JPH06224158A - Dry etching method - Google Patents

Abstract

PURPOSE:To enable a dry etching process to be carried out high in etching selectivity when a GaAs/AlGaAs laminate is selectively dry-etched by a method wherein AlN is formed on the exposed surface of AlGaAs. CONSTITUTION:A mixed gas of Cl2/N2 is used in a process wherein a recess 5a used for the formation of the gate of a HEMT is processed, wherein an N<+>-GaAs layer 5 on an N<+>-AlGaAs layer 4 is etched as a wafer is heated at a temperature of 70 deg.C or so. Ga and As are removed as chloride. As and N are not able to react with each other to produce compound, but Ga produces reaction product GaN low in vapor pressure reacting with N, and GaN is conducive to protecting a side wall. When the N<+>-AlGaAs layer 4 is exposed, an Al, N deposit film 7 low in vapor pressure is formed on the exposed N<+>-AlGaAs layer 4, whereby an etching operation is stopped. The AlN deposit film 7 can be removed off by sputtering.etching with rare gas after an etching operation is finished.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method applied to the manufacture of semiconductor devices and the like.
The present invention relates to a method for performing selective anisotropic etching of a laminated system of non-Al-containing / Al-containing compound semiconductors represented by an AlGaAs laminated system under practical conditions.

[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.

GaAs layer on the AlGaAs layer
Selective etching of chlorofluorocarbon type gas
RIE using a mixed gas of (CFC-based gas) and a rare gas
Generally performed by (reactive ion etching)
Target. For example, Japanese Journal
l of Applied Physics, Vol.
20. , No. 11 (1981), p. L847-85
0 for CCl₂F₂Example of using a He / He mixed gas
Has been done. In this case, Ga is mainly chloride and As is
GaAs layer by forming fluoride and chloride
Are removed. Etching reaches the underlying AlGaAs layer
Then, AlF having a low vapor pressure is exposed on the exposed surface. _x(Fluoride
Aluminum) is formed and etching is stopped or reduced.
Speed up. In the above literature, the value of the selection ratio at this time is about 2
It is reported as 00. Also, the side wall surface of the pattern is
Strike mask and CCl₂F₂Derived from gas decomposition products
The gate is protected by the adhesion of carbon-based polymer
・ The anisotropic shape of the recess is also secured.

Alternatively, a method of avoiding damage to the layer to be etched due to the incident energy of ions in RIE has been proposed. For example, JP-A-3-29
In the 1930 publication, GaAs / AlGa is heated while heating the substrate by a gas etching mechanism in which a reactive gas remains in a molecular state and reacts with a material layer to be etched.
A technique for performing selective etching of an As laminated system is disclosed. Cl ₂ is used as the reactive gas, and O ₂ is added to secure the selectivity. That is, according to this technique, aluminum oxide Al _x O _y (typically Al ₂ O) having an extremely low vapor pressure is exposed on the exposed surface of the AlGaAs layer.
By generating ₃ ), the background selectivity is secured.

[0007]

However, there are still some problems inherent in the prior art. First, above C
Cl ₂ F ₂ is known as a code name of CFC-12, and is a compound corresponding to a so-called specific CFC, which is scheduled to be totally abolished in the near future from the viewpoint of global environment protection. Therefore, in the future dry etching, it is necessary to promote a CFC removal measure (CFC removal measure), and the practicality of CCl ₂ F ₂ is significantly reduced.

In the technique disclosed in the above publication, Al is used.
_{Although x} O _y is used for stopping etching, Al ₂ O _{3 which} is a typical example of this has a boiling point near 3000 ° C. under normal pressure, and it is difficult to remove it in a subsequent process. Furthermore, since the reactive gas is used in its molecular state,
Substrate 350-600 to facilitate the etching reaction.
Etching is performed while heating to ℃. Since the resist mask cannot withstand use as an etching mask under such a high temperature, the SiO ₂ mask is used in the above publication. However, this means that an extra step is required for forming and removing the etching mask, and there is a great possibility that the idea of high throughput, high reliability, and low cost is reversed.

Therefore, the present invention selects a compound semiconductor layer containing no aluminum (hereinafter referred to as a non-Al containing compound semiconductor layer) on a compound semiconductor layer containing aluminum (hereinafter referred to as an Al containing compound semiconductor layer). It is an object of the present invention to provide a method capable of performing anisotropic etching based on a practical mechanism.

[0010]

The dry etching method of the present invention is proposed in order to achieve the above-mentioned object, and is a non-Al-containing compound laminated on an Al-containing compound semiconductor layer on a substrate. When selectively etching the semiconductor layer, this etching is performed using an etching gas capable of generating halogen-based active species and nitrogen-based active species under discharge dissociation conditions, and exposing the Al-containing compound semiconductor layer. It is stopped by forming aluminum nitride on the surface.

The present invention also uses at least one of a chlorine-based active species and a bromine-based active species as the halogen-based active species.

Further, the present invention is to remove the aluminum nitride by using plasma of an inert gas after the etching is completed.

[0013]

[Function] The point of the present invention is that non-Al-containing / Al-containing
Substrate selection in selective etching of compound semiconductor laminated systems
The property of depositing aluminum nitride (AlN)
It is to secure more. AlN is boiling under normal pressure
The point is 2000 ℃, under normal dry etching conditions
Has a low vapor pressure, and the Al-containing compound semiconductor layer has a low surface pressure.
In this way, it fully plays the role of stopping the etching. Only
However, the Al disclosed in the above publication₂O ₃Better than
Since the boiling point is very low, the removal after etching is completed by Al₂
O₃Easier than. The etch in the present invention
In the reaction, halogen-based active species are the main etching species.
Proceed by giving.

Here, generally speaking, the halogen-based active species are typically three of the fluorine-based active species, the chlorine-based active species and the bromine-based active species, but the latter two are particularly used in the present invention. Conventionally, in the selective etching of a GaAs / AlGaAs laminated system, a fluorine-based active species is generally used, and AlF _x (typically AlF ₃ ) is deposited on the exposed surface of the AlGaAs layer to stop the etching. It was a way of thinking.
This is because the vapor pressure of AlF _x under etching conditions is low. However, in the present invention, by intentionally excluding the fluorine-based active species from the etching reaction system, Al
The production efficiency of AlN having a vapor pressure lower than that of F _x is increased. AlN can be removed by lightly etching with plasma of an inert gas after completion of etching.

Although the etching reaction product in this case is chloride or bromide, generally, there is almost no compound having extremely low vapor pressure among chlorides and bromides of the elements constituting the compound semiconductor. There is no substantial hindrance to the progression of.

[0016]

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

[0017] Example 1 This example, the present invention is applied to a gate recess process of HEMT, and the n ⁺ -GaAs layer on n ⁺ -AlGaAs layer using a Cl ₂ / N ₂ mixed gas was etched Example Is. This process will be described with reference to FIGS. The wafer used as the etching sample in this example is a semi-insulating GaA as shown in FIG.
s epi-Ga having a thickness of about 500 nm which is formed on the substrate 1 by epitaxial growth and functions as a buffer layer.
As layer 2, AlGaAs layer 3 having a thickness of about 2 nm, n ⁺ -Al having a thickness of about 30 nm doped with n-type impurities such as Si
The GaAs layer 4, similarly containing n-type impurities, has a thickness of about 100 n.
An n ⁺ -GaAs layer 5 of m and a resist mask (PR) 6 patterned into a predetermined shape are sequentially laminated. The patterning of the resist mask 6 is performed by exposure and development processing by an electron beam drawing method, and the opening diameter of the opening 6a is about 300 nm.

In order to etch the n ⁺ -GaAs layer 5, this wafer was set in an RF bias application type magnetic field microwave plasma etching apparatus. An example of etching conditions is shown below. Cl ₂ flow rate 20 SCCM N ₂ flow rate 10 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GHz) RF bias power 20 W (2 MHz) Wafer temperature 70 ° C.

Here, the Cl ^* generated from Cl ₂ is n
As-Ga in the ⁺ -GaAs layer 5 is AsCl ₃ ,
Pull out in the form of GaCl ₃ etc. These radical reactions are assisted by the incident energy of ions such as Cl _x ⁺ and N _x ⁺ , so that the etching can be performed smoothly without heating the wafer to several hundreds of degrees Celsius as in conventional gas etching. I was able to proceed to.

On the other hand, N ^* produced from N ₂ produces GaN. This GaN is a compound that begins to sublime at around 800 ° C. under normal pressure, but has a low vapor pressure under the above etching conditions and is deposited on the sidewall surface of the pattern together with the carbon-based polymer derived from the decomposition product of the resist mask 6. Then, a sidewall protection film (not shown) was formed. This GaN
Due to the side wall protection effect and the ion assist effect, the recess 5a having an anisotropic shape was formed as shown in FIG.

N ^* does not react with As. In the conventional technique of stopping etching by Al _x O _y , G
Both a and As could produce oxides, but only Ga produces nitrides in this example. Such a small number of reaction products is advantageous in controlling the etching reaction system. When the etching progressed and the bottom surface of the etching reached the n ⁺ -AlGaAs layer 4, the AlN deposition film 7 was formed on the exposed surface, and the etching virtually stopped. This AlN deposited film 7 showed excellent etching resistance even during overetching.

Next, in order to remove the AlN deposition layer 7, as an example, sputter etching was performed under the following conditions. Ar flow rate 50 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GHz) RF bias power 5 W (2 MHz) Wafer temperature 70 ° C. In this process, Ar ⁺ is incident on the wafer with relatively little energy. As shown in FIG.
The 1N deposited layer 7 was removed based on the ion sputtering action. This removal was much easier than the removal of Al ₂ O ₃ . Further, the resist mask 6 did not retreat extremely by this sputter etching.

Subsequent formation of the gate electrode was carried out according to a conventional method. This process will be described with reference to FIGS. 4 and 5. That is, first, as shown in FIG. 4, as an example, a thickness of about 200 n is obtained by electron beam evaporation.
m Al layer was formed. This vapor deposition makes good use of the fact that the step coverage (step coverage) deteriorates inside the recess 5a having a fine opening diameter. By this process, the upper Al layer 8a was formed on the surface of the resist mask 6, and the lower Al layer 8b to be a gate electrode later was formed on the bottom of the recess 5a.

After that, when the resist mask 6 is lifted off, the upper Al layer 8a is simultaneously removed as shown in FIG. 5, and the gate electrode is formed leaving only the lower Al layer 8b at the bottom of the recess 5a. I was able to. The above C
Even when HBr was used in place of l ₂ , etching could be performed in almost the same manner.

[0025]Example 2 In this embodiment, in the same gate recess processing,⁺
-GaAs layer 5 is Cl ₂/ NOCl (nitrosyl chloride)
This is an example of etching using. First, shown in FIG.
Wafer as a magnetic field microwave plasma etching device
Set, n as an example under the following conditions⁺-GaAs layer 5
Was etched.

Cl ₂ flow rate 10 SCCM NOCl flow rate 20 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GHz) RF bias power 10 W Wafer temperature 70 ° C.

In this step, the etching proceeds due to the action of Cl ^* produced from both Cl ₂ and NOCl.
The contribution of N ^*, the mechanism for stopping the etching, and the like are as described in the first embodiment. During the etching, a carbon-based polymer is generated due to a decomposition product of the resist mask 6, and a C—N bond or —N═O group (nitrosyl group) is introduced into this carbon-based polymer. This strengthened the structure. This carbon-based polymer contributes to the side wall protection together with GaN which is an etching reaction product, and the side wall protection effect is improved by such structural strengthening. Therefore, although the RF bias power was halved as compared with Example 1, similarly good anisotropic processing could be performed.

The subsequent steps of removing the AlN deposition layer 7, forming the gate electrode, etc. are as described in the first embodiment. The same etching could be performed when NOBr (nitrosyl bromide) was vaporized by He gas bubbling and used instead of NOCl.

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

The present invention is not limited to the HEMT manufacturing described above as long as the process requires selective etching of a laminated system of non-Al-containing / Al-containing compound semiconductors. For example, quantum holes or semiconductor laser devices. It can also be applied to the processing etc.

The composition of the etching gas is the same as that described above.
It is not limited. For example, a halogen-based active species
As the supply source, the above-mentioned Cl₂And HBr, BCl₃, B
Br ₃, Br₂As a source of nitrogen-based active species.
N of the statement₂Other than NO, N₂O, NO₂Various nitric oxide such as
Is supplied simultaneously with halogen-based active species and nitrogen-based active species
As a source, in addition to NOCl and NOBr mentioned above, NOCl₂
(Nitrosyl dichloride), NOCl₃(Nitrosi trichloride
Le), NO₂Cl (nitrile chloride), NOBr₂(Two odors
Nitrosyl chloride), NOBr₃(Nitrosyl tribromide), N
O₂Br (nitrile bromide) or the like can be used.

In addition, it goes without saying that the etching apparatus used, the etching conditions, the structure of the sample wafer, etc. can be changed as appropriate.

[0033]

As is apparent from the above description, according to the present invention, selective anisotropic etching of a laminated system of non-Al-containing / Al-containing compound semiconductors represented by a GaAs / AlGaAs laminated system is performed. It can be performed within a practical temperature range in which the resist mask can be used, and with excellent underlayer selectivity and anisotropy.

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

[Brief description of drawings]

[FIG. 1] n ⁺ in the gate recess processing of HEMT
FIG. 6 is a schematic cross-sectional view showing a wafer in which a resist mask is formed on a GaAs layer.

FIG. 2 is a plan view showing that the n ⁺ -GaAs layer of FIG. 1 is etched to form a recess, and A is formed on the exposed surface of the n ⁺ -AlGaAs layer.
It is a schematic sectional drawing which shows the wafer in the state in which the 1N deposition layer was formed.

FIG. 3 is a schematic cross-sectional view showing a wafer in a state where the AlN deposition layer is removed.

FIG. 4 is a schematic cross-sectional view showing a wafer in a state where an upper Al layer and a lower Al layer are respectively deposited on the surface of the resist mask and the bottom surface of the recess.

FIG. 5 is a schematic cross-sectional view showing a state where the resist mask and the upper Al layer on the surface thereof are removed, and the lower Al layer (gate electrode) is left only on the bottom surface of the recess.

[Explanation of symbols]

1 ... Semi-insulating GaAs substrate 2 ... epi-GaAs layer 3 ... AlGaAs layer 4 ... n ⁺ -AlGaAs layer 5 ... n ⁺ -GaAs layer 5a ... Recess 6 ... Resist mask 6a ... Opening 7 ... AlN deposition layer 8a ... Upper Al layer 8b ... Lower Al layer (gate electrode)

Claims (3)

[Claims] 1. A dry etching method for selectively etching a compound semiconductor layer containing no aluminum laminated on a compound semiconductor layer containing aluminum on a substrate, wherein the etching is halogen-based active species under discharge dissociation conditions. And an etching gas capable of generating nitrogen-based active species, and stopping by generating aluminum nitride on the exposed surface of the compound semiconductor layer containing aluminum. 2. The dry etching method according to claim 1, wherein the halogen-based active species is at least one of chlorine-based active species and bromine-based active species. 3. The dry etching method according to claim 1, wherein the aluminum nitride is removed using plasma of an inert gas after the etching is completed.