Compound Semiconductor
Photolithography is a key process in semiconductors, but it's not ideal for microcircuit fabircation with certain metals. For cirtical process such as III-V group, II-VI group or MEMS, the most commonly used metal is chromium. Unlike aluminum, chrimium is not easy to be etched. In this kind of situation, we need to use lift-off process. Below is the simplified illustration for lift-off process.
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For industrial applications, large wafer size will pose great challenge to deposit metal thin film perpendicularly & uniformly, as larger wafer size tends to incur poor uniformity. However Temescal has a solution to this. Temescal is an US-based company dedicated in e-beam evaporation technology and provides following industry-proven solutions to sovle this dilemma.
Uniformity Mask
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Because the vapor deposition profile is related to a cosine distribution, in a single rotation almost half of the evaporant flux must be interrupted towards the center line where deposition is fastest. This requires the mask to block the vapor in the areas where normally one would expect thicker deposition layers. Above data shows the result of vapor being modified by Uniformity Mask. Substrates on the carrier shows good uniformity < +/- 3% across the wafer. While it improves thickness uniformity, the tradoff is material collection efficiency. When it comes to the deposition of expensive precious metals, such as Au & Pt, we need different solution whcih guarantees higher material collection efficiency. The solution is HULA system.
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