Disco Corporation (Tokyo, Japan) has developed a unique laser wafer slicing method called key amorphous-black repetitive absorption (KABRA; which is trademark-registered and patent-pending, with 40 related patents) that achieves high-speed production of silicon carbide (SiC) wafers, which are anticipated as the next-generation power device material. The process increases the number of wafers produced from a single ingot, and dramatically improves productivity.
|A wafer after separation.|
The existing methods for slicing wafers from a SiC ingot typically use a diamond wire saw. However, these methods require a number of diamond wire saws for mass-producing wafers because the processing time is long, as SiCs have high rigidity. The number of wafers produced from a single ingot is also small because of the great amount of material lost in the slicing sections. This has been a major factor that increases the cost of producing SiC power devices, hindering their introduction into the market and the widespread use of the SiC power devices.
|The difference of modified layer forming direction.|
The unique method forms a flat light-absorbing separation layer (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: 1. that SiC can be decomposed by a focused laser and separated into silicon (Si) and carbon (C) in an amorphous state, and 2. that the light absorption coefficient is approximately 100,000 times larger than that of SiC. As a result of this development, the company has succeeded in forming KABRA layers inside the ingot both vertically and in the direction of the laser incident, finding the optimal laser slicing method. In addition, this process can be applied to various types of SiC ingots, including single-crystal (4H, 6H, and semi-insulation) and multi-crystal ingots.
|The KABRA process flow involves 1. forming a KABRA layer inside the ingot by laser irradiation; 2. separating and producing a wafer, followed by grinding the wafer to the specified thickness; 3. grinding the upper surface of the ingot for the next laser irradiation; and 4. repeating processes 1-3 and slicing the wafers.|
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.
|A comparison of processing time between the KABRA process and the existing process. When producing a specified thickness of 350µm from φ4in. and 20mm-thick SiC ingot. Existing process: General values based on user info.|
KABRA forms a layer that becomes the base point for separating the wafer by decomposing SiC into amorphous silicon and amorphous carbon with continuous laser irradiation, and then making the black amorphous efficiently absorb the light. Its advantages include greatly reduced processing time, no need for the lapping process, and the number of wafers produced increases 1.5 times more than that of existing processes.
For more information, please visit www.disco.co.jp.