Method and apparatus for polishing a semiconductor wafer.

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a method and an apparatus for polishing a semiconductor wafer, and more particularly to an improved method and an apparatus for obtaining a substantially uniform polishing action on the surface of a wafer.

【0002】

[Conventional technology and its problems]

In this technique, various methods and tools for polishing semiconductor wafers are known. Generally, these tools include an upper plate and a lower plate, between which wafers are inserted for polishing. During work, the two plates move relative to each other, and a slurry consisting of an abrasive solution with or without a corrosive is fed between the plates to perform the abrasive and wash away the material removed from the wafer.

【0003】

However, it became clear at the time of polishing that the load applied to the wafer causes the concentration of slurry in contact with the edge of the wafer to be higher than that of the center of the wafer. As a result, the polishing action at the edges becomes stronger, which causes non-uniformity in the thickness between the center and the edges, resulting in insufficient flatness of the wafer.

【0004】

Efforts have been made in this technique to make the polishing action on the wafer more uniform. For example, US Pat. No. 4,313,284, issued to Walsh in February 1982, discloses methods and equipment for adjusting the surface shape of the upper plate of a wafer carrier. When performing this method, a vacuum source is connected to the carrier and the pressure difference is used to deform the carrier into a concave shape. This shape is thereby required to match the surface of the carrier with the surface of the lower plate or turntable (to which the abrasive pad is attached) that deforms due to thermal and mechanical stresses during polishing.

【0005】

Another approach is disclosed in U.S. Pat. No. 4,450,652 issued to Walsh on May 29, 1984, in which the temperature of the top and bottom surfaces of the turntable is kept constant. As a result, the bending deformation due to heat of the wafer carrier and the turntable is kept in the same state. The temperature difference is kept constant by detecting the temperature of the polishing pad and adjusting the pressure applied to the wafer.

【0006】

Both of the above references are modified so that the curvature of the wafer carrier surface matches the curvature of the turntable. Deformation also occurs by changing the pressure applied to the wafer. However, neither reference material attempts to adjust the curvature of the wafer carrier surface so that it bends against the turntable and the degree of abrasive action varies depending on the point on the wafer surface.

【0007】

[Means for solving problems]

Therefore, according to the present invention, an improved method for polishing the surface of a workpiece has been discovered. The process preferably involves mounting the semiconductor wafer on a wafer carrier made of at least two materials with different coefficients of thermal expansion and polishing the wafer surface. Radial curvature is controlled by adjusting the temperature of the carriers, resulting in a convex (or concave) bias on the wafer. As a result, if desired, it is possible to enhance the polishing action at the center (or edge) of the wafer so that the thickness of the surface of the wafer to be polished is uniform.

【0008】

According to another aspect of the present invention, an improved device for polishing the surface of a workpiece is obtained. In the preferred embodiment, the device is used for polishing the surface of a semiconductor wafer and is located above the rotary turntable assembly, the polishing pad supported by the assembly, and during polishing. It is composed of a rotary wafer carrier that holds a wafer arranged between the polishing pad and the polishing pad, and a temperature adjusting means connected to the carrier. An important feature is that the wafer carrier is made up of at least two materials with different coefficients of thermal expansion. By adjusting the temperature of the carrier with a temperature adjusting means and controlling the curvature in the radial direction, a concave bias or a convex bias is applied to the wafer attached to the carrier during polishing.

【0009】

The above and other objectives, features, and advantages of the present invention will be clarified by the following more detailed description of the preferred embodiments of the present invention.

【0010】

[Example]

With reference to the drawings, FIG. 1 shows an improved device for polishing the semiconductor wafer 1. The device includes a wafer carrier 2 coupled to a spindle 3, which is further suitable for moving (rotating) the carrier 2 in the directions indicated by arrows 4a, 4b, and 4c. Coupling to any motor or drive means (not shown). The spindle 3 supports the carrier 2 and thus the load 5 acting on the wafer 1 during polishing. The carrier 2 is provided with an edge portion 6 that prevents the wafer 1 from sliding off from under the carrier 2 when the carrier 2 rotates.

【0011】

As shown, the semiconductor wafer 1 to be polished according to the method of the present invention is sandwiched between the carrier 2 and the rotary turntable assembly entirely under the carrier 2, indicated by number 7. It is attached to carrier 2 so that it can be used. The turntable assembly 7 includes a polishing table 8 to which the polishing pad 9 is attached, which is indicated by an arrow 11 around the shaft 10 by a compatible motor or drive means (not shown). Rotate in the direction of display.

【0012】

During grinding, it is common to inject a slurry (not shown) between the wafer carrier 2 and the polishing table 8. Due to the load 5 acting on the wafer carrier 2, as mentioned above, the high concentration slurry generally comes into contact with the wafer edge, resulting in a stronger polishing action at the edge. To overcome this problem, a unique wafer carrier structure according to the present invention is used. Referring to FIG. 3, the wafer carrier 2 has an upper portion 12 and a lower portion 13, which are made of materials having different coefficients of thermal expansion. In general, the two parts 12 and 13 consist of any compatible material, preferably metal, and are joined by a compatible brazing material 14, such as silver brazing, which is known to those skilled in the art.

【0013】

As will be described in more detail later, the temperature of the wafer carrier 2 is adjusted, but since the upper portion 12 and the lower portion 13 are made of materials having different coefficients of thermal expansion, the radius of the carrier 2 is correspondingly adjusted. There will be a change in the curvature of the direction. The temperature of carrier 2 is well regulated by circulating a compatible fluid, such as water, through the carrier. The upper portion 12 is provided with a fluid chamber 15 in the form of a winding channel arranged on the surface of the brazing material 14. The winding structure is advantageous for uniform temperature control of carrier 2. The heating / cooling fluid of the carrier 2 is injected into or recovered from the chamber through the fluid inlet 16 and the fluid outlet 17 inside the spindle 3, respectively. The fluid flow path of the winding channel is best shown in Figure 2.

【0014】

In reality, the wafer carrier 2 has a structure that exhibits a relatively flat shape as shown in FIG. 3 at a reference temperature, which is usually room temperature. Generally, the lower portion 13 is made of the material with the higher coefficient of thermal expansion, but this is not necessary. Therefore, if it is desired to apply a convex bias to the wafer 1 mounted on the carrier 2, the temperature of the carrier is raised by allowing the temperature of the water flowing through the fluid chamber 15 to exceed the reference temperature, as shown in FIG. Bend the outer edge of the carrier upwards, as indicated by the arrows 18a, 18b, and 18c shown. As a result, the polishing action at the center of the wafer is strengthened, and the high slurry concentration compensates for the situation where the polishing action at the wafer edge is generally strong.

【0015】

On the other hand, depending on the specific device used and the properties of the required polishing action, the carrier 2 can be cooled to below the reference temperature to increase the polishing rate at the edge of the wafer 1. As a result, the outer edge of the carrier 2 bends downward, and the wafer 2 is subjected to a concave bias.

【0016】

The upper and lower portions 12 of the carrier can be made of any suitable material, respectively, as long as the required coefficients of thermal expansion with respect to the degree of bending of the carrier are sufficiently different. Of course, the greater the difference in the relative thermal expansion coefficients of the materials used, the greater the degree of bending with respect to a given temperature change. Conversely, as the difference in coefficient of thermal expansion decreases, so does the degree of bending with respect to a given temperature change, which can be particularly advantageous if more precise control is desired. For example, if the coefficients of thermal expansion are exactly the same, the degree of bending with respect to a given temperature change can be negligible. A wide range of materials can be selected, but metals are generally preferred, and in one of the most desirable embodiments, stainless steel, such as 304 stainless steel, is used as the lower portion 13 and Hastelloy C "as the upper portion 12. Nickel-based alloys such as (available from Union Carbide Corp.) are used.

【0017】

As will be apparent to those skilled in the art, it is possible to make various modifications to the methods and devices without departing from the spirit of the present invention. For example, it is possible to make the lower portion 13 out of the material with the lower coefficient of thermal expansion, which is desirable if it is desired to raise the temperature of the carrier and bend the carrier 2 in a concave shape. Under such circumstances, if the temperature of the carrier is lowered below the reference temperature, the carrier 2 will, of course, bend in a concave shape.

【0018】

Therefore, the method and apparatus of the present invention enable a uniform polishing action on the wafer surface in a wide range of implementation. Further, if desired, the temperature modulation of the carrier 2 can be dynamically adjusted so that uniform polishing in the radial direction can be performed. This is desirable, for example, when the polishing pad 9 wears during use.

【0019】

Further, the methods and devices of the present invention include, for example, silicon such as single crystal silicon or polysilicon, ordinary insulating materials such as silicon dioxide, other inorganic or organic insulating materials such as polyimide, ordinary conductive materials such as metals, and the like. It can be used for polishing a wide variety of wafer surface materials. Further, it is possible to uniformly remove the material by polishing the surface according to the fluctuation of the fine composition.

【0020】

Of course, a wide range of materials, such as glass, that is, geographic features can be polished. Further, in some situations, it may be desirable to form a surface with a desired degree of curvature instead of a uniform flat surface. Other modifications should be obvious to those skilled in the art.

【0021】

[Effect of the invention]

The present invention has achieved improved methods and devices that provide a nearly uniform polishing action on the surface of the workpiece.

[Simple explanation of drawings]

[Figure 1]

It is the schematic of the partial sectional view about the apparatus for polishing a semiconductor wafer according to the Example of this invention.

[Figure 2]

It is a somewhat enlarged cross-sectional view of the wafer carrier drawn along line 2-2 of FIG.

[Fig. 3]

It is a partially cutaway sectional view of a wafer carrier drawn along line 3-3 of FIG.

[Fig. 4]

It is sectional drawing similar to FIG. 3 of the wafer carrier which applies a convex bias to a wafer.

[Explanation of symbols]

1. Semiconductor wafer 2. Wafer carrier 3. Spindle 6. Edge part 7. Turntable assembly 8. Abrasive table 9. Abrasive pad 10. Shaft 12. Upper part of wafer carrier 13. Wafer carrier lower part 14. Brazing material 15. Fluid chamber 16. Fluid inlet 17. Fluid outlet