Substrate processing apparatus, substrate processing method and bonding method

A substrate processing apparatus includes a chuck configured to attract and hold a substrate; an observer configured to observe multiple positions within a second surface of the substrate attracted to and held by the chuck, the second surface being opposite to a first surface thereof which is in contact with the chuck; and an analyzer configured to analyze observation results of the multiple positions. When a singularity regarding a height from a surface of the chuck attracting and holding the substrate exists on the second surface, the analyzer specifies a position of the singularity on the chuck.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Japanese Patent Application No. 2019-034842 filed on Feb. 27, 2019, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The various aspects and embodiments described herein pertain generally to a substrate processing apparatus, a substrate processing method and a bonding method.

BACKGROUND

A bonding apparatus described in Patent Document 1 is equipped with an upper chuck configured to attract a substrate at an upper side from above it and a lower chuck configured to attract a substrate at a lower side from below it. While being held to face each other, the two substrates are bonded. To elaborate, the bonding apparatus brings a central portion of the upper substrate attracted by the upper chuck into contact with a central portion of the lower substrate attracted by the lower chuck by pressing down the central portion of the upper substrate. Accordingly, the central portions of the two substrates are bonded by an intermolecular force or the like. Then, the bonding apparatus expands a bonding region between the two substrates from the central portions of the substrates to peripheral portions thereof.

SUMMARY

In an exemplary embodiment, a substrate processing apparatus includes a chuck configured to attract and hold a substrate; an observer configured to observe multiple positions within a second surface of the substrate attracted to and held by the chuck, the second surface being opposite to a first surface thereof which is in contact with the chuck; and an analyzer configured to analyze observation results of the multiple positions. When a singularity regarding a height from a surface of the chuck attracting and holding the substrate exists on the second surface, the analyzer specifies a position of the singularity on the chuck.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the various drawings, same or corresponding parts will be assigned same reference numerals, and redundant description may be omitted. In the following description, the X-axis direction, the Y-axis direction and the Z-axis direction are orthogonal to each other, and the X-axis and Y-axis directions are horizontal directions whereas the Z-axis direction is a vertical direction. A rotational direction around a vertical axis is also referred to as “θ direction.” In the present specification, below means vertically below, and above means vertically above.

FIG.1is a plan view illustrating a bonding system1according to an exemplary embodiment.FIG.2is a side view illustrating the bonding system1according to the exemplary embodiment.FIG.3is a side view illustrating a state before a first substrate and a second substrate are bonded according to the exemplary embodiment. The bonding system1shown inFIG.1forms a combined substrate T (seeFIG.7B) by bonding a first substrate W1and a second substrate W2.

The first substrate W1is, for example, a semiconductor substrate such as a silicon wafer or a compound semiconductor wafer on which multiple electronic circuits are formed. The second substrate W2is, for example, a bare wafer on which no electronic circuit is formed. The first substrate W1and the second substrate W2have the substantially same diameter. Further, the second substrate W2may have an electronic circuit formed thereon.

In the following description, the first substrate W1may sometimes be referred to as “upper wafer W1”; the second substrate W2, “lower wafer W2”; and the combined substrate T, “combined wafer T.” Further, in the following description, as depicted inFIG.3, among surfaces of the upper wafer W1, a surface to be bonded to the lower wafer W2will be referred to as “bonding surface W1j”, and a surface opposite to the bonding surface W1jwill be referred to as “non-bonding surface W1n”. Further, among surfaces of the lower wafer W2, a surface to be bonded to the upper wafer W1will be referred to as “bonding surface W2j”, and a surface opposite to the bonding surface W2jwill be referred to as “non-bonding surface W2n.”

As depicted inFIG.1, the bonding system1includes a carry-in/out station2and a processing station3. The carry-in/out station2and the processing station3are arranged in this sequence along the positive X-axis direction. Further, the carry-in/out station2and the processing station3are connected as a single body.

The carry-in/out station2includes a placing table10and a transfer section20. The placing table10is equipped with a multiple number of placing plates11. Provided on the placing plates11are cassettes C1, C2and C3each of which accommodates therein a plurality of (e.g.,25sheets of) substrates horizontally. For example, the cassette C1accommodates therein upper wafers W1; the cassette C2, lower wafers W2; and the cassettes C3, combined wafers T.

The transfer section20is provided adjacent to the positive X-axis side of the placing table10. Provided in the transfer section20are a transfer path21extended in the Y-axis direction and a transfer device22configured to be movable along the transfer path21. The transfer device22is configured to be movable in the X-axis direction as well as in the Y-axis direction and pivotable around the Z-axis. Further, the transfer device22is also configured to transfer the upper wafers W1, the lower wafers W2and the combined wafers T between the cassettes C1to C3placed on the placing plates11and a third processing block G3of the processing station3to be described later.

Further, the number of the cassettes C1to C3placed on the placing plates11is not limited to the shown example. In addition, besides the cassettes C1to C3, a cassette or the like for collecting a problematic substrate may be additionally provided on the placing plates11.

A multiple number of, for example, three processing blocks G1, G2and G3equipped with various kinds of devices are provided in the processing station3. For example, the first processing block G1is provided at a front side (negative Y-axis side ofFIG.1) of the processing station3, and the second processing block G2is provided at a rear side (positive Y-axis side ofFIG.1) of the processing station3. Further, the third processing block G3is provided at a side of the carry-in/out station2(negative X-axis side ofFIG.1) of the processing station3.

Provided in the first processing block G1is a surface modifying apparatus30configured to modify the bonding surface W1jof the upper wafer W1and the bonding surface W2jof the lower wafer W2. In the surface modifying apparatus30, a SiO2bond on the bonding surfaces W1jand W2jof the upper wafer W1and the lower wafer W2is cut to be turned into SiO of a single bond, so that the bonding surfaces W1jand W2jare modified such that these surfaces are easily hydrophilized afterwards.

Furthermore, in the surface modifying apparatus30, for example, an oxygen gas or a nitrogen gas as a processing gas is excited into plasma under a decompressed atmosphere to be ionized. As these oxygen ions or nitrogen ions are irradiated to the bonding surfaces W1jand W2jof the upper wafer W1and the lower wafer W2, the bonding surfaces W1jand W2jare plasma-processed to be modified.

In the second processing block G2, a surface hydrophilizing apparatus40and a bonding apparatus41are disposed. The surface hydrophilizing apparatus40is configured to hydrophilize and clean the bonding surfaces W1jand W2jof the upper wafer W1and the lower wafer W2with, for example, pure water. In this surface hydrophilizing apparatus40, while rotating the upper wafer W1or the lower wafer W2held by, for example, a spin chuck, the pure water is supplied onto the upper wafer W1or the lower wafer W2. Accordingly, the pure water supplied onto the upper wafer W1or the lower wafer W2is diffused onto the bonding surface W1jof the upper wafer W1or the bonding surface W2jof the lower wafer W2, so that the bonding surfaces W1jand W2jare hydrophilized.

The bonding apparatus41is configured to bond the upper wafer W1and the lower wafer W2, which are hydrophilized, by an intermolecular force. A configuration of the bonding apparatus41will be discussed later.

In the third processing block G3, as shown inFIG.2, transition (TRS) devices50and51for the upper wafer W1, the lower wafer W2and the combined wafer T are provided in two levels in this order from below.

Further, as illustrated inFIG.1, a transfer section60is formed in a region surrounded by the first processing block G1, the second processing block G2and the third processing block G3. A transfer device61is provided in the transfer section60. The transfer device61is equipped with, for example, a transfer arm which is configured to be movable in a vertical direction and a horizontal direction and pivotable around a vertical axis. The transfer device61is moved within the transfer section60and transfers the upper wafers W1, the lower wafers W2and the combined wafers T with respect to preset devices within the first processing block G1, the second processing block G2and the third processing block G3which are adjacent to the transfer section60.

Furthermore, as depicted inFIG.1, the bonding system1includes a control device70. The control device70controls an operation of the bonding system1. The control device70may be implemented by, for example, a computer and includes a CPU (Central Processing Unit)71, a recording medium72such as a memory, an input interface73and an output interface74. The control device70carries out various kinds of controls by allowing the CPU71to execute a program stored in the recording medium72. Further, the control device70receives a signal from an outside through the input interface73and transmits a signal to the outside through the output interface74. The control device70is an example of an analyzer.

The program of the control device70is recorded in an information recording medium and installed from the information recording medium. The information recording medium may be, by way of non-limiting example, a hard disc (HD), a flexible disc (FD), a compact disc (CD), a magnet optical disc (MO), or a memory card. Further, the program may be installed by being downloaded from a server through Internet.

FIG.4is a plan view illustrating the bonding apparatus41according to the exemplary embodiment.FIG.5is a side view illustrating the bonding apparatus41according to the exemplary embodiment.

As depicted inFIG.4, the bonding apparatus41includes a processing vessel100having a hermetically sealable inside. A carry-in/out opening101for the upper wafer W1, the lower wafer W2and the combined wafer T is formed on a lateral side of the processing vessel100at a side of the transfer region60. A shutter102for opening/closing the carry-in/out opening101is provided at the carry-in/out opening101. The processing vessel100is an example of a processing chamber.

Provided within the processing vessel100are an upper chuck140configured to attract and hold a top surface (non-bonding surface W1n) of the upper wafer W1from above and a lower chuck141configured to place thereon the lower wafer W and attract and hold a bottom surface (non-bonding surface W2n) of the lower wafer W2from below. The lower chuck141is provided under the upper chuck140and configured to be arranged to face the upper chuck140in parallel. The upper chuck140and the lower chuck141are arranged apart from each other in the vertical direction.

As depicted inFIG.5, the upper chuck140is held by an upper chuck holder150which is provided above the upper chuck140. The upper chuck holder150is provided at a ceiling surface of the processing vessel100. The upper chuck140is fixed to the processing vessel100with the upper chuck holder150therebetween.

The upper chuck holder150is equipped with an upper imaging device151A configured to image a top surface (bonding surface W2j) of the lower wafer W2held by the lower chuck141. By way of example, a CCD camera is used as the upper imaging device151A. The upper chuck holder150is also equipped with an upper displacement meter151B configured to measure a displacement of the top surface (bonding surface W2j) of the lower wafer W2held by the lower chuck141. By way of example, a LED displacement meter is used as the upper displacement meter151B. The upper imaging device151A is an example of an imaging device, and the upper displacement meter151B is an example of a displacement meter.

The lower chuck141is supported by a first lower chuck mover160provided below the lower chuck141. The first lower chuck mover160moves the lower chuck141in the horizontal direction (Y-axis direction) as will be described later. Further, the first lower chuck mover160is also configured to be capable of moving the lower chuck141in the vertical direction and rotate the lower chuck141around a vertical axis.

The first lower chuck mover160is equipped with a lower imaging device161A configured to image a bottom surface (bonding surface W1j) of the upper wafer W1held by the upper chuck140(seeFIG.5). The lower imaging device161A may be, by way of example, a CCD camera. The first lower chuck mover160is also equipped with a lower displacement meter161B configured to measure a displacement of the bottom surface (bonding surface W1j) of the upper wafer W1held by the upper chuck140. The lower displacement meter161B may be, by way of non-limiting example, a LED displacement meter.

The first lower chuck mover160is fastened to a pair of rails162which is provided at a bottom side of the first lower chuck mover160and extends in the horizontal direction (Y-axis direction). The first lower chuck mover160is configured to be movable along the rails162.

The rails162are disposed on a second lower chuck mover163. The second lower chuck mover163is fastened to a pair of rails164which is disposed at a bottom side of the second lower chuck mover163and extends in the horizontal direction (X-axis direction). The second lower chuck mover163is configured to be movable in the horizontal direction (X-axis direction) along the rails164. Further, the rails164is disposed on the placing table165which is disposed at a bottom of the processing vessel100.

The first lower chuck mover160, the second lower chuck mover163, and so forth constitute a position adjuster166. The position adjuster166is configured to perform position adjustment in the horizontal direction between the upper wafer W1held by the upper chuck140and the lower wafer W2held by the lower chuck141by moving the lower chuck141in the X-axis direction, the Y-axis direction and the θ direction. Further, the position adjuster166is also configured to perform position adjustment in the vertical direction between the upper wafer W1held by the upper chuck140and the lower wafer W2held by the lower chuck141by moving the lower chuck141in the Z-axis direction.

Further, although the position adjuster166of the present exemplary embodiment carries out the position adjustment between the upper wafer W1and the lower wafer W2in the horizontal direction by moving the lower chuck141in the X-axis direction, the Y-axis direction and the θ direction, the present disclosure is not limited thereto. The way how the position adjuster166performs this position adjustment in the horizontal direction is not particularly limited as long as the upper chuck140and the lower chuck141are moved relatively to each other in the X-axis direction, the Y-axis direction and the θ direction. By way of example, the position adjuster166may perform the position adjustment between the upper wafer W1and the lower wafer W2by moving the lower chuck141in the X-axis direction and the Y-axis direction and by moving the upper chuck140in the θ direction.

Furthermore, although the position adjuster166of the present disclosure carries out the position adjustment between the upper wafer W1and the lower wafer W2in the vertical direction by moving the lower chuck141in the Z-axis direction, the present disclosure is not limited thereto. The way how the position adjuster166performs this position adjustment in the vertical direction is not particularly limited as long as the upper chuck140and the lower chuck141can be moved relatively to each other in the Z-axis direction. By way of example, the position adjuster166may perform the position adjustment between the upper wafer W1and the lower wafer W2in the vertical direction by moving the upper chuck140in the Z-axis direction.

FIG.6is a cross sectional view illustrating the upper chuck and the lower chuck according to the exemplary embodiment, showing a state immediately before the upper wafer and the lower wafer are bonded.FIG.7Ais a cross sectional view illustrating a state in the middle of bonding between the upper wafer and the lower wafer according to the present exemplary embodiment.FIG.7Bis a cross sectional view illustrating a state upon the completion of the bonding between the upper wafer and the lower wafer according to the present exemplary embodiment. Solid-lined arrows inFIG.6,FIG.7AandFIG.7Bindicate a direction in which air is suctioned by a vacuum pump.

The upper chuck140and the lower chuck141are, for example, configured as vacuum chucks. In the present exemplary embodiment, the upper chuck140corresponds to a first holder described in claims, and the lower chuck141corresponds to a second holder described in the claims. The upper chuck140has, at the surface (bottom surface) thereof facing the lower chuck141, an attraction surface140ato which the upper wafer W1is attracted. Meanwhile, the lower chuck141has, at the surface (top surface) facing the upper chuck140, an attraction surface141ato which the lower wafer W2is attracted.

The upper chuck140has a chuck base170. The chuck base170has a diameter equal to or larger than a diameter of the upper wafer W1. The chuck base170is supported by a supporting member180. The supporting member180is disposed to cover at least the chuck base170when viewed from the top, and is fixed to the chuck base170by, for example, screws. The supporting member180is supported by a plurality of supporting columns181(seeFIG.5) provided at the ceiling surface of the processing vessel100. The supporting member180and the plurality of supporting columns181constitute the upper chuck holder150.

A through hole176is formed through the supporting member180and the chuck base170in the vertical direction. A position of the through hole176corresponds to a central portion of the upper wafer W1attracted to and held by the upper chuck140. A push pin191of a striker190is inserted into this through hole176.

The striker190is provided on a top surface of the supporting member180and is equipped with the push pin191, an actuator unit192and a linearly moving mechanism193. The push pin191is a columnar member extending along the vertical direction and is supported by an actuator unit192.

The actuator unit192is configured to generate a constant pressure in a certain direction (here, a vertically downward direction) by air supplied from, for example, an electro-pneumatic regulator (not shown). By the air supplied from the electro-pneumatic regulator, the actuator unit192is capable of controlling a press load applied to the central portion of the upper wafer W1as it is brought into contact with the central portion of the upper wafer W1. Further, a leading end of the push pin191is movable up and down in the vertical direction through the through hole176by the air from the electro-pneumatic regulator.

The actuator unit192is supported at the linearly moving mechanism193. The linearly moving mechanism193moves the actuator unit192in the vertical direction by a driving unit including a motor, for example.

The striker190is configured as described above, and controls a movement of the actuator unit192by the linearly moving mechanism193and controls the press load upon the upper wafer W1from the push pin191by the actuator unit192.

The striker190presses the upper wafer W1attracted to and held by the upper chuck140and the lower wafer W2attracted to and held by the lower chuck141to allow the upper wafer W1and the lower wafer W2to come into contact with each other. To elaborate, the striker190transforms the upper wafer W1attracted to and held by the upper chuck140, thus allowing the upper wafer W1to be pressed in contact with the lower wafer W2. The striker190corresponds to a pressing unit described in the claims.

A plurality of pins171is provided on a bottom surface of the chuck base170, and these pins171are in contact with the non-bonding surface W1nof the upper wafer W1. The upper chuck140is composed of the chuck base170, the plurality of pins171, and so forth. The attraction surface140aof the upper chuck140which attracts and holds the upper wafer W1is divided into multiple regions in a diametrical direction, and generation of an attracting force and release of the attracting force are performed for divided regions individually.

Further, the lower chuck141may be configured the same as the upper chuck140. The lower chuck141has a plurality of pins in contact with the non-bonding surface W2nof the lower wafer W2. The attraction surface141aof the lower chuck W1which attracts and holds the lower wafer W2is divided into multiple regions in the diametrical direction, and generation of an attracting force and release of the attracting force are performed for divided regions individually.

FIG.8is a flowchart illustrating a part of a processing performed by the bonding system according to the exemplary embodiment. Further, the various processes shown inFIG.8are performed under the control of the control device70.

First, a cassette C1accommodating a plurality of upper wafers W1, a cassette C2accommodating a plurality of lower wafers W2and an empty cassette C3are placed on the preset placing plates11of the carry-in/out station2. Then, an upper wafer W1is taken out of the cassette C1by the transfer device22and is transferred to the transition device50of the third processing block G3of the processing station3.

Subsequently, the upper wafer W1is transferred into the surface modifying apparatus30of the first processing block G1by the transfer device61. In the surface modifying apparatus30, an oxygen gas as the processing gas is formed into plasma to be ionized under the preset decompressed atmosphere. The oxygen ions are irradiated to the bonding surface W1jof the upper wafer W1, and the bonding surface W1jis plasma-processed. As a result, the bonding surface W1jof the upper wafer W1is modified (process S101).

Then, the upper wafer W1is transferred into the surface hydrophilizing apparatus40of the second processing block G2by the transfer device61. In the surface hydrophilizing apparatus40, the pure water is supplied onto the upper wafer W1while rotating the upper wafer W1held by the spin chuck. The supplied pure water is diffused on the bonding surface W1jof the upper wafer W1, and hydroxyl groups (silanol groups) adhere to the bonding surface W1jof the upper wafer W1modified in the surface modifying apparatus30, so that the bonding surface W1jis hydrophilized (process S102). Further, the bonding surface W1jof the upper wafer W1is cleaned by this pure water used to hydrophilize the bonding surface W1j.

Thereafter, the upper wafer W1is transferred into the bonding apparatus41of the second processing block G2by the transfer device61(process S103). At this time, the front surface and the rear surface of the upper wafer W1are inverted. That is, the bonding surface W1jof the upper wafer W1is turned to face down.

Afterwards, within the bonding apparatus41, the transfer arm of the transfer device61is moved to be located under the upper chuck140. Then, the upper wafer W1is delivered to the upper chuck140from the transfer arm. The upper wafer W1is attracted to and held by the upper chuck140with the non-bonding surface W1nthereof in contact with the upper chuck140(process S104).

While the above-described processes S101to S104are being performed on the upper wafer W1, a processing of the lower wafer W2is performed. First, the lower wafer W2is taken out of the cassette C2by the transfer device22and transferred into the transition device50of the processing station3by the transfer device22.

Thereafter, the lower wafer W2is transferred into the surface modifying apparatus30by the transfer device61, and the bonding surface W2jof the lower wafer W2is modified (process S105). Further, the modification of the bonding surface W2jof the lower wafer W2in the process S105is the same as the above-stated process S101.

Then, the lower wafer W2is transferred into the surface hydrophilizing apparatus40by the transfer device61, and the bonding surface W2jof the lower wafer W2is hydrophilized (process S106). Further, the bonding surface W2jis cleaned by the pure water used to hydrophilize the bonding surface W2j. The hydrophilizing of the bonding surface W2jof the lower wafer W2in the process S106is the same as the hydrophilizing of the bonding surface W1jof the upper wafer W1in the above-described process S102.

Subsequently, the lower wafer W2is transferred into the bonding apparatus41by the transfer device61(process S107).

Then, within the bonding apparatus41, the transfer arm of the transfer device61is moved to be located above the lower chuck141. Then, the lower wafer W2is delivered onto the lower chuck141from the transfer arm. The lower wafer W2is attracted to and held on the lower chuck141with the non-bonding surface W2nthereof in contact with the lower chuck141(process S108).

Thereafter, the position adjustment in the horizontal direction between the upper wafer W1held by the upper chuck140and the lower wafer W2held by the lower chuck141is performed (process S109). In this position adjustment, the alignment marks W1a, W1band W1c(seeFIG.9AtoFIG.9C) previously formed on the bonding surface W1jof the upper wafer W1or the alignment marks W2a, W2band W2cpreviously formed on the bonding surface W2jof the lower wafer W2(seeFIG.9AtoFIG.9C) are used.

An operation of the position adjustment of the upper wafer W1and the lower wafer W2in the horizontal direction will be elaborated with reference toFIG.9AtoFIG.9C.FIG.9Ais a diagram for describing an operation of performing the position adjustment between the upper imaging device and the lower imaging device according to the present exemplary embodiment.FIG.9Bis a diagram for describing an imaging operation through which the upper imaging device images the lower wafer and an imaging operation through which the lower imaging device images the upper wafer according to the present exemplary embodiment.FIG.9Cis a diagram for describing an operation of performing the position adjustment between the upper wafer and the lower wafer according to the present exemplary embodiment.

First, as shown inFIG.9A, the position adjustment between the upper imaging device151A and the lower imaging device161A in the horizontal direction is performed. To elaborate, the lower chuck141is moved in the horizontal direction by the position adjuster166to allow the lower imaging device161A to be located under the upper imaging device151A approximately. Then, a common target149is checked by the upper imaging device151A and the lower imaging device161A, and a position of the lower imaging device161A in the horizontal direction is finely adjusted so that the positions of the upper imaging device151A and the lower imaging device161A in the horizontal direction are coincident.

Then, as depicted inFIG.9B, the lower chuck141is moved in the vertically upward direction by the position adjuster166. Then, while moving the lower chuck141in the horizontal direction by the position adjuster166, the alignment marks W2c, W2band W2aon the bonding surface W2jof the lower wafer W2are imaged in sequence by using the upper imaging device151A. Concurrently, while moving the lower chuck141in the horizontal direction, the alignment marks W1a, W1band W1con the bonding surface W1jof the upper wafer W1are imaged in sequence by using the lower imaging device161A.FIG.9Bshows a state in which the alignment marks W2cof the lower wafer W2is imaged by the upper imaging device151A and the alignment mark W1aof the upper wafer W1is imaged by the lower imaging device161A.

The obtained image data are output to the control device70. Based on the image data obtained by the upper imaging device151A and the image data obtained by the lower imaging device161A, the control device70controls the position adjuster166to adjust the position of the lower chuck141in the horizontal direction. This horizontal position adjustment is carried out such that the alignment marks W1a, W1band W1cof the upper wafer W1and the alignment marks W2a, W2band W2cof the lower wafer W2are respectively overlapped, when viewed in the vertical direction. In this way, the horizontal positions of the upper chuck140and the lower chuck141are adjusted, and the horizontal positions (for example, including positions in the X-axis direction, the Y-axis direction and the θ direction) of the upper wafer W1and the lower wafer W2are adjusted.

Thereafter, as indicated by solid lines inFIG.9C, the position adjustment in the vertical direction between the upper wafer W1held by the upper chuck140and the lower wafer W2held by the lower chuck141is performed (process S110). To elaborate, the position adjuster166moves the lower chuck141in the vertically upward direction, thus allowing the lower wafer W2to approach the upper wafer W1. Accordingly, as shown inFIG.6, a distance WS1between the bonding surface W2jof the lower wafer W2and the bonding surface W1jof the upper wafer W1is adjusted to, e.g., 50 μm to 200 μm. For example, the distance WS1may be measured by the upper displacement meter151B and the lower displacement meter161B.

Subsequently, after releasing the attracting and holding of the central portion of the upper wafer W1by the upper chuck140(process S111), the push pin191of the striker190is lowered, so that the central portion of the upper wafer W1is pressed down (process S112), as shown inFIG.7A. If the central portion of the upper wafer W1comes into contact with the central portion of the lower wafer W2and the central portion of the upper wafer W1and the central portion of the lower wafer W2are pressed against each other with a preset force, the central portion of the upper wafer W1and the central portion of the lower wafer W2which are pressed against each other are begun to be bonded. Then, a bonding wave whereby the upper wafer W1and the lower wafer W2are gradually bonded from the central portion toward the peripheral portions thereof is generated.

Here, since the bonding surface W1jof the upper wafer W1and the bonding surface W2jof the lower wafer W2are modified in the processes S101and S105, respectively, a Van der Waals force (intermolecular force) is generated between the bonding surfaces W1jand W2j, so that the bonding surfaces W1jand W2jare bonded. Further, since the bonding surface W1jof the upper wafer W1and the bonding surface W2jof the lower wafer W2are hydrophilized in the processes S102and S106, respectively, hydrophilic groups between the bonding surfaces W1jand W2jare hydrogen-bonded, so that the bonding surfaces W1jand W2jare firmly bonded.

Thereafter, while pressing the central portion of the upper wafer W1and the central portion of the lower wafer W2with the push pin191, the attracting and holding of the entire upper wafer W1by the upper chuck140is released (process S113). Accordingly, as depicted inFIG.7B, the entire bonding surface W1jof the upper wafer W1and the entire bonding surface W2jof the lower wafer W2come into contact with each other, and the upper wafer W1and the lower wafer W2are bonded. Thereafter, the push pin191is raised up to the upper chuck140, and the attracting and holding of the lower wafer W2by the lower chuck141is released.

Thereafter, the combined wafer T is transferred to the transition device51of the third processing block G3by the transfer device61, and then is transferred into the cassette C3by the transfer device22of the carry-in/out station2. Through these processes, the series of operations of the bonding processing are completed.

<Foreign Substance Inspection on Lower Chuck>

The series of operations of the bonding processing described in the processes S101to S113shown inFIG.8are repeated, so that the combine wafers T are manufactured repeatedly. Meanwhile, in the processes in which the upper wafer W1and the lower wafer W2are brought into contact with and bonded to each other as shown inFIG.6, the lower wafer W2may be attracted to and held by the lower chuck141in the state that a foreign substance adheres to the non-bonding surface W2n. If such a foreign substance exists, the lower wafer W2may be deformed and protrusion of the upper wafer W2may occur. As a result, a void may be formed between the lower wafer W2and the upper wafer W1. Furthermore, if the foreign substance remains on the lower chuck141, the void may be continuously formed afterwards unless the foreign substance is eliminated.

As a resolution, in the present exemplary embodiment, foreign substance inspection is performed appropriately after the lower wafer W2is attracted to and held by the lower chuck141(process S108) and before the horizontal position adjustment between the upper wafer W1and the lower wafer W2is performed (process S109). FIG.10is a flowchart illustrating a method of performing the foreign substance inspection according to the exemplary embodiment. Various processes shown inFIG.10are performed under the control of the control device70.

First, if the lower wafer W2is attracted to and held by the lower chuck141, the top surface (bonding surface W2j) of the lower wafer W2is observed (process S11).

Then, if protrusion, which satisfies a preset condition, does not exist on the bonding surface W2jof the lower wafer W2(process S12), the bonding processing is performed (process S13). That is, the horizontal position adjustment between the upper wafer W1and the lower wafer W2is performed (process S109), and the processes S110to S113are then performed. Details of a method of performing the observation in the process S11and making the determination upon the presence or absence of the protrusion in the process S12will be elaborated later. The preset condition is related to a height from the top surface of the lower chuck141, and the protrusion is caused mainly by the foreign substance. The protrusion is an example of a singularity.

Meanwhile, if the protrusion, which satisfies the preset condition, is found on the bonding surface W2jof the lower wafer W2(process S12), the lower wafer W2is taken out of the bonding apparatus41(process S14).

Then, it is detected whether the protrusion is found at the same position of two sheets of lower wafers W2consecutively (process S15). If the protrusion is detected at the same position, it means that the foreign substance exists, and if the processing is continued in this state, there is a high likelihood that the void may be formed at a next combined wafer T. Thus, the bonding processing is stopped (process S16). In this case, the stopping of the bonding processing is notified to the operator by using, for example, a lamp or a sound, or both of them. Further, in case that there is a host computer which manages the bonding system1, the stopping of the bonding processing may be notified to the host computer.

Meanwhile, if the protrusion is not detected at the same position of the two sheets of lower wafers W2consecutively, the transfer (process107) and the attracting/holding (process S108) of another lower wafer W2are performed (process S17). This is because that if the protrusion is detected only at a single sheet of lower wafer W2, the foreign substance having caused the protrusion may be removed from the bonding apparatus41when this lower wafer W2is taken out of the bonding apparatus41in the process S14and may not remain on the lower chuck141. After transferring and attracting/holding this another lower wafer W2, the bonding surface W2jof this lower wafer W2is observed (process S11).

According to the present exemplary embodiment, the foreign substance inspection upon the top surface of the lower chuck141can be performed appropriately. Accordingly, even if the foreign substance is carried into the bonding apparatus41by being attached to the non-bonding surface W2nof the lower wafer W2and this foreign substance remains on the top surface of the lower chuck141, this foreign substance can be detected appropriately.

Further, in the present exemplary embodiment, presence or absence of the protrusion is determined by observing the top surface (bonding surface W2j) of the lower wafer W2attracted to and held by the lower chuck141. By way of example, in case that the foreign substance has a thin needle shape extending in the Z-axis direction, this foreign substance may be difficult to detect if the lower wafer W2is observed from directly above without being placed on the lower chuck141. If the lower wafer W2is placed on the lower chuck141, however, this lower wafer W2may be deformed over a wide range by being affected by the foreign substance, and the protrusion of this lower wafer W2may occur. Thus, a feature indicting the presence of the foreign substance appears in a wide range across the top surface of the lower wafer W2, so that it is easy to detect the presence of the foreign substance.

First Example of Method of Observing Top Surface of Lower Wafer and Determining Presence or Absence of Protrusion

Now, a first example of the method of observing the top surface of the lower wafer in the process S11and determining presence or absence of the protrusion in the process S12will be explained.FIG.11is a schematic diagram illustrating the first example of the method of observing the top surface of the lower wafer and determining presence or absence of the protrusion.FIG.12is a flowchart illustrating the first example of the method of observing the top surface of the lower wafer and determining presence or absence of the protrusion. Further, various processes shown inFIG.12are performed under the control of the control device70.

In the first example, the top surface of the lower wafer W2is observed by using the upper imaging device151A. To be more specific, observation patterns are previously formed at multiple positions on the top surface of the lower wafer W2, and focus adjustment is performed for each observation pattern by the upper imaging device151A. Then, a distance to each observation pattern in the Z-axis direction is specified based on a focus position. For example, as illustrated inFIG.11, on the top surface of the lower wafer W2, intersection points between a multiple number of straight lines202extending in the X-axis direction and arranged at a regular distance therebetween in the Y-axis direction and a multiple number of straight lines203extending in the Y-axis direction and arranged at a regular distance therebetween in the X-axis direction are set as measurement points, and the observation patterns are provided at these measurement points. The distance between the straight lines202and203is set to be, e.g., 10 mm to 30 mm. The observation patterns may not be provided in a region201on a periphery of the lower wafer W2where no semiconductor chip or the like is formed.

In the first example, the lower chuck141is moved in the horizontal direction by the position adjuster166to allow the upper imaging device151A to be located above one of the measurement points (process S21).

Then, the focus adjustment by the upper imaging device151A is performed, and a focus position of the observation pattern at the corresponding measurement point is measured (process S22). Then, the focus position is recorded (process S23).

The series of processes S21to S23are repeated until the measuring and the recoding of the focus position are completed for all of the measurement points (process S24).

Upon the completion of the measuring and the recording of the focus position for all the measurement points (process S24), the focus positions are analyzed, and it is determined whether the protrusion exists. That is, it is determined whether there is a measurement point where a Z-coordinate Z1of a focus position is larger than a Z-coordinate Z2of a focus position at a nearby measurement point and a difference between the Z-coordinates Z1and Z2exceeds a preset threshold value Zth, for example, 10 μm (process S25).

If there is no measurement point where the Z-coordinate Z1is larger than the Z-coordinate Z2and the difference therebetween exceeds the threshold value Zth, it is deemed that the lower wafer W2does not have the protrusion on the entire top surface thereof, and the processing is ended. In this case, the processing then proceeds to the process S13(seeFIG.10).

Meanwhile, if there is a measurement point where the Z-coordinate Z1is larger than the Z-coordinate Z2and the difference therebetween exceeds the threshold value Zth, it is deemed that the protrusion exists at the corresponding measurement point, and an X-coordinate and a Y-coordinate of the corresponding measurement point are specified and recorded, and the processing is ended (process S26). In this case, the processing then proceeds to the process S14(seeFIG.10). For example, as depicted in FIG.13, if a Z-coordinate Z1at a measurement point204is larger than a Z-coordinate Z2at a nearby measurement point and the difference therebetween is larger than the threshold value Zth, an X-coordinate and a Y-coordinate of the measurement point204are specified and recorded. The measurement point204are adjacent to two measurement points in the X-axis direction and two measurement points in the Y-axis direction. If the aforementioned relationship is established between the measurement point204and at least one of these neighboring measurement points, the X-coordinate and the Y-coordinate of the measurement point204are specified and recorded. In the process S15, it is determined, based on the X-coordinate and the Y-coordinate recorded in the process S26, whether the protrusion exists at the same measurement point on two sheets of lower wafers consecutively.

In the first example, the above-described series of processes are performed. According to the first example, a height of the protrusion can be specified accurately.

Further, the reference for the determination of the presence or absence of the protrusion in the process S25is not limited to the above-described example. By way of example, it may be determined whether there exists a measurement point, within the all measurement regions, where a difference from a minimum Z-coordinate Zmin exceeds a predetermined threshold value Zth, for example, 10 μm.

Furthermore, as shown inFIG.14, even if the upper imaging device151A is not located directly above a foreign substance210on the lower chuck141, the protrusion can still be detected if the upper imaging device151A is located above a range211where the lower wafer W2is protruded because of the foreign substance210. Thus, it is desirable to set the distance between the measurement points based on a size of the foreign substance which causes the formation of the void between the lower wafer W2and the upper wafer W1.

Second Example of Method of Observing Top Surface of Lower Wafer and Determining Presence or Absence of Protrusion

Now, a second example of the method of observing the top surface of the lower wafer in the process S11and determining presence or absence of the protrusion in the process S12will be explained.FIG.15is a flowchart illustrating the second example of the method of observing the top surface of the lower wafer and determining presence or absence of the protrusion. Further, various processes shown inFIG.15are performed under the control of the control device70.

In the second example, the top surface of the lower wafer W2is observed by using the upper imaging device151A. To elaborate, observation patterns are previously formed at multiple positions on the top surface of the lower wafer W2, and a focus is fixed based on, for example, a distance between the upper imaging device151A and the lower wafer W2in the foreign substance inspection, and it is determined whether a proper contrast is obtained for each observation pattern. For example, as in the first example, the intersection points between the straight lines202and the straight lines203are set as the measurement points, and the observation patterns are formed at these measurement points.

In the second example, the focus is first set and fixed based on the distance between the upper imaging device151A and the lower wafer W2or the like (process S31). The focus set in the process S31is a focus for the observation pattern when the top surface of the lower wafer W2attracted to and held by the lower chuck141is observed in the state that no foreign substance exists on the top surface of the lower chuck141. Thus, if no foreign substance exits across the entire top surface of the lower chuck141, the observation pattern at each measurement point can be observed with a high contrast.

Subsequently, the lower chuck141is moved in the horizontal direction by the position adjuster166to allow the upper imaging device151A to be located above one of the measurement points (process S32).

Thereafter, while maintaining the focus fixed, the observation pattern is observed by the upper imaging device151A, and a height of the contrast thereof is measured (process S33).

Then, the height of the contrast measured in the process S33is analyzed, and it is determined whether the height of the contrast is equal to or larger than a threshold value (process S34). If the height of the contrast measured in the process S33is equal to or higher than the threshold value, it is deemed that no protrusion exists at the corresponding measurement point, so the processing proceeds to a process S36. Here, the height of the contrast obtained when the protrusion is caused as a result of the foreign substance having a height of, e.g., 10 μm is used as the threshold value for the height of the contrast.

Meanwhile, if the contrast measured in the process S33is not equal to or larger than the threshold value, it is deemed that an out-focus is caused as the protrusion exists at the corresponding measurement point, and an X-coordinate and a Y-coordinate of the corresponding measurement point are specified and recorded (process S35). Then, the processing proceeds to the process S36.

The series of processes S31to S35are repeated until the measuring of the contrast is performed for all the measurement points and the recording of the coordinates of measurement point having a contrast less than the threshold value is completed, and, then, the processing is ended (process S36).

If the contrasts at all the measurement points are equal to or larger than the threshold value, it is determined that no protrusion exists on the entire top surface of the corresponding lower wafer W2, and the processing proceeds to the process S13(seeFIG.10). Meanwhile, if a contrast at a certain measurement point is less than the threshold value, it is determined that the protrusion exists on the top surface of the corresponding lower wafer W2, and the processing proceeds to the process S14(seeFIG.10).

In the second example, the above-described series of processes are performed. According to the second example, since the focus adjustment need not be performed at each measurement point, a time required to complete the series of processes can be shortened.

Third Example of Method of Observing Top Surface of Lower Wafer and Determining Presence or Absence of Protrusion

Now, a third example of the method of observing the top surface of the lower wafer in the process S11and determining presence or absence of the protrusion in the process S12will be explained.FIG.16is a first schematic diagram illustrating the third example of the method of observing the top surface of the lower wafer and determining presence or absence of the protrusion.FIG.17is a second schematic diagram illustrating the third example of the method of observing the top surface of the lower wafer and determining presence or absence of the protrusion.FIG.18is a flowchart illustrating the third example of the method of observing the top surface of the lower wafer and determining presence or absence of the protrusion. Further, various processes shown inFIG.18are performed under the control of the control device70.

In the third example, the top surface of the lower wafer W2is observed by using the upper displacement meter151B. To be more specific, while scanning the entire top surface of the lower wafer W2as illustrated inFIG.16or while scanning a peripheral portion of the top surface of the lower wafer W2as illustrated inFIG.17, a displacement (Z-displacement) (Z-coordinate) of the top surface of the lower wafer W2in the Z-axis direction is measured by the upper displacement meter151B.

In the third example, scanning is first begun by moving the lower chuck141in the horizontal direction by the position adjuster166(process S41). While carrying on the scanning, the Z-displacement (Z-coordinate) of the top surface of the lower wafer W2is measured by the upper displacement meter151B, and the measured Z-displacement is recorded (process S42). A scanning target may be the entire top surface of the lower wafer W2as illustrated inFIG.16, or may be the peripheral portion of the top surface of the lower wafer W2as illustrated inFIG.17.

The series of processes S41and S42are repeated until the measuring and recording of the Z-displacement is completed for the entire scanning target (process S43).

Upon the completion of the measuring and the recording of the Z-displacement for all of measurement points (process S43), the Z-displacements are analyzed to determine whether the protrusion exists. That is, it is determined whether there is a point, within a region of the scanning target, where a difference from a minimum Z-coordinate Zmin exceeds a predetermined threshold value Zth, e.g., 10 μm (process S44).

If there is no point where the difference from the minimum Z-coordinate Zmin exceeds the threshold value Zth, it is determined that no protrusion exists on the entire top surface of the corresponding lower wafer W2, and the processing is ended. In this case, the processing then proceeds to the process S13(seeFIG.10).

Meanwhile, if there is a point where the difference from the minimum Z-coordinate Zmin exceeds the threshold value Zth, it is determined that the protrusion exists, and a X-coordinate and a Y-coordinate of the corresponding point are specified and recorded, and then the processing is ended (process S45). In this case, the processing then proceeds to the process S14(seeFIG.10). In the process S15, it is determined, based on the X-coordinate and the Y-coordinate recorded in the process S45, whether the protrusion exists at the same point on two sheets of lower wafers W2consecutively.

In the third example, the above-described series of processes are performed. According to the third example, since the focus adjustment is not required before and during the observation, a time required for the series of processes can be further shortened. Furthermore, the lower wafer W2need not have patterns for focus adjustment.

Further, by scanning the entire top surface, as depicted inFIG.16, high-accuracy foreign substance inspection can be carried out. Further, if the most recent processing in which the bonding processing is performed is a processing, such as chemical mechanical polishing, in which positions to which the foreign substances easily adhere are concentrated at the peripheral portion of the wafer, scanning the peripheral portion as shown inFIG.17may be enough. By scanning only the peripheral portion, the time required to complete the series of processes can be further reduced. By way of example, a scanning target upon the peripheral portion may be a region ranging from 30 mm from an edge of the wafer.

Further, in the bonding processing of the wafers, a size of an allowable foreign substance may differ depending on the electronic circuit formed on the wafer. In case of scanning the entire top surface as shown inFIG.16, scanning pitches P and P′ may be varied based on the size of the allowable foreign substance. To elaborate, if the allowable foreign substance is comparatively large, the protrusion can be detected even if the scanning pitch P is enlarged as compared to a case where the allowable foreign substance is small. By enlarging the scanning pitches P and P′, presence or absence of the protrusion can be determined, and the time required for the series of processes can be reduced.

In addition, the reference for the determination of the presence or absence of the protrusion in the process S44is not limited to the above-described example. By way of example, if there is a point where the Z-coordinate is maximum, it may be possible to make a determination upon whether a difference between this maximum Z-coordinate and a Z-coordinate of a nearby point where the Z-coordinate is minimum is equal to or larger than a threshold value Zth. Further, for this point, it may be possible to determine whether a gradient of the variation of the Z-coordinate between the point where the Z-coordinate is maximum and the point where the Z-coordinate is minimum is equal to or larger than a preset threshold value Sth.

In the first example, the second example and the third example, the foreign substance inspection using the upper imaging device151A and the foreign substance inspection using the upper displacement meter151B may be combined.

A frequency of the foreign substance inspection is not particularly limited. For example, the foreign substance inspection may be performed whenever the lower wafer W2is carried in, whenever a preset number of combined wafers T are processed, or before a first lower wafer W2of each lot is carried in. Furthermore, the foreign substance inspection may be performed whenever the preset number of combined wafers T are processed and, also, before the first lower wafer W2of each lot is carried in. Further, the foreign substance inspection may be performed at any required time.

In the flowchart shown inFIG.10, the processing is stopped when the foreign substance is detected at the same position on the two sheets of lower wafers W consecutively. However, the processing may be stopped when the foreign substance is detected at the same position on three or more lower wafers W2consecutively. Furthermore, the processing may be stopped when the foreign substance is detected at a single sheet of lower wafer W2.

When taking out the lower wafer W2in the process S14, the upper wafer W1attracted to and held by the upper chuck140may be taken out along with the lower wafer W2. In this case, the transfer (process S103) and the attracting/holding (process S104) of another upper wafer W1may be performed in the process S17.

An automatic cleaning device such as a cleaning pad for the lower chuck141may be embedded in the bonding apparatus41, and the foreign substance on the top surface of the lower chuck141may be removed by driving the automatic cleaning device instead of stopping the processing in the process S16. In case of removing the foreign substance by using the automatic cleaning device, the lower wafer W2taken out in the process S14may be used as the another lower wafer W2in the process S17.

If a determination on the processing stop is made in a certain foreign substance inspection, there is a likelihood that the foreign substance may adhere to combined wafers T which are manufactured during a period until the corresponding foreign substance inspection after the most recent foreign substance inspection, and these combined wafers T may be soft-marked. This information may be stored in the host computer which manages characteristics of the combined wafer T.

When determining whether to carry on or stop the processing, not only the size of the protrusion on the lower wafer W2but also the position where the protrusion exists may be considered. By way of example, assume that a multiple number of semiconductor chips are diced from the lower wafer W2. If the protrusion occurs at the center of the lower wafer W2, the void may affect multiple semiconductor chips within an XY plane in all directions with respect to the protrusion. Meanwhile, if the protrusion occurs near the edge of the lower wafer W2, the number of semiconductor chips which are affected by the void, if any, may be small at the edge portion of the lower wafer W2. In this way, a yield differs depending on the position of the protrusion. Further, even if the number of high-quality semiconductor chips obtained from a single sheet of combined wafer T is reduced to a certain extent, it may be desirable, in the interests of time, to perform the cleaning of the lower chuck141after the bonding processing for the rest of wafers accommodated in the bonding system1is completed. Accordingly, by assigning a weight to each of the size of the protrusion and the position of the protrusion, for example, the determination upon whether to carry on or stop the processing may be made in consideration of all of these factors. In this case, the number of remaining wafers accommodated in the bonding system1may be additionally considered.

As the lower wafer W2attracted to and held on the lower chuck141in the foreign substance inspection, a dummy wafer which is not used in the manufacture of a real product may be used. Particularly, if the displacement meter is used, it is desirable that a dummy wafer having uniform color on the entire surface thereof is used as the lower wafer W2. Since the surface color of the dummy wafer is uniform on the entire surface thereof, it is possible to detect presence or absence of the protrusion accurately with the displacement meter. Further, in this case, it is desirable to provide the dummy wafer within the bonding system1.

According to the exemplary embodiment, the foreign substance adhering to the chuck can be detected appropriately.

So far, the exemplary embodiments or the like have been described in detail. However, the exemplary embodiments are not limiting, and various changes and modifications may be made without departing from the scope of the present disclosure as claimed in the following claims.