JPH05309558A - Polishing method of laminating wafer - Google Patents

Abstract

PURPOSE:To improve the polishing accuracy of the thickness of an SOI wafer layer being an element forming layer, in a manufacturing process of an SOT semiconductor base with a laminating wafer. CONSTITUTION:A laminating wafer 11 is stuck on a transparent mount plate 3 by using a transparent wax, and a polishing pad 1 is made in a transparent body. The laser beams a laser oscillator 4 generates are made to the beams with the wavelength equal to the thickness required to the element forming layer of the laminating wafer 11 by a wavelength converting device 5, and injected to the laminating wafer 11 in the whole reflecting angles through the polishing pad 1 and a slurry 10 with the refration factor higher than that of the laminating wafer 11. Since the light permeates when an SOI wafer of the laminating wafer 11 is made into a desired thickness, a polishing is carried out until a light detector 6 detects the permeation light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bonded wafer polishing method for realizing a thickness required for an element forming layer in a bonded wafer polishing process.

[0002]

2. Description of the Related Art Bonded wafers obtained by directly bonding an insulating layer between two Si wafers and bonding them by a bonding technology (bonding technology) are ICs with high breakdown voltage, high speed and high reliability. Has been attracting attention as a method of realizing this. The bonded wafer is an oxide film Si obtained by oxidizing the surface of the upper Si wafer of the two Si wafers.
O2 is formed and the upper Si wafer or SO
The I wafer and the lower Si wafer, that is, the base wafer are cleaned and then bonded at room temperature. When this is heat-treated at a high temperature of about 800 to 1100 ° C., the upper Si wafer and the lower Si wafer have an oxide film S.
Fully adhered via iO2. Next, an oxide film SiO2
The SOI wafer on which is formed is rough-ground and finish-ground by using, for example, a surface grinder, and is further polished to remove SO.
The I wafer is thinned to a predetermined thickness. By such a procedure, an SOI semiconductor substrate having an insulating layer, that is, an oxide film SiO2, interposed between the SOI wafer and the base wafer is manufactured.

[0003]

With one of the bonded wafers, that is, the SOI wafer, most of the thickness is removed by polishing by the above-described polishing method, and 1 μm is removed.
It is extremely difficult to leave a layer of m or less as an element forming layer with a uniform thickness. In particular, the variation in the thickness of the element forming layer is large and the accuracy is about ± 0.5 μm, so that the manufacturing yield of the SOI semiconductor substrate is low. In addition, the bonded wafer is removed from the wafer polishing machine and the SOI
The method of measuring the thickness of the wafer cannot improve the work efficiency. The present invention has been made in view of the above-mentioned conventional problems, and in the manufacturing process of an SOI semiconductor substrate, the bonding for polishing the Si layer, which is an element forming layer, to a desired thickness with high accuracy and efficiency. It is an object of the present invention to provide a method for polishing a bonded wafer.

[0004]

In order to achieve the above object, a method of polishing a bonded wafer according to the present invention is a method of polishing a wafer having a wavelength equal to a predetermined thickness of a wafer to be polished at a total reflection angle. When light is transmitted through the wafer to be polished, or light having a wavelength equal to a predetermined thickness of the wafer to be polished is incident on the wafer to be polished at a polarization angle, and polarized light reflected from the wafer to be polished is blocked. Polishing is completed when the polarized light passes through the polarizing plate arranged as described above. Specifically, the mount plate of the wafer polishing machine is made of a transparent body, and the mount plate is pasted with transparent wax. While bonding the bonded wafer, a slurry having a refractive index higher than that of the wafer to be polished is flown between the polishing pad and the bonded wafer. Light having a wavelength equal to the thickness required for the element forming layer of the bonded wafer is incident on the bonded wafer at a total reflection angle, and a photodetector disposed below the mount plate is incident on the bonded wafer. When the transmitted light of the light is detected, a series of controls for finishing the polishing of the bonded wafer is performed. Further, as a method for polishing a bonded wafer as an alternative to the above, the mount plate of the wafer polishing machine is made of a transparent body, and the bonded wafer is bonded to the mount plate using transparent wax, and the element of the bonded wafer Polarized light that has a wavelength equal to the thickness required for the forming layer is incident on the wafer to be polished at a polarization angle from below the mount plate and is provided in a direction perpendicular to the polarization plane of the polarized light reflected from the wafer to be polished. When light passes through the plate, a series of controls for detecting the light and ending the polishing of the bonded wafer may be performed.

[0005]

When the transparent first medium has a refractive index n1 and the second medium has a refractive index n2, and n1> n2, sin θ> n
When the light travels from the first medium to the second medium at an incident angle θ such that 2 / n1, the light is totally reflected at the boundary surface. However, when the thickness t of the second medium becomes equal to the wavelength λ of light, part of the light that has been totally reflected up to that point will be transmitted through the second medium. The polishing method according to claim 2 utilizes the above phenomenon, wherein a slurry having a refractive index higher than that of an SOI wafer is used, and light having a wavelength equal to a desired thickness t1 of the SOI wafer is totally reflected on the SOI wafer. Incident at an angle,
When the light transmitted through the SOI wafer is polished until it is detected, the thickness of the SOI wafer becomes a desired thickness t1. By performing such a series of controls, the bonded wafer is kept attached to the mount plate while the SOI is being attached.
The time when the thickness of the wafer is polished to a desired size can be grasped, and the polishing can be finished at this time.

Further, the incident angle is defined as the polarization angle (Brewster angle).
When the light is projected onto the medium as above, the reflected light becomes polarized light, and when a polarizing plate is provided in the direction perpendicular to the polarization plane of this polarized light, the reflected light cannot pass through the polarizing plate. But,
When the thickness t of the medium becomes equal to the wavelength λ of the incident light, it passes through the polarizing plate. The polishing method according to claim 3 utilizes this phenomenon. Light having a wavelength equal to the desired thickness t1 of the SOI wafer is incident on the SOI wafer at a polarization angle, and the light detected by the photodetector passes through the polarizing plate. By performing a series of control to finish the polishing of the bonded wafer when it is detected
The thickness of the OI wafer can be controlled, and polishing can be terminated when the desired thickness is reached.

[0007]

Embodiments of the bonded wafer polishing method according to the present invention will be described below with reference to the drawings.
FIG. 1 is an explanatory diagram showing a schematic configuration of an embodiment of a method for polishing a bonded wafer according to claim 2, and FIG. 2 is an explanatory diagram showing light reflection and transmission states. In these figures, the polishing pad 1 of the wafer polishing machine is a transparent body, and is fixed to the tip of a drive shaft 2a that is rotated and moved up and down by a pad drive device 2. The mount plate 3 is
A laser oscillator 4 and a wavelength conversion device 5 are provided above the polishing pad 1 as a transparent body made of, for example, SiO2. A photodetector 6 is provided below the mount plate 3, and the output wiring of the photodetector 6 is connected to the control device 7. On the other hand, output wirings are connected from the control device 7 to the laser oscillator 4, the wavelength conversion device 5, the pad drive device 2, the display device 8 and the alarm device 9, respectively. The laser light oscillated from the laser oscillator 4 and projected through the wavelength conversion device 5 moves in accordance with the movement of the polishing pad 1 so as to enter the polishing pad 1, and the light detection is interlocked with this movement. The container 6 is also configured to move. Further, the slurry 10 used for this polishing operation has a refractive index n of Si single crystal.
2 has a refractive index n1 higher than 3.42.

The bonded wafer 11 is a so-called SOI substrate in which two single crystal Si wafers are bonded via an insulating layer SiO2, and an element is formed according to a manufacturing process of a bonded SOI substrate formed by a direct bonding technique. The Si single crystal layer is polished to a thickness close to a predetermined thickness. The bonded wafer 11 is adhered onto the mount plate 3 using transparent wax. The laser light oscillated by the laser oscillator 4 is converted by the wavelength conversion device 5 so that λ = t1 when a predetermined wavelength λ, that is, the target thickness of the SOI wafer is t1, and then the polishing pad 1 and the slurry are converted. 10 and 10 and is incident on the bonded wafer 11 at a total reflection angle θ.
Here, as shown in FIG. 2, the light transmitted through the polishing pad 1 and the slurry 10 is incident on the upper surface of the upper Si layer 11a constituting the bonded wafer 11 at a total reflection angle θ.
When t> λ, the incident light is totally reflected on the upper surface of the upper Si layer 11a, so that transmitted light is not detected by the photodetector 6 and polishing by the polishing pad 1 is continued during this time. t =
At λ, a part of the light that has been totally reflected on the upper surface of the upper Si layer 11a is transmitted through the upper Si layer 11a, and S
iO2 layer 11b, lower Si layer 11c, wax layer 12,
The light passes through the mount plate 3 and proceeds below the mount plate 3. When the photodetector 6 detects this transmitted light, it outputs a signal to the control device 7, and the control device 7 sends a polishing end command signal to the pad driving device 2, so that the polishing pad 1 rises and the display device 8 polishes. The end is displayed. If any abnormality occurs during the above polishing work,
The control device 7 outputs a command signal to the alarm device 9, the alarm device 9 is activated, the drive shaft 2a of the pad drive device 2 is raised, and the polishing is stopped.

In this embodiment, the polishing pad is made transparent and the laser beam is projected onto the bonded wafer through the polishing pad and the slurry. However, the present invention is not limited to this, and the incident angle to the bonded wafer is total reflection. The laser light may be directly projected onto the slurry at an angle so as to form an angle. In this case, the polishing pad may be opaque.

FIG. 3 is an explanatory view showing the schematic construction of an embodiment of the method for polishing a bonded wafer according to the third aspect. In the figure, a mount plate 3 of the wafer polishing machine is a transparent body made of, for example, SiO2, and a laser oscillator 4, a wavelength converter 5, a polarizing plate 12, and a photodetector 6 are arranged below the mount plate 3, respectively. The output wiring of the photodetector 6 is connected to the control device 7. On the other hand, from the control device 7, to the laser oscillator 4, the wavelength conversion device 5, the pad drive device 2 for rotating and raising and lowering the polishing pad 1 of the wafer polishing machine, the display device 8, and the alarm device 9, respectively. Output wiring is connected. Further, the bonded wafer 11 is bonded onto the mount plate 3 by using transparent wax.

The laser light oscillated by the laser oscillator 4 has a predetermined wavelength λ, that is, SO, by the wavelength converter 5.
When the target thickness of the I wafer is t1, the mount plate 3, the transparent wax layer 12, and the lower Si layer 11 of the bonded wafer 11 are converted so that λ = t1.
c and the SiO2 layer 11b, respectively, and the upper part S
The light is incident on the lower surface of the i-layer 11a with a polarization angle. A part of this incident light is reflected by the lower surface and the upper surface of the upper Si layer 11a, but the reflected light becomes polarized light, is transmitted through the respective layers, and is incident on the polarizing plate 13. Here, the polarizing plate 13 is the upper part S
The photodetector 6 cannot detect the polarized light because it is installed in the direction perpendicular to the polarization plane of the polarized light reflected from the i layer 11a. However, when the thickness t of the upper Si layer 11a becomes equal to λ, part of the polarized light reflected from the upper Si layer 11a passes through the polarizing plate 13 and is incident on the photodetector 6. When the photodetector 6 detects this passing light, the control device 7
The control device 7 sends a polishing end command signal to the pad drive device 2, so that the polishing pad 1 is raised and the display device 8 displays the polishing end.

In the third aspect and the present embodiment, the mount plate and the wax are made transparent, and the laser beam is projected onto the bonded wafer from below the mount plate. However, the present invention is not limited to this, and from above the bonded wafer. Laser light may be projected onto the slurry at an angle such that the incident angle with respect to the bonded wafer becomes a polarization angle.

[0013]

As described above, according to the present invention, light having a wavelength equal to a desired thickness is applied to a bonded wafer at a total reflection angle through a slurry having a refractive index higher than that of the bonded wafer. Since the polishing is performed until the light incident and transmitted through the bonded wafer is detected, according to this method, it is possible to easily improve the polishing accuracy of the SOI semiconductor substrate, which has conventionally been difficult to control the accuracy. Also,
In a method in which light having a wavelength equal to a desired thickness is incident on a bonded wafer at a polarization angle, a polarizing plate is provided in a direction in which reflected light does not pass, and polishing is performed until light passes through the polarizing plate, Similarly to the above, the improvement of the polishing accuracy can be easily achieved. Further, according to the polishing method of the present invention, it is possible to directly detect whether or not the SOI wafer has a desired thickness in a state where the bonded wafer is still attached to the mount plate. Then, the polishing pad rises and polishing is stopped, so that the polishing work efficiency of the bonded wafer can be improved.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of a method for polishing a bonded wafer according to claim 2;

FIG. 2 is an explanatory diagram showing a reflection and transmission state of light in FIG.

FIG. 3 is a structural explanatory view showing an embodiment of a method for polishing a bonded wafer according to claim 3;

[Explanation of symbols]

 1 Polishing Pad 3 Mount Plate 4 Laser Oscillator 5 Wavelength Converter 6 Photodetector 7 Controller 10 Slurry 11 Bonded Wafer 12 Transparent Wax Layer 13 Polarizing Plate

Claims (3)

[Claims] 1. A light having a wavelength equal to a predetermined thickness of a wafer to be polished is incident on the wafer to be polished at a total reflection angle and the light is transmitted through the wafer to be polished, or a predetermined thickness of the wafer to be polished. Is incident on the wafer to be polished at a polarization angle, and when the polarized light passes through a polarizing plate arranged to block the polarized light reflected from the wafer to be polished, polishing is terminated. And a method for polishing a bonded wafer. 2. A mount plate of a wafer polishing machine is composed of a transparent body, and a bonded wafer is bonded to the mount plate using a transparent wax, and a wafer to be polished is bonded between the polishing pad and the bonded wafer. Flowing a slurry having a higher refractive index than the refractive index,
Light having a wavelength equal to the thickness required for the element forming layer of the bonded wafer is incident on the bonded wafer at a total reflection angle, and a photodetector disposed below the mount plate is incident on the bonded wafer. The method for polishing a bonded wafer according to claim 1, wherein a series of controls for terminating the polishing of the bonded wafer is performed when the transmitted light of light is detected. 3. A mount plate of a wafer polishing machine is made of a transparent body, and a bonded wafer is bonded to the mount plate by using transparent wax, and a thickness required for an element forming layer of the bonded wafer. Light having a wavelength equal to is incident on the wafer to be polished at a polarization angle from below the mount plate, and when the light passes through a polarizing plate provided in a direction perpendicular to the polarization plane of the polarized light reflected from the wafer to be polished, The method for polishing a bonded wafer according to claim 1, wherein a series of controls for detecting this and ending the polishing of the bonded wafer are performed.