JPH0824099B2 - Alignment device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for aligning and temporarily fixing joints for highly accurate bonding of silicon semiconductor devices.

[Conventional technology]

In recent years, the limit for increasing the density of conventional integrated circuits is beginning to be seen, and a method of aiming for higher density by stacking device layers is being researched.

In particular, a method of thinning a device made by a normal silicon device process is described in “Development of SOI technology for polishing thin LSI of 0.5 to 1 μm and sticking to insulating plate” on page 76 of Nikkei Electronics 1986.10.6. It has been developed as described in the published paper, and a stacked device can be realized by stacking these.

The device thus manufactured has the advantage of good crystallinity and is expected to grow in the future.

FIGS. 2A to 2F are cross-sectional views of the silicon substrate, which are shown in the order of steps of the method for forming a two-layer device structure by the thin film stacking method. First, as shown in FIG. 2A, the second active layer 13 is formed on the silicon substrate 12.

Next, as shown in FIG. 2B, a silicon single crystal support substrate 15 is bonded to the upper surface of the second active layer 13 using an adhesive 14. Thereafter, as shown in FIG. 2C, the silicon substrate 12 is removed by rough polishing and mechanochemical polishing, leaving only the second active layer 13. Next, as shown in FIG. 2 (d), the first active layer 16 is placed on a silicon substrate 17 on which the first active layer 17 and the second active layer 13 are positioned relative to each other. Make an alignment. Then, as shown in FIG. 2 (e), the adhesive 18 is used for adhesion. Finally, Fig. 2 (f)
After the supporting substrate 15 is removed by rough polishing and mechanochemical polishing, the adhesive 14 remaining on the second active layer 13 is removed by means such as plasma ashing to complete a two-layer device structure, as shown in FIG. To do.

I explained how to create a two-layer device here,
Needless to say, by repeating the same steps, a device structure having a further multilayer structure can be formed.

However, when laminating devices thinned by this method, it is necessary to perform vertical alignment through a supporting substrate of a silicon single crystal wafer as shown in FIG. 2 (d),
Since it cannot be observed with visible light, a normal microscope etc. could not be used and precise alignment was impossible. Here, if the support substrate is changed to a transparent substrate such as glass or quartz, alignment with visible light is possible, but when the wafer is bonded, if the thermal expansion coefficient of the support substrate and silicon are different, bonding or the like may occur. There is a problem that the device layer expands and contracts due to the difference in expansion coefficient when heat is applied.

[Problems to be Solved by the Invention]

As described above, in the conventional alignment method using visible light, the joint surface cannot be observed and alignment is impossible. Further, it was difficult to bond the wafer.

An object of the present invention is to solve the above-mentioned drawbacks of the related art and to provide an aligning apparatus and a wafer bonding method that can perform alignment in μm unit when laminating devices by a thin film laminating method.

[Means for solving the problem]

1. The aligning device of the present invention is a device created 2
A mechanism for holding the wafers with the device forming surfaces facing each other, a mechanism for precisely moving at least one of the wafers in a horizontal plane to align each other, and an optical system for alignment using an infrared microscope, It is provided with a mechanism for moving at least one of the wafers in the vertical direction to bring the two wafers into pressure contact with each other.

2. The wafer bonding method of the present invention uses the aligning device described in item 1 to bond the two wafers in a pre-baked state after the polyimide resin has been applied to at least one of the device forming surfaces. It is characterized by

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a partially sectional front view showing an embodiment of the aligning device of the present invention. This aligning device includes upper and lower chucks 3 and 6 for holding a wafer and a lower chuck 6 for X and Y.
Moving table 7 that can be moved or rotated in any direction
And a Z stage 8 for vertically moving the moving table 7.
And a holder 4 for holding the upper chuck, and an infrared microscope 9 that moves above the upper chuck 3 by a microscope moving stage 11. Here, a device is created on the lower wafer 1 and the device surface is held upward. The upper wafer 2 is made into a thin film and is adhesively held on a supporting substrate so that the device surface is held downward. The relationship between the lower wafer 1 and the upper wafer 2 is similar to the relationship shown in FIG.

On the other hand, the upper chuck 3 holds the upper surface of the upper wafer 2 by a method such as vacuum chucking or adhesion, and is made of a material such as quartz glass or sapphire having sufficient rigidity and good infrared transmittance. The holder 4 supports the upper chuck 3 on the outer peripheral portion thereof and is fixed to the main body 5. further,
The lower chuck 6 holds the lower surface of the lower wafer 1 by a method such as vacuum chuck or adhesion.
The lower surface of the lower wafer 1 is held by a method such as vacuum chucking or adhesion, and is set on a moving table 7 that holds the lower wafer 1 so that it can be precisely moved in the X, Y, and θ directions in a horizontal plane. This moving table 7 is installed on the Z stage 8,
The Z stage 8 has a structure in which the lower wafer 1 is moved upward to bring the lower wafer 1 into close contact with the upper wafer 2. The infrared microscope 9 on the upper chuck 3 observes the positional relationship between the lower wafer 1 and the upper wafer 2 through the upper chuck and displays it on the monitor 10. For example, infrared rays with a wavelength of 1.2 μm or more have good transmittance for silicon. It is possible to observe and align the two device layers through the Si support substrate.
The microscope moving stage 11 is a moving mechanism for moving the infrared microscope 9 to perform alignment at a plurality of positions on the wafer, and is fixed to the main body 5.

Next, the operation of this aligning device will be described. On the surface of at least one of the lower wafer 1 and the upper wafer 2 on which the device is formed, for example, a polyimide resin (eg, DuPont 2570) is spun on as an adhesive,
Prebaking (for example, 110 ° C., 1 hour) is performed to form a uniform polyimide resin layer (not shown). Next, when the wafer in this state is pressed with a pressure of about 100 g / cm ² per unit area, the wafer is fixed in close contact. The fixed assembly of the two wafers is removed from the aligning device and is transferred to another pressurizing / heating device for main bonding. As a result, no cracks or defects were found on the device formation surface of the wafer.

In the present embodiment, the case where a thin film wafer bonded to the supporting substrate is used as the upper wafer 2 is described. However, when only a two-layer device is formed, it is formed on a normal silicon substrate. It is also possible to hold the device surface downward and join the devices by aligning. Further, the two wafers are aligned and brought into close contact with each other by moving the lower wafer, but if similar effects can be obtained, part or all of them may be moved by moving the upper wafer. further,
The structure is such that one infrared microscope 9 is used for alignment while moving, but it goes without saying that alignment can be made easier by using a plurality of microscopes or by using a binocular microscope as the objective lens. . On the other hand, as the structure of the upper chuck 3, a case has been described in which a material having a high infrared transmittance is used to hold the entire upper surface of the upper wafer. This is possible by adopting a structure such as provision. In this way, when using an infrared microscope, the resolution is 2 μm when observed at about 500 times on a 12-inch monitor.
As a result, it is possible to realize highly accurate laminated stacking.

〔The invention's effect〕

As described above, according to the alignment apparatus of the present invention, it is possible to perform precision alignment through a silicon wafer, which has been impossible in the past, and to perform alignment after alignment without using a special fixing jig. The two wafers are brought into close contact with each other by pressure and fixed to each other, so that subsequent handling is easy. Furthermore, by using a polyimide resin as an adhesive, not only a wafer bonding method that does not cause cracks can be obtained, but this aligning device has excellent characteristics and is extremely effective when laminating thin film devices. .

[Brief description of drawings]

FIG. 1 is a partial cross-sectional front view showing an embodiment of the alignment apparatus of the present invention, and FIGS. It is sectional drawing of a silicon substrate. 1 ... Lower wafer, 2 ... Upper wafer, 3 ... Upper chuck,
4 ... Holder, 5 ... Main body, 6 ... Lower chuck, 7 ...
Moving stage, 8 ... Z stage, 9 ... Infrared microscope, 10 ... Monitor, 11 ... Microscope moving stage, 12 ...
Silicon substrate, 13 ... Second active layer, 14 ... Adhesive, 15
…… Support substrate, 16 …… First active layer, 17 …… Silicon substrate, 18 …… Adhesive.

Claims (2)

[Claims] 1. A mechanism for holding two wafers on which devices are formed with their device formation surfaces facing each other, a mechanism for precisely moving at least one of the wafers in a horizontal plane to align each other, and infrared rays. An aligning device comprising: an optical system for aligning using a microscope; and a mechanism for moving at least one wafer in the vertical direction to bring the two wafers into pressure contact with each other. 2. Using the aligning device according to claim 1,
A wafer bonding method characterized in that a polyimide resin is applied to at least one device formation surface of a single wafer and then bonded in a pre-baked state.