JP2003229412A - Dry-etching method and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop an etching stop layer for a nitrided gallium compound semiconductor which is eagerly desired to effect highly accurate dry etching of the nitrided gallium compound semiconductor. <P>SOLUTION: A layer containing Al in the nitride semiconductor or containing Al<SB>x</SB>Ga<SB>y</SB>In<SB>1-x-y</SB>N (0≤x, 0≤y, x+y≤1) is employed as the etching stop layer, while etching is effected by etching gas containing at least oxygen and chlorine. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device of nitride semiconductor and a dry etching method used for manufacturing the same.

[0002]

2. Description of the Related Art Gallium nitride-based compound semiconductors have a direct transition type band structure, and the bandgap energy is in the range where blue to violet emission can be obtained. Researches on light-emitting devices and semiconductor lasers using them have been conducted. It is being actively conducted.

A high-brightness blue LED in which a gallium nitride-based compound semiconductor is laminated on a sapphire substrate has already been put to practical use. Similarly, a semiconductor laser has a life of more than 1000 hours at the time of announcement, etc. It is coming.
If the blue-violet nitride semiconductor laser is put to practical use, the recording capacity of the optical disk can be increased to 25 GB or more per single-sided single layer, so that practical use and high reliability are required.

GaN, AlGaN, InGaN, I
Since gallium nitride-based compound semiconductors such as nAlGaN have high withstand voltage, high thermal conductivity, and high saturation electron velocity, they are promising as materials for high frequency power transistors. In the HEMT structure using the AlGaN / GaN heterostructure, a high concentration of two-dimensional electron gas (2DEG) is accumulated near the hetero interface in the GaN film. Since the two-dimensional electron gas is spatially separated from the donor impurity doped in the AlGaN film and accumulated, it exhibits high electron mobility and thus low source resistance is obtained. Further, since this two-dimensional electron gas has a high saturated electron velocity even in a high electric field region, high frequency characteristics such as a high cutoff frequency are expected.

As described above, gallium nitride-based compound semiconductors are useful material systems from both light emitting devices and electronic devices, and it is strongly desired to develop techniques such as epitaxial growth, process and evaluation of gallium nitride-based compound semiconductors. There is. From the viewpoint of process technology, it is known that gallium nitride-based compound semiconductors are chemically stable and wet etching is difficult. Therefore, dry etching is mainly used for etching during the manufacturing process of an element using a gallium nitride-based compound semiconductor. In dry etching, a chlorine-based gas (chlorine Cl ₂ , carbon tetrachloride CCl ₄ , silicon tetrachloride SiCl ₄ ,
Boron trichloride BCl ₃ etc.) is used.

[0006]

FIG. 1 shows the structure of a semiconductor laser according to a conventional method.

In dry etching of gallium nitride-based compound semiconductors, no effective etching stop layer has been found so far. Therefore, the control of the etching thickness in the dry etching process must be time control. With time control, accurate etching in units of Å cannot be performed, and if accurate etching cannot be performed, the performance of the created device will be unstable.

In fact, when forming a ridge stripe in the fabrication of a nitride semiconductor laser, the first p-type is formed as shown in FIG.
The type Al _0.07 Ga _0.93 N cladding layer 8 needs to be etched with 1000 Å left, and in that case, highly accurate etching thickness control is required. However, in the current technology, due to the time control, the etching thickness differs from the design or varies between lots, which causes instability of light confinement, increase in threshold current, and deterioration of current-voltage characteristics. It brings about the harmful effects.

Further, variations in the etching thickness within the surface of the sample also occur due to the flow of the etching gas in the etching chamber and the anisotropy of the sample. This variation in the etching thickness within the sample plane also causes an increase in the threshold value and deterioration of the current-voltage characteristic, which lowers the yield of the device.

FIG. 2 is a sectional view of a field effect transistor having a HEMT structure using a conventional AlGaN / GaN hetero structure. As shown in the figure, on the substrate 21 made of silicon carbide or sapphire, the channel layer made of the GaN film 23, the n-type Al, and the buffer layer made of the AlN film 22 are interposed.
An electron supply layer made of the GaN layer 25 and a cap layer made of the n-type GaN layer 26 are sequentially formed. A predetermined region of the cap layer is etched to form a recess, and the gate electrode 27 is formed in the recess. A source electrode 28 and a drain electrode 29 are formed on both sides of the gate electrode 27 on the n-type GaN layer 26 which is a cap layer. In the conventional field effect transistor, the high-concentration two-dimensional electron gas 24 is formed in the vicinity of the hetero interface between the channel layer made of the GaN film 23 and the electron supply layer made of the n-type AlGaN layer 25. Therefore, the switching operation of the FET can be realized by controlling the concentration of the two-dimensional electron gas by applying the voltage to the gate electrode 27.

In the prior art, in order to reduce the contact resistance of the ohmic electrodes which are the source electrode 28 and the drain electrode 29, the HEMT structure having the cap layer is adopted. However, when etching is performed in a predetermined region of the cap layer to form a recess and the gate electrode 27 is formed in the recess, precise etching control is difficult.
The remaining thickness 30 shown in FIG. Due to variations in the remaining thickness 30 within the wafer surface or between lots, variations occur in the threshold voltage V _th , variations in the drain current, and the yield decreases.

Under the circumstances described above, development of an etching stop layer in dry etching of gallium nitride-based compound semiconductors has been earnestly desired.

[0013]

[Means for Solving the Problems] Dryer according to the present invention
The etching method overcomes the above problems.
Layer containing Al in dry etching of semiconductor
Nozawa Al_xGa_yIn _1-xyN (0 ≦ x, 0 ≦ y, x +
y ≦ 1) as an etching stop layer and oxygen
Etching with etching gas containing chlorine and chlorine
It is characterized by things. Hereinafter, the present invention will be described in more detail.
To do.

The dry etching according to the present invention is intended for gallium nitride-based compound semiconductors. Oxide is formed on the surface to be etched by adding oxygen to the etching gas during dry etching of the nitride semiconductor with chlorine gas. This oxide layer has a higher bond energy between atoms than the nitride layer, and thus is hard to be etched.
Above all, the binding energy between Al and oxygen is Ga and oxygen, In
It is about 1.5 times the binding energy between oxygen and oxygen.
Therefore, the presence of the bond between aluminum and oxygen on the surface lowers the etching rate.

That is, here, by lowering the RF bias applied to the substrate, cooling the chamber, etc., Al
If the parameters of dry etching are properly set so that the etching rate of oxides is greatly reduced, and a layer having a high aluminum composition is used as an etching stop layer in combination with an etching gas containing oxygen, a layer having a high aluminum composition is used as an etching stop layer. Work as.

If the concentration of oxygen contained in the etching gas is too low, the oxide layer will not be formed, and the concentration will be 5%.
The above is preferable, and since the etching does not proceed even if it is too much, the upper limit of the oxygen concentration is preferably about 80%. The aluminum composition of the etching stop layer is higher than that of the surroundings of the etching stop layer, preferably 25% or more, but it functions even if it is less than that.

As the etching gas of the present invention, a chlorine-based gas instead of chlorine, such as chlorine Cl ₂ , carbon tetrachloride CCl ₄ , silicon tetrachloride SiCl ₄ , boron trichloride BCl.
It can also be implemented by using ₃ or the like.

According to the method of the present invention, an oxide of Al is formed on the surface after etching. As it is, the stable Al oxide affects the subsequent process, specifically, the formation of the electrode and the like. Therefore, the Al oxide formed on the surface after the etching is used as a rare gas (He, Ar, Xe, N).
It is desirable to remove it by dry etching according to e). Further, it is also possible to use an ordinary photolithography process to remove at least a part of the Al oxide. Further, at least a part of the Al oxide formed on the surface after the etching is used as a rare gas (He, Ar,
By removing by dry etching using a mixed gas of Xe, Ne) and nitrogen, ohmic contact can be easily obtained in the subsequent electrode formation on the surface to be etched.

It is said that the surface of the surface to be etched becomes rich in group III by dry etching using only rare gas. It is considered that this group III rich state is alleviated by the supply of group V by performing dry etching with a mixed gas with nitrogen.

Dry etching with a mixed gas containing a large amount of oxygen may slow the etching rate. In order to avoid this, etching is performed only with chlorine until the etching stop layer is reached, and immediately after the etching stop layer is reached. It is ideal to introduce oxygen into the substrate, but in reality, considering variations in the etching rate, etching up to several hundred Å above the etching stop layer with chlorine alone or with a gas with a small oxygen concentration,
A method of increasing the oxygen concentration stepwise or continuously when the remaining amount reaches several hundred Å is also effective as a method for shortening the etching time and improving productivity and improving etching accuracy. .

In addition, the substantial bias applied to the sample is
When the RF bias is decreased or the pressure is changed by a means such as changing the pressure, the etching rate of the etching stop layer is greatly decreased as compared with the surrounding layer having a low Al composition, and as a result, the etching stop layer selection ratio is significantly increased. Increase,
This state is shown in FIG. This is considered to occur because the binding energy of Al—N is high. Applying this, etching is performed with chlorine only or a gas with a small oxygen concentration up to several hundred Å above the etching stop layer, and from this point, the oxygen concentration is increased stepwise or continuously. By substantially lowering the bias, the selection ratio is improved, the etching stop layer works more effectively, and accurate etching can be realized.

Further, in the blue-violet semiconductor laser structure, it is often not used from the viewpoint of the relationship of the refractive index and blocking of carriers, but in the case of an electronic device, by adding In to the region to be etched, the etching rate and the etching rate are increased. The selection ratio with respect to the stop layer can be improved. This is because the binding energy between In and N is Ga-N,
Resulting from the lower binding energy between Al and N, I
Since the layer containing n is easily etched, the etching rate becomes high. As described above, the selection ratio of the etching stop layer can be improved by lowering the bias applied to the sample instead of the higher etching rate, and more accurate etching control can be performed.

In a semiconductor device, an insulating film is formed on the exposed surface by etching with SiO ₂ or SiN,
Although it is essential to passivate. In the present invention, during dry etching, Al chlorides and Al oxides, which are etching products, are also attached to the sidewalls of the mesas and the ridge stripe by being sputtered from the etching bottom surface by the physical sputtering effect. The deposits on the side walls act as an important protective film for realizing anisotropic etching during the etching. The deposit on the side wall and the Al oxide layer formed on the etching bottom surface function as they are as an insulating film for the etching exposed surface. If this is used as an insulating film, SiO ₂ or S
The step of forming iN can be omitted, which leads to simplification of the process.

The fact that the present invention does not depend on the plasma gas generation method is clear from the principle of the present invention described in detail, and ECR (electron cyclotron resonance) plasma,
Whether ICP (inductively coupled) plasma, magnetron plasma or the like needs to be optimized for each condition, there is no problem in applying the present invention.

It is noted that Japanese Patent Application No. 11-32329 is characterized by etching with a gas containing oxygen or plasma generated from the gas, and the etching stop layer is made of Al _x G.
Although a dry etching method characterized by comprising a _1-x N (0 ≦ x ≦ 1) is described, the gist of the method is completely different from that of the present invention. This will be described below.

In the invention described in Japanese Patent Application No. 11-32329,
Oxide forms an oxide film and decomposes it with hydrogen to promote etching, and the oxygen content is 0.0
It is a very small amount of 1% to 3%, and the reaction vessel supplied with oxygen and hydrogen must be heated to 500 to 1200 ° C. However, in the present invention, the etching progresses due to chlorine or chlorine radicals, the oxygen content is preferably 5% or more, and the reaction vessel is preferably cooled. In view of the above, it is apparent that the gist of the invention described in Japanese Patent Application No. 11-32329 is completely different from that of the present invention.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 3 shows a cross section of a semiconductor laser device according to an embodiment of the present invention.
The details will be described below. MO on the sapphire C-plane substrate 1
The following structures are sequentially stacked by using CVD.

MBE (Molecular Beam Epitaxy) and HV
There is no problem in stacking the following structures by using another crystal growth method such as PE (hydride vapor phase epitaxy). Although a sapphire C-plane substrate was used as the substrate in this embodiment, a selective growth substrate, a silicon carbide substrate, a GaN substrate, or an Al substrate is used.
There is no problem even if another substrate such as a GaN substrate is used.

A low temperature buffer layer 2 made of n-type AlGaN, an n-type GaN layer 3, an n-type Al _0.3 Ga _0.7 N etching stop layer 201, an n-type Al _0.07 Ga _0.93 N cladding layer 4, an n-type GaN light guide layer 5, GaInN / GaN multiple quantum well active layer 6, p-type GaN optical guide layer 7, first p-type Al _0.07 Ga _0.93 N cladding layer 202, p-type Al _0.3 G
a _0.7 N etching stop layer 203, second p-type Al
_{The 0.07} Ga _0.93 N cladding layer 204 and the p-type GaN contact layer 9 are sequentially stacked. The film thickness of the first p-type Al _0.07 Ga _{0. 93} N cladding layer 202 considering confinement of light 1000
Å About good. Further, the p-type Al _0.3 Ga _0.7 N etching stop layer 203 has a high Al composition and causes lattice mismatch with the surroundings. In this embodiment, since the Al composition is 30%, the film thickness can be stacked up to about 1500Å from the viewpoint of epitaxial growth, but it is desirable to set the film thickness to about 10 to 200Å because it is used as an etching stop layer. The Al composition of the etching stop layer can take a higher value by adding In to relax the lattice mismatch.

Next, 700 to 900 are used to activate the p-type layer.
Anneal at 20 ° C. for 20 minutes. Subsequently, a mask for dry etching is laminated on the nitride semiconductor. Examples of the mask for etching include SiO ₂ and SiN.
The use of a resist as a mask is not desirable in the present invention because the resist is severely etched by oxygen. The stacked masks are patterned into stripes by a normal photolithography technique and used as a mask. After forming the mask, etching is performed using an ICP dry etching apparatus. A mixed gas of chlorine and oxygen is used as an etching gas.

The etching time is set longer than when etching is performed by time control. P-type GaN during etching
The contact layer 9 and the second p-type Al _0.07 Ga _0.93 N clad layer 204 are etched without any problem. The etching is p-type Al _0.3 Ga _0.7 N etching stop layer 203.
At that point, aluminum oxide is formed on the etching surface so as to cover the entire etching surface by the effect of oxygen gas and high-composition Al. Therefore, the etching is stopped in the p-type Al _0.3 Ga _0.7 N etch stop layer 203, so that a desired film ridge stripe first p-type Al _0.07 Ga _{0. 93} N cladding layer 202 remained having a thickness formed To be done.

Subsequently, the Al oxide film formed on the surface is removed by dry etching using a mixed gas of Ar and nitrogen.

After that, also in etching up to the n-type GaN layer 3, the n-type Al _0.3 Ga _0.7 N etching stop layer 2 is formed.
Up to 01, Al oxide formed after etching with a mixed gas of oxygen and chlorine is removed by dry etching with a mixed gas of Ar and nitrogen. Insulation film 1
The semiconductor laser device is completed through steps such as formation of 1, the formation of the p-electrode 10 and the n-electrode 12, element isolation, and the like. In the obtained semiconductor laser device, the film thickness of the first p-type Al _0.07 Ga _0.93 N clad layer 202 is uniform between lots or even within the lot, and has a thickness as designed, which stabilizes light confinement. Therefore, a decrease in the threshold current was observed as compared with the device that did not use the etching stop layer. In addition, since the variation within the wafer surface is suppressed, the yield is also improved.

(Embodiment 2) The same procedure as in Embodiment 1 is performed until the laser structure is laminated on the sapphire substrate. Then, annealing is performed at 700 to 900 ° C. for 20 minutes to activate the p-type layer.

Next, a mask for dry etching is laminated on the nitride semiconductor. The stacked masks are patterned into stripes by a normal photolithography technique and used as a mask. The sample with the mask formed is IC
Etching is performed using a P dry etching apparatus. A mixed gas of chlorine and oxygen is used as an etching gas.

At the time of dry etching, first of all, the etching is performed halfway using only chlorine. Second p-type Al _0.07 Ga
The thickness of the _0.93 N clad layer 204 is 4000 Å, and when the etching rate of dry etching using only chlorine is 1500 Å / min, the second p-type Al _0.07 Ga _0.93 N clad layer 204 is set to 5 _% in consideration of the variation in the rate.
Etching is performed for 140 seconds so as to leave about 00Å. When 140 seconds have passed, oxygen is added to the etching gas, and the RF bias applied to the sample is further lowered, whereby the etching rate is 60Å / min.
However, as shown in FIG. 4, the selectivity between the Al _0.07 Ga _0.93 N cladding layer and the Al _0.3 Ga _0.7 N etching stop layer is improved, and the controllability of the etching thickness is significantly improved. The etching is continued for 12 minutes as it is.

The semiconductor laser obtained through the steps following the above etching step has the same reduction of the threshold current as in the first embodiment.
Effects such as an increase in yield were seen.

Since the method described in Example 2 improves the etching stop layer selection ratio, it is possible to make the etching stop layer thinner than in Example 1. The use of a thin etching stop layer is useful because it can suppress the generation of defects and cracks due to lattice mismatch. HE using nitride semiconductor
This thin etching stopper layer is also effective when forming the MT.

(Embodiment 3) FIG. 5 is a cross-sectional view of a HEMT structure field effect transistor using an AlGaN / GaN heterostructure, which is one embodiment of adaptation to the electronic device of the present invention. As shown in the figure, a 50 nm thick AlN film 2 is formed on a substrate 21 made of silicon carbide or sapphire.
GaN film 2 with a thickness of 1500 nm through the second buffer layer 2
15 nm thick n-type AlGaN
An electron supply layer composed of the layer 25 and a cap layer composed of the n-type GaN layer 26 are sequentially formed. A as electron supply layer
The Al composition of the lGaN layer 25 is, for example, 0.2, and the n-type impurity concentration of Si in the AlGaN layer 25 is, for example, about 2 × 10 ¹⁸ cm ⁻³ . S in the n-type GaN layer 26 on the AlGaN layer 25 which is an electron supply layer
The n-type impurity concentration of i is, for example, about 5 × 10 ¹⁸ cm ⁻³ . A predetermined region of the cap layer is etched to form a recess, and the gate electrode 27 is formed in the recess. In addition, the n-type GaN layer 26 that is the cap layer
A source electrode 28 and a drain electrode 29 are formed on both sides of the upper gate electrode.

In this embodiment, the dry etching method of the present invention is used to etch the n-type GaN cap layer 26 up to the AlGaN / GaN hetero interface to form a recess for arranging the gate electrode. In the present embodiment, the portion to be etched is formed of GaN, and further, after the hetero interface where etching is to be stopped, it is formed of AlGaN that can function as an etching stop layer. Unlike the case, it is not necessary to provide an etching stop layer structurally. A mask is formed on a portion to be left after etching by using a photolithography method, and dry etching is performed by an ICP etching apparatus. The etching chamber is pre-etched under the same conditions as the actual condition before introducing the sample, and the sample is introduced into the etching chamber after being evacuated to 2 × 10 ⁻⁴ [Pa] or less in order to avoid mixing of impurities. A mixed gas of chlorine and oxygen was used as an etching gas, the concentration of oxygen was 20%, the total flow rate was 80 sccm, and the chamber pressure during etching was 0.5 [Pa]. The sample introduced into the chamber was cooled to about -30 to 20 ° C in order to increase the selection ratio. The etching time was longer than that calculated by the usual etching rate.
After that, dry etching was performed using a mixed gas of a rare gas and nitrogen in order to remove the Al oxide film generated by the etching.

As described above, the n-type GaN layer 26, which is the cap layer, is etched by the dry etching of the present invention, and the hetero interface between the electron supply layer made of the n-type AlGaN layer 25 and the n-type GaN layer 26 is etched. Up to this time, a recess to be the gate region was formed so that the gate length of the FET was about 0.5 μm. Nickel and gold were stacked in this recess and the gate electrode 27 was formed by the lift-off method.

In this embodiment, a high-concentration two-dimensional electron gas (2) is formed near the hetero interface between the channel layer made of the GaN film 23 and the electron supply layer made of the n-type AlGaN layer 25.
DEG) 24 is formed. Therefore, the gate electrode 27
A switching operation of the FET can be realized by controlling the concentration of the two-dimensional electron gas by applying a voltage to the FET. At this time, the distance between the gate electrode 27 and the hetero interface where the two-dimensional electron gas 24 is formed determines the concentration of the two-dimensional electron gas, and as a result, the threshold voltage V _{th of the} FET and the drain current under a constant gate bias are obtained. decide. However, in the dry etching of the present invention, etching is performed with an electron supply layer made of the n-type AlGaN layer 25 and an n-type AlGaN layer 25.
Since it is possible to stop the hetero interface with the GaN layer 26 with good controllability, the depth can be controlled satisfactorily without the distance between the hetero interface and the gate electrode 27 varying, and thus, within the wafer surface or between lots. It is possible to reduce variations in the threshold voltage V _th and the drain current of the FET.

(Embodiment 4) FIG. 6 is an embodiment of the application to the electronic device of the present invention, AlGaN / AlGa.
FIG. 6 is a cross-sectional view of a HEMT structure field effect transistor using an InN hetero structure. As shown in the figure, on a substrate 21 made of silicon carbide or sapphire, a 50 nm thick A
A 1500 nm thick G layer is formed through the buffer layer of the 1N film 22.
Channel layer consisting of aN film 23, 15 nm thick n-type A
Electron supply layer composed of lGaN layer 25, n-type AlGaIn
A cap layer composed of the N layer 601 is sequentially formed.
The Al composition of the AlGaN layer 25 serving as the electron supply layer is, for example, 0.2, and the Al composition of the n-type AlGaInN cap layer 601 is A composition of the AlGaN layer 25 serving as the electron supply layer.
1 composition.

[0044] The AlGaN layer 25 n-type impurity concentration of Si in the example 2 × 10 ¹⁸ cm ^- is added about ^3. N-type AlG on AlGaN layer 25 which is an electron supply layer
The n-type impurity concentration of Si in the aInN layer 601 is, for example, about 5 × 10 ¹⁸ cm ⁻³ . A predetermined region of the cap layer is etched to form a recess, and the gate electrode 27 is formed in the recess. A source electrode 28 and a drain electrode 29 are formed on both sides of the gate electrode on the n-type AlGaInN layer 601 which is a cap layer.

In this embodiment, n-type AlGaInN is used.
The dry etching method of the present invention is used to etch the cap layer 601 up to the AlGaN / AlGaInN hetero interface to form a recess for arranging the gate electrode 27. In this embodiment, the portion to be etched is Al
Since it is formed of GaInN and further formed of AlGaN that can function as an etching stop layer after the hetero interface where etching is desired to be stopped,
In particular, there is no need to structurally provide an etching stop layer. Further, since the AlGaInN layer contains In, the etching rate is higher than that of the n-type GaN cap layer 26 described in Example 3, and the selection ratio at the AlGaN / AlGaInN interface is also improved, so that the etching with higher precision is performed. And the etching time can be shortened. Further, since the resistance is low even in the element completed by using the AlGaInN layer as the cap layer, the characteristics as an element are improved.

A mask is formed by a photolithography technique on a portion to be left after etching, and dry etching is performed by an ICP etching apparatus. The etching chamber is pre-etched under the same conditions as the production before introducing the sample, and is 2 × 10 ⁻⁴ [Pa] to avoid mixing of impurities.
The sample is introduced into the etching chamber after vacuuming to the following. A mixed gas of chlorine and oxygen was used as an etching gas, the concentration of oxygen was 20%, the total flow rate was 80 sccm, and the chamber pressure during etching was 0.5 [Pa]. The sample introduced into the chamber was cooled to about -30 to 20 ° C in order to increase the selection ratio. In order to eliminate variations within the wafer surface, the etching time was set longer than that calculated at the normal etching rate. After that, dry etching is performed using a mixed gas of a rare gas and nitrogen, and n
The Al oxide film formed during the etching of the type AlGaInN layer 601 was removed.

As described above, the n-type AlGaInN layer 601 which is the cap layer is etched by the dry etching of the present invention, and the hetero interface between the electron supply layer formed of the n-type AlGaN layer 25 and the n-type AlGaInN layer 601 is formed. Up to this time, a recess to be the gate region was formed so that the gate length of the FET was about 0.5 μm. Nickel and gold are stacked in this recess and the gate electrode 2 is formed by using the lift-off method.
Formed 7.

In this embodiment, a high-concentration two-dimensional electron gas 24 is formed in the vicinity of the hetero interface between the channel layer made of the GaN film 23 and the electron supply layer made of the n-type AlGaN layer 25.
Is formed. Therefore, the switching operation of the FET can be realized by controlling the concentration of the two-dimensional electron gas by applying the voltage to the gate electrode 27. At this time, the distance between the gate electrode 27 and the hetero interface where the two-dimensional electron gas 24 is formed determines the concentration of the two-dimensional electron gas, and as a result, the threshold voltage V _{th of the} FET and the drain current under a constant gate bias are obtained. decide. But,
In the dry etching of the present invention, the etching is n
-Type AlGaN layer 25 as electron supply layer and n-type AlGa
Since the hetero interface with the InN layer 601 can be stopped with good controllability, the depth can be controlled satisfactorily without the distance between the hetero interface and the gate electrode 27 varying. Therefore, the threshold value within the wafer surface or between lots can be controlled. It is possible to reduce variations in the voltage V _th and the drain current of the FET.

Although the semiconductor laser and the FET have been described as examples in the above embodiments, the etching method of the present invention is not limited to these processes, and devices using other nitride semiconductors, LE for example
It is needless to say that the present invention can be applied to processes of light emitting devices such as D, HEMT, HBT, MESFET, and electronic devices.

[0050]

As described above, according to the present invention, it is possible to perform dry etching of a gallium nitride compound semiconductor with high accuracy.

[Brief description of drawings]

FIG. 1 is a sectional view of a conventional laser structure.

FIG. 2 is a sectional view of a conventional FET structure.

FIG. 3 is a sectional view of a laser structure having an etching stop layer according to an embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between bias, selection ratio, and etching rate.

FIG. 5 is a sectional view of an FET structure having an AlGaN / GaN interface according to an embodiment of the present invention.

FIG. 6 is an AlGaN / AlGa according to an embodiment of the present invention.
Sectional view of FET structure with InN interface

[Explanation of symbols]

1 Sapphire substrate 2 n-type AlGaN buffer layer 3 n-type GaN layer 4 n-type Al _0.07 Ga _0.93 N cladding layer 5 n-type GaN light guide layer 6 GaInN / GaN multiple quantum well active layer 7 p-type GaN light guide layer 8 p-type Al _0.07 Ga _0.93 N cladding layer 9 p-type GaN contact layer 10 p electrode 11 insulating film 12 n electrode 21 substrate 22 AlN buffer layer 23 GaN channel layer 24 2DEG 25 n-AlGaN electron supply layer 26 n-GaN cap layer 27 gate electrode 28 source electrode 29 drain electrode 30 remaining thickness 201 n-type Al _0.3 Ga _0.7 N etching stop layer 202 first p-type Al _0.07 Ga _0.93 N cladding layer 203 p-type Al _0.3 Ga _0.7 N etching stop layer 204 second p-type Al _0.07 Ga _0.93 N cladding layer 601 n-AlGaInN cap layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiya Yokokawa             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5F004 AA01 BD05 CA02 CA03 CA06                       DA04 DA22 DA23 DA26 DB19                       EA06 EA07 EA13 EA23 EA28                 5F073 AA04 AA45 AA53 AA55 AA74                       CA07 CB05 DA05 DA25 EA29                 5F102 GB01 GC01 GD01 GJ10 GK04                       GL04 GM04 GM08 GN04 GQ01                       GR04 GR10 GT03 HC01 HC15

Claims (9)

[Claims] 1. A layer containing Al in a nitride semiconductor,
Nozawa Al_xGa_yIn _1-xyN (0 ≦ x ≦ 1, 0 ≦ y ≦
1, x + y ≦ 1) is used as an etching stop layer,
And an etching gas containing at least oxygen and chlorine
Of nitride semiconductor, characterized by performing etching
Li etching method. 2. A dry etching method for a nitride semiconductor, wherein an oxide of Al is formed on the surface after dry etching. 3. At least a part of the Al oxide formed on the surface after dry etching is used as a rare gas (He, Ar, X).
3. The dry etching method for a nitride semiconductor according to claim 1, wherein the dry etching is performed by dry etching using e, Ne). 4. At least part of the Al oxide formed on the surface after dry etching is replaced with a rare gas (He, Ar, X).
3. The dry etching method for a nitride semiconductor according to claim 1, wherein the dry etching is performed by dry etching using a mixed gas of e, Ne) and nitrogen. 5. A dry etching method for a nitride semiconductor, characterized in that the amount of oxygen supplied to the etching gas is 0 or a small amount at the beginning of etching and increases stepwise or continuously from the middle of etching. 6. A dry etching method for a nitride semiconductor, wherein the substantial bias applied to the sample during etching changes stepwise or continuously from the middle of etching. 7. A nitride system having a clad layer of two layers of the first conductivity type and a second conductivity type and an active layer sandwiched between the clad layers, and forming a mesa or a ridge stripe by etching. 1. A semiconductor light emitting device comprising a compound semiconductor, wherein the surface to be etched and the insulating film on the side wall of the mesa or ridge stripe are formed of an oxide of Al. 8. A G layered on the AlGaN electron supply layer
It has an aN cap layer and is etched by GaN.
A semiconductor device, wherein a gate electrode is disposed in a recess formed by removing a part of the cap layer, and the gate electrode and the AlGaN electron supply layer are in contact with each other. 9. A layered on the AlGaN electron supply layer
The AlGaInN cap layer is provided, and the gate electrode is disposed in the recess formed by removing a part of the AlGaInN cap layer by etching.
A semiconductor device characterized in that the GaN electron supply layer is in contact.