Why Pre-Diffusion Cleans Are Important for Silicon Wafer Cleaning

Pre-diffusion cleans are done many times during the semiconductor manufacturing process, and each time the chemical residues and particles left on the wafers must be removed as completely as possible. If silicon wafers still have surface contamination when they are placed in the diffusion oven, the diffusion will become uneven and the resulting semiconductor products will come out defective or inferior.

Pre-diffusion cleans are a critical requirement in the silicon wafer cleaning process.  Particle contamination on silicon wafer surfaces prior to diffusion can significantly reduce the yield of electronic components in semiconductor manufacturing plants and research facilities.

Particle contaminants may be diffused into the silicon and create electric defects, or they may block diffusion behind the particle. After diffusion, these contaminants may affect etching and interfere with the microscopic conductors. The resulting semiconductor components may have to be discarded. As silicon microscopic structures become smaller, particles have become more disruptive on both the electrical and the physical scale.

Pre-diffusion cleaning is carried out by immersing silicon wafers in chemical or megasonic baths. Surface impurities are dislodged, dissolved or chemically neutralized. The complete wafer cleaning process may take more than one process and the following methods are commonly used:

RCA cleaning – Consists of two components, SC1 and SC2 (SC stands for “standard clean”). For SC1, the wafers are immersed in a solution of ammonium hydroxide and hydrogen peroxide, which remove all the organic compounds from the wafer surfaces. In SC2, the wafers are placed in a solution of hydrochloric acid and hydrogen peroxide that removes any remaining metal ions.

Piranha cleaning – Consists of a sulfuric and hydrogen peroxide mixture that quickly removes material such as photo resist. It also produces hydroxylation of the silicon wafer surface, making it hydrophilic or attractive to water, a characteristic useful for some subsequent process steps.

Megasonic cleaning – Uses high-frequency sound waves in a cleaning solution to dislodge contaminants from the surface of the silicon wafer. This cleaning method does not use harsh chemicals, and the generator used to produce a signal in the MHz range at a specified power level can be fine tuned to optimize cleaning.

For more details read the complete article titled, “Why Pre-Diffusion Cleans Are Important for Silicon Wafer Cleaning”. For a free quote or consultation contact Modutek at 866-803-1533 or email Modutek@modutek.com.

Advantages of Using the KOH Etching Process

The KOH etching process uses a solution of potassium hydroxide to etch silicon wafers and produce microscopic structures in the silicon. In subsequent processing steps, microscopic structures are followed to manufacture integrated circuits, processors, and other electronic devices.

 One of the advantages of using KOH etching is that it is relatively safe compared to other etching processes. It also etches silicon fast and can be precisely controlled. These factors are important especially for batch processing where the process step must be precisely done repeatedly. Unlike other chemical processes that are required for specific cleaning and etching steps, KOH is ideal for general silicon etching.

 In preparing the KOH solution, KOH is added to water in an etching tank made of a material that is impervious to aggressive chemicals. Silicon wafers are masked with silicon nitride or silicon dioxide, substances that KOH does not etch. Once the wafers are immersed in the KOH solution, the silicon is removed from the areas that are not masked by the chemical action of the KOH solution.

 The etch rate can be controlled by changing the concentration of the solution and by changing the temperature. Other factors that influence the etch rate are the crystal lattice planes of the silicon and the presence of boron doping.

 Because the KOH etching process is very sensitive to temperature, it is important to maintain the temperature at the exact set point. That’s why the temperature controller should be accurate during the process and from one batch to the next. Tight control during the etching process ensures that the etch rate remains constant while maintaining precisely the same temperature for a given setpoint from one batch to the next. This ensures accurate reproducibility of process conditions and identical results across different batches.

Modutek’s Teflon tanks allow operators to benefit from all the advantages of the KOH etching process. The tanks are specifically designed for KOH etching and feature a wide temperature range, tight temperature control, and rapid heating. Custom tank sizes are available and custom installations can be done to fit any new or existing wet bench application.

Read the complete article “Advantages of Using the KOH Etching Process” for more details on how Modutek’s Teflon tanks can help operators get all the benefits of KOH etching. For a free consultation or quote contact Modutek at 866–803–1533 or email modutek@modutek.com.