JP3898261B2 - Semiconductor wafer holding mechanism - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of a holding mechanism for holding a wafer when polishing a semiconductor wafer.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, semiconductor wafers such as silicon wafers and GaAs wafers have been required to have a very high level of flatness. As a polishing plate for holding a wafer when polishing the wafer, ceramic or glass is used on the back side of the wafer. 2. Description of the Related Art A polishing plate is known in which a processing pressure applied to a wafer is made uniform in a surface by using a material having high rigidity such as the like, and the flatness of the processing surface is increased.
In addition, when simultaneously polishing a plurality of wafers by the so-called batch method, a plurality of wafers are set and polished in the same plate. Even in this case, the wafer back surface is increased in order to increase the flatness of the processed surface of each wafer. Generally, the side rigidity is increased.
[0003]
In addition, extremely high accuracy is required for the parallelism of the wafers, and in the case of a batch method in which a plurality of wafers are set on the same plate and processed simultaneously, the thickness of the wafer before being set in the same plate If there is variation, the processing pressure becomes non-uniform during polishing, and as a result, the parallelism of the processed wafer deteriorates. Therefore, the thickness of the wafer is measured before processing, and is finely classified according to the thickness, and set and polished in the same plate in such a combination that the variation in thickness is reduced.
[0004]
[Problems to be solved by the invention]
However, the method of increasing the rigidity of the polishing plate in order to ensure the flatness of the processed surface has a limit in making the processing pressure uniform, particularly when the thickness of each wafer before processing varies in the batch method.
Further, in order to ensure the parallelism of the wafers, the method of measuring and classifying the thicknesses of the respective wafers in advance has a problem that it takes time and increases man-hours.
[0005]
Therefore, it is possible to obtain good flatness and parallelism without taking steps such as increasing the rigidity of the plate and eliminating the work of measuring and classifying the wafer thickness before processing. A mechanism was desired.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention , as a holding mechanism for holding the wafer in the holding hole of the plate at the time of polishing the semiconductor wafer, a holding mechanism having a fluid-filled space portion for directly pressurizing the wafer from the back surface is used. .
Then, the back surface of the wafer is directly pressurized by the fluid sealed in the fluid enclosure space, and the surface side of the wafer is polished. By directly pressurizing the back surface of the wafer, uniform pressure can be applied to the entire surface of the wafer. The processing pressure on the side can be made uniform.
[0007]
Further, the holding mechanism is constituted by the plate and a top ring provided with a fluid introduction path that is in contact with the back surface of the plate and communicates with the holding hole, and the fluid-filled space portion is formed in the holding hole. did.
Then, the wafer is inserted and held in the holding hole of the plate, the top ring is brought into contact with the back side of the plate, fluid is supplied from the fluid introduction path into the holding hole, and the fluid pressure is supplied from the back side of the wafer. Pressurize with.
[0008]
The fluid sealed in the fluid sealing space is air or water. The fluid pressure was set to a range of 20 to 100% of the polishing pressure.
At this time, if it is 20% or less, the pressurizing effect is not sufficient, and if it is 100% or more, the fluid leaks and further pressurization cannot be performed.
[0009]
Further , an elastic sealing material was provided at the contact portion between the top ring and the plate and the contact portion between the holding hole and the wafer.
These sealing materials prevent leakage of the fluid sealed in the fluid sealing space.
[0010]
Further, in the holding hole, provided with a rotating mechanism for rotatably holding a wafer.
If the wafer is rotated by this rotating mechanism, the wafer rotates during polishing, and the pressure applied to the wafer can be made more uniform over the entire area.
[0011]
Further, as the rotation mechanism, a ring member that can rotate along the inner peripheral portion of the holding hole and a ring-shaped sealing material that is attached to the ring member are provided.
If the ring members are rotated together with the rotation of the wafer, the wafer can be rotated more smoothly, which is more effective in terms of uniform pressure.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the accompanying drawings.
1 is a longitudinal sectional view of the holding jig of the present invention, FIG. 2 is a perspective view of the top ring as viewed from below, FIG. 3 is a perspective view of the polishing plate, and FIG. ) Is a state view seen from below, and FIG. 4 is an enlarged cross-sectional view showing a holding state of the holding hole and the sealing material.
[0013]
A holding jig as a semiconductor wafer holding mechanism of the present invention is configured as a jig for holding a wafer when polishing a wafer such as a silicon wafer or a GaAs wafer. This holding jig 1 is shown in FIG. As shown, it comprises a polishing plate 2 for holding a plurality of wafers W, and a top ring 3 for pressing the back surface of the polishing plate 2.
[0014]
Then, the back side of each wafer W,... Is pressurized with a fluid pressure, which will be described later, and pressed against the polishing tool 4 on the surface side, and the surface of the wafer W,. The polishing tool 4 includes a rotatable surface plate 5 and a non-woven polishing pad 6 attached to the surface side of the surface plate 5.
[0015]
As shown in FIG. 2, the top ring 3 includes a disk-shaped portion having substantially the same diameter as the disk-shaped polishing plate 2, and an intermediate portion excluding the peripheral edge portion 3 a on the lower surface of the disk-shaped portion. A circular recess A1 is formed by engraving, and a fluid passage A2 opening toward the circular recess A1 is formed in the central portion of the top ring 3. A fluid introduction path is formed by the circular recess A1 and the fluid passage A2. A is formed.
Air or water fluid can be supplied from the fluid introduction path A.
[0016]
Further, the peripheral portion 3 a of the top ring 3 can be placed in contact with the peripheral portion on the upper surface side of the polishing plate 2 so that a predetermined pressure can be applied to the polishing plate 2. . Further, a rubber O-ring 7 as a sealing material is fitted on the outer lower surface of the peripheral edge 3 a of the top ring 3, and the O-ring 7 makes contact between the lower surface of the peripheral edge 3 a and the upper surface of the polishing plate 2. The surface is sealed.
Incidentally, the weight of the top ring 3 is, for example, 200 to 300 kg.
[0017]
As shown in FIG. 3, the polishing plate 2 includes a plurality (four in this embodiment) of through-hole holding holes 2a,... Along the inner peripheral edge of each of the holding holes 2a. In addition to a synthetic rubber such as SBR and NBR as a seal material, a ring-shaped seal ring 8 made of a soft synthetic resin such as a polymer material having a rubber-like elasticity or a fluoropolymer, vinyl chloride, and the like is provided. When W,... Are inserted, the outer periphery of the wafer W can be held in a sealed state by the seal rings 8,. As shown in FIG. 1, with the top ring 3 placed on the polishing plate 2, each holding hole 2a,... Communicates with the circular recess A1.
[0018]
Further, as shown in FIG. 4, the seal ring 8,... Has a step portion d formed on the inner peripheral edge of the holding hole 2 a, and the fixing ring 9 is fitted to the step portion d with the seal ring 8 interposed therebetween. If the fluid pressure is applied from above with the inner peripheral edge of the seal ring 8 superimposed on the upper surface of the wafer W, the same part can be sealed. ing.
[0019]
Therefore, as shown in FIG. 1, after setting the wafers W in the holding holes 2a of the polishing plate 2, the top ring 3 is placed on the polishing plate 2 in an overlapping manner. When a fluid such as air is introduced, the abutting surface of the peripheral portion 3a of the top ring 3 and the polishing plate 2 is sealed by an O-ring 7, and a seal ring 8 is provided between each holding hole 2a,. Therefore, a sealed fluid filled space B is formed inside each holding hole 2a.
Therefore, the wafers W,... Can be pressed against the polishing tool 4 with a uniform pressure by the fluid pressure in the fluid enclosure spaces B,.
[0020]
Incidentally, the embodiment of FIG. 5 is a configuration example diagram in the case where the rotation mechanisms 11 of the wafers W are provided inside the holding holes 2a.
The rotating mechanism 11 includes a movable ring 12 mounted on the step portion d of the holding hole 2a and rotatable along the inner peripheral edge of the holding hole 2a, and a seal ring 8 fixed to the movable ring 12 by a bolt 10. Thus, the inner peripheral edge of the seal ring 8 can be superimposed on the upper surface of the wafer W.
[0021]
In this case, the wafer W at the time of polishing can freely rotate in the holding hole 2a together with the movable ring 12, and the processing pressure at the time of polishing can be made more uniform.
[0022]
【Example】
Here, under the following processing conditions, etc., four wafers W having a thickness difference of 100 μm at the maximum are set on the same polishing plate 2, and air is introduced into the fluid filled space B of the holding hole 2a. While pressurizing W, an experiment was conducted in which polishing was performed using an alkaline polishing liquid containing colloidal silica.
At this time, when setting the wafer W, each wafer W is placed on the polishing pad 6 and set in each holding hole 2a in such a manner as to cover the polishing plate 2.
[0023]
(Processing conditions)
・ Wafer: P-type silicon wafer grown by CZ method, 4 sheets differing in diameter 150mm, thickness 530-630μm ・ Rotating speed of surface plate 5: 40rpm
-Top ring 3 rotational speed: 40 rpm
・ Polishing pressure: 200 gf / cm ²
・ Back air pressure: 80gf / cm ²
[0024]
As a result of polishing under the above processing conditions, TTV before polishing (TOTAL THICKNESS VARIATION, that is, the difference between the maximum thickness and the minimum thickness on the entire wafer surface) is 1.7 μm, and TTV after polishing is 1.8 μm, which is parallel to the flatness. The degree was almost the same as the accuracy before processing, and it was confirmed that the shape of the wafer W was not broken by polishing.
Incidentally, when a wafer with similar variations was polished by a conventional method, the TTV before polishing was 1.8 μm and the TTV after polishing was 15.7 μm, and it was also confirmed that the wafer W shape was greatly collapsed by polishing. .
[0025]
At this time, in the present invention, since pressure is directly applied by air from the back side of the wafer W,..., Even if there is a difference in thickness of the wafer W,. It is possible to apply a uniform processing pressure. In addition, when the wafers W,... Are rotatable, more uniform polishing can be performed.
In the above embodiment, the back air pressure is set to 40% of the polishing pressure. However, if this is set to 100% or more of the polishing pressure, air leaks, and if it is 20% or less, effective pressurization can be performed. I could not do it. Further, water may be used as the pressurized fluid instead of air.
[0026]
The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
[0027]
【The invention's effect】
As described above, in the present invention, when polishing a semiconductor wafer, the wafer is directly pressurized from the back side by the fluid sealed in the fluid sealing space, so that uniform pressure can be applied to the entire area of the wafer, flatness, A parallelism can be satisfactorily polished. At this time, since the pressure is directly applied by the fluid pressure, even if there is a difference in the thickness of the wafer, the same plate can be used for polishing.
Further, if a rotation mechanism for rotatably holding the wafer is provided in the holding hole of the polishing plate, the pressure applied to the wafer during polishing can be made more uniform over the entire region, which is more effective.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a holding jig of the present invention.
FIG. 2 is a perspective view of a top ring as viewed from below.
FIGS. 3A and 3B are perspective views of a polishing plate, wherein FIG. 3A is a state seen from above, and FIG. 3B is a state view seen from below.
FIG. 4 is an enlarged cross-sectional view showing a holding state of a holding hole and a sealing material.
FIG. 5 is a configuration example in the case where a rotation mechanism is provided in the holding hole.
[Explanation of symbols]
1 ... holding jig, 2 ... polishing plate,
2a ... holding hole, 3 ... top ring,
3a ... peripheral edge, 4 ... polishing tool,
5 ... Surface plate, 6 ... Polishing pad,
7 ... O-ring, 8 ... Seal ring,
9 ... fixing ring, 10 ... bolt,
11 ... rotating mechanism, 12 ... movable ring,
A: Fluid introduction path, A1: Circular recess,
A2 ... fluid passage, B ... fluid-filled space,
d ... Step, W ... Wafer.

Claims (5)

  A holding mechanism for holding a wafer in a holding hole of a plate during polishing of a semiconductor wafer, comprising a fluid-filled space for directly pressurizing the wafer from the back surface, and the wafer can be rotated in the holding hole A holding mechanism for a semiconductor wafer, comprising a rotation mechanism for holding the semiconductor wafer.   2. The semiconductor wafer holding mechanism according to claim 1, wherein the holding mechanism includes the plate and a top ring provided with a fluid introduction path that is in contact with a back surface of the plate and communicates with the holding hole. A holding mechanism for a semiconductor wafer, wherein the space is formed in the holding hole. 3. The semiconductor wafer holding mechanism according to claim 2 , wherein an elastic sealing material is provided on the contact portion between the top ring and the plate and the contact portion between the holding hole and the wafer. Retention mechanism. 4. The semiconductor wafer holding mechanism according to claim 1 , wherein the fluid sealed in the fluid sealing space is air or water. 5.   5. The semiconductor wafer holding mechanism according to claim 1, wherein the rotating mechanism is attached to the ring member and a ring member that is rotatable along an inner periphery of the holding hole. 6. A semiconductor wafer holding mechanism which is a ring-shaped sealing material.

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