JPH0831801A - Dry etching method - Google Patents

Abstract

PURPOSE:To selectively perform patterning without using chloro-fluorocarbon gas by etching a compound semiconductor containing no Al and formed on a compound semiconductor layer containing Al with a mixture gas containing an organic compound gas which has a C-O bond and F system. CONSTITUTION:A compound semiconductor 5 containing no Al and is formed on a compound semiconductor layer 4 containing Al, and over it, a resist mask 6 with a specified opening diameter is formed, and then, dry etched in mixture gas of organic compound gas having C-O bond and F system gas, so that, on the side faces of the resist mask 6 and the semiconductor layer 5, wall protective films 7 are formed. And, when the semiconductor layer 4, substrate, is exposed, a AlF2 etching stopper layer is formed on the surface. Thus, without raising the particle level and causing any pattern transfer difference, anisotropic processing of the compound semiconductor layer 5 is enabled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method, and more particularly, to a dry etching method for selectively patterning an Al-free compound semiconductor layer laminated on an Al-containing compound semiconductor layer.

[0002]

2. Description of the Related Art GaAs MESFET (Metal
MMIC (Monolithic) in which a semiconductor FET is integrated on a single semiconductor chip.
The Microwave IC) has characteristics such as high-speed response in the high frequency region of the GHz band, low noise, low power consumption, and the like, and thus its application is spreading widely as a semiconductor device for mobile communication and satellite communication in recent years.

As a semiconductor device intended to further increase the speed of a GaAs MESFET, HEMT (Hi
gh Electron Mobility Tran
system) has been developed. This device has a 2-DEG (TwoD) confined at a heterojunction interface with, for example, an n-type AlGaAs layer on a non-doped GaAs layer.
(imaging Electron Gas)
However, it utilizes the phenomenon that it can move in the plane at high speed. Even in this HEMT, there is a demand for higher precision in a dry etching method as a device processing technique for realizing high performance and high integration.

In particular, the step of selectively etching the GaAs layer laminated on the AlGaAs layer to form the gate recess is an important step for determining the threshold voltage of the HEMT, the heterojunction FET or the like. This is the lower layer AlG
This is because the impurity concentration and the thickness of the aAs layer are designed in advance so that an FET having a desired threshold voltage can be obtained by selectively removing the upper GaAs layer with good controllability.

As a selective etching method for the GaAs layer laminated on the AlGaAs layer, a method of using a mixed gas of a CCl _x F _y type chlorofluorocarbon type gas and a rare gas is generally used. This is the reaction product with high vapor pressure, which is GaCl _x , AsF _y and AsCl _x.
And GaAs is removed by etching, while AlF _x having a small vapor pressure is formed on the surface of the lower AlGaAs layer when it is exposed.
This is because F _x serves as an etching stopper to achieve a high selection ratio. As an example, Japanese Jou
rnal of Applied Physics 20
-11, L847-850 (1981) contains CCl ₂
It has been reported that a selection ratio of 200 was achieved by using an F ₂ / He mixed gas.

However, many chlorofluorocarbon-based gases are designated as specific CFCs.
Cl ₂ F ₂ (Freon 12) is one of them. These specified CFCs are considered to be one of the causes of the depletion of the ozone layer of the earth, and their production and use are prohibited for the purpose of environmental protection. Therefore, there is an urgent need to establish an etching gas that can substitute for the chlorofluorocarbon-based gas and a technique for using it, that is, a dechlorofluorocarbon process.

Further, the chlorofluorocarbon type gas produces a large amount of fluorocarbon type polymer by discharge dissociation and adheres to the side surface of the pattern during etching to form a side wall protective film, which contributes to improvement of anisotropy. On the other hand, this fluorocarbon polymer is also deposited and accumulated on the inner wall surface of the etching chamber, which tends to cause fluctuations in the etching rate and deterioration of the particle level.

[0008]

Therefore, an object of the present invention is to selectively pattern an Al-free compound semiconductor layer laminated on an Al-containing compound semiconductor layer without using a chlorofluorocarbon-based gas. A dry etching method is provided.

Another object of the present invention is to prevent Al-containing compound semiconductors stacked on an Al-containing compound semiconductor layer without causing an increase in particle level or a pattern conversion difference due to excessive deposition of a sidewall protective film. It is an object of the present invention to provide a dry etching method capable of anisotropically processing a layer. Other problems of the present invention will be apparent from the description in the present specification and the description of the accompanying drawings.

[0010]

The dry etching method of the present invention was devised in order to solve the above-mentioned problems, and a compound semiconductor layer containing no Al is stacked on a compound semiconductor layer containing Al. , An organic compound gas having a C—O bond and an F-based gas are used for etching.

The dry etching method of the present invention is
etching a part of the Al-free compound semiconductor layer laminated on the compound semiconductor layer containing 1 in the layer thickness direction with a mixed gas containing an organic compound gas having a C—O bond and an F-based gas; Two-step etching is performed by the first etching step and the second etching step of etching the remaining portion of the compound semiconductor layer not containing Al in the layer thickness direction by increasing the mixing ratio of the F-based gas in the mixed gas. It is a thing.

Examples of the organic compound gas having a C—O bond include alcohol, ether, ketone, ester, carboxylic acid and aldehyde. These organic compounds are
Many of them exist in a liquid state at room temperature, but in the case of a liquid compound, a compound having a relatively low molecular weight that can be easily vaporized by a heating bubbling method or a baking method and introduced into the etching chamber is preferable. Examples of such alcohols, ethers, ketones, esters and carboxylic acids include methanol, ethanol, n-propanol, i-
Propanol, n-butanol, i-butanol, se
c-butanol, t-butanol, dimethyl ether,
Methyl ethyl ether, diethyl ether, acetone,
Methyl ethyl ketone, methyl isobutyl ketone, methyl acetate, ethyl acetate, formic acid, acetic acid, formaldehyde, acetaldehyde and the like can be used alone or in combination.

Further, the dry etching method of the present invention is
The mixed gas containing an organic compound gas having a C—O bond and an F-based gas further contains one of a Cl-based gas and a Br-based gas.

The F-based gas used in the present invention is NF ₃ or SF.
A general-purpose gas containing F atoms such as ₆ may be used, but S ₂ F
Sulfur fluoride gas such as ₂ , SF ₂ , SF ₄ and S ₂ F ₁₀ may be used.

The Cl-based gas and Br used in the present invention
The system gas may be a general-purpose gas containing Cl atoms such as Cl ₂ or HBr or Br atoms, but S ₂ Cl ₂ , S ₃ C
l ₂ , SCl ₂ , S ₂ Br ₂ , S ₃ Br ₂ and SBr
Sulfur chloride-based gas or sulfur bromide-based gas such as ₂ may be used.

[0016]

The point of the present invention is that the constituent material of the sidewall protective film, which is indispensable for anisotropic etching, is mainly obtained by the decomposition product of the resist mask, and the film quality is enhanced to improve the ion bombardment resistance and radical attack resistance. Even if the amount of adhesion of the side wall protective film is increased and the side wall protective film is reduced, a sufficient side wall protective effect and a surface protective effect of the layer to be etched can be obtained.

When attempting to establish a CFC-free process, it becomes impossible to determine the constituent material of the carbon-based polymer as the sidewall protective film as the dissociation product of the CFC-based etching gas. Therefore, the source of the side wall protective film must be a decomposition product of the resist mask. To this end, in order to enhance the side wall protection effect, it is conceivable to increase the incident ion energy during etching and positively sputter the resist mask in order to supply a large amount of decomposition products of the resist mask. However, with this method, the selectivity with respect to the resist is lowered, and there is a risk of ion damage to the underlayer and deterioration of the particle level.

Therefore, in the dry etching method of the present invention, a method of mixing an organic compound gas having a C--O bond into the etching gas is adopted as a means for strengthening the film quality of the carbon-based polymer as the sidewall protective film. These organic compound gases such as alcohols, ethers, ketones, esters, carboxylic acids and aldehydes are all represented by the general formula C _x H _y O _z , and active species of H and CO generated under discharge dissociation conditions are plasma. By supplementing the halogen radicals therein, the halogen content in the carbon-based polymer is reduced. Furthermore, the generation of atomic groups having a polarized structure having C—H bonds or C—O bonds in plasma increases the degree of polymerization of the carbon-based polymer due to the decomposition products of the resist mask. In recent years, a carbon-based plasma polymer having such a structure is more chemically and physically stable than a conventional carbon-based plasma polymer having a repeating unit structure of simply-(CX) _n- or-(CH) _n-. (Where X is a halogen element and n is a natural number). This is because the C—O bond (1077 kJ / mol) is C when comparing the bond energy between two atoms.
It is also supported by the fact that it is larger than the -C bond (607 kJ / mol). All of these enhance the film quality of the side wall protective film and enhance the effect of protecting the pattern side surface from the attack of incident ions or radicals.

As described above, since the film quality of the carbon-based polymer as the side wall protective film is enhanced, the incident ion energy required for anisotropic processing can be reduced and the selectivity ratio to the resist mask is improved. Further, by this, even if the photoresist coating film is thinner than before, it is possible to form a resist mask that can sufficiently withstand practical use, which contributes to the improvement of resolution in lithography and also the difference in processing dimension conversion can be reduced.

Further, the effect of reducing the incident ion energy also leads to the improvement of the selection ratio with respect to the base. Further, since the amount of carbon-based polymer deposited as the sidewall protection film can be reduced, it is possible to reduce particle contamination as compared with the conventional case.

By the way, when etching a compound semiconductor layer not containing Al laminated on a compound semiconductor layer containing Al with a high selectivity, AlF _x having a small vapor pressure is formed on the compound semiconductor layer containing Al, Using this as an etching stopper is effective in principle. Therefore, in the present invention, a mixed gas of an organic compound gas having a C—O bond and an F-based gas is adopted as the etching gas.

Although the present invention is based on the above technical idea as a basic principle, a method aiming at further high anisotropy, low particle size and high selection ratio is also proposed. One of them is to achieve the above-mentioned object by making the etching into two stages and increasing the mixing ratio of the F-based gas in the second etching process more than in the first etching process.
At this time, in the first etching step of the former stage, most of the compound semiconductor layer not containing Al is removed in the layer thickness direction, and the surface of the underlying compound semiconductor layer containing Al is exposed just before or partially exposed. It is a so-called just etching process with some parts. Therefore, if the second etching step in which the mixing ratio of the F-based gas is increased at this stage, that is, the overetching step is switched to, the generation of AlF _x as an etching stopper is promoted, and the selectivity is improved.

If a Cl-based gas or a Br-based gas is further added to the above-mentioned mixed gas system, the etching rate can be increased. That is, if the F-based gas alone is used as the halogen-based gas, a reaction product having a large vapor pressure may not be obtained depending on the constituent elements of the compound semiconductor, and a sufficient etching rate may not be obtained. In such a case, by allowing a chemical species such as Cl ^* or Br ^* to coexist in the etching reaction system, the reaction product having a large vapor pressure can be used, and the etching speed can be increased. Further, as the carbon-based polymer, CCl _x , CBr _x, or the like having a composition that facilitates deposition can be used together.

Further, in the present invention, the above-mentioned side wall protection is provided.
In addition to the protective mechanism, sulfur-based materials also serve as side wall protective films.
Propose a method to use together. Free as a sulfur-based material
Sulfur or Polythiazyl (SN)_nTo use
Can be. S is S₂F ₂, SF₂, SF_Four, S₂
F_Ten, S₂Cl₂, S₃Cl₂, SCl₂, S₂B
r ₂, S₃Br₂And SBr₂One of
By dissociating the sulfur-containing gas from the discharge,
It should be deposited on the substrate to be etched that is controlled below room temperature.
And are possible. In addition, polythiazyl is a halogen
Further N for sulfur gas₂, NF₃, N₂F_Fourand
N₂H_FourBy adding N-based gas such as
Deposition on the substrate to be etched controlled to below room temperature
It is possible. In any case, these halogenated
NF is sulfur gas₃And Cl₂General-purpose halogen-based gas such as
May be used in combination with a halogenated sulfur-based gas
It may be used as an etchant. However,
The most common SF for Ugas ₆Is F atom in one molecule
The F / S ratio, which is the ratio of the
However, it does not generate free sulfur in the plasma, so
C) Not suitable for the purpose of using a sidewall-based material as a protective film.
Yes.

By using a sulfur-based material in combination as the side wall protective film, it is possible to reduce the deposition of carbon-based polymer which is a decomposition product of the resist mask. Therefore, the incident energy of ions required for sputtering the resist mask can be reduced. It can be reduced and the selection ratio with respect to the resist mask is improved. Further, the reduction of carbon-based polymer deposition means reduction of particle contamination. This is because these sulfur-based materials can be removed by sublimation only by heating the substrate to be etched after plasma etching is completed. The sublimation temperature is about 90 ° C or higher for sulfur and about 150 for polythiazyl.
The temperature is higher than 0 ° C., and after sublimation, no particle contamination or contamination is left on the substrate to be etched.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings. In addition, each of the examples described below is based on HE
This is an example in which a substrate bias application type ECR plasma etching apparatus is used as an etching apparatus, which is applied to MT gate recess processing.

[0027] Example 1 This example, n ⁺ -AlGaAs layer of n ⁺ -GaAs
The layers are methanol (CH ₃ OH, bp = 64.6 ° C.) /
This is an example of selective etching using a mixed gas of NF ₃ / Ar, which will be described with reference to FIGS.
As shown in FIG. 1A, the etching sample used in this example is a non-doped GaAs buffer layer 2 epitaxially grown to a thickness of 500 nm on a semi-insulating GaAs substrate 1, and a non-doped AlGaAs layer 3 having a thickness of about 2 nm. , A Si-doped n ⁺ -AlGaAs layer 4 having a thickness of about 30 nm, and an n ⁺ -GaAs layer 5 also containing n-type impurities 10
The resist mask 6 having a predetermined opening diameter is formed on the surface of the resist mask 6 by sequentially growing the thickness of 0 nm. The resist mask 6 is formed by, for example, electron beam lithography to
It is formed with an opening width of 00 nm.

This substrate to be etched is placed on the substrate stage of a substrate bias application type ECR plasma etching apparatus, and as an example, n ⁺ -G is obtained under the following etching conditions.
The aAs layer 5 was etched. CH ₃ OH flow rate 40 sccm NF ₃ flow rate 40 sccm Ar flow rate 90 sccm Gas pressure 1.5 Pa Microwave power 850 W (2.45 GHz) RF bias power 50 W (2 MHz) Substrate temperature 20 ° C. In this etching process, NF F ^* generated by dissociation of ₃ is As in As ⁺ ₃ , AsF in n ⁺ -GaAs
_In the form of ₅ and Ga in the form of GaF ₃ , the etching proceeds. However, since the vapor pressure of GaF ₃ is small at the substrate temperature under this etching condition, Ar in the mixed gas is
Was added, in combination with ion sputtering by Ar ⁺ in addition to NF _x ^+, it is removed GaF _3.

At the same time, a carbon-based polymer having a repeating unit structure of-(CF) _n --and-(CH) _n-, which is derived from the decomposition product of the resist mask 6, is produced.
As shown in (b), the resist mask 6 and n ⁺ -Ga
The sidewall protection film 7 is formed by adhering to the side surface of the As layer 5 pattern. This carbon-based polymer has a smaller composition ratio of F atoms than a polymer of the same kind under the conventional etching conditions, and also has a C content.
It is a strong one that incorporates O-bonds in its network structure. Therefore, in this embodiment, although the amount of carbon-based polymer produced is not as large as that under the conventional etching conditions, the side wall protective film 7 exhibits high etching resistance and is suitable for anisotropic processing of the n ⁺ -GaAs layer 5. Contribute. FIG.
Although the thickness of the side wall protective film 7 is exaggerated in (b), it is actually an extremely thin film.

When the underlying n ⁺ -AlGaAs layer 4 is exposed, an AlF _x layer (not shown) is formed on the surface of the underlying n ⁺ -AlGaAs layer 4, the etching rate is greatly reduced, and it becomes a substantial etching stopper layer. Next, an O ₂ plasma treatment was performed to burn off the side wall protective film 7 and form a recess 8 having a vertical wall as shown in FIG. 1 (c). It should be noted that the O ₂ plasma treatment may be a very mild treatment that does not remove the resist mask 6 by ashing.

The formation of the gate electrode, which is the subsequent process, is as follows.
Any known method may be used. An example thereof is shown in FIG.
That is, Al-based metal electron beam evaporation was performed on the entire surface of the sample shown in FIG.
The l-based metal layer 9 is formed. This deposition has a fine recess 8
2 is positively utilized, and a gate electrode pattern 9a is independently formed at the bottom of the recess 8 as shown in FIG. Next, when the resist mask 6 is removed with a resist remover,
The Al-based metal layer 9 is lifted off, and only the gate electrode pattern 9a can be left on the bottom of the fine recess 8. This state is shown in FIG.

According to the present embodiment, by adding CH ₃ OH to the etching gas, selective etching of the GaAs layer having good anisotropy with respect to the AlGaAs layer becomes possible.

Example 2 In this example, n ⁺ -Ga on the same n ⁺ -AlGaAs layer was used.
The As layer is formed of dimethyl ether (CH ₃ OCH ₃ , bp = −).
This is an example of selective etching using a mixed gas of 24 ° C.) / NF ₃ / Cl ₂ , and this will be described again with reference to FIGS.

The substrate to be etched used in this example is the same as that used in Example 1 and shown in FIG. Using this substrate to be etched as an example, patterning is performed under the following etching conditions. CH ₃ OCH ₃ flow rate 30 sccm NF ₃ flow rate 30 sccm Cl ₂ flow rate 50 sccm Gas pressure 1.5 Pa Microwave power 850 W (2.45 GHz) RF bias power 30 W (2 MHz) Etching substrate temperature 20 ° C. This etching process Then, F ^* generated by dissociation from NF ₃
And Cl ^* generated by dissociation from Cl ₂ becomes the main etching species, and As in the n ⁺ -GaAs layer 5 is mainly As.
In the form of F ₃ , AsF ₅ and AsCl ₃ and Ga to G
It is extracted in the form of aCl ₃ and patterning proceeds with a practical etching rate.

At the same time,-(CF) _n- ,-(CCl) _n- derived from the decomposition products of the resist mask 6 are produced.
A carbon-based polymer having a repeating unit structure of or-(CH) _n -is formed and adheres to the resist mask 6 and the side surface of the n ⁺ -GaAs layer 5 pattern as shown in FIG. Form. This carbon-based polymer is more likely to contain F atoms or Cl than a polymer of the same kind under the conventional etching conditions.
It has a small atomic composition ratio and is a strong one having a CO bond incorporated in its network structure. Further, in this embodiment, the amount of the carbon-based polymer produced is not as large as that under the conventional etching conditions, but the sidewall protection film 7 exhibits high etching resistance and contributes to anisotropic processing of the n ⁺ -GaAs layer 5. To do. In FIG. 1B, the side wall protective film 7 is
Similarly, although the thickness is exaggerated, it is actually an extremely thin film.

When the underlying n ⁺ -AlGaAs layer 4 is exposed, an AlF _x layer (not shown) is formed on the surface of the underlying n ⁺ -AlGaAs layer 4, the etching rate is greatly reduced, and it becomes a substantial etching stopper layer. Next, an O ₂ plasma treatment was performed to burn off the side wall protective film 7 and form a recess 8 having a vertical wall as shown in FIG. 1 (c).

The formation of the gate electrode, which is the subsequent process, is as follows.
This is the same as in the first embodiment. According to this example, CH ₃ OC
By adding H ₃ to the etching gas, selective etching of the GaAs layer having good anisotropy with respect to the AlGaAs layer becomes possible. Further, in this example, Ga can be removed as a chloride having a large vapor pressure, so that etching progressed at a high speed even though the RF bias power was reduced as compared with Example 1. Similar excellent anisotropic etching can be performed by using HBr or Br ₂ which is a Br type gas instead of Cl ₂ which is a Cl type gas used in the present embodiment. In this case,-
Higher etching resistance than (CCl) _n- (CB
Since a carbon-forming polymer containing r) _{n −} as a repeating unit is generated, it is possible to further improve the selection ratio with respect to the resist mask 6.

Embodiment 3 In this embodiment, the etching process is divided into two stages and the same n⁺−
N on the AlGaAs layer ⁺-The GaAs layer is CH₃OH /
NF₃/ Cl₂Just etching using mixed gas
After that, NF in this mixed gas₃Increase the flow rate ratio of⁺−
An over etch for removing the remaining portion of the AlGaAs layer.
This is an example of the punching, and this is shown in FIGS.
It will be described with reference to FIG.

The substrate to be etched shown in FIG. 3 (a) used in this embodiment is the same as that shown in FIG. 1 (a) used in the first embodiment, and its explanation is omitted. This substrate to be etched is patterned as an example under the following first etching conditions, and the n ⁺ -GaAs layer 5 is just etched. CH ₃ OH flow rate 40 sccm NF ₃ flow rate 30 sccm Cl ₂ flow rate 50 sccm Gas pressure 1.5 Pa Microwave power 850 W (2.45 GHz) RF bias power 30 W (2 MHz) Etching substrate temperature 20 ° C. The mechanism and the like are almost the same as those in the second embodiment. After completion of the just etching, the substrate to be etched is slightly n-shaped at the bottom of the recess 7 as shown in FIG.
The remaining portion 5a of the ⁺ -GaAs layer remained.

Therefore, the etching conditions were switched as follows by way of example, and a second etching step for removing the residual portion 5a of the n ⁺ -GaAs layer, that is, overetching was performed. CH ₃ OH flow rate 40 sccm NF ₃ flow rate 60 sccm Cl ₂ flow rate 20 sccm Gas pressure 1.5 Pa Microwave power 850 W (2.45 GHz) RF bias power 15 W (2 MHz) Etching substrate temperature 20 ° C. In the etching process, since the mixture ratio of NF ₃ is increased as compared with the first etching process, AlF _x on the exposed surface of the n ⁺ -AlGaAs layer 4 is increased.
Is promoted. Since the RF bias power is halved compared to the first etching step, n ⁺ -GaAs
Even after removing the residual portion 5a of the layer, there was no adverse effect on the n ⁺ -AlGaAs layer 4. This state is shown in Figure 3.
It is shown in (c). Subsequently, the side wall protective film 7 was removed by O ₂ plasma treatment to complete the recess 8 having the vertical wall as shown in FIG. 3D.

In the present embodiment, the selective ratio with respect to the n ⁺ -AlGaAs layer 4 was 100 or more due to the two-step etching, and no damage layer was found on the surface of the n ⁺ -AlGaAs layer 4.

Embodiment 4 This embodiment has the same n⁺-N on the AlGaAs layer⁺-GaA
Acetone (CH ₃COCH₃, Bp = 56.5
℃) / NF₃/ S₂Cl₂Low temperature etching using mixed gas
This is an example of the above-mentioned explanation, and this will be explained with reference to FIG. 1 again.
It

Since the substrate to be etched shown in FIG. 1A used in this embodiment is the same as that in the first embodiment, its explanation is omitted. Using this substrate to be etched as an example, patterning is performed under the following etching conditions. CH ₃ COCH ₃ flow rate 40 sccm NF ₃ flow rate 30 sccm S ₂ Cl ₂ flow rate 50 sccm Gas pressure 1.5 Pa Microwave power 850 W (2.45 GHz) RF bias power 20 W (2 MHz) Etched substrate temperature 20 ° C. In the etching process, F generated by dissociation from NF ₃
^* And Cl ^* generated by dissociation from S ₂ Cl ₂ are main etching species, and As in the n ⁺ -GaAs layer 5 is mainly A.
Patterning proceeds by extracting sF ₃ , AsF ₅ and AsCl ₃ and Ga in the form of GaCl ₃ .

At the same time,-(CF) _n- ,-(CCl) _n- derived from the decomposition products of the resist mask 6 are produced.
As shown in FIG. 1B, the carbon-based polymer having the repeating unit structure of or-(CH) _n- and the sulfur that is dissociated and produced from S ₂ Cl ₂ are used as the resist mask 6 and n ⁺ -G.
The sidewall protection film 7 is formed by adhering to the side surface of the aAs layer 5 pattern. This carbon-based polymer has a smaller composition ratio of F atoms and Cl atoms than a polymer of the same kind under the conventional etching conditions, and is a strong one having a CO bond incorporated in its network structure. It has a high etching resistance. Underlayer n ⁺ -AlGaAs layer 4
The mechanism for stopping the etching when the surface is exposed is the same as in the previous embodiments.

After the etching is completed, the sulfur in the side wall protection film sublimes when the substrate to be etched is heated to about 90 ° C. or higher and does not leave a trace on the substrate to be etched. Alternatively,
It is also possible to burn and remove together with the carbon-based polymer during the O ₂ plasma treatment for removing the sidewall protective film 7. This state is shown in FIG.

According to this example, the contribution of the strong side wall protective film containing sulfur compared to Examples 1 and 2
Good anisotropic etching proceeded even under the condition that the RF bias power was lowered, and the selectivity to the resist mask 6 was also improved. Further, since the amount of carbon-based polymer deposited can be relatively reduced, it also contributes to reduction of particle contamination.
Although S ₂ Cl ₂ is used as the Cl-based gas in this embodiment, a Br-based gas such as S ₂ Br ₂ may be used.

Example 5 This example has the same n⁺-N on the AlGaAs layer⁺-GaA
Acetone (CH ₃COCH₃, Bp = 56.5
℃) / NF₃/ S₂Br₂/ N₂Low temperature with mixed gas
This is an example of etching, which will be explained with reference to FIG. 1 again.
Reveal

Since the substrate to be etched shown in FIG. 1A used in this embodiment is the same as that in the first embodiment, its explanation is omitted. Using this substrate to be etched as an example, patterning is performed under the following etching conditions. CH ₃ COCH ₃ flow rate 40 sccm NF ₃ flow rate 30 sccm S ₂ Br ₂ flow rate 50 sccm N ₂ flow rate 20 sccm gas pressure 1.5 Pa microwave power 850 W (2.45 GHz) RF bias power 15 W (2 MHz) to be etched Substrate temperature 20 ° C. In this etching process, F generated by dissociation from NF ₃ is generated.
^* And Br ^* generated by dissociation from S ₂ Br ₂ are main etching species, and As in the n ⁺ -GaAs layer 5 is mainly A.
Patterning proceeds by extracting sF ₃ , AsF ₅ and AsBr ₃ , and Ga in the form of GaBr ₃ .

At the same time,-(CF) _n- ,-(CCl) _n- derived from the decomposition products of the resist mask 6 are produced.
A carbon-based polymer having a repeating unit structure of or-(CH) _n- is attached to the side surface of the resist mask 6 and the pattern of the n ⁺ -GaAs layer 5 as shown in FIG. . The sidewall protection film 7 contains sulfur that is dissociated and produced from S ₂ Br ₂ and polythiazyl that is produced by N atoms by the dissociation of N ₂ . Among them, the carbon-based polymer has a smaller composition ratio of F atoms and Br atoms than a polymer of the same kind under the conventional etching conditions, and is a strong one having a CO bond incorporated in its network structure.
It exhibits high etching resistance in combination with the deposition of polythiazyl. The mechanism for stopping the etching when the surface of the underlying n ⁺ -AlGaAs layer 4 is exposed is the same as in the previous embodiments.

The polythiazil in the side wall protective film sublimes when the substrate to be etched is heated to about 150 ° C. or higher after the etching is completed, and does not leave a trace on the substrate to be etched. Alternatively, it is also possible to burn and remove together with the carbon-based polymer during the O ₂ plasma treatment for removing the sidewall protective film 7. This state is shown in FIG.

According to this example, a strong solution containing polythiazyl was used.
Due to the contribution of the solid side wall protective film, R
Good even if the F bias power is further reduced
As anisotropic etching progresses, the resist mask 6
n⁺The selection ratio for the -AlGaAs layer 4 is also improved. Well
Since the amount of carbonaceous polymer deposited can be reduced relatively,
-It also contributes to the reduction of particle contamination. In this example,
Is S as Br-based gas ₂Br₂Was used, but S₂Cl₂
You may use Cl type gas, such as.

Embodiment 6 In this embodiment, the etching process is divided into two stages and the same n⁺−
N on the AlGaAs layer ⁺-The GaAs layer is CH₃OCH
₃/ S₂F₂/ Cl₂Just etch using mixed gas
And then S in the mixed gas₂F₂High flow rate
First, n⁺-For removing the remaining portion of the AlGaAs layer,
This is an example of over-bar etching, which is again shown in FIG.
This will be described with reference to (a) to (d).

The substrate to be etched shown in FIG. 3 (a) used in this embodiment is the same as that shown in FIG. 1 (a) used in the first embodiment, and its explanation is omitted. This substrate to be etched is patterned as an example under the following first etching conditions, and the n ⁺ -GaAs layer 5 is just etched. CH ₃ OCH ₃ flow rate 40 sccm S ₂ F ₂ flow rate 30 sccm Cl ₂ flow rate 50 sccm Gas pressure 1.5 Pa Microwave power 850 W (2.45 GHz) RF bias power 30 W (2 MHz) Etched substrate temperature 20 ° C. main In the etching step, the content of the halogen element is small and the carbon-based polymer in which the C—O bond and the C—H bond are reinforced by the introduction and the sulfur by the dissociation of S ₂ F ₂ have a high ion impact resistance. Anisotropic etching proceeds while forming the sidewall protective film 7. After completion of the just etching, the substrate to be etched was in a state where some residual portion 5a of the n ⁺ -GaAs layer remained at the bottom of the recess 7 as shown in FIG. 3 (b).

Next, the etching conditions were switched as follows by way of example, and a second etching step for removing the residual portion 5a of the n ⁺ -GaAs layer, that is, overetching was performed. CH ₃ OCH ₃ flow rate 40 sccm S ₂ F ₂ flow rate 50 sccm Cl ₂ flow rate 30 sccm Gas pressure 1.5 Pa Microwave power 850 W (2.45 GHz) RF bias power 15 W (2 MHz) Etched substrate temperature 20 ° C. In the second etching step, since the mixture ratio of S ₂ F ₂ is increased as compared with the first etching step, AlF _x on the exposed surface of the n ⁺ -AlGaAs layer 4 is increased.
Is promoted. Since the RF bias power is halved compared to the first etching step, n ⁺ -GaAs
Even after removing the residual portion 5a of the layer, there was no adverse effect on the n ⁺ -AlGaAs layer 4. This state is shown in Figure 3.
It is shown in (c). Subsequently, the side wall protective film 7 was removed by O ₂ plasma treatment to complete the recess 8 having the vertical wall as shown in FIG. 3D.

In this embodiment, the side wall protective film is used in combination with the deposition of sulfur, and the etching is performed in two stages, so that n ⁺ -
The selection ratio for the AlGaAs layer 4 is 150 or more,
No damage layer was observed on the surface of the n ⁺ -AlGaAs layer 4.

Although the present invention has been described above with reference to six embodiments, the present invention is not limited to these embodiments.

First, in each of the above-described embodiments, the combination system of GaAs / AlGaAs is exemplified as the laminated system of the compound semiconductor layers not containing Al laminated on the compound semiconductor layer containing Al, but the upper layer contains Al. Alternatively, the present invention can be applied to selective etching of a conventionally known laminated system of compound semiconductors containing Al in the lower layer. As such a combination, for example, GaP / AlGaP, InP /
AlInP, GaN / AlGaN, InAs / AlIn
A laminated system of a compound semiconductor of 2 element system / 3 element system such as As or 3 element system / 4 element system can be exemplified.

Furthermore, the present invention is applicable to the HEMT of each of the above embodiments if the process requires selective etching of a laminated system of non-Al-containing compound semiconductor / Al-containing compound semiconductor.
In addition to the above manufacturing process, it can be applied to processing of MESFETs, semiconductor laser devices, quantum well devices, and the like.

As an organic compound gas containing a C--O bond,
CH₃OH, CH₃OCH₃, CH ₃COCH₃Exemplify
However, alcohol with a relatively low molecular weight and large vapor pressure,
Ethers, ketones, esters, carboxylic acids and aldes
Hide or the like can be used as appropriate. These organic compounds
Is a liquid compound at room temperature, although it often exists as a liquid at room temperature.
In this case, the heating bubbling method or baking method should be used.
It may be used after being converted into an etching chamber.

NF ₃ and S used in the examples as F-based gas
_In addition to ₂ F ₂ , SF ₆ , N ₂ F ₄ , ClF ₃ , XeF ₂ ,
Compounds having F atoms such as F ₂ can be used. SF ₂ , S
Sulfur fluoride-based gas such as F ₄ and S ₂ F ₁₀ can be used as a gas that also serves as a sulfur supply source as a sidewall protective film.

In addition to Cl ₂ , S ₂ Cl ₂ and S ₂ Br ₂ used in the examples as Cl-based gas and Br-based gas, HC
1, BCl ₃ , HBr, BBr ₃ , Br _{2 and the} like can be used. Sulfur chloride-based gas and sulfur bromide-based gas such as S ₃ Cl ₂ , SCl ₂ , S ₃ Br ₂ and SBr ₂ can be used as a gas that also serves as a sulfur supply source as a sidewall protective film.

Although the substrate bias application type ECR plasma etching apparatus has been exemplified as the etching apparatus, a more general parallel plate type RIE apparatus, a helicon wave plasma etching apparatus capable of processing with high density plasma, and an ICP.
(Inductively Coupled Plasma
a) Etching device, TCP (Transformer)
A Coupled Plasma) etching device or the like can be used.

[0063]

As is apparent from the above description, the present invention selectively removes an Al-free compound semiconductor layer laminated on an Al-containing compound semiconductor layer without using a chlorofluorocarbon-based gas. It has become possible to provide a CFC-free dry etching method for patterning.

Further, according to the present invention, by adopting a strong side wall protective film, Al laminated on the compound semiconductor layer containing Al can be formed without causing an increase in particle level and a pattern conversion difference due to its excessive deposition. It has become possible to anisotropically process a compound semiconductor layer not containing it.

Similarly, by strengthening the side wall protective film, it is possible to reduce the incident ion energy required for anisotropic etching. Therefore, the selection ratio with respect to the compound semiconductor layer containing the underlying Al is improved, damage can be reduced, and the selection ratio with the resist mask is also improved, which is advantageous in reducing the dimensional conversion difference due to receding of the resist pattern or the like.

As described above, the present invention can meet the high requirements of the manufacturing process of the compound semiconductor device, and at the same time, the dechlorofluorocarbon process becomes possible, which can contribute to the clean environment.

[Brief description of drawings]

FIG. 1 is a first example to which the present invention is applied.
FIG. 4A is a schematic cross-sectional view illustrating the steps in the order of steps, in which FIG.
aAs layer, n ⁺ -AlGaAs layer and n ⁺ -GaAs
Layers are sequentially formed, (b) is a state in which the n ⁺ -GaAs layer is etched while forming the sidewall protective film, and (c) is a state in which the sidewall protective film is removed and the recess is completed.

2A and 2B are schematic cross-sectional views for explaining the process following FIG. 1, in which FIG. 2A is a state in which an Al-based metal layer is formed, and FIG. 2B is a lift-off of the Al-based metal layer to form a gate electrode at the bottom of the recess. It is a state where the pattern is left.

3A and 3B are schematic cross-sectional views for explaining Embodiments 3 and 6 to which the present invention is applied, in the order of steps, and FIG.
GaAs buffer layer, AlGaAs layer on aAs substrate,
A state in which an n ⁺ -AlGaAs layer and an n ⁺ -GaAs layer are sequentially formed, (b) shows n ⁺ -G while forming a sidewall protective film.
A state in which a part of the aAs layer in the layer thickness direction is etched,
(C) is a state in which the remaining portion of the n ⁺ -GaAs layer in the layer thickness direction is etched, and (d) is a state in which the sidewall protective film is removed and the recess is completed.

[Explanation of symbols]

1 semi-insulating GaAs substrate 2 GaAs buffer layer 3 AlGaAs layer 4 n ⁺ -AlGaAs layer 5 n ⁺ -GaAs layer 5a n ⁺ -residual portion of GaAs layer 6 resist mask 7 sidewall protection film 8 recess 9 Al-based metal layer 9a gate Electrode pattern

Claims (6)

[Claims] 1. A compound semiconductor layer not containing Al, which is stacked on a compound semiconductor layer containing Al, is etched by a mixed gas containing an organic compound gas having a C—O bond and an F-based gas. And a dry etching method. 2. A part of the Al-free compound semiconductor layer laminated on the Al-containing compound semiconductor layer in the layer thickness direction,
A first etching step of etching with a mixed gas containing an organic compound gas having a C—O bond and an F-based gas, and a residual portion of the compound semiconductor layer not containing Al in the layer thickness direction in the mixed gas. And a second etching step of increasing the mixing ratio of the F-based gas for etching. 3. An organic compound gas having a C—O bond,
At least one selected from the group consisting of alcohols, ethers, ketones, esters, carboxylic acids and aldehydes
The dry etching method according to claim 1 or 2, wherein the dry etching method is a type. 4. The dry etching method according to claim 1, wherein the mixed gas further contains one of a Cl-based gas and a Br-based gas. 5. The F-based gas is S ₂ F ₂ , SF ₂ , SF ₄
3. The dry etching method according to claim 1, wherein the dry etching method is any one selected from the group consisting of S ₂ F ₁₀ and S ₂ F ₁₀ . 6. The Cl-based gas and the Br-based gas are S ₂ C.
l ₂ , S ₃ Cl ₂ , SCl ₂ , S ₂ Br ₂ , S ₃ Br ₂
5. The dry etching method according to claim 4, wherein the dry etching method is any one selected from the group consisting of and SBr ₂ .