JP4617788B2 - Bonded wafer evaluation method and bonded wafer evaluation apparatus - Google Patents

Description

  The present invention relates to a method for evaluating a bonded wafer manufactured by a bonding method, and more particularly to a method for evaluating a bonded wafer in which the width of a terrace portion existing on the outer peripheral portion of the bonded wafer is measured.

  In recent years, SOI wafers having an SOI structure in which an SOI (Silicon On Insulator) layer is formed on an electrically insulating silicon oxide film have been developed to achieve high-speed performance, low power consumption, high pressure resistance, and environmental resistance. Because of its excellent properties and the like, it is particularly attracting attention as a high-performance LSI wafer for electronic devices. This is because, in an SOI wafer, a silicon oxide film called a BOX (Buried Oxide) layer exists between the base wafer and the SOI layer. Therefore, an electronic device formed in the SOI layer has a high withstand voltage and a soft error rate of α rays. This is because it has the great advantage of being lowered.

  A silicon wafer as a raw material for such an SOI wafer is obtained by slicing a single crystal ingot by manufacturing a single crystal ingot by a method such as the Czochralski method (CZ method) or the floating zone method (FZ method). It is manufactured through a process of processing into a wafer, a process of lapping, etching, grinding, and polishing the wafer, a process of mirror polishing the surface, a process of cleaning, and the like.

And from the silicon wafer manufactured in this way, the SOI wafer is roughly manufactured by the following two kinds of methods.
The first method is a SIMOX (Separation by Implanted Oxygen) method in which oxygen ions are implanted from the surface layer of a silicon wafer and a silicon oxide film is formed between two silicon single crystal layers by subsequent heat treatment. The second method is a bonding method in which a base wafer and a bond wafer are bonded together through an oxide film, and then the bond wafer is thinned to form an SOI structure. Although both have characteristics, the bonding method, which is the second method, has been attracting attention in terms of the excellent crystallinity of the SOI layer.

A schematic view of an SOI wafer manufactured by such a bonding method is shown in FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view of a portion A in FIG. 3A.
The SOI wafer 30 includes a base wafer 31, a BOX layer 32, and an SOI layer 33. When the SOI wafer 30 is manufactured using the bonding method, a region where bonding does not occur is generated on the outer peripheral portion due to the shape of the material wafer. In addition, even in the region where bonding occurs, there is a region where the bonding strength is not sufficient on the outer periphery, and there is a concern of peeling during the device manufacturing process. There is also a case to keep. As described above, a region where the SOI layer does not exist (a region where bonding does not occur and a region where the SOI layer is intentionally removed) is referred to as a terrace portion 34. As can be seen from the figure, the terrace portion 34 has no SOI layer 33 on the base wafer 31. The width of the terrace portion 34 is usually about 1 to 3 mm. However, since the SOI layer is not formed on the terrace portion, the user of the SOI wafer cannot make a device on the terrace portion. For this reason, for the purpose of guaranteeing the effective area of the SOI layer capable of device fabrication, delivery specifications are defined for the width of the terrace portion for each user.

  The evaluation of the effective area of the SOI layer is usually performed by extracting the SOI wafer from the production lot, measuring the width of the terrace portion at four points on the outer peripheral portion of the wafer, and obtaining the maximum width and average width.

  FIG. 4 is a schematic diagram showing a conventional method for measuring the width of a terrace portion. Conventionally, the width of the terrace portion is measured by observing the SOI wafer 30 with a low-magnification optical microscope 40 and measuring the distance from the outer peripheral edge of the SOI layer to the outer peripheral edge of the base wafer using a scale. (For example, refer to Patent Document 1). Then, the SOI wafer 30 was rotated, the terrace width was measured at several locations on the outer periphery of the SOI wafer, and the maximum width and average width were obtained.

  However, as can be seen from FIG. 3B, since the outermost periphery of the SOI wafer 30 is chamfered, the terrace portion 34 is not flat and is inclined at the chamfered portion. Therefore, the distance to the optical microscope differs between the outer peripheral edge of the SOI layer and the outer peripheral edge of the base wafer. Therefore, the optical microscope has a problem that it is difficult to accurately measure the width of the terrace portion due to the influence of the depth of focus. Further, the method using such an optical microscope has a problem that it is difficult to automate the measurement of the terrace width.

JP 2002-305292 A

  The present invention has been made in view of such problems, and an object of the present invention is to provide a method for evaluating a bonded wafer that can easily and accurately measure the width of the terrace portion on the outer periphery of the bonded wafer.

  The present invention has been made to solve the above-described problems. At least, after bonding a base wafer and a bond wafer, the bonded wafer in which the bond wafer is thinned to form a thin film on the base wafer is evaluated. A method of reflecting light emitted from a light source on a surface of a bonded wafer and projecting the reflected light on a light receiving surface to obtain a projected image of the surface of the bonded wafer; Is used to measure the width of the terrace portion where the thin film is not present on the base wafer present on the outer peripheral portion of the bonded wafer (Claim 1).

  In this way, by obtaining a projected image of the bonded wafer surface by the magic mirror method, and using the projected image to observe the outer peripheral portion of the bonded wafer, the outer peripheral edge of the base wafer and the outer peripheral edge of the thin film are sharpened. Can be observed. In the present invention, the distance from the outer peripheral edge of the base wafer to the outer peripheral edge of the thin film, that is, the width of the terrace portion is measured using a sharp projection image obtained by the magic mirror method. Can be measured. Therefore, stable quality evaluation of the bonded wafer becomes possible.

  In the bonded wafer evaluation method of the present invention, the width of the terrace portion can be automatically measured using the projection image.

  As described above, the outer peripheral edge of the base wafer and the outer peripheral edge of the thin film can be clearly identified from the projection image obtained by the magic mirror method. Therefore, the width of the terrace portion can be automatically measured by performing image processing on the projected image. Thus, by automating the measurement, the terrace width can be measured quickly.

  In this case, it is preferable that the slip dislocation is also inspected simultaneously from the projection image.

  When a projected image of the bonded wafer surface is obtained by the magic mirror method and the bonded wafer is observed using the projected image, slip dislocation can also be observed simultaneously. Therefore, the bonded wafer can be efficiently evaluated by observing the slip dislocation simultaneously with the measurement of the width of the terrace portion.

  In this case, the bonded wafer to be evaluated can be an SOI wafer.

  Since SOI wafers are excellent in high-speed performance, low power consumption, high pressure resistance, environmental resistance, etc., in recent years, they have attracted particular attention as high-performance LSI wafers for electronic devices. Yes. Therefore, stable quality evaluation of SOI wafers is required. The present invention is a method particularly suitable for the quality evaluation of such an SOI wafer.

Furthermore, the present invention is an apparatus for evaluating a bonded wafer in which a bond wafer is thinned and a thin film is formed on the base wafer after the base wafer and the bond wafer are bonded, and at least on the bonded wafer surface. The base existing on the outer peripheral portion of the bonded wafer by using a light source for irradiating light, a light receiving surface for projecting light reflected on the bonded wafer surface, and a projection image of the bonded wafer surface obtained by the magic mirror method An apparatus for evaluating a bonded wafer, comprising: means for measuring a width of a terrace portion where the thin film is not present on the wafer; and display means for displaying a measurement result of the obtained terrace width is provided. 5).

  The bonded wafer evaluation apparatus of the present invention obtains a projected image of the bonded wafer surface by the magic mirror method, and measures the width of the terrace portion using this projected image. As described above, the projection image obtained by the magic mirror method can clearly observe the outer peripheral edge of the base wafer and the outer periphery of the thin film. Furthermore, the apparatus of the present invention automatically measures the distance from the outer peripheral edge of the base wafer to the outer peripheral edge of the thin film, that is, the width of the terrace portion, by processing this projection image in the terrace width measuring means. To do. Therefore, by using the bonded wafer evaluation apparatus of the present invention, the width of the terrace portion can be measured quickly and accurately. And stable quality evaluation of a bonded wafer is attained.

  As described above, according to the present invention, the width of the terrace portion on the outer periphery of the bonded wafer is measured using the projection image obtained by the magic mirror method, so the width of the terrace portion is easily and accurately measured. It is possible. Therefore, stable quality evaluation of the bonded wafer becomes possible.

Hereinafter, the best mode for carrying out the present invention will be described, but the present invention is not limited thereto.
FIG. 2 is an explanatory view of the bonded wafer evaluation apparatus of the present invention.
The bonded wafer evaluation apparatus 20 includes a light source 21 that irradiates light on the surface of the bonded wafer 25, a light receiving surface 22 that projects light reflected by the surface of the bonded wafer 25, and a surface of the bonded wafer 25. Means (terrace width measuring means) 23 for measuring the width of the terrace portion 28 where the thin film 26 does not exist on the base wafer 27 existing on the outer peripheral portion of the bonded wafer 25 using the projection image, and measurement of the obtained terrace width Display means 24 for displaying the result is provided. Specifically, the bonded wafer is evaluated as follows using this apparatus.

  Note that the bonded wafer 25 shown in FIG. 2 includes a thin film 26 and a base wafer 27. However, the present invention is not limited to this, and can be applied to any bonded wafer in which the width of the terrace portion on the outer periphery of the bonded wafer needs to be measured. For example, it is a bonded SOI wafer having a three-layer structure of a base wafer, a BOX layer, and an SOI layer (thin film). The present invention can also be applied to a bonded wafer between a silicon wafer, a bonded wafer between a silicon wafer and an insulating substrate (quartz, alumina, sapphire, silicon carbide, etc.), a bonded wafer between insulating substrates, and the like. .

  First, light such as a halogen lamp or laser is irradiated from the light source 21 toward the surface of the bonded wafer 25 through the projection lens 29, and the light reflected on the surface of the bonded wafer 25 is projected onto the light receiving surface 22. That is, a projection image of the surface of the bonded wafer 25 is obtained by the magic mirror method.

Here, the basic principle of the magic mirror method will be described. When a parallel light beam is incident on a completely flat mirror surface from a light source, contrast between light and dark is not observed in the image projected on the light receiving surface. However, if there is a slight concave surface on the mirror surface, the reflected light is collected and projected brightly, whereas on the convex surface, the reflected light spreads and is observed dark. Advantages of such a magic mirror method include that the sample can be measured without any modification, non-destructive, non-contact, and automatable.
When the bonded wafer 25 is viewed, the terrace portion 28 present on the outer peripheral portion thereof is concave with respect to the thin film 26. For this reason, if the magic mirror method is used, the terrace portion 28 is observed very brightly.
As an example of using the magic mirror method for evaluating a silicon wafer, observation of shallow irregularities (referred to as peel) on the surface of a mirror-polished wafer (paragraph (0004) of JP-A-9-252100), bonded wafers Observation of unbonded regions called voids (Japanese Patent Laid-Open No. 5-302885) is known. However, the present inventors are the first to find that the outer terrace portion of the bonded wafer can be evaluated using the magic mirror method.

  FIG. 1 is an image of the outer peripheral portion of the SOI wafer actually obtained by the magic mirror method, and the portion indicated by A in FIG. 3A is observed. The portion that looks bright, that is, the white portion is the terrace portion 34. As can be seen from FIG. 1, in the image of the outer peripheral portion of the SOI wafer obtained by the magic mirror method, the terrace portion 34 appears white, and the outer peripheral end of the SOI layer 33 and the outer peripheral end of the SOI wafer 30 are identified very clearly. I understand that I can do it.

Next, the terrace width measuring means 23 automatically measures the width of the terrace portion using the projected image of the bonded wafer surface. As described above, the outer peripheral edge of the thin film and the outer peripheral edge of the base wafer can be clearly identified from the projection image obtained by the magic mirror method. Therefore, if this projection image is subjected to image processing, the outer peripheral edge of the thin film and the outer peripheral edge of the bonded wafer can be easily and accurately analyzed. As an image processing method, for example, an image of an observed terrace portion is divided into cells of a certain size (for example, a 0.1 mm square), and is divided into two colors, black (a portion other than the terrace portion) and white (terrace portion). The cell row which is binarized and viewed from the cell row on the outer peripheral side of the wafer is determined as the outer peripheral edge of the base wafer 31 when the white region begins to spread, and the cell row in the region where the black region begins to spread is thinned (SOI layer 33) It is possible to use a method of converting to the terrace width by determining the outer peripheral edge of the cell line and taking the difference between the row numbers of these cell rows. Therefore, the terrace width measuring means 23 performs image processing on the projected image, analyzes the outer peripheral edge of the thin film and the outer peripheral edge of the bonded wafer, and obtains the distance between the outer peripheral edge of the thin film and the outer peripheral edge of the bonded wafer from the analysis result. Thus, the width of the terrace portion is measured. At this time, as in a normal method, it is preferable to measure the width of the terrace portion at four points on the outer peripheral portion of the wafer and obtain the maximum width and average width.
The display unit 24 displays the obtained terrace width measurement result.

  Thereby, it is possible to measure the width of the terrace portion easily and accurately. Then, stable quality evaluation of the bonded wafer can be performed. Moreover, since the width | variety of a terrace part can be automatically measured with the said apparatus, quick evaluation is attained.

  Further, slip dislocation inspection may be performed simultaneously from the projected image of the bonded wafer surface obtained by the magic mirror method. As can be seen from FIG. 1, slip dislocations 10 can also be observed from the image of the outer peripheral portion of the SOI wafer obtained by the magic mirror method. Therefore, the bonded wafer can be efficiently evaluated by observing the slip dislocation simultaneously with the measurement of the width of the terrace portion.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has the same configuration as the technical idea described in the claims of the present invention. It is included in the technical scope of the invention.

It is an example of the image of the SOI wafer outer peripheral part obtained by the magic mirror method. It is explanatory drawing of the evaluation apparatus of the bonded wafer of this invention. It is the schematic of the SOI wafer produced by the bonding method. (A) Top view, (b) Partial sectional view. It is a schematic diagram which shows the measuring method of the width | variety of the conventional terrace part.

Explanation of symbols

10 ... Slip dislocation,
20 ... Bonded wafer evaluation device, 21 ... Light source,
22 ... light receiving surface, 23 ... terrace width measuring means, 24 ... display means,
25 ... Bonded wafer, 26 ... Thin film, 27, 31 ... Base wafer,
28, 34 ... terrace, 29 ... projection lens,
30 ... SOI wafer, 32 ... BOX layer, 33 ... SOI layer,
40: Optical microscope.

Claims (5)

  At least a method for evaluating a bonded wafer in which a base wafer and a bond wafer are bonded together, and then the bond wafer is thinned to form a thin film on the base wafer, and light emitted from a light source is applied to the surface of the bonded wafer. The projected image of the bonded wafer surface is obtained by a magic mirror method in which the reflected light is projected onto the light receiving surface, and the projected image is used to obtain the projected image on the base wafer existing on the outer peripheral portion of the bonded wafer. A method for evaluating a bonded wafer, comprising measuring a width of a terrace portion without the thin film.   The method for evaluating a bonded wafer according to claim 1, wherein the width of the terrace portion is automatically measured using the projected image.   The method for evaluating a bonded wafer according to claim 1, wherein slip dislocation is also inspected simultaneously from the projected image.   The bonded wafer evaluation method according to any one of claims 1 to 3, wherein the bonded wafer to be evaluated is an SOI wafer. An apparatus for evaluating a bonded wafer in which a bond wafer is thinned and a thin film is formed on the base wafer after bonding the base wafer and the bond wafer, and at least a light source for irradiating the bonded wafer surface with light The thin film is formed on the base wafer existing on the outer periphery of the bonded wafer by using a light receiving surface for projecting the light reflected on the bonded wafer surface and a projection image of the bonded wafer surface obtained by the magic mirror method. An apparatus for evaluating a bonded wafer, comprising: means for measuring a width of a non-terrace portion; and display means for displaying a measurement result of the obtained terrace width.

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