JPH05226303A - Dry etching method - Google Patents

Abstract

PURPOSE:To increase side wall protecting effect at the time of over-etching without changing discharge condition of gas composition or the like, and improve substratum selectivity and anisotropy, in selective etching of GaAs/ AlGaAs system without using CFC (chlorofluorocarbon) gas. CONSTITUTION:An S(sulfur) cover 13 is arranged on the inner wall surface of a process chamber 4 of a microwave plasma etching equipment having magnetic field, and an alternate multiple magnetic field ring constituted of a plurality of permanent magnets 14 is arranged on the outer periphery side. Multi-cusp magnetic field is formed inside the ring, and the diffusion of ECR plasma P in the wall surface direction is restrained. When the permanent magnet 14 is set at a position E, the contact area between the ECR plasma P and the S cover 13 is reduced, so that S supply amount is decreased. When the permanent magnet 14 is set at a position F, S supply amount is increased. By using S2F2/S2Cl2 mixed gas, and making the above contact area large at the time of over-etching, highly anisotropic processing is enabled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method applied to the manufacture of semiconductor devices, etc.
(High electron mobility transistor) GaAs / AlGaAs selective etching in the gate recess formation process is performed without using chlorofluorocarbon (CFC) gas, and the side wall protection effect is strengthened during the process, and the relative The present invention relates to a method of changing conditions such as radical reduction of radicality by changing the confined state of plasma.

[0002]

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

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

In particular, the step of selectively etching the GaAs / AlGaAs laminated system to form the gate recess is an important technique for determining the threshold voltage of a heterojunction FET such as HEMT or hetero MIS structure FET. This is because the impurity concentration, thickness, etc. of the lower AlGaAs layer are set in advance so that an FET having an appropriate threshold voltage can be constructed by removing only the upper GaAs layer. GaA on this AlGaAs layer
As a selective etching method for the s layer, a method using a mixed gas of CFC gas such as CCl ₂ F ₂ and a rare gas is typical. This is because Ga mainly forms a chloride and As forms a fluoride and a chloride to remove the GaAs layer, while when the underlying AlGaAs layer is exposed, AlF ₃ having a low vapor pressure is formed on the surface. As a result, the etching rate decreases, and a high selection ratio can be obtained.

[0005] For example, Japanese Journal
al of Applied Physics, Vo
l. 20. , No. 11 (1981) p. L847-8
In 50, an example in which a selectivity of 200 is achieved by using a CCl ₂ F ₂ / He mixed gas is reported.

However, the above selective dry etching has the following problems. First, the above CCl
CFC gases such as ₂ F ₂ are one of the compounds commonly called so-called CFC gases, and are well known to be one of the causes of the depletion of the ozone layer of the earth. Therefore, they will be manufactured and used in the near future. It is prohibited to carry. Therefore, also in the field of dry etching, it is urgently necessary to develop an alternative gas and its use technology.

Further, the above-mentioned CFC gas tends to generate a large amount of fluorocarbon polymer in the etching reaction system. This polymer contributes to anisotropic processing because it is deposited on the side wall of the pattern and exhibits a side wall protection effect.
On the other hand, the etching rate becomes unstable and particles
It is easy to cause deterioration of the level. Further, annealing at about 300 ° C. is also necessary to recover irradiation damage due to ions during etching.

As a technique for solving such various problems, the applicant of the present application has previously disclosed in Japanese Patent Application No. 3-308327 that halogenation capable of producing free S (sulfur) under discharge dissociation conditions. GaAs / Al using sulfur as etching gas and S deposition for sidewall protection
A technique for performing selective anisotropic etching of a GaAs laminated system is proposed. In this technique, as the sulfur halide, S ₂ F ₂ , S ₂ Cl ₂ , and S ₂ B having a relatively large S / X ratio [ratio of the number of S atoms in the molecule to the number of halogen (X) atoms] are used.
r ₂ etc. are used. Since the wafer at this time has only to be maintained at a temperature at which S can be held without being sublimated, the above technique does not need to cool the wafer to an extremely low temperature range as in the conventional general low temperature etching. Also deposited S
Can be easily sublimated and removed by heating the wafer to approximately 90 ° C. or higher after etching, and there is no concern that particle contamination will occur.

[0009]

By the way, in the field of dry etching, it has been generally recognized that how to prevent a decrease in anisotropy in the overetching step is always a major issue. Because the material layer to be etched is extremely reduced in the over etching process,
This is because a large excess of radicals causes lateral migration on the wafer surface, removing the sidewall protection film that has already been formed or touching the sidewall of the pattern. Etching of compound semiconductor layers is no exception.

In the case of the S deposition process, this problem can be solved by increasing the apparent S / X ratio of the etching reaction system in the over etching process more than in the just etching process. That is, the radical production amount is relatively decreased and the S deposition amount is relatively increased. For example, the above-mentioned Japanese Patent Application No. 3-30
8327 also proposes a technique of adding H ₂ S to an etching gas in an overetching process. This is because H ^* generated by dissociation from H ₂ S removes excess halogen radicals in the form of hydrogen halide and also supplies S from H ₂ S itself, increasing the S / X ratio of the etching reaction system. It is what makes them. Thus S
The acceleration of the deposition of Pd also leads to reduction of incident ion energy required for anisotropic processing, and as a result, it becomes possible to improve the underlayer selectivity.

However, in order to promote the practical application of the S deposition process, it is important to search for another approach and select the most suitable method from among as many options as possible according to the content of the process. Is considered to be. In this process, it is also necessary to recognize the advantages and disadvantages of the prior art. For example, as mentioned above,
Although the technique of adding H ₂ S or the like to the gas has the simplicity that it can be carried out without modification of the etching apparatus,
There is a concern that the time required for stabilizing the gas flow rate and the discharge state may decrease the throughput.

Therefore, according to the present invention, the selective anisotropic etching of the non-Al-containing compound semiconductor layer on the Al-containing compound semiconductor layer can be carried out on the basis of the S deposition process without causing a decrease in throughput. It is an object to provide an etching method.

[0013]

The present invention is proposed to achieve the above objects. That is, the dry etching method according to the first invention of the present application is a method for selectively etching a non-Al-containing compound semiconductor layer stacked on an Al-containing compound semiconductor layer, and is an axis of an inner wall surface of a processing chamber. An ECR plasma device in which at least a part of the direction is covered with an S-based material layer, and an auxiliary magnetic field forming means is arranged on the outer peripheral portion of the processing chamber so as to face the covered portion of the S-based material layer. use,
An etching gas containing at least a fluorine-based compound is introduced into this ECR plasma device, and etching is performed while changing the contact area between the ECR plasma and the S-based material layer by operating the auxiliary magnetic field forming means. ..

In the dry etching method according to the second invention of the present application, the auxiliary magnetic field forming means are arranged at substantially equal intervals along the circumferential direction of the processing chamber and are alternately arranged along the radial direction of the processing chamber. It is constituted by a plurality of permanent magnets magnetized to have opposite polarities, and the change of the contact area is achieved by moving the auxiliary magnetic field forming means along the axial direction of the processing chamber. ..

In the dry etching method according to the third invention of the present application, the auxiliary magnetic field forming means are arranged at substantially equal intervals along the circumferential direction of the processing chamber and are alternately arranged along the radial direction of the processing chamber. It is constituted by a plurality of coils excited so as to have opposite polarities, and the change in the contact area is achieved by controlling the current applied to the auxiliary magnetic field forming means.

Further, in the dry etching method according to the fourth invention of the present application, at least a part of the inner wall surface of the processing chamber in the axial direction is coated with the S-based material layer, and the coating site of the S-based material layer. The ECR plasma device is provided so as to circulate the outer peripheral portion of the processing chamber facing each other and is excited along the axial direction so as to have the same polarity. Etching that contains at least fluorine compounds in plasma equipment
It is characterized in that etching is performed while introducing a gas and changing the distance between the plurality of coils along the axial direction while changing the density of ECR plasma in the vicinity of the S-based material layer.

[0017]

In the present invention, in the S deposition process, the magnetic field orientation is controlled in order to change the amount of S produced without changing the composition of the etching gas during the process.
Although the control of the magnetic field orientation for the purpose of controlling the incident ion energy and improving the homogeneity of the plasma density has been performed conventionally, the control of the magnetic field orientation in the present invention is provided on the inner wall surface of the processing chamber. The purpose is to change the contact state between the S-based material layer and the ECR plasma.

The first invention of the present application is to control the above-mentioned magnetic field orientation by operating the auxiliary magnetic field forming means. E
CR plasma is plasma that is generated when electrons that are circularly moving in a magnetic field resonately absorb microwave energy that matches the cyclotron angular frequency. Therefore, it goes without saying that the ECR plasma device is provided with a magnetic field forming means for generating plasma. The auxiliary magnetic field forming means is provided separately from the magnetic field forming means and does not directly participate in plasma generation.
Control the state of plasma confinement. In the present invention, a part of the inner wall of the processing chamber in the axial direction is coated with the S-based material layer, and an appropriate auxiliary magnetic field forming means is installed at a portion substantially corresponding to this coating portion and operated. Plasma, which is an aggregate of charged particles, has a property that it is difficult to diffuse in the direction orthogonal to the magnetic flux. Therefore, if the above-mentioned auxiliary magnetic field forming means can form a magnetic flux along a part of the inner wall surface of the chamber, the ECR is generated while the magnetic flux exists.
The contact area between the plasma and the S-based material layer covering the inner wall surface of the chamber is reduced, and the amount of S supplied from this S-based material layer to the etching reaction system is reduced. On the contrary, if the magnetic flux disappears, the contact area increases, so that the S supply amount from the S-based material layer increases. In this way, the S / X ratio of the etching reaction system can be easily changed.

The second invention of the present application more specifically defines the above-mentioned auxiliary magnetic field forming means, and uses a plurality of permanent magnets. These permanent magnets are arranged at substantially equal intervals along the circumferential direction of the processing chamber, and are magnetized so as to have opposite polarities alternately along the radial direction of the processing chamber. Make up the ring. The magnetic field configuration formed by the arrangement of such magnets is known as a multicusp magnetic field, and the diffusion of ECR plasma near the inner wall surface of the processing chamber is restricted in this magnetic field. Therefore, when it is desired to reduce the contact area between the ECR plasma and the S-based material layer on the inner wall surface of the chamber, the alternating multipole magnetic field ring may be placed at a position that substantially circulates the area covered by the S-based material layer. On the contrary, when it is desired to increase the contact area, the alternating multipole magnetic field ring may be moved to a position where it does not overlap with the coating portion.

The third invention of the present application is similar to the second invention.
A multi-cusp magnetic field is used, but a coil is used instead of a permanent magnet to turn the magnetic field on / off.
It can be controlled by F. That is, if it is desired to reduce the contact area between the ECR plasma and the S-based material layer on the inner wall surface of the chamber, the coil may be energized to be excited, and if it is desired to be increased, the energization may be stopped. Therefore, it is not necessary to move the alternating multipole field ring axially of the processing chamber as is the case when using permanent magnets.

In the ECR plasma device, the EC
The technique of forming a multicusp magnetic field on the downstream side of the magnetic field forming means (main coil) used for forming the R plasma and confining the plasma is already known in JP-A-63-244600. Generally, in the ECR plasma apparatus, a strong parallel magnetic field is formed by the main coil along the axial direction of the processing chamber, and diffusion of charged particles in the radial direction is restricted. Moreover, since the energy distribution of the microwaves input to the plasma generator is generally not uniform, this also causes a distribution in the plasma density. Therefore, the non-uniformity of the plasma density in the plasma generation part is difficult to be mitigated even after the ECR plasma is transported to some extent, which causes the non-uniformity of etching. The technique described in the above publication solves this problem and improves the uniformity of ECR plasma.

On the other hand, the present invention mainly focuses on the control of the amount of S produced in the etching reaction system, but based on the same principle as the technique described in the above publication, while the multi-cusp magnetic field exists, The uniformity of ECR plasma can be improved.

In the fourth invention of the present application, instead of changing the confined state of the plasma by using the auxiliary magnetic field forming means as in the above-mentioned three inventions, the magnetic field gradient is changed by using the coil itself for forming the ECR plasma. By letting
The density of the ECR plasma that contacts the S-based material layer on the inner wall surface of the processing chamber is changed. Here, a plurality of the coils are provided and are excited so as to have the same polarity along the axial direction of the processing chamber. The magnetic field formed in the plasma generating part by these coils is a parallel magnetic field, but if the distance between the coils is small, the magnetic field gradient in the vicinity of the inner wall surface of the processing chamber becomes steep, and conversely, if it is large, the magnetic field gradient becomes gentle. When the magnetic field gradient is gentle, diffusion of charged particles is promoted and the uniformity of plasma density can be enhanced. In other words, the plasma density near the inner wall surface of the processing chamber can be increased. This is because the microwave energy distribution has a certain width as described above,
This is because the gentler the magnetic field gradient is, the wider the area in the processing chamber that can satisfy the ECR condition by adapting to the energy fluctuation range.

Therefore, when it is desired to increase the amount of S supplied from the S-based material layer, the distance between the coils should be increased to increase the plasma density near the inner wall surface. vice versa,
When it is desired to reduce the S supply amount, the separation distance may be set small.

[0025]

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

[0026] Example 1 This example the second aspect of the present invention is applied to a gate recess process of HEMT, n ⁺ -AlGaAs layer of n ⁺ -G
Example in which the contact area between the S cover and the ECR plasma was changed by a permanent magnet between the just etching step and the overetching step when the aAs layer was etched using a mixed gas of S ₂ F ₂ / S ₂ Cl ₂ Is.

First, before describing the actual etching process, an example of the structure of the RF bias application type magnetic field microwave plasma etching apparatus used for carrying out the present invention and a method of using the same will be described.
A schematic configuration of the above device is shown in FIG. This device
Magnetron 1 for generating 2.45 GHz microwaves, rectangular waveguide 2 connected to the magnetron 1 via a matching device, a microwave power meter, an isolator, etc. (not shown) and guiding the microwaves, the rectangular waveguide 2 is connected through a microwave introduction window 3 made of a quartz glass plate or the like, and a processing chamber 4 for internally generating ECR plasma P by electric discharge; a wafer 10 installed in the processing chamber 4 The wafer mounting electrode 8 and the processing chamber 4 are circulated to meet the ECR condition of 8.7.
The solenoid coil 7 and the like capable of achieving a magnetic field strength of 5 × 10 ^-2 T (875 Gauss) is a basic constituent element.

A gas supply pipe 5 is opened above the processing chamber 4 so that a gas required for processing is supplied from the direction of arrow A into the chamber. Further, an exhaust hole 6 is opened on the bottom surface side of the processing chamber 4 so that the inside of the chamber is highly vacuum exhausted in the direction of arrow B by a vacuum system (not shown). An RF power source 12 for applying an RF bias is applied to the wafer mounting electrode 8 and a blocking capacitor 11 for shutting off a DC component.
And the like. Further, inside the wafer mounting electrode 8, a cooling pipe 9 for coping with low temperature etching is provided.
Is buried. An appropriate cooling medium such as a chiller (not shown) connected to the outside of the apparatus is supplied to the cooling pipe 9 and circulated in the directions of the arrows C ₁ and C ₂ to bring the wafer temperature during etching to a predetermined temperature. It will be maintained.

In the present embodiment, in addition to the above-mentioned structure, the device has the following two special ideas. The first is a part of the inner wall surface of the processing chamber 4 which is slightly below the orbiting position of the solenoid coil 7 along the axial direction indicated by the line Y-Y, that is, a part of which is downstream from the ECR position. Is covered with an S-based material layer. As a specific example of this S-based material layer, a belt-shaped S cover 13 is used here. However, the S cover 13 does not necessarily have to continuously circulate the inner wall portion of the processing chamber 4, and may have, for example, a configuration in which a block-shaped solid is attached to the inner wall portion. Further, as another S-based material layer, an S layer directly formed on the inner wall surface of the chamber by introducing a gas that generates S under discharge dissociation conditions and performing a preliminary discharge, and a ceramic layer such as alumina or silicon nitride Material obtained by sintering S powder on the surface, material obtained by adding S powder to raw material powder of ceramics, and molding by powder sintering, plasma C
Polythiazyl (SN) _x formed directly by the VD method or the like
Layers and the like can also be used.

The second measure is that auxiliary magnetic field forming means is provided on the outer peripheral portion of the processing chamber 4. The auxiliary magnetic field forming means is composed of a plurality of permanent magnets 14 arranged at substantially equal intervals along the circumferential direction of the processing chamber 4. Each of the permanent magnets 14 is integrally connected to a driving unit (not shown), and can be moved up and down in the arrow D direction between the position E and the position F along the axial direction of the processing chamber 4 (the Y-Y line direction). ing. Here, the position E is a position that overlaps the disposition position of the S cover 13 as shown in FIG. 1A, and the position F is a position that does not overlap as shown in FIG. 1B. Is.

Here, in order to show the arrangement state of the permanent magnets 14 in a more understandable manner, a sectional view taken along the line XX is shown in FIG. FIG. 2A shows that when the permanent magnet 14 is at the position E,
FIG. 2B shows the case at the position F, respectively. In the example shown in FIG. 2A, eight permanent magnets 14
Are arranged at equal intervals along the circumferential direction of the processing chamber 4, and adjacent permanent magnets 14 are opposite to each other in the radial direction of the processing chamber 4. According to such an arrangement, a star-shaped multicusp magnetic field is formed by the magnetic lines of force extending from the N pole of a magnet to the S poles of magnets on both sides, and E
The CR plasma P is confined inside this.

Here, when a multi-cusp magnetic field is formed at the position E, the diffusion of plasma in the direction of the inner wall surface of the processing chamber 4 is suppressed, so that the contact area between the S cover 13 and the ECR plasma P is reduced. Decrease. Therefore, the amount of S supplied to the ECR plasma P is reduced. On the other hand, when the multi-cusp magnetic field is formed at the position F, the diffusion of plasma toward the inner wall surface of the processing chamber 4 at the position E is not hindered at all, so that the S cover 13
And the contact area between ECR plasma P increases. Therefore, the amount of S supplied into the ECR plasma P increases.

The multi-cusp magnetic field also contributes to converging the divergent magnetic field near the wafer 10 formed by the solenoid coil 7 to make the plasma density uniform.

Next, the above-mentioned magnetic field microwave plasma
Actually GaAs / AlGaAs using the etching equipment
Selective etching was performed. This process will be described with reference to FIGS. As shown in FIG. 3, the wafer 10 used as an etching sample in this embodiment is formed by epitaxial growth on a semi-insulating GaAs substrate 21 and has a thickness of about 500 nm that functions as an epi-GaAs layer 22. , Thickness about 2
nm AlGaAs layer 23, an n ⁺ -AlGaAs layer 24 with a thickness of about 30 nm doped with an n-type impurity such as Si,
Similarly, about 100 nm thick n ⁺ -Ga containing n-type impurities
An As layer 25 and a resist mask (PR) 26 patterned into a predetermined shape are sequentially laminated. The patterning of the resist mask 26 is performed by exposure and development processing by an electron beam drawing method, and the opening diameter of the opening 26a is about 300 nm.

This wafer 10 was set on the wafer mounting electrode 8 of the above-mentioned magnetic field microwave plasma etching apparatus, and the ethanol refrigerant was circulated through the cooling pipe 9. Also,
The permanent magnet 14 has a position E (see FIG. 1A). ]] Was set. In this state, as an example, the above n ⁺
-The GaAs layer 25 was just etched. S ₂ F ₂ flow rate 20 SCCM S ₂ Cl ₂ flow rate 20 SCCM Gas pressure 1.3 Pa (10 mTorr) Microwave power 850 W (2.45 GHz) RF bias power 20 W (2 MHz) Wafer temperature −10 ° C. This S ₂ F ₂ / S ₂ The Cl ₂ mixed gas system was previously proposed by the applicant of the present application in Japanese Patent Application No. 3-308327. In this just etching process, S ₂ F
Ga in the n ⁺ -GaAs layer 5 is mainly GaCl ₃ due to F ^* and Cl ^* generated by dissociation from ₂ and S ₂ Cl _2.
, And As was removed in the form of AsF ₃ , AsF ₅ , AsCl _3, etc. This radical reaction is S ⁺ , SF _x
It is assisted by incident ion energy such as ⁺ , Cl _x ⁺ and SCl _x ⁺ . The ions in the ECR plasma P at this time descend along the divergent magnetic field formed by the solenoid coil 7 and, in the vicinity of the wafer 10, the permanent magnet 14 is formed as shown in FIG. The multi-cusp magnetic field prevents diffusion in the radial direction, and the light is incident on the wafer 10 almost perpendicularly to contribute to anisotropic processing.

On the other hand, S ₂ F ₂ and S ₂ Cl ₂ also release S into the ECR plasma P. This S is deposited on the side wall of the pattern where vertical incidence of ions does not occur in principle.
The side wall protective film 27 was formed as shown in (3) to contribute to the achievement of anisotropy. As a result, the recess 25a having the vertical wall
Was formed. The just etching is performed with n ⁺ -Al
The process was terminated when the GaAs layer 24 was exposed and AlF _x (mainly x = 3) was formed on the surface thereof, and the etching rate was significantly reduced. The base selection ratio at this point is about 30
Met. At this time, n ⁺ -GaAs is formed on the wafer 10.
A slight residue 25b of the layer 25 remained.

Therefore, in order to remove the residue 25b,
Position the permanent magnet 14 at position F (see FIG. 1B). ], And overetching was performed under the same conditions as above.
In this over-etching step, the multi-cusp magnetic field near the wafer 10 disappeared, and the S cover 13 and the ECR plasma P were brought into full contact with each other as shown in FIG. 2B. As a result, S is supplied from the S cover 13 into the ECR plasma P, and the apparent S of the etching reaction system is
The / F ratio was increased and the side wall protection effect was strengthened. Further, along with this, the radical property of the etching reaction system was relatively weakened. As a result, as shown in FIG.
The anisotropic shape of the recess 25a was maintained well even after the removal of the. In addition, the etching rate on the vertical incidence plane of ions was also significantly reduced, and the underlying selectivity was improved to 60 or more.

When the wafer 10 is heated to about 90 ° C. after the etching is completed, the side wall protection film 27 is quickly sublimated and removed as shown in FIG. 6, and does not cause any particle contamination on the wafer 10. It was The subsequent steps are the same as the normal HEMT manufacturing steps. That is, as an example, a thickness of about 200 is obtained by electron beam evaporation.
nm Al layer was formed. This vapor deposition makes use of the fact that the step coverage (step coverage) is deteriorated inside the recess 25a having a fine opening diameter, and as shown in FIG. An upper Al layer 28a was formed on the surface, and a lower Al layer 8b to be a gate electrode later was formed on the bottom of the recess 25a.

After that, when the resist mask 6 is lifted off by a conventional method, the upper Al layer 28a is simultaneously removed as shown in FIG. 8 and only the lower Al layer 28b at the bottom of the recess 25a can be left. It was

Example 2 In this example, the third invention of the present application is applied to the gate recess processing of HEMT, and the contact area between the S cover and the ECR plasma is adjusted between the just etching step and the over etching step. This is an example in which it is changed by the auxiliary coil. The magnetic field microwave plasma etching apparatus used in this example is replaced with the permanent magnet 14 used in Example 1,
The auxiliary coil 17 is provided.

FIG. 9 shows a sectional view taken along line XX in this case.
9A shows the case where the auxiliary coil 17 is excited at the position E, and FIG. 9B shows the case where it is not excited. In the example shown in FIG. 9A, eight auxiliary coils 17 are arranged at equal intervals along the circumferential direction of the processing chamber 4. Each auxiliary coil 17 is composed of a magnetic core 15 and a conductive wire 16 wound around the magnetic core 15. Adjacent auxiliary coils 17 are excited to have opposite polarities by making the conducting directions of the conductive wires 16 opposite to each other. ing. The formation of the multicusp magnetic field and the confined state of the ECR plasma P due to the formation of the multicusp magnetic field are almost the same as when the permanent magnet 14 is used.

However, when the auxiliary coil 17 is used,
Since the multicusp magnetic field disappears when the power supply to the conducting wire 16 is stopped, the contact area between the S cover 13 and the ECR plasma P can be maintained even when the auxiliary coil 17 is left at the position E as shown in FIG. 9B. Can be changed.

Using this magnetic field microwave plasma etching apparatus, recess processing was actually performed using a mixed gas of S ₂ F ₂ / S ₂ Cl ₂ . The used wafer 10 is
It is the same as that shown in FIG. First, the auxiliary coil 17
Is excited at position E, and n ⁺ -Ga is applied under the same conditions as in the first embodiment.
The As layer 25 was just etched. In this just etching step, etching proceeded by the same mechanism as that described in Example 1.

Next, over-etching was performed under the same conditions except that the excitation of the auxiliary coil 17 was stopped. In this over-etching step, the contact area between the ECR plasma P and the S cover 13 increased with the disappearance of the multicusp magnetic field, and high selection and high anisotropic processing were realized.

Example 3 In this example, the fifth invention of the present application is applied to the gate recess processing of HEMT, and a selective etching of a GaAs / AlGaAs laminated system is performed by using a mixed gas of S ₂ F ₂ / S ₂ Br _2. This is an example in which the density of the ECR plasma contacting the S cover is changed by changing the magnetic field gradient between the just etching step and the over etching step when performing.

First, an example of the structure of the RF bias application type magnetic field microwave plasma etching apparatus used in this embodiment will be described with reference to FIG. In addition,
Part of the reference numerals in FIG. 10 are common to those in FIG. This device differs from the device of FIG. 10 described above in that the auxiliary magnetic field forming means is not provided, and instead of the single solenoid coil 7, unitized solenoid coils 7a, 7
b is provided, and the S cover 13 is
Within the range surrounded by the coils 7a and 7b, that is, ECR
This is the point formed in the area including the position. The solenoid coils 7a and 7b are connected to driving means (not shown), respectively, so as to extend in the direction of arrow G between the position H and the position I along the axial direction (Y-Y line direction) of the processing chamber 4. It is supposed to be movable. Where position H
Is a position where the solenoid coils 7a and 7b are close to each other as shown in FIG. 10 (a), and a position I is a position separated from each other as shown in FIG. 10 (b). ..

Since the solenoid coils 7a and 7b are excited to have the same polarity along the axial direction of the processing chamber 4, the magnetic fields formed in the plasma generating section by these coils are parallel magnetic fields, but The magnetic field gradient near the inner wall surface of the processing chamber 4 changes depending on the distance between them. That is, as shown in FIG. 10A, when the solenoid coils 7a and 7b are close to each other, the magnetic field gradient near the inner wall surface is high. Therefore, the ECR
The density of plasma P is high near the center of the processing chamber 4 and low near the S cover 13. Therefore, the amount of S supplied from the S cover 13 is small, and S of the etching reaction system
The / X ratio is relatively low.

On the contrary, when the solenoid coils 7a and 7b are separated from each other as shown in FIG. 10 (b), the magnetic field gradient near the inner wall surface is low. Therefore,
The diffusion of the ECR plasma P toward the inner wall surface is promoted, and S
The plasma density near the cover 13 increases. Therefore, the supply amount of S is increased, and S of the etching reaction system is increased.
The / X ratio can be relatively increased.

Using this magnetic field microwave plasma etching apparatus, recess processing was actually carried out using an S ₂ F ₂ / S ₂ Br ₂ mixed gas. The used wafer 10 is
It is the same as that shown in FIG. First, the solenoid coils 7a and 7b are set to the position H as shown in FIG.
Set to. In this state, as an example, the n ⁺ -GaAs layer 25 was just-etched under the following conditions.

S ₂ F ₂ flow rate 20 SCCM S ₂ Br ₂ flow rate 20 SCCM Gas pressure 1.3 Pa (10 mTorr) Microwave power 850 W (2.45 GHz) RF bias power 20 W (2 MHz) Wafer temperature -10 ° C. This mixed gas system is also The applicant of the present application first filed Japanese Patent Application No. 3-308.
It was proposed in the specification of No. 327. The etching mechanism in this step was almost the same as that of Example 1 in which Cl was replaced by Br, and the recess 25a having a similar anisotropic shape was formed. However, here S
Since the density of the ECR plasma P near the cover 13 is low, the supply of S from the S cover 13 hardly occurs.

Then, overetching was performed under the same conditions except that the solenoid coils 7a and 7b were set at the position I as shown in FIG. 10 (b). In this step, since the density of the ECR plasma P near the S cover 13 is increased, the amount of S supplied from the S cover 13 is increased and the formation of the sidewall protective film 27 is promoted. Therefore, highly selective and highly anisotropic etching was realized.

Although the present invention has been described above based on the three embodiments, the present invention is not limited to these embodiments. First, although the GaAs / AlGaAs laminated system is exemplified as the laminated system of the compound semiconductor layers in each of the above-described embodiments, the present invention is not limited to the conventionally known laminated system of compound semiconductor layers as long as Al is contained in the lower layer side. Is also applicable.
For example, GaP / AlGaP, InP / AlInP,
The present invention can also be applied to selective etching of a two-element / three-element laminated system such as GaN / AlGaN or InAs / AlInAs, or a three-element / four-element laminated system.

Further, as the etching gas, S ₂ F ₂ / S is used as a gas system capable of supplying F ^* and depositing S.
_{The 2} Cl ₂ mixed gas system and the S ₂ F ₂ / S ₂ Br ₂ mixed gas system have been exemplified, but in addition to these, various types as proposed by the applicant of the present invention in Japanese Patent Application No. 3-308327. The gas system of can be applied. For example,
S ₂ F ₂ / Cl ₂ system, S ₂ Cl ₂ / ClF ₃ system, S ₂ F
₂ / Cl ₂ / H ₂ S system and the like.

In addition, the number and arrangement of permanent magnets and auxiliary coils forming the auxiliary magnetic field forming means, the structure of the wafer, the type of etching apparatus, the etching conditions and the like can be changed as appropriate.

[0055]

As is apparent from the above description, according to the present invention, the contact area between the S-based material layer provided on a part of the inner wall surface of the processing chamber of the ECR plasma device and the ECR plasma, or the S-based material. The density of the ECR plasma in contact with the layer is changed by the magnetic field configuration, which controls the amount of S produced in the ECR plasma. Therefore, if the deposition of S is applied to an etching process that utilizes sidewall protection, the balance between the radical amount and the S deposition amount can be easily controlled. By this method, if the laminated system of the non-Al-containing / Al-containing compound semiconductor layers typified by the GaAs / AlGaAs laminated system is etched, the anisotropy and selectivity in the overetching step can be greatly improved.

The present invention is extremely effective in manufacturing a semiconductor device using, for example, a compound semiconductor based on a fine design rule, and is highly integrated to form an MMIC or the like. It makes a contribution.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one configuration example of an RF bias application type magnetic field microwave plasma etching apparatus used for carrying out the dry etching method of the present invention, and a usage state thereof, (a) Shows a state in which the permanent magnet is arranged at a position overlapping with the S cover, and (b) shows a state in which it is arranged at a position not overlapping.

2 is a cross-sectional view taken along line XX of the magnetic field microwave plasma etching apparatus of FIG. 1, in which (a) is a permanent magnet disposed at a position overlapping the S cover and a multicusp magnetic field is provided near the S cover. The formed state, (b) shows the state where the multicusp magnetic field is extinguished by arranging them in non-overlapping positions.

FIG. 3 is a schematic cross-sectional view showing a state where a resist mask is formed on an n ⁺ -GaAs layer in a process example in which the present invention is applied to HEMT gate recess processing.

FIG. 4 is a schematic cross-sectional view showing a state where the n ⁺ -GaAs layer of FIG. 3 is just-etched while forming a sidewall protective film to form a recess.

FIG. 5 shows n ⁺ -GaA of FIG. 4 after overetching.
It is a schematic sectional drawing which shows the state in which the residue of the s layer was removed.

6 is a schematic cross-sectional view showing a state in which the side wall protective film of FIG. 5 is removed.

7 is a schematic cross-sectional view showing a state in which an Al layer is deposited on the surface of the resist mask and the bottom surface of the recess in FIG.

FIG. 8 is the resist mask of FIG. 7 and the upper Al on the surface thereof.
FIG. 6 is a schematic cross-sectional view showing a state where the layer is lifted off and a lower Al layer (gate electrode) is left only on the bottom surface of the recess.

FIG. 9 is a cross-sectional view taken along line XX of another configuration example of the RF bias application type magnetic field microwave plasma etching apparatus used for carrying out the dry etching method of the present invention, and FIG. The state where the coil is excited to form a multicusp magnetic field near the S cover, and the state (b) shows the state where the excitation is stopped to extinguish the multicusp magnetic field.

FIG. 10 is a schematic cross-sectional view showing still another configuration example of the RF bias application type magnetic field microwave plasma etching apparatus used for carrying out the dry etching method of the present invention, and its usage state; (a) shows a state where the solenoid coils are arranged close to each other to increase the magnetic flux density in the vicinity of the S cover, and (b) shows a state where the solenoid coils are separated to reduce the magnetic flux density.

[Explanation of symbols]

4 ... Processing chamber 7, 7a, 7b ... Solenoid coil 8 ... Wafer mounting electrode 10 ... Wafer 13 ... S cover 14 ... Permanent magnet 17 ... Auxiliary coil 18 ... .. Equal magnetic field plane P ... ECR plasma 21 ... Semi-insulating GaAs substrate 22 ... epi-GaAs layer 23 ... AlGaAs layer 24 ... n ⁺ -AlGaAs layer 25 ... n ⁺ - GaAs layer 25a ... Recess 25b ... (n ⁺ -GaAs layer) residue 26 ... Resist mask 27 ... Side wall protective film (S) 28a ... Upper Al layer 28b ... Lower Al Layer (gate electrode)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 21/338 29/812

Claims (4)

[Claims] 1. A dry etching method for selectively etching a non-Al-containing compound semiconductor layer laminated on an Al-containing compound semiconductor layer, wherein at least a part of an inner wall surface of the processing chamber in the axial direction is a sulfur-based material layer. And an auxiliary magnetic field forming means is provided on the outer peripheral portion of the processing chamber so as to face the coating portion of the sulfur-based material layer, and an ECR plasma device is used. A dry etching method comprising introducing an etching gas containing a system compound and performing etching while changing a contact area between the ECR plasma and the sulfur-based material layer by operating the auxiliary magnetic field forming means. 2. A plurality of the auxiliary magnetic field forming means are arranged at substantially equal intervals along the circumferential direction of the processing chamber and are magnetized so as to have opposite polarities alternately along the radial direction of the processing chamber. 2. The dry etching method according to claim 1, wherein the contact area is changed by moving the auxiliary magnetic field forming means along the axial direction of the processing chamber. 3. The plurality of auxiliary magnetic field forming means are arranged at substantially equal intervals along the circumferential direction of the processing chamber and are excited so as to have opposite polarities alternately along the radial direction of the processing chamber. 2. The dry etching method according to claim 1, wherein the dry etching method comprises a coil, and the change of the contact area is achieved by controlling a current applied to the auxiliary magnetic field forming means. 4. A dry etching method for selectively etching a non-Al-containing compound semiconductor layer laminated on an Al-containing compound semiconductor layer, wherein at least part of an inner wall surface of the processing chamber in the axial direction is a sulfur-based material layer. A plurality of magnets that are coated so as to face the coating portion of the sulfur-based material layer and circulate around the outer peripheral portion of the processing chamber, and are excited to have the same polarity along the axial direction. EC equipped with a coil
The sulfur-based material layer is formed by using an R plasma device, introducing an etching gas containing at least a fluorine-based compound into the ECR plasma device, and changing the distance between the plurality of coils along the axial direction. The dry etching method is characterized in that etching is performed while changing the density of ECR plasma in the vicinity of.