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Press Release

August 8 2016

High-Speed SiC Wafer Production with Greatly Reduced Material Loss:
KABRA®*1 Laser Slicing Technology Developed through New Processing Method

*1: Patent pending (40 related patents as of August 8) / Trademark registered (Registration no. 5850324)

DISCO Corporation (Head Office: Ota-ku in Tokyo, President: Kazuma Sekiya) has developed a unique laser ingot slicing method called "KABRA." 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 dramatically improves productivity. We are now accepting requests for test cuts.

Development Background

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.

KABRA Process Characteristics
This unique method forms a flat light-absorbing separation layer (KABRA layer*2) 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) (Fig. 1, a). 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 approx. 100,000 times larger than that of SiC. As a result of this development, we have succeeded in forming KABRA layers inside the ingot both vertically and in the direction of the laser incident*3, finding the optimal laser slicing method (Fig. 1, b). 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.
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.
Photo 1: Wafer after separation (φ4 inches)
Fig. 1: Difference of modified layer forming direction

*2:Key Amorphous-Black Repetitive Absorption: Forming a layer which 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.
*3: Patent pending

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.
 
Example of Existing Process: Diamond Wire Saw
Fig. 2: Comparison of processing time between KABRA process and existing process
(When producing a specified thickness of 350 µm from φ4-inch and 20 mm thick SiC ingot. Existing process: General values based on user info.)
Advantages
Photo 2: Wafer after separation (φ6 inches)
1. Processing time is greatly reduced
Existing processes require approx. two hours to slice a wafer from a φ4-inch SiC ingot (2 to 3 days for one ingot)*4, 5. In contrast, this process can greatly reduce the processing time and requires only 25 minutes to slice a wafer (approx. 18 hours for one ingot)*6. In addition, this process only takes approx. 30 minutes*6 to slice a wafer from a φ6-inch SiC ingot even though the existing process requires over 3 hours*5 (Photo 2).
2.Lapping process is no longer required
For wire processing, a lapping process is required to remove approx. 50 µm*5 of undulations generated on the surface of a processed wafer. However, this process does not require lapping because the wafer undulation after separation can be controlled (Fig. 2), making it possible to greatly reduce the initial costs and running costs.
3.Number of wafers produced increases 1.5 times more than that of existing processes
Although wire processing produces approx. 200 µm*5 of material loss per wafer at the slicing sections (kerf loss), this process essentially has no material loss. In addition, the removal amount of the KABRA layer after separation can be suppressed to approx. 100 µm. This improves the number of wafers produced from a single ingot approx. 1.5 times more than the existing process.
*4: When producing a specified thickness of 350 µm from φ4-inch and 20 mm thick SiC ingot
*5: Typical value based on users' information
*6: Total processing time including laser irradiation, separation, and ingot grinding

Table 1: Superiority of the KABRA Process
(When producing a specified thickness of 350 µm from φ4-inch and 20 mm thick SiC ingot)
Existing process*7 KABRA process*8
Cutting time 2-3 days 10 min.
(Laser irradiation + separation)
Ingot slice total process time (per wafer) 1.6-2.4 hr. 25 min.
Material loss during cutting (per wafer) Approx. 200 µm None
Material loss during grinding (per wafer) Approx. 100 µm
(Double-sided lapping)
Approx. 100 µm
(Processing mark grinding)
No. of wafers from one ingot 30 wafers 44 wafers
Lapping 16 hr.
(Concurrent processing of multiple wafers)
Not required
Total processing time per ingot 2.5 - 3.5 days 18 hr.
*7: When lapping is performed after slicing with a loose abrasive type diamond wire saw (30 multiple wires). All values are general values based on users' information.
*8: DISCO's values are at the time of this releasing.

Comment from Kazuma Sekiya, COO and General Manger of Engineering R&D Division

The KABRA process is a unique process that forms a layer which serves as the base point for separation from the laser irradiation point by separating SiC into silicon and carbon with laser irradiation. I expect that a number of wafer manufacturers will employ this process to promote the widespread use of SiC power devices so that we can be closer to achieving a green society.

Future Plans
  • Test Cuts and Chargeable Processing Service: We have been receiving and performing test cuts in the head office and R&D center
  • Academic Conference Presentations: The Japan Society for Precision Engineering Autumn Meeting / The Japan Society of Applied Physics Autumn Meeting in September 2016
  • Displayed at SEMICON Japan 2016: The KABRA dedicated equipment is scheduled to be displayed for the first time December 14-16, 2016
DISCO's Strength

DISCO, a precision equipment manufacturer, can adopt developed processing techniques for equipment internally, and develop and commercialize equipment depending on the customer's application, such as for R&D or mass production purposes. In addition, we conduct test cuts until the customer is satisfied with the results and select the optimal processing conditions for installing equipment at the customer's site. Even after equipment installation, we continue contributing to evolve our customers' manufacturing processes with a quick support of dedicated engineers at over 50 affiliates in over 18 countries/regions.

Related Patents *As of August 8, 2016

Unexamined Patent Publication Nos. 2015-223589, 2016-062949, 2016-111143, 2016-111144, 2016-111145, 2016-111146, 2016-111147, 2016-111148, 2016-111149, 2016-111150, 2016-127186, and 2016-124015
Patent Application Nos. 2015-023576, 2015-023577, 2015-023578, 2015-028509, 2015-078028, 2015-078029, 2015-078030, 2015-079711, 2015-083642, 2015-083643, 2015-112316, 2015-112317, 2015-114581, 2015-139679, 2015-141898, 2015-141899, 2015-144350, 2015-144351, 2015-160848, 2015-160849, 2015-181950, 2015-222369, 2016-001647, 2016-001941, 2016-076734, 2016-078613, 2016-111163, and 2016-116126

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  Reference Information: Origin of the Name of "KABRA" and its Logo
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