JPH08264497A - Wafer fitting base - Google Patents

Abstract

PURPOSE: To improve a net working rate of an apparatus by easily replacing a rear surface pad of a wafer fitting base and controlling a replacement frequency in a wafer grinding apparatus. CONSTITUTION: A rear surface pad attached to a wafer fitting base is divided into a center rear surface pad 4 in the region where a hole 3 for pressurizing and absorption during mounting or removal of the wafer on the stage and a peripheral rear surface pad 5 which will be deteriorated fast. Thereby, on the occasion of deterioration of the rear surface pad, it can be replaced easily only with replace of the peripheral rear surface pad 5. Moreover, an availability factor of the wafer grinding apparatus which can reduce the replacement frequency can be improved by forming the peripheral rear surface pad 5 with a material having a higher elasticity recovery rate than that of the center rear surface pad 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer mounting base for use in a wafer polishing apparatus, and more particularly to a semiconductor wafer mounting base.

[0002]

2. Description of the Related Art In a manufacturing process of a semiconductor device, a wafer polishing apparatus for polishing and flattening steps due to elements and wirings is used (for example, see Japanese Patent Application Laid-Open No. 3-259520). First, the structure of a conventional wafer polishing apparatus will be described. FIG. 9 is a plan view of a wafer polishing apparatus, and FIG. 10 is a sectional view of the apparatus. The disk-shaped polishing platen 13 rotates. A polishing cloth 14 made of foamed polyurethane is pasted on the polishing platen 13. A polishing agent supply port 17 for supplying a polishing agent above the polishing platen 13, and a wafer mounting base 16
Is provided. The wafer is held on the bottom of the wafer mounting base 16. A pressing mechanism for pressing a wafer onto a polishing cloth on a polishing platen above the wafer mounting base 16;
A rotation mechanism that rotates the wafer in the same direction as the rotation of the polishing platen is provided.

A conventional mounting base for a semiconductor wafer will be described with reference to the drawings. FIG. 11 is a plan view (bottom) of the wafer mounting base, and FIG. 12 is a cross-sectional view of the mounting base. The mounting base is the stage 1, the back pad 18, and the retainer ring 2.
Composed of and. The stage 1 is provided with a plurality of holes 3 for adsorbing a wafer at the time of transportation and for pressing from the back surface of the wafer during wafer removal and polishing. The back pad 18 is made of a foamed synthetic resin such as foamed polyurethane and is affixed to the stage 1 with a double-sided adhesive tape, and has a hole corresponding to the hole 3 of the stage 1. The wafer 6 has its back surface pad 1 with its front surface facing the polishing platen.
8 attached to the base. The back pad 18 has elasticity and absorbs the influence of the hole 3 of the stage 1, the trace of dust and the warpage of the wafer on polishing. The retainer ring 2 prevents the wafer from coming off the mounting base even if the frictional force between the polishing cloth and the wafer during polishing becomes larger than the adhesive force between the back surface pad 18 and the wafer. Wafer 6
Protrudes from the retainer ring 2 by a thickness of about one third or less of the wafer. When the amount of protrusion changes, the clearance between the retainer ring 2 and the polishing cloth during polishing also changes, so the amount of the polishing agent supplied between the wafer and the polishing cloth changes, and the polishing rate and polishing uniformity are changed. fluctuate.

In the thus configured wafer polishing apparatus, an abrasive is supplied from an abrasive supply port onto a rotating polishing table, and the wafer 6 is pressed against the polishing cloth 14 while rotating the mounting base. Thereby, the step on the wafer 6 is polished. For example, as shown in FIG. 8, it is assumed that a plasma oxide film (interlayer insulating film) on the A1 wiring 11 formed on the semiconductor substrate 9 via the insulating film 10 is polished under predetermined conditions. . Thereby, the convex portions of the plasma oxide film 12 can be selectively polished to flatten the plasma oxide film 12.

However, when a large amount of wafers are polished, the back pad 18 deteriorates, and the polishing rate and the uniformity of polishing in the wafer surface fluctuate, so that stable work cannot be performed. Therefore, if the required uniformity cannot be obtained,
The required uniformity was obtained by replacing the deteriorated back pad 18 with a new one.

[0006]

However, the above-mentioned conventional wafer polishing apparatus has the following problems.

Conventionally, since the polishing rate and the uniformity of polishing cannot be stabilized after processing 400 wafers, the frequency of replacement of the back pad 18 is high.

When replacing the back pad 18, after the back pad is attached, a hole is opened in the back pad corresponding to the hole of the stage 1, or a hole is made in the back pad in advance and the back pad is attached. At this time, it is necessary to match with the hole of stage 1. When opening a plurality of holes after attaching the back surface pad, it is necessary to open the holes accurately and with good reproducibility, so that the work efficiency is poor and the work takes about one hour.
When a hole is formed in the back surface pad in advance, it is difficult to align a plurality of holes of the stage 1 with the holes of the back surface pad. Efficiency is poor due to the skill required for work,
Even if a backside pad with holes is prepared, the work takes about 40 minutes.

The causes of deterioration of the backside pad, which is frequently replaced, are as follows. As shown in FIG. 7, the peripheral portion of the back pad serves as an entrance of the polishing agent 8 when the polishing agent 8 enters between the wafer 6 and the back pad during polishing.
The abrasive 8 is rubbed against the foam cells by the edge 60 of the wafer 6. Therefore, the bubbles of the foam at the peripheral portion of the back pad 18 are clogged with the abrasive 8, and the elastic recovery rate is degraded from the elastic recovery rate at the central portion. In particular, the polishing agent 8 accumulates between the retainer ring 2 and the orientation flat portion at the edge portion of the orientation flat portion in which the peripheral edge portion of the circular wafer is partially flattened, so that the deterioration of the peripheral portion of the back surface pad 18 is further increased.

Further, when the wafer is pressed from the back surface during polishing, the pressure received from the wafer by the back surface pressure is reduced in the central portion of the back surface pad, but is not reduced in the peripheral portion of the back surface pad. Therefore, when a large amount of wafers are polished, the history of pressure received from the wafer is different between the central portion and the peripheral portion of the back surface pad, and the peripheral portion of the elastic recovery rate is further deteriorated.

Due to the deterioration of the elastic recovery rate of the peripheral portion of the back pad 18, the wafer retainer ring 2
The amount of protrusion from the head is reduced. Then, since the clearance between the retainer ring 2 and the polishing cloth during polishing changes, the amount of the polishing agent supplied between the wafer and the polishing cloth also changes. Therefore, when the back pad 18 is deteriorated, the polishing rate and the uniformity of polishing within the wafer surface are deteriorated as compared with the first use.

Further, by making the back pad 18 a hard material having a high elastic recovery rate, deterioration of the back pad can be suppressed. However, traces of holes and dust on the stage 1 at the center and warpage of the wafer 6 can be suppressed. Is not absorbed by the back pad and appears on the polished wafer. Therefore, sufficient polishing uniformity cannot be obtained.

[0013]

According to the present invention, a wafer mounting pad is characterized in that a back surface pad is separated into a peripheral portion and a central portion having a hole corresponding to a hole of a stage. A base is obtained. According to another feature of the present invention, the back surface pad is separated into a peripheral portion where deterioration is fast and a central portion where a hole is opened corresponding to the hole of the base,
A wafer mounting base is obtained in which the peripheral back surface pad uses a material having a higher elastic recovery rate than the central rear surface pad.

According to another feature of the present invention, the back pad is separated into a peripheral portion and a central portion having a hole corresponding to the hole of the stage, and the peripheral portion and the central portion are separated from each other. The wafer mounting base characterized in that a buffer member is provided at the boundary of the wafer mounting base.

Further, a cushioning member is held in a groove provided on the stage, and the cushioning member is 0.5 times larger than the back surface pad.
A wafer mounting base characterized by being provided so as to protrude by not less than mm is obtained.

[0016]

【Example】

[Embodiment 1] FIG. 1 is a plan view of a wafer mounting base according to an embodiment of the present invention. FIG. 2 is a sectional view of the wafer mounting base. In these figures, the wafer 6 is attached to the mounting base by water suction via the stage 1 and the holes in the central rear pad 4 and water filling through the central rear pad 4 and the peripheral rear pad 5. During polishing, the wafer 6 is vacuum-sucked by the holes of the stage 1 and the back pad,
In order to obtain uniform polishing, the back surface of the wafer 6 is pressed to such an extent that the wafer does not jump out during polishing, or the pressurization or depressurization is not performed. After the polishing, the wafer 6 is removed from the hole by applying pressure. The retainer ring 2 prevents the wafer from coming off the mounting base due to the frictional force between the polishing cloth and the wafer being larger than the adhesive force between the back surface pad and the wafer during polishing. The polishing agent is supplied from the gap between the polishing pad 14 and the retainer ring 2 during polishing.

A central back pad 4 is attached to a region where a hole is opened corresponding to the hole of the stage 1. A peripheral back surface pad 5 is attached to the outer circumference. The width of the peripheral back pad 5 can be a width from the outermost periphery to the outside of the region where the holes of the base exist. In the polishing of a wafer having a diameter of 15 cm, the holes of stage 1 are distributed from the center of the stage to a position having a radius of 4 cm, and when the back surface is pressed during polishing, the diameter of the outer periphery is 15 cm and 3 cm. A peripheral back pad 5 having a width is used. At this time, the central back surface pad 4 has a radius of 4.5 cm. In the case where the back surface pressing is not performed, a peripheral back pad 5 having an outer diameter of 15 cm and a width of 1.5 cm is used. At this time, the radius of the central back pad 4 is 6 cm.
When 400 wafers are polished and the polishing rate and polishing uniformity cannot be stably obtained, the deteriorated peripheral back surface pad is replaced. At this time, the inner periphery of the peripheral back pad is adhered to the outer periphery of the central back pad. Since there is no need to open holes or align the holes, the operation is easy and can be completed in about 15 minutes. The central back surface pad is replaced by polishing 5000 wafers. The holes may be opened in the central back surface pad in correspondence with the holes in the stage after or after the attachment.

[Embodiment 2] FIG. 3 is a plan view of a wafer mounting base according to a second embodiment of the present invention. FIG. 4 is a sectional view of the wafer mounting base. In the wafer mounting base according to the present embodiment, the peripheral back pad 5 is
The difference from the first embodiment is that a material having a higher elastic recovery rate is used. For example, when the peripheral backside pad 5 made of a material having a low foam cell density and a high elastic recovery rate is used as a measure against clogging of the polishing agent as compared with the central backside pad 4, the backside pad and the backside of the wafer 6 are It is possible to obtain resistance to the dirt of the abrasive 8 that has entered the gap. When a hole of the stage 1 is located at a position with a radius of 4 cm from the center of the stage when polishing a wafer having a diameter of 15 cm, a peripheral back pad 5 having an outer diameter of 15 cm and a width of 1.5 cm is used. . At this time, the radius of the central back pad 4 is 6 cm. The area of the central back pad is made larger than that of the first embodiment, and the central back pad absorbs the effects of holes in the stage, dust, and warpage of the wafer. When the compression ratio of the center rear pad is 30% and the compression ratio of the peripheral rear pad is 10%, the peripheral rear pad can obtain a stable polishing rate and polishing uniformity up to 1400 wafers.

[Embodiment 3] FIG. 5 is a plan view of a wafer mounting base according to a third embodiment of the present invention. FIG. 6 is a sectional view of the wafer mounting base. The wafer mounting base according to the present embodiment includes a central back pad 4 and a peripheral back pad 5.
A buffer member 7 having the same elastic characteristics as the back surface pad is provided at the boundary between the buffer pad 7 and the pad. In this case, a groove 70 for mounting the buffer member 7 is formed in advance on the stage 1 of the mounting base. The size of the central back pad 4 and the inner size of the peripheral back pad 5 are adjusted by the width of the buffer member.
The compression ratio of the center rear pad is 30%, the compression ratio of the peripheral rear pad is 10%, and the buffer member is made of a synthetic resin softer than the rear pad and having a compression ratio of 50%. When the cushioning member is attached, the surface of the cushioning member is set to be 0.5 mm higher than the surface of the back pad. With this setting, the cushioning member is crushed when the wafer is mounted, and the difference in the thickness of the pad at the boundary between the central portion and the peripheral portion is mitigated, so a margin for the difference in thickness between the pads is secured. it can. Thereby, uniformity of polishing can be easily obtained without strictly controlling the thickness of the back pad. Further, even if the bonding positions of the center back pad 4 and the peripheral back pad 5 are shifted, the gap between the back pads can be reduced by the crushed cushioning member, so that the margin for the back pad bonding can be secured. As a result, the operation of attaching the peripheral back pad becomes easy, and the operation is completed in about 8 minutes.

[0020]

[Effect of the Invention] When the uniformity of polishing within the wafer surface is deteriorated due to the deterioration of the back surface pad, only the peripheral back surface pad needs to be replaced, and further, the opening or positioning of the hole is not required and the work efficiency is improved. .

Further, by using a material that does not easily deteriorate the material of the peripheral back pad, the replacement frequency of the peripheral back pad is reduced, and the operating rate is improved.

By providing a buffer member at the boundary between the central rear pad and the peripheral rear pad, the thickness of the rear pad can be easily controlled, and a margin for attaching the rear pad can be ensured, thereby improving the working efficiency. .

[Brief description of drawings]

FIG. 1 is a plan view of a wafer mounting base according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a wafer mounting base according to the first embodiment of the present invention.

FIG. 3 is a plan view of a wafer mounting base according to a second embodiment of the present invention.

FIG. 4 is a sectional view of a wafer mounting base according to a second embodiment of the present invention.

FIG. 5 is a plan view of a wafer mounting base according to a third embodiment of the present invention.

FIG. 6 is a sectional view of a wafer mounting base according to a third embodiment of the present invention.

FIG. 7 is a model diagram showing a wafer edge portion of a wafer mounting base during polishing.

FIG. 8 is a diagram for explaining a polishing process.

FIG. 9 is a plan view of a conventional wafer polishing apparatus.

FIG. 10 is a sectional view of a conventional wafer polishing apparatus.

FIG. 11 is a plan view of a conventional wafer mounting base.

FIG. 12 is a sectional view of a conventional wafer mounting base.

[Explanation of symbols]

 1 Stage 2 Retainer Ring (Holding Member) 3 Hole 4 Central Back Pad 5 Peripheral Back Pad 6 Wafer 7 Buffer Member 8 Abrasive

Claims (5)

[Claims] 1. A wafer mounting base for holding a wafer to be polished in a wafer polishing apparatus, a stage in which a hole for pressing the wafer from the back surface is opened, and a back surface pad sandwiched between the wafer and the stage, The backside pad is composed of a ring-shaped wafer holding member, and the backside pad is divided into a central portion in which holes are opened corresponding to the holes of the stage and a peripheral portion located outside the central portion. Wafer mounting base characterized by 2. The peripheral back pad according to claim 1,
A wafer mounting base made of a material having a higher elastic recovery rate than the central rear surface pad. 3. The wafer mounting base according to claim 1, wherein a buffer member is provided at a boundary between the back pad in the central portion and the back pad in the peripheral portion. 4. The wafer mounting base according to claim 3, wherein said buffer member is held in a groove provided in said stage. 5. The buffer member according to claim 4, wherein the buffer member projects from the back pad by at least 0.5 mm.
The wafer mounting base described.