Key Differences in Three Silicon Wafer Orientations

01

What is crystal orientation?

Simply put, crystal orientation refers to the “path” along which atoms are arranged in a specific direction inside a crystal. Crystal orientation is usually denoted by square brackets [hkl] to represent directions, round brackets (hkl) to represent planes, and angle brackets to represent families of directions.

As shown in the figure below, [100] represents the direction along the x-axis of the lattice, [110] represents the diagonal direction (x+y), and [111] represents the space diagonal direction (x+y+z).

<100> is a family of directions, consisting of all equivalent [100]-type directions. <100> is perpendicular to the (100) crystal plane.

02

Why is crystal orientation so important?

Each orientation corresponds to different densities, atomic spacing, and bonding strengths. On a macroscopic level, the physical and chemical properties of a crystal vary significantly.

This is mainly reflected in:

1. Defect density: Certain planes like (111) have relatively low surface defect densities.
2. Surface smoothness: Surfaces like (100) tend to be flatter and smoother.
3. Dopant solubility: Dopant atoms embed into the lattice differently depending on orientation.
4. Etching rate: Wet and dry etching rates vary significantly across different planes.
5. Epitaxial growth: The quality and rate of epitaxial growth depend on the crystal plane.

03

Applications of different crystal orientations:

<100>: Silicon wafers with this orientation account for the majority of total wafer production. Nearly all advanced CMOS logic chips are standardized on <100> silicon wafers. DRAM, SRAM, and flash memory also mainly use <100>-oriented silicon wafers.

<110>: These wafers make up only about 5% of wafer production. RF or power devices occasionally use silicon wafers with this orientation. MEMS processes frequently use <110>, <111>, or other custom orientations based on application.

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