JP2770101B2 - Polishing method of bonded wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A bonded wafer obtained by interposing an insulating layer between two Si wafers and bonding them by a direct bonding technology (bonding technology) has a high IC withstand voltage, high speed, and high reliability. It is attracting attention as a method of realizing the realization. The bonded wafer oxidizes the surface of the upper Si wafer of the two Si wafers to form an oxide film Si.
O2 is formed and the upper Si wafer, SO
The I wafer and the lower Si wafer, that is, the base wafer, are subjected to a cleaning process 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 form an oxide film S
Complete adhesion through iO2. Next, an oxide film SiO2
Is formed, for example, by using a surface grinder for rough and finish grinding, and further polished for SOI.
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, ie, the SOI wafer, most of the thickness of the bonded wafer is removed by polishing by the above-mentioned polishing method.
It is extremely difficult to leave a layer having a thickness of m or less as a device forming layer with a uniform thickness. In particular, the manufacturing yield of the SOI semiconductor substrate is low because the thickness of the element formation layer varies greatly and has an accuracy of about ± 0.5 μm. Also, the bonded wafer is removed from the wafer polisher 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. In the manufacturing process of an SOI semiconductor substrate, a bonding method for polishing a Si layer, which is an element forming layer, to a desired thickness with high precision 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 for polishing a bonded wafer according to the present invention comprises the steps of: applying light having a wavelength equal to a predetermined thickness of a wafer to be polished to the 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 to be terminated 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 is attached to the mount plate using a transparent wax. Attaching the bonded wafer and flowing a slurry having a refractive index higher than that of the wafer to be polished between the polishing pad and the bonded wafer. Light having a wavelength equal to the thickness required for the element formation layer of the bonded wafer was incident on the bonded wafer at a total reflection angle, and the photodetector disposed below the mount plate was incident on the bonded wafer. When the transmitted light is detected, a series of controls for terminating the polishing of the bonded wafer are performed. Further, as a method of polishing a bonded wafer instead of the above, a mount plate of a wafer polishing machine is composed of a transparent body, a bonded wafer is bonded to the mount plate using a transparent wax, and an element of the bonded wafer is bonded. Light having a wavelength equal to the thickness required for the formation layer is incident on the wafer to be polished at a polarization angle from below the mount plate, and polarized light provided in a direction perpendicular to the polarization plane of polarized light reflected from the wafer to be polished. When light passes through the plate, the light may be detected and a series of controls for terminating the polishing of the bonded wafer may be performed.

[0005]

The refractive index of the transparent first medium is n1, the refractive index of the second medium is n2, and when n1> n2, sin θ> n
When light travels from the first medium to the second medium at an incident angle θ such that 2 / n 1, 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 the light, a part of the light that has been totally reflected up to that point passes through the second medium. The polishing method according to claim 2 utilizes the above phenomenon, and uses a slurry having a refractive index higher than the refractive index of the SOI wafer, and totally reflects light having a wavelength equal to the desired thickness t1 of the SOI wafer to the SOI wafer. Incident at an angle,
When the polishing is performed until the light transmitted through the SOI wafer is detected, the thickness of the SOI wafer becomes a desired thickness t1. By performing such a series of controls, the SOI can be performed while the bonded wafer remains attached to the mount plate.
The point in time when the thickness of the wafer has been polished to the desired size can be ascertained, and the polishing can be terminated at this point.

[0006] The incident angle is defined as a polarization angle (Brewster angle).
When the light is projected onto the medium, the reflected light becomes polarized light. If a polarizing plate is provided in a direction perpendicular to the polarization plane of the 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, the light passes through the polarizing plate. The polishing method according to claim 3 utilizes this phenomenon, in which light having a wavelength equal to the thickness t1 of a desired SOI wafer is incident on the SOI wafer at a polarization angle, and a light detector passes light having passed through the polarizing plate. By performing a series of controls to end the polishing of the bonded wafer when it is detected, the S
The thickness of the OI wafer can be controlled, and the polishing can be completed when the desired thickness is reached.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for polishing a bonded wafer according to the present invention will be described below with reference to the drawings.
FIG. 1 is an explanatory view 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 view showing a reflection and transmission state of light. In these figures, a polishing pad 1 of a wafer polishing machine is a transparent body, and is fixed to a tip end of a drive shaft 2a which rotates and moves up and down by a pad driving device 2. The mounting plate 3
For example, a laser oscillator 4 and a wavelength converter 5 are disposed above the polishing pad 1 by 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 a control device 7. On the other hand, output wires 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 converter 5 moves in accordance with the movement of the polishing pad 1 so as to be incident on the polishing pad 1, and the light detection is performed in conjunction with the movement. The vessel 6 is also configured to move. The slurry 10 used for this polishing operation has a refractive index n of a Si single crystal.
It has a refractive index n1 higher than 2 = 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 single-crystal Si layer is polished to near a predetermined thickness of the layer. The bonded wafer 11 is bonded on the mount plate 3 using a transparent wax. The laser light oscillated by the laser oscillator 4 is converted by the wavelength converter 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 10 and is incident on the bonded wafer 11 at the 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 the transmitted light is not detected by the photodetector 6, and the polishing by the polishing pad 1 is continued during this time. t =
At λ, part of the light that has been totally reflected on the upper surface of the upper Si layer 11a passes through the upper Si layer 11a,
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 drive device 2. The end is displayed. If any abnormalities occur during the above polishing work,
The control device 7 outputs a command signal to the alarm device 9, and the alarm device 9 is operated, and at the same time, the drive shaft 2a of the pad drive device 2 is raised, and polishing is stopped.

In this embodiment, the polishing pad is made of a transparent material, 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. The laser light may be directly projected onto the slurry at an angle that makes the angle. In this case, the polishing pad may be opaque.

FIG. 3 is an explanatory diagram showing a schematic configuration of an embodiment of the method for polishing a bonded wafer according to the third aspect. In FIG. 1, a mount plate 3 of a wafer polisher 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 provided 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, the laser oscillator 4, the wavelength conversion device 5, the pad driving device 2 for rotating and lifting the polishing pad 1 of the wafer polishing machine, the display device 8, and the alarm device 9, respectively. Output wiring is connected. The bonded wafer 11 is bonded on the mount plate 3 using a transparent wax.

The laser light oscillated by the laser oscillator 4 has a predetermined wavelength λ, ie, SO
Assuming that the target thickness of the I wafer is t 1, after conversion so that λ = t 1, the mount plate 3, the transparent wax layer 12, and the lower Si layer 11 of the bonded wafer 11
c and the SiO2 layer 11b, respectively.
The light is incident on the lower surface of the i-layer 11a at a polarization angle. A part of the incident light is reflected on the lower surface and the upper surface of the upper Si layer 11a, and the reflected light becomes polarized light, passes through each layer, and is incident on the polarizing plate 13. Here, the polarizing plate 13 has an upper S
The photodetector 6 cannot detect the polarized light, because the light detector 6 is installed in a 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 the aforementioned λ, a part of the polarized light reflected from the upper Si layer 11a passes through the polarizing plate 13 and enters the photodetector 6. When the light detector 6 detects this passing light, 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 is raised and a display of polishing completion is displayed on the display device 8.

In claim 3 and the present embodiment, the mount plate and the wax are made transparent, and the laser light is projected onto the bonded wafer from below the mount plate. However, the present invention is not limited to this, and the laser beam is projected 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 the refractive index of the bonded wafer. Polishing is performed until light that is incident and transmitted through the bonded wafer is detected. According to this method, the polishing accuracy of an SOI semiconductor substrate, which has conventionally been difficult to control, can be easily improved. Also,
Light having a wavelength equal to the desired thickness is incident on the bonded wafer at a polarization angle, a polarizing plate is provided in a direction in which the reflected light does not pass, and the polishing method is performed until light passes through the polarizing plate. In the same manner as described above, improvement in polishing accuracy can be easily achieved. Furthermore, 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 while keeping the bonded wafer attached to the mount plate, and to obtain the desired thickness. Then, the polishing pad rises to stop the polishing, so that the efficiency of polishing the bonded wafer can be improved.

[Brief description of the drawings]

FIG. 1 is a structural explanatory view showing one 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 one embodiment of a method for polishing a bonded wafer according to claim 3;

[Explanation of symbols]

 Reference Signs List 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)

(57) [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. When light having a wavelength equal to is incident on the wafer to be polished at a polarization angle and the polarized light passes through a polarizing plate arranged to block polarized light reflected from the wafer to be polished, polishing is terminated. Polishing method for bonded wafers. 2. A mounting plate of a wafer polishing machine is formed of a transparent body, and a bonded wafer is bonded to the mounting plate using a transparent wax, and a polishing target wafer is sandwiched between a polishing pad and a 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 formation layer of the bonded wafer was incident on the bonded wafer at a total reflection angle, and the photodetector disposed below the mount plate was incident on the bonded wafer. 2. The method for polishing a bonded wafer according to claim 1, wherein a series of controls for terminating polishing of the bonded wafer are performed when light transmitted is detected. 3. A mount plate of a wafer polishing machine is made of a transparent body, a bonded wafer is bonded to the mount plate using a transparent wax, and a thickness required for an element formation layer of the bonded wafer is provided. When light having a wavelength equal to is incident on the wafer to be polished at a polarization angle from below the mount plate, and the light passes through a polarizing plate provided in a direction perpendicular to the polarization plane of polarized light reflected from the wafer to be polished, 2. The method for polishing a bonded wafer according to claim 1, wherein a series of controls for detecting the detection and terminating the polishing of the bonded wafer are performed.