JPS6394629A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent a semiconductor substrate material vaporized by laser irradiation from adhering again on the sidewall surface of a recessed part by a method wherein a semiconductor substrate is installed in an atmosphere containing at least halogenated hydrogen of a pressure lower than the atmospheric pressure. CONSTITUTION:An airtight container 101 is provided with a transparent window 104 to laser light 105, gas introducing ports 107, 108 and 109 and a gas exhaust vent 110. There is a substrate supporting stand 102 provided with a heater 106 in the container and a GaAs substrate 103 is put on the substrate supporting stand 102. The GaAs substrate is installed in mixed gas obtainable by including 15 % of hydrogen chloride in nitrogen containing 5 % of hydrogen, a xenon chloride excimer laser is irradiated on the substrate surface and a laser precessing for a via-hole is performed. Moreover, in a state that the temperature of the GaAs substrate 103 is held at 400 degrees, the mixed gas is used in a depressed state that the pressure thereof is lower than the atmospheric pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a pie hole used in a microwave monolithic integrated circuit.

Prior Art In microwave monolithic integrated circuits, it is necessary to connect certain electrodes directly from the backside ground electrode of the integrated circuit board. As this method, there is a pie-hole electrode formation technique. Figure 4 shows a pie-hole electrode. In the same figure, 4
01 is a semiconductor substrate, 402 is an electrode on the surface of the substrate, 4
03 is a back ground electrode, and 404 is a pie hole.

As shown in the figure, an electrode 402 on the front surface of the substrate and a back surface ground electrode 403 are connected through a pie hole 404.

Chemical etching, plasma etching, etc. are used to manufacture such via holes, but the method of processing using a strong laser beam allows the cross-sectional shape of the via hole to be processed arbitrarily, and the processing speed is fast. It has recently come into use due to its advantages.

FIG. 5 shows the formation of a pie hole by laser processing. 5
00 is a laser beam that is irradiated from the back surface of the semiconductor substrate 401. Reference numeral 403 indicates the bottom of the pie hole 404. When the pie hole is formed by laser processing, the processing is stopped before the bottom 405 of the recess reaches the surface of the substrate, and the remaining substrate is processed by another method that has selectivity with respect to gold scraps. The semiconductor substrate is etched away by an etching method, for example, chemical etching or plasma etching, the back surface of the electrode is exposed, and the electrode is installed from the back surface of the substrate by vapor deposition and electroplating.

In such a method of forming a pie hole, it is required that the cross-sectional shape of the recess be trapezoidal as shown in FIG. 5, and that the side surfaces of the recess be smooth. In order to form an electrode (Fig. 4 402), a thin conductive IIq layer is formed from the back surface of the substrate using vapor deposition technology, and then gold (Au) of about 1 μm to 10 μm is deposited using electroplating technology.
In the process of forming an electrode film, if the cross-sectional shape of the recess is not trapezoidal with smooth side surfaces, the conductive film on the side surfaces formed by vapor deposition may be partially insulated and isolated into islands. This results in incomplete electroplating in the subsequent process. There are several methods for obtaining a trapezoidal cross section in laser processing, but a commonly used method is to proceed with processing by changing the beam shape and beam size of the processing laser. However, in forming a recess by laser processing according to the conventional technique, it is difficult to form a recess having a trapezoidal cross-sectional shape and smooth side surfaces for the following reasons.

As the depth of the recess increases, the semiconductor substrate material evaporated by laser irradiation re-adheres to the side walls of the recess. In particular, as a semiconductor substrate, III-based semiconductors such as GaAs
In the case of -V group compound semiconductors, the vapor pressure of group III elements is extremely low, making complete evaporation of the substrate material difficult. These redepositions not only form protrusions on the side walls of the recess by themselves, but also prevent the processing laser beam from uniformly irradiating the bottom of the recess. For this reason, unevenness occurs on the side wall surface of the recess, making it difficult to form a pie hole having a smooth trapezoidal shape. For this reason, the productivity of forming pie holes by laser processing was not as high as expected, which was a major problem in practice.

Problems to be Solved by the Invention In view of the above points, the problem to be solved by the present invention is that the semiconductor substrate material evaporated by laser irradiation re-adheres to the side wall surface of the recess. By preventing adhesion, a pie hole having a smooth trapezoidal shape as designed can be obtained.

Means for Solving the Problem A means for solving the problem in view of the above points is a method of etching the surface of a semiconductor substrate by irradiating the semiconductor substrate with a laser beam. by placing the semiconductor substrate in an atmosphere containing at least hydrogen halide, or desirably placing the semiconductor substrate in an atmosphere containing at least hydrogen halide at a pressure lower than atmospheric pressure; The temperature must be above room temperature.

In addition, in the method of corroding the surface of a semiconductor substrate by irradiating the semiconductor substrate with a laser beam, the semiconductor substrate is placed in a vacuum. In a method of etching a substrate surface, a semiconductor substrate is placed in a plasma atmosphere containing at least a halogen compound.

Effect The effect of the present invention is that by placing the processed substrate in an atmosphere containing hydrogen halide, the semiconductor material that has been melted at a high temperature or evaporated quickly becomes a halogen compound and diffuses into the atmosphere, as described above. This is to prevent the semiconductor material evaporated by laser irradiation from re-adhering to the side walls of the recess, and by placing the processed substrate in a high vacuum, the evaporation of the semiconductor material melted at high temperature is promoted, and the evaporated semiconductor material is The material quickly diffuses into the vacuum,
This is to prevent the semiconductor material evaporated by the laser irradiation described above from re-adhering to the side wall of the recess.Furthermore, by placing the processed substrate in a plasma atmosphere containing halogen compounds, it is possible to prevent the semiconductor material that has been evaporated from high temperature melting or evaporation. At the same time, by constantly activating the surface of the semiconductor substrate, it prevents the evaporated semiconductor material from re-adhering to the side walls of the four parts.

Example The present invention will be explained in more detail by way of examples.

FIG. 1 shows a first embodiment. In the figure, 101 is an airtight container with a window 104 transparent to the laser beam 105, gas inlets 107, 108, and 109, and a gas exhaust port 1.
It is equipped with 10. The container had a substrate support 102 equipped with a heater 106, and the GaAs substrate 103 used in the example was placed on the substrate support 102. Nitrogen, hydrogen, and hydrogen chloride were introduced from the gas inlets, respectively. Further, the heater 106 is used to heat the GaAs substrate.

In this example, 15
% of hydrogen chloride (HCI) in a mixed gas containing G
An aAs substrate was placed, and a xenon chloride (XeC1) excimer laser (wavelength: 306 nm) was irradiated onto the surface of the substrate to perform laser processing for forming a pie hole. As a result,
It was possible to significantly reduce the re-adhesion of the substrate material to the sidewalls of the recesses formed on the substrate.

In this case, the semiconductor substrate material that is evaporated or melted to a high temperature by the irradiation with the excimer laser beam 105 reacts with hydrogen chloride in the atmosphere and becomes gallium chloride and arsenic chloride, which fly away into the atmosphere without re-attaching to the substrate. It is thought that the

In this example, 5% hydrogen was mixed into the mixed gas, but this was for gettering of impurity oxygen (0°) in the atmosphere.

In this example, a mixed gas containing hydrogen chloride was used.
Similar effects can be expected with other hydrogen halides, such as hydrogen bromide (HBr) and hydrogen fluoride (HF). Particularly in the case of silicon semiconductors, hydrogen fluoride may be effective.

Furthermore, in this example, laser processing was performed while the temperature of the GaAs substrate 103 was maintained at 400 degrees.

This temperature is to promote the chemical reaction between the hydrogen halide and the semiconductor substrate, but since arsenic decomposes in GaAs semiconductors at high temperatures, a temperature of 400 degrees or less is desirable.

Furthermore, in this example, the pressure of the mixed gas was used in a reduced pressure state lower than atmospheric pressure. By laser processing in a mixed gas atmosphere under reduced pressure, gas molecules can be
Alternatively, since the diffusion rate of the reactive acid organisms increases, hydrogen halide is quickly supplied and the reactive acid organisms are removed even at the bottom of the recess for a deep Bayer hole, making it possible to minimize re-adhesion of the substrate material. I can do it.

Next, a second embodiment will be explained using FIG. 2.

In the figure, 201 is a vacuum container and a laser beam 205
A transparent window 204 is provided. Furthermore, GaAs
The substrate 203 was placed on a substrate support stand 202 having a heater 206 for heating the substrate. A vacuum exhaust port 207 is connected to a vacuum pump.

In this example, the inside of the vacuum container is lXl0-6T
While maintaining the vacuum level at a pressure of orr, and
Laser processing was performed by irradiating excimer laser light 205 with the cutting board temperature maintained at 400 degrees. As a result, re-adhesion of the substrate material to the sidewalls of the recesses formed on the substrate 203 could be significantly reduced.

The reason why we were able to significantly reduce the redeposition of the substrate material is that the substrate material melted in a high vacuum, especially the G
This is because in the case of a As s, the vapor pressure of Group III Ga was relatively increased, which promoted the evaporation of the material.

In this example, processing was performed in a high vacuum of 1×1 O−6 Torr, but it goes without saying that similar effects can be obtained at lower pressures.

Further, the heating of the substrate is to assist in the evaporation of the substrate material, and if a suitable protective film is used on the surface of the GaAs substrate, an even higher substrate temperature can be achieved.

FIG. 3 shows a third embodiment of the present invention. Reference numeral 301 is an airtight container equipped with gas inlets 308, 309, 310 and an exhaust port 311, and further equipped with a window 304 transparent to laser light 305. There is. A GaAs substrate 303 is placed on a substrate support stand 302 having a heater 307 for heating the substrate. Inside the airtight container, there is another electrode plate 306 facing the substrate support 302 as one electrode, and an AC power source 312 for applying a high frequency AC electric field to generate plasma discharge between these electrodes. . The GaAs substrate is heated to about 100 degrees, and a mixed gas of argon gas and carbon chloride fluoride gas (CG12F2) is introduced into the container at a pressure of about 0.5 Torr, which is turned into a plasma state by an alternating electric field. ing. In this state, excimer laser light 205 was irradiated to perform laser processing for forming a pie hole. As a result, it was possible to significantly reduce re-adhesion of the substrate material to the sidewalls of the recesses formed on the substrate, and a pie hole having smooth sidewalls was obtained.

Laser irradiation was able to significantly reduce the re-adhesion of the substrate material to the side walls of the recesses formed on the substrate in the plasma of chlorofluorocarbon gas because the chemical reaction of the halogen compounds was significantly accelerated by the generation of plasma. It is thought that the substrate material that was melted and evaporated quickly became a halide and was scattered without re-adhering to the side wall of the pie hole. In addition, in the plasma of chlorofluorocarbon gas, Ga
The As substrate is etched at an etching rate of 0.1 to 0.5 .mu.m/min, and therefore, even if the substrate material is reattached, it is considered that it is removed by the plasma.

In this example, plasma using a mixed gas of argon gas and chlorofluorocarbon gas (CC12F2) was used, but similar effects can be expected with mixed gases with other halogen compounds. Further, the reason why the substrate temperature was maintained at 100 degrees was to assist the evaporation of the substrate material.

Effects of the Invention By using the present invention, the substrate material is effectively melted and evaporated in laser processing for forming via holes using excimer laser light, etc., and the substrate material is prevented from re-adhering to the side wall. It was possible to form a pie hole with a smooth cross-section at high speed and efficiently.

[Brief explanation of the drawing]

101... Airtight container, 103... GaAs substrate, 1
05...Excimer laser light, 107.108.109
...Gas inlet, 201...Vacuum container, 203...
・GaAs substrate, 205... Excimer laser light, 20
7... Vacuum exhaust port, 301... Airtight container, 303...
...GaA sj & plate, 305... Excimer laser light, 302.306... Electrode for plasma generation, 308
．． 809.310...Gas inlet, 312...RF
power supply.

Claims (5)

[Claims] (1) A method for etching the surface of a semiconductor substrate by irradiating the semiconductor substrate with a laser beam, the semiconductor device being characterized in that the semiconductor substrate is placed in an atmosphere containing at least hydrogen halide. Production method. (2) The method for manufacturing a semiconductor device according to claim 1, wherein the semiconductor substrate is placed in an atmosphere containing at least hydrogen halide at a pressure lower than atmospheric pressure. (3) The method for manufacturing a semiconductor device according to claim 1 or 2, wherein the temperature of the semiconductor substrate is room temperature or higher. (4) A method for manufacturing a semiconductor device, in which the surface of the semiconductor substrate is corroded by irradiating the semiconductor substrate with a laser beam, the semiconductor substrate being placed in a vacuum. (5) In the method of etching the surface of the semiconductor substrate by irradiating the semiconductor substrate with a laser beam, the semiconductor device is characterized in that the semiconductor substrate is placed in a plasma atmosphere containing at least a halogen compound. Production method.