Silicon wafers manufacturing

Si wafer manufacTurer

The semiconductor industry is manufacturing chips that are included in all electronic devices, telephones, computer, television, watch industries, optics, photonics, micro sensors, MEMS, etc… 

To manufacture those devices in mass production, the starting raw material has been silicon since more than 45 years. Today, new materials are arriving in this industry, but silicon is still in first position.

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The silicon used for wafer manufacturing has a very high purity (from 10E-9 up to 10E-11) in order to get a monocrystalline structure.

Silicon wafer manufacturing process

The process to manufacture wafers is made of 8 major steps we detail hereafter:

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Ingot pulling process for silicon wafer:

The high purity polysilicon is melted in a furnace (up to 1500°C) then a seed is soaked in the melting silicon. The molten silicon is pulled very slowly from an oriented dash. With all the motions (seed and crucible rotations, pull up), the solid Silicon becomes a monocrystalline ingot. During this process called Czochralsky (Cz process), the orientation, diameter and dopants are under control: the final Si material gets the required specifications.

Silicon round grinding: formatting the ingot to cylinder with flat

Image5.pngAs the diameter of the ingot from the furnace is not perfect, a round grinding step is needed to get a perfect cylinder, ready for making wafers with the right dimensions. During this step, a major flat is made in order to specify the orientation. According to SEMI Standard, a secondary flat is optionally positioned to identify the orientation and the type.

Monocrystalline ingot slicing

The ingot, ready for slicing process, is fixed on a table of the diamond inner diameter saw. The cutting is made wafer by wafer and the thickness is chosen according to the customer specification. The table of the machine can be oriented to get an off orientation if needed.

Silicon wafer edge grinding

As the cutting process is creating sharp edge, a step for edge grinding is necessary to eliminate peripheral stress and scratches. At the end of this step, the final diameter is setted.

Silicon wafer lapping

The wafers are putted on satellites for double side grinding. This step allows to eliminate the saw marks, improve the TTV (Total Thickness Variation) and flatness. This stage is the last one which mechanically removes material from the wafer.

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Silicon wafers etching: acid and caustic application

All these previous mechanical steps will generate some troubles on the surface of the wafer. This sub-surface stress is reduced by a chemical etching. Acid or basic solutions are used depending on the final aspect and required roughness of the backside generally not polished.

Silicon wafer polishing: single or double side

Following customer request, the wafer is either polished on one side or both sides in order to achieve mirror surface without defects. Chemical Mechanical Polishing is used (CMP) in order to avoid sub-surface damages. With the classical process, the roughness (RMS) can be guaranteed at 7A. This roughness can be improved <3A if needed.

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Silicon wafer final cleanings and packaging

The final wet cleaning and packaging are made in a Class 100 clean room. All types of contaminants such as metals, particles, organics, etc... are removed by several chemistry (RCA), scrubbing, and spin drying. The wafers are packaged under vacuum with a double bag ready for shipment.

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All steps are available in our facilities and can be handled either totally or partially.

 

Siltronix ST, 2017

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