Achieving Uniform Contact with Silicon Wafer

In summary, the Joule Heater is having difficulty reaching the desired temperature and speed due to the non-uniform contact area. Gold film and copper contacts are being considered, but they might not be able to handle the temperatures.
  • #1
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2
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Hi all,

I am currently working to build a Joule Heater that will be used to heat samples to upwards of 1000*C in seconds in vacuum. While the temperature and speed is definitely there, the contacts are always non-uniform -- making the data hardly repeatable. I am using a ~70mmx10mm Silicon wafer that is clamped on either side by 2 contacts. My problem is that on either side there is a "hotspot" where the contact is the best, all of the current flows through these two hot spots. There is 2 problems with this -1- it limits the temperature I can reach because the temperature at the "hotspots" is much much higher than the temperature of the center of the wafer. -2- it extremely prohibits repeatably, which is key.

I have tried stainless steel contacts as well as tantalum contacts, both rough and polished. I have tried several different clamping techniques as well. No matter what I try, there is always a point of "best contact" -- which makes me wonder, is uniform contact even possible (at least with the funds I have available)?
 
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  • #2
Make sure that there is no SiO2 in the contact area. Etching with HF might help.

Can you evaporate a thin film of gold onto the contact area?

After that I would try clamping polished copper contacts.
 
  • #3
I have tried etching to no avail. As for a thin gold film and copper contacts, I do not believe they can handle the temperatures we're hoping to achieve. I would like to try polished copper at lower temperatures though, to see if there is an improvement.

As for the process of evaporating gold, we don't have the means to do that atm but are actually in the process of building a system that can.
 
  • #4
I am not sure about copper handling these temperatures either. The melting point is just a hair above your working temperature. Gold is even closer. With a bit of luck the copper will stay quite a bit cooler than the Si which has much higher resitance. Au will diffuse into Cu, so you might need a blocking layer of Ni on the Cu contacts.

Pt is much better, 1700K. After that you are into more exotic metals like Rh, Ru and Ir.

Graphite electrodes might also be worth looking at. But you might have noticed that I am starting to fish in the dark.
 
  • #5
Have you considered heating using an arc lamp?
Peak Systems Inc. (No longer in business) had a patent for Rapid Thermal Heating using an arc lamp. You might be able to get a copy of this patent.
 

Related to Achieving Uniform Contact with Silicon Wafer

1. What is the importance of achieving uniform contact with a silicon wafer?

Achieving uniform contact with a silicon wafer is crucial in the semiconductor industry as it ensures consistency and reliability in the manufacturing process. It helps to prevent defects and ensure that the resulting electronic devices perform as intended.

2. How is uniform contact achieved with a silicon wafer?

Uniform contact with a silicon wafer is achieved through a process called lithography, which involves transferring a pattern onto the wafer surface using light or electron beams. This pattern is then etched onto the wafer to create the desired circuit design.

3. What factors can affect uniform contact with a silicon wafer?

Several factors can affect uniform contact with a silicon wafer, including the quality of the wafer surface, the type of lithography used, and the accuracy of the alignment between the mask and wafer. Temperature and humidity can also impact the process and must be carefully controlled.

4. What are the potential consequences of not achieving uniform contact with a silicon wafer?

If uniform contact is not achieved, it can result in defects in the electronic devices produced, leading to reduced performance or even failure. This can be costly for manufacturers and can also impact the reliability of the final product.

5. Are there any advanced techniques for achieving better uniform contact with silicon wafers?

Yes, there are advanced techniques such as multiple patterning and immersion lithography that can improve the uniformity of contact with silicon wafers. These techniques involve additional steps and equipment, but they can result in higher precision and better control over the manufacturing process.

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