JPH1076439A - Thin plate holding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve uniformity of height within a surface on the surface of a semiconductor wafer. SOLUTION: A device comprises a chuck table 2 having plural blocks of vacuum suction stages 3 disposed on an elastic vacuum stage base 4, and a fine displacement adjusting table 11 having plural fine displacement adjusting units 13 disposed on a fine displacement adjusting base 12 which are provided to correspond to the respective vacuum suction stages 3 to vertically move separately from each other for pushing the stage base 4 from the back surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin plate holding device, and more particularly to a thin plate holding device capable of correcting irregularities on the surface of a thin plate, for example, a semiconductor wafer, and holding the thin plate by vacuum suction.

[0002]

2. Description of the Related Art There are the following methods for a wafer chuck when performing processing such as CMP (chemical mechanical polishing).

[0003] First, as shown in FIG. 13, there is a method in which a cushioning material such as foamed polyurethane or suede is inserted as a backing material between a table and a wafer, and is pressed and adsorbed.

Second, as shown in FIGS. 14A to 14C, there is a method of vacuum-sucking a wafer through a groove, a hole or a porous material. In this method, a backing material may be used in some cases.

Third, as shown in FIG. 15, there is a method of heating a table and bonding a wafer with wax.

Fourth, as shown in FIG. 16, there is a method in which a very small amount of water, oil, or the like is interposed between a table and a wafer whose surface is smoothed by lapping or the like and bonded by linking.

[0007]

The above-mentioned conventional wafer chucking method has the following problems.
First, the first method shown in FIG. 13 has a problem that the wafer cannot be held under uniform conditions due to unevenness in the material of the backing material, unevenness in the amount of supplied water, and the like. And
A serious problem is that there is no solid surface to hold the wafer.

Next, the second method shown in FIG. 14 has a problem that it is easily affected by dust.

Next, the third method shown in FIG. 15 has serious problems that automation is difficult, tact is long, and thickness unevenness of wax is large.

The fourth method shown in FIG. 16 has a problem that automation is difficult, adhesive strength is weak, and adhesive strength and the state of adhesion are greatly affected by the state of the back surface of the wafer.

As a problem common to the above-mentioned respective methods, there is a problem that it is difficult to make the wafer surface a flat surface suitable for processing because the wafer is held with the back surface as a reference. That is, since each of the above-described methods chucks on a table that is not deformed, the wafer is held on the basis of the back surface, and there is unevenness in the thickness of the wafer, a change in the thickness due to the device manufacturing process, and the like. This remains as an error factor on the machined surface side.

In particular, in the case of emphasizing uniformity in CMP, variations in the height of the wafer surface change the effective processing pressure, and many high places are processed. Therefore, there is a limit in further improving the uniformity of the CMP processing. In particular, it is conceivable that the variation in the height of the wafer surface will be further increased as the diameter of the wafer increases, so it is necessary to maintain the processing accuracy by simply expanding the conventional equipment in response to the increase in the diameter. It is considered impossible.

The present invention has been made to solve such a problem, and has as its object to improve the uniformity of the in-plane height of the surface of a thin plate, for example, a semiconductor wafer.

[0014]

According to the present invention, there is provided a thin plate holding apparatus comprising:
A chuck table in which a plurality of block-shaped vacuum suction stages are arranged on an elastic stage base, and a chuck table provided corresponding to each of the vacuum suction stages, the height of which changes independently from each other, and the stage base is moved from the back side. A minute displacement adjustment table in which a plurality of pushing minute displacement adjusting units are arranged on a minute displacement adjusting base.

Therefore, according to the thin plate holding apparatus of the present invention, one thin plate, for example, a semiconductor wafer is vacuum-sucked on a plurality of block-shaped vacuum suction stages, and the height of the surface is raised and lowered in fine displacement adjustment units. By doing so, it is possible to change the size of the stage via the chuck table and the vacuum suction stage, thereby improving the in-plane uniformity of the height of the surface of a thin plate, for example, a wafer.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

FIGS. 1A and 1B schematically show a first embodiment of a thin plate holding apparatus according to the present invention, wherein FIG. 1A is a plan view and FIG. 1B is a BB view of FIG. FIG. In the drawing, 1 is a thin semiconductor wafer to be held, 1a
Indicates an area for one chip. Reference numeral 2 denotes a block chuck table on which a plurality of block-shaped vacuum suction stages 3, 3,... Provided for each chip 1a are arranged on a stage base 4.

As shown in FIGS. 2A and 2B, each of the block-shaped vacuum suction stages 3 has a suction vacuum groove 5 and a vacuum suction hole 6 communicating therewith. The part corresponding to the self 1 is vacuum-sucked from the back surface. As shown in FIG. 2B, the vacuum groove 5 for suction is necessary even when the amount of deformation of the wafer due to vacuum suction and the amount of deformation when receiving the processing pressure are combined when processing pressure and vacuum suction are applied. It has a width (pitch) that can maintain flatness.

The stage base 4 has a lattice-shaped groove formed on the back surface in accordance with the pattern of the chip 1a of the wafer 1. As shown in FIG. 3, the height of a minute displacement adjusting unit (13) described later is adjusted. It can be elastically deformed according to the change. This is because, in addition to the inherent thickness variation of the wafer 1, the state of the thickness variation of the wafer 1 before CMP, which can be obtained through various device manufacturing processes, is determined by TTV [Thickness variation of the entire wafer FIG. A), for example, is as large as about 5 μm for an 8-inch diameter wafer, but the LTV [thickness variation within a size at an arbitrary position in the wafer; FIG. Is about 0.8 μm in the size of 20 × 20 mm, so that the stage base 4 is made up of a series of blocks each having substantially the same size as each chip 1 a so that a desired small value can be obtained. This is because the height can be adjusted in units of substantially the same size as the chip 1a. In addition, WA
RP (warpage) [variation in the overall height when the wafer is freed; see FIG. 4 (C), for example, about 70 μm for an 8-inch wafer] is applied to the stages 3, 3,... Since it is directly chucked, it is corrected at the time of the vacuum suction.

The stage base 4 is made of metal, for example, SUS.
It is made of a stainless steel or an iron-based steel material, and has elasticity necessary for changing the height of the minute displacement adjusting unit (13), which will be described later, according to a change in the height. The height of the surface of the semiconductor wafer 1 is set to several μm or 0.1 μm. The above-mentioned metals are suitable for those having the elasticity required to transmit a displacement for changing a very small size such as several μm.

FIG. 5 is a cross-sectional view schematically showing the outer peripheral edge of the block chuck table 2. As shown in FIG.
A very small amount of pure water can be supplied to the groove 7 from the outside through a pure water supply hole 8. In this way, a very small amount of pure water can be discharged through the gap between the semiconductor wafer 1 and the stage base 4. Thus, when the degree of vacuum for vacuum suction of the wafer 1 is increased, it is possible to prevent foreign matters such as dust and slurry from flowing into and adhering to the stage 3 due to the flow of air. FIGS. 6A and 6B are a cross-sectional view and a reduced plan view showing another example of forming a temperature adjustment water channel formed in the stage base 4. (A) shows an example having a discharge type temperature adjusting water channel 9, and (B) shows an example having a circulation type temperature adjusting water channel 10.

As described above, the water passage 9 or 10 is formed in the stage base 4 and the temperature-adjusted water is constantly flowed through the water passage 9 or 10, so that heat generated by processing and deformation due to heat from the motor can be suppressed.

Reference numeral 11 [refer to FIG. 1B] denotes a fine displacement adjustment table which is located below and supports the block chuck table 2. The fine displacement adjustment base 12 is made of a highly rigid material, for example, ceramics. A plurality of minute displacement adjustment units 13 are provided on the reference numeral 12. The units 13 are provided at positions corresponding to the respective vacuum suction stages 3, and the height thereof can be adjusted independently. FIGS. 7 (A) and 7 (B) show another example of the fine displacement adjusting unit. FIG. 7 (A) shows two wedge-shaped plates 14 and 15 each made of a rigid body overlapped with each other so that their inclined surfaces are aligned. An example is shown in which the height of the upper plate 15 is raised or lowered by moving the lower plate 14 to one side or the other side along the tilt direction by using screws 16 or the like. (B) shows an example in which the piezoelectric element 17 is used and its height is changed by a voltage applied thereto.

FIG. 8 is a cross-sectional view showing an example of a method of fixing the minute displacement adjusting unit 13. The lower part of the center of the stage 3 is passed through a hole 18 formed in the base 4, and the unit 13 is screwed with the unit 13. And fixed.

According to such a thin plate holding apparatus, one semiconductor wafer 1 is vacuum-sucked on a plurality of block-shaped vacuum suction stages 3, and the height of the surface is made independent for each minute displacement adjusting unit 13. By changing the height
It can be changed for each stage 3 via the stage base 4 and the vacuum suction stage 3. Therefore, wafer 1
In-plane uniformity of the surface height can be improved.

Here, the CMP for the semiconductor wafer 1 will be considered using an 8-inch wafer as an example. And 8
Table 1 below shows the standard specifications and silicon properties of the inch wafer.

[0027]

[Table 1]

For flattening in a semiconductor process, the irregularities on the wafer surface are usually determined by design rules (line width).
It is generally said that the following is required.
This is because a process margin resulting from the depth of focus of a stepper that exposes a pattern is taken into consideration.
In the case of the 25 μm rule, the unevenness of the wafer surface is about ± 0.1
μm, that is, about ± 100 nm or less is required.

The global flattening required in CMP is exactly the same. In the polishing process, even if the mechanical accuracy of the apparatus can be approached to zero as much as possible, as shown in Table 1 above, the influence of the original thickness variation of the wafer, particularly the TTV (see FIG. 4 (A)). Is considered to remain as an error in the in-plane uniformity within the wafer even when the polishing characteristics are considered. An example is shown below.

In the polishing, the convexities on the surface of the material to be polished have a higher processing pressure than the concaves and a higher removal rate by the processing, so that the convexities can be selectively removed. Accordingly, the localization of the unevenness on the surface of the material to be polished before the processing is gradually reduced.
Since it selectively acts on a large swell corresponding to V, it is considered that this appears as an error in the in-plane uniformity.

Normally, since an elastic body such as polyurethane is used as a polishing pad in CMP, the mechanical accuracy is not directly transferred to the surface of the material to be polished due to the characteristics of polishing, but it appears to some extent in a relaxed form.

For example, as shown in FIG.
m, LTV (see FIG. 4B) is 0.8 μm, and a step (pattern) is 1 μm.
Then, this step 1 μm is removed by CMP (0.1 μm).
m. ). In this case, assuming that the machine accuracy is transferred by cutting or grinding on the basis of the back surface, when the step of the chip A at a low position becomes 0.1 μm, the chip B at a high position is removed by −5.9 μm. In other words, the shape is not uniform, and even the groundwork is lost.

Therefore, a step of 1 μm is formed by polishing with a pad of urethane or the like while leaving the TTV of 5 μm.
However, in practice, if there is a difference in height of as much as 5 μm, the removal amount of the chip A is several to several tens% larger than the removal amount of the chip B at present. It can be seen that the uniformity of the removal amount needs to be ± 5% or less in order to remove the chip on the entire surface of the wafer to a step of 0.1 μm by removing 1 μm.

To summarize the above, the diameter is 8 μm and 1 μm
When a TTV wafer of about 5 μm with a pattern step of about 5 μm is polished on the basis of the back side, the step is removed and the LTV is removed.
Although 0.8 μm can be neglected, the removal amount of the chips A and B has a uniformity error of several% to several tens% due to the TTV of 5 μm.

From the above results, it was found that 5 μm of TTV was converted to LTV.
Of about 0.8 μm or less of
It can be seen that the step of 1 μm can be uniformly removed to about 0.1 μm by MP.

Therefore, if the back side can be checked directly and the TTV of 5 μm can be corrected to 0.8 μm or less on the basis of the back side, it is considered to be optimal as a thin plate holding apparatus for CMP. And according to the illustrated thin plate holding device of the present invention,
That is possible. Next, the groove width of the suction vacuum groove will be discussed with reference to FIG. Within the normally considered processing conditions, the processing pressure P ₁ = 0.5 × 10 ⁵ N /
mm ² , and the vacuum pressure P ₁ is about 1.0 × 10 ⁵ N / mm ² . At this time, the calculation result of the change amount δ (the amount of deflection of the surface) when the silicon wafer shown in Table 1 is supported at both ends is given by the following equation (1).

[0037]

(Equation 1)

By substituting each value into the above equation (1), the following equation (2) is obtained.

[0039]

(Equation 2)

In order to make δ _max 0.8 or less, it is necessary to satisfy the condition of the following equation (3).

[0041]

(Equation 3)

That is, if the groove width is equal to or less than 6.89 mm, no undulation greater than LTV occurs during processing.

From the above, according to the thin plate holding device,
Since the height can be adjusted for each chip size by the fine displacement adjustment unit, TTV can be corrected, so that in-plane uniformity can be improved, and mechanical precision transferability can be improved, and dust and the like can be improved. The processing step can be reduced. In addition, as a total process, other process margins are expanded, the accuracy specifications of the input wafer are relaxed, and costs are reduced (the accuracy specifications of the input wafer are relaxed,
(E.g., by allowing the wafer to have a larger diameter).

Further, the fine displacement adjustment table of the thin plate holding device enables the automatic adjustment of the surface adjustment, and also enables the design according to the actual wafer pattern.

FIGS. 11 (A) and 11 (B) show a round type of the block chuck table of the thin plate holding device, wherein FIG. 11 (A) is a plan view and FIG. 11 (B) is a BB line of FIG. FIG. 12A and 12B show a rectangular block chuck table of the thin plate holding device, wherein FIG. 12A is a plan view, and FIG. 12B is a cross-sectional view taken along line BB of FIG. FIG. Thus, the present invention can be implemented in various modes.

[0046]

According to the thin plate holding apparatus of the present invention, one thin plate, for example, a semiconductor wafer is vacuum-sucked on a plurality of block-shaped vacuum suction stages, and the height of the surface is adjusted by moving each minute displacement adjusting unit up and down. By doing so, it can be changed for each stage via the chuck table and the vacuum suction stage, and the in-plane uniformity of the height of the surface of a thin plate, for example, a wafer, can be enhanced.

[Brief description of the drawings]

FIGS. 1A and 1B schematically show a first embodiment of a thin plate holding device according to the present invention, wherein FIG.
(B) is a sectional view taken along line BB of (A).

FIGS. 2A and 2B are cross-sectional views showing a vacuum chuck stage and a semiconductor wafer, wherein FIG. 2A shows an undeformed state, and FIG. Indicates the status.

FIG. 3 is a cross-sectional view showing a deformation of (a stage base of) a block chuck table by a minute displacement adjusting unit.

FIGS. 4A to 4C are TTV, LTV and WAR
It is explanatory drawing of P.

FIG. 5 is a sectional view schematically showing an outer peripheral portion of a block chuck table.

FIGS. 6A and 6B are a cross-sectional view and a reduced plan view showing another example of forming a temperature adjustment water channel formed in a stage base 4. FIGS.

FIGS. 7A and 7B are diagrams showing another example of the minute displacement adjustment unit.

FIG. 8 is a sectional view showing one example of fixing the minute displacement adjusting unit.

FIG. 9 is a diagram showing a wafer shape as an example in consideration of CMP.

FIG. 10 is a diagram referred to when considering the groove width of the suction vacuum groove.

FIGS. 11A and 11B show a round type of the block chuck table of the thin plate holding device.
(A) is a plan view, and (B) is a sectional view taken along line BB of (A).

FIGS. 12A and 12B show a square-shaped block chuck table of the thin plate holding device.
(A) is a plan view, and (B) is a sectional view taken along line BB of (A).

FIG. 13 is a view showing a first conventional example of a method of chucking a wafer during CMP.

FIG. 14 is a view showing a second conventional example of a method of chucking a wafer during CMP.

FIG. 15 is a view showing a third conventional example of a method of chucking a wafer during CMP.

FIG. 16 is a diagram showing a fourth conventional example of a method of chucking a wafer during CMP.

[Explanation of symbols]

1 ... thin plate (semiconductor wafer), 2 ... block chuck table, 3 ... vacuum chuck stage, 4 ...
・ Stage base, 7 ・ ・ ・ Small amount of pure water jet, 9, 10
··· Temperature adjustment water channel, ·····································································································

Claims (4)

[Claims] 1. A chuck table in which a plurality of block-shaped vacuum suction stages are arranged on an elastic stage base, and a plurality of vacuum suction stages are provided corresponding to the respective vacuum suction stages, and their heights can be changed independently of each other. And a fine displacement adjustment table in which a plurality of fine displacement adjustment units for pushing the stage base from the backside are arranged on the fine displacement adjustment base. 2. A thin plate holding apparatus for holding a semiconductor wafer, wherein a vacuum suction stage is provided corresponding to an area of each chip of the wafer. 3. The thin plate holding device according to claim 1, wherein a pure water micro-jetting groove for jetting pure water is formed in a peripheral portion of a surface of the stage base. 4. The thin plate holding device according to claim 1, wherein a temperature adjusting water channel for flowing temperature adjusting water is formed in the stage base.