JP2003229413A - Dry etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop a dry etching method, eliminated or reduced in the generation of damage, since the development of an etching stop layer in the dry etching of nitrided gallium compound semiconductor is eagerly desired, and the damage in a surface processed by etching becomes sometimes the reason of the deterioration of characteristics of the element in the dry etching process. <P>SOLUTION: A layer containing In in the nitride semiconductor is employed as the etching stop layer while the dry etching is effected by etching gas containing the gas of chlorine base. <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 GaN, AlGaN, InGaN, In
Since gallium nitride-based compound semiconductors such as AlGaN, GaInNAs, and GaInNAsP have high dielectric strength, high thermal conductivity, and high saturation electron velocity, they are promising as materials for high-frequency power transistors. Al
In the HEMT structure using the GaN / 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.

The gallium nitride-based compound semiconductor has a direct transition type band structure.
It is possible to obtain a wide range of bandgap energies that can emit light up to infrared at long wavelengths and up to ultraviolet at short wavelengths by using AlGaN. Therefore, light emitting devices and semiconductors using gallium nitride-based compound semiconductors can be obtained. Research on lasers is also 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 blue-violet semiconductor laser has a life of over 5000 hours at the time of announcement, etc. and is close to practical use. I have come to the point. 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. Further, as for a device that emits ultraviolet light, a white light source using an ultraviolet LED for exciting a phosphor has been proposed, and therefore, potential demand is great and active research is being conducted. It is said that the gallium nitride-based compound semiconductor laser that emits light with a wavelength of 1.55 μm for optical communication has an improved characteristic temperature that represents the temperature dependence of the threshold current, compared with the InP-based laser that is currently in practical use. It has been energetically presented at academic conferences.

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, chlorine gas is generally used as an etching gas, for example, chlorine Cl ₂ , carbon tetrachloride CCl ₄ , silicon tetrachloride SiC.
l ₄ , boron trichloride BCl _{3 and the} like are used.

[0006]

In dry etching of gallium nitride-based compound semiconductors, an effective etching stopper layer has not been found until now. Therefore, time control has been used to control the etching thickness in the dry etching process. Time control does not allow etching with controllability in units of Å, and as a result, the performance of the fabricated device becomes unstable.

In practice, when forming a ridge stripe in the fabrication of a nitride semiconductor laser, a p-type clad layer is formed in 10 layers.
It is necessary to etch so as to leave 00Å, and in that case, highly accurate etching thickness control is required. However, in the current technology, due to the time control, the etching thickness is different from the design or varies between lots, which causes adverse effects such as an increase in threshold current and deterioration of current-voltage characteristics.

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 surface also causes an increase in the threshold value and deterioration of the current-voltage characteristics, which lowers the yield of the device.

Under these circumstances, the development of an etching stop layer in dry etching of gallium nitride-based compound semiconductors has been earnestly desired in order to accurately control the film thickness. Further, in the dry etching process, the etched surface may be damaged, which may cause deterioration of the characteristics of the device. Therefore, development of a dry etching method with little or no damage is desired.

The present invention provides an etching stop layer for accurately controlling the film thickness, an etching method with less damage, and a semiconductor device realized by them.

[0011]

The dry etching method according to the present invention overcomes the above problems. I
A dry etching method for a nitride semiconductor, wherein a layer containing n is used as an etching stop layer and a chlorine-based etching gas is used. Hereinafter, the present invention will be described in detail.

The principle of effective functioning of the etching stop layer in dry etching is that the reaction products generated during the reaction between the etching stop layer and the etching gas during the progress of etching are different from the etching gas other than the etching stop layer. Two cases are often used: utilizing a substance that is more stable than the reaction product of (1) or utilizing the height of the energy threshold value for etching of the etching stop layer. The present invention utilizes the stability of the former reaction product.

Chlorine-based gases such as chlorine Cl ₂ , carbon tetrachloride CCl ₄ , silicon tetrachloride SiCl ₄ , boron trichloride BC
The reaction formula during the etching of the nitride semiconductor with l ₃ etc. can be expressed as follows.

6Cl + 2M ^* N → 2M ^* Cl ₃ + N ₂ Here, the supply form of chlorine varies depending on the type of gas used and the conditions at the time of etching, but is represented simply as Cl for simplicity. M ^* is a group III metal, in this case mainly Al,
Represents either Ga or In.

This formula is based on the reaction between chlorine and a nitride semiconductor.
It shows that chloride of the group III element is generated, vaporized and released from the etching surface. InCl ₃ is a compound of In and chlorine, and InCl ₃ generated during dry etching using a chlorine-based gas is a chlorine compound Al of Al or Ga.
It has a higher boiling point than Cl ₃ and GaCl ₃ . Specifically, InCl ₃ is 583 ° C., AlCl ₃ is 180 ° C., G
aCl ₃ is 201 ° C.

This is because the vapor pressure of the chlorine compound of In is low, and therefore the In produced during etching is
Since InCl ₃ which is a chloride of the above has a low vapor pressure, it is difficult for the vaporization part in the chemical etching mechanism of the above reaction with chlorine and vaporization desorption to occur, so that ion assist or physical sputtering If the effect is not utilized, it is originally difficult to etch as compared with other chlorinated compounds of Al and Ga. Therefore, the chlorine compound of In formed on the surface of the In-containing layer during the etching using the chlorine-based gas can form a layer more stable against etching than other etching products.

However, under the usual etching conditions for nitride semiconductors, the layer containing In is also etched without problems. This indicates that InCl ₃ is easily vaporized and desorbed under the usual etching conditions for nitride semiconductors. In addition, it has been reported that the etching rate of the layer containing In is higher than that of the layer not containing In, which is the reverse of the present invention. Since these have a high bond energy between group III and nitrogen of the nitride semiconductor, a normal dry etching process first sets severe etching conditions such as low pressure and high bias to the sample in order to break the bond between group III and nitrogen. This is a result of being done.

We have found that it is possible to achieve both the etching of a nitride semiconductor and the use of a layer containing In as an etching stop layer. Therefore, by using this, dry etching with high film thickness controllability can be achieved. Provide a way.

Specifically, the etching may be performed under the condition that the bond between the group III and nitrogen can be cut and InCl ₃ is hard to be vaporized and desorbed. With such a condition, it is desirable that the pressure is high from the viewpoint of preventing vaporization and desorption of the reaction product,
It is desirable to cool the sample. The lower the bias applied to the sample, the better. FIG. 1 shows the etching rate dependence of GaN and GaInN with respect to the pressure of the etching gas. GaN and GaI at a certain pressure in FIG.
In the portion where the etching rate of nN is exchanged and the pressure is higher than this point, the etching rate of GaInN is smaller than that of GaN and the selection ratio is larger than 1, and the GaInN layer is used as an etching stop layer for GaN. It is possible. This difference in etching rate becomes larger by cooling the sample, so
It is better to cool the sample because a larger selection ratio can be obtained. Further, when the applied bias is lower, the effect of physical sputtering is suppressed, so that the selection ratio is increased.

Since the etching rate decreases under these conditions, the etching away from the etching stop layer is performed under normal conditions, and the etching employing these conditions is performed only in the vicinity of the etching stop layer. By doing so, the etching time can be kept within a practical range, and both throughput, controllability, and device performance can be satisfied.

In addition to chlorine, rare gases (He, Ar, Xe, Ne) may be added to the etching gas in order to facilitate the formation of plasma during etching. It is not desirable from the viewpoint of suppressing the sputtering effect.

By utilizing the above, the layer containing In can be used as an etching stop layer.

In the description, only N was taken up as the group V element, but the bond energy between the group III and P, As is lower than the bond energy with N, and etching proceeds without any problem. In addition, the present invention can be applied to a system containing P and As without any problem.

It is preferable that the composition of In in the etching stop layer is as high as possible. It is preferable that the composition is 20% or more. However, in the case of GaInN having a high composition of In, on GaN or
This is not preferable because it deviates from the lattice matching condition on AlGaN and causes lattice mismatch, which causes defects and cracks. Therefore, Al is added to the etching stop layer so as to reduce the lattice mismatch instead of InGaN.
The use of an aInN layer can also suppress the occurrence of defects and cracks.

Further, when the etching method according to the present invention is used, since etching is performed under a milder condition than ordinary dry etching, damage due to dry etching can be reduced.

There is also a dry etching method in which an oxide film is formed as an etching stop layer of another nitride semiconductor, but in that case, since the oxide film is strong, the oxide film after the dry etching is formed. It may be difficult to remove or may become a new source of damage. InCl ₃ generated by the etching method of the present invention is much easier to remove than oxides, and can be removed by performing heat treatment in vacuum, for example.
Therefore, damage in the dry etching process can be reduced as much as possible.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 2 is an embodiment of the application to the electronic device of the present invention, AlGaN /
FIG. 3 is a cross-sectional view of a HEMT structure field effect transistor using a GaN heterostructure. As shown in FIG. 2, a GaN channel layer 203 having a thickness of 1500 nm and an n-type AlGa layer having a thickness of 15 nm are provided on a substrate 201 made of silicon carbide or sapphire via an AlN buffer layer 202 having a thickness of 50 nm.
An N electron supply layer 205, an n-type GaInN etching stop layer 220, and an n-type GaN cap layer 206 are sequentially formed. The Al composition of the AlGaN electron supply layer 205 is 0.2, for example, and the In composition of the n-type GaInN etching stop layer 220 is 0.2. The n-type impurity concentration of Si in the AlGaN electron supply layer 205 is, for example, about 2 × 10 ¹⁸ cm ⁻³ . The n-type impurity concentration of Si in the n-type GaN cap layer 206 on the AlGaN electron supply layer 205 is, for example, about 5 × 10 ¹⁸ cm ⁻³ . Further, a predetermined region of the n-type GaN cap layer 206 is etched to form a recess, and the gate electrode 207 is formed in the recess. A source electrode 208 and a drain electrode 209 are formed on both sides of the gate electrode 207 on the n-type GaN cap layer 206.

In this embodiment, the n-type GaN cap layer 206 is etched, but since the cap layer is thin, the etching rate is slow, but controllability is prioritized and the layer containing In acts as an etching stop layer. Etching is performed.

A mask is formed by a photolithography method 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. Chlorine was used as an etching gas, the total flow rate was 100 sccm, and the chamber internal pressure during etching was 3 [Pa]. The sample introduced into the chamber is -30 to 2 in order to increase the selectivity to the etching stop layer.
It was cooled to about 0 ° C. The etching time was longer than that calculated by the usual etching rate. InC generated by etching after completion of etching with chlorine
Dry etching was performed with a mixed gas of Ar and N ₂ to remove l ₃ .

As described above, the n-type GaN cap layer 206 is etched by the dry etching according to the present invention to obtain the n-type AlGaN electron supply layer 205 and the n-type Ga.
A recess which forms a gate region up to the hetero interface of the InN etching stop layer 220 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 207 was formed by the lift-off method.

In this embodiment, a high-concentration two-dimensional electron gas (2DEG) 204 is formed near the hetero interface between the GaN channel layer 203 and the n-type AlGaN electron supply layer 205. Therefore, the switching operation of the FET can be realized by controlling the concentration of the two-dimensional electron gas 204 by applying a voltage to the gate electrode 207.
At this time, the distance between the gate electrode 207 and the hetero interface where the two-dimensional electron gas 204 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, the etching is performed on the n-type AlGaN electron supply layer 205.
Since the nN etching stop layer 220 can be stopped with good controllability, the depth can be satisfactorily controlled without the distance between the hetero interface and the gate electrode 207 varying. Therefore, the threshold voltage V within the wafer surface or between lots can be controlled.
It is possible to reduce variations in _th and the drain current of the FET.

(Embodiment 2) 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. MOCV on the sapphire C-plane substrate 301
The following structures are sequentially laminated using D (metal organic chemical vapor deposition). MBE (Molecular Beam Epitaxy) and HVP
There is no problem even if the following structures are laminated by using another crystal growth method such as E (hydride vapor phase epitaxy). Although the sapphire C-plane substrate is used as the substrate in this embodiment, the selective growth substrate, the silicon carbide substrate, the GaN substrate, or the AlG substrate.
There is no problem even if another substrate such as an aN substrate is used.

Low temperature buffer layer 3 made of n-type AlGaN
02, n-type GaN layer 303, n-type Ga _0.8 In _0.2 N etching stop layer 351, n-type Al _0.07 Ga _0.93 N cladding layer 304, n-type GaN optical guide layer 305, GaIn
N / GaN multiple quantum well active layer 306, p-type GaN optical guide layer 307, first p-type Al _0.07 Ga _0.93 N cladding layer 352, p-type Ga _0.8 In _0.2 N etching stop layer 3
53, the second p-type Al _{0. 07} Ga _0.93 N cladding layer 354,
The p-type GaN contact layer 309 is sequentially stacked. First p
The film thickness of the type Al _0.07 Ga _0.93 N cladding layer 352 is preferably about 1000 Å in consideration of light confinement.

Since it is relatively difficult to form an etching stop layer containing In in the middle of the cladding layer containing Al because the growth temperature is different, the In composition is set to 20% in this embodiment. .

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 , SiN, and photoresist. 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. Chlorine 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 354 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 354 is formed to a thickness of 5 in consideration of the variation in the rate.
Etching is performed for 140 seconds because it is desired to leave about 00Å. When 140 seconds have passed, the RF bias applied to the sample is lowered and the pressure is raised, whereby the etching rate is reduced, but the conditions are changed such that the layer containing In acts as an etching stop layer. Note that this change may be performed stepwise or continuously. As described above, after reaching the etching stop layer, InCl ₃ is formed on the etched surface and the etching is stopped. After etching, InCl ₃ is formed on the etching surface so as to cover the entire etching surface. This InCl ₃ is removed by subsequent heating in the etching chamber so that the next step is not affected. As a result, a ridge stripe is formed on the first p-type Al _0.07 Ga _0.93 N cladding layer 352 having a desired film thickness.

Subsequently, the insulating film 311 is formed and the p-electrode 310 is formed.
Then, the semiconductor laser device is completed through steps such as formation of the n-electrode 312 and device isolation. The obtained semiconductor laser device has a first p-type Al _0.07 Ga between lots or even within a lot.
_{The 0.93} N clad layer 352 has a uniform film thickness as designed, and the light confinement and the current confinement are stabilized, so that the threshold current is higher than that of the device without the etching stop layer. Was observed. In addition, since the variation within the wafer surface is suppressed, the yield is also improved.

[0038]

According to the present invention, in the dry etching process, the etched surface is hardly (or little) damaged, and as a result, it does not cause the deterioration of the device characteristics (or it is almost impossible). Absent).

[Brief description of drawings]

FIG. 1 is a diagram showing dependence of etching rate on pressure.

FIG. 2 is a cross-sectional view of a FET structure having an etching stop layer according to an embodiment of the present invention.

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

[Explanation of symbols]

201 substrate 202 AlN buffer layer 203 GaN channel layer 204 2DEG 205 n-type AlGaN electron supply layer 206 n-type GaN cap layer 207 gate electrode 208 source electrode 209 drain electrode 220 n-type GaInN etching stop layer 301 sapphire substrate 302 n-type AlGaN buffer layer 303 n-type GaN layer 304 n-type Al _0.07 Ga _0.93 N clad layer 305 n-type GaN optical guide layer 306 GaInN / GaN multiple quantum well active layer 307 p-type GaN optical guide layer 308 p-type Al _0.07 Ga _0.93 N clad layer 309 p Type GaN contact layer 310 p electrode 311 insulating film 312 n electrode 351 n type Ga _0.8 In _0.2 N etching stop layer 352 first p type Al _0.07 Ga _0.93 N clad layer 353 p type Ga _0.8 In _0.2 N etching stopper. Layer 354 Second p-type Al _0.07 Ga _0.93 N cladding layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiya Yokokawa             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5F004 DA04 DA05 DA11 DA13 DA22                       DA23 DB19 EA06 EA07 EA10                       EA23 EA28 EA34 FA07                 5F073 AA04 AA45 AA53 AA74 CA07                       CB05 DA05 DA16 DA22 DA24                       EA29                 5F102 GB01 GC01 GD01 GJ10 GK04                       GL04 GM04 GM08 GN04 GQ01                       GR04 GR10 GT03 HC15 HC19

Claims (7)

[Claims] 1. A dry etching method for a nitride semiconductor, which comprises using a layer containing In as an etching stop layer in a nitride semiconductor and performing dry etching with an etching gas containing a chlorine-based gas. 2. The dry etching method for a nitride semiconductor according to claim 1, wherein In chloride is formed on the surface after etching. 3. The dry etching method for a nitride semiconductor according to claim 1, wherein the In chloride formed on the surface after etching is removed by wet etching. 4. The dry etching method for a nitride semiconductor according to claim 1, wherein the In chloride formed on the surface after etching is removed by a treatment in vacuum or in an inert gas. 5. The dry etching method for a nitride semiconductor according to claim 1, wherein the In chloride formed on the surface after etching is removed by heat treatment in vacuum or in an inert gas. 6. The dry etching method for a nitride semiconductor according to claim 1, wherein the In chloride formed on the surface after etching is removed by a dry etching treatment in vacuum or in an inert gas. 7. A group III element containing at least one of Al, Ga and In, and a group V element containing N or N
In addition to P, As, a semiconductor device made of a nitride semiconductor containing at least one of
More than one nitride semiconductor layer are stacked, and at least one of the layers is higher than the preceding and following layers.
A semiconductor element having an n composition and having a high In composition acts as an etching stop layer.