Different Manufacturing Processes Used to Make Silicon Wafers

There are several different manufacturing processes that are used to make silicon wafers. These include Etching, Lapping, Grinding, and Polishing. Which one you choose will depend on the end product you want.

Etching

Etching silicon wafers is the process of selectively removing selected parts from the surface of the wafer. The process is based on physical methods and includes wet and dry chemical etching procedures. Various etching solutions are used, such as hydrofluoric acid (HF), potassium hydroxide (KOH), phosphoric acid, and alkali hydroxides.

One of the main characteristics of etched silicon wafers is the flatness of the surface. This is achieved by the use of a carrier cage with rotating lapping plates. Typical etched silicon wafers have a thickness of about 900 mm and a diameter of about 300 mm. Depending on the desired geometry, etching is conducted in several directions, ranging from vertical to horizontal.

A certain number of etched silicon wafers have improved surface properties. These characteristics are believed to be the result of reduced overall oxidation rate and the presence of a reduced concentration of water in the caustic etchant. Another interesting aspect of the present invention is the reduction in the size of bubbles on the etched wafer. The presence of a smaller bubble results in less masking and a more uniform etching process. In addition, the etching rate is decreased by up to 40%.

Polishing

The process of polishing silicon wafers is an essential step in semiconductor production. A smooth, uniform surface helps create a high quality product. This is achieved by removing material through mechanical abrasion and a combination of chemicals. Silicon wafers are normally processed in two steps. First, the outer surface is polished using a ceramic turntable, which rotates as polishing solutions are dispensed. During the second stage, a layer of planarization is removed, which produces a mirror like surface.

In order to achieve the desired surface, each step must be performed correctly. Each one is critical to achieving an even, smooth finish. First, the surface of the silicon wafer is roughed to a fineness of about ten nanometers Ra. An optical interferometer is used to measure the roughness. Using a simple, economical rough polishing method is important in providing a smoother wafer.

Rough polishing is completed for a period of 400 to 600 seconds. The surface is then washed and rinsed with deionized water.

Lapping

Lapping silicon wafers is a process that removes surface defects and roughness. The process consists of abrasive machining. Abrasive powders, such as aluminum oxide or diamond, are used. During the lapping process, silicon wafers are lapped in a slurry of abrasive grains. It improves the smoothness of the wafers and also improves their parallelism.

Lapping silicon wafers manufacturing to achieve a flat surface and a thickness tolerance of 0.00254 mm. However, there are some technical challenges in this process. This article outlines some of the technical issues involved and discusses some solutions to the problems.

Generally, the process of lapping a silicon wafer involves selecting the abrasive media and selecting the parameters of the machine. The choice of abrasive media can affect the surface finish and damage removal of the silicon wafer.

In order to determine the time, pressure, and other parameters of the lapping process, artificial neural network simulation was carried out. Simulations were performed for a 105 mm diameter wire-sawn silicon wafer. These results showed that the time taken for the lapping process was inversely related to the diameter of the wafer.

Grinding

Silicon wafers are a very important substrate material in micro electronic devices. However, the thinness of the wafers makes them susceptible to stress cracking. In order to avoid stress cracking, the grinding process must be controlled in order to maintain the desired thickness of the wafers. Unfortunately, the current methods are not effective in this regard. Therefore, there is a need for more accurate methods of measuring the wafers during the grinding process.

Various techniques have been proposed for controlling the pressure and speed of the grinding wheel during the grinding process. The present invention is a new and improved method for monitoring the position of the grinding surface during the grinding process. This invention is useful for a variety of applications, including the grinding of silicon and metallic layers.

In the disclosed embodiment of the invention, the control system includes a controller 27 which determines the actual position of the grinding surfaces 24. The controller 27 is connected to a feed rate motor 31 via electrical conductors 33, 36 and 37.