Improvements in wafer temperature measurements

Abstract

Accurate and repeatable wafer temperature measurement and control is critical in many semiconductor processing applications. Many of these applications are done at moderate pressures ͑0.5-2 Torr͒ where thermal contact resistance between the wafer and a contact temperature probe is high, and could vary wafer to wafer. The result is an unpredictable difference between the actual wafer temperature and contact measurement probe due to heat transfer across this interface from exothermic reactions, hot plasma gases, or radiant heating. In some applications, this temperature difference is so great that backside helium cooled electrostatic chucks are used to minimize this effect. In many applications, the use of this type of solution is not practical but accurate and repeatable wafer temperature measurement is still required. A new temperature sensor has been developed that utilizes gas injection through a pinhole in a thermocouple pad that creates a ''microenvironment'' between the pad and the wafer. This results in reduced thermal contact resistance, and more accurate and repeatable temperature measurement. Temperature data on the operation of this probe will be presented, verifying the robustness of this probe. Additionally, diffuse reflectance spectroscopy will be used as a noncontact temperature measurement technique to corroborate data from the new gas-cushion thermocouple.

Optical Diagnostics for Thin Film Processing

“…Diffuse reflectance spectroscopy (DRS) measures the temperature-dependent change in near-bandgap light transmitted through a wafer, diffusely reflected by the wafer backside and transmitted through the top of the wafer, and has been used to measure and control temperature as precisely as ±0.5 • C during the growth of several ternary III-V semiconductors (77,234,262,263). An algorithm has been developed that corrects for the distortions in the band-edge profile from interference and/or absorption in the growing epilayer (264).…”

Low-Coherence Interferometry-Based Non-Contact Temperature Monitoring of a Silicon Wafer and Chamber Parts during Plasma Etching

“…There are various methods capable of measuring temperature during plasma processing. [6][7][8][9] Typical methods employ thermocouples based on metal wires. 7) However, the electromagnetic waves applied to the electrodes are disturbed by these wires, so that the plasma becomes localized and non-uniform.…”

“…[6][7][8][9] Typical methods employ thermocouples based on metal wires. 7) However, the electromagnetic waves applied to the electrodes are disturbed by these wires, so that the plasma becomes localized and non-uniform. Another common method employs pyrometers, which are non-contact devices.…”

On-Wafer Temperature Monitoring Sensor for Condition Monitoring of Repaired Electrostatic Chuck

“…In-situ wafer temperature measurement started in the 1980s with fiber optic temperature probes, employing Fluorooptic ® by Luxtron to measure the local surface temperature of the wafer during plasma processing, and the need for helium (He) backside cooling was addressed to control the temperature on the wafer [25]. Later reports addressed the use of thermocouples, diffusion and specular reflectance spectroscopy, infrared thermometry, pyrometer, and thermopiles for the improvements in wafer temperature measurement, and more in-situ wafer temperature measurements were investigated [26][27][28]. According to recent research, the development of a state-ofthe-art temperature sensor based on a semiconductor process is currently underway, and efforts are being made to measure the temperature more precisely [29][30][31].…”