JP2002335009A - Method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device, wherein a substrate turning to a seed crystal for epitaxial growth is formed by a new manufacturing method, and a semiconductor layer is epitaxially grown on the substrate. SOLUTION: A temporary substrate of single crystal which is composed of first semiconductor material is prepared. A retaining layer composed of second semiconductor material which is different from the first semiconductor material is grown on the surface of the temporary substrate by using a liquid epitaxial growth method. The temporary substrate is eliminated, and the retaining layer is left. A first layer composed of third semiconductor material different from the first semiconductor material is epitaxially grown on the surface of the retaining layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device by epitaxially growing a semiconductor layer on a substrate formed of a semiconductor material for which it is difficult to form a bulk single crystal substrate. On how to do it.

[0002]

2. Description of the Related Art As an element for outputting light in an infrared wavelength region (infrared region having a wavelength of 920 nm or less) having high light receiving sensitivity of a photodiode using silicon, Zn-doped GaAs is used.
There is known a double hetero light-emitting diode in which an s layer is sandwiched between AlGaAs layers. This double hetero structure is usually formed on a GaAs substrate. Light emitted from the GaAs light emitting layer is absorbed by the GaAs substrate. Therefore,
Light cannot be extracted to the substrate side.

An n-type AlGaAs cladding layer, a p-type GaAs active layer and a p-type AlGaAs cladding layer are formed on a GaAs substrate by a liquid phase epitaxial growth method.
Then, a technique for removing the GaAs substrate by mechanical polishing or the like is known (see the prior art in Japanese Patent Application Laid-Open No. 63-31885). However, with this method, it is difficult to obtain a light-emitting element that can operate with high efficiency and high speed.

Japanese Patent Application Laid-Open No. 63-312885 discloses a technique of forming an AlGaAs cladding layer and an AlGaAs or GaAs active layer on an AlGaAs substrate by metal organic chemical vapor deposition (MOCVD). However, it only states that an AlGaAs substrate is prepared, but does not disclose any method for manufacturing an AlGaAs substrate.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a semiconductor device in which a substrate serving as a seed crystal for epitaxial growth is manufactured by a new manufacturing method, and a semiconductor layer is epitaxially grown thereon. is there.

[0006]

According to one aspect of the present invention, there is provided a step of preparing a temporary single-crystal substrate made of a first semiconductor material, and a step of forming a temporary substrate on the temporary substrate by a liquid phase epitaxial growth method. Growing a support layer made of a second semiconductor material different from the first semiconductor material, removing the temporary substrate, and leaving the support layer; A third material different from the first semiconductor material;
Epitaxially growing a first layer made of a semiconductor material described above.

[0007] By removing the temporary substrate from the support layer, the support layer can be used as a seed crystal substrate for epitaxial growth. Since the temporary substrate has been removed,
This manufacturing method is particularly effective when a light emitting layer is formed on a support layer and light is extracted to the support layer side.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a semiconductor device according to an embodiment of the present invention will be described with reference to FIGS.

A temporary substrate 1 made of GaAs shown in FIG. 1A is prepared. The main surface of the temporary substrate 1 is a (100) plane of GaAs. The temporary substrate 1 is doped with Zn to have p-type conductivity, and its concentration is 2 to 2.
It is 5 × 10 ¹⁹ cm ⁻³ .

On the main surface of the temporary substrate 1, Al _0.26 Ga having a thickness of 40 μm is formed by liquid phase epitaxy (LPE).
_0.74 As high concentration layer 2 and 150 μm thick Al _0.26 Ga
_{A 0.74} As low concentration layer 3 is grown in order. These two layers are referred to as a support layer 4. LPE mainly includes a temperature difference method and a slow cooling method. Here, the temperature difference method is employed as described later. As the growth apparatus, for example, a slide boat type apparatus can be used. The high-concentration layer 2 and the low-concentration layer 3 are doped with Zn during growth so that the Zn concentration becomes 1 × 10 ¹⁸ cm ⁻³ and 5 × 10 ¹⁷ cm ⁻³ , respectively.

The growth solution used was GaAs in a Ga solvent.
s, Al and Zn are dissolved. The vertical temperature gradient of the growth solution filled in the melt bath is about 5
° C / cm, and the temperature of the lower part of the growth solution in contact with the seed crystal is 830 to 850 ° C. The temperature and the temperature gradient at the lower part of the growth solution are kept almost constant during the growth.

The steps up to the state shown in FIG. 1B will be described. The temporary substrate 1 made of GaAs shown in FIG. 1 is removed by etching. Thereby, only the support layer 4 remains. The temporary substrate 1 made of GaAs can be etched using an etching solution in which ammonia water and hydrogen peroxide solution are mixed at a volume ratio of 20: 1. The concentration of the ammonia water is 28% by weight, and the concentration of the hydrogen peroxide solution is 31% by weight.

Next, the surface of the low concentration layer 3 is ground to reduce unevenness. Further, after the ground surface is polished to remove processing damage, final finishing by chemical mechanical polishing (CMP) is performed. Generally, a semiconductor layer grown by the temperature difference method has poorer surface flatness than a semiconductor grown by the slow cooling method. By performing the final finish by CMP,
The flatness of the surface can be improved.

As shown in FIG. 2, AlGa is formed on the surface of the low concentration layer 3 by metal organic chemical vapor deposition (MOCVD).
Each layer from the As buffer layer 5 to the GaAs contact layer 12 is grown. The buffer layer 5 is formed of p-type Al _0.26 Ga _0.74 As doped with Zn, has a thickness of 0.2 μm, and a Zn concentration of 1 × 10 ¹⁸ cm ⁻³ .

The lower cladding layer 6 is formed of Zn-doped p-type Al _0.32 Ga _0.68 As, has a thickness of 1.0 μm, and a Zn concentration of 1 × 10 ¹⁸ cm ⁻³ .
The lower carrier confinement layer 7 is formed of Al _0.18 Ga _0.82 As not intentionally doped with impurities, and has a thickness of 1 μm.
0 to 50 nm. The Z of the lower carrier confinement layer 7
The background concentration of n is 5 × 10 ¹⁶ to 1 × 10 ¹⁷ c
m ^-3 .

The active layer 8 is formed of InGaAs and has a thickness of 2.4 to 5 nm. The composition ratio of In in the active layer 8 is 0.12 to 0.25. Upper carrier confinement layer 9
Is Al _0.18 Ga not intentionally doped with impurities.
It is formed of _0.82 As and has a thickness of 10 to 50 nm. The background concentration of Si in the upper carrier confinement layer 9 is 5 × 10 ¹⁶ to 1 × 10 ¹⁷ cm ⁻³ . The upper cladding layer 10 is made of n-type Al _0.32 Ga doped with Si.
_0.68 As, its thickness is 5.5 μm, its Si
The concentration is 1 × 10 ¹⁸ cm ⁻³ .

The current spreading layer 11 is made of n-doped Si.
Type Al _0.18 Ga _0.82 As, the thickness of which is 4.
5 μm, and its Si concentration is 1 × 10 ¹⁸ cm ⁻³ . The contact layer 12 is formed of n-type GaAs doped with Si, the thickness is 0.1 μm, and the Si concentration is 2 ×
It is 10 ¹⁸ cm ^-3 .

On the contact layer 12, N
An n-side electrode 15 in which an i-layer, a Ge layer, and an Au layer are stacked is formed. The n-side electrode 15 has, for example, an X-shaped planar shape by a lift-off method. On the surface of the high concentration layer 2 constituting a part of the support layer 4, a p-side electrode 16 in which an Au layer and an AuZn alloy layer are sequentially stacked from the support layer 4 side is formed. The p-side electrode 16 has a honeycomb shape by a lift-off method.

By applying a forward bias between the n-side electrode 15 and the p-side electrode 16 and injecting carriers into the active layer 8, light emission in the infrared region (wavelength 800 to 920 nm) can be generated. it can.

In the above embodiment, the support layer 4 made of AlGaAs becomes a substrate having a physical supporting force,
It becomes a MOCVD seed crystal. Since GaAs is not used as the substrate material, light can be extracted not only from the contact layer 12 side but also from the support layer 4 side. Since the contact layer 12 made of GaAs is very thin, it is removed by an acid treatment in a later chip forming step. For this reason, there is no obstacle to light extraction. When the wavelength at which the peak of the emission spectrum of the active layer 8 gives is shorter than the wavelength corresponding to the band gap of the semiconductor material forming the temporary substrate 1, the effect of removing the temporary substrate 1 is particularly high.

The lower carrier confinement layer 7, the active layer 8, and the upper carrier confinement layer 9 are formed by MOCVD. For this reason, compared with the case of forming by LPE, the uniformity of the film thickness can be improved, and high luminous efficiency can be realized. Note that molecular beam epitaxial growth (MBE) may be used instead of MOCVD.

FIG. 3 shows the relationship between the half-width of the X-ray rocking curve of the (400) plane of the support layer 4 and the output retention ratio.
The horizontal axis represents the half-width of the X-ray rocking curve in the unit of “reverse secant (arc sec)”, and the vertical axis represents the output maintenance ratio in the unit of “%”. The output maintenance ratio is a relative value of the light output after 1000 hours of energization, based on the light output in the initial state.

The half width of the X-ray rocking curve of the support layer 4 varies depending on the grinding, polishing and CMP conditions of the support layer 4. For example, when the grinder particle size at the time of grinding is reduced, a decrease in crystallinity due to grinding can be suppressed.

It can be seen that the output maintenance ratio decreases as the half width of the X-ray rocking curve increases. Generally, it is desired to secure an output maintenance ratio of 70% or more. For this reason, it is preferable that the inverse secant of the half width of the X-ray rocking curve of the (400) plane of the support layer 4 be 100 or less.

FIG. 4A is a view on the right in the depth direction.
1 shows the distribution of the composition ratio. The horizontal axis represents the depth from the surface of the support layer 4 in the unit of “μm”, and the right vertical axis represents the Al composition ratio. In the above embodiment, the Al composition ratio of the support layer 4 was 0.2, but the sample shown in FIG.
The l composition ratio is controlled to be 0.28. When the growth is performed by the temperature difference method, the temperature of the outermost growth surface is kept almost constant, so that the Al composition ratio can be made almost constant.

FIG. 4B shows an example of the emission spectrum of the active layer 8. The vertical axis represents wavelength, and its scale is
The vertical axis of the right figure corresponds to the wavelength corresponding to the band gap of AlGaAs having the Al composition ratio. The horizontal axis represents the emission intensity. Most part of the emission spectrum is A
It is located on the longer wavelength side than the wavelength corresponding to the 1 composition ratio 0.28. Therefore, the light emitted from the active layer 4 is transmitted through the support layer 4 without being absorbed by the support layer 4. Therefore, light can be efficiently extracted to the support layer 4 side.

FIG. 4B shows, as a comparative example, A by the slow cooling method.
4 shows the distribution of the Al composition ratio when an lGaAs layer is grown. When the slow cooling method is used, the temperature of the outermost growth surface changes, so that the Al composition ratio also changes. When the temperature is lowered to a certain temperature and reheating is performed, the Al composition ratio changes discontinuously. Therefore, the distribution of the Al composition ratio becomes triangular. Therefore, for example, even if the Al composition ratio is controlled to be 0.28, a part where the composition ratio becomes 0.28 or less also appears. The portion having an Al composition ratio of 0.28 or less absorbs a part of the light emitted from the active layer 8 (the portion L in the emission spectrum of FIG. 4B). For this reason, the light extraction efficiency to the support layer 4 side decreases.

Further, a region having a low potential appears in a portion where the Al composition ratio changes discontinuously, and carriers are accumulated therein. The accumulated carriers become a factor that hinders high-speed operation. Furthermore, the region having a large Al composition ratio has a relatively high electric resistance, so that the resistance of the entire device is increased.

As described above, the support layer 4 used as a substrate for forming a light emitting element is preferably grown by a temperature difference method.

FIG. 5 shows the measurement results of the transmittance of p-type Al _0.26 Ga _0.74 As for light having a wavelength of 860 nm. The horizontal axis represents the Zn concentration in the unit “cm ⁻³ ”, and the vertical axis represents the transmittance. The circle symbol, square symbol, and triangle symbol in the figure indicate the transmittance of the AlGaAs sample having a thickness of 32.5 μm, 75 μm, and 150 μm, respectively.

It can be seen that the transmittance decreases as the impurity concentration increases. Therefore, from the viewpoint of increasing the transmittance, it is preferable to lower the impurity concentration of the support layer 4 in order to extract light from the support layer 4 side. However, FIG.
In order to reduce the contact resistance between the support layer 4 and the p-side electrode 16 shown in FIG. 3, it is preferable to increase the impurity concentration of the support layer 4. More specifically, the impurity concentration is set to 1 to 3 × 10 ¹⁸ c
m- ³ is preferred.

The support layer 4 serves as a seed crystal for crystal growth by LPE and has a function as a support substrate having physical support force. Therefore, the thickness of the support layer 4 is set to 100
It is preferably at least 200 μm, more preferably at least 200 μm. For example, when the impurity concentration of the support layer 4 is 2 × 10 ¹⁸ cm ⁻³ and the thickness is 150 μm, the transmittance is reduced to about 0.68 as shown in FIG.

In the above-described embodiment shown in FIG. 2, the portion of the support layer 4 that contacts the p-side electrode 16 is formed as the high-concentration layer 2 so that the contact resistance is reduced and the other portions are formed as the low-concentration layer. By setting 3, the mechanical strength is secured while suppressing a decrease in transmittance. The impurity concentration of the low concentration layer 3 is 2
It is preferred to be about 5 × 10 ¹⁷ cm ⁻³ . In addition, it is preferable that the high-concentration layer 2 be thinner than the low-concentration layer 3 so that the ratio of the high-concentration layer 3 in the support layer 4 is less than 50%.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0035]

As described above, according to the present invention,
A support layer made of a semiconductor material different from that of the temporary substrate is epitaxially grown on the temporary substrate by LPE, and then the temporary substrate is removed. This makes it possible to manufacture a seed crystal substrate made of a semiconductor material for which it is difficult to manufacture a bulk substrate. A high-quality semiconductor layer can be grown on the seed crystal substrate by vapor phase epitaxial growth, molecular beam epitaxial growth, or the like.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a substrate for describing a method of manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a semiconductor device manufactured by a method of manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a half width of an X-ray rocking curve of a support layer and an output maintenance ratio of a semiconductor device.

FIG. 4A is a graph showing a distribution of an Al composition ratio and an emission spectrum of a support layer manufactured by a method according to an example, and FIG. 4B is manufactured by a method according to a comparative example. 5 is a graph showing a distribution of an Al composition ratio of a support layer and an emission spectrum.

FIG. 5 is a graph showing a relationship between a p-type impurity concentration of a support layer and transmittance.

DESCRIPTION OF SYMBOLS 1 Temporary substrate made of GaAs 2 AlGaAs high concentration layer 3 AlGaAs low concentration layer 4 Support layer 5 AlGaAs buffer layer 6 AlGaAs lower cladding layer 7 AlGaAs lower carrier confinement layer 8 AlGaAs active layer 9 AlGaAs upper carrier confinement Layer 10 AlGaAs upper cladding layer 11 AlGaAs current diffusion layer 12 GaAs contact layer 15 p-side electrode 16 n-side electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideyuki Watanabe 2-9-13 Nakameguro, Meguro-ku, Tokyo Stanley Electric Co., Ltd. F-term (reference) 5F041 AA31 CA04 CA22 CA34 CA36 CA63 CA65 CA74 CA85 5F053 AA03 AA36 DD05 DD12 FF02 GG01 HH04 KK01 KK04 LL04 RR03

Claims (7)

[Claims] A step of preparing a temporary single-crystal substrate made of a first semiconductor material; and a second step of forming a second substrate different from the first semiconductor material on a surface of the temporary substrate by a liquid phase epitaxial growth method. Growing a support layer made of a semiconductor material of the following; removing the temporary substrate and leaving the support layer; and forming a third semiconductor different from the first semiconductor material on the surface of the support layer. Epitaxially growing a first layer made of a material. 2. The method according to claim 1, further comprising: forming the third layer on the first layer.
Epitaxially growing an active layer made of a fourth semiconductor material having a band gap smaller than the band gap of the semiconductor material; and forming a band gap larger than the band gap of the fourth semiconductor material on the active layer. Epitaxially growing a second layer made of a fifth semiconductor material having a wavelength at which a peak of an emission spectrum of the active layer is shorter than a wavelength corresponding to a band gap of the first semiconductor material. The method of manufacturing a semiconductor device according to claim 1, wherein the thickness of the active layer and the third to fifth semiconductor materials are selected such that: 3. The first semiconductor material is GaAs, the second semiconductor material, the third semiconductor material, and the fifth semiconductor material are AlGaAs, and the fourth semiconductor material is InGaAs. A method for manufacturing a semiconductor device according to claim 1. 4. In the step of growing the support layer,
The temperature difference is provided above and below the solution in which the first semiconductor material to be grown is dissolved, the temporary substrate is arranged on the low temperature side, and the support layer is grown on the surface of the temporary substrate. 4. The method for manufacturing a semiconductor device according to any one of items 1 to 3. 5. The method according to claim 1, further comprising a step of chemically and mechanically polishing a growth surface of the support layer after removing the temporary substrate and before growing the first layer. A method for manufacturing a semiconductor device. 6. The step of growing the support layer, the step of growing a first support layer while doping the second semiconductor material with an impurity serving as an acceptor or a donor; 6. The method according to claim 1, further comprising the step of growing the second support layer while doping the impurity under a condition that the impurity concentration is lower than the impurity concentration of the first support layer. Of manufacturing a semiconductor device. 7. The method according to claim 6, wherein the first support layer is thinner than the second support layer.