JP3282243B2 - Dry etching method - Google Patents

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, and more particularly to a HEMT.
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-FETs (metal
semiconductor field effect
MMIC (monolithic microwave) in which ttransistor is integrated on a single substrate
IC) has features such as high-speed high-frequency response, low noise, and low power consumption, and has recently been used as a device for mobile communication and satellite communication.

In 1980, the above-mentioned GaAsMES-F
HEMT from research aimed at further speeding up ET
(High electron mobility t
ransistor) has been developed. This is Ga
This is a device utilizing the fact that a two-dimensional electron gas at a heterojunction interface of an As compound semiconductor can move at high speed without being scattered by impurities. Research for realizing high integration of this HEMT is also being continued, and the demand for a dry etching technique for processing the HEMT is also moving toward higher precision and higher selectivity.

[0004] Above all, the step of selectively etching a GaAs / AlGaAs stacked system to form a gate recess is an important technique for determining the threshold voltage of a heterojunction FET such as a HEMT or a hetero MIS structure FET. This is because the impurity concentration and thickness of the lower AlGaAs layer are set in advance so that an FET having an appropriate threshold voltage can be formed by removing only the upper GaAs layer. GaAs on this AlGaAs layer
As a method for selectively etching the s layer, a method using a mixed gas of a CFC (chlorofluorocarbon) gas such as CCl ₂ F ₂ and a rare gas is typical. This is Ga
Is mainly formed of chloride and As forms fluoride and chloride, so that the GaAs layer is removed, but when the underlying AlGaAs layer is exposed, AlF having a low vapor pressure is used.
_{This is because x} (aluminum fluoride) is formed on the surface, the etching rate is reduced, and a high selectivity can be obtained.

[0005] For example, Japanese Journal
al of Applied Physics, Vo
l. 20. , No. 11 (1981), p. L847-
850 reports an example of achieving a selectivity of 200 using a CCl ₂ F ₂ / He mixed gas.

[0006]

However, the above-mentioned CFC gas such as CCl ₂ F ₂ is a kind of a compound commonly called so-called chlorofluorocarbon gas, and is known to cause the ozone layer depletion on the earth. Therefore, production and use will be prohibited in the near future. Therefore, in the field of dry etching, it is urgently necessary to develop an alternative gas and a technique for using the same.

Further, the above-mentioned CFC gas tends to generate a large amount of fluorocarbon-based polymer in the etching reaction system. This polymer contributes to anisotropic processing because it deposits on the pattern side wall and exhibits a side wall protection effect.
On the other hand, instability of the etching rate and particle
It is easy to cause deterioration of the level. Therefore, the present invention provides a compound semiconductor layer containing no Al (hereinafter, referred to as a non-Al-containing compound semiconductor layer) on a compound semiconductor layer containing 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 which can be performed under clean conditions.

[0008]

SUMMARY OF THE INVENTION The dry etching method of the present invention is proposed to achieve the above-mentioned object, and comprises a non-A layer formed on an Al-containing compound semiconductor layer.
The l-containing compound semiconductor layer is selectively etched by using an etching gas containing a thiocarbonyl compound having a fluorine atom and a thiocarbonyl group in a molecule.

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

[0010] The present invention also relates to a sedimentary chlorine compound or a similar sedimentary bromine compound capable of releasing free sulfur under discharge dissociation conditions instead of the non-sedimentary chlorine compound or the non-sedimentable bromine compound. At least one of these is used.

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

According to the present invention, instead of the non-depositable fluorine-based compound, a sedimentary fluorine-based compound capable of releasing free sulfur under discharge dissociation conditions is used.

The present invention also provides that the etching gas is H
_At least one selected from the group consisting of ₂ , H ₂ S and a silane compound
It contains various kinds of halogen / radical consuming compounds.

According to the present invention, the etching gas supplies nitrogen-based species into the plasma under discharge dissociation conditions.

The present invention further provides 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 by using any of the above-mentioned etching gases, and the generation of fluorine-based chemical species in plasma. Changing the component mixture ratio of the etching gas so as to increase the ratio relatively than in the just etching step,
An over-etching step of etching the remaining portion of the non-Al-containing compound semiconductor layer.

[0016]

When the carbon-based polymer constituting the side wall protective film required for anisotropic processing is not to be supplied from the gas phase when establishing a CFC removal process, the supply source is not required to be a resist mask. Not get. However, if ions having high incident energy are sputtered to supply a large amount of decomposition products of the resist mask, the selectivity of the resist is inevitably reduced, 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 use S deposition together with
Reduces the amount of carbon-based polymer deposited,
An advantage of the present invention is that excellent anisotropic processing can be realized even under conditions where the energy is reduced.

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

The thiocarbonyl group further increases its polarity by being incorporated into the carbon-based polymer, and has the function of increasing the electrostatic attraction of the carbon-based polymer to the negatively charged wafer being etched. I do. It is considered that this also improves the etching resistance of the carbon-based polymer.

As described above, by enhancing the film quality of the carbon-based polymer itself, incident ion energy required for anisotropic processing can be reduced, and resist selectivity can be improved. This makes it possible to form an etching mask that can withstand practical use even from a relatively thin photoresist coating film, and to prevent the occurrence of a difference in processing dimension conversion, while achieving high resolution in photolithography. It also produces secondary effects. In addition, a reduction in incident ion energy naturally leads to an improvement in base selectivity. Furthermore, the amount of carbon-based polymer deposited necessary for achieving high anisotropy and high selectivity can be reduced, so that particle contamination can be reduced as compared with the prior art.

Further, S (sulfur) is released from the thiocarbonyl compound into the plasma under discharge dissociation conditions. This S accumulates on the surface of the substrate (wafer) if its temperature is controlled to approximately room temperature or lower, depending on conditions. Therefore, the incident ion energy can be further reduced, and the damage can be reduced. Also, the amount of carbon-based polymer deposited can be relatively reduced,
Particle contamination can be more effectively reduced. In addition, S easily sublimates when the wafer is heated to about 90 ° C. or higher, and thus there is no possibility that S itself becomes 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 main etching species of the non-Al-containing compound semiconductor layer. However, non-A
Since the underlayer 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, fluorine-based chemical species such as F ^* must be present in the etching reaction system. 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. Thereby, in principle, selective anisotropic processing can be realized with an etching gas having a single composition.

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

The chlorine-based compound and the bromine-based compound are non-sedimentary compounds that do not generate sedimentary substances under discharge dissociation conditions, or are sedimentary compounds that release free S (sulfur). It may be. In the latter case, the deposition amount of the carbon-based polymer can be further reduced by an amount that can be expected to deposit S, so that high selectivity and low contamination are further improved.

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

In this case, the fluorine-based compound may be a non-depositable compound or a desorbable compound capable of releasing S.

The present invention is based on the above concept, but proposes another method for further reducing 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 ^* generated from these halogen / radical consuming compounds capture part of the halogen / radical and remove them in the form of hydrogen halide or silicon halide. Therefore, the apparent S / X of the etching reaction system
[The ratio of the number of S atoms to the number of X (halogen) atoms] increases,
Is promoted. In this case, F ^{*, which} is the basis for achieving the selectivity to the Al-containing compound semiconductor layer, also decreases,
This is covered by the increase in the amount of S deposited.

The second method is to use an etching gas that can release nitrogen (N) -based chemical species. The source of the N-based chemical species may be the above-mentioned non-depositable 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 thiocarbonyl compound or the sedimentary halogen compound with an N-based species. Various compounds can be considered as the sulfur nitride-based compound,
A typical example is polymeric polythiazyl (SN).
_x . Since (SN) _x has a repetitive covalent bond of SNSN-... And exhibits higher etching resistance than single S, the surface protection effect is improved by using this. .

Moreover, the sulfur nitride-based compound sublimates or decomposes when the wafer is heated to about 130 ° C. or higher. Alternatively, it can be easily burned and removed even by O ₂ plasma treatment, and there is no possibility of becoming a particle contamination source at all.

In the third method, the etching is divided into two steps, ie, a just etching step and an over-etching step.
This is a method of increasing the generation ratio of fluorine-based chemical species in plasma in the over-etching step. In the over-etching 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 region to be etched. Therefore, if the generation amount of the fluorine-based chemical species is increased at this stage, the generation of AlF _x on the exposed surface is promoted, and the selectivity is improved. This generation ratio can be changed, for example, by increasing the flow ratio of the compound capable of releasing the fluorine-based species compared to the just etching step.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

[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 in which etching is performed using the above. This process is illustrated in FIG.
This will be described with reference to (a), (c), and (d).

The wafer used as an etching sample in the present embodiment is, as shown in FIG.
A thickness of about 500 nm formed by epitaxial growth on a semi-insulating GaAs substrate 1 and functioning as a buffer layer
Epi-GaAs layer 2, AlGaAs having a thickness of about 2 nm
Layer 3, about 30 n thick doped with n-type impurities such as Si
An n ⁺ -AlGaAs layer 4 having a thickness of m, an n ⁺ -GaAs layer 5 having a thickness of about 100 nm containing an n-type impurity, 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 by an electron beam lithography method, and the opening 6a has an opening diameter of about 300.
nm.

The wafer was set on a wafer mounting electrode of a magnetic field microwave plasma etching apparatus of RF bias application type, and as an example, the above n ⁺ -GaAs was formed 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 replaces As in n ⁺ -GaAs layer 5 with AsF ₃ ,
The Ga is extracted in the form of AsF ₅ or the like, and Ga is extracted in the form of GaF ₃ or the like. However, since GaF ₃ has a low vapor pressure in a normal etching reaction system, Ar ⁺ , C ⁺ , C
The incident ion energy of S ⁺ , CSF ^{+ and the} like is slightly increased, and is removed by ion sputtering.

[0037] At the same time, the resist · CF _x derived from the decomposition products of the mask 6 is produced, further being rigidly carbonaceous polymer incorporated into the thiocarbonyl group or C-S bond such as its structure Generated. Furthermore, and also it generates free S from CSF _2. These carbon-based polymers and S are
A side wall protective film 7 as shown in FIG. 1C was formed.
As a result, a recess 5a having a vertical wall was formed. Although the side wall protective film 7 in the figure 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 is not something that makes you.

Further, when the underlying n ⁺ -AlGaAs layer 4 was exposed, AlF _x was formed on the surface thereof, and played a role of greatly reducing the etching rate.

The sidewall protective film 7 was easily removed as shown in FIG. 1D by performing an O ₂ plasma treatment after completion of the etching.

The subsequent formation of the gate electrode may be performed according to a conventionally known method. This process will be described with reference to FIG. That is, an Al layer having a thickness of about 200 nm was formed as an example by performing electron beam evaporation of Al on the wafer. This deposition is performed in a step 5a inside the recess 5a having a fine opening diameter.
2 (a), 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, as shown in FIG. Layers 8b were each formed.

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

Embodiment 2 In this embodiment, the same n ⁺ -GaAs layer is formed by using CSF ₂ / C
This is an example in which etching is performed using a 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
Ga was extracted in the form of l _{3 and the} like, and Ga was mainly extracted in the form of GaCl _{3 and the} like. In this embodiment, Ga can be removed in the form of chloride having a high vapor pressure, so that high-speed etching proceeds despite the RF bias power being reduced by half compared to the first embodiment.

Further, CCl _x was generated from the decomposition product of the resist mask 6, and a thiocarbonyl group and a CS bond were introduced into the CCl _x , thereby forming a strong side wall protective film 7. At this time, the supply amount of the decomposition product is determined by the RF bias
Less than Example 1 due to reduced power, but with less CCl _x
Since the depositing property of CF was superior to that of CF _x , the side wall protection effect did not decrease at all.

According to the present embodiment, the recess 5a having a good anisotropic shape could be formed. In this embodiment, the selectivity with respect to the n ⁺ -AlGaAs layer 4 is about 5
It was 0.

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

Embodiment 3 In this embodiment, the same n ⁺ -GaAs layer is formed by using CSF ₂ / S
_This is an example in which etching is performed using a ₂ Cl ₂ mixed gas. An example of the 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
Also contributed to the formation of the sidewall protective film 7, thereby increasing the contribution of S. Therefore, excellent anisotropic processing could be performed despite the RF bias power being slightly lower than that of the second embodiment. In addition, the relative amount of carbon-based polymer deposited could be further reduced, and low pollution could be thoroughly achieved.

Embodiment 4 In this embodiment, the same n ⁺ -GaAs layer is
_This is an example in which etching is performed using a ₂ (thiocarbonyl chloride) / SF ₆ mixed gas. An example of the 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. In this etching process, Cl generated from CSCl ₂ is used.
^* And F ^* generated from SF ₆ became the main etching species, and the etching proceeded. The mechanism for strengthening the carbon-based polymer is almost as described above in Example 2.

Embodiment 5 In this embodiment, the same n ⁺ -GaAs layer is formed by using CSCl ₂ /
Etching was performed using an S ₂ F ₂ mixed gas. An example of the 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 when halogen atoms are exchanged between the thiocarbonyl compound and the sulfur halide. I do. Therefore, except for a slight difference in discharge dissociation efficiency, etc., the etching mechanism is the same as that of the third embodiment.
Is almost the same as

Embodiment 6 In this embodiment, the same n ⁺ -GaAs layer is formed by forming CSCl ₂ /
Etching was performed using an SF ₆ / H ₂ S mixed gas. An example of the 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 gas composition described above corresponds to the gas composition of Example 4 with H ₂ S added. In this etching process, CSC
Some of F ^* and Cl ^* generated from l ₂ and SF ₆ are H ₂ S
Consumed by H ^* produced from H ₂ S
Is released from the S, so that S in the etching reaction system is released.
The / X ratio increased, and highly anisotropic processing could be performed under low bias conditions.

Embodiment 7 In this embodiment, the same n ⁺ -GaAs layer is formed by using CSCl ₂ /
Etching was performed using NF ₃ mixed gas. An example of the 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 not only a source of F ^* but also a source of N atoms. In this embodiment, this N atom and CSCl ₂
Reacts with the S atoms released from the GaN to form (SN) _x and other sulfur nitride-based products, and partially constitute the sidewall 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 O ₂ plasma treatment after the etching.

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

First, on the wafer shown in FIG. 1A, as an example, the n ⁺ -GaAs layer 5 was just etched under the following conditions. CSF ₂ flow rate 20 SCCM (flow rate ratio 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 the just etching is shown in FIG.
In some of the recesses 5a, a small amount of the remaining portion 5b of the n ⁺ -GaAs layer 5 remained at the bottom.

Next, as an example, the etching conditions were changed as follows, and over-etching was performed to remove the remaining 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 step, the flow rate ratio of CSF ₂ is increased as compared with the just etching step. On the exposed surface of the n ⁺ -AlGaAs layer 4, Al
The generation of F _x was promoted. Also, the RF bias power is reduced by half compared to the just etching process. As a result, as shown in FIG. 1C, even after the removal of the remaining portion 5b, no adverse effect was exerted on the underlying n ⁺ -AlGaAs layer 4.

In this embodiment, the selectivity with respect to the n ⁺ -AlGaAs layer 4 was improved to 100 or more.

Although the present invention has been described based on the eight embodiments, the present invention is not limited to these embodiments. First, in each of the above-described embodiments, a GaAs / AlGaAs stacked system is exemplified as a stacked system of compound semiconductor layers. However, the present invention can be applied to other conventionally known stacked systems of compound semiconductors 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 / three-element stacked system such as aN / AlGaN and InAs / AlInAs, or a three-element / four-element stacked system.

Further, the present invention is not limited to the above-described HEMT manufacturing as long as the process requires selective etching of a non-Al-containing / Al-containing compound semiconductor laminated system. It can also be applied to processing of

In each of the above examples, CSF ₂ and CSCl ₂ were used as thiocarbonyl compounds. These compounds have a structure in which two F atoms or Cl atoms are bonded to a 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 a Br atom. In this case, it can be expected that high resist selectivity is achieved by the generation of CBr _x .

As the non-depositable chlorine compound, HCl, BCl ₃ or the like can be used in addition to the above-mentioned Cl ₂ . As the non-depositable bromine-based compound, the above-mentioned Example 2
In addition to HBr mentioned above, Br ₂ , BBr _{3 and the} like can be used. As the non-depositable 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 source of nitrogenous species.

Although H ₂ S has been exemplified as the halogen / radical consuming compound, basically similar results can be obtained by using H ₂ or a silane compound. The etching gas used in the present invention includes a sputtering effect, a 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 configuration of the sample wafer, the etching apparatus to be used, the etching conditions, and the like can be appropriately changed.

[0063]

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

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

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating an example of a process in which the present invention is applied to a gate recess processing of a HEMT in the order of the steps, and FIG. 1 (a) shows a resist mask formed on an n ⁺ -GaAs layer; State, (b) is n ⁺ -GaAs
The layer is etched with the formation of the sidewall protective film, a recess is formed, and the remaining portion of the n ⁺ -GaAs layer is generated, (c) is a state in which the n ⁺ -GaAs layer is entirely etched, or With the remaining parts removed,
(D) shows a state in which the sidewall protective film has been removed.

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

[Explanation of symbols]

DESCRIPTION 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 ... Remaining portion (of n ⁺ -GaAs layer) 6... Resist mask 6a... Opening 7... Sidewall protective film 8a... Upper Al layer 8b... Lower Al layer (gate electrode)

Claims (8)

(57) [Claims] An aluminum-free compound semiconductor layer laminated on an aluminum-containing compound semiconductor layer is selected using an etching gas containing a thiocarbonyl compound having a fluorine atom and a thiocarbonyl group in a molecule. A dry etching method characterized by selectively etching. 2. The dry etching method according to claim 1, wherein the etching gas contains at least one of a non-deposited chlorine-based compound and a non-deposited bromine-based compound. 3. An etching gas comprising at least one of a sedimentary chlorine-based compound capable of releasing free sulfur or a sedimentary bromine-based compound 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, comprises 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 method of discharging a compound semiconductor layer containing no aluminum, which is laminated on a compound semiconductor layer containing aluminum, 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 selectively etching using an etching gas containing a depositing fluorine-based compound capable of releasing free sulfur under dissociation conditions. 6. An etching gas comprising H ₂ , H ₂ S,
The dry etching method according to any one of claims 1 to 5, 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 to the 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-free compound semiconductor layer using the etching gas according to claim 1; An over-etching step of changing the component mixture ratio of the etching gas so as to increase the generation ratio of the chemical species relatively than in the just etching step, and etching the remaining part of the compound semiconductor layer not containing aluminum. A dry etching method characterized in that: