Semiconductor Wafer Cleaning: Removing 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 Terminology by Process:
|Wafer Cleaning Process||The removal of particle and chemical impurities from the semiconductor surface without damaging or deleteriously altering the substrate surface.|
Metal, Silicide Cleaning
Pre-deposition (dielectric, metal),
(aka Wafer Strip)
Photoresist strip and clean,
Contact Hole Etching
Silicon etching, and
Wafer Cleaning by Purpose:
|Create a surface that is free from particulate, metallic, and organic contaminations. In some cases, such as deposition of epitaxial Si, it needs to have aH-terminated Si surface that is free from any native oxide or chemical oxide. Native Oxide removal|
|Particle removal from surface using chemical or mechanical scrubbing such as Megasonic|
|Metallic Ion Removal Clean||Eliminate metallic ions that has detrimental effect on device performance|
|Post Etch Clean||Remove photoresist and polymers left after
etch process removal- Remove photoresist that can be hardened by plasma damage or high dose implantation- Remove solid residue, “etch polymer” formed during RIE process
Silicon Wafer Cleaning- FEOL, BEOL, RCA Clean, SPM Clean Pirhana Etch
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 clean or “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.
The importance of clean substrate surfaces in the fabrication of semiconductor microelectronic devices has been recognized since the dawn of solid state device technology in the 1950s. It is now well know that the device performance, reliability, and product yield of Si circuits are critically affected by the presence of chemical contaminants and particulate impurities on the wafer or device surface.
The objective of wafer cleaning and surface conditioning is the removal of particle and chemical impurities from the semiconductor surface without damaging or deleteriously altering the substrate surface. The surface of the wafer mush not be affected in such a manner that roughness, pitting, or corrosion negates the results of the cleaning process.
The manufacturing of an integrated circuit requires hundreds of process steps, depending on the specific type of device. Most steps are performed as unit processes with the complete wafers before dicing them into individual chips. Approximately 15-20% of the steps are wafer cleaning operations, which indicates the importance of wafer cleaning and surface conditioning.
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.
Megasonic wafer 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.