JPH06151384A - Dry etching method - Google Patents

Abstract

PURPOSE:To realize the selective anisotropic etching of GaAs/AlGaAs laminate series without the use of a CFC(chlorofluorocarbon). CONSTITUTION:In the processing of a gate recess 5a of a HEMT, an n<+>-GaAs layer 5 on an n<+>-GaAs layer 4 is etched using an etching gas that contains a thiocarbonyl compound and can generate F* under electric discharge dissociation conditions. A carbon-based polymer that has a deposition characteristic and is derived from a decomposition product of a resist mask 6 is strengthened by the introduction of >C=S base radicals or C-S linkages. Moreover, S (sulphur) which is dissociated from the thiocarbonyl compound is also deposited. Therefore, a strong side wall protective film 7 can be created even when the amount of the deposition of the carbon-based polymer is relatively decreased, and superior anisotropic processing can be effected by a low incident ion energy. Specific examples of the composition of the gas include CSF2/Cl2, CSCl2/SF6 or the like.

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 applied to the manufacture of semiconductor devices, etc.
The present invention relates to a method of performing GaAs / AlGaAs selective etching or the like in a gate / recess forming step of a (high electron mobility transistor) without generating particle contamination.

[0002]

2. Description of the Related Art GaAs MES-FET (metal
semiconductor field effec
MMIC (monolithic microwave) in which a single transistor is integrated on a single substrate.
IC) has features such as high-speed and high-frequency response, low noise, and low power consumption, and has recently been used as a device for mobile communication and sanitary communication.

In 1980, the above GaAs MES-F
From research aimed at further speeding up ET, HEMT
(High electron mobility t
(Transistor) has been developed. This is Ga
This is a device that utilizes the fact that the two-dimensional electron gas at the heterojunction interface of an As compound semiconductor can move at high speed without being scattered by impurities. The HEMT is also being researched to realize high integration, and the demand for a dry etching technique for processing the HEMT is also toward higher precision and higher selection ratio.

In particular, the step of selectively etching the GaAs / AlGaAs laminated system to form the gate recess is an important technique for determining the threshold voltage of a heterojunction FET such as HEMT or hetero MIS structure FET. This is because the impurity concentration, thickness, etc. of the lower AlGaAs layer are set in advance so that an FET having an appropriate threshold voltage can be constructed by removing only the upper GaAs layer. GaA on this AlGaAs layer
A typical method of selectively etching the s layer is a method using a mixed gas of CFC (chlorofluorocarbon) gas such as CCl ₂ F ₂ and a rare gas. This is Ga
Is a chloride, and As forms a fluoride and a chloride to remove the GaAs layer, while the underlying AlGaAs layer is exposed to a low vapor pressure AlF.
_{This is because x} (aluminum fluoride) is formed on the surface, the etching rate is reduced, and a high selection ratio is obtained.

[0005] For example, Japanese Journal
al of Applied Physics, Vo
l. 20. , No. 11 (1981), p. L847 ~
In 850, an example in which a selectivity ratio of 200 is achieved by using a CCl ₂ F ₂ / He mixed gas is reported.

[0006]

However, the above-mentioned CFC gas such as CCl ₂ F ₂ is one of the compounds commonly called so-called CFC gas, and it is well known that it causes the ozone layer depletion of the earth. Therefore, it is prohibited to manufacture or use in the near future. Therefore, also in the field of dry etching, it is urgently necessary to develop an alternative gas and its use technology.

Further, the above-mentioned CFC gas tends to generate a large amount of fluorocarbon polymer in the etching reaction system. This polymer contributes to anisotropic processing because it is deposited on the side wall of the pattern and exhibits a side wall protection effect.
On the other hand, the etching rate becomes unstable and particles
It is easy to cause deterioration of the level. Therefore, the present invention provides a compound semiconductor layer (hereinafter, referred to as a non-Al-containing compound semiconductor layer) that does not contain Al on a compound semiconductor layer that includes aluminum (Al) (hereinafter, referred to as an Al-containing compound semiconductor layer). Selective etching without using CFC gas
Moreover, it is an object of the present invention to provide a dry etching method that can be performed under clean conditions.

[0008]

The dry etching method of the present invention is proposed in order to achieve the above-mentioned object, and is a non-A layer laminated on an Al-containing compound semiconductor layer.
The 1-containing compound semiconductor layer is selectively etched using an etching gas containing a thiocarbonyl compound having a fluorine atom and a thiocarbonyl group in the molecule.

The present invention also provides that the etching gas comprises:
It contains at least one of a non-depositing chlorine compound and a non-depositing bromine compound.

The present invention also provides, in place of the non-depositing chlorine-based compound or the non-depositing bromine-based compound, a deposition-type chlorine-based compound or also a deposition-based bromine-based compound capable of releasing free sulfur under discharge dissociation conditions. At least one of the above is used.

The present invention also provides a non-Al-containing compound semiconductor layer laminated on an Al-containing compound semiconductor layer, a thiocarbonyl compound having at least one of a chlorine atom or a bromine atom and a thiocarbonyl group in the molecule, The selective etching is performed using an etching gas containing a non-depositing fluorine compound.

The present invention also uses, instead of the non-depositable fluorine-based compound, a deposited fluorine-based compound capable of releasing free sulfur under discharge dissociation conditions.

The present invention also provides that the etching gas is H 2.
_At least 1 selected from ₂ , H ₂ S and silane compounds
It contains a variety of halogen / radical consuming compounds.

The present invention also provides that the etching gas supplies nitrogen-based chemical species into the plasma under discharge dissociation conditions.

The present invention further includes a just etching step of etching the non-Al-containing compound semiconductor layer substantially by the thickness of the non-Al-containing compound semiconductor layer using any one of the above-mentioned etching gases, and generation of fluorine-based chemical species in plasma. Changing the mixture ratio of the components of the etching gas so that the ratio is relatively higher than in the just etching step,
And an over-etching step of etching the remaining portion of the non-Al-containing compound semiconductor layer.

[0016]

When establishing the de-CFC process, if the carbon-based polymer forming the sidewall protective film required for anisotropic processing is not supplied from the gas phase, the supply source must be the resist mask. I don't get. However, if this is sputtered with ions having a high incident energy in order to supply a large amount of decomposition products of the resist mask, the resist selectivity will inevitably decrease, and damage to the underlayer and particle contamination cannot be prevented. .

The point of the present invention is to enhance the film quality of the carbon-based polymer itself and to combine the deposition of S,
It reduces the deposition amount of carbon-based polymer and
The point is to achieve excellent anisotropic processing even under conditions where the energy is reduced.

In the present invention, a thiocarbonyl group (> C =) is used as a method for strengthening the film quality of the carbon-based polymer itself.
A thiocarbonyl compound having S) is used. The thiocarbonyl group plays an important role of first introducing a C—S bond into the carbon-based polymer to strengthen the chemical bond. This means that the C—S bond (713.4 kJ / mol) is C—C when the bond energies between two atoms are compared.
It is also intuitively understood from the fact that it is larger than the binding (607 kJ / mol).

Further, the thiocarbonyl group has a function of increasing its polarity by being taken into the carbon-based polymer and enhancing the electrostatic adsorption force of the carbon-based polymer to the wafer which is being negatively charged and is being etched. To do. It is considered that this also improves the etching resistance of the carbon-based polymer.

By thus strengthening the film quality of the carbon-based polymer itself, the incident ion energy required for anisotropic processing can be reduced and the resist selectivity can be improved. This means that it is possible to form an etching mask that can withstand practical use even with a relatively thin photoresist coating film, and it is possible to prevent the occurrence of processing size conversion differences while achieving high resolution in photolithography. It also has a secondary effect. In addition, reduction of incident ion energy leads to improvement of base selectivity, as a matter of course. Furthermore, since the amount of carbon-based polymer required to achieve high anisotropy and high selectivity can be reduced, particle contamination can be reduced as compared with the conventional technique.

Further, S (sulfur) is released from the thiocarbonyl compound into the plasma under discharge dissociation conditions. Although depending on the conditions, this S is deposited on the surface of the substrate (wafer) if the temperature of the substrate (wafer) is controlled below room temperature. Therefore, the incident ion energy can be further reduced, and the damage can be thoroughly reduced. In addition, the amount of carbon-based polymer deposited can be relatively reduced,
Particle contamination can be reduced more effectively. Moreover, S easily sublimes when the wafer is heated to approximately 90 ° C. or higher, so that S itself does not become a source of particle contamination. Alternatively, it can be burned and removed by O ₂ plasma treatment.

The halogen atom contained in the thiocarbonyl compound is any one of fluorine, chlorine and bromine. These halogen atoms contribute as the main etching species of the non-Al-containing compound semiconductor layer. However, non-A
Since the achievement of the underlying selectivity in the etching of the laminated system of the l-containing / Al-containing compound semiconductor layer is based on the generation of AlF _x in principle, the etching reaction system must have a fluorine-based chemical species such as F ^*. is necessary.

In the present invention, a thiocarbonyl compound having a fluorine atom and a thiocarbonyl group in the molecule is used as an etching gas satisfying the above requirements. In principle, this enables selective anisotropic processing with a single composition etching gas.

However, depending on the constituent elements of the compound semiconductor layer, a reaction product having a high vapor pressure cannot be obtained when the halogen-based chemical species present in the etching reaction system are only fluorine-based chemical species, and the etching rate is significantly reduced. There is fear. Therefore, the present invention further proposes to add at least one of a chlorine compound and a bromine compound to the above thiocarbonyl compound. As a result, chemical species such as Cl ^* , Br ^*, etc. can contribute to the etching reaction system, and the etching speed can be increased. In addition, a carbon-based polymer having a composition such as CCl _x , CBr _x or the like that is more likely to be deposited is used. You can expect it.

The chlorine-based compound and the bromine-based compound may be non-depositing compounds that do not form a depositing substance under discharge dissociation conditions, or depositing compounds that release free S (sulfur). May be In the latter case, the amount of carbon-based polymer deposited can be further reduced by the amount that S can be expected to be deposited, so that high selectivity and low contamination can be further improved.

The present invention also proposes, as another etching gas composition, a composition in which halogen atoms are exchanged between the thiocarbonyl compound and the chlorine compound or the bromine compound. That is, the thiocarbonyl compound contains a chlorine atom or a bromine atom, and the fluorine compound is added to this. Even with this gas composition, the effects described above can be expected.

Also in this case, the fluorine-based compound may be either a non-depositing compound or a depositing compound capable of releasing S.

The present invention is based on the above idea, but proposes another method aiming at further reduction of pollution and damage. The first is to add at least one halogen / radical consuming compound selected from H ₂ , H ₂ S and silane compounds to the etching gas. H ^* and Si ^* produced from these halogen / radical consuming compounds trap a part of the halogen / radicals and remove them in the form of hydrogen halide or silicon halide. Therefore, the apparent S / X of the etching reaction system is
[Ratio of the number of S atoms and the number of X (halogen) atoms] increases, and S
Accumulation of In this case, F ^{*, which} is the basis for achieving the selectivity for the Al-containing compound semiconductor layer, is also reduced,
This is covered by the increase in the S deposition amount.

The second method is to use, as an etching gas, one capable of releasing nitrogen (N) type chemical species. The source of the N-based chemical species may be the above-mentioned non-depositing fluorine-based compound, chlorine-based compound, bromine-based compound, or another nitrogen-based compound containing no halogen atom. In any case, this method is intended to produce a sulfur nitride-based compound by reacting S released from the above-mentioned thiocarbonyl compound or the accumulating halogen compound with an N-based chemical species. Various compounds can be considered as the sulfur nitride compound,
A typical example is polymeric polythiazyl (SN).
_x . (SN) _x has a repetitive covalent bond chain of S-N-S-N -... and exhibits higher etching resistance than S of a single substance. Therefore, by using this, the surface protection effect is improved. .

Moreover, the sulfur nitride compound is sublimated or decomposed when the wafer is heated to approximately 130 ° C. or higher. Alternatively, it can be easily burned and removed by the O ₂ plasma treatment, and there is no fear of becoming a particle contamination source.

The third method is to perform etching in two stages, a just etching process and an over etching process,
This is a method of increasing the production ratio of fluorine-based chemical species in plasma in the over-etching step. In the overetching step, most of the non-Al-containing compound semiconductor layer is removed, and the underlying Al-containing compound semiconductor layer is exposed in many parts of the etched region. Therefore, if the production amount of the fluorine-based chemical species is increased at this stage, the production of AlF _x on the exposed surface is promoted and the selectivity is improved. This production ratio can be changed by, for example, increasing the flow rate ratio of the compound capable of releasing the fluorine-based chemical species as compared with the just etching step.

[0032]

EXAMPLES Specific examples of the present invention will be described below.

[0033] Example 1 This example, the present invention is applied to a gate recess process of HEMT, n ⁺ -AlGaAs layer of n ⁺ -GaAs layer CSF ₂ (fluoroaryl thiocarbonyl) / Ar mixed gas This is an example of etching using. This process is illustrated in Figure 1.
Description will be made with reference to (a), (c), and (d).

The wafer used as an etching sample in this example is as shown in FIG.
It is formed on the semi-insulating GaAs substrate 1 by epitaxial growth and has a thickness of about 500 nm that functions as a buffer layer.
Epi-GaAs layer 2, AlGaAs having a thickness of about 2 nm
Layer 3, thickness of about 30 n doped with n-type impurities such as Si
m n ⁺ -AlGaAs layer 4, similarly an n ⁺ -GaAs layer 5 having a thickness of about 100 nm containing n-type impurities, and a resist mask (PR) 6 patterned in a predetermined shape are sequentially laminated. is there. The patterning of the resist mask 6 is performed by exposure and development processing by an electron beam drawing method, and the opening diameter of the opening 6a is about 300.
nm.

This wafer was set on the wafer mounting electrode of a magnetic bias microwave plasma etching apparatus of RF bias application type, and as an example, the above n ⁺ -GaA was used under the following conditions.
The s layer 5 was etched. CSF ₂ flow rate 20 SCCM Ar flow rate 30 SCCM gas pressure 1.3 Pa (= 10 mTo
rr) Microwave power 850 W (2.45 GH)
z) RF bias power 40 W (2 MHz) Wafer temperature 20 ° C.

In this etching process, F ^* generated from CSF ₂ is As in the n ⁺ -GaAs layer 5, AsF ₃ ,
Extract AsF ₅ etc. and Ga in the form GaF ₃ etc. However, since the GaF ₃ low vapor pressure at normal etching reaction system, Ar ⁺ in the above conditions, C ^+, C
The incident ion energy of S ⁺ , CSF ^+, etc. is slightly increased, and is removed by the ion sputtering action.

At the same time, CF _x is generated due to the decomposition products of the resist mask 6, and thiocarbonyl groups, C—S bonds, etc. are further incorporated into the structure to form a strong carbon-based polymer. Generated. Furthermore, free S was also produced from CSF ₂ . These carbon-based polymers and S are
A side wall protective film 7 as shown in FIG. 1 (c) was formed.
As a result, the recess 5a having the vertical wall was formed. Although the side wall protective film 7 in the drawing is drawn thick for convenience of illustration, it is actually an extremely thin film, and a dimensional conversion difference occurs between the resist mask 6 and the recess 5a to be formed. It's not something to let you do.

When the underlying n ⁺ -AlGaAs layer 4 is exposed, AlF _x is formed on the surface thereof, which plays a role of significantly reducing the etching rate.

The sidewall protection film 7 could be easily removed by performing an O ₂ plasma treatment after the etching, as shown in FIG. 1 (d).

Subsequent formation of the gate electrode may be performed by a conventionally known method. This process will be described with reference to FIG. That is, by performing electron beam evaporation of Al on the wafer, an Al layer having a thickness of about 200 nm was formed as an example. This vapor deposition is performed in steps inside the recess 5a having a fine opening diameter.
The deterioration of the coverage (step coverage) is used conversely. As shown in FIG. 2A, an upper Al layer 8a is formed on the surface of the resist mask 6 and a lower Al layer is formed on the bottom of the recess 5a. Layers 8b were each formed.

Next, when the resist mask 6 is lifted off, the upper Al layer 8a is also removed at the same time as shown in FIG. 2B, leaving only the lower Al layer 8b to be the gate electrode at the bottom of the recess 5a. I was able to.

Example 2 In this example, the same n ⁺ -GaAs layer was used as CSF ₂ / C.
This is an example of etching using l ₂ mixed gas. First,
The wafer shown in FIG. 1A was set in a magnetic field microwave plasma etching apparatus, and as an example, the n ⁺ -GaAs layer 5 was etched under the following conditions.

CSF ₂ flow rate 20 SCCM Cl ₂ flow rate 20 SCCM Gas pressure 1.3 Pa (= 10 mTo
rr) Microwave power 850 W (2.45 GH)
z) RF bias power 20 W (2 MHz) Wafer temperature 20 ° C

[0044] In this etching process, becomes Cl ^* main etching species generated from F ^* and Cl ₂ generated from CSF _2, mainly AsF ₃ a As, AsF _5, ASC
In the form of l ₃ etc., and Ga was mainly extracted in the form of GaCl ₃ etc. In this example, Ga can be removed in the form of chloride having a high vapor pressure, so that high-speed etching proceeded even though the RF bias power was halved compared to Example 1.

Further, CCl _x was generated due to the decomposition product of the resist mask 6, and a thiocarbonyl group and a C—S bond were introduced into this to form a strong sidewall protective film 7. The supply amount of decomposition products at this time is
Although less than in Example 1 due to the reduction in power, CCl _x
Since the depositability of is superior to that of CF _x , the sidewall protection effect was not reduced at all.

Also in this example, the recess 5a having a good anisotropic shape could be formed. In this embodiment, the selection ratio with respect to the n ⁺ -AlGaAs layer 4 is about 5.
It was 0.

Even if HBr was used in place of Cl ₂ described above, good anisotropic processing could be similarly performed.
In this case, since CBr _x is generated as the carbon-based polymer, the selectivity with respect to the resist mask 6 can be further improved.

Example 3 In this example, the same n ⁺ -GaAs layer was used as CSF ₂ / S.
_This is an example of etching using a ₂ Cl ₂ mixed gas. An example of etching conditions is as follows. CSF ₂ flow rate 20 SCCM S ₂ Cl ₂ flow rate 20 SCCM Gas pressure 1.3 Pa (= 10 mTo
rr) Microwave power 850 W (2.45 GH)
z) RF bias power 15 W (2 MHz) Wafer temperature 20 ° C. In this etching process, in addition to CSF ₂ , S ₂ Cl ₂
The release of S atoms also increased the contribution of S in the formation of the sidewall protective film 7. Therefore, although the RF bias power was slightly lowered as compared with Example 2, good anisotropic processing could be performed. Further, the relative amount of the carbon-based polymer deposited could be further reduced, and the reduction of pollution could be thoroughly achieved.

Example 4 In this example, the same n ⁺ -GaAs layer was used as CSCl.
_This is an example of etching using a mixed gas of ₂ (thiocarbonyl chloride) / SF ₆ . An example of etching conditions is as follows. CSCl ₂ flow rate 20 SCCM SF ₆ flow rate 20 SCCM gas pressure 1.3 Pa (= 10 mTo
rr) Microwave power 850 W (2.45 GH)
z) RF bias power 20 W (2 MHz) Wafer temperature 20 ° C. Cl generated from CSCl _{2 in} this etching process
^The etching proceeded with F ^* generated from ^* and SF _{6 as the} main etching species. The mechanism for strengthening the carbon-based polymer is almost as described above in Example 2.

Example 5 In this example, the same n ⁺ -GaAs layer was formed into CSCl ₂ /
Etching was performed using S ₂ F ₂ mixed gas. An example of etching conditions is as follows. CSCl ₂ flow rate 20 SCCM S ₂ F ₂ flow rate 20 SCCM gas pressure 1.3 Pa (= 10 mTo
rr) Microwave power 850 W (2.45 GH)
z) RF bias power 15 W (2 MHz) Wafer temperature 20 ° C. The above gas composition corresponds to the gas composition of Example 3 in which halogen atoms are exchanged between the thiocarbonyl compound and the sulfur halide. To do. Therefore, except for a slight difference in discharge dissociation efficiency, the etching mechanism is the same as in Example 3.
Is almost the same as.

Example 6 In this example, the same n ⁺ -GaAs layer was formed into CSCl ₂ /
Etching was performed using SF ₆ / H ₂ S mixed gas. An example of etching conditions is as follows. CSCl ₂ flow rate 20 SCCM SF ₆ flow rate 20 SCCM H ₂ S flow rate 10 SCCM gas pressure 1.3 Pa (= 10 mTo
rr) Microwave power 850 W (2.45 GH)
z) RF bias power 15 W (2 MHz) Wafer temperature 20 ° C. The above gas composition corresponds to the gas composition of Example 4 to which H ₂ S is added. In this etching process, CSC
Part of F ^* and Cl ^* produced from l ₂ and SF ₆ is H ₂ S.
Consumed by H ^* generated from H ₂ S
Is released from S, the S in the etching reaction system is released.
The / X ratio was increased, and highly anisotropic processing could be performed under low bias conditions.

Example 7 In this example, the same n ⁺ -GaAs layer was used as CSCl ₂ /
Etching was performed using an NF ₃ mixed gas. An example of etching conditions is as follows. CSCl ₂ flow rate 20 SCCM NF ₃ flow rate 20 SCCM Gas pressure 1.3 Pa (= 10 mTo
rr) Microwave power 850 W (2.45 GH)
z) RF bias power 10 W (2 MHz) Wafer temperature 20 ° C. Here, NF ₃ is a source of F ^* as well as a source of N atoms. In this example, the N atom and CSCl ₂
Reacting with the S atoms released from the above, a sulfur nitride-based product such as (SN) _x was generated, and partly constituted the side wall protective film 7. As a result, highly anisotropic processing could be performed under the condition that the RF bias power was further reduced.

Incidentally, the sulfur nitride-based compound could be easily removed together with the carbon-based polymer by performing the O ₂ plasma treatment after the etching.

Embodiment 8 In this embodiment, the same n ⁺ -GaAs layer etching process is performed in two steps, just etching is performed using a CSF ₂ / S ₂ Cl ₂ mixed gas, and then CS in the above mixed gas is used.
The remaining portion of the n ⁺ -GaAs layer was removed by increasing the flow rate of F ₂ and performing overetching. This process will be described with reference to FIGS. 1 (a), 1 (b) and 1 (c).

First, for the wafer shown in FIG. 1A, the n ⁺ -GaAs layer 5 was just-etched under the following conditions as an example. CSF ₂ flow rate 20 SCCM (flow rate 50
%) S ₂ Cl ₂ flow rate 20 SCCM gas pressure 1.3 Pa (= 10 mTorr)
r) Microwave power 850 W (2.45 GHz) RF bias power 20 W (2 MHz) Wafer temperature 20 ° C The state of the wafer at the end of just etching is shown in Fig. 1 (b).
In some of the recesses 5a, a slight residual portion 5b of the n ⁺ -GaAs layer 5 was left at the bottom thereof.

Next, the etching conditions were switched as follows by way of example, and over-etching was performed to remove the residual portion 5b. CSF ₂ flow rate 30 SCCM (flow rate ratio 75
%) S ₂ Cl ₂ flow rate 10 SCCM gas pressure 1.3 Pa (= 10 mTorr)
r) Microwave power 850 W (2.45 GHz) RF bias power 10 W (2 MHz) Wafer temperature 20 ° C. In this overetching process, the flow rate ratio of CSF ₂ is increased as compared with the just etching process. Al on the exposed surface of the n ⁺ -AlGaAs layer 4
The production of F _x was promoted. Also, the RF bias power is halved compared to the just etching process. As a result, as shown in FIG. 1C, the underlying n ⁺ -AlGaAs layer 4 was not adversely affected even after the residual portion 5b was removed.

In this example, the selection ratio for the n ⁺ -AlGaAs layer 4 was improved to 100 or more.

Although the present invention has been described based on the eight examples, the present invention is not limited to these examples. First, in each of the above-described embodiments, the GaAs / AlGaAs laminated system is exemplified as the laminated system of compound semiconductor layers, but the present invention can be applied to other known compound semiconductor laminated systems as long as Al is contained in the lower layer side. Applicable. For example, GaP / AlGaP, InP / AlInP, G
The present invention can also be applied to etching of a two-element system / three-element system laminated system such as aN / AlGaN, InAs / AlInAs, or a three-element system / 4-element system laminated system.

Further, the present invention is not limited to the production of HEMT as described above as long as the process requires selective etching of a laminated system of a non-Al-containing / Al-containing compound semiconductor, and for example, a quantum wire or a semiconductor laser device. It can also be applied to the processing etc.

In each of the above examples, CSF ₂ and CSCl ₂ were used as the thiocarbonyl compound. These compounds are structurally composed of two F atoms or Cl atoms bonded to the carbon atom of a thiocarbonyl group. In the thiocarbonyl compound that can be used in the present invention, at least one of these halogen atoms may be Br atom. In this case, it can be expected that high resist selectivity can be achieved by the generation of CBr _x .

As the non-depositing chlorine-based compound, HCl, BCl ₃ or the like can be used in addition to Cl ₂ described above. As the non-depositing brominated compound, the above-mentioned Example 2 is used.
In addition to the HBr mentioned above, Br ₂ , BBr ₃ or the like can be used. As the non-depositing fluorine-based compound, ClF ₃ , NF ₃ or the like can be used instead of SF ₆ described above. NF ₃ will also serve as a supply source of nitrogen-based chemical species.

H ₂ S has been exemplified as the halogen / radical consuming compound, but basically the same result can be obtained by using H ₂ or a silane compound. The etching gas used in the present invention includes sputtering effect, cooling effect,
A rare gas such as He or Ar may be added for the purpose of obtaining a dilution effect. In addition, it goes without saying that the structure of the sample wafer, the etching apparatus used, the etching conditions and the like can be changed as appropriate.

[0063]

As is apparent from the above description, according to the present invention, in the selective anisotropic etching of the laminated system of the non-Al-containing / Al-containing compound semiconductor represented by the GaAs / AlGaAs laminated system, By using the etching gas containing the thiocarbonyl compound, the film quality of the carbon-based polymer is enhanced, and S also contributes to the sidewall protection. As a result, high anisotropy and high selectivity can be achieved even if the amount of carbon-based polymer deposited is reduced. Therefore, it is possible to suppress particle contamination and significantly improve the yield of semiconductor devices.

The present invention is extremely effective in manufacturing a semiconductor device using, for example, a compound semiconductor based on a fine design rule, and is highly integrated to form an MMIC or the like. It makes a contribution. Of course, it goes without saying that the present invention provides an excellent measure against CFC removal.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating a process example in which the present invention is applied to a gate recess processing of HEMT in the order of the steps, and FIG. 1A shows a resist mask formed on an n ⁺ -GaAs layer. State, (b) is n ⁺ -GaAs
The layer is etched while forming the sidewall protection film, a recess is formed, and a residual portion of the n ⁺ -GaAs layer is generated, (c) is a state in which the n ⁺ -GaAs layer is completely etched, or With the rest removed,
(D) shows the state where the side wall protective film is removed.

FIG. 2 is a schematic cross-sectional view illustrating a step of forming a gate electrode inside a recess in the order of the steps, FIG. 2A is a surface of a resist mask and a bottom surface of a recess, and an upper Al layer and a lower Al layer are respectively formed. FIG. 3B is a schematic cross-sectional view showing a state where the resist mask and the upper Al layer on the surface of the resist mask are removed, and the lower Al layer (gate electrode) is left only on the bottom surface of the recess.

[Explanation of symbols]

1 ... Semi-insulating GaAs substrate 2 ... epi-GaAs layer 3 ... AlGaAs layer 4 ... n ⁺ -AlGaAs layer 5 ... n ⁺ -GaAs layer 5a ... Recess 5b ... Residual part (of n ⁺ -GaAs layer) 6 ... Resist mask 6a ... Opening 7 ... Side wall protective film 8a ... Upper Al layer 8b ... Lower Al layer (gate electrode)

Claims (8)

[Claims] 1. A compound semiconductor layer containing no aluminum, which is laminated on a compound semiconductor layer containing aluminum, is selected by using an etching gas containing a thiocarbonyl compound having a fluorine atom and a thiocarbonyl group in the molecule. Dry etching method characterized in that it is selectively etched. 2. The dry etching method according to claim 1, wherein the etching gas contains at least one of a non-depositing chlorine compound and a non-depositing bromine compound. 3. The etching gas contains at least one of a depositable chlorine-based compound capable of releasing free sulfur or a depositable brominated compound also capable of releasing sulfur under discharge dissociation conditions. The dry etching method according to claim 1. 4. A compound semiconductor layer containing no aluminum, which is laminated on a compound semiconductor layer containing aluminum, containing a thiocarbonyl compound having at least one of a chlorine atom or a bromine atom and a thiocarbonyl group in a molecule, A dry etching method characterized by selectively etching using an etching gas containing a depositable fluorine-based compound. 5. A compound semiconductor layer containing no aluminum, which is laminated on a compound semiconductor layer containing aluminum, is discharged with a thiocarbonyl compound having at least one of a chlorine atom or a bromine atom and a thiocarbonyl group in a molecule. A dry etching method characterized by performing selective etching using an etching gas containing a depositable fluorine-based compound capable of releasing free sulfur under dissociation conditions. 6. The etching gas is H ₂ , H ₂ S,
The dry etching method according to claim 1, further comprising at least one halogen / radical consuming compound selected from silane compounds. 7. The dry etching method according to claim 1, wherein the etching gas supplies nitrogen-based chemical species into plasma under discharge dissociation conditions. 8. A just etching step of etching the aluminum-free compound semiconductor layer substantially by the thickness of the aluminum-containing compound semiconductor layer by using the etching gas according to claim 1 or 7, and fluorine-based plasma in plasma. An over-etching step of changing the composition ratio of the etching gas so as to increase the generation ratio of the chemical species relative to that in the just etching step, and etching the remaining part of the compound semiconductor layer not containing aluminum. A dry etching method characterized by the above.