JPS62122141A - Checking method for semiconductor substrate - Google Patents

Abstract

PURPOSE:To enable the detection of an unbonded part irrespective of the impurity concentration of a wafer on the reverse side, by applying an infrared ray onto one surface of a semiconductor substrate and by detecting the infrared ray reflected therefrom to measure the reflection intensity distribution on the semiconductor substrate. CONSTITUTION:An infrared ray 4 is made to fall on one surface of a sample 3 to be checked which is obtained by bonding a wafer 1 of high impurity concentration and a wafer 2 of low impurity concentration together, and the intensity of reflection 5 therefrom is measured. The infrared ray entering the sample to be checked is reflected partly by a bonding interface 6, and this reflection is stronger in an unbonded part than in a bonded part. Accordingly, the unbonded part can be detected by measuring the intensity of the reflected infrared ray.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for inspecting a semiconductor substrate obtained by bonding two semiconductor wafers together.

[Technical background of the invention and its problems]

When polishing strips of mirror-polished silicon or other semiconductor wafers are brought into contact with each other in a clean atmosphere and subjected to heat treatment, the two will firmly stick together and a bonded semiconductor substrate will be obtained. The substrates bonded in this manner are thermally and chemically stable because no foreign matter such as adhesive is present. If this semiconductor wafer contact-R method is used, semiconductor substrates with a pn structure or an n''/n- structure used in device manufacturing can be easily obtained.

However, when bringing the polished surfaces into contact, if foreign matter such as dust is present 7 or if the polishing is not good, that part will not stick and will remain an unbonded part.

When a device is manufactured using bonded semiconductor substrates, any device that hits the unbonded portion will of course be defective. Not only that, but during the device manufacturing process 2, such as polishing or high-temperature heat treatment, the unbonded portions may crack and peel off, and in the worst case, the manufacturing equipment itself may break.

Therefore, the semiconductor substrate obtained by bonding the wafers is
It is necessary to inspect whether there are any unbonded parts inside before proceeding to the next step.

One possible method for inspecting bonded semiconductor substrates is to transmit infrared rays through the silicon substrate and determine unbonded areas from the in-plane distribution of the intensity; however, this method requires infrared rays to be transmitted through the semiconductor substrate. , substrates with high impurity concentrations cannot be inspected.

When applying semiconductor wafer bonding technology industrially,
For example, a high-concentration p-type wafer and a low-concentration n-type wafer may be bonded to form a p''/n-structure, or a high-concentration and a low-concentration n-type wafer may be bonded to form an n''/n-structure. 1. Conventional inspection methods that transmit infrared rays cannot be used for semiconductor substrates with such structures, where one side of the wafer often has a high concentration of impurities.In order to apply adhesive technology industrially, a new inspection method was developed. A method was needed.

Furthermore, even for semiconductor substrates made by bonding wafers with low impurity concentrations, conventional inspection methods require placing an infrared source and a detector on both sides of the semiconductor substrate in order to transmit infrared rays. There were problems with the installation space and how to hold the sample during inspection.

[Purpose of the invention]

The present invention makes it possible to detect unbonded parts of semiconductor substrates obtained by bonding, even if the impurity concentration on one side of the wafer is high. The purpose is to provide a testing method for

[Summary of the invention]

An overview of the present invention will be explained with reference to FIG. The present invention is characterized in that infrared rays (4) are incident on one surface of the test sample (■) obtained by bonding a high impurity density wafer (■) and a low impurity concentration wafer (■), and the intensity of the reflected light (■) is measured. do. At this time, the infrared rays are made to enter from the low impurity concentration wafer side.

The ability to detect unbonded parts using this method is based on the following principle. That is, a portion of the infrared rays incident on the sample to be inspected is reflected at the bonded interface 0, but this reflection is stronger in the unbonded portion than in the bonded portion. Therefore, by measuring the intensity of reflected infrared rays, it is possible to determine the unbonded areas.

Although a sample in which wafers with different impurity concentrations are bonded together has been described, the inspection method of the present invention is not limited to this, and can also be applied to samples in which wafers have the same impurity concentration. That is, it is sufficient that the wafer on the side where the infrared rays are incident will pass the infrared rays. This limit varies somewhat depending on the type and thickness of the wafer, the wavelength and intensity of the infrared rays, and the performance of the infrared detector, but if the impurity concentration is 10i7 cm-' or less, the unbonded portion can be detected.

The wavelength of the infrared rays used may be any wavelength that can be transmitted through one side of the wafer. However, InSb and Cd1 are used for infrared detection.
Since 1gTe is often used, the wave intensity to which the detector is sensitive is 1.5 μm to 6 pm for InSb, Cd11
For gTe, 1.5 to 15 μm is practical.

The sample can be held during inspection by, for example, fixing the back side with a commonly used vacuum chuck, or even leaving it on a wafer transport belt, and no special jig is required.

〔Effect of the invention〕

In the semiconductor substrate inspection method of the present invention, infrared rays that pass through one side of the bonded wafer and are reflected at the bonded interface are detected.

Therefore, the unbonded portion can be detected regardless of the impurity concentration of the wafer on the opposite side.

In addition, in this inspection method, the infrared source and detector are placed on the same side of the sample, so there are fewer spatial restrictions when installing the inspection device compared to conventional methods that transmit infrared rays.

As described above, the semiconductor substrate inspection method of the present invention has great effects in industrially applying direct bonding technology.

[Embodiments of the invention]

An n-type silicon wafer with an impurity concentration of 101s101s and a thickness of 380 μm and an impurity concentration of 101014a',
) An n-type silicon wafer with a height of 380 μm was directly bonded to create a semiconductor substrate as a sample to be inspected. At this time, adhesion, which is normally performed in a clean atmosphere of class 2 or lower, was performed at class 1000 to prevent unbonded areas from forming due to the presence of dust.

Next, this test sample, an infrared source, and an infrared detector were arranged as shown in FIG. In FIG. 1, ■ is a sample, ■ is an infrared source, and (8) is an infrared detector. The infrared source was a black-painted copper plate heated to 50℃, and the detector was a commercially available infrared &! Thermometer “A G A ther”
+++ovision 680'' was used.

In images obtained with an infrared thermometer, areas with strong reflected infrared rays appear relatively white, and areas with weak reflected infrared rays appear relatively black. The edge of the wafer is beveled, so it is not bonded, and the reflected infrared intensity in this area is strong.

An unbonded area with strong reflected infrared ray intensity was also detected inside the bonded substrate from the center to the right.

For confirmation, this bonded substrate was diced with a diamond plate at a pitch of 1 mm, and the parts with high reflection intensity were peeled off and not bonded.

For comparison, an infrared ray @ (17), a sample (13), and a detector (18) were arranged as shown in Figure 2, and an attempt was made to conduct an inspection using infrared transmission, but no unbonded portion could be detected.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the semiconductor substrate inspection method of the present invention;
FIG. 2 is a diagram showing a conventional inspection method. 1...High concentration wafer 2...Low concentration wafer 3
．． 13... Semiconductor substrate to be inspected 4, 14... Incident infrared rays 5... Reflected infrared rays 6... Direct adhesive interface 7.17... Infrared source 8, 18... Detector agent Patent attorney Nori Chika Yudo Shi Kikuo Takehana

Claims (5)

[Claims] (1) A method for inspecting a semiconductor substrate, which comprises irradiating one surface of the semiconductor substrate with infrared rays, detecting the reflected infrared rays, and measuring the reflection intensity distribution on the semiconductor substrate. (2) The method for inspecting a semiconductor substrate according to claim 1, wherein the semiconductor substrate is made by directly bonding two semiconductor wafers. (3) The method for inspecting a semiconductor substrate according to claim 1, wherein the infrared rays are irradiated from the wafer side of the semiconductor substrate where the impurity concentration is not high. (4) The method for inspecting a semiconductor substrate according to claim 2, wherein the impurity concentration of at least one of the two directly bonded wafers is 10^1^7 cm^-^3 or less. . (5) The method for inspecting a semiconductor substrate according to claim 1, wherein the wavelength of the infrared rays is 1.5 to 15 μm.