High-Speed SiC Wafer Production

The Kabra process flow: 1. Form a KABRA layer inside the ingot by laser irradiation. 2. Separate and produce a wafer. Grind the wafer to the specified thickness. 3. Grind the upper surface of the ingot for the next laser irradiation. Repeat processes 1 to 3 and slice the wafers. (Source: Disco)

The Kabra process flow:
1. Form a KABRA layer inside the ingot by laser irradiation.
2. Separate and produce a wafer. Grind the wafer to the specified thickness.
3. Grind the upper surface of the ingot for the next laser irradiation.
Repeat processes 1 to 3 and slice the wafers. (Source: Disco)

Disco Corporation has developed a unique laser ingot slicing method called KABRA (Key Amorphous-Black Repetitive Absorption). Implementing this process achieves the high-speed production of silicon carbide (SiC) wafers, which are anticipated as the next-generation power device material, increases the number of wafers produced from a single ingot, and improves productivity.

Wafer after separation (φ4 inches, source: Disco)

Wafer after separation (φ4 inches, source: Disco)

The existing methods for slicing wafers from a SiC ingot have been mainly adopted by using a diamond wire saw. However, these methods require a number of diamond wire saws for mass-producing wafers because the processing time is long due to the high rigidity of SiC. The number of wafers produced from a single ingot is also small due to a great amount of material lost in the slicing sections.

This has been a major factor which increases the cost of producing SiC power devices, hindering their introduction into the market and the widespread use of the SiC power devices.

This new method forms a flat light-absorbing separation layer, the KABRA layer, at a specified depth by irradiating a continuous, vertical laser from the upper surface of the SiC and creating wafers using a previously non-existing slicing method.

Conventional laser processing is not suitable for slicing, because the modified layer formed by laser irradiation, in principle, extends in the direction of the laser incident (portrait orientation). However, Disco has developed this laser slicing method focusing on two facts: The SiC can be decomposed by a focused laser and separated into silicon (Si) and carbon (C) in an amorphous state, and the light absorption coefficient is approx. 100,000 times larger than that of SiC.

This process can be applied to various types of SiC ingots, including single-crystal (4H, 6H, and semi-insulation) and multi-crystal ingots. One of the major characteristics is that this process can be applied to monocrystal ingots, regardless of the off-angle of the crystal c-axis.

The advantages of the process are:

  • Processing time is reduced
  • Lapping process is no longer required
  • Number of wafers produced increases 1.5 times more than that of existing processes (Source: Disco)

Link: Disco Corporation, Tokyo, Japan

 

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