JP3186264B2 - 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 etched using an etching gas containing a compound having a fluorine atom in addition to at least one functional group selected from a carbonyl group, a thionyl group, a sulfuryl group, a nitrosyl group, and a nitrile group in a molecule. Is what you do.

According to the present invention, the etching gas further contains at least one of a chlorine compound and a bromine compound.

[0010] The present invention also provides another etching gas composition comprising, in addition to at least one functional group selected from a carbonyl group, a thionyl group, a sulfuryl group, a nitrosyl group and a nitrile group, a chlorine atom or a bromine atom in a molecule. And a mixed system containing a compound having at least one of the above and a fluorine-based compound.

The present invention also 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, and an over-etching step of etching the remaining portion of the non-Al-containing compound semiconductor layer. In the latter over-etching step, the composition ratio of the etching gas is changed so that the generation ratio of fluorine-based chemical species in the plasma is increased in the latter over-etching step.

The present invention further provides that the etching gas produces free sulfur in the plasma under discharge dissociation conditions.

[0013]

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 that by enhancing the film quality of the carbon-based polymer itself, a sufficiently high side wall protection effect or surface protection effect can be exhibited even if the deposition amount is reduced, resulting in high selectivity and low selectivity. The point is to achieve damage and low pollution.

As a method for enhancing the film quality of the carbon-based polymer itself, in the present invention, a carbonyl group (> C =
O), thionyl group (> S = O), sulfuryl group (> SO
₂ ), nitrosyl group (-N = O), nitrile group (-NO
₂ ) A compound having any functional group is used. The above functional group can have a structure in which a C atom, an S atom, or an N atom has a positive charge and an O atom has a negative charge, and has a high polymerization promoting activity. Therefore, when such a functional group or an atomic group derived therefrom is present in the plasma, the degree of polymerization of the carbon-based polymer increases, and the resistance to ion incidence and radical attack can be increased. Further, when the above-described functional group is introduced into the carbon-based polymer, the chemical and physical stability is higher than that of a conventional carbon-based polymer having a repeating structure of -CX _2- (X represents a halogen atom). Increases have also been clarified by recent studies. This is because, when the bond energy between two atoms is compared, a C—O bond (1077 k
J / mol), C—S bond (713 kJ / mol), C
It can be intuitively understood that the -N bond (770 kJ / mol) is larger than the CC bond (607 kJ / mol).

Further, these functional groups are incorporated into the carbon-based polymer to increase the polarity thereof, thereby increasing the electrostatic attraction of the carbon-based polymer to the negatively charged wafer being etched. I do. This also improves the surface protection effect 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.

The halogen atom contained in the compound molecule having the above functional group is any one of fluorine (F), chlorine (Cl) and bromine (Br). These halogen atoms contribute as main etching species of the non-Al-containing compound semiconductor layer. However, since the underlayer selectivity in the etching of the stacked system of the non-Al-containing / Al-containing compound semiconductor layer is based on the generation of AlF _x in principle, fluorine-based chemical species such as F ^* are used in the etching reaction system. It needs to be present.

In the present invention, a compound having at least one of the above functional groups and an F atom in a 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, if only fluorine-based chemical species are present in the etching reaction system, a reaction product having a high vapor pressure cannot be obtained depending on the constituent elements of the compound semiconductor layer, and the etching rate is significantly reduced. There is a fear. Therefore, the present invention further proposes adding at least one of a Cl-based compound and a Br-based compound to the compound having the above functional group. 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 present invention also proposes another etching gas composition in which halogen atoms are exchanged between the above-mentioned components. That is, a Cl atom or a Br atom is included in the compound molecule having the above-described functional group, and the F-based compound is added to the Cl atom or the Br atom. According to this gas composition, almost the above-described effects can be expected.

The present invention is based on the above concept, but also proposes a method for further reducing pollution and damage. One of them is to make etching into two stages, a just etching process and an over etching process, and to increase the generation ratio of F type chemical species in plasma in the over etching process. 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 F-based chemical species is increased at this stage, the generation of AlF _x on the exposed surface is promoted.

The most realistic and simple way to increase the generation ratio of F-based chemical species is to use F among the constituents of the etching gas.
An object of the present invention is to increase the flow ratio of the compound capable of releasing a system chemical species as compared with the just etching step.

As another method, it is proposed to use sulfur (S) for protecting the side wall in addition to the carbon-based polymer. S can be deposited by using an etching gas having a composition capable of releasing free S into plasma under discharge dissociation conditions. S can be deposited on the surface of the wafer if the temperature is controlled to approximately room temperature or lower, depending on the conditions. In this case, S may be supplied from any of the above-mentioned F-based compounds, Cl-based compounds, and Br-based compounds at the same time as the halogen-based species, or may be supplied from a separately added sulfur-based compound. Absent. In any case, the amount of carbon-based polymer required to secure anisotropy can be reduced as much as S can be expected to be deposited, so that the incident energy of ions for sputtering the resist mask can be reduced and the resist selectivity can be reduced. Can be improved. In addition, particle contamination can be reduced by reducing the amount of the carbon-based polymer. And S
When the wafer is heated to a temperature of about 90 ° C. or higher, it easily sublimates, and there is no concern that the wafer itself becomes a source of particle contamination.

[0025]

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

[0026] Example 1 This example, the present invention is applied to a gate recess process of HEMT, the n ⁺ -GaAs layer on n ⁺ -AlGaAs layer with COF ₂ (carbonyl fluoride) / Ar mixed gas This is an example of etching by etching. 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 this 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.

This wafer is 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 is formed under the following conditions.
The s layer 5 was etched. COF 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 COF ₂ converts As in n ⁺ -GaAs layer 5 into AsF ₃ , AsF _{5, and the} like. 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, under the above-mentioned conditions, the incident ion energy of Ar ⁺ , C ⁺ , CO ⁺ , COF ^{+ and the} like is slightly increased, and this is removed by ion sputtering. It is.

[0029] At the same time, CF _x is generated from the decomposition products of the resist mask 6, produces a robust carbonaceous polymer further carbonyl group and C-O bond or the like is incorporated in the structure did. Although the amount of this carbon-based polymer is not as large as that of the conventional process, it is deposited on the pattern side wall to form the side wall protective film 7 as shown in FIG. , Contributed to anisotropic processing. As a result, the recess 5a having the vertical wall is formed.
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. At this time, in the portion where 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.

Next, when the above wafer was subjected to O ₂ plasma treatment, as shown in FIG. 1D, the sidewall protective film 7 was removed by burning.

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 vapor deposition is based on the fact that step coverage (step coverage) is degraded inside the recess 5a having a fine opening diameter, and as shown in FIG. An upper Al layer 8a was formed on the surface of the substrate, and a lower Al layer 8b was formed on the bottom of the recess 5a.

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 SOF ₂ / A
Etching was performed using a mixed gas of r. The etching conditions were the same as in Example 1 except that COF ₂ was replaced with SOF ₂ . In the present embodiment, the etching mechanism of the n ⁺ -GaAs layer 5 using F ^* as the main etching species, the side wall protection mechanism, the mechanism for achieving the base selectivity, and the like are almost as described above in the first embodiment. However, in this embodiment, the carbon-based polymer incorporating a thionyl group, a C—S bond, and the like contributes to the formation of the sidewall protective film 7.

Embodiment 3 In this embodiment, the same n ⁺ -GaAs layer is formed by using COF ₂ / C
Etching was performed using l ₂ mixed gas. The following shows an example of the etching conditions. COF 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.

[0035] In this etching process, becomes Cl ^* main etching species generated from F ^* and Cl ₂ generated from COF _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.

Also, CCl _x is generated from the decomposition product of the resist mask 6, and this is added to a carbonyl group or C-
O-bonds were introduced, and a strong sidewall protective film 7 was formed.
The supply amount of degradation products at this time, although less than in Example 1 due to the reduction of RF bias power, since the deposition of CCl _x is better than CF _x, the sidewall protection effect is reduced at all Did not.

According to this embodiment, the recess 5a having a good anisotropic shape can 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 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 4 In this embodiment, the same n ⁺ -GaAs layer is formed by using SOF ₂ / C
Etching was performed using l ₂ mixed gas. The etching conditions were the same as in Example 3 except that COF ₂ was changed to SOF ₂ . In the present embodiment, the etching mechanism of the n ⁺ -GaAs layer 5 using F ^* and Cl ^* as main etching species, the side wall protection mechanism, the mechanism for achieving base selectivity, and the like are almost the same as those described in the third embodiment. . However, in this embodiment, a carbon-based polymer incorporating a thionyl group, a C—S bond, and the like is included as a component of the sidewall protective film 7. In the present embodiment, high-speed anisotropic etching progressed in spite of the fact that the RF bias power was reduced by half compared to the second embodiment using the SOF ₂ / Ar system.

In this embodiment, the selectivity with respect to the n ⁺ -AlGaAs layer 4 was about 50.

Even when HBr was used instead of 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.

Example 5 In this example, the same n ⁺ -GaAs layer was etched using a mixed gas of NO ₂ F (nitrile fluoride) / Cl ₂ . An example of the etching conditions is shown below. NO ₂ F 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.

[0043] In this etching process, it becomes Cl ^* main etching species generated from F ^* and Cl ₂ generated from NO ₂ F, etching reaction proceeded. Further, a CCl _x polymer derived from the decomposition product of the resist mask 6 was formed, and a nitrile group and a C—N bond were introduced into the CCl _x polymer, thereby forming a strong sidewall protective film 7. According to this embodiment,
The recess 5a having a favorable anisotropic shape could be formed.

Embodiment 6 In this embodiment, the same n ⁺ -GaAs layer is formed by using COCl
Etching was performed using a ₂ (carbonyl chloride) / NF ₃ mixed gas. An example of the etching conditions is shown below. COCl 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 20 W (2 MHz) Wafer temperature 20 ° C. In this etching process, Cl generated from COCl ₂ is used.
^* And F ^* generated from NF ₃ became the main etching species, and the etching proceeded. The mechanism for strengthening the carbon-based polymer is almost as described above for Example 3 using the COF ₂ / Cl ₂ system.

Embodiment 7 In this embodiment, the same n ⁺ -GaAs layer is
_This is an example of etching using a ₂ (thionyl chloride) / NF ₃ mixed gas. The etching conditions were the same as in Example 6, except that SOCl ₂ was used instead of COCl ₂ . However, since SOCl ₂ is a liquid substance at room temperature, it was vaporized by He gas bubbling and then introduced into the etching chamber.

In this etching process, Cl ^* generated from SOCl ₂ and F ^* generated from NF ₃ became main etching species, and the etching progressed. The mechanism for strengthening the carbon-based polymer is almost as described above in Example 4 using the SOF ₂ / Cl ₂ system.

Embodiment 8 In this embodiment, the same n ⁺ -GaAs layer is formed by using COBr
Etching was performed using a ₂ (carbonyl bromide) / NF ₃ mixed gas. An example of the etching conditions is as follows. COBr 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 15 W (2 MHz) Wafer temperature 20 ° C. However, since COBr ₂ is a liquid substance at normal temperature, He
After being vaporized by gas bubbling, it was introduced into the etching chamber.

In this etching process, the etching proceeds with Br ^* generated from COBr ₂ and F ^* generated from NF _{3 as the} main etching species, and As is mainly As.
F ₃ , AsBr ₃ and Ga were mainly removed in the form of GaBr ₃ . Further, in this embodiment, CBr _x having a lower vapor pressure than the above-mentioned CCl _x is generated as a carbon-based polymer, and a carbonyl group or a C—O bond is incorporated into this CBr _x to form a strong sidewall protective film 7. Was done. Therefore,
Although the RF bias power is lower than that of the sixth or seventh embodiment, good anisotropic processing was realized. Further, since CBr _x protects the surface of the resist mask 6 by covering it, the resist selectivity was also improved as compared with the embodiment 6 or the embodiment 7.

Embodiment 9 In this embodiment, the same n ⁺ -GaAs layer is formed by SOBr
Etching was performed using a ₂ (thionyl bromide) / NF ₃ mixed gas. The etching conditions in this embodiment are the same as those in Embodiment 8 except that SOBr ₂ is used instead of COBr ₂ .
Since SOBr _{2 is} also a liquid substance at room temperature, it was introduced into the etching chamber after being vaporized by bubbling He gas.

In this embodiment, the etching mechanism of the n ⁺ -GaAs layer 5 using F ^* and Br ^* as main etching species,
The side wall protection mechanism, the mechanism for achieving the base selectivity, and the like are substantially the same as those described in the eighth embodiment. However, in this embodiment, a carbon-based polymer incorporating a thionyl group, a C—S bond, and the like is included as a component of the sidewall protective film 7.

Embodiment 10 In this embodiment, the same n ⁺ -GaAs layer is formed by using NO ₂ Br
Etching was performed using a (nitrile bromide) / NF ₃ mixed gas. The etching conditions of this embodiment are the same as those of the eighth embodiment except that NO ₂ Br is used instead of COBr ₂ . In this embodiment, CB strengthened with a nitrile group or a C—N bond
Since the r _x polymer forms the strong side wall protective film 7, favorable high selective anisotropic processing could be performed under low bias conditions.

Embodiment 11 In this embodiment, the same n ⁺ -GaAs layer was etched by using a mixed gas of NOCl (nitrosyl chloride) / SF ₆ . An example of the etching conditions is shown below. NOCl 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, a CCl _x polymer reinforced by a nitrosyl group or a C—N bond is used to form a strong sidewall protective film 7.
Was formed. The use of SF _6, which can release a large amount of F ^* from one molecule, also improved the underlayer selectivity.

Embodiment 12 In this embodiment, the etching process is divided into two steps,
After just etching the n ⁺ -GaAs layer using a ₂ / NF ₃ mixed gas, over-etching is performed to remove the remaining portion of the n ⁺ -GaAs layer by increasing the flow rate ratio of NF _{3 in} the mixed gas. Was. This process is illustrated in FIG.
Description will be made with reference to (a), (b), and (c).

First, on the wafer shown in FIG. 1A, as an example, the n ⁺ -GaAs layer 5 was just etched under the following conditions. COCl ₂ flow rate 20 SCCM NF ₃ flow rate 20 SCCM (content ratio in etching gas 50%) 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. The state of the wafer at the end of just etching is shown in FIG.
At the bottom of the recess 5a.
The remaining portion 5b of the ⁺ -GaAs layer 5 was left.

Next, as an example, the etching conditions were changed as follows, and over-etching was performed to remove the remaining portion 5b. COCl ₂ flow rate 10 SCCM NF ₃ flow rate 30 SCCM (content ratio in etching gas: 75%) 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. In this over-etching step, since the content ratio of NF ₃ is increased as compared with the just-etching step, the exposed surface of the n ⁺ -AlGaAs layer 4 is exposed. AlF on top
Production of _x was promoted. Also, the RF bias power was 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, n ⁺ -Al
The selectivity with respect to the GaAs layer 4 was improved to 100 or more.

Embodiment 13 This embodiment is an example of a two-stage etching using a mixed gas of SO ₂ Cl ₂ (sulfuryl chloride) / NF _{3. In} the over-etching process, the NF _{3 in} the composition is smaller than that in the just etching process. Increased flow ratio. In both the just etching step and the over etching step, the etching conditions were the same as those in the first embodiment except that SO ₂ Cl ₂ was used instead of COCl _2.
All the same as 2. Since SO ₂ Cl ₂ is a liquid substance at room temperature, it was vaporized by He gas bubbling and then introduced into the etching chamber.

The SO ₂ Cl ₂ is the same as the SO ₂ Cl ₂ described in the seventh embodiment.
Since the number of O atoms in the molecule is one more than that of Cl ₂ , the amount of carbon-based polymer deposited in this example was slightly reduced by the combustion effect of O ^* . However, a strong carbon-based polymer containing a sulfuryl group, a thionyl group as a fragment thereof, a C—S bond, and the like was generated, and the side wall protection effect was not reduced at all. Of course, concerns about particle contamination have been further reduced.

Also in this embodiment, the selectivity to the n ⁺ -AlGaAs layer 4 was 100 or more.

Embodiment 14 This embodiment is an example of two-stage etching using a NOCl / SF ₆ mixed gas. In the over-etching step, the flow rate ratio of SF _{6 in} the composition was increased as compared with the just etching step. An example of the etching conditions in the just etching step is as follows.

NOCl flow rate 20 SCCM SF ₆ flow rate 20 SCCM (content ratio in etching gas 50%) 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.

Next, as an example, the etching conditions were changed as follows, and over-etching was performed to remove the remaining portion 5b. NOCl flow rate 10 SCCM SF ₆ flow rate 30 SCCM (content ratio in etching gas: 75%) 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. In this over-etching step, F ^* per molecule is used ^.
Since the flow rate ratio of SF ₆ , which is originally large, was further increased, the amount of F ^* generated in the etching reaction system was extremely large, and high underlayer selectivity was achieved.

Embodiment 15 This embodiment is an example of two-stage etching using a NOF / Cl ₂ mixed gas. In the over-etching step, the flow ratio of NOF in the composition is increased as compared with the just-etching step. An example of the etching conditions in the just etching step is as follows.

NOF flow rate 20 SCCM (50% content ratio in etching gas) 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.

Next, as an example, the etching conditions were changed as follows, and over-etching was performed to remove the remaining portion 5b. NOF flow rate 30 SCCM (content ratio in etching gas 75%) Cl ₂ flow rate 10 SCCM gas pressure 1.3 Pa (= 10 mTo)
rr) Microwave power 850 W (2.45 GH)
z) RF bias power 5 W (2 MHz) Wafer temperature 20 ° C. This embodiment is different from the above-described embodiments 12 to 14 in that chemical species (here, F ^* and nitrosyl) contributing to selectivity are achieved. ), And the compound (here, ClF) that supplies the main etching species.
₂ ) The flow rate is controlled independently. That is, if F ^{* is} to be increased during over-etching, the nitrosyl group will also increase, while the relative content of the main etching species will decrease. Therefore, even under the condition that the RF bias power at the time of over-etching was further reduced as compared with Example 14, good selective anisotropic processing could be performed.

Embodiment 16 In this embodiment, the same n ⁺ -GaAs layer is formed by using COF ₂ / S
Etching was performed by a one-step process using a ₂ Cl ₂ mixed gas. An example of the etching conditions is as follows. COF 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 the carbon-based polymer reinforced by the introduction of a carbonyl group or the like, S generated by dissociation from S ₂ Cl ₂ is also a sidewall protective film. 7 components. Therefore, as compared with Example 3 using the COF ₂ / Cl ₂ system, good anisotropic etching progressed even under the condition that the RF bias power was slightly lowered, and the selectivity to the resist mask 6 was improved. In addition, since the amount of carbon-based polymer produced could be relatively reduced, particle contamination was effectively suppressed. S was easily removed by sublimation or burned off when O ₂ plasma treatment was performed to remove the sidewall protective film 7, and did not remain on the wafer at all.

Embodiment 17 In this embodiment, the same n ⁺ -GaAs layer is formed by using SOF ₂ / S
Etching was performed using a ₂ Cl ₂ mixed gas. The etching conditions in this example are the same as those in Example 16 except that SOF ₂ was used instead of COF ₂ . Although the etching reaction mechanism and the mechanism for achieving the underlayer selectivity are almost the same as those described in Embodiment 16, in this embodiment, a thionyl group, C—S
S was added to the carbon-based polymer reinforced by the introduction of bonds and the like, and effective sidewall protection was performed.

Embodiment 18 In this embodiment, a mixed gas containing COCl ₂ / S ₂ F ₂ mixed gas was used.
This is an example of step etching. In the over-etching process, the S
It increased the flow ratio of ₂ F _2. The conditions of the just etching step are as follows as an example.

COCl ₂ flow rate 20 SCCM S ₂ F ₂ flow rate 20 SCCM (content ratio in etching gas 50%) 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 just etching step, the sidewall protective film 7 is formed by the reinforced carbon-based polymer and S generated from S ₂ F _2.
Was formed. Therefore, favorable anisotropic etching progressed even under the condition of lower bias compared to the just etching step of Example 12 using the COCl ₂ / NF ₃ system.

Next, the etching conditions were switched as follows as an example, and over-etching was performed to remove the remaining portion 5b. COCl ₂ flow rate 10 SCCM S ₂ F ₂ flow rate 30 SCCM (content ratio in etching gas: 75%) Gas pressure 1.3 Pa (= 10 mTo)
rr) Microwave power 850 W (2.45 GH)
z) RF bias power 5 W (2 MHz) Wafer temperature 20 ° C. In this over-etching step, the content ratio of S ₂ F ₂ is increased as compared with the just-etching step, so that the generation amount of F ^* and S is reduced. This was increased compared to the just etching step, and high selective etching could be performed.

Embodiment 19 In this embodiment, the SOCl ₂ /
Using the S ₂ F ₂ mixed gas, the flow ratio of S ₂ F ₂ in the mixed gas was increased in the over-etching step. The etching conditions of this embodiment are the same as those of the eighteenth embodiment in both the just-etching step and the over-etching step, except that COCl ₂ is replaced with SOCl ₂ .

According to this embodiment, very excellent selective anisotropic etching could be performed.

Although the present invention has been described based on the nineteenth 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, GaN
/ Two-element system such as AlGaN, InAs / AlInAs /
The present invention can be applied to etching of a three-element stacked system, 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 stacked system of non-Al-containing / Al-containing compound semiconductors. It can also be applied to processing of

In the present invention, the following compounds can be used in addition to the various compounds described in each Example. First, compounds having a carbonyl group and a halogen atom in the molecule include the above-mentioned COF ₂ , COCl ₂ , COBr ₂
COClF (carbonyl chloride fluoride), COBr
F (carbonyl fluoride fluoride), COIF (carbonyl fluoride fluoride) and the like can be used. Further, the number of carbonyl groups in the molecule is not limited to one, and for example, C ₂ O ₂ F ₂ (oxalyl fluoride), C ₂ O ₂ Cl ₂ (oxalyl chloride), C ₂ O ₂ Br ₂ (oxalyl bromide) ), Etc., compounds having two carbonyl groups can also be used. In this case, it can be expected that reinforcement of the carbon-based polymer is promoted.

Examples of the compound having a thionyl group and a halogen atom in the molecule include the aforementioned SOF ₂ , SOCl ₂ , S
In addition to OBr ₂ , SOF ₄ (thionyl tetrafluoride), SOC
lBr (thionyl chloride bromide) or the like can be used. The compound having a sulfuryl group and a halogen atom in the molecule, other aforementioned SO ₂ Cl _2, SO ₂ ClF
(Sulfuryl chloride), SO ₂ BrF (sulfuryl bromide) and the like can be used.

Compounds having a nitrosyl group and a halogen atom in the molecule include, in addition to the above-mentioned NOF and NOCl,
NOCl ₂ (nitrosyl dichloride), NOCl ₃ (nitrosyl trichloride), NOBr (nitrosyl bromide), NOBr
₂ (nitrosyl dibromide), NOBr ₃ (nitrosyl tribromide) and the like can be used. Further, as the compound having a nitrile group and a halogen atom in the molecule, NO ₂ Cl (nitrile chloride) can be used in addition to the above-mentioned NO ₂ F and NO ₂ Br.

As the chlorine-based compound, the above-mentioned Cl ₂ , S
Other _{2 Cl 2, HCl, BCl 3} , and S ₃ Cl _2,
Other sulfur chlorides such as SCl ₂ can be used. Among them, sulfur chloride also serves as a source of S. As the bromine compound, in addition to the above-mentioned HBr, Br ₂ , BBr
₃ , and sulfur bromide such as S ₃ Br ₂ , S ₂ Br ₂ , SBr _{2 and the} like can be used. Of these, sulfur bromide also serves as a source of S.

As the fluorine-based compound, NF ₃ ,
In addition to SF ₆ and S ₂ F ₂ , ClF ₃ and SF ₂ and SF
_4, can be used S ₂ F other sulfur fluoride such as _10. Of these, sulfur fluoride also serves as a supply source of S. As the S supply source, H ₂ S can be used in addition to compounds capable of simultaneously supplying halogen-based chemical species such as sulfur fluoride, sulfur chloride, and sulfur bromide described above.

The etching gas used in the present invention includes:
A rare gas such as Ar or He may be appropriately added in the sense of expecting a sputtering effect, a dilution effect, a cooling effect, and the like. In addition, it goes without saying that the configuration of the sample wafer, the etching conditions, the etching apparatus to be used, the combination of the compound having various functional groups and the halogen compound, and the like can be appropriately changed.

[0080]

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 various polar functional groups, it is possible to enhance the film quality of the carbon-based polymer and achieve high anisotropy and high selectivity even if the deposition amount is reduced.

Therefore, the present invention is extremely effective in, for example, manufacturing a semiconductor device using a compound semiconductor based on a fine design rule. Make a significant contribution. Of course, the present invention is excellent in de-CFC
Needless to say, it provides a countermeasure.

[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 AlF _x layer is selectively etched. 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)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-87026 (JP, A) JP-A-61-256638 (JP, A) JP-A-2-12817 (JP, A) JP-A-2- 256235 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/3065 C23F 4/00 H01L 21/338

Claims (5)

(57) [Claims] A compound semiconductor layer containing no aluminum, which is laminated on a compound semiconductor layer containing aluminum, is formed of at least one compound selected from a carbonyl group, a thionyl group, a sulfuryl group, a nitrosyl group, and a nitrile group in a molecule. A dry etching method characterized by selectively etching using an etching gas containing a compound having a fluorine atom in addition to a functional group. 2. The dry etching method according to claim 1, wherein said etching gas contains at least one of a chlorine compound and a bromine compound. 3. A compound semiconductor layer containing no aluminum, which is laminated on a compound semiconductor layer containing aluminum, comprising at least one compound selected from a carbonyl group, a thionyl group, a sulfuryl group, a nitrosyl group, and a nitrile group in a molecule. A dry etching method characterized by selectively etching using an etching gas containing a compound having at least one of a chlorine atom and a bromine atom in addition to a functional group, and a fluorine-based compound. 4. 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 2; An over-etching step of changing the component mixture ratio of the etching gas so that the generation ratio of the chemical species can be relatively increased as compared with the just etching step, and etching the remaining part of the compound semiconductor layer not containing aluminum. A dry etching method comprising: 5. The dry etching method according to claim 1, wherein said etching gas generates free sulfur in plasma under discharge dissociation conditions.