JP2010140943A - Method of evaluating laminated wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To well detect failures that are not detected by a conventional infrared spectroscopy or ultrasonic flaw examination method, relating to a method of evaluating a laminated wafer. <P>SOLUTION: In the evaluation method, two silicon wafers are laminated together, and then a reinforcing thermal treatment for enhancing adhesion of the laminate and a process for forming a thin film are performed sequentially, to evaluate a state of the interface of lamination of a wafer to be manufactured. The evaluation method includes a step of, after the reinforcing thermal treatment but before the processing for forming thin-film, releasing a laminated wafer with the lamination interface as a border, and the next step of directly viewing the state of a surface that has been a laminated interface and observing with a microscope. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an evaluation method for evaluating the state of a bonded interface of a bonded wafer.

Regarding a bonded wafer (SOI wafer) manufactured by bonding an active layer silicon wafer and a supporting silicon wafer, infrared spectroscopy (so-called IR method) or ultrasonic flaw detection is used as a method for evaluating the bonding interface. The law is already known.
In simple terms, infrared spectroscopy is a method of irradiating an object with infrared rays, spectrally analyzing the transmitted or reflected light, obtaining a spectrum, and imaging the spectrum to know the state of the object. The ultrasonic flaw detection method is simply a method of irradiating a target object with ultrasonic waves directly or through water or the like and imaging the reflected wave to know the state of the target object.

Such infrared spectroscopy and ultrasonic flaw detection methods are disclosed in, for example, Patent Document 1, so please refer to them.
JP 2007-258555 A

However, according to these infrared spectroscopy and ultrasonic flaw detection methods, it is possible to detect voids (voids) at the bonding interface, but to detect places where there is no void at the bonding interface but the bonding state is weak. It is not possible.
If such a weakly bonded portion exists, the active layer may be peeled off in the device process, which may cause a characteristic defect. Therefore, it is very important to detect defects that cannot be detected by infrared spectroscopy or ultrasonic flaw detection.

  The present invention has been devised in view of such a problem, and provides a method for evaluating a bonded wafer, in which defects that cannot be detected by conventional infrared spectroscopy and ultrasonic flaw detection methods can be detected well. The purpose is to provide.

  In order to achieve the above-mentioned object, the bonded wafer evaluation method of the present invention is such that, after bonding two silicon wafers, a tempering heat treatment and a thinning process are performed in order to enhance the bonding adhesiveness. A method for evaluating a state of a bonded interface of a bonded wafer to be manufactured, the step of separating the bonded wafer after the strengthening heat treatment and before the thinning process, with the bonded interface as a boundary, and thereafter And a step of directly observing the state of the surface that was the bonding interface and observing it using a microscope (claim 1).

In addition, it is preferable that the temperature of this tempering heat processing is 1000 degreeC or more (Claim 2).
The microscope is preferably an atomic force microscope.
Moreover, it is preferable to peel off the bonded wafer using a blade (Claim 4). At this time, the blade of the blade is inserted from an unbonded portion of the edge of the bonded wafer, and the bonded wafer is peeled off. It is more preferable if it is made (Claim 5).

  Furthermore, before peeling off the bonded wafer, it is preferable to inspect the state of the bonded interface using infrared spectroscopy or ultrasonic flaw detection.

According to the bonded wafer evaluation method of the present invention, since the bonded wafer is peeled off at the bonding interface, it is possible to directly observe the state of the bonded interface directly by visual observation or using a microscope. In addition, it is possible to satisfactorily detect a minute surface state that cannot be detected in a bonded state and foreign matter present at the interface.
Further, even a bonded wafer that has been subjected to tempering heat treatment and has increased adhesive strength can be easily and satisfactorily peeled by using a blade.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 3 are for explaining a bonded wafer evaluation method according to an embodiment of the present invention, and FIG. 1 is a flowchart of a bonded wafer manufacturing method including the evaluation process. 2 is a schematic cross-sectional view showing how the wafer is peeled off for the evaluation, and FIG. 3 is a photomicrograph showing defects detected by the evaluation. In FIG. 2, the dimensions of the wafer and the blade are exaggerated for easy understanding of the gist of the present invention.

[Overview]
First, a bonded wafer (hereinafter referred to as an SOI wafer) to be evaluated according to the present invention will be described. As shown in FIGS. 1 and 2, the SOI wafer includes a supporting silicon wafer 1 and an active layer as a supporting substrate. A bonding step S10 for bonding the active layer silicon wafer 2 to be formed, and a heat treatment step S20 for performing a bond strengthening heat treatment at a temperature of 1000 ° C. or higher in order to improve the adhesion (bonding) of the bonding; The thin film forming step S30 for thinning the active layer silicon wafer 2 using grinding, etching, or the like is performed in this order.

The evaluation of the SOI wafer of the present invention is performed as the evaluation step S25 between the heat treatment step S20 and the thinning step S30.
This evaluation method will be described in detail. Since the edge of the SOI wafer before thinning is not bonded due to the chamfered shape, the blade 3a of the blade 3 is inserted from this unbonded portion, and the SOI wafer is inserted. Is forcibly separated at the boundary of the bonding interface. The blade 3 is a peeling jig having a sharp tip, and more specifically, a blade such as a cutter having a blade 3a made of metal or ceramic.

And after peeling, the state of the surface that was the bonding interface is directly observed under a condensing lamp, and after the observation, it is further observed using a microscope (for example, an atomic force microscope). Yes.
At the time of peeling, if the blade 3a is inserted from an appropriate portion of the unbonded portion, the blade 3a is moved along the outer periphery of the SOI wafer to peel off the entire periphery, and then the blade 3a is moved. It is preferable that the SOI wafer is separated from the SOI wafer, and finally, the entire surface of the SOI wafer is peeled off directly by hand or using an appropriate jig.

In FIG. 2, the blade 3 is held by the holder 3b so that the operator can safely handle the blade 3a. However, the shape of the blade 3 is not limited to this, and at least the blade 3a I just need it.
In addition, the state of the bonded interface may be inspected using at least one of infrared spectroscopy (IR method) and ultrasonic flaw detection method before peeling. In particular, inspection by infrared spectroscopy is preferably performed after bonding and before tempering heat treatment, and inspection by ultrasonic flaw detection is preferably performed after tempering heat treatment and before peeling.

Specific examples will be described below.
[Example 1]
After inspecting that there is no defect in infrared spectroscopy and ultrasonic flaw detection in a non-thinned SOI wafer with a diameter of 150 mm that has been subjected to bond strengthening heat treatment at 1100 ° C, The SOI wafer was peeled off using the unbonded portion which is a chamfered portion as a base point.

  Then, when the surface which became an interface at the time of bonding under a halogen lamp condensing lamp was directly observed visually, the site | part which has a defect in the bonding interface was confirmed. Specifically, in the visual observation, the defect appeared as a clouded circle, and the roughness of the surface was confirmed. Further, when the defect was further observed with an atomic force microscope, it was confirmed that a rough surface area having a diameter of 774 μm and a height of 5.6 nm as shown in FIG. 3 is a rough surface area, which is shown by a fine hatch between the wafers 1 and 2 in FIG. This rough surface area was not detected by infrared spectroscopy or ultrasonic flaw detection because the gap between the two wafers was filled without any gap at the bonding interface.

[effect]
According to such a method for evaluating a bonded wafer of the present invention, the SOI wafer is peeled off at the bonding interface, so the surface that was the bonding interface using direct observation under a condenser lamp or a microscope. This state can be observed directly, and a fine surface state that cannot be detected in the bonded state and foreign matter present at the interface can be detected well.

Further, even an SOI wafer that has been subjected to tempering heat treatment and has increased adhesive strength can be easily and satisfactorily peeled by using the blade 3.
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

It is a flowchart of the manufacturing method of a bonded wafer shown including the process of performing the evaluation method of the bonded wafer which concerns on one Embodiment of this invention. It is a figure which shows the evaluation method of the bonded wafer which concerns on one Embodiment of this invention, Comprising: It is typical sectional drawing which shows a mode that a wafer is peeled for the evaluation. It is a microscope picture which shows the defect detected by the evaluation method of the bonded wafer which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon wafer for support 2 Silicon wafer for active layer 3 Blade 3a Blade 3b Holder

Claims (6)

After bonding two silicon wafers, a method for evaluating the state of the bonding interface of the bonded wafers produced by sequentially performing a tempering heat treatment and a thinning process for increasing the bonding adhesiveness. ,
After the strengthening heat treatment and before the thinning process, the step of peeling the bonded wafer with the bonding interface as a boundary, and then directly observing the state of the surface that was the bonding interface and using a microscope And a step of observing the bonded wafer. The method for evaluating a bonded wafer according to claim 1, wherein the temperature of the tempering heat treatment is 1000 ° C. or higher. 3. The method for evaluating a bonded wafer according to claim 1, wherein the microscope is an atomic force microscope. The method for evaluating a bonded wafer according to claim 1, wherein the bonded wafer is peeled off using a blade. 5. The method for evaluating a bonded wafer according to claim 4, wherein the blade of the blade is inserted from an unbonded portion of the edge of the bonded wafer, and the bonded wafer is peeled off. The state of the bonding interface is inspected by using an infrared spectroscopy method or an ultrasonic flaw detection method before the bonded wafer is peeled off. Evaluation method for bonded wafers.

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