JP2007194347A - Laminating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the number of devices taken out of an SOI substrate by preventing occurrence of voids at the periphery of a laminate substrate. <P>SOLUTION: The advancing speed of laminating is set within a specified range to prevent occurrence of voids. In the case (for example) of laminating of silicon wafers of 725 μm in thickness together, the speed is set to be 0.1-50 mm/second. The advancing speed of lamination is controlled by viscosity, kind, and pressure of atmosphere. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an apparatus for bonding a plurality of semiconductor substrates, and more particularly to a semiconductor substrate bonding apparatus used when bonding semiconductor devices having an SOI structure by a bonding method.

  In a semiconductor manufacturing process, a technique for manufacturing an SOI substrate by using a bonding method is known (for example, see Patent Document 1). This technique applies a direct wafer bonding technique in which a silicon epitaxial layer grown on porous silicon is bonded to an amorphous substrate or a single crystal silicon substrate via an oxide film.

  As a bonding apparatus, Patent Document 1 is disclosed.

In the bonding, the mirror surfaces are opposed to each other with a very small interval, and one of the two substrates kept in a substantially horizontal state with the gas sandwiched between them is pressed and brought into contact, and the entire surface is joined starting from that point. . In general, the state in which the junction region expands is called a contact wave, and the traveling speed is called a contact wave speed. It is disclosed in the literature that the contact wave speed varies depending on the viscosity of the atmosphere and the atmospheric pressure when bonding. (See Non-Patent Document 1)
The contact wave speed depends on the bonding strength, and the higher the strength, the higher the tendency. The bonding strength depends on the state of the wafer surface. In general, the larger the moisture adsorption amount in the non-condensing range, the higher the bonding strength. Moreover, when organic substance contamination etc. adhere, bonding strength will fall.
JP 2004-266070 A (Semiconductor Wafer Bonding; Tong, Gosele)

  When wafer bonding is performed by the above method, fine voids of about 0.1 to 1 mmφ frequently occur in the range of 3 to 5 mm from the edge of the outer periphery of the wafer, resulting in a defect. When the bonding start point is at the outer periphery of the wafer, voids tend to occur near the edge opposite to the start point with respect to the wafer center (FIG. 1). Further, when bonding is started from the center of the wafer, it tends to occur almost all around.

  As a result of our intensive investigations, it was clarified that voids occur when the contact wave speed exceeds 50 mm / sec (Fig. 2). In general, for example, when bonding is started from the center of the wafer, the contact wave speed is rapidly accelerated from the vicinity of the outermost periphery of 5 mm. That area coincides with the void generation area. Therefore, the contact wave speed is always set to 50 mm / second or less in order to prevent generation of peripheral voids. For this purpose, it is effective to reduce the contact wave speed particularly in the latter half of the bonding.

  On the other hand, the contact wave speed becomes smaller as the bonding strength becomes lower. Therefore, if the contact wave speed is lowered by lowering the bonding strength of the whole wafer or the like, voids are not generated on the outer periphery of the wafer. In that case, however, the contact wave near the bonding start point becomes extremely slow in order to reduce the outermost contact wave speed. In the case of extremely slow bonding, bonding is started simultaneously from a plurality of locations, as is practically the case where the entire wafer surface is bonded at the same time. As a result, voids are formed on the entire wafer surface. In addition, if the contact wave speed is extremely slow, it takes a long time for production, which is disadvantageous in terms of cost. In that sense, it is desirable that the contact wave speed is not extremely slow.

  In addition, the contact wave speed depends on the bonding strength, and the bonding strength is sensitive to subtle disturbances. Therefore, in production, it is beneficial to always monitor the contact wave speed and keep it at an appropriate speed. In view of the above knowledge, the present invention is a bonding apparatus having a function of controlling the progress speed of bonding in accordance with the progress of bonding, and the bonding apparatus whose progress speed control method is atmosphere control, or It is an object of the present invention to provide a bonding apparatus that has both a function of monitoring a contact wave speed in bonding and a function of adjusting the contact wave speed accordingly.

  Further, the traveling speed detection function can be performed by a non-contact height meter. Specifically, it is a method using a laser displacement meter or interference with an optical flat surface.

  The traveling speed detection function can be based on image analysis using light having a wavelength that is transparent to the object to be bonded. For example, in the case of bonding silicon, the contact wave can be observed using near infrared light having a wavelength of about 1100 nm. Generally, the bonded portion looks higher in luminance than the unbonded portion. In this way, the progress of the contact wave can be observed. In addition, for example, when pasting members that are transparent to visible light such as quartz, interference fringes appear along the gap, so that the progress of the contact wave can be confirmed directly by visual observation. It is also possible to shoot with a camera.

  It is disclosed in the above document that the traveling speed of the contact wave can be slowed by increasing the pressure of the bonding environment or increasing the viscosity of the atmosphere. Based on this knowledge, the traveling speed can be controlled by controlling the pressure of the bonding environment or by controlling the type of atmosphere in the bonding environment. The viscosity of the atmosphere varies depending on the type of gas.

  With the above function, the generation of voids can be prevented by maintaining the contact wave speed at 0.1 mm / second or more and 50 mm / second or less.

  The contact wave speed at which voids were generated was 0.1 mm / second or more and 50 mm / second or more in this experiment, but this value may vary if the members to be bonded are different. For example, it may vary depending on the type of material constituting the substrate, the flatness of the surface, the thickness of the substrate, and the like. The apparatus of the present invention can cope with such a situation by changing the target speed to be set, and is not necessarily limited to 0.1 mm / second or more and 50 mm / second.

  According to the present invention, in a semiconductor substrate bonding apparatus used when bonding a semiconductor device having an SOI structure by the bonding method, it is possible to prevent voids from occurring in the peripheral portion of the bonded substrate and to remove a device from the SOI substrate. The number can be improved.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

This is an apparatus for bonding two silicon wafers with a diameter of 200 mm and a thickness of 725 μm at room temperature. The place where the bonding is performed is an airtight structure, and a pressure gauge and a pump are connected. First, the edge of the wafer is pushed from the top while keeping the two wafers substantially horizontal at 1 atmosphere, and the contact wave is started. The contact wave speed is almost constant at 22 mm / sec at the start of bonding, but accelerates to 60 mm / sec near 5 mm at the end. Therefore, raising the pressure to 8 seconds after the start of bonded, reducing the contact wave velocity v _cw. For example, according to the graphs in the literature, near the atmospheric pressure, v _cw is proportional to x ^−0.2 with respect to the atmospheric pressure X. Therefore, for example, if the contact wave speed is 60 mm / sec at 1 atm, the pressure is 50 mm / sec at 2.5 atm and 40 mm / sec at 7 atm. By adjusting the contact wave speed in this way, it is possible to realize bonding without voids on the entire surface.

This is an apparatus for bonding two silicon wafers with a diameter of 200 mm and a thickness of 725 μm at room temperature (FIG. 3). The lower wafer is vacuum chucked on a quartz stage, irradiated with IR light (light near 1100 nm wavelength) from below, and observed from above with a camera sensitive to IR light. The place where the bonding is performed is an airtight structure, and a pressure gauge and a pump are connected. Under this environment, the edge of the wafer is pushed from the top with the two wafers kept substantially horizontal to start the contact wave. The progress of the contact wave is monitored with an IR camera. Focusing on the contrast at the center of the wafer, the time when the brightness becomes a certain level or more is regarded as the time when the contact wave passes through the center of the wafer, and the contact wave speed is calculated. Bonding starts from the end of the wafer at time t0, and when the time when the contact wave passes through the center of the wafer is t1, the contact wave speed v _cw is v _cw = 100 / (t1−t0) [mm / sec] It is expressed. In general, voids are generated after the contact wave exceeds half, so there are no voids at this point. When the contact wave speed exceeds 50 mm / sec in the pasting after the center, a void is formed. Therefore, the pump is operated and the air pressure is increased at a rate in accordance with the above-mentioned literature, thereby reducing the contact wave speed. For example, according to the graphs in the literature, near the atmospheric pressure, v _cw is proportional to x ^−0.2 with respect to the atmospheric pressure X. Thus, for example, if the contact wave speed is 60 mm / second at 1 atmosphere, the pressure is 50 mm / second at 2.5 atmospheres and 40 mm / second at 7 atmospheres. In this way, the contact wave speed is adjusted.

This is an apparatus for bonding two silicon wafers with a diameter of 200 mm and a thickness of 725 μm at room temperature (FIG. 4). The lower wafer is vacuum chucked on the stage, and the height of the upper wafer is measured by a laser displacement meter from above. The place where the bonding is performed is an airtight structure, and a pressure gauge and a pump are connected. Under this environment, the edge of the wafer is pushed from the top with the two wafers kept substantially horizontal to start the contact wave. The progress of the contact wave is monitored with a laser displacement meter. Paying attention to the height of the central portion of the wafer, the time when the height falls below a certain level is regarded as the time when the contact wave passes through the center of the wafer, and the contact wave speed is calculated. Bonding starts from the end of the wafer at time t0, and when the time when the contact wave passes through the center of the wafer is t1, the contact wave speed v _cw is v _cw = 100 / (t1−t0) [mm / sec] It is expressed. In general, voids are generated after the contact wave exceeds half, so there are no voids at this point. When the contact wave speed exceeds 50 mm / sec in the pasting after the center, a void is formed. Therefore, the pump is operated and the air pressure is increased at a rate in accordance with the above-mentioned literature, thereby reducing the contact wave speed. For example, according to the graphs in the literature, near the atmospheric pressure, v _cw is proportional to x ^−0.2 with respect to the atmospheric pressure X. Therefore, for example, if the contact wave speed is 60 mm / sec at 1 atm, the pressure is 50 mm / sec at 2.5 atm and 40 mm / sec at 7 atm. In this way, the contact wave speed is adjusted.

Further, according to the same document, it is disclosed that v _cw becomes faster as the reciprocal x [μP] of the viscosity of the atmosphere increases. In the literature, the relationship is v _cw [cm / s] = Ax + B (A and B are constants). According to the Chemical Handbook (Maruzen), the viscosity of air at 25 ° C and 1 atm is 18.20μPa seconds (1μPa seconds = 10μP relationship), so if the contact wave speed is 55cm / second in air, Ne gas is used in the atmosphere. If (29.50 μPa second) is used, it becomes 49 cm / second. Thus, the contact wave speed can be controlled by selecting the atmosphere.

The figure which shows the tendency for a void to generate | occur | produce in the edge vicinity on the opposite side of a starting point with respect to a wafer center, when the bonding start point is an outer peripheral part of a wafer. The figure which shows the relationship between contact wave speed and generation | occurrence | production of a void. The figure which shows the bonding apparatus in Example 2, and a flowchart. FIG. 10 is a diagram illustrating a bonding apparatus according to a third embodiment.

Claims (10)

  A bonding apparatus having a function of controlling a progress speed of bonding in accordance with the progress of bonding, wherein the progress speed control method is atmosphere control.   The bonding apparatus according to claim 1, wherein the control of the atmosphere controls the atmospheric pressure of the bonding environment.   The bonding apparatus according to claim 1, wherein the atmosphere control controls a type of atmosphere in a bonding environment.   The bonding apparatus according to claim 1, wherein the control of the atmosphere controls the viscosity of the atmosphere of the bonding environment.   A bonding apparatus characterized by having a function of detecting a progressing speed of bonding and a function of controlling a progressing speed of bonding.   The bonding apparatus according to claim 5, wherein the traveling speed detection function is a non-contact height meter.   The bonding apparatus according to claim 5, wherein the traveling speed detection function is image analysis using light having a wavelength that is transparent to a bonding target.   A bonding method characterized by using both the act of detecting the progress speed of bonding and the action of controlling the progress speed of bonding.   The bonding method according to claim 8, wherein the bonding speed is 50 mm / second or less.   The bonding method according to claim 8, wherein the bonding speed is 0.1 mm / second or more.

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