JPS63136526A - Dry etching method - Google Patents

Abstract

PURPOSE:To form an etching through-hole to a forward tapered shape by adding nitrogen gas into the mixed gas of BCl3 gas and Cl2 gas in a dry etching method for a compound semiconductor base body using the mixed gas as an etching gas. CONSTITUTION:An SiO2 film 2 as an etching mask is deposited onto the rear of a GaAs semiconductor base body 1, the film 2 is removed selectively and a hole is bored, and the rear is exposed. A protective film 3 consisting of a metal as an etching stopper such as Au/Pt/Ti is formed. The sample is admitted into a chamber for a reactive ion etching device, inside of the chamber is evacuated and N2 gas is introduced, and BCl3 gas and Cl2 gas are respectively induced at the rates of 20CC/min and 2CC/min. Displacement is adjusted so that pressure in the chamber at that reaches 1.7Pa. RF power is applied and the gases are activated, and an SiO2 mask opening section is etched and a through- hole 4' is shaped to the GaAs base body 1. Accordingly, the through-hole 4' is formed to a forwardly tapered shape, thus shaping a via hole having a complete electrical connection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for dry etching a compound semiconductor substrate, and particularly to the components of an etching gas.

(Prior technology) The so-called dry etching force method, which etches a semiconductor substrate in a gas, has superior microfabrication performance and reproducibility compared to the conventional Couette etching force method, and also has less uneven etching and is easier to use in post-processing. It has many advantages, such as being less susceptible to contamination because it does not require the use of large amounts of water. Furthermore, in the dry etching method, when etching is performed with a mask selectively provided, it is possible to reduce etching in the direction of lateral force on the semiconductor substrate in contact with the mask, that is, side etching. This method is attracting attention as a method that allows the cross-sectional shape to be enlarged to a nearly vertical shape. For this reason, it is widely used as a gross process in the recent semiconductor device manufacturing process, for example, GaAs
It has become an indispensable technology for processing semiconductor substrates and forming electrodes in the production of MMICs.

As an example of using dry etching, the process of forming a peer hole in a semiconductor substrate will be described. Pier hole is PET
In order to reduce the source inductance of a semiconductor substrate, a hole is opened that penetrates from the back surface to the surface, and this hole is filled with source metal to connect the source electrode on the front side and the back surface of the substrate by electrostatic fishing. Reactive 1' on-entetching (RIE), which is a vertically etchable natri etching method, is effective. Peerhole formation by RIE is described in, for example, "J, Vac, Sci, Techn.
ol, B3 fl) Jan/Feb 1985
, P 355-'4.

Below, as a conventional example of the present invention, GaAs was prepared by the R, IE method.
A case will be described in which a through hole for forming a peer hole is formed in the base body. Conventionally, in order to form a pier hole in a ()aAs substrate, 70·n12 (CC12F2) gas,
A mixed gas of CCl2F2 gas and 02 gas, and a mixed gas of BCg3 and C1 have been used. Here, we will discuss the case of forming through holes using a mixture of B C13 and C20 with less etching residue.
This will be explained using the process cross-sectional view in Figure tc).

As shown in Figure 3 (ta), the surface orientation is (100) and the thickness is 10.
A 5i01 film 2 serving as an etching gas is deposited on the surface of a 0 μm (jaAs conductive substrate), and this SiO□ film 2 is selectively removed to open a 30 μm true hole and expose the surface of the GaAs substrate 1. do.

Further, a protective film 3 is provided on the surface of the GaAs substrate 1 to prevent the etching gas from going around during the etching process. Next, this Ga
After putting the As substrate 1 into the etching chamber A and performing vacuum evacuation, the B C1 gas and the C1 gas were heated to h20C.
C/min, 2CC/min. Then R
, F' is applied with a force of, for example, 480 W to activate the gas, and the back surface of the selectively exposed GaAs substrate is exposed as shown in Fig. 3fb.
), tc) are formed.

Here, the through hole 4 seen from the direction of Figure 3fb)
01 analysis diagram, and FIG. 3(C) is a sectional view of the through hole 4 seen from the <011> direction. As shown in Figure 3 (bl), B (1) The platform is etched with a mixed gas of gas and C12 gas to form a through hole 4. The shape of the through hole is a reverse taper, that is, the 5iO1 film on the side wall of the through hole. The angle θ with respect to 2 becomes an acute angle.If the etched Wr surface shape becomes inversely tapered in this way, after forming the through hole, in the step 2 of electrically connecting the source metal parts to each other by vacuum evaporation,
The electrical connection is incomplete because the deposited metal does not spread throughout the through hole.

In addition, as shown in Fig. 3 (tc), in the conventional method, the etching spreads greatly in the direction of the lateral force, and the side etching tC3
In figure fc)! ) is 40 μm compared to 100 μm in the case of wet etching, which is an improvement, but is still insufficient.

Therefore, when forming a through hole by etching, it is necessary to widen the interval between the mask openings in order to avoid overlapping other adjacent through holes. This poses a problem in that in order to form a peer hole, it is necessary to design a FET pattern by widening the distance between the source electrodes of the FET, which increases extra source resistance and source inductance. Furthermore, the degree of integration decreases significantly in terms of pattern arrangement, and the degree of freedom for high-density design is lost.

(Problems to be Solved by the Invention) As mentioned above, when a through hole for forming a pier hole is formed using a mixed gas of B C1 gas and CI gas used in the conventional dry etching method, There are problems in that the holes have a reverse taper shape and the side etching is large, resulting in incomplete electrical connections and failure to improve the degree of integration.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a dry etching method for a compound conductor substrate using BCI as an etching gas and a mixed gas of gas and C6 gas. An object of the present invention is to provide a dry etching method characterized by adding nitrogen gas to the dry etching method.

(Function) The present inventor applied the above-mentioned method to the process of forming pi-γ holes in a GaAs substrate. Figure 1 shows the results.
The through hole formed in the GaAs substrate has a tapered shape when viewed from the <O]1> direction as well. It is assumed that this is because N2 gas reacts with BCl3 gas to generate BN, which suppresses etching, resulting in a larger amount of etching on the exposed surface of the GaAs substrate than on the opposite surface, forming a tapered shape in the order of the through hole i. be done.

(Example) The following is an example of an uninvented implementation sequence.℃, the same as the conventional example ((J
The case of forming a through hole in an aAs semi-integrated substrate will be explained with reference to the drawings. In the present invention, G shown in FIG.
a As semiconductor substrate 1 is used. That is, G a A S with plane orientation (100) and thickness G ] 00 ttm
5i0 which becomes an etching mask on the back side of [4 body base]
2 film 2 is deposited, and this 5i02 film 2 is selectively removed to open a 30 μml hole to form a GaAs substrate]
expose the back side of. Further, when penetrating the surface of the GaAs substrate 1, a metal, for example A u / P, is used as an etching stopper to prevent the etching gas from going around.
A storage odor 3 consisting of T/T i is provided.

Therefore, this sample is placed in a chamber of an RIE apparatus, and the pressure in the chamber is evacuated to 5×10 Pa or less to remove impurity gas. Next, add N2 gas to a pressure of 7X10.
After stirring in the chamber until Pa, B (J
3 gas and C/2 gas at 20 CC/min each, 2 CC
/min into the chamber. At this time, the exhaust volume is adjusted so that the pressure inside the chamber is 1.7 Pa. Next, the BP' electric power was changed to 480W, 711W to activate the gas, and the 5iOz mask opening was etched for 60 minutes to form the through hole 4' in the GaAs substrate 1.

The shape of the cross section of the through hole obtained in this way is as shown in FIG. In addition, the shape of the through hole 4' when viewed from the 01]> direction also becomes a forward taper similar to that shown in Fig. 1.This is because the N2 gas reacts with the B(J, gas). B.N.
is generated and etching is suppressed, resulting in Q a
A s 4G, it is estimated that there are more etched lids on the exposed side of the body 1 than on the opposite side, and the through hole 4' is formed in a downwardly tapered shape.

Therefore, since the through-hole 4' is formed in a downwardly tapered manner, the metal deposited when vacuum evaporation is performed from the forehead on the GaAs substrate 101 in the post-process of electrically connecting the source metals to each other is It becomes possible to form a pier hole that extends throughout the through hole 4' and has a complete electrical connection.

FIG. 2 (ta+, tb) is a plan view when the through hole 4' is formed in the GaAs substrate 1 by the above method.
Figure (a): This is a view from the front side with the protective film 3 removed to expose the through hole 4', and Figure 2+b) is a view from the back side.
FIG. 3 is a diagram showing a view through the iO1 membrane. As shown in FIG. 2(a), the surface shape of the through hole 4' is 30 nm in diameter, which is the same shape and size as the etching mask diameter. Also, the shape of the back side is the dotted part of the etching mask diameter (Figure 2 + b))
30μml, the brunt of the through hole 4' is 60μml
It is. Therefore, the side etching current is 15 μm, which is significantly reduced compared to the conventional method.

In addition, although the inventor repeated the same experiment several times, the shape of the through hole 4' always had a cross section of I$1'r- as shown in FIG.
In the bar, the planes are a, b, as shown in Figure 2 (a), tb).
It was confirmed that the effects of the present invention can be obtained with extremely good reproducibility.

Note that when adding N2 gas to a mixed gas of B(1) gas and C12 gas, the i of the N2 gas varies depending on the etching conditions of the dry etching device, so the optimum amount should be determined according to these conditions. Furthermore, it has been found that side etching increases when N2 gas is added in an amount greater than the appropriate weight.

Further, in the above-described embodiment, a case was shown in which an ordinary IE apparatus was used as the etching apparatus, but the present invention is not limited to the etching apparatus in any way, but may be performed using another apparatus using BCl gas and C12 gas, for example. A similar effect can be obtained by using a reactive ion beam etching (RIBE) device or the like. Further, the semi-solid substrate subjected to heat treatment is not limited to GaAs, and the invention can be applied to a wide range of compound conductor substrates in general.

〔Effect of the invention〕

As described above, according to the present invention, BCl2 gas and C1
By dry etching the compound semiconductor substrate by adding N and gas to the mixed gas, the etched through hole is formed in a forward tapered shape. It is possible to provide a dry etching method suitable for forming.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a through hole formed by the dry etching method according to the present invention, viewed from the (011) direction, and FIG.
0), FIG. 2(b) is a plan view of the plane orientation (100) and 2 of the through hole formed according to the present invention, and FIG. It is a process sectional view of the bent hole. 1-=GaAs#-j4 body substrate, 2.-Si02 film, 3..4 film, 4.4'... through hole. Agent Patent Attorney Chika Nori Yudo Takehana Kikuo Kaya 1 Kuchino 59L & Father-in-law 2ro

Claims (1)

[Claims] A dry etching method for a compound semiconductor substrate using a mixed gas of boron trichloride gas and chlorine gas as an etching gas, characterized in that nitrogen gas is added to the mixed gas.