JP3298226B2 - 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 the like.
The present invention relates to a method of performing GaAs / AlGaAs selective etching or the like in a gate recess forming step of an EMT (high electron mobility transistor) without causing 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 is widely 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.

As a method of selectively etching a GaAs layer on this AlGaAs layer, a CF such as CCl ₂ F ₂ is used.
A typical method uses a mixed gas of C (chlorofluorocarbon) gas and a rare gas. This is because Ga mainly forms chloride and As forms fluoride and chloride, whereby the GaAs layer is removed, while the underlying Al
At the time when the GaAs 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.

[0006] 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.

[0007]

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. Production,
The ban on use is imminent. 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 carbon-based polymer in the etching reaction system. This carbon-based polymer contributes to anisotropic processing by depositing on the pattern side wall and exerting the side wall protection effect, but on the other hand, it causes instability of the etching rate and deterioration of the particle level. easy. 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). An object of the present invention is to provide a dry etching method which enables selective etching to be performed under clean conditions without using a CFC gas.

[0009]

The dry etching method of the present invention is proposed to achieve the above-mentioned object, and comprises a compound semiconductor layer containing aluminum, a compound semiconductor layer not containing aluminum, A resist mask is sequentially stacked, and the aluminum-free compound semiconductor layer is patterned using an etching gas containing at least one inorganic oxide selected from carbon oxide, nitrogen oxide, and sulfur oxide and a fluorine-based compound. The etching is performed while forming a sidewall protective film of a carbon-based polymer on the sidewall.

The compounds having high utility as the carbon oxide include CO (carbon monoxide), CO ₂ (carbon dioxide) and C ₃ O ₂ (tricarbon dioxide, boiling point 7 ° C.). Carbon dioxide is also known as a compound called carbon suboxide, which has a larger number of carbon atoms in the molecule than the number of oxygen atoms, and is generated when a silent discharge is performed in carbon monoxide. Pentacarbon dioxide, dodecacarbon nine oxide (melittic anhydride), and the like.

In addition, nitrogen oxides having high practicality include N 2
₂ O (dinitrogen oxide), NO (nitrogen monoxide), N ₂ O
₃ (dinitrogen trioxide), NO ₂ (nitrogen dioxide), NO
₃ (nitrogen trioxide). Other known nitric oxides include N ₂ O ₅ (dinitrogen pentoxide).
And N ₂ O ₆ (dinitrogen hexaoxide), the former having a sublimation point of 3
A solid at 2.4 ° C. (1 atm), the latter being an unstable solid.

Further, as highly practical sulfur oxide
Is SO (sulfur monoxide), SO_Two(Sulfur dioxide)
Can be mentioned. There are several other types of sulfur oxide
Although it is known, near room temperature, complicated phases and
Many exist as mixtures having a composition. for example
If S_TwoO_Three(Sulfur trioxide) becomes S, S by heating
O, SO_TwoIt is a solid that decomposes into SO_Three(Io trioxide
C) is a liquid near room temperature, or α-type with a different melting point,
It is a solid that takes either β-type or γ-type. S_TwoO₇
(Sulfur heptoxide) is a solid with a melting point of 0 ° C and a sublimation point of 10 ° C.
is there. Furthermore, SO _Four(Sulfur tetroxide) is a solid with a melting point of 3 ° C.
Although it is a body, it generates oxygen and decomposes it, producing sulfur dioxide
Generate.

In the present invention, a gas containing at least one of a chlorine compound and a bromine compound is used as the etching gas.

[0014] The present invention also provides an etching process for two.
Stepping and just etching the non-Al-containing compound semiconductor layer substantially by the thickness of the non-Al-containing compound semiconductor layer using any of the above-described etching gases, and then adjusting the generation ratio of the fluorine-based chemical species in the plasma during the just etching The composition ratio of the etching gas is changed so as to be relatively higher than that, and the remaining portion of the non-Al-containing compound semiconductor layer is over-etched.

The present invention further uses a gas which generates free sulfur in plasma under discharge dissociation conditions as the etching gas.

[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, sputtering ions with high incident energy in order to supply a large amount of decomposition products of the resist mask will inevitably reduce the selectivity of the resist and the underlayer, and will cause damage to the underlayer and particles Pollution 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 exerted even if the deposition amount is reduced. The point is to achieve damage and low pollution.

In the present invention, at least one of carbon oxide, nitrogen oxide and sulfur oxide is used as one of the components of the etching gas. These inorganic oxides have multiple bonds between different atoms in the molecule and exist as resonance hybrids of several polarization structures, but certain of these polarization structures have high polymerization promoting activity. Have. As a result, the degree of polymerization of the carbon-based polymer derived from the decomposition product of the organic material layer increases, and a strong sidewall protective film is formed.

Decomposition products of these inorganic oxides include carbonyl groups (> C ＝ O), nitrosyl groups (—N ＝ O), nitrile groups (—NO ₂ ), thionyl groups> S ＯO) and a polar group such as a sulfuryl group (—SO ₂ ) can be introduced. When such a polar group is introduced into a carbon-based polymer, chemical and physical stability may be increased as compared with a conventional carbon-based polymer having a repeating structure of -CX _2- (X represents a halogen atom). Recent studies have revealed this.

The rationale for the reason for this phenomenon is roughly the following two points. One of them is a C—O bond (1077
kJ / mol), C—N bond (770 kJ / mol),
N—O bond (631 kJ / mol), C—S bond (71
This is the fact that the interatomic bond energies of 3 kJ / mol) are all larger than the CC bond (607 kJ / mol).

The other is that the introduction of the above functional group increases the polarity of the carbon-based polymer and increases its electrostatic attraction to the negatively charged wafer being etched. 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 means that a relatively thin photoresist coating film can be used to form an etching mask that can withstand practical use. This can prevent the occurrence of a difference in processing size conversion, while achieving high resolution in photolithography. It produces 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.

By the way, since the underlayer selectivity in the etching of the laminated system of the non-Al-containing / Al-containing compound semiconductor layer is based on the generation of AlF _x in principle, the etching reaction system includes fluorine-based compounds such as F ^*. It is necessary that the species be present. In the present invention, as an etching gas satisfying such requirements, a fluorine-based compound is used as another component in addition to the above-described inorganic oxide.

However, if the fluorine-based chemical species present in the etching reaction system is only a fluorine-based chemical species, 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 possibility that it will decrease. Therefore, the present invention further proposes to add at least one of a Cl-based compound and a Br-based compound to the above-mentioned etching gas. 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 is based on the above concept, but also proposes a method for further increasing the selection, lowering the contamination and reducing the 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, and the selectivity is improved.

The most realistic and simple method for increasing 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 is a sublimable substance, which can be deposited on the surface of a wafer under a high vacuum at which normal dry etching is performed, when the temperature of the wafer is controlled to about 90 ° C. or lower, depending on conditions. it can. In this case, S is the above-mentioned F-based compound, Cl-based compound,
It may be supplied from any of the Br-based compounds simultaneously with the halogen-based chemical species, or may be supplied from a sulfur-based compound added separately.

When a nitrogen-based chemical species is present in the etching reaction system, at least a part of the S reacts with the nitrogen-based chemical species to form various nitrides such as polythiazyl (SN) _x. Sulfur-based compounds may be formed. This sulfur nitride-based compound is a sublimable or thermally decomposable substance, and can be deposited on the surface of the wafer when the temperature of the wafer is controlled to about 130 ° C. or lower.

If the deposition of S or sulfur nitride-based compound can be expected, the amount of carbon-based polymer deposited can be reduced accordingly. For this reason, the incident energy of ions for sputtering the resist mask can be reduced to improve the resist selectivity, and particle contamination can be reduced. Note that S and sulfur nitride-based compounds are
After the etching is completed, the wafers can be easily removed according to a mechanism such as sublimation, decomposition, combustion, or the like by heating the wafers to a temperature equal to or higher than the above-described temperature or performing an oxygen-based plasma treatment, or resist ashing is performed. If it is a process, it may be burned and removed at the time of this ashing. In any case, there is no concern that S or the sulfur nitride-based compound itself may be a source of particle contamination.

[0030]

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

[0031] Example 1 This example, the present invention is applied to a gate recess process of HEMT, the n ⁺ -GaAs layer on n ⁺ -AlGaAs layer was etched using a CO / NF ₃ / Ar mixed gas It is an example. This process is shown in FIGS. 1 (a), (c), (d)
This will be described with reference to FIG.

In this embodiment, the etching sample
The wafer used as shown in FIG.
Epitaxial growth on semi-insulating GaAs substrate 1
About 500 nm thick formed 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
m for n⁺-AlGaAs layer 4, similarly containing n-type impurities
N about 100 nm thick ⁺-GaAs layer 5, in a predetermined shape
Patterned resist mask (PR) 6 is sequentially
It is formed by lamination. Of the resist mask 6
Patterning is performed by exposing and developing by electron beam lithography.
The opening diameter of the opening 6a is about 300
nm.

This wafer was set on a wafer mounting electrode of an RF bias applied magnetic field microwave plasma etching apparatus, and as an example, the above n ⁺ -GaAs was formed under the following conditions.
The s layer 5 was etched. CO flow rate 40 SCCM NF ₃ flow rate 40 SCCM Ar flow rate 90 SCCM Gas pressure 1.5 Pa Microwave power 850 W (2.45 GH)
z) RF bias power 40 W (2 MHz) Wafer mounting electrode temperature 20 ° C. In this etching process, F ^* generated from NF ₃ is n.
^{The As in the +} −GaAs layer 5 is extracted in the form of AsF ₃ , AsF _{5 and the} like, and Ga is extracted in the form of GaF _{3 and the} like. Where G
Since aF ₃ has a low vapor pressure in a normal etching reaction system, the above-mentioned conditions are preferable because ArF is used to promote desorption of GaF _3.
It is intended to take advantage of the ⁺ ion sputtering action.

[0034] 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. However, the side wall protective film 7 in the figure is drawn much thicker than it actually is for the sake of illustration.

As a result, a recess 5a having a vertical wall was formed. 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 side wall 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 SO / NF ₃
Etching was performed using a / Ar mixed gas. The etching conditions were the same as in Example 1 except that CO was replaced with SO. In this embodiment, n in which F ^* is the main etching species
The etching mechanism of the ⁺ -GaAs layer 5, the side wall protection mechanism, the mechanism for achieving the underlayer selectivity, and the like are almost the same as those described in the first embodiment. However, in this embodiment, a thionyl group or a C
The carbon-based polymer incorporating the -S bond or the like is
Will contribute to the formation of

According to the present embodiment, the recess 5a having a good anisotropic shape could be formed.

Embodiment 3 In this embodiment, the same n ⁺ -GaAs layer is formed by using NO / NF ₃
Etching was performed using a / Ar mixed gas. The etching conditions were the same as in Example 1 except that CO was changed to NO. In this embodiment, n in which F ^* is the main etching species
The etching mechanism of the ⁺ -GaAs layer 5, the side wall protection mechanism, the mechanism for achieving the underlayer selectivity, and the like are almost the same as those described in the first embodiment. However, in this embodiment, the carbon-based polymer incorporating a nitrosyl group, a C—N bond, and the like contributes to the formation of the sidewall protective film 7.

According to the present embodiment, the recess 5a having a good anisotropic shape can be formed.

Embodiment 4 In this embodiment, the same n ⁺ -GaAs layer is formed by forming C ₃ O ₂ / N
Etching was performed using an F ₃ / Cl ₂ mixed gas. The following shows an example of the etching conditions. C ₃ O ₂ flow rate 40 SCCM NF ₃ flow rate 30 SCCM Cl ₂ flow rate 50 SCCM Gas pressure 1.5 Pa Microwave power 850 W (2.45 GH)
z) RF bias power 30 W (2 MHz) Wafer mounting electrode temperature 20 ° C.

In this etching process, NF_ThreeGenerate from
F^*And Cl_TwoCl generated from ^*Is the main etching species
Where As is mainly AsF_Three, AsF_Five, AsCl
_ThreeAnd Ga is mainly GaCl_ThreePull in the form of
I got through. In the present embodiment, Ga is converted to chloride having a high vapor pressure.
RF bias and RF bias
Fast etchin despite reduced power
Progress.

Further, CCl _x is generated from the decomposition product of the resist mask 6, and a carbonyl group or C—O bond derived from C ₃ O ₂ is introduced into the CCl _x to form a strong sidewall protective film 7. Been formed. The amount of decomposition products supplied at this time is
Although less than that of Example 1 due to the reduction of the RF bias power, since the deposition property of CCl _x was superior to that of CF _x , the sidewall 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 5 In this embodiment, the same n ⁺ -GaAs layer is formed by using SO ₂ / NF
Etching was performed using a ₃ / Cl ₂ mixed gas. The etching conditions were the same as in Example 4 except that C ₃ O ₂ was replaced with SO 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 fourth embodiment. . However, in this embodiment,
A carbon-based polymer incorporating a thionyl group, a C—S bond, or the like is included as a component of the sidewall protective film 7.

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.

Embodiment 6 In this embodiment, the same n ⁺ -GaAs layer is formed by N ₂ O / NF.
Etching was performed using a ₃ / Cl ₂ mixed gas. The etching conditions were the same as in Example 4 except that C ₃ O ₂ was changed to N ₂ O. 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 fourth embodiment. . However, in this embodiment,
A carbon-based polymer incorporating a nitrosyl group, a C—N bond, or the like is included as a component of the sidewall protective film 7.

[0052]Example 7 In this embodiment, the etching process is divided into two stages and the CO / N
F_Three/ Cl_TwoN using mixed gas⁺-GaAs layer
After the strike etching, the NF _ThreeContent of
Increase the ratio to n⁺-For removing the remainder of the GaAs layer
Over-etching was performed. 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. CO flow rate 40 SCCM NF ₃ flow rate 30 SCCM (content ratio in etching gas 25%) Cl ₂ flow rate 50 SCCM gas pressure 1.5 Pa Microwave power 850 W (2.45 GH)
z) RF bias power 30 W (2 MHz) Wafer mounting electrode 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, the etching conditions were switched as follows, as an example, and over-etching was performed to remove the remaining portion 5b. CO flow rate 40 SCCM NF ₃ flow rate 60 SCCM (content ratio in etching gas 50%) Cl ₂ flow rate 20 SCCM gas pressure 1.5 Pa Microwave power 850 W (2.45 GH)
z) RF bias power 15 W (2 MHz) Wafer mounting electrode temperature 20 ° C. In this over-etching step, the content ratio of NF ₃ is increased as compared with the just-etching step, so that the n ⁺ -AlGaAs layer 4 is formed. AlF on the exposed surface of
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 ⁺ -A
The selectivity with respect to the lGaAs layer 4 was improved to 100 or more.

Embodiment 8 In this embodiment, the same n ⁺ -GaAs layer is formed by forming C ₃ O ₂ / N
Etching was performed by a one-step process using a mixed gas of F ₃ / S ₂ Cl ₂ . An example of the etching conditions is as follows. C ₃ O ₂ flow rate 40 SCCM NF ₃ flow rate 30 SCCM S ₂ Cl ₂ flow rate 50 SCCM Gas pressure 1.5 Pa Microwave power 850 W (2.45 GH)
z) RF bias power 20 W (2 MHz) Wafer mounting electrode temperature 20 ° C.

In this etching process, in addition to the carbon-based polymer reinforced by the introduction of carbonyl groups and the like, S ₂ C
S generated by dissociation from l ₂ was also added to the components of the sidewall protective film 7. Further, a part of S reacted with N-based chemical species derived from NF ₃ to generate a sulfur nitride-based compound mainly composed of polythiazyl (SN) _x . Therefore, CO / NF ₃ / C
Compared with the just etching process of the seventh embodiment using the l 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.

Further, since the amount of carbon-based polymer produced could be relatively reduced, particle contamination was effectively suppressed. S and the sulfur nitride-based compound were easily removed by sublimation or burned off by O ₂ plasma treatment for removing the sidewall protective film 7, and did not remain on the wafer at all.

Embodiment 9 This embodiment is an example of two-step etching using a mixed gas of NO / S ₂ F ₂ / Cl _{2. In} the over-etching step, the S ₂ in the mixed gas is compared with the just-etching step. It increased the flow ratio of F _2. The conditions of the just etching step are as follows as an example.

NO flow rate 40 SCCM S ₂ F ₂ flow rate 30 SCCM (content ratio in etching gas 25%) Cl ₂ flow rate 50 SCCM Gas pressure 1.5 Pa Microwave power 850 W (2.45 GH)
z) RF bias power 20 W (2 MHz) Wafer mounting electrode temperature 20 ° C. In this just etching step, S generated from a reinforced carbon-based polymer, S ₂ F ₂ , and S is NO
The sidewall protective film 7 was formed by a sulfur nitride-based compound or the like generated by reacting with the derived N-based chemical species. Therefore, favorable anisotropic etching progressed even under the condition where the bias was lower than that in Example 6.

Next, the etching conditions were switched as follows, as an example, and over-etching was performed to remove the remaining portion 5b. NO flow rate 40 SCCM S ₂ F ₂ flow rate 50 SCCM (content ratio in etching gas: 42%) Cl ₂ flow rate 30 SCCM gas pressure 1.5 Pa Microwave power 850 W (2.45 GH)
z) RF bias power 10 W (2 MHz) Wafer mounting electrode temperature 20 ° C. In this overetching step, the content ratio of S ₂ F ₂ is increased compared to the just etching step, so that F ^* and S The amount of generation increased compared to the just etching step, and highly selective etching could be performed.

Although the present invention has been described based on the nine 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, InAs / AlInAs, or a three-element / four-element stacked system.

Furthermore, the present invention is not limited to the above-described HEMT gate recess processing as long as the process requires etching of a stacked system of non-Al-containing / Al-containing compound semiconductors. The present invention is also applicable to processing of a semiconductor laser device and the like.

Examples of the fluorine compound include NF ₃ ,
In addition to S ₂ F ₂ , SF ₆ , ClF ₃ , SF ₂ , SF ₄ , S
It can be used ₂ F ₁₀ or the like. The latter three are
Also serves as a source of S. As the chlorine-based compound, the above-mentioned C
l ₂ , S ₂ Cl ₂ , HCl, BCl ₃ , and S ₃
Other sulfur chlorides such as Cl ₂ , SCl ₂ can be used. Of these, sulfur chloride also serves as a source of S.

As the bromine compound, in addition to the above-mentioned HBr, Br ₂ , BBr ₃ , S ₃ BBr ₂ , S ₂ Br
₂ , sulfur bromide such as SBr ₂ can be used. Of these, sulfur bromide 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.

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 inorganic oxide and the various halogen compounds, and the like can be appropriately changed.

[0066]

As is apparent from the above description, in the present invention, a non-A layer represented by a GaAs / AlGaAs stacked system is used.
In the selective anisotropic etching of a laminated system of l-containing / Al-containing compound semiconductors, the film quality of a carbon-based polymer is enhanced by using an etching gas containing any of carbon oxide, nitrogen oxide, and sulfur oxide. High anisotropy and high selectivity can be achieved even when the deposition amount is reduced. If these inorganic oxides are used in combination with a sulfur compound that can release S under discharge dissociation conditions, higher selectivity, lower contamination, lower damage, and the like can be achieved.

Therefore, 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 also very effective in forming an MMIC or the like by highly integrating the semiconductor device. 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 state where the layer is just etched with the formation of the sidewall protective film, (c) is a state where overetching of the n ⁺ -GaAs layer is completed and the recess is completed, and (d) is a state where the sidewall protective film is removed. Represents each state.

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 Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065 H01L 21/338

Claims (4)

(57) [Claims] An aluminum-containing compound semiconductor layer, an aluminum-free compound semiconductor layer, and a patterned resist mask are sequentially laminated. The aluminum-free compound semiconductor layer is formed from carbon oxide, nitrogen oxide, or sulfur oxide. Etching containing at least one selected inorganic oxide and a fluorine compound
A dry etching method for performing etching while forming a sidewall protective film of a carbon-based polymer on a pattern sidewall using a gas. 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. An aluminum laminated on a compound semiconductor layer containing aluminum by using an etching gas containing at least one kind of inorganic oxide selected from carbon oxide, nitrogen oxide and sulfur oxide and a fluorine compound. A just etching step of substantially etching the compound semiconductor layer not containing by the thickness of the layer, and a component of the etching gas such that the generation ratio of fluorine-based chemical species in plasma is relatively increased as compared with the just etching step. An over-etching step of changing a mixing ratio and etching a remaining portion of the compound semiconductor layer not containing aluminum. 4. The dry etching method according to claim 1, wherein said etching gas generates free sulfur in plasma under discharge dissociation conditions.