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Calorimetric Device for Diagnostics

IP.com Disclosure Number: IPCOM000039545D
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 4 page(s) / 30K

Publishing Venue

IBM

Related People

Shivashankar, SA: AUTHOR

Abstract

Electrical discharges in reactive gases, especially RF discharges, have been increasingly employed in the manufacture of LSI and VLSI circuits. To monitor and to understand the chemical processes occurring in such discharges, techniques, such as optical spectroscopy and mass spectroscopy, have been applied. No attempt is reported to have been made to measure the heat of chemical reactions responsible. Such understanding is important to the optimization of process parameters and to the design of appropriate equipment. If the heat of a specific (gas-surface) reaction in a specific system is known, the temperature changes due to the reaction may be used to monitor the reaction rate (etch/deposition) and to determine the reaction end point in a calibrated manner.

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Calorimetric Device for Diagnostics

Electrical discharges in reactive gases, especially RF discharges, have been increasingly employed in the manufacture of LSI and VLSI circuits. To monitor and to understand the chemical processes occurring in such discharges, techniques, such as optical spectroscopy and mass spectroscopy, have been applied. No attempt is reported to have been made to measure the heat of chemical reactions responsible. Such understanding is important to the optimization of process parameters and to the design of appropriate equipment. If the heat of a specific (gas-surface) reaction in a specific system is known, the temperature changes due to the reaction may be used to monitor the reaction rate (etch/deposition) and to determine the reaction end point in a calibrated manner.

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This technique is an adaptation of the method of thermal relaxation originally developed to measure heat capacities of small (solid) samples at cryogenic temperatures [1, 2]. The principle of thermal relaxation is applied to the determination of the heat of reaction (oxidation) of a sample deposited on a suitable substrate which is placed in a reactive gas electrical discharge. The calorimeter is schematically depicted in Fig. 1a with a photoresist or polyimide coating 10 (sample) on a silicon wafer 12 (substrate) as a specific example. The wafer is placed on a specially designed aluminum ring sample holder 14, detailed in Figs. 1b and 1c. The wafer rests on the ring at several pedestal points 16 (four in Fig. 1b) with a thermally conducting material l8 such as silicon heat sink compound used to provide a fixed small thermal contact between the wafer l2 and the metal ring l4. A suitable small temperature sensor 20, such as a thermocouple, is attached to the bottom of the wafer. The aluminum ring sample holder l4 is placed in very good thermal contact (zero thermal resistance) on a watercooled metal sample platform 22. This platform is an electrode in an RF discharge system. In a microwave plasma downstream configuration, no external potential is usually applied to the sample platform. When an electrical discharge is initiated (in an appropriate gas mixture at low presure), sample etching beg'ns. The etching process generates a heat of reaction which raises the temperature T of the substrate above that (To) of the water-cooled platform. When the etch rate reaches a steady value, T attains a constant level about To . This steady-state temperature differential is defined as To . When etching is terminated by extinguishing the discharge, the wafer temperature T relaxes to the initial value To through the thermal conductance provided by the four thermal contact pads. The instantaneous temperature differential T(t) is given by the following decay equation as shown in 1, 2: (1) This thermal relaxation is schematically shown in Fig. 2a. Thus, a plot of (log10 T(t)) vs. t is a straight line with the slope

1

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(Fig. 2b)

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