PolySilicon Layers

Polysilicon is an ultra-pure form of silicon with excellent insulating properties and heat resistance. Polycrystalline silicon has two forms, bulk and granular, and granular is more popular in thin applications and high-qualified applications. Alfa Chemistry can produce doped or undoped polysilicon layers according to user requirements. The dopant is inversely proportional to the resistivity. The lightly doped polysilicon layer will have a high resistivity. The resistivity is the main factor that determines the dopant content in the polysilicon layer.

Alfa Chemistry provides various polysilicon films by adjusting the deposition conditions. We can provide polysilicon films composed of standard or small grain films, as well as ideal film stress levels for many specific microelectromechanical systems (MEMS) applications.

Alfa Chemistry's Preparation Method

Undoped Polysilicon Layers

Alfa Chemistry uses low pressure chemical vapor deposition (LPCVD) to deposit undoped polysilicon layers, which is the most common polysilicon deposition method. The process is carried out in a low temperature furnace at 560 ℃ - 650 ℃ to prevent contamination and form a highly uniform polysilicon layer.

The main process flow of LPCVD is as follows:

Doped Polysilicon Layers

The doped polysilicon layer provided by Alfa Chemistry contains a combination of three main dopants, namely arsenic (As), phosphorus (P) and boron (B).

The following methods are used for doping polysilicon:

① Diffusion: A layer of heavily doped glass is diffused onto the undoped silicon wafer. At high temperatures, the polysilicon layer can diffuse and anneal onto the substrate. This method is very easy to achieve high doping concentration.

② Implantation: This method is usually used when high conductivity is not required. The process involves direct bombardment of the polysilicon layer with high-energy ions and then annealing to harden the wafer. Ion implantation can more accurately control the dopant concentration.

③ In-situ: This deposition process is performed by adding phosphine (PH3) and diborane (B2H6) gases to the reaction gas. Due to the introduction of dopants during the deposition process, it is possible to change the physical properties of the layer, which affects the grain size and orientation of the polysilicon.

Alfa Chemistry Polysilicon Specifications

Test Instruments

Alfa Chemistry's testing equipment includes, but are not limited to, the following:

• Scanning Probe Display Micromirror
• X-ray Diffractometer
• Semiconductor Characteristic Tester

Polysilicon Layer Applications

The application fields of polysilicon layer include, but are not limited to, the following:

• Capacitor plate electrodes
• Hard mask during etching
• Interconnects
• Gate electrodes