JPS6366931A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE: To stop laser beam machining immediately before a recessed section is penetrated, and to improve the productivity of laser beam machining by estimating the thickness of a semiconductor substrate in the bottom of the recessed section by the intensity of transmitted beams where second beams overlapped to the optical path of laser beams for machining are transmitted through the substrate. CONSTITUTION:When a groove or a recessed section is formed from the surface of a semiconductor substrate 101 by irradiating the semiconductor substrate 101 with laser beams 102, second beams 105 different from said laser beams 102 are overlapped to the optical path of laser beams 102, and the thickness of the substrate in the bottom of the recessed section 103 is estimated by the intensity of transmitted beams where second beams 105 are transmitted through the semiconductor substrate 101. A semi- insulating GaAs substrate is used as the semiconductor substrate 101, pulse beams having a wavelength of 280nm by an excimer laser as laser beams 102 for machining, an infrared laser as the second beams 105 and a photomultiplier as a detector 106. Laser beams for machining are stopped when an output from the detector reaches a fixed value, thus stopping etching immediately before the recessed section for a viahole is penetrated.

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 2 shows a pie-hole electrode. In the same figure, 2
01 is a semiconductor substrate, 202 is an electrode on the surface of the substrate, 2
03 is the back ground ti, and 204 is the pie hole.

As shown in the figure, the electrode on the front surface of the substrate and the ground electrode on the back surface are connected by 205.

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

Figure 3 shows the formation of a pie hole by laser processing, 2
01 is a semiconductor substrate, and 301 is a laser beam irradiated from the back surface of the semiconductor substrate. 302 is the bottom of the pie hole, 303 is the surface electrode used in the integrated circuit,
When forming a pie hole by laser processing, the processing must be stopped before the bottom of the recess reaches the surface of the substrate.This means that if the recess is penetrated by laser processing, the electrodes formed on the surface will also be exposed to the laser beam. be melted or sublimated. This poses a major obstacle to electrode formation. Therefore, the laser processing for forming the pie hole is stopped just before the recess penetrates, and the remaining substrate is etched using other etching methods that have this selectivity.
For example, the semiconductor substrate must be etched away by chemical etching or plasma etching to expose the backside of the electrode.

However, stopping the laser processing just before the bottom of the recess reaches the substrate surface is a round-trip process for the following reason.

(1) During laser processing, it is difficult to estimate the etching rate of the substrate as a reproducible and accurate value due to changes in the focal length due to vertical movement of the processing surface and re-deposition of the molten substrate material that occurs during processing. Can not.

(2) Since the bottom of a recess formed by laser processing is not necessarily flat, the recess often penetrates locally.

For these reasons, the productivity of laser processing has been extremely low, which has been a major problem.

Problems to be Solved by the Invention The problems to be solved by the present invention are that in laser processing, there is no efficient means to stop the processing immediately before the recess penetrates, so the productivity of laser processing is low. That is the point.

Means for solving the problem In view of the above points, a means for solving the problem is to irradiate the semiconductor substrate with a laser beam serving as the first beam to form grooves or recesses from the surface of the semiconductor substrate. In the forming method, a second light beam different from the laser beam is superimposed on the optical path of the laser beam, and the second light beam determines the thickness of the substrate at the bottom of the groove or recess depending on the intensity of transmitted light passing through the semiconductor substrate. The present invention is to use a semiconductor device manufacturing method characterized by estimating .

The present invention utilizes the phenomenon that the intensity of transmitted light passing through a semiconductor substrate is inversely proportional to the thickness of the substrate, and as the thickness of the substrate at the bottom of the recess formed by laser processing becomes thinner as processing progresses, Since the transmitted light intensity at the bottom of the recess increases, it becomes a good monitor of the substrate thickness at the bottom. In general, if α is the absorption coefficient of light in a semiconductor, then the thickness of the substrate d
This relationship is pcxexp(-αd), but by appropriately selecting the wavelength, the transmitted light intensity can be sufficiently varied.

Example An embodiment according to the present invention will be described with reference to FIG.

101 is a semiconductor substrate, 102 is a laser beam that is the first beam for processing, 103 is the bottom of a recess made by laser processing, 104 is a surface electrode, and 105 is a second laser beam according to the present invention. 106 is a detector that measures the transmitted light intensity of the second laser beam. In this example, semi-insulating GaAs is used as the semiconductor substrate.
As the laser beam for processing the substrate, pulsed light having a wavelength of 280 nm produced by an excimer laser using xenon chloride was used. As the second laser beam, an infrared laser was used in consideration of the transmission characteristics of the semiconductor substrate.

Furthermore, a commonly used photomultiplier was used as a detector for measuring the transmitted intensity of the infrared light.

The laser beam A11l102 is superimposed on the second laser beam 105, and processing is started. At the beginning of processing, most of the laser beam 105 is absorbed by the semiconductor substrate because the substrate is sufficiently thick, and no output appears on the detector, but as processing progresses, the amount of laser beam NjA 105 transmitted increases. The output from the detector increases. By stopping the processing laser beam when the output of the detector reached a predetermined value, it was possible to stop etching just before the recess for the pie hole penetrated.

In the embodiment, a laser beam is used as the second light beam, but it is clear that the second light beam is not limited to a laser beam. Any light can be selected depending on the transmission characteristics of the material to be processed, but similar effects can be expected in either case.

Effects of the Invention According to the present invention, a reproducible and highly productive processing method for forming a groove or a recess for forming a pie hole by laser processing has been realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the step of forming a piere hole according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the piere hole, and FIG. 3 is a diagram illustrating laser processing according to the prior art. 101...Semiconductor substrate, 102...Laser beam 103...Bottom of recess, 104...Surface metal electrode 105...Second laser beam, 106...Second laser beam laser beam detector. Name of agent: Patent attorney Toshio Nakao II

Claims (1)

[Claims] In a method of forming grooves or recesses from the surface of a semiconductor substrate by irradiating the semiconductor substrate with a first laser beam, a second light beam different from the laser beam is superimposed on the optical path of the laser beam. . A method of manufacturing a semiconductor device, characterized in that the thickness of the substrate at the bottom of the recess is estimated based on the intensity of light transmitted through the semiconductor substrate by the second light beam.