New Reliable Structure for High Temperature Measurement of Silicon Wafers Using a Specially Attached Thermocouple
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New Reliable Structure for High Temperature Measurement of Silicon Wafers Using a Specially Attached Thermocouple S.A. Cohen, T.O. Sedgwick, and J.L. Speidell IBM T. J. Watson Research Center Yorktown Heights, New York 10598
ABSTRACT Accurate wafer temperature measurement is very important in the area of material processing. In Short Time Annealing, for example, it is necessary to monitor temperature peaks of up to 1200'C which are only a few seconds in duration. This paper describes a structure consisting of a silicon wafer with a specially attached thermocouple. This structure is capable of reliable high temperature measurements of up to 1200'C and is also capable of surviving repeated cycling at that temperature.
INTRODUCTION Accurate temperature measurement is basic to the control and understanding of many materials processes. In VLSI technology where device dimensions are continuing to be scaled down, there is an increasing demand for improved process temperature control. In shallow junction formation there are numerous studies employing the short time annealing (STA) technique to activate ion implanted dopants and remove defects [1]. In STA, Si wafers are treated to temperatures as high as 1200'C, held for a few seconds, then cooled. The associated heating rates can be as high as hundreds of degrees per second. Temperature measurements in STA systems which are more demanding than most have to date been primitive in most cases. Most frequently, investigators have used thermocouples to measure temperatures but without specifying the contacting or attachment scheme [2,31 or have simply rested the wafer on the thermocouple or vice versa [4,5,61. A more reliable scheme has been to attach the thermocouple to one surface of a wafer with alumina cement. Such an attached thermocouple has been used to calibrate a tungsten-halogen STA system versus output power or is used as an in-situ temperature control element [7]. A thermal sensor inserted in the edge of diameter respectively, system [8]. However, silicon surface area to
Mat. Res.
consisting of a thermocouple mounted on a quartz rod and a 2.5mm thick silicon annulus, 2 in. and 1.5 in. outer and inner has been used to probe temperatures in a tungsten-halogen since the temperature rate of change is inversely related to the volume ratio, the temperature of such a sensor, which is much
Soc. Symp. Proc. Vol.
23 (1984) Published by Elsevier Science Publishing Co.,
Inc.
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thicker than a standard silicon wafer, will also be expected to be much different, a fact which will be important in very rapid transient experiments. In STA systems which transfer energy to a wafer by irradiating one side only, optical pyrometers can easily be used on the opposite side. Annealing studies using both argon discharge lamp annealing [9] and graphite strip heaters [10,11] have employed pyrometers and in one case a good correlation between pyrometer and a thermocouple simply bonded to the surface of a wafer has been reported [10]. In STA systems utilizing isotropic irradiation, an
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