Semiconductor Wafer Cleaning
Wafer Cleaning: Remove contaminants to improve yields
Purity of wafers and cells is critical in the semiconductor and MEMs manufacturing process. MEI is your partner in maintaining purity with high throughput, automated silicon wafer cleaning, whether you’re doing research or in high volume production. MEI offers a wide range of semiconductor wafer cleaning equipment.
Semiconductor Wafer Cleaning by Process:
|Wafer Cleaning Process||Specific Wafer Cleaning Application|
|Pre-Cleaning||Pre-Diffusion Cleaning Pre-Oxidation Cleaning Pre-CVD, Metal, Silicide Cleaning|
|Post-Cleaning||PR Strip Solvent Strip Post-CMP Cleaning Post-CVD, Metal Cleaning|
|Etching||Nitride Strip Oxide Etching Contact Hole Etching|
Wafer Cleaning by Purpose:
|Native oxide film elimination for the oxide film
|Particles on film surface removal|
|Metallic Ion Removal Clean||Eliminate metallic ions that cause leakage currents and break voltages|
|Remove photoresist and polymers left after
etch process removal
removal through H3PO4 process
Polymer Removal Clean
|Metal polymers removal through solvent cleaning|
|Particle removal through
Silicon Wafer Cleaning
Cleaning silicon wafers is necessary to remove both inorganic and organic residues.
Often, Silicon wafers are cleaned by a solvent clean, followed by a dionized water (DI) rinse;
this is often followed by an RCA clean and DI rinse to remove organic contaminants, followed by an HF dip to remove oxides and DI rinse and dry.
The surface contamination of wafers, especially by particle contaminants, is a major problems in the semiconductor industry, and becomes more critical as geometries get smaller and smaller. The yield on silicon wafers is inversely related to the defect density (driven by particle count and cleanliness) of the wafers. One way to decrease defect density is to use efficient silicon wafer cleaning techniques that remove particle contaminants efficiently. Small particles are especially difficult to remove from silicon wafers because of the strong electrostatic forces between the particles and the substrate.
Standard Wafer cleaning chemistry has remained essentially unchanged in the past 25 years and is based on hot alkaline and acidic hydrogen peroxide solutions, a process known as “RCA Standard Clean.” This is still the primary method used in the industry. What has changed is its implementation with optimized equipment: from simple immersion to centrifugal spraying, megasonic cleaning and ultrasonic techniques, and enclosed system processing that allow simultaneous removal of both contaminant films and particles.
In addition the specialized piranha clean is used for removing photoresist.
RCA clean is used to remove organic residues from silicon wafers. In the process, it oxidizes the silicon
and leaves a thin oxide layer on the surface of the wafer.
The general recipe for RCA-1 is: 5 parts water (H2O), 1 part 27% ammonium hydroxide (NH4OH), 1 part 30% hydrogen peroxide (H2O2).
Modern wafer manufacturing facilities use stringent contamination control protocols, and they use a variety of methods for cleaning wafers, often involving mechanical and wet chemical baths and rinses. These methods are often used in combination with megasonic tanks and ultrasonic cleaning baths.
Ultrasonic cleaning involves a variety of complex mechanisms, including cavitation, mechanical vibration, etc. A typical ultrasonic source is a plane surface that oscillates at a single frequency, producing a longitudinal wave.
Piranha etch is used to clean photoresist and other hard to remove organic residue from silicon wafers. For wafer cleaning, Piranha etch, is a mixture of sulfuric acid (H2SO4) and hydrogen peroxide (H2O2)
Many different mixture ratios are commonly used for Si wafer cleaning. A typical mixture is 3:1 concentrated sulfuric acid to 30% hydrogen peroxide solution; other protocols may use a 4:1 or even 7:1 mixture.