WAFER POLISHING HEAD

Abstract

A wafer polishing head according to the invention is disclosed. In the wafer polishing head, an automatic control device is additionally installed outside the wafer polishing head for automatically adjusting a pressure applied on a retaining ring. This ensures the bottom of the retaining ring always lower than that of a carrier, thereby preventing a semiconductor wafer from slip during polishing. Furthermore, a liquid pressure generated to press the carrier can efficiently alleviate wabble during polishing. Therefore, the wafer polishing head of the invention can greatly improve a polishing uniformity.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a chemical mechanical polishing (CMP) device, and in particular to a wafer polishing head controlled by gas and liquid pressures.

2. Description of the Related Art

Chemical mechanical polishing (CMP) is a global planarization technique. In chemical mechanical polishing, the rear surface of a semiconductor wafer is fixed by a wafer polishing head. Then, the front surface of the semiconductor wafer is pressed against a polishing pad which is installed on a removable platen. When polishing, a chemical agent conducive to CMP is continuously supplied to the platen. By the chemical reaction between the chemical agent and the front surface of the semiconductor wafer and mechanical polishing, the front surface of the semiconductor wafer can be completely planarized.

The wafer polishing head is used to safely and firmly hold the semiconductor wafer without any damage or contamination on the semiconductor wafer. In an early phase, a semiconductor wafer was adhered on a carrier with a material like wax. After polishing, the wax must be completely removed or the semiconductor wafer is contaminated. Currently, a wafer adhering layer is additionally disposed on the bottom of the carrier. Since the wafer adhering layer is made of a porous material, a semiconductor wafer can be firmly held on the carrier by creating a vacuum environment. However, a high-speed rotation could cause the semiconductor wafer slipping during polishing. Therefore, a retaining ring is additionally installed to surround the semiconductor wafer, thereby preventing the semiconductor wafer from slip. The retaining ring must be rigid and uneasily react with any chemical agent. Typically, Delrin and Tecktron are used to make the retaining ring.

FIG. 1A is a cross-sectional view illustrating a wafer polishing head 10 according to the invention. Referring to FIG. 1A, a carrier 12 is a main body of the wafer polishing head 10. A wafer adhering layer 14, made of an adhesive and porous material like felt, is disposed on the bottom of the carrier 12. Since the wafer adhering layer 14 is porous, the rear surface of a semiconductor wafer 16 can be firmly held on the wafer adhering layer 14 by creating a vacuum environment during wafer loading. A retaining ring 18 surrounds the carrier 12 and the semiconductor wafer 16, wherein the bottom of the retaining ring 18 must have a lower position than that of the carrier 10, such that the semiconductor wafer 16 can be prevented from damage during polishing. Furthermore, a first pressure chamber 20 is disposed directly above the retaining ring 18. A diaphragm 22 is disposed on the bottom the first pressure chamber 20 and contact the retaining ring 16. When a gas flows into the first pressure chamber 20, the diaphragm 22 is deformed to press again the retaining ring 18, thereby fixing the retaining ring 18. A second pressure chamber 24 is disposed directly on the carrier 12. When a gas flows into the second pressure chamber 24, a force is created to push the semiconductor wafer 16 via the carrier 12.

FIG. 1B is a flow chart illustrating a pressure control of the wafer polishing head 10 of FIG. 1A. In FIG. 1B, a gas source 26 supplies a required gas to the first pressure chamber 20, the second pressure chamber 22 and the carrier 12.

During polishing, the retaining ring 26 always contacts the diaphragm 22, resulting in an abrasion therebetween. Under this condition, it is easy to cause the semiconductor wafer 16 slipping if the bottom of the carrier 12 is lower than that of the retaining ring 18. To resolve this problem, it is necessary to regularly adjust the retaining ring 18 thereby to maintain the bottom of the retaining ring 16 at a lower position than that of the carrier 10.

As can be obviously seen from the above, the prior wafer polishing head uses a gas pressure to provide a vertical force to the semiconductor wafer and the polishing pad, thereby alleviating wabble during polishing. However, the gas pressure depends on the stability of the gas source. As a result, it is easy to cause wabble on the semiconductor wafer and the polishing pad, resulting in a poor polishing uniformity. Moreover, the retaining ring always contacts the polishing pad, causing an abrasion therebetween. In this case, it is easily to make the semiconductor wafer slip if the bottom of the carrier is lower than that of the retaining ring. To overcome this problem, the retaining ring must be regularly and manually adjusted to an appropriate position, and pressures generated by a gas to press the carrier and the retaining ring are also manually adjusted to different proper pressure values even though the gas comes from the same gas source.

SUMMARY OF THE INVENTION

In view of the above, an object of the invention is to provide a wafer polishing head which uses a liquid pressure to press a carrier thereby to obtain a better polishing uniformity. Furthermore, a pressure applied on a retaining ring is automatically adjusted by an automatic control device, thereby allowing the retaining ring to efficiently prevent a semiconductor wafer from slip during polishing.

As to the wafer polishing head according to the invention, an automatic control pressure device, which is additionally installed outside the wafer polishing head, can automatically adjust a pressure applied on a retaining ring, thereby ensuring a polished semiconductor wafer does not slip away. In addition, the wafer polishing head can greatly alleviate wabble on the carrier by using a liquid pressure to press the carrier. Accordingly, the wafer polishing head of the invention can greatly improve a polishing uniformity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only, and thus do not limit the present invention, and wherein:

FIG. 1A is a cross-sectional view illustrating a wafer polishing head according the prior art;

FIG. 1B is a flow chart illustrating a pressure control of the wafer polishing head of FIG. 1A;

FIG. 2A is a cross-sectional view illustrating a wafer polishing head according to a preferred embodiment of the invention; and

FIG. 2B is a flow chart illustrating a pressure control of the wafer polishing head of FIG. 2A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2A is a cross-sectional view showing a wafer polishing head 60 according to a preferred embodiment of the invention. In FIG. 2A, a carrier 62 is disposed at the center region of the wafer polishing head 60. A wafer adhering layer 64, such as a porous plank like felt, is disposed beneath the carrier 62. Like the prior art, the rear surface of a semiconductor wafer 66 can be firmly held on the wafer adhering layer 64 in a vacuum environment. A retaining ring 72 surrounds the carrier 62, wherein the bottom of the retaining ring 72 must be maintained lower than that of the carrier 62. Moreover, a first pressure chamber 68 is disposed directly above the retaining ring 72 with a diaphragm 70 therebetween against the retaining ring 72. A second pressure chamber 74 is disposed directly on the carrier 62 and partly filled by a liquid 76, such as silicon oil, which has low volatility and chemical reactivity.

Referring to FIG. 2B, a gas source 80 supplies a required gas to the first pressure chamber 68 and the second pressure chamber 74. To control the pressure of the first pressure chamber 68, a gas coming from the gas source 80 must be first adjusted by an automatic control pressure device 90, and then transmitted to the first pressure chamber 68. As an example in the embodiment, the automatic control pressure device 90 consists of a converter 92, a controller 94 and a pressure regulator 96. With respect to the control flow of the wafer polishing head 60, a pressure signal generated by the first pressure chamber 68 is first transmitted to the converter 92, such as an analog/digital (A/D) converter. The pressure signal is converted to a digital signal by the converter 92, and then transmitted to the controller 94. After the digital signal is calculated and compared to a set value by the controller 94, the controller 94 transmits an electronic signal to the pressure regulator 96, such as a control valve, thereby controlling a gas flow to the first pressure chamber 68 from the gas source 80. Thus, the diaphragm 70 can be deformed to apply a proper pressure on the retaining ring 72. As a result, the bottom of the retaining ring 72 is frequently maintained lower than that of the carrier 62, thereby preventing the semiconductor wafer 66 from slip. Moreover, a gas flowing to the second pressure chamber 74 from the gas source 80 plus the liquid 76 therein creates a liquid pressure on the semiconductor wafer 66.

In summary, the advantages of the wafer polishing head according to the invention are as follows:

(1) A polishing uniformity is greatly improved since the liquid pressure generated to press the carrier can efficiently alleviate wabble, and make the carrier and the semiconductor wafer parallel to each other.

(2) The retaining ring is adjusted by the automatic control pressure device without manual adjustments. This ensures that the bottom of the retaining ring is always lower than that of the carrier. Therefore, the semiconductor wafer can be well protected during polishing and the lifetime of the retaining ring is extended.

While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

Claims

1. A wafer polishing head for planarizing a wafer comprising a carrier for loading the wafer, a wafer adhering layer disposed beneath the carrier, a retaining ring surrounding the carrier and the wafer adhering layer, the wafer polishing comprising: a first pressure chamber having a first inner pressure disposed above the retaining ring; a second pressure chamber having a second inner pressure disposed on the carrier; and an automatic control system respectively coupled to the first pressure chamber and the second pressure chamber for adjusting a relative height between the carrier and the retaining ring.

2. A wafer polishing head for planarizing a wafer comprising a carrier for loading the wafer, a wafer adhering layer disposed beneath the carrier, a retaining ring surrounding the carrier and the wafer adhering layer, the wafer polishing comprising: a first pressure chamber having a first inner pressure disposed above the retaining ring; and a second pressure chamber having a second inner pressure disposed on the carrier, wherein a relative height between the retaining ring and the carrier can be adjusted by changing the first and second inner pressure.

3. A wafer polishing head for planarizing a wafer comprising a carrier for loading the wafer, a wafer adhering layer disposed beneath the carrier, a retaining ring surrounding the carrier, the wafer adhering layer, a first pressure chamber having a first inner pressure disposed above the retaining ring, and a second pressure chamber having a second inner pressure disposed on the carrier, the wafer polishing comprising: an automatic control system respectively coupled to the first pressure chamber and the second pressure chamber for adjusting a relative height between the carrier and the retaining ring.