MEASURING THE TEMPERATURE OF SI AND GAAS USING DIFFUSE REFLECTANCE SPECTROSCOPY

IN RESPONSE TO CUSTOMER DEMAND FOR AN IN SITU, ACCURATE, AND REPEATABLE TEMPERATURE MEASUREMENT OF SILICON (SI) AND GALLIUM ARSENIDE (GAAS), RESEARCHERS ARE USING A NEW TEMPERATURE SENSOR TO MEASURE THE TEMPERATURE OF SI AND GAAS ABOVE 800 DEGREES CENTIGRADE, AND AS HIGH AS 1100 DEGREES CENTIGRADE. THE TECHNIQUE USES A SYSTEM CALLED DIFFUSE REFLECTANCE SPECTROSCOPY (DRS). THE PRINCIPAL BEHIND DRS IS THAT IT MEASURES THE CHANGING BAND GAP ENERGY OF THE SEMI-CONDUCTOR AS A FUNCTION OF TEMPERATURE. THE SENSOR USES A LIGHT SOURCE LOCATED OUT OF THE GROWTH CHAMBER. THE LIGHT IS MODULATED SO THAT IT CAN BE DETECTED IN THE PRESENCE OF OTHER LIGHT SOURCES, SUCH AS THE HEATER SOURCE. THE DIFFUSE REFLECTANCE FROM THE SUBSTRATE CARRIES BAND GAP ABSORPTION INFORMATION THAT IS ANALYZED BY SOFTWARE BASED ALGORITHMS TO DETERMINE TEMPERATURE. PRELIMINARY MEASUREMENTS OF GAAS USING DRS SHOW A SMOOTH VARIATION OF THE OPTICAL WAVELENGTHS ASSOCIATED WITH THE ABSORPTION THRESHOLD BETWEEN 4 DEGREES K AND 1000 DEGREES K. THE LAWS OF PHYSICS AND THERMODYNAMICS SUGGEST THAT THE BAND GAP MEASUREMENT CAN BE MADE ABOVE THESE TEMPERATURES. RESEARCHERS ARE DEVELOPING TECHNIQUES AND IMPROVEMENTS TO THE DRS SENSOR TECHNOLOGY TO MEASURE ABOVE 1100 DEGREES CENTIGRADE.