Substrates Used for Ellipsometry Measurements

Silicon for Ellipsometry?

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What are Common Silicon Wafer Specs Used for Ellipsometry?

Silicon wafers are commonly used as substrates in ellipsometry, and their specifications can vary widely depending on the specific needs of the experiment. However, there are some common specifications that are often seen:

1. Diameter: Silicon wafers can come in a variety of diameters, but some of the most common include 100mm (4 inches), 150mm (6 inches), 200mm (8 inches), and 300mm (12 inches). The diameter chosen often depends on the requirements of the deposition and measurement equipment.

2. Orientation: The crystal orientation of the silicon wafer is often specified. This refers to the alignment of the silicon crystal lattice in the wafer. The most common orientations are (100) and (111).

3. Type/Dopant: Silicon wafers can be either p-type (doped with boron) or n-type (doped with phosphorus or arsenic). The type of dopant used can affect the electrical and optical properties of the wafer.

4. Resistivity: This is a measure of how strongly the wafer opposes the flow of electric current, and it can be tuned by changing the level of doping.

5. Thickness: Silicon wafers come in a variety of thicknesses, with common values ranging from about 200 to 800 micrometers.

6. Surface Finish: Wafers can be single-sided polished (SSP) or double-sided polished (DSP). For ellipsometry, the top surface (which is going to be coated) is generally polished to a mirror finish.

7. Flatness: This is a measure of the deviation in the surface flatness of the wafer. A more flat wafer can result in more accurate ellipsometry measurements.

Remember, these are general guidelines. The specific requirements can vary depending on the experimental setup and the research goals.

How is Thermal Oxide Used?

Thermal oxide, often known as silicon dioxide (SiO2), is a thin insulating layer that is commonly grown on the surface of a silicon wafer through a process called thermal oxidation. In this process, silicon is heated to high temperatures in the presence of oxygen or steam, which causes an oxide layer to form.

Thermal oxide has many applications, especially within the semiconductor industry:

1. MOSFET Fabrication: One of the most common uses of thermal oxide is in the fabrication of Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), a type of transistor used in most modern electronic devices. In MOSFETs, the thermal oxide serves as the gate insulator, separating the gate terminal from the underlying semiconductor material.

2. Masking Layer: Thermal oxide can also serve as a mask during ion implantation or diffusion processes. Certain dopants cannot easily penetrate the oxide layer, which allows specific areas of the silicon wafer to be selectively doped.

3. Insulation Layer: In integrated circuits, thermal oxide can be used as an interlayer dielectric, providing insulation between different conducting layers.

4. Surface Passivation: Thermal oxide can also passivate the silicon surface, reducing the density of electronic states and thereby minimizing unwanted surface recombination of charge carriers. This is particularly important in photovoltaic (solar cell) applications.

5. Capacitors: Due to its high dielectric constant and reliability, thermal oxide is often used as the dielectric layer in capacitors, including those in dynamic random-access memory (DRAM) devices.

6. Protective Coating: It provides a protective coating against contamination and damage during subsequent fabrication steps.

7. Optical Applications: Because of its transparency to visible light and well-characterized refractive index, SiO2 is also used in various optical devices and applications.