Patent Application
20060249079
1. Field of the Invention
The present invention relates to equipment of semiconductor processes. More particularly, the present invention relates to a wafer heater that causes less thermal stress in the wafer, and a wafer chuck including the wafer heater to have heating capability.
2. Description of the Related Art
In a semiconductor process requiring higher temperature, a wafer is usually heated by a heater disposed on the wafer chuck that holds the wafer in the process. A conventional wafer chuck with heating capability has a ceramic ring and an air-drawing means under the opening of the ceramic ring. The ceramic ring is thermally coupled with a heat source, and the wafer to be treated is placed on the ceramic ring and fixed thereon through suction of the air-drawing means. The heat from the heat source is conducted to the wafer via the ceramic ring, so that the wafer can be heated to desired temperature. The ceramic ring is used in the wafer chuck mainly for its superior hardness and heat-resistance.
However, since the ceramic ring does not contact with the whole lower surface of the wafer, temperature difference inevitably occurs on the wafer. For current use, the ceramic ring has relatively higher thermal conductivity, such that the temperature difference and the resulting thermal stress are frequently overly large to cause wafer breakage.
In view of the foregoing, this invention provides a wafer heater that causes less thermal stress and thereby effectively prevents wafer breakage.
This invention also provides a wafer chuck with heating capability that includes the wafer heater of this invention.
The wafer heater of this invention includes a body also serving as a heat source, a ceramic ring on the body and a buffer ring on the body. The ceramic ring is thermally coupled with the body as a heat source. The buffer ring contacts with the ceramic ring, and has a top surface higher than the top surface of the ceramic ring so that a wafer can be placed on the top surface of the buffer ring without contacting the ceramic ring. The thermal conductivity coefficient (μ1) of the buffer ring is smaller than that (μ2) of the ceramic ring. The product (p1=μ1×A1) of the thermal conductivity coefficient (μ1) and the top surface area (A1) of the buffer ring is also smaller than the product (p2=μ2×A2) of the thermal conductivity coefficient (μ2) and the top surface area (A2) of the ceramic ring.
To understand the effect of this invention, the following equation of thermal conduction is discussed:
Q=μ×A×ΔT (1)
wherein Q is the thermal conduction rate of a thermal conductor, μ is the thermal conductivity coefficient of the same, A is the contact area (or the top surface area) of the same, and ΔT is the temperature difference. According to equation (1), decreasing the product of μ and A will decreases the thermal conduction rate “Q” of the thermal conductor. Since the thermal conductivity coefficient of the buffer ring and the product of thermal conductivity coefficient and top surface area of the same are smaller than those of the ceramic ring, the thermal conduction from the body of the wafer heater to the wafer placed on the buffer ring is slowed down. Therefore, the temperature difference on the wafer is smaller as compared with the prior art, so that less thermal stress is generated lowering the possibility of wafer breakage.
The wafer chuck of this invention is based on the above wafer heater of this invention, wherein an air-drawing means is further disposed in the region of the body surrounded by the ceramic ring, i.e., the region under the opening of the ceramic ring. When a wafer is placed on the top surface of the buffer ring, vacuum can be generated, by the air-drawing means, in the space enclosed by the body, the ceramic ring, the buffer ring and the wafer, so as to hold the wafer tightly on the wafer chuck.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
Referring to
The ceramic ring 120 and the buffer ring 125 both are disposed on the end of the body 110 contacting with each other. The air-drawing means 130 is disposed in the region of the body 110 surrounded by the ceramic ring 120, i.e., the region of the body 110 exposed in the opening of the ceramic ring 120. Such a wafer chuck 100 is suitably used in a plasma photoresist ashing apparatus.
More specifically, as shown in
The thermal conductivity coefficient (μ1) of the buffer ring 125 is smaller than that (μ2) of the ceramic ring 120 (μ1<μ2). Such a buffer ring 125 can be made from a heat-resistant polymer. For use in plasma photoresist ashing processes that are usually conducted under relatively lower temperature, quite a lot polymer materials can meet the requirement of heat resistance to be used as the material of the buffer ring 125.
Moreover, the product (p1=μ1×A1) of the thermal conductivity coefficient (μ1) and the top surface area (A1) of the buffer ring 125 is smaller than the product (p2=μ2×A2) of the thermal conductivity coefficient (μ2) and the top surface area (A2) of the ceramic ring 120 (P1<P2). In the above description, the top surface area of the buffer ring 125 is defined as the area of the top surface of the buffer ring 125 that directly contacts with the wafer 10. Similarly, the top surface area of the ceramic ring 120 is defined as the area of the top surface of the ceramic ring 120 that would directly contact with the wafer 10 if the buffer ring 125 were absent as in the prior art. To meet this requirement of P1<P2, it is feasible to set the top surface area (A1) of the buffer ring 125 smaller than that (A2) of the ceramic ring 120 (A1<A2).
In addition, the air-drawing means 130 in the region of the body 110 surrounded by the ceramic ring 120 may include many holes formed on the surface of the region, wherein the holes are connected to an air pump (not shown) via, for example, an air channel (not shown) within the body 110. When the wafer 10 is placed on the top surface of the buffer ring 125 and the air-drawing means 130 is turned on by switching the air pump on, the wafer 10 can be held tightly on the wafer chuck 100 through suction of the air-drawing means 130.
Since the thermal conductivity coefficient of the buffer ring and the product of thermal conductivity coefficient and top surface area of the same are smaller than those of the ceramic ring, the thermal conduction from the body of the wafer chuck to the wafer is slowed down. Therefore, the temperature difference on the wafer is smaller as compared with the prior art, so that less thermal stress is generated lowering the possibility of wafer breakage.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
