Browse Prior Art Database

High Uniformity Hot Plate Adapter

IP.com Disclosure Number: IPCOM000045200D
Original Publication Date: 1983-Feb-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 3 page(s) / 68K

Publishing Venue

IBM

Related People

Kaplan, LH: AUTHOR [+2]

Abstract

Large hot plates available from laboratory supply companies are incompatible with modern lithographic processing and its need for precise control of all steps. Many processes, for example, require very fine control of the post exposure bake step. Many resist systems lose sensitivity rapidly as a function of high prebake temperature. Yet, wafers have become progressively larger, requiring commensurately larger hot plates for reasonable throughput. Commercially available hot plates, having square surface areas approximately 24 cm. on a side, are commonly employed for hot plate baking operations. But such units have both spatial and temporal non-uniformity which is unsuited to lithography.

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High Uniformity Hot Plate Adapter

Large hot plates available from laboratory supply companies are incompatible with modern lithographic processing and its need for precise control of all steps. Many processes, for example, require very fine control of the post exposure bake step. Many resist systems lose sensitivity rapidly as a function of high prebake temperature. Yet, wafers have become progressively larger, requiring commensurately larger hot plates for reasonable throughput. Commercially available hot plates, having square surface areas approximately 24 cm. on a side, are commonly employed for hot plate baking operations. But such units have both spatial and temporal non-uniformity which is unsuited to lithography.

The temporal problems arise from overly coarse thermostat systems and have been partially solved in the past by powering the unit with an adjustable power supply (variac) and setting the thermostat so that it never opens. The spatial problem, however, is not as easy to address. Fig. 1 shows a temperature map of one commercial hot plate, which is typical of commercially available hot plates. A variation of over 60 degrees C is seen over the entire 24x24 cm. surface. Even for a central area of 5 cm. radius, the non-uniformity range is still about 15 degrees C.

Solution of the spatial problem is sometimes attempted by the use of a metal plate to even out temperature. Fig. 2 shows the limited improvement achievable with this approach. A 20 degrees C range is observed over the entire surface, and a 5 degrees range can be obtained within the limits of a 5 cm. radius of the center.

The problems described above are especially important in a laboratory development situation, although many manufacturing lines also use commercial hot plates. In the latter case, of course, expensive custom designed equipment is sometimes built for the purpose. However, the present design will provide highly uniform, relatively inexpensive hot plate capacity for both development and manufacturing applications. Furthermore, it consists of a stand alone item which can be used separately as an accessory to commercial...