In-Situ, Across Wafer Temperature Measurement Apparatus for Semiconductor Fabrication Equipment

The measurement of process variables such as temperature, stress/strain, force, and pressure at different locations on a wafer are critical for the control and understanding of many different semiconductor process steps. Such equipment as plasma etchers, chemical mechanical polishers (CMP), hot plates, ovens and many others require uniform across-wafer process temperatures and accurate control of the temperatures. The objective of this thesis was to embed sensors in a silicon wafer for use on (in) semiconductor processing equipment. In this research, chemical mechanical polishing (CMP) was chosen as the specific process since wafer temperature can result in varying process conditions across the wafer. The sensor vehicles developed in this thesis consist of three wafers stacked together with a 1/4 x 3 slot cut into the center wafer to house the sensors and interconnect wiring. A Dallas Semiconductor digital temperature sensor (DS18S20) was chosen because it requires less extensive electronic components and has a quicker response time than most standard sensors. To communicate with the sensors a Microchip PIC16F84 microcontroller was used. It is small and has good data storage capabilities, a serial port, and several digital and analog I/O ports. The wiring from the sensors extends from the wafer to a signal conditioning circuit (which includes the microcontroller) which converts the digital signal to an RS232 format. A wireless modem transmits the RS232 data real-time to a personal computer for storage and analysis. Two temperature sensing wafer vehicles were produced. The first had two sensors and was mainly used for proof-of-concept. It was tested on both bare Si wafers and on copper-coated wafers. The temperature was shown to increase during polish - more so with the copper-coated wafer. For further verification and to look for temperature gradients between sensors during polish, a second wafer vehicle was produced that housed 4 sensors. The manufacturing conditions for this vehicle resulted in slight warping of the wafer above the sensors. Because of the warping, the polishing was not uniform and temperature readings were not accurate. This result indicated the importance of optimization of the manufacturing process (i.e. perfect alignment of the wafers with each other and smooth, uniform epoxy between the wafers). The main objectives of this thesis have been met. Across-wafer temperature can now be measured in-situ and recorded real-time during CMP using the sensing vehicle designed here. Improvements upon this work will allow the sensing vehicle to be used in a larger variety of semiconductor manufacturing environments