JPH05275508A - Method for evaluating contacting boundary of bonded semiconductor wafer - Google Patents

Abstract

PURPOSE:To provide a method for evaluating the contacting boundary of a bonded wafer, such as an SOI wafer, etc., by which the presence/absence o microscopic crystalline distortion which occurs at the contacting boundary can be discriminated in a short time in a nondestructive, noncontacting, and noncontaminative state. CONSTITUTION:The presence/absence of microscopic crystalline distortion at the contacting boundary of a bonded semiconductor wafer is discriminated by utilizing such a significant difference that the number decreasing speed of exciting electrons at the contacting boundary becomes faster at a part where the microscopic crystalline distortion exists than a normal part and the lifetime of the wafer becomes shorter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor wafer such as an SOI wafer manufactured by a bonding method, which has a microscopic crystalline strain which is likely to occur at the bonding interface when the wafer is bonded. The present invention relates to a method for evaluating a bonded interface of a bonded semiconductor wafer by measuring a lifetime for confirming the presence or absence of the bonded semiconductor wafer.

[0002]

2. Description of the Related Art An SOI structure in which a silicon single crystal is grown on an insulator has hitherto attracted attention due to its high withstand voltage and high speed. In recent years, a bonded wafer having an SOI structure, which has a large area, has no crystal defects, and is capable of freely controlling the specific resistance, the oxygen concentration, and the like, has come to be obtained. This bonded SOI wafer has advantages such as good crystallinity in the device manufacturing region, stable interface by using the thermally oxidized side interface as the device side, and easy mass production. There is.

However, since the bonding step for obtaining such an SOI wafer is performed immediately after washing for imparting hydrophilicity, silanol groups (Si-OH) existing on the surfaces of two semiconductor wafers before bonding are used. And hydrogen ions are likely to react due to heat treatment after bonding to cause defects such as voids (air bubbles). Furthermore, in addition to these relatively large defects, microscopic crystalline strain generated at the bonding interface due to uneven adhesion force during bonding must be checked in the inspection process.

In order to reduce the defective rate of products, it is preferable to detect these defects by inspecting all products. For that purpose, an inspection method that can be performed in a non-contact, non-destructive, and non-contamination state is required. .. As an inspection method satisfying these conditions, an infrared transmission method, an ultrasonic flaw detection method, an X-ray topography method and the like have been developed, and these are effective for detecting voids which are relatively large defects. For example, as disclosed in JP-A-62-122141, a method utilizing a difference in reflected light intensity of irradiated infrared light between a normal portion and a bubble portion, which is disclosed in JP-A-62-122142. When a semiconductor wafer is irradiated with ultrasonic waves as if there is a bubble portion at the bonding interface, a reflected wave with a time difference between the front and back surfaces and the non-bonded portion (bubble portion) is used. As disclosed in Japanese Patent Application Laid-Open No. 2-106052, there is proposed a method of acquiring a Langtopograph of a bonded wafer using X-rays and processing an image thereof to detect an unbonded portion. ..

[0005]

According to the above method, relatively large defects such as bubbles can be effectively detected, but microscopic defects such as crystalline strain cannot be detected. Only, the X-ray topograph method is effective for detecting concentric crystal distortion as shown in FIG. However, according to this method, it takes a huge amount of time to obtain the data, and X
Since there is a limit to the installation location of the line scanning device and the measurement is performed in a room under normal conditions, the bonded wafer as a sample is easily contaminated and has a drawback that it is close to destructive inspection. As a result of these, it is desired to develop a simple and reliable inspection method capable of performing non-contact, non-destructive, and non-contamination determination of the presence or absence of concentric microscopic crystalline strain at the bonded interface of a bonded wafer. ing.

[0006]

Such problems are achieved by the present invention described below. That is, in the present invention, the bonded semiconductor wafer obtained by bonding two semiconductor wafers, for example, the presence or absence of crystallographic strain occurring at the bonding interface of an SOI wafer, is irradiated with a laser beam, for example. This is detected by measuring the recombination lifetime of the carriers generated.

[0007]

When an Ar laser, for example, is irradiated onto the surface of a bonded silicon wafer, the electrons excited from the valence band of silicon to the conduction band by the energy of the laser light pass after about 10 ^-6 seconds. It recombines with holes in the valence band and disappears. From the peak concentration of this excited electron, 1 /
The time until the concentration decreases in e is the recombination lifetime (τ _R ). Here, since the excited electron recombination is easier in the lattice defect portion of the wafer having a lattice shape distortion than in the crystal structure portion of the wafer having a normal lattice shape, the lifetime of the excited electron is It is short and therefore has a short lifetime. Therefore, when this lifetime is measured, as shown in FIG. 1, there is a significant difference in lifetime between a normal wafer and a wafer having crystalline strain. Therefore, the presence or absence of crystalline strain is determined from the data. be able to.

The specific constitution of the present invention will be described in detail below. The SOI wafer obtained by bonding and bonding two silicon wafers with a thermal oxide film to which the evaluation method of the present invention is applied intervenes has good crystallinity in the device manufacturing region, and the interface on the thermally oxidized side is stable. A wide range of applications are expected due to the fact that it is easy to mass-produce. In bonding the SOI wafers, first, two hydrophilically treated silicon wafers are directly superposed and bonded by hydrogen bonding or van der Waals force. Then, the superposed wafers are heat-treated at a high temperature of 1000 ° C. or higher to complete the bonding. Finally, surface grinding, polishing,
Alternatively, one wafer is processed to a desired thickness (1 to 10 μm) by etching. If the conditions of the bonding step are insufficient, the above-described defects may occur at the bonding interface, but the present invention can detect the presence or absence of microscopic crystalline strain, which has been difficult in the past. , By measuring the recombination lifetime of the bonded wafer. This recombination lifetime may be measured by a usual method. That is, the laser light may be irradiated from one surface of the bonded wafer to excite electrons, and the time from the peak concentration of the excited electrons to the concentration of the excited electrons of 1 / e may be measured. As described above, when the crystalline strain is present at the bonding interface, the lifetime is shortened, so that the presence / absence can be determined. Furthermore, there is a great advantage that measurement and detection can be performed without polishing one wafer to about 1 to 10 μm as in the case of measuring a thermal wave signal. The lifetime measurement method includes a reflection microwave method, a capacitance probe method, a coaxial cable method, a strip line method, an additive eddy current method, and the like.

To determine whether or not the measured data is due to the crystalline strain at the bonding interface, a silicon wafer having no crystalline strain at the bonding interface and a sample wafer (bonded wafer) to be measured are prepared. Data (lifetime) is obtained, these data are compared, and when a difference is recognized between the data, it may be determined that this difference is the data of the crystalline strain between the interfaces. It should be noted that the confirmation as to whether or not the crystalline strain exists at the bonding interface of the wafer to be measured can be performed in advance by the X-ray topography method. Also,
Lifetime is measured at multiple measurement points on the wafer.
It is preferable to measure the points arranged at regular intervals in the radial direction of the wafer. Here, as the excitation light, a laser light having a wavelength longer than the band gap of the semiconductor forming the wafer to be measured, for example, a silicon wafer having a wavelength of 904 nm or more is used.

The lifetime (τ
_{Since R} ) shows a significant difference between the presence and absence of crystalline strain at the bonded interface, the evaluation method of the present invention is very effective in determining the presence or absence of crystalline strain. Particularly, the present invention is
It is effective for detecting concentric crystal distortion that may occur when two wafers are bonded together. Further, the present invention is
Since the measurement can be done in a clean room, it is completely non-destructive,
The measurement can be performed in a non-contact and non-contaminated state. The evaluation method of the present invention is applicable not only to SOI wafers but also to bonded wafers in which wafers having no oxide film are bonded to each other, or to all semiconductor wafers having a two-layer structure such as an epitaxial wafer. It is possible.

[0011]

EXAMPLES Examples of the present invention will be described in detail below.

The surface of the P type mirror-polished (10
0), caliber 5 inch, thickness 620 μm, specific resistance 3Ω · c
m, oxygen concentration [Oi] <1.5 × 10 ¹⁸ cm ^-3 (old AS
TM) two silicon wafers are prepared. These two silicon wafers were laminated and bonded at room temperature. Then, the two silicon wafers are integrated by a heat treatment at 1100 ° C. for 120 minutes to bond the wafer 1.
Got Further, two silicon wafers produced under exactly the same conditions as the bonded wafer 1 are also laminated and bonded to each other to obtain another bonded wafer 2
Got The bonded wafer 1, which is bonded in this way
When 2 was evaluated by the X-ray topography method, it was confirmed that they were exactly the same except that concentric crystal strain was present at the bonded interface of the bonded wafer 1. 2 and 3
Are XRT photographs of the bonded wafer 1 and the bonded wafer 2. Then, a plurality of samples are prepared for each of the bonded wafers 1 and 2, and a device-formed side surface of which is polished to a thickness of about 5 μm and a surface of which is bonded without being polished. Got ready. Further, as a pretreatment, these four kinds of bonded wafers 1 and 2 are mixed with an aqueous solution of HF / pure water = 1: 5.
It was immersed for 0 seconds, and then rinsed with pure water for 3 minutes. Then, the recombination lifetime of each of the bonded wafers 1 and 2 was measured as follows.

First, a laser beam (from the front surface or the back surface of the wafer) is applied to a predetermined position of each of the bonded wafers 1 and 2. The irradiation conditions are as follows. Beam source: laser diode Beam diameter: 0.2 mm (when irradiated from the front surface of the wafer) 2.0 mm (when irradiated from the back surface of the wafer) Wavelength: 904 nm This laser light is applied in the radial direction of the bonded wafers 1 and 2 (OF
The measurement spots were set and irradiated at a pitch of 5 mm along (in the direction parallel to) and the recombination lifetime (τ _R ) was measured at 21 points in total. The lifetime was measured by the reflection microwave method. The lifetime is measured by irradiating the spot with a microwave of 10 GHz after laser light irradiation and measuring the signal intensity of the microwave.

FIG. 1 shows the result of this measurement. In the figure, (A) is a graph showing the lifetime measured value τR for each bonded wafer. In the figure (B), the surface of the bonded wafer on which the device is formed is polished to 5 μm as an active layer.
When left behind, the same (C) was used as an active layer without polishing.
The bonded wafers 1 and 2 each having a thickness of 0 μm are shown. For these bonded wafers 1 and 2, the case where the laser light is irradiated from the surface on the active layer side is indicated by Δ ○, and the case where the active layer is irradiated from the back surface side is indicated by ● ▲. Further, Δ ▲ indicates the case where the above-mentioned bonded wafer has a crystalline distortion, and ○ ● indicates the case where the bonded wafer does not have a crystalline distortion. That is, in this graph (A), ◯ indicates a bonded wafer (B in FIG. 2) having no crystalline strain.
The case where the laser light is irradiated from the front surface side, and the black circle shows the case where the laser light is irradiated from the back surface side of the bonded wafer having no crystal distortion. Further, Δ indicates the case of irradiating the bonded wafer having crystallinity distortion from the front surface side, and ▲ indicates the case of irradiating the same wafer with laser light from the back surface side. As shown in this graph, the lifetime measurement value of the bonded wafers 1 and 2 having no crystalline strain was 10 to 5 μsec. On the other hand, the lifetime measured value of the wafer having the crystalline strain was 3 to 0.5 μsec. As described above, it is apparent that the bonded wafers 1 and 2 have a significant difference in the measured lifetime value (τ _R ) depending on the presence or absence of the crystalline strain. Furthermore, since it has been confirmed in advance that concentric crystalline strain exists at the bonding interface between the bonded wafers 1 and 2, the difference between the lifetime measurement values at the same position on the wafer indicates the presence or absence of crystalline strain. It is shown. Thus, since the lifetime value of the portion where the crystalline strain exists is smaller than that of the other normal portion, the evaluation method of the present invention may determine the presence or absence of the crystalline strain of the bonding interface. confirmed.

In the above example, the case where the evaluation method of the present invention is applied to a bonded wafer obtained by bonding a mirror-finished wafer having no thermal oxide film has been described. It is needless to say that the present invention can be applied to a bonded wafer having an SOI structure in which wafers having the above are bonded.

[0016]

The method for evaluating the bonded interface of a bonded wafer according to the present invention is effective in determining the presence or absence of crystalline strain, which has been conventionally considered difficult, and the measurement is non-destructive, non-contact, non-contaminating. It is a simple and reliable method because it can be performed in a state and data can be obtained in a short time. In addition, it is not necessary to grind the surface of the bonded wafer when measuring the lifetime, and it is possible to evaluate the bonding interface in the manufacturing process of the silicon wafer before the polishing step.

[Brief description of drawings]

FIG. 1 is a graph showing lifetime measured values obtained by measurement according to the evaluation method of the present invention.

FIG. 2 is a photograph showing the presence or absence of concentric crystalline strain obtained by X-ray topography on a bonded wafer.

FIG. 3 is a photograph showing the presence / absence of concentric crystalline strain obtained by an X-ray topography method for a bonded wafer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Etsuro Morita 1-297 Kitabukuro-cho, Omiya-shi, Saitama Prefecture Central Research Laboratory, Mitsubishi Materials Corporation (72) Hisashi Furuya 1-297 Kitabukuro-cho, Omiya-shi, Saitama Mitsubishi Materials Co., Ltd. Central Research Institute (72) Inventor Takayuki Shingouchi 1-297 Kitabukuro-cho, Omiya City, Saitama Prefecture Mitsubishi Materials Corporation Central Research Laboratory (72) Inventor Kenichi Ueda 3-8-16 Iwamoto-cho, Chiyoda-ku, Tokyo Sanryo Material Silicon Co., Ltd.

Claims (1)

[Claims] 1. The bonding interface of a bonded semiconductor wafer is characterized in that the presence or absence of crystalline strain occurring at the bonding interface of a bonded semiconductor wafer formed by bonding two semiconductor wafers is determined by lifetime measurement. Evaluation methods.