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How to Remove Plasma Etch Polymer

When a chemist or electrician wants to modify the chemical and physical properties of the surface of an integrated circuit wafer, it is known as plasma processing. One form of this processing is called plasma etching, which uses a glow discharge (known as plasma) from a specific gas. The discharge is released as pulses in a stream at high speed directly onto a sample circuit. The source of the plasma, known as etch species, can take one of two characteristics -- charged, which are classified as ions, or neutral, which is made up of atoms and radicals. As etch processing begins, the discharge being streamed onto the circuit will create volatile etch residue as a result of the chemical reaction between the etched material and the etch species created by the plasma. The physical and chemical properties of the circuit eventually are changed as the atoms from the plasma stream attach to or penetrate the surface. Depending on the gas that is used for the plasma stream, plasma etch polymer can form as a residue after the process.

Things You'll Need

Integrated wafer circuits
Plasma etch polymer remover (PRX-127)
Heavy-duty protective gloves
Surgical mask
Protective eyewear or goggles
Stripping tanks
Deionized (DI) water rinse tank
Spin dryer or spin-rinse dryer

Instructions

- 1
  Plasma etch polymer will likely be formed after using plasma etch processing with fluorocarbon-based gases such as carbon hydrotrifluoride and octafluoropropane. These gases create unsaturated compounds in the plasma that are then transferred to the integrated circuit wafers. These must be removed in order for further plasma processing to continue.
- 2
  
  Take extreme caution around hazardous chemicals.
  
  Plasma etch polymer remover, known as PRX-127, is a chemical compound comprised of elements of ether, sulfoxide and hydroxide, and is extremely hazardous to breathe in or touch. It is recommended that before attempting to use this product, gloves, eyewear and mask should be worn. A wet-bench immersion process is one of the safer ways to handle this compound, and requires very little physical interaction.
- 3
  Fill two stripping tanks that are designed specifically for a wet-bench process with the PRX-127 solution and bring to a temperature of 70 to 90 degrees Celsius. Place the affected circuit wafers carefully into one of the tanks using protective gloves. The wafers should stay in the solution for at least five minutes but no longer than 20 minutes for optimal effect. A mechanical or sonic-based agitation method is recommended during the first bath.
- 4
  Transfer the wafers from the first stripping tank to the second once the bath cycle is complete, and soak the wafers again for five to 20 minutes without additional agitation. This second bath will remove existing layers of polymer underneath the residue on the surface of the wafer.
- 5
  
  Deionized water is completely pure water, with no other minerals.
  
  Remove the wafers from the PRX-127 solution and transfer them to a third tank filled with SVC-300 rinse, a solution that is used primarily for paint removal. It's quite safe to use as it is nontoxic and nonflammable and will not damage the wafers. The wafers should stay in this solution for two to three minutes. Transfer the wafers into a final solution -- deionized water -- inside a rinse tank for six to eight cycles and then use a spin dryer or spin-rinse dryer to remove all traces of the solution. The wafers should be completely free of polymers, and are now safe to be used again for further plasma etched processing.

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