μm below.

Next, as shown in FIG. 16E, the silicon substrate 2 was treated by using a mixed solution of hydrofluoric acid and nitric acid.
03 is removed, the sapphire substrate 20 is removed.
2 and a GaN substrate 200 including a light absorbing portion 201, which is to be a nitride semiconductor substrate. Here, the GaN substrate 2
The AlN layer 204 is formed on the back surface of No. 00.

Next, as shown in FIG. 16F, the AlN layer 20 was polished by using an abrasive having a very small particle size.
4 is removed and the back surface of the GaN substrate 200 is mirror-finished.

The present inventors formed a line-and-space resist pattern similar to that of the first embodiment on a semiconductor substrate according to the sixth embodiment via a film to be processed by exposure using g-line. Then, when the film to be processed is etched using the resist pattern as a mask, the dimension of the patterned film to be processed is almost 100% by setting the transmittance of the light absorbing portion 201 to 80% or less.
It was within the specified range. This is because light that is reflected from the back surface of the substrate and then returns to the front surface of the substrate after entering from the front surface of the substrate passes through the light absorbing portion 201 twice, so that the transmittance of the light absorbing portion 201 is 80% and Even when the mirror has a backside reflectance of about 20%, the substantial backside reflectance is 2%.
This is because 0% × 80% × 80% ≒ 13%, so that pattern formation can be performed well.

That is, according to the sixth embodiment, Ga
Since the light absorbing portion 201 is formed in the region on the back surface side of the N substrate 200, the intensity of light reflected on the back surface of the substrate after entering from the front surface of the substrate can be reduced. Therefore, GaN
In a photolithography process for manufacturing a semiconductor device using the substrate 200, a situation in which exposure light incident from the front surface of the substrate is reflected on the back surface of the substrate and is exposed to an area other than a predetermined exposure area in the resist film. Can be avoided. Therefore, the pattern accuracy in the photolithography process can be improved, so that the production yield of the nitride semiconductor device can be improved.

According to the sixth embodiment, the GaN layer serving as the GaN substrate 200 is doped with impurities to form the light absorbing portion 2.
Since 01 is formed, a decrease in crystallinity of the nitride semiconductor substrate having the light absorbing portion can be prevented.

[0199] Hereinafter, the requirements necessary to reduce the transmittance of the light absorbing portion 201 to 80% or less will be described.

Generally, when a specific type of impurity is introduced into a semiconductor, light absorption occurs. Here, the direction perpendicular to the main surface of the semiconductor substrate is defined as the z direction, the light absorption coefficient at a position z in the semiconductor substrate is defined as α (z), and the position z
Where I (z) is the light intensity at, the following (Equation 1) is established from the relationship between the amount of light attenuation and the light absorption coefficient of the light intensity I (z).

[0201]

(Equation 1)

Further, the region of the semiconductor substrate into which impurities are introduced, that is, the light absorbing portion is moved from position z1 to position z2.
And the thickness of the light absorbing portion (z2-z1) is z
0, and the light intensity at the time of entering the light absorbing portion is I ₀
And the intensity of the light at the time of passing through the light absorbing portion is I, the following (Equation 2) is established.

[0203]

(Equation 2)

Here, the following (Equation 3)

(Equation 3) Is the average of the light absorption coefficients α (z) from the position z1 to the position z2, and if this is set to α, the following (Equation 4) is eventually established.

[0205]

(Equation 4)

Here, when the range of the thickness z0 of the light absorbing portion is obtained using (Equation 4) under the condition that the transmittance I / I ₀ is 80% or less, the following (Equation 5) is obtained.

[0207]

(Equation 5)

That is, 0.223 / α is the value of the light absorbing portion 2
01 is the minimum required thickness of the light absorbing portion 201 to make the transmittance of 80% or less.

On the other hand, with respect to the impurity density in the light absorbing portion 201, it is preferable that the impurity density is high because α becomes large and the thickness of the light absorbing portion 201, that is, the impurity layer can be reduced. A shift occurs in the lattice constant of the crystal in the substrate, which causes deterioration of the crystallinity of the substrate. Therefore, when the impurity for forming the light absorbing portion 201 is As, the impurity density is 1 ×
It is preferably in the range of about 10 ¹³ cm ^{-3 to} about 1 × 10 ²⁰ cm ^-3 .

[0210] In the sixth embodiment, As is used as an impurity for forming the light absorbing portion 201.
The impurity is not particularly limited as long as it is a material that generates a level for absorbing exposure light when introduced into the GaN layer. For example, C (carbon), O (oxygen), Si, S (sulfur) , Cl (chlorine) or P (phosphorus) can be used instead of As. Also when C, O, Si, S, Cl or P is used as an impurity for forming the light absorbing portion 201, the impurity density is about 1 × 10 ¹³ cm ⁻³ to 1 × 10 ²⁰ cm ⁻ , similarly to As. It is preferred that the range be up to about ³ . When C is introduced into the GaN layer, a C-containing gas such as CH ₄ may be used during the crystal growth of the GaN layer. When O is introduced into the GaN layer, an O-containing gas such as NO ₂ may be used during crystal growth of the GaN layer. When introducing Si into the GaN layer, a Si-containing gas such as SiH ₄ may be used during the crystal growth of the GaN layer. When S is introduced into the GaN layer, an S-containing gas such as SF ₆ may be used during the crystal growth of the GaN layer. Further, when introducing Cl into the GaN layer, for example, the group V / group III raw material supply ratio (the ratio of the supply flow rate of ammonia per minute to the supply flow rate of gallium chloride per minute) at the time of crystal growth of the GaN layer. The content may be set to 100 or less so that Cl can be easily introduced into the nitrogen site of GaN. When P is introduced into the GaN layer, for example, phosphine may be mixed with ammonia for crystal growth of the GaN layer. Further, as described above, C, O, Si,
By appropriately selecting a gas to be used, such as S, Cl, P, or As, and introducing it into the GaN layer as an impurity, it is possible to prevent the occurrence of contamination or the like in the crystal growth apparatus.

Further, in the sixth embodiment, the light absorbing portion 201 is provided in the region on the back surface side of the GaN substrate 200. If the thickness z0 of the light absorbing portion satisfies the above (Equation 5), Impurities may be introduced into the entire substrate so that the entire substrate serves as a light absorbing portion.

In the sixth embodiment, the light absorbing portions 201 are uniformly provided in the region on the back surface side of the GaN substrate 200. Instead, the light absorbing portions 201 are arranged in a direction parallel to the substrate surface. May be distributed non-uniformly. With this configuration, not only the light is absorbed by the light absorbing portion but also the light is scattered by the light absorbing portion, so that the intensity of the reflected light can be further reduced. At this time, GaN
The following effects can be obtained by introducing impurities only into the lower part of the predetermined exposure region of the resist film on the substrate 200. That is, when forming a device while covering the vicinity of the active layer on the substrate with a resist pattern, for example, when manufacturing a ridge-type laser device, no impurity is introduced into the lower part of the substrate near the active layer. Thus, by reducing impurities diffused from the substrate to the vicinity of the active layer, it is possible to prevent an increase in operating current or the like due to light absorption by the impurities. On the other hand, patterning can be performed on a semiconductor layer other than the active layer on the substrate with a high yield by the effect of improving the pattern accuracy in the photolithography process. Here, as a method of doping impurities into the GaN substrate so that the light absorbing portions are unevenly distributed, for example, a method of ion-implanting impurities using an ion beam, or a method of growing a nitride semiconductor layer for forming a substrate. And a method using a combination of selective growth and buried growth. In the latter method, after selectively growing a nitride semiconductor layer while doping impurities by covering a region in which impurities are not to be doped with a mask, burying growth of the nitride semiconductor layer is performed without doping impurities. Do.

In the sixth embodiment, the GaN layer is made to absorb light by introducing impurities into the GaN layer. Alternatively, a point defect may be formed in the GaN layer to make the GaN layer light absorbing. Light absorption may be provided. At this time, for example, a point defect can be formed in the GaN layer by injecting protons or the like into the GaN layer.

In the sixth embodiment, the type of exposure light used in the photolithography step is not particularly limited, but light of a wavelength that propagates without being absorbed in the GaN substrate 200, for example, g-line Alternatively, when i-rays or the like are used as the exposure light, the pattern accuracy can be dramatically improved as compared with the related art.

Further, in the sixth embodiment, the type of the resist film used in the photolithography step may be a positive type or a negative type.

In the sixth embodiment, GaN is used as the material of the nitride semiconductor substrate. However, the present invention is not limited to this, and is made of GaN, InN, AlN, or a mixed crystal thereof.
A group III nitride semiconductor may be used. At this time, if these group III nitride semiconductors are the main components of the substrate,
The substrate may include other materials.

(Seventh Embodiment) Hereinafter, a semiconductor substrate and a method for manufacturing the same according to a seventh embodiment, a semiconductor device using the semiconductor substrate, and a method for manufacturing the semiconductor device will be described with reference to the drawings. .

FIG. 17 is a sectional view of a semiconductor substrate according to the seventh embodiment.

As shown in FIG. 17, the semiconductor substrate according to the seventh embodiment includes a group III nitride semiconductor layer, specifically,
An aN layer 300 is formed. In addition, the GaN layer 300 (hereinafter, referred to as GaN layer 300)
The thickness of the GaN substrate 300 may be, for example, 250 μm, and both surfaces are mirror-finished.

The feature of the seventh embodiment is that a plurality of light absorbing elements, such as As, introduced into the surface portion of the GaN substrate 300 so as to generate a level absorbing exposure light such as g-line or i-line. Part (part that absorbs light incident from the substrate surface)
301 is formed in a stripe shape. The width of each light absorbing part 301 (width along the direction parallel to the substrate surface) is about 310 μm, and the interval between each light absorbing part 301 is about 10 μm.

FIGS. 18A to 18E are cross-sectional views showing each step of the method for manufacturing a semiconductor substrate according to the seventh embodiment shown in FIG.

First, as shown in FIG. 18A, the unevenness 300 having a step of about 1/10 or more of the wavelength λ of the exposure light.
a provided on the back surface and having a thickness of 300 μm
Prepare 00. The GaN substrate 300 can be manufactured by using the method for manufacturing a semiconductor substrate according to the first embodiment.

Next, as shown in FIG.
On the surface of the substrate 300, a plurality of hard masks 302 made of SiO ₂ are formed by photolithography.
Here, the width of each hard mask 302 is 300 μm, and the interval between each hard mask 302 is 20 μm. In the photolithography process for forming the hard mask 302, the unevenness 300a on the back surface of the GaN substrate 300 functions as a light scattering portion (see the first embodiment), so that the pattern accuracy of the hard mask 302 is improved.

Next, as shown in FIG. 18C, the hard mask 302 is used to form As on the surface of the GaN substrate 300.
Is introduced to form the plurality of light absorbing portions 301 in a stripe shape.

Here, the method of injecting As into the GaN substrate 300 is not particularly limited. Hereinafter, the method of injecting As into the GaN substrate in the method of manufacturing a semiconductor substrate according to the seventh embodiment will be described with reference to FIG. An example will be described. FIG.
As shown in FIG. 9, Ga provided with a hard mask 302
After forming the GaAs layer 303 on the surface of the N substrate 300, the GaN substrate 300 is placed in a reaction tube 350 made of quartz or the like.
On the susceptor 351 in the inside. Then, the reaction tube 35
Ammonia is supplied from the gas inlet 350a of the reaction tube 350, and the ammonia in the vicinity of the susceptor 351 is heated to 1000 ° C.
Heat to about. As a result, A in the GaAs layer 303
s diffuses into the surface of the GaN substrate 300 and
1 is formed. The used ammonia is supplied to the reaction tube 350
From the gas discharge port 350b. The susceptor 3
51 is made of, for example, graphite. Further, as the heating means 352, a tubular resistance wire heater or the like is used.

Performing the As implantation step shown in FIG. 19 in an ammonia atmosphere can prevent nitrogen from being released from the back surface (rough surface) of GaN substrate 300 due to nitrogen generated by decomposition of ammonia. Because. Therefore, As implantation may be performed in an atmosphere of another gas having a nitrogen atom instead of ammonia.

Further, the G formed on the GaN substrate 300
Since the aAs layer 303 does not need to be single crystal,
The s layer 303 may be formed by a sputtering method. Further, instead of the GaAs layer 303, an As layer or a compound layer containing As may be formed.

The temperature at which As is diffused into the GaN substrate 300 may be lower than 1000 ° C. In this case, since the diffusion speed of As decreases, the desired light absorbing portion 3
In order to obtain a distribution shape of 01, that is, a diffusion profile of As, it is necessary to lengthen the diffusion time of As. However,
In order to diffuse As so that the light transmittance of the light absorbing portion 301 is sufficiently reduced in a practical diffusion time of several hours to several tens of hours, the diffusion temperature of As should be set to 700 ° C. or more. Is preferred.

The width of each light absorbing portion 301 obtained by the As implantation process shown in FIG. 19 is 310 μm wider than the width of each hard mask 302 due to the diffusion of As.
Therefore, the interval between the light absorbing portions 301 is 10 μm. Note that the thickness of each light absorbing portion 301 is about 5 μm.

Next, as shown in FIG. 18D, the hard mask 30 is formed by wet etching using hydrofluoric acid or the like.
2 is removed, the GaN substrate 30 having the irregularities 300a is removed.
0 is polished, and the back surface is mirror-finished as shown in FIG.

The light absorbing section 301 thus obtained is
When manufacturing a nitride semiconductor device using the GaN substrate 300, for example, a high-performance ridge-type laser device having a low operating current can be manufactured with high yield.

Hereinafter, a method of manufacturing a semiconductor device using a semiconductor substrate according to the seventh embodiment, specifically, a method of manufacturing a ridge-type laser device will be described with reference to FIGS.
This will be described with reference to (a) to (d).

First, as shown in FIG. 20A, a GaN substrate 300 having a light absorbing portion 301 (see FIG. 17) is prepared. Hereinafter, only the region (that is, the ridge structure forming region) sandwiched between the pair of light absorbing portions 301 in the GaN substrate 300 and the vicinity thereof will be described with reference to the drawings.

Next, as shown in FIG.
A quantum well active layer comprising an n-type Al _0.1 Ga _0.9 N cladding layer 310 having a thickness of 1 μm, an In _0.2 Ga _0.8 N well layer having a thickness of 30 nm and an In _0.02 Ga _0.98 N barrier layer having a thickness of 50 nm on a substrate 300. 311, 2 μm thick p-type Al _0.1 G
An a _0.9 N cladding layer 312 is sequentially formed. For forming each of these nitride semiconductor layers, for example, the MOVPE method can be used. In addition, for example, 100
When each nitride semiconductor layer is grown at a temperature of about 0 ° C., As in the light absorbing portion 301 is further diffused, so that the distribution region of the light absorbing portion 301 is enlarged as shown in FIG. I do. Thus, for example, in the vicinity of the interface between the GaN substrate 300 and the n-type Al _0.1 Ga _0.9 N cladding layer 310, the distance between the light absorbing portions 301 becomes about 2 to 3 μm, and in the vicinity of the quantum well active layer 311 Absorber 3
The distance between 01 is about 5 μm.

Next, as shown in FIG.
After forming a positive resist film 313 on the l _0.1 Ga _0.9 N cladding layer 312, as shown in FIG. 20D, a ridge structure forming region (light absorbing portion 30) having a width of about 3 μm is formed.
The resist film 313 is irradiated with g-rays as exposure light through a photomask 360 covering the region sandwiched between them.
At this time, since the light absorbing portion 301 exists in a region of the GaN substrate 300 (including each nitride semiconductor layer) that is not covered by the photomask 360, the intensity of light reflected from the back surface of the GaN substrate 300 during exposure is increased. Is reduced. As a result, after the exposure light is diffracted around the photomask 360 toward the inside of the photomask 360, the GaN substrate 30
Thus, it is possible to prevent a situation where the light is reflected by the back surface of the photomask 360 and the portion of the resist film 313 below the photomask 360 is exposed.

Next, as shown in FIG. 21A, a resist pattern 313A is formed by developing the resist film 313 and removing a portion of the resist film 313 irradiated with exposure light. At this time, since unnecessary exposure of the resist film 313 is prevented as described above, the resist pattern 313A can be formed with high accuracy.

Next, as shown in FIG. 21B, using the resist pattern 313A as a mask, p-type Al _0.1 Ga _0.9.
The N-clad layer 312 is subjected to, for example, reactive ion etching using Cl gas plasma to form a ridge structure 312a. At this time, the p-type Al _0.1
As a result of the side etching of the Ga _0.9 N cladding layer 312, the ridge structure 312a becomes trapezoidal.

Next, as shown in FIG. 21C, after removing the resist pattern 313A using an organic solvent or the like,
As shown in FIG. 21D, a p-electrode 314 having a multilayer structure of Ni (nickel) and Au (gold) having a thickness of about 1 μm is formed on the ridge structure 312a.
An n-electrode 315 having a multilayer structure of Ti (titanium) and Al and having a thickness of about 1 μm is formed on the back surface of the aN substrate 300. At this time, since the back surface of the GaN substrate 300 is mirror-finished (see FIG. 18E), the n-electrode 315 can be formed with good adhesion while preventing disconnection. Thereafter, although not shown, the nitride semiconductor laser device is completed by dividing the GaN substrate on which the nitride semiconductor layer structure shown in FIG. 21D is formed, ie, the semiconductor wafer, by cleavage.

FIG. 22 shows the cross-sectional structure of a nitride semiconductor laser device manufactured by the above-described method, that is, the semiconductor device according to the seventh embodiment, which shows the distribution of light emitting regions when the device emits light. It is shown together with.

Incidentally, since the As impurity absorbs light having a wavelength of about 400 nm, if the As impurity is present in the light emitting region, the light emitted from the nitride semiconductor laser device is absorbed and the luminous efficiency is reduced. Occurs. However, in the seventh embodiment, as shown in FIG. 22, the light emitting region 316 has the light absorbing portion 3 having the As impurity.
01, the laser light is not absorbed, so that a decrease in luminous efficiency can be prevented.

As described above, according to the seventh embodiment, since the light absorbing portions 301 are formed on the front surface of the GaN substrate 300, the intensity of light reflected from the back surface of the substrate after being incident from the front surface of the substrate. Can be reduced. Therefore, GaN
In a photolithography process for manufacturing a semiconductor device using the substrate 300, a situation in which exposure light incident from the surface of the substrate is reflected on the back surface of the substrate and is exposed to areas other than the predetermined exposure area in the resist film. Can be avoided. Therefore, the pattern accuracy in the photolithography process can be improved, so that the production yield of the nitride semiconductor device can be improved.

According to the seventh embodiment, the light absorption section 3 is formed by injecting impurities into the GaN layer serving as the GaN substrate 300.
Since 01 is formed, a decrease in crystallinity of the nitride semiconductor substrate having the light absorbing portion can be prevented.

Further, according to the seventh embodiment, the light absorbing portion 301 is formed by introducing impurities only into the portion of the resist film on the GaN substrate 300 below the predetermined exposure region. Therefore, impurities diffused from the GaN substrate 300 in the vicinity of the active layer on the GaN substrate 300 can be reduced to prevent an increase in operating current due to light absorption by the impurities and to improve the pattern accuracy in the photolithography process. Thereby, other nitride semiconductor layers other than the active layer can be patterned with good yield.

According to the seventh embodiment, since the back surface of the GaN substrate 300 is mirror-finished, the GaN substrate 3
00 can be used to simplify the semiconductor device manufacturing process.

In the seventh embodiment, the light absorbing portion 301 is provided on the GaN substrate 300. However, instead of this, a light scattering portion (see the first embodiment, etc.) or an antireflection film, that is, a light transmitting portion is provided. A unit (see the second embodiment and the like) may be provided.

In the seventh embodiment, a semiconductor device having a ridge structure is manufactured by using the GaN substrate 300. Alternatively, a semiconductor device having a groove structure may be manufactured.

In the seventh embodiment, the type of exposure light used in the photolithography process is not particularly limited, but light having a wavelength that propagates in the GaN substrate 300 without being absorbed, for example, g-line Alternatively, when i-rays or the like are used as the exposure light, the pattern accuracy can be dramatically improved as compared with the related art.

Also, in the seventh embodiment, FIG.
Although a positive resist film is used in the photolithography steps shown in FIGS. 21C and 21D and FIG. 21A, a negative resist film may be used instead. In this case, a photomask that covers an area other than the ridge structure forming area (area sandwiched between the light absorbing portions 301) is used, and the resist film is developed to remove a portion of the resist film to which the exposure light has not been irradiated. Thus, a resist pattern is formed.

In the seventh embodiment, GaN is used as the material of the nitride semiconductor substrate. However, the present invention is not limited to this, and is made of GaN, InN, AlN, or a mixed crystal thereof.
A group III nitride semiconductor may be used. At this time, if these group III nitride semiconductors are the main components of the substrate,
The substrate may include other materials.

[0250]

According to the present invention, by providing a light scattering portion, a light transmitting portion or a light absorbing portion on a semiconductor substrate containing a Group III nitride as a main component, light reflected from the rear surface of the substrate after being incident from the substrate surface. In the photolithography process for manufacturing a nitride semiconductor device,
It is possible to avoid a situation in which a region other than the predetermined exposure region in the resist film is exposed. Therefore, the pattern accuracy in the photolithography process can be improved, so that the production yield of the nitride semiconductor device can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor substrate according to a first embodiment of the present invention.

FIGS. 2A to 2E are cross-sectional views illustrating respective steps of a method for manufacturing a semiconductor substrate according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a MOVPE apparatus used in the method for manufacturing a semiconductor substrate according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of an HVPE apparatus used in the method for manufacturing a semiconductor substrate according to the first embodiment of the present invention.

FIG. 5 is a view showing a state in which a resist film formed on the semiconductor substrate according to the first embodiment of the present invention is being exposed.

FIG. 6 shows the reflectivity of exposure light on the back surface of the substrate and the appearance of the resist pattern forming a line portion when a line and space resist pattern having a line portion and a space portion having a width of 2 μm is formed on a GaN substrate. It is a figure showing the relation with non-defective rate.

FIG. 7 is a sectional view of a semiconductor substrate according to a second embodiment of the present invention.

FIGS. 8A to 8C are cross-sectional views illustrating respective steps of a method for manufacturing a semiconductor substrate according to a modification of the second embodiment of the present invention.

FIG. 9 is a sectional view of a semiconductor substrate according to a third embodiment of the present invention.

FIGS. 10A to 10E are cross-sectional views illustrating respective steps of a method for manufacturing a semiconductor substrate according to a third embodiment of the present invention.

FIG. 11 is a sectional view of a semiconductor substrate according to a fourth embodiment of the present invention.

FIG. 12 is a sectional view of a semiconductor substrate according to a fifth embodiment of the present invention.

FIGS. 13A to 13E are cross-sectional views illustrating steps of a method for manufacturing a semiconductor substrate according to a fifth embodiment of the present invention.

FIGS. 14A to 14C are cross-sectional views illustrating steps of a method for manufacturing a semiconductor substrate according to a fifth embodiment of the present invention.

FIG. 15 is a sectional view of a semiconductor substrate according to a sixth embodiment of the present invention.

FIGS. 16A to 16F are cross-sectional views illustrating respective steps of a method for manufacturing a semiconductor substrate according to a sixth embodiment of the present invention.

FIG. 17 is a sectional view of a semiconductor substrate according to a seventh embodiment of the present invention.

FIGS. 18A to 18E are cross-sectional views illustrating respective steps of a method for manufacturing a semiconductor substrate according to a seventh embodiment of the present invention.

FIG. 19 is a diagram illustrating an example of a method of implanting As into a GaN substrate in a method of manufacturing a semiconductor substrate according to a seventh embodiment of the present invention.

FIGS. 20A to 20D are cross-sectional views illustrating steps of a method of manufacturing a semiconductor device using a semiconductor substrate according to a seventh embodiment of the present invention.

FIGS. 21A to 21D are cross-sectional views illustrating steps of a method for manufacturing a semiconductor device using a semiconductor substrate according to a seventh embodiment of the present invention.

FIG. 22 is a sectional view of a semiconductor device using a semiconductor substrate according to a seventh embodiment of the present invention.

FIG. 23 is a view showing a state in which a resist film formed on a conventional nitride semiconductor substrate is exposed.

[Explanation of symbols]

Reference Signs List 100 GaN layer (GaN substrate) 100a Unevenness 101 Sapphire substrate 102 Silicon substrate 103 AlN layer 104 Aluminum oxide layer 105 Gallium oxide layer 106 Light scattering part 106a SiO ₂ grain 107 GaN layer 108 Al _0.1 Ga _0.9 N layer 109 Light absorbing part 109a Si Layer 110 First Si layer 111 First resist pattern 112 First GaN layer 113 Second Si layer 114 Second GaN layer 150 Reaction tube 150a Gas inlet 150b Gas outlet 151 Substrate to be processed 152 Susceptor 153 Heating Means 160 Reaction tube 160a First gas inlet 160b Second gas inlet 160c Gas outlet 161 Substrate to be processed 162 Susceptor 163 Ga 164 in molten state Dish 165 Heating means 171 Resist film 171a Should be exposed originally Region 172 Photomask 172a Opening 173 Incident light (exposure light) 174 Outgoing light 175 Reflected light 200 GaN layer (GaN substrate) 201 Light absorbing unit 202 Sapphire substrate 203 Silicon substrate 204 AlN layer 300 GaN layer (GaN substrate) 300a Unevenness 301 Light absorbing part 302 Hard mask 303 GaAs layer 310 n-type Al _0.1 Ga _0.9 N clad layer 311 quantum well active layer 312 p-type Al _0.1 Ga _0.9 N clad layer 312 a ridge structure 313 resist film 313 A resist pattern 314 p electrode 315 n electrode 316 Light-emitting area 350 Reaction tube 350a Gas inlet 350b Gas outlet 351 Susceptor 352 Heating means 360 Photomask

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Masaya Manno 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-house F term (reference) 5F041 AA31 CA40 CA77 5F052 CA10 KA10 5F073 AA13 CA02 CB02 DA21 DA35

Claims (49)

[Claims] 1. A semiconductor layer comprising a group III nitride as a main component, and a scattering portion for scattering incident light incident on the semiconductor layer from one surface of the semiconductor layer is provided on another surface or inside the semiconductor layer. A semiconductor substrate provided in a semiconductor device. 2. The scattering section according to claim 1, wherein the other surface of the semiconductor layer is provided with unevenness having a step of about 1/10 or more of the wavelength of the incident light. Semiconductor substrate. 3. The semiconductor substrate according to claim 2, wherein the reflectance of the incident light on the other surface of the semiconductor layer is about 13% or less. 4. The wavelength of the incident light is 365 nm or 43 nm.
The semiconductor substrate according to claim 3, wherein the thickness is 6 nm. 5. The scatterer is provided inside the semiconductor layer, and the scatterer is configured to receive the incident light.
The semiconductor substrate according to claim 1, further comprising a particle or a layer made of a material having a different refractive index from the group nitride. 6. The semiconductor substrate according to claim 5, wherein the diameter of the particles made of the material is about 1/10 or more of the wavelength of the incident light. 7. The width of the layer made of the material along a direction parallel to the one surface is about 1/10 or more of the wavelength of the incident light.
A semiconductor substrate according to claim 1. 8. The semiconductor substrate according to claim 5, wherein the thickness of the layer made of the material is at least about 1/10 of the wavelength of the incident light. 9. The particle or layer made of the material is provided along a direction parallel to the one surface, and the scattering portion is provided along a direction parallel to the one surface. 6. The semiconductor substrate according to claim 5, wherein another semiconductor layer provided and comprising the group III nitride as a main component and the grains or layers are alternately stacked. 10. The semiconductor substrate according to claim 5, wherein the thickness of the scattering portion is at least about 1/10 of the wavelength of the incident light. 11. The semiconductor substrate according to claim 5, wherein said material is Si, SiO ₂ , SiN or Al ₂ O ₃ . 12. The semiconductor substrate according to claim 5, wherein said scattering portion has a transmittance for said incident light of 80% or less. 13. The wavelength of the incident light is 365 nm or 4 nm.
13. The semiconductor substrate according to claim 12, wherein the thickness is 36 nm. 14. A semiconductor layer comprising a group III nitride as a main component, and a transmission portion for transmitting incident light incident on the semiconductor layer from one surface of the semiconductor layer is provided on another surface of the semiconductor layer. A semiconductor substrate characterized in that: 15. The transmission part, wherein a layer made of a material having a different refractive index from the group III nitride with respect to the incident light is formed on the other surface of the semiconductor layer. The semiconductor substrate according to claim 14, wherein: 16. The device according to claim 15, wherein the layer made of the material is a plurality of layers, and at least two of the plurality of layers have different refractive indexes with respect to the incident light. A semiconductor substrate according to claim 1. 17. The refractive index of the material for the incident light is 9 times the refractive index of the group III nitride for the incident light.
16. The semiconductor substrate according to claim 15, wherein the ratio is about / 10 or less. 18. The material may be SiO ₂ , SiN or Al.
The semiconductor substrate according to claim 15 which is a ₂ O _3. 19. The material constitutes the semiconductor layer.
The semiconductor substrate according to claim 15, wherein the semiconductor substrate is a compound of a group III element and oxygen. 20. The material is Al _x Ga ₁ -xN (where 0 <
16. The semiconductor substrate according to claim 15, wherein x ≦ 1). 21. The semiconductor substrate according to claim 14, wherein the transmittance of the transmission portion with respect to the incident light is 80% or more. 22. The wavelength of the incident light is 365 nm or 4 nm.
22. The semiconductor substrate according to claim 21, wherein the thickness is 36 nm. 23. A light-emitting device, further comprising: a scattering portion provided between the other surface of the semiconductor layer and the transmission portion or inside the semiconductor layer and scatters the incident light. The semiconductor substrate according to claim 14, wherein: 24. An at least one part of the semiconductor layer, comprising a semiconductor layer containing a group III nitride as a main component, wherein an absorbing part for absorbing incident light incident on the semiconductor layer from one surface of the semiconductor layer is provided. A semiconductor substrate, comprising: 25. The semiconductor substrate according to claim 24, wherein a transmittance of the absorbing portion to the incident light is 80% or less. 26. The wavelength of the incident light is 365 nm or 4 nm.
26. The semiconductor substrate according to claim 25, wherein the thickness is 36 nm. 27. The semiconductor substrate according to claim 24, wherein said absorbing section is made of a material having a larger absorption coefficient with respect to said incident light than said group III nitride. 28. The semiconductor substrate according to claim 27, wherein the material is a plurality of materials having different absorption coefficients for the incident light. 29. The semiconductor substrate according to claim 27, wherein the material includes at least one of Si and W. 30. The semiconductor substrate according to claim 24, wherein the absorbing section is formed by adding an impurity to the semiconductor layer so as to generate a level for absorbing the incident light. 31. The method according to claim 31, wherein the impurities are C, O, Si, S, C
31. The semiconductor substrate according to claim 30, comprising at least one of l, P, and As. 32. The relationship of z0 ≧ 0.223 / α holds, where α is an absorption coefficient of the absorbing portion with respect to the incident light and z0 is a thickness of the absorbing portion. 30. The semiconductor substrate according to 30. 33. The semiconductor substrate according to claim 24, wherein the absorbing section is formed by forming a point defect in the semiconductor layer. 34. The semiconductor substrate according to claim 33, wherein said point defects are formed by introducing protons into said semiconductor layer. 35. The semiconductor substrate according to claim 24, wherein the absorbing portions are unevenly distributed along a direction parallel to one surface of the semiconductor layer. 36. A step of partially forming a light scattering portion made of a material having a different light refractive index from the group III nitride on the first semiconductor layer mainly containing a group III nitride; On the first semiconductor layer including the light scattering portion, the II
Crystal-growing a second semiconductor layer containing Group I nitride as a main component, thereby forming a semiconductor substrate composed of the first semiconductor layer, the light scattering portion and the second semiconductor layer. A method of manufacturing a semiconductor substrate. 37. The step of partially forming the light scattering portion includes the steps of: forming a film to be the light scattering portion over the entire surface of the semiconductor layer; and partially forming a mask pattern on the film. Forming the light scattering portion by removing the part of the film that is not covered by the mask pattern by etching the film using the mask pattern, 37. The method according to claim 36, further comprising: removing a mask pattern. 38. A step of forming irregularities having a step larger than a predetermined value on the back surface of the semiconductor layer containing a group III nitride as a main component, and forming the irregularities on the back surface of the semiconductor layer on which the irregularities are formed.
Forming a buried film made of a material having a different photorefractive index from the group III nitride to form a semiconductor substrate composed of the semiconductor layer and the buried film. Manufacturing method. 39. a step of partially forming a light absorbing portion made of a material having a larger light absorption coefficient than the group III nitride on the first semiconductor layer mainly containing a group III nitride; The II above the first semiconductor layer including the light absorbing portion.
Crystal-growing a second semiconductor layer containing Group I nitride as a main component, thereby forming a semiconductor substrate composed of the first semiconductor layer, the light absorbing portion, and the second semiconductor layer. A method of manufacturing a semiconductor substrate. 40. A light absorbing portion is formed by injecting an impurity into a semiconductor layer containing Group III nitride as a main component to generate a level for absorbing light, thereby forming a light absorbing portion from the semiconductor layer and the light absorbing portion. A method of manufacturing a semiconductor substrate, comprising a step of forming a semiconductor substrate to be configured. 41. The step of forming the light absorbing portion includes forming a mask pattern partially on the semiconductor layer, and implanting the impurity into the semiconductor layer using the mask pattern. 41. The method according to claim 40, further comprising: partially forming the light absorbing portion in the semiconductor layer; and removing the mask pattern. 42. A semiconductor substrate having a scattering portion for scattering light incident from one surface provided on another surface or inside thereof and comprising a Group III nitride as a main component, and a semiconductor comprising the Group III nitride. A structure formed on the one surface of the semiconductor substrate by using photolithography and etching for the layer. 43. A semiconductor substrate having a transmission portion for transmitting light incident from one surface on another surface and containing a group III nitride as a main component, and a semiconductor layer made of the group III nitride. A structure formed on the one surface of the semiconductor substrate by using photolithography and etching. 44. A semiconductor substrate comprising a group III nitride-based semiconductor substrate, wherein at least a portion for absorbing light incident from one surface is provided on the semiconductor substrate and the group III nitride semiconductor layer. A structure formed on the one surface of the semiconductor substrate by using photolithography and etching. 45. The semiconductor device according to claim 42, wherein said structure has a ridge structure or a groove structure. 46. The semiconductor device according to claim 44, wherein the structure has a ridge structure, and the absorber is not provided below the ridge structure in the semiconductor substrate.
3. The semiconductor device according to claim 1. 47. A scatterer for scattering light incident from one surface is provided on another surface or inside, and the scatterer is provided on the one surface of the semiconductor substrate containing a group III nitride as a main component. Forming a semiconductor layer made of a group III nitride, forming a positive or negative resist film on the semiconductor layer, and exposing the resist film to light through a photomask having an opening. Irradiating the resist film, and developing the resist film to remove a portion of the resist film irradiated with the exposure light when the resist film is a positive type, and to remove the portion when the resist film is a negative type. Removing a portion of the resist film that has not been exposed to the exposure light, thereby forming a resist pattern; and using the resist pattern as a mask with respect to the semiconductor layer. Performing a step of performing etching. 48. A transmitting portion for transmitting light incident from one surface is provided on another surface, and the II portion is formed on the one surface of the semiconductor substrate containing a group III nitride as a main component.
Forming a semiconductor layer made of a group I nitride, forming a positive or negative resist film on the semiconductor layer, and exposing the resist film to light through a photomask having an opening. Irradiating the resist film, and developing the resist film to remove a portion of the resist film irradiated with the exposure light when the resist film is a positive type and when the resist film is a negative type, Removing a portion of the resist film that was not irradiated with the exposure light, thereby forming a resist pattern; and etching the semiconductor layer using the resist pattern as a mask. Characteristic pattern formation method. 49. A semiconductor substrate containing a group III nitride as a main component, wherein the group III nitride is provided on at least a portion of the semiconductor substrate. Forming a semiconductor layer made of a material, forming a positive or negative resist film on the semiconductor layer, and irradiating the resist film with exposure light through a photomask having an opening. And developing the resist film to remove a portion of the resist film irradiated with the exposure light when the resist film is positive and to remove the resist film when the resist film is negative. Removing the portion of the semiconductor layer not irradiated with the exposure light, thereby forming a resist pattern, and using the resist pattern as a mask to the semiconductor layer Performing a step of performing etching.