JPH05198536A - Dry etching method - Google Patents

Abstract

PURPOSE:To improve the base selectivity and anisotropy by reducing the quantity of radicals at overetching without changing the discharge condition such as gas composition, etc., in the selective etching of GaAs/AlGaAs without using CFC (chlorofluorocabon) gas. CONSTITUTION:An Al cover 13 is provided at the inwall of the processing chamber 4 of a microwave plasma etching device having a magnetic field, and the contact area between this Al cover 13 and ECR plasma P is adjusted by the operation of a lifter type shutter 14 (or rotary shutter 15). If this contact area is made small at just etching and large at overetching, using S2F2/S2Cl2 mixture gas, mainly Cl* out of halogen radical in the latter is removed in the shape of AlClx, and the stacking of S and the formation of AlFx are promoted. The contact area can also be changed by the control of the magnetic field coordination.

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.
(High electron mobility transistor) GaAs / AlGaAs selective etching or the like in the gate recess forming step is possible without using chlorofluorocarbon (CFC) gas and controlling the amount of radicals generated during the process. ..

[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 the GaAs layer is removed by forming Ga mainly as a chloride and As as a fluoride and a chloride, while AlF ₃ having a low vapor pressure is formed on the surface when the underlying AlGaAs layer is exposed. 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 easily produces 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]

In order to control the production amount of halogen radicals in plasma without changing the composition of etching gas or other discharge conditions,
It was considered that a part of the inner wall surface of the processing chamber is covered with a material layer capable of consuming halogen / radicals, and the contact state between this material layer and plasma is changed by some method. Also,
As a material layer that can consume this halogen radical, A
It has been found that the l-based material layer is suitable. The present invention is proposed based on these findings.

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 laminated on an Al-containing compound semiconductor layer, and At least a part of the wall surface is covered with an Al-based material layer, and
Using a plasma device equipped with a shutter member capable of varying the contact area between the 1-based material layer and the plasma, the plasma device is used for etching containing at least a fluorine compound.
It is characterized in that etching is performed while introducing a gas and changing the contact area between the plasma and the Al-based material layer by operating the shutter member.

In the dry etching method according to the second invention of the present application, at least a part of the inner wall surface of the processing chamber in the axial direction is covered with an Al-based material layer, and this A
An ECR plasma apparatus is used in which auxiliary magnetic field forming means is disposed on the outer peripheral portion of the processing chamber so as to face the coating portion of the 1-based material layer, and an etching gas containing at least a fluorine-based compound is used in the ECR plasma apparatus. Introduced,
It is characterized in that etching is performed while changing the contact area between the ECR plasma and the Al-based material layer by operating the auxiliary magnetic field forming means.

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 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 fourth 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 fifth invention of the present application, at least a part of the inner wall surface of the processing chamber in the axial direction is covered with an Al-based material layer, and the coating site of the Al-based material layer is covered. 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. An etching gas containing at least a fluorine-based compound is introduced into the plasma device, and the distance between the plurality of coils is changed along the axial direction to change the density of ECR plasma in the vicinity of the Al-based material layer. It is characterized in that the etching is performed while performing.

[0019]

In the present invention, as described above, it is necessary to change the contact state between the Al-based material layer provided on the inner wall surface of the processing chamber and the plasma by some method. As the method, the present inventor roughly considered two methods: (a) a method of disposing a movable shutter member in the processing chamber, and (b) a method of controlling the magnetic field orientation.

The first invention of the present application utilizes the movable shutter member (a) described above to make the contact area between the Al-based material layer and the plasma variable. That is, when the contact area between the two is small, the radical consumption by the Al-based material layer is small, and when the contact area is large, the radical consumption is large. Therefore, if the contact area is relatively small in the just etching process and relatively large in the over etching process, the shutter member of the shutter member can be changed without changing other parameters such as the wafer temperature and the composition ratio of the etching gas. The amount of radicals in the etching reaction system can be easily controlled only by a mechanical operation. Therefore, the time required for stabilizing the discharge state can be shortened and the throughput can be improved. In particular, if the present invention is applied to the S deposition process as described above, the S / X ratio of the etching reaction system can be easily changed.

The radicals consumed by the Al-based material layer are halogen radicals generated in plasma. In the etching of a laminated system of non-Al-containing / Al-containing compound semiconductors, in principle, the achievement of the underlayer selectivity is Al.
Since it is based on the generation of F _x , F ^* is always present in the plasma. Other halogen radicals are Cl ^* , Br ^*, etc., which are appropriately selected and used according to the constituent elements of the compound semiconductor so that the etching reaction product can have a sufficiently high vapor pressure. However, among the reaction products of these halogen radicals and the Al-based material layer, those having a high vapor pressure and easily exhausted to the outside of the etching reaction system are AlCl _x , AlBr _x, etc., and Al having a low vapor pressure is used.
F _x remains in the system. Therefore, the amount of F in the system becomes relatively large as compared with other halogens, and this also achieves high selectivity.

The second invention of the present application is particularly intended for a process in which an ECR plasma device is used as the plasma device, and the magnetic field orientation control of the above (b) is performed by operating the auxiliary magnetic field forming means. is there. ECR plasma is plasma that is generated when electrons that are circularly moving in a magnetic field resonantly absorb microwave energy that matches the cyclotron angular frequency. Therefore, needless to say, the ECR plasma device is provided with the magnetic field forming means for plasma generation (corresponding to the above-mentioned main coil). The auxiliary magnetic field forming means is provided separately from the magnetic field forming means and does not directly participate in plasma generation, but controls the confined state of plasma. In the present invention, a part of the inner wall of the processing chamber in the axial direction is coated with an Al-based material layer, and an appropriate auxiliary magnetic field forming means is installed at a portion substantially corresponding to the coated 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 is capable of forming a magnetic flux along a part of the inner wall surface of the chamber, contact between the ECR plasma and the Al-based material layer covering the inner wall surface of the chamber while the magnetic flux exists. If the area decreases and the magnetic flux disappears, the contact area increases. Since the halogen radicals are contained in the ECR plasma as described above, the halogen radicals are consumed almost in proportion to the contact area.

A third 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 Al-based material layer on the inner wall surface of the chamber,
This alternating multipole magnetic field ring may be placed at a position that substantially surrounds the area covered with the Al-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 fourth invention of the present application is similar to the third 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 Al-based material layer on the inner wall surface of the chamber, the coil may be energized and 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, 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 focuses on controlling the amount of radicals 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 is present, ECR is performed. The uniformity of plasma can be improved.

In the fifth 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 second invention to the fourth invention, the ECR is performed.
By changing the magnetic field gradient using the plasma forming coil itself, the density of the ECR plasma that contacts the Al-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 section 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 is steep, and conversely, it is 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 energy distribution of the microwave has a certain width as described above, so that the gentler the magnetic field gradient is,
This is because the region in the processing chamber that can satisfy the ECR condition by adapting to the energy fluctuation range becomes wider.

Therefore, when it is desired to increase the amount of halogen radicals consumed in the ECR plasma by the Al-based material layer, the distance between the coils should be increased to increase the plasma density near the inner wall surface. On the contrary, when it is desired to reduce the consumption of halogen radicals, the separation distance may be set small.

[0029]

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

[0030] Example 1 This example, a first aspect of the present invention is applied to a gate recess process of HEMT, n ⁺ -AlGaAs on n ⁺ -Ga
When the As layer is selectively etched using a mixed gas of S ₂ F ₂ / S ₂ Cl ₂ , the contact area between the Al cover disposed on the inner wall surface of the processing chamber and the ECR plasma exceeds the just etching process. In this example, the shutter operation is changed between the etching process and the etching process.

Before entering the description of the actual etching process, first, a configuration example of a magnetic field microwave plasma etching apparatus of RF bias application type used in carrying out the present invention and a method of using the same will be described. To do. A schematic configuration of the above device is shown in FIG. This device includes a magnetron 1 for generating a microwave of 2.45 GHz, a rectangular waveguide 2 which is connected to the magnetron 1 via a matching device, a microwave power meter, an isolator, etc., which are not shown, and which guides the microwave. A processing chamber 4 connected to the rectangular waveguide 2 through a microwave introduction window 3 made of a quartz glass plate or the like for generating ECR plasma P inside by discharge, and a wafer 10 installed in the processing chamber 4 7. To circulate the wafer mounting electrode 8 for mounting and the processing chamber 4 to satisfy the ECR condition.
A solenoid coil 7 and the like capable of achieving a magnetic field strength of 75 × 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 Al-based material layer. As a specific example of this Al-based material layer, a belt-shaped Al cover 13 formed by a sputtering method is used here. However,
The Al cover 13 does not necessarily have to continuously circulate the inner wall portion of the processing chamber 4, and may have a configuration in which a solid block or foil is attached to the inner wall portion. Furthermore, an Al target for sputtering or the like can be used as the other Al-based material layer.

The surface of the Al cover 13 may be passivated by AlF _{3 if the} number of treatments is increased.
In such a case, the Al cover 13 can be biased and the AlF ₃ can be sputter-removed or the Al cover 13 can be replaced, and the wafer is removed and cleaned every time several wafers are processed. It is especially desirable to take measures such as

The second idea is that a cylindrical elevating shutter 14 that can be moved up and down in the direction of arrow D by a driving means (not shown) is provided on the inner peripheral side of the Al cover 13. 1A shows a state where the Al cover 13 is almost completely shielded from the ECR plasma P by the elevating shutter 14 (shutter opening 0%), and FIG. 1B shows the elevating shutter 14 being lowered. Shows the state where the entire surface of the Al cover 13 is exposed (shutter opening 100%).

FIG. 2 is a perspective view showing the interior of the processing chamber 4 with a part thereof broken away, in order to more clearly show the disposition state of the elevating shutter 14. The side wall surface of the processing chamber 4, the elevating shutter 14, and the wafer mounting electrode 8 are all arranged concentrically. The contact area between the Al cover 13 and the ECR plasma P can be arbitrarily adjusted by changing the elevation distance of the elevation shutter 14 in the direction of arrow D.

The elevating shutter 14 can be constructed by appropriately selecting a material that does not consume radicals and does not cause unnecessary contamination in the etching reaction system. In this embodiment and the second embodiment described later, the elevating shutter 14 made of stainless steel is adopted. In the S deposition process, S is also deposited on the surfaces of the internal constituent members of the processing chamber 4. Therefore, if, for example, a heating means is also incorporated in the elevating shutter 14 so that the S deposited on the surface can be removed by sublimation by heating it every time one etching is completed, reproducibility can be improved. It is extremely effective in raising it.

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. As shown in FIG. 1A, the elevating shutter 14 was set at a position where the Al cover 13 was shielded from the ECR plasma P. 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. Shutter opening 0% The S ₂ F ₂ / S ₂ Cl ₂ mixed gas system was 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 ⁺ , S
It is assisted by incident ion energy such as F _x , Cl _x ⁺ , SCl _x ⁺ . On the other hand, S ₂ F ₂ and S ₂ Cl ₂
Also emits S into the ECR plasma P. This S was deposited on the side wall portion of the pattern where vertical incidence of ions does not occur in principle and formed a side wall protective film 27 as shown in FIG. 4, which contributed to the achievement of anisotropy. As a result, the recess 25a having the vertical wall was formed.

The just etching is performed by n ⁺ -AlG
The aAs layer 24 was exposed, and AlF _x (mainly x = 3) was formed on the surface of the aAs layer 24, and the etching rate was significantly reduced. The base selection ratio at this point was about 30. At this time, some residue 25b of the n ⁺ -GaAs layer 25 remained on the wafer 10.

Therefore, in order to remove the residue 25b,
Over etching was performed. The elevating shutter 14 at this time is, as shown in FIG.
3 was lowered to a position where the entire surface was exposed. Other conditions were the same as those in the just etching process. In this over-etching process, since the shutter opening is set to 100%, the ECR plasma P is not covered by the Al cover 1.
Sufficiently contact with 3 and F ^* and Cl ^{* in} plasma are AlF
_x , spent to produce AlCl _x . However, of these, the one that is efficiently removed to the outside of the system is A, which has a high vapor pressure.
lCl is _x, is lower AlF _x vapor pressure is left to the system, than relatively Cl rich F atmosphere to emerge. Therefore, in this etching reaction system, the apparent S / X ratio is increased to accelerate the deposition of S, and
^On the surface of the ⁺ -AlGaAs layer 24, the production of AlF _x was given priority over the production of other halides. As a result, FIG.
As shown in (3), the residue 25b could be removed while maintaining the good anisotropic shape of the recess 25a. 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 according to 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

Embodiment 2 This embodiment is also the HEM to which the first invention of the present application is applied.
It is an example of the gate recess processing of T, but unlike Example 1, it has a magnetic field microwave plasma with a rotary shutter.
An etching device is used, and S is used as an etching gas.
_{A 2} F ₂ / S ₂ Br ₂ mixed gas was used.

The magnetic field microwave plasma etching apparatus used in this embodiment is similar to that shown in FIG. 1 when a schematic sectional view is shown, but a perspective view showing a partially broken interior of the processing chamber 4 is shown in FIG. become that way. That is, the apparatus of the present embodiment is provided with the cylindrical rotary shutter 15 having the slit-shaped opening 15a, and the Al cover 13a is also formed in a belt shape following the opening pattern of the opening 15a. .. The rotary shutter 15 is rotatable in the direction of arrow E by a driving unit (not shown).

Now, the positional relationship between the rotary shutter 15 and the Al cover 13a will be described with reference to FIG. This figure is a cross-sectional view taken along line XX of FIG. 9, where (a) is the state in which the Al cover 13a is blocked by the rotary shutter 15 (shutter opening 0%), and (b) is the entire surface of the Al cover 13a. Shows a state of being exposed through the opening 15a (shutter opening 100%). Al cover 13a and EC
The contact area with the R plasma P can be arbitrarily adjusted by changing the rotation angle of the rotary shutter 15.

Gate recess processing was actually carried out using the above-mentioned magnetic field microwave plasma etching apparatus. The wafer 10 used in this example is the same as that shown in FIG. 3 described above. This wafer 10 was set on the wafer mounting electrode 8 described above, and the opening degree of the rotary shutter 15 was set to 0% as shown in FIG. 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. Shutter opening 0% This S ₂ F ₂ / S ₂ Br ₂ mixed gas system was also proposed by the applicant of the present application in Japanese Patent Application No. 3-308327. The etching mechanism in this just etching step was almost the same as that of Example 1 in which chlorine was replaced by bromine, and the recess 25a (see FIG. 4) having a similar anisotropic shape was formed.

Next, in order to remove the residual residue 25b, overetching was performed under the same conditions except that the opening degree of the rotary shutter 15 was set to 100% as shown in FIG. 10 (b). In this overetching process, E
F ^* and Br ^* in the CR plasma P reacted with Al supplied from the Al cover 13a and were consumed for the production of AlF _x and AlBr _x . However, among these, AlBr _x , which has a high vapor pressure, is mainly efficiently removed to the outside of the system, so that an atmosphere richer in F than Br appears.
Therefore, in this etching reaction system, the apparent S
/ X ratio is increased to accelerate the deposition of S, and n ⁺ -
On the surface of the AlGaAs layer 24, the production of AlF _x has priority over the production of other halides. Also in this embodiment, the good anisotropic shape of the recess 25a is maintained, and the n
It was possible to remove the residue 25b while maintaining a high selectivity of 60 or more with respect to the ⁺ -AlGaAs layer 24.

Embodiment 3 In this embodiment, the third invention of the present application is applied to the gate recess processing of HEMT, and the contact area between the Al cover and ECR plasma is adjusted between the just etching step and the over etching step. This is an example of changing with a permanent magnet.

First, a structural example of a magnetic field microwave plasma etching apparatus used for carrying out the present invention,
And the usage thereof will be described with reference to FIG. Note that some of the reference numerals in FIG. 11 are common to those in FIG. The structure of the magnetic field microwave plasma etching apparatus used in this embodiment is one in which auxiliary magnetic field forming means is provided instead of the elevating shutter 14 or the rotary shutter 15 shown in FIG.

This auxiliary magnetic field forming means is used in the processing chamber 4
It is composed of a plurality of permanent magnets 16 arranged at substantially equal intervals along the circumferential direction. Each of the permanent magnets 16 is integrally connected to a driving unit (not shown), and can be moved up and down in the arrow F direction between the position G and the position H along the axial direction (Y-Y line direction) of the processing chamber 4. ing. Here, the position G means the Al cover 13 as shown in FIG.
11 is a position that overlaps with the arrangement position of FIG.
It is a position where they do not overlap as shown in (b).

Here, in order to show the arrangement state of the permanent magnets 16 in a more understandable manner, a sectional view taken along line XX is shown in FIG. 12A shows the case where the permanent magnet 16 is at the position G, and FIG. 12B shows the case where the permanent magnet 16 is at the position H. In the example shown in FIG. 12A, eight permanent magnets 16 are arranged at equal intervals along the circumferential direction of the processing chamber 4, and adjacent permanent magnets 16 are arranged in the radial direction of the processing chamber 4. Along with the opposite polarity. According to such an arrangement, a star-shaped multicusp magnetic field is formed by the magnetic force lines from the N pole of a magnet to the S poles of the magnets on both sides, and the ECR plasma P is confined inside this.

Here, when a multi-cusp magnetic field is formed at the position G, the diffusion of plasma toward the inner wall surface of the processing chamber 4 is suppressed, so that the Al cover 13 is formed.
The contact area between the and ECR plasma P decreases. Therefore, the amount of halogen radicals consumed in the ECR plasma P is reduced. On the other hand, when the multi-cusp magnetic field is formed at the position H, the processing chamber 4 at the position G is
Since the plasma diffusion in the direction of the inner wall surface is not hindered at all, the contact area between the Al cover 13 and the ECR plasma P increases. Therefore, the amount of halogen radicals consumed in the ECR plasma P increases.

The multi-cusp magnetic field also serves to converge the divergent magnetic field in the vicinity of the wafer 10 formed by the solenoid coil 7 to make the plasma density uniform.

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 permanent magnet 16 was set at the position G as shown in FIG. 11A, and the n ⁺ -GaAs layer 25 was just-etched under the same conditions as in Example 1. The etching mechanism in this just etching process is almost as described in the first embodiment.
However, in the ECR plasma P, S ⁺ , SF ⁺ , Cl ⁺ ,
Ions such as SCl _x ⁺ descend along the divergent magnetic field formed by the solenoid coil 7 and, in the vicinity of the wafer 10, as shown in FIG.
The multi-cusp magnetic field formed by 6 blocks the diffusion in the radial direction, and makes the wafer 10 incident almost vertically to assist anisotropic processing. Moreover, since the contact area between the Al cover 13 and the ECR plasma P is reduced by the multi-cusp magnetic field, F ^* in the ECR plasma P,
Little Cl ^* is consumed.

In the subsequent over-etching step, the permanent magnet 16 was moved to the position H as shown in FIG. 11 (b). The other etching conditions were the same as those in the just etching process. In this over-etching step, the multi-cusp magnetic field near the wafer 10 disappears, and the above-described FIG.
As shown in (b), the Al cover 13 and the ECR plasma P were entirely in contact with each other. Thereby, mainly Cl ^* in the ECR plasma P was consumed, the deposition of S was promoted and the formation of AlF _x was promoted. As a result, recess 25a
The anisotropic shape of was maintained well, and the underlying selectivity was also improved.

In this example, excellent low stain resistance and reproducibility were achieved as compared with Examples 1 and 2. This is the ECR plasma P and Al in this embodiment.
This is because the change of the contact area with the cover 13 is performed mainly by controlling the magnetic field orientation, and since a movable member such as a shutter is not introduced into the processing chamber 4, there are essentially few particle generation sources.

Example 4 In this example, the fourth invention of the present application is applied to the gate recess processing of HEMT, and the contact area between the Al cover and the ECR plasma is adjusted between the just etching step and the overetching step. This is an example in which it is changed by the auxiliary coil.
The magnetic field microwave plasma etching apparatus used in this embodiment has an auxiliary coil 19 in place of the permanent magnet 16 used in the third embodiment.

FIG. 13 shows a sectional view taken along line XX in this case. 13A shows the case where the auxiliary coil 17 is excited at the position G, and FIG. 13B shows the case where the auxiliary coil 17 is not excited. In the example shown in FIG. 13A, eight auxiliary coils 19 are arranged at equal intervals along the circumferential direction of the processing chamber 4. Each auxiliary coil 19
It is composed of a magnetic core 17 and a conducting wire 18 wound around the magnetic core 17, and adjacent auxiliary coils 19 are excited to have opposite polarities by making the conducting directions of the conducting wires 18 opposite to each other. Formation of multicusp magnetic field and E
The confined state of the CR plasma P is almost the same as when the permanent magnet 16 is used.

However, when the auxiliary coil 19 is used,
Since the multicusp magnetic field disappears when the power supply to the conducting wire 18 is stopped, as shown in FIG. 13B, even if the auxiliary coil 19 is left at the position G, the Al cover 13 and EC
The contact area of the R plasma P can be changed.

Using this magnetic field microwave plasma etching apparatus, recess processing was actually performed using an S ₂ F ₂ / S ₂ Cl ₂ mixed gas. The used wafer 10 is
It is the same as that shown in FIG. First, the auxiliary coil 19
Is excited at position G, and n ⁺ -Ga is conducted under the same conditions as in the third embodiment.
The As layer 25 was just etched. In this just etching process, etching proceeded by the same mechanism as that described in Example 3.

Next, over-etching was performed under the same conditions except that the excitation of the auxiliary coil 19 was stopped. In this over-etching process, the contact area between the ECR plasma P and the Al cover 13 increased with the disappearance of the multicusp magnetic field, and high selection and high anisotropic processing were realized.

Example 5 In this example, the fifth invention of the present application is applied to the gate recess processing of HEMT, and the magnetic field gradient is changed between the just etching step and the overetching step to form an Al cover. This is an example in which the density of the contacting ECR plasma is changed.

First, a configuration example 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,
Some of the reference numerals in FIG. 14 are common to those in FIG. 11. This device differs from the device of FIG. 11 described above in that the auxiliary magnetic field forming means is not provided, and a single solenoid coil 7 is used.
Unitized solenoid coil 7a instead of
7b is disposed, and the Al cover 13 is further circulated by the solenoid coils 7a and 7b, that is, E
This is a point formed in the area including the CR position.
The solenoid coils 7a and 7b are connected to driving means (not shown), respectively, so that the solenoid coils 7a and 7b are moved in the direction of the arrow I between the position J and the position K along the axial direction of the processing chamber 4 (the YY line direction). It is supposed to be movable. Here, the position J is a solenoid, as shown in FIG.
It is a position where the coils 7a and 7b are close to each other, and a position K
Are the positions separated from each other as shown in FIG.

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. The magnetic field gradient near the inner wall surface of the processing chamber 4 changes depending on the distance between them. That is, when the solenoid coils 7a and 7b are close to each other as shown in FIG. 14 (a), the magnetic field gradient near the inner wall surface is high. Therefore, the ECR
The density of the plasma P is high near the center of the processing chamber 4 and low near the Al cover 13. Therefore, the halogen / radical consumption is small, and the S / X ratio of the etching reaction system is relatively low.

On the contrary, when the solenoid coils 7a and 7b are separated from each other as shown in FIG. 14B, 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 A
The plasma density near the l-cover 13 is increased.
Therefore, the amount of halogen / radical consumption is increased, and the S / X ratio of the etching reaction system can be relatively increased.

Using this magnetic field microwave plasma etching apparatus, recess processing was actually performed 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, position the solenoid coils 7a and 7b at the position J as shown in FIG.
Set to. In this state, the n ⁺ -GaAs layer 25 was just-etched under the same conditions as in Example 2.

The etching mechanism in this step is almost as described in the second embodiment. However, here A
Since the density of the ECR plasma P near the 1 cover 13 is low, F ^* and Br ^* are hardly consumed. Next, the solenoid coils 7a and 7b are attached to the
Overetching was performed under the same conditions except that the position K was set as shown in FIG. In this process,
Since the density of the ECR plasma P in the vicinity of the Al cover 13 becomes high, the consumption amount of Br ^* mainly increases, so that S is relatively easily deposited and AlF _x is easily generated. Therefore, highly selective and highly anisotropic etching was realized.

The present invention has been described above based on the five embodiments, but 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, etc. can be appropriately changed.

[0074]

As is apparent from the above description, according to the present invention, the contact area between the Al-based material layer provided on a part of the inner wall surface of the processing chamber of the plasma device and the plasma can be easily adjusted by operating the shutter member. Can be changed to. Further, particularly in the case of the ECR plasma device, the contact area between the Al-based material layer and the ECR plasma or the density of the ECR plasma in contact with the Al-based material layer can be changed by controlling the magnetic field orientation. In any case, without changing the other discharge conditions, plasma or EC
It is possible to easily change the amount of halogen radicals in the R plasma, particularly halogen radicals other than F ^* , during the etching process. By this method,
By etching the laminated system of the non-Al-containing / Al-containing compound semiconductor layers represented by the GaAs / AlGaAs laminated system, the anisotropy and selectivity in the overetching process can be significantly 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) Is a lift shutter A
1 shows a state where the cover is shielded, and (b) shows a state where the entire surface of the Al cover is exposed.

FIG. 2 is a schematic perspective view showing a lift shutter and its peripheral members of the magnetic field microwave plasma etching apparatus of FIG.

FIG. 3 is a schematic cross-sectional view showing a state in which 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 partially cutaway view of a rotary shutter and its peripheral members in 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. It is a schematic perspective view.

10 is a cross-sectional view taken along line XX in FIG. 9, (a) showing a state where the Al cover is shielded by a rotary shutter, (b).
Represents the state where the entire surface of the Al cover is exposed.

FIG. 11 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 in a position overlapping with the Al cover, and (b) shows a state in which it is arranged in a position not overlapping.

12 is a cross-sectional view taken along line XX of the magnetic field microwave plasma etching apparatus of FIG. 11, in which (a) is a permanent magnet disposed at a position overlapping the Al cover and a multicusp magnetic field is provided near the Al cover. The formed state, (b) shows the state where the multicusp magnetic field is extinguished by arranging them in non-overlapping positions.

FIG. 13 is a sectional view taken along line X-X of another 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, wherein (a) is an auxiliary coil. Is excited to form a multicusp magnetic field in the vicinity of the Al cover, and (b) shows a state in which the excitation is stopped to extinguish the multicusp magnetic field.

FIG. 14 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 in which the solenoid coils are arranged close to each other to increase the magnetic flux density near the Al cover, and (b) shows a state in which the solenoid coils are separated from each other to reduce the magnetic flux density.

[Explanation of symbols]

4 ... Processing chamber 7, 7a, 7b ... Solenoid coil 8 ... Wafer mounting electrode 10 ... Wafer 13, 13a ... Al cover 14 ... Elevating shutter 15 ... Rotation Shutter 16 ... Permanent magnet 19 ... Auxiliary coil 20 ... Equal magnetic field surface 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 29/812 H05H 1/46 9014-2G

Claims (5)

[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 is covered with an Al-based material layer. And using a plasma device equipped with a shutter member capable of varying the contact area between the Al-based material layer and plasma, and introducing an etching gas containing at least a fluorine-based compound into the plasma device, A dry etching method, wherein etching is performed while changing the contact area between plasma and the Al-based material layer by operating a member. 2. 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 Al.
An ECR plasma device is used which is covered with a system material layer, and in which an auxiliary magnetic field forming means is arranged on the outer peripheral portion of the processing chamber so as to face the coating site of the Al system material layer. A dry etching method, characterized in that an etching gas containing at least a fluorine-based compound is introduced into and the etching is performed while changing the contact area between the ECR plasma and the Al-based material layer by operating the auxiliary magnetic field forming means. 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 magnetized so as to have opposite polarities alternately along the radial direction of the processing chamber. 3. The dry etching method according to claim 2, wherein the contact area is changed by moving the auxiliary magnetic field forming means along the axial direction of the processing chamber. 4. 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 excited so as to have opposite polarities alternately along the radial direction of the processing chamber. 3. The dry etching method according to claim 2, wherein the dry etching method comprises a coil, and the change in the contact area is achieved by controlling the current applied to the auxiliary magnetic field forming means. 5. 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 Al.
Is coated with a system material layer, and is arranged so as to circulate around the outer peripheral portion of the processing chamber facing the coating portion of the Al system material layer, and is excited so as to have the same polarity along the axial direction. Using an ECR plasma device provided with a plurality of coils prepared by introducing an etching gas containing at least a fluorine-based compound into the ECR plasma device,
A dry etching method characterized in that etching is performed while changing the distance between the plurality of coils along the axial direction to change the density of ECR plasma in the vicinity of the Al-based material layer.