JPH04206930A - Chuck for polishing semiconductor wafer - Google Patents

Abstract

PURPOSE:To prevent uneven polishing or flaws from appearing on a substrate to be polished, such as a wafer, and to increase the accuracy of the degree of local flatness of the substrate surface by using acrylic for a wafer chuck and by making the thickness of the wafer chuck thick and by specifying the diameter of a suction hole. CONSTITUTION:A wafer chuck 1 is made of acrylic material. On the surface of the wafer chuck 1, 0.5mm-wide spiral grooves for suction are formed. And, vacuum paths 3 to be connected to the spiral grooves for suction 2 are located in the specified pattern and are connected to a vacuum path 5 installed at the side of a rotary holder for polishing 4. The thickness of the acrylic material of the wafer chuck 1 is 3-50mm. When the thickness of the acrylic material is less than 3mm, the specified microroughness accuracy cannot be obtained. When the thickness of the acrylic material is more than 50mm, processing or adjustment of the wafer chuck 1 is hard to do. By making the diameter of the suction hole 3a the same as the width of the spiral groove for suction 2 or smaller, the surface pressure due to suction pressure can be held down for holding the local deformation below the devil mirror level.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to the improvement of a wafer chuck for a polishing device for highly accurate polishing of semiconductor wafers for use in semiconductor integrated circuits, particularly VLSIs, etc., which vacuum-chucks the wafers. A wafer chuck part made of a specific resin with the required thickness is installed.
A spiral groove is provided on the suction surface, and a communication port to the vacuum path with an opening diameter smaller than the groove width is provided at the bottom of the groove, which prevents defects such as scratches on the wafer and further improves the extremely flat surface of the substrate. This invention relates to a chip for polishing semiconductor wafers that significantly improves polishing performance.

Conventional technology Semiconductors and wafers used in VLSI etc. are required to have highly accurate flatness, and the polishing methods used to achieve this flatness include polishing with diamond abrasive grains and polishing with polyrasher in a liquid containing fine abrasive grains. Mechanochemical polishing in which wafers are rotated while facing each other has been carried out, and the structure for holding the wafer during this polishing is considered important, and various structures for holding the substrate to be polished have been proposed.

For example, as a flex method, JP-A-1-210259
No. 1-289657 proposes that the flex method can obtain highly accurate flatness when measuring the flatness based on the substrate surface, but the flex method can obtain highly accurate flatness when the substrate is flexibly formed at the time of polishing. Because it imitates the polishing surface plate, the influence of the thickness variation (parallelism) before polishing is inherited after polishing, and the wafer thickness variation (Total Thickne
ss Variation (TTV) is said to be bad.

Also, JP-A No. 1-193171, JP-A No. 1-2165
In the wax method proposed in No. 40, etc., wafers are pasted flat on a surface plate with wax, and pressed on a polishing surface plate for polishing. There is a problem in that air is trapped in the wax between the substrate and the substrate, forming air pockets.

Problems to be Solved by the Invention During polishing, the air pocket causes local elastic deformation of the wafer, resulting in the formation of bulges in that area. In view of such problems, for example, Japanese Patent Application Laid-Open No. 64-2858, Japanese Patent Application Laid-Open No. 64-45
Holding of the substrate to be polished by vacuum suction with high mechanical precision, as proposed in No. 567, has come to be used.

However, although this method solved the problem of the dents caused by the air pockets mentioned above, a new problem occurred: scratches on the back side of the substrate due to the material of the wafer cutter that holds and contacts the substrate.

Furthermore, as the required polishing accuracy becomes significantly higher, the accuracy of the micro-roughness of the wafer has become a new problem.

When holding a substrate to be polished by vacuum suction, this invention prevents defects such as polishing unevenness and scratches on the substrate to be polished such as a wafer, and also prevents the occurrence of defects such as uneven polishing and scratches on the substrate to be polished, which is a new problem. The object of the present invention is to provide a wafer chuck having a configuration that can improve the accuracy of the wafer.

Means for Solving the Problems This invention provides a semiconductor wafer polishing apparatus having a mechanism for holding a substrate to be polished by vacuum suction, which prevents the occurrence of polishing unevenness and scratches on the wafer, and improves local flatness. As a result of various studies regarding the material of the wafer chuck and the vacuum suction mechanism, it was discovered that the purpose could be achieved by using acrylic for the wafer chuck, increasing the thickness of the plate, and specifying the suction hole diameter. completed.

This invention provides a semiconductor wafer, in which a wafer chuck for suctioning and supporting the wafer is installed on the upper surface of a rotating polishing holder, and a vacuum path for vacuum suctioning the wafer is provided on the wafer chuck and the boulder body. In a polishing device, a spiral groove for vacuum suction is provided on the surface of a wafer chuck made of =4-acrylic, and a suction hole having an opening diameter smaller than the groove width and communicating with the vacuum path is provided at the bottom of the spiral groove. This is a chuck for polishing semiconductor wafers.

The present invention is a chuck for polishing semiconductor wafers having the above-mentioned configuration, characterized in that: - The thickness of the wafer chuck is 3 to 50 mm, and the suction hole diameter for vacuum suction is 0.5 mm or less.

Furthermore, in the above configuration, the present invention is characterized in that the surface shape of the chuck on which the wafer is placed is a coplanar surface formed by direct lapping with a polishing plate without placing the wafer on the polishing device. This is a chuck for polishing semiconductor wafers.

Function The present invention is characterized in that acrylic is used as the material for holding the substrate to be polished. Acrylic has lower hardness than semiconductor wafers, especially silicon, so when polishing the wafer substrate, regardless of whether it is held directly or indirectly, it prevents the occurrence of scratches on the so-called back side of the wafer that is not polished. be able to.

On the other hand, because conventional wafer chucks for polishing are flat, the gap between the lapping machine and the chuck becomes smaller during polishing, which reduces the amount of polishing liquid that acts on the wafer, which tends to cause clouding, and the resulting flatness is low. There was a problem.

Therefore, in order to make the force acting on the wafer uniform during polishing, the polishing disk is brought into direct contact with the vacuum suction surface of the wafer chuck, and the polishing disk and wafer chuck are moved relative to each other while supplying the polishing liquid. By forming a coplanar surface, the wafer is held by vacuum suction on the coplanar surface, and the uneven polishing pressure during polishing acts more uniformly, improving the flatness after polishing.

However, by using the vacuum adsorption method using acrylic as a wafer polishing method, a new problem arose after polishing, which was that the impression of the magic mirror image, which is one of the micro-roughness evaluation methods, deteriorated. be.

In the case of polishing by vacuum suction, the pressure due to suction becomes a much larger blood pressure than the polishing pressure. When this suction pressure and polishing pressure are applied, a considerably large bending stress is generated in the acrylic plate, which causes deformation of the acrylic plate.

When polishing a semiconductor wafer with this deformation,
The deformation of the acrylic is directly transferred to the wafer, resulting in a magic mirror image with patterns such as unevenness in the adhesive when the acrylic material is fixed to a holder with double-sided adhesive tape, for example.

This is because the deformation of acrylic due to bending stress is greatly affected by the Young's modulus and thickness of the material, and thin acrylic is on the order of being able to be evaluated at the magic mirror evaluation level (sensitivity: 0.01 pm unevenness). This is because deformation occurs.

Therefore, in this invention, the thickness of the acrylic material of the wafer chuck is set to 3 to 50 mm. The thickness of the acrylic material is 3m
If it is less than 5 m, the required micro-roughness accuracy cannot be obtained;
If it exceeds 0 mm, it becomes difficult to process and modify, making it unusable. Preferably the thickness is 5 mm to 20 mm.

In addition, the inventors also found that when the suction hole diameter is large, the surface pressure due to the suction pressure increases, and the resulting distortion creates a magic mirror image that is affected by the vacuum suction hole in a very local area, causing the above-mentioned co-slip surface. It has been found that by forming such a material, the adsorption pore diameter tends to be enlarged, and the micro-roughness accuracy decreases.

Therefore, in this invention, a spiral groove for vacuum suction is provided on the surface of a wafer chunk made of acrylic, and a communication port to a vacuum path having an opening diameter smaller than the groove width is provided at the bottom of the spiral groove to reduce the suction hole diameter. By making it smaller, you can get a good-looking magic mirror image. That is, in order to obtain the required micro-roughness accuracy, it is necessary that the spiral groove width be 0.5 mm or less.

By using acrylic for the wafer chuck and increasing its thickness, this invention can prevent scratches caused by vacuum suction, and can suppress the effects of distortion on the back side with much smaller deformation than the magic mirror evaluation level. Since this is possible, a magic mirror image that does not transfer the shape of the back surface such as tape unevenness can be obtained.

Furthermore, by reducing the suction hole diameter to tJz less than the groove width of the suction spiral groove, it is possible to suppress surface pressure due to suction pressure and suppress local deformation to a level below that of a magic mirror.

Embodiment FIG. 1 shows a holder for polishing a semiconductor wafer and a wafer chuck according to the present invention.

Here, an example will be described in which a wafer chuck (1) is attached to a polishing rotating holder (4) using a double-sided adhesive tape (6) for adhesion in order to vacuum adsorb one wafer.

The wafer chuck (1) is made of acrylic material, and a 0.5 mm wide suction spiral groove (2) is provided on the surface, and a vacuum path (3) communicating with the suction spiral groove (2) is provided at the bottom of the wafer chuck (1). Polishing rotary boulders (4) (I
It consists of a structure that communicates with a vacuum path (5) provided in ll.

Fix the wafer to the wafer chuck (1) for polishing,
When detaching, use the vacuum path (5) on the holder (4) side.
) can be easily done by simply turning on and off the vacuum pump connected to the

First, as shown in Figure 2, when the thickness of the wafer chuck (1) was set to 2 mm and the diameter of the suction hole (3a) was set to 0.8 mm to form a sliding surface, the actual hole diameter expanded due to polishing sag. If you examine the magic mirror image after polishing, you will see Figure 3C.
As shown in Figure 2, there are many black spots of suction holes (indicated by ○ in Figure IIX), and there are also tape irregularities on the back side (12X
(indicated by horizontal lines in the figure) were seen over a wide area.

Next, the thickness of the acrylic material of the wafer chuck (1) is 3
mm, and the diameter of the suction hole (3a) was set to 0.7 mm to form a co-sliding surface and the magic mirror image was examined.

As a result, when the thickness of the acrylic material was 2 mm, the image was distorted due to the influence of tape unevenness on the back side, but as shown in Figure 3, when the thickness was <3 mm, a magic mirror image with almost no influence was obtained. However, even if the suction hole (3a) diameter is set to 0.7 mm, there are still traces (11) of the suction hole, and the influence of the suction hole can be seen.

Furthermore, the thickness of the wafer chuck (1) is set to 5 mm,
The magic mirror image obtained when the suction hole (3a) diameter was set to 0.5 mm and polished is shown in FIG. 3a.

As shown in FIG. 3a, it was possible to obtain an excellent mirror image in which there was no effect of tape unevenness on the back surface and no effect of suction holes.

The relationship between the magic mirror image and accuracy is that the vertical resolution of the precision measuring device is 0.1 to 0.3 pm, and the magic mirror image contrast is 0.01.
Since the thickness is on the order of μm, when the thickness of the acrylic material is increased, the improvement in the magic mirror image is equivalent to 0.01 to 0.3 pm in terms of accuracy.Effects of the InventionThe wafer chuck for polishing semiconductor wafers according to the present invention has the following advantages: By using acrylic as a material,
The occurrence of JnEW on the back side of the wafer can be suppressed, and by increasing the thickness of the acrylic to 3 mm to 50 mm in the mirror image, which is an evaluation of micro-roughness, the influence of the acrylic back surface can be eliminated. Furthermore, by making the diameter of the vacuum suction hole smaller than the width of the spiral groove, a magic mirror image that is not affected by the suction hole can be obtained.
Defects such as scratches are not generated on the wafer, and the local flatness of the substrate surface can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a holder for polishing semiconductor wafers according to the present invention. FIG. 2 is a longitudinal cross-sectional view of a conventional semiconductor wafer polishing holder. FIGS. 3a to 3c are explanatory diagrams showing the mirror image after polishing, looking at the effects of the thickness of the acrylic material and the suction holes. 1... Wafer chuck, 2... Spiral groove for suction, 3
．． 5... Vacuum path, 3a... Adsorption hole, 4...
Holder, 6... Double-sided adhesive tape, 10... Wafer, 11... Trace, 12... Tape unevenness on back side.

Claims (1)

[Scope of Claims] 1. A semiconductor in which a wafer chuck for suctioning and supporting a wafer is installed on the upper surface of a polishing rotating holder, and a vacuum path for vacuum suctioning the wafer is provided in the wafer chuck and the holder body. A wafer polishing device characterized by having a spiral groove for vacuum suction on the surface of a wafer chuck made of acrylic, and a suction hole having an opening diameter less than the groove width and communicating with the vacuum path at the bottom of the spiral groove. A chuck for polishing semiconductor wafers. 2. The semiconductor wafer polishing chuck according to claim 1, wherein the wafer chuck has a plate thickness of 3 to 50 mm and a suction hole diameter for vacuum suction of 0.5 mm or less. 3. Claim 1 or Claim 2, wherein the surface shape of the chuck on which the wafer is placed is a coplanar surface formed by direct lapping with a polishing plate without placing the wafer on the polishing device. A chuck for polishing semiconductor wafers as described above.