This experiment is separated into five sections, including initial acetone-sonicate cleansing, chemical etching using HF, Poly (4-vinyl pyridine) spin coating, UV cross link, final cleaning of excess polymer. The following statement belongs to initial acetone-sonicate cleansing, chemical etching using HF.
Introduction:
A clean and controlled sample plays an important role for further analysis in the following experiment. The procedure intends to remove an oxide layer on the silicon wafer with Hydrofluoric acid (HF). This goal will be fulfilled using the techniques of sonicating and chemical etching.

Purpose:
Remove an oxide layer on the silicon wafer with Hydrofluoric acid (HF).

Preliminary Cleaning
The required tools include a diamond scribe, tweezers, and gloves. Gloves must be used throughout the process (never touching the wafer with bare hands). The wafer is cut into approximately 2 cm by 2 cm pieces by pressing it firmly with a diamond scribe.
The silicon pieces are then sonicated. For that process acetone and DI-water, in the ratio of 1:1 by volume, are poured into a glass beaker. Two silicon wafers, which must not touch, are placed into the solvent and the sonicator is turned on for five minutes at constant room temperature. Carefully take out sonicated wafers using tweezers and place onto a clean stage (Petri dish). Then using clean cue tips, manually wipe the wafers to ensure a clean surface.
Subsequently, the clean pieces of silicon are picked up by a pair of tweezers and stored in a small plastic container lined with tissue (Caution: Use only one corner to move the wafer to prevent damage.). Be sure that the silicon wafers are placed surface up.
Cleaning with Hydrofluoric Acid (HF)
For a higher cleaning quality, a chemical etching method is performed using HF. The wafers are brought to an HF chemical facility.
The required equipment includes gloves, body protection, mask, protective sleeves, DI-water, HF, NaOH, two containers, a timer, tweezers and tissues. A user should have received the proper training before using the HF facility. For safety, it is important to wear shoes at the chemical etching room. In case of an accident any exposed skin could be damaged.
The HF chemical etching takes place inside a chemical hood. Two pairs of tight gloves and a lab coat with tight sleeves should be worn to protect your hands. The body protector and mask should be worn throughout the etching process. There should be a set of at least ten tissues on the bench for cleaning.
The process starts by cleaning a Nalgene container using DI-water. Warning: never use a glass container because the HF will etch the container. First, water is poured into the hole inside the bench, which is designed for liquid disposal. The hole can only be used to pour liquid, and no tissues can be thrown in. In addition, the container must be big enough to hold the silicon wafer. After cleaning the container with DI-water, pour 10 mL of HF in a controlled manner into the container. The HF assays 48 % reagent from Sigma-Aldrich is poured into the container. The timer is set for one minute. When the wafer is vertically dipped into the container, the timing starts.

The trick to holding the wafer stable is to place one hand under the other so as to support the hand that holds the wafer. When the time is up, the wafer is removed. After dipping the wafers in HF, rinse them with DI-water. Not only should the wafer be cleaned, but also the tweezers. The other container is used to hold the DI-water. Water is poured into the hole inside the bench.

The clean wafers are then put on clean tissue to eliminate extra water, and then placed in a clean box with the polished side up.
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