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.

The key to high yields in lift-off process ilies in step 4. In this very step, it's extremely critical to deposit metal thin film perpendicularly & uniformly onto the wafer sruface.
If the metal thin film fails to be deposited perpendicularly, the side wall of photoresist will be deposited with metal. This will makes it impossible to remove photoresist with acetone and cause defects in device.
If the metal thin film fails to be deposited uniformly unto the wafer surface, it will cause defects in device as well.

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

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.

HULA Substrate Carrier

The Temescal machine with the HULA system offers a completely unique approach to deposition of highly uniform metal stacks. Other manufacturers resort either to a very long distance from crucible to sample or to using shadow masks. The long distance leads to excessive waste of material which is a particular concern when dealing with expensive noble metals such as gold or platinum. Shadow masks must be designed for specific materials and specific deposition conditions and thus starkly limit the process window available for depositions. All in all the HULA option provides an efficient solution for reduced material consumption and maximum process window, which to our knowledge, no other supplier can achieve. Further advantages of evaporation without a mask are higher effective deposition rates, leading to faster cycle times and superior material collection efficiency, which is especially important when depositing expensive precious metals, such as Au & Pt.

Auratus

At the heart of every electron beam evaporation system is a vapor cloud—a unique, repeatable flux distribution characteristic of radiation from a point source.

But these flux clouds can vary. They change because of a variety of factors in the deposition process—like deposition material, deposition power, crucible size, the use of a crucible liner and beam spot focus.

With precision lift-off coating, the goal is an even, predictable deposition layer across a batch of wafers. Uniformity masks are the conventional solution for managing the flux cloud, trimming the heaviest zones of deposition to match that of the least flux zones’ collection.

On a conventional box coater, an inefficient optimization to the flux cloud typically results in an excessive use of process metals. And with so many variables, how do you design an optimal mask?

For over a decade, Temescal has been dedicated to mapping and better understanding the dynamics of the flux cloud. Through extensive testing and research, we have collected hundreds of vapor cloud maps and used these maps to advance and automate the process of lift-off uniformity mask design.

Temescal E-bem Deposition Systems

Our newly designed family of coaters offer solutions to processing requirements that range from small scale R&D or preproduction applications to large scale, high volume production fabrication lines. Ideal for either lift off or step coverage processes, these cleanroom compatible systems accept a multitude of accessories to meet almost any requirement.

In addition, our coaters are designed to optimize flexibility and efficiency in installation as well as operation. Fully automated processing via the Temescal control system maximizes throughput as well as ease of use. The PLC Based TCS provides fully integrated process and vacuum control, recipe driven pump to vent processing with datalogging, and automated pump, vent, and regeneration cycles that run independently of recipe processing. For more information please check "E-beam deposition systems".

: Administrator; 10 June 2020; 10 June 2020; 01 July 2020