Silicon Thermal Conductivity Material Properties

1. Silicon Thermal Conductivity Material Properties

2. 1 Facts Thermal conductivity is one of many thermal properties of the material silicon. Other properties include specific heat (0.70 Joules per gram degree Kelvin) which helps determine power required to raise the temperature of the wafer, boiling point (2,628 degrees Kelvin), melting point (1,683 K), critical temperature (5,159 K), thermal diffusivity (.9 cm2 per second), linear thermal expansion or thermal expansion coefficient (2.6 • 10-6 C-1), Debye temperature (640 K) and others.

3. 2 Values Thermal conductivity changes as temperature changes. "You need to keep the required operating temperature in mind when using thermal conductivity to determine temperature distribution across the wafer," warns Michael Klebig, a Silicon Valley sales engineer specializing in the application of heat in semiconductor wafer processing. "The wrong thermal conductivity means you won't achieve the temperature uniformity you need and the performance of the devices will be compromised. If it's bad enough, you won't be able to continue to the next step of the semiconductor processing sequence. The wafer will be useless."

4. 3 Impurities There are two types of impurities in the silicon chip manufacturing process. First, are impurities inherent in the original silicon ingot. The second type of impurity is known as a dopant, an impurity deliberately introduced in the manufacturing process to change the electrical properties of silicon in specific, exposed areas on a wafer. As the level of impurities increases, thermal conductivity decreases. "When designing for temperature uniformity, you must make adjustments in response to the lower conductivity value of doped silicon," says Klebig. "Doped silicon above 100 degrees Kelvin has negligible impact on thermal conductivity."

5. 4 Expert Insight Determining temperature uniformity by use of thermal conductivity and other thermal properties is an extremely complex task. "As a result," says Klebig, "you should utilize best known methods when designing for temperature uniformity, such as 3D thermal finite element analysis (FEA) computer modeling. Large engineering organizations typically have their own FEA modeling groups. If you don't have access to such a resource within your company, contact an FEA engineering firm."

6. 5 Warning Be aware that thermal conductivity material properties are different for silicon in liquid form. Liquid silicon has three times the thermal conductivity of solid silicon.

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