How Thin Can Silicon Wafers Be Sliced?

Limits of Wafer Slicing

One problem with cutting silicon with a thickness of only 3 micrometers is that the ability of the silicon disk to absorb light photons is greatly reduced. However, we have successfully supplied wafers as thin as 2 microns.

New technologies that allow thin wafers made of silicon crystals to grow by cutting them into large cylinders could contribute to this further thinning. For example, researchers have produced 110-micron silicon wafers cut with wire saws, confirming they were less likely to break during cutting than conventional 100-micron silicon wafers.

From Ingot to Wafer: The Process

The first step in semiconductor manufacturing is to slice a silicon ingot to the desired diameter and Orientation (Ori). The silicon ingot is fully grown and ground to a rough diameter using a diamond edge saw.

1. Slicing: The material is sliced into wafers using a diamond wire saw. The thinner the slice, the more yield is possible, but "kerf loss" (material turning to dust during sawing) is a major efficiency factor. Standard sawing produces wafers approximately 180um to 200um thick before polishing.

2. Lapping: Once sliced, the process is called lapping. This procedure smoothes the edges of the wafer and reduces the risk of breakage during subsequent manufacturing steps. Lapping removes saw marks and scratches.

3. Etching & Cleaning: The silicon ingot is cleaned and etched with chemicals (like nitric acid or acetic acid) to remove microscopic cracks and damage to the surface caused by the mechanical stress of sawing.

4. Polishing: Wafers are polished to a mirror finish (SSP or DSP) to ensure the highest flatness.

Total Thickness Variation (TTV) & Yield

When cutting ultra-thin wafers, vibration can cause cracks or variations in thickness. This is measured as TTV (Total Thickness Variation). High TTV leads to warp and bow, which can destroy the wafer during lithography.

Rayton Solar has claimed to cut electronic-grade silicon on a wafer that is only 3 microns thick, compared to a standard silicon wafer that is 200 microns thick. Other startups, such as 1366 Technologies, are working to make silicon solar cells as thin as possible to reduce cost.