TECHNICAL REPORT

Development of Grinding Wheel with Extended Service Life(nanoVi®) for SiC Power-semiconductor Wafers— Optimization of Wheel Components —K. MINESHIMA S. SHIMADA T. KOJIMA T. KATO

There is currently demand for more stable quality and lower costs in the manufacturing processes of SiC
power semiconductors. In this development activity, we focused on the compounding ratios and dispersibility ofthe constituent elements of grinding wheels (abrasive grains, bonding agents, and pores) and investigated theirrelationships with grinding performance. Based on these results, we developed the grinding wheel nanoVi®, which
has a service life that is 2.3 times longer than conventional grinding wheels.
Key Words: SiC power semiconductor, grinding wheel

In this report, we focus on the compounding ratiosand dispersibility of the constituent elements of grinding
wheels shown in Fig. 2 (abrasive grains, bonding agents,and pores), and investigated their relationships withgrinding performance. We also developed a grinding
wheel that meets market needs, and have introduced ithere.

1. Introduction
At present, manufacture of the 6-inch size of SiC
power semiconductors is the mainstream, and fullscale mass production is in progress. As a result, there isgrowing demand for more stable quality and lower costsin the wafer manufacturing process. The grinding wheels
which are the tools used in this production also require
more stable cutting quality and longer service lives.
JTEKT has since 2019 been a part of the Tsukuba
Power Electronics Constellations (TPEC) led by theNational Institute of Advanced Industrial Science andTechnology. As shown in Fig. 1, we have developed
grinding wheels that are suitable for the post-slicing
grinding and for back grinding in the manufacturing
process for SiC power semiconductors.

Abrasive grains: Grind the workpiece
Bonding agent:
Bonds the abrasive
grains together

SiC wafer (workpiece)

Pores: Eject the chips

Fig. 2 Function of each element in SiC wafer grinding

Part where used

Part where used
Grinding wheel To dicing andlater processes

Grinding wheel

Ingot

Slice

Grinding

Chips

CMP

Circuit formation

Back grinding

Fig. 1 Semiconductor wafer manufacturing process and grinding wheel applications

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JTEKT ENGINEERING JOURNAL English Edition No. 1020E (2024)®

−Development of Grinding Wheel with Extended Service Life (nanoVi ) for SiC Power-semiconductor Wafers — Optimization of Wheel Components — −2. Relationship between Compounding
Ratios of Constituent Elements andGrinding Performance
We p r o d u c e d g r i n d i n g w h e e l s w i t h d i ff e r e n tcompounding ratios of grinding wheel constituent
elements (abrasive grains, bonding agents, and pores),and conducted evaluations of grinding performance(in this report, spindle current and wear rate) under theconditions shown in Table 1. We conducted multivariate
analysis of the obtained results to identify the elements
which have strong correlation with grinding performance.
Table 1 Grinding test conditions
Grinding test Vertical rotary surface grinding
equipment machine (5.5 kW)
Workpiece 6-inch SiC wafer
Grinding
wheel#2000 vitrified
diamond wheel

Grinding
conditions

Feed rate: 0.5 mm/s
Wheel peripheral speed: 19.6 m/s
Workpiece peripheral speed: 2.4 m/s

Evaluation
items

Spindle current (indicator of cuttingquality)

Wear rate (indicator of grinding
wheel service life)

The results are shown in Fig. 3. This is a relation
diagram in a matrix consisting of scatter diagrams
showing the correlation function between individual
elements and histograms of each element (the redline indicates the average value). In particular, thecombinations shown in the beige scatter diagrams
are combinations of elements with strong correlation
functions. According to these, the grinding wheel
constituent elements which have a strong correlation
function with spindle current are the bonding agent andthe amount of pores. The coefficient of correlation whichindicates the strength of the correlation function between
each element and spindle current is 0.48 for the amountof abrasive grains, however it is 0.90 for the amountof bonding agent and −0.91 for the amount of pores.
(Correlation functions indicate stronger correlation when
the coefficient of correlation is closer to 1 or −1.)
We also learned that there is a high negative correlation(coefficient of correlation −0.85) between spindle current
and the wear rate.
Based on these results, we focused on the amountof bonding agent and amount of pores, which were thegrinding wheel constituent elements that were strongly
correlated with spindle current, and readjusted thematerial compounding ratios in order to determine theJTEKT ENGINEERING JOURNAL English Edition No. 1020E (2024)

compounding ratio which produces both high cutting
quality and long grinding wheel service life.
Diagonalelements

Spindlecurrent

Spindlecurrent

Wear rate

Amont ofbonding agent

Amountof pores

Amount ofabrasive grains

Coefficient of correlation 0.85

0.90

0.91

0.48

0.64

0.58

0.26

−0.940.30

Wear rate

0.85
Amont ofbonding agent

Amountof pores

Amount ofabrasive grains

0.90

0.64

0.91

0.58

0.94

0.48

0.26

0.30

0.42

0.42

Fig. 3 Multivariate relation diagram between grinding
performance and component

3. Relationship between Constituent
Element Dispersibility and Grinding
Performance
Using the material compounding ratio that produces
both cutting quality and service life as described above,
we produced wheels (1) and (2) in which the constituent
elements (abrasive grains, bonding agents, and pores)
were unevenly distributed within the structure of thegrinding wheel, as well as wheel (3) in which the elements
were evenly distributed. Grinding evaluations wereconducted using these three types of wheels under thegrinding test conditions shown in Table 1 to investigate
the effects that constituent element dispersibility has ongrinding wheel grinding performance.
The conditions of uneven distribution of constituent
elements within the structure were considered low
dispersibility, and the conditions of even and uniform
mixing were considered high dispersibility. The lowest
sample (1) was considered 0, and the highest sample(3) was considered 1, and dispersibility was expressedas an index from 0 to 1. (Higher values indicate higherdispersibility.)
The relationship between constituent element
dispersibility and the grinding wheel wear rate is shownin Fig. 4. These results show that the wear rate was lower
in structure (3) that had high dispersibility compared tostructures (1) and (2) with low dispersibility.

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−Development of Grinding Wheel with Extended Service Life (nanoVi ) for SiC Power-semiconductor Wafers — Optimization of Wheel Components — −20

4. Development of a New Long Life
Grinding Wheel

Wear rate, %(1)15(3)

(2)

1050

We quantified the relationships of constituent element
ratios and their dispersibility with grinding performance,and through this development we developed a highstrength bonding agent so the grinding layer structure
could maintain suitable surface conditions for a prolonged
time during grinding.
The new grinding wheel nanoVi® that was developed
using these technologies succeeded in delivering stable
cutting quality, and extending the grinding wheel service
life by 2.3 times over existing grinding wheels as shownin Fig. 6.

Good00.2

0.40.6

0.8

1Dispersibility (index)

Fig. 4 Relation between dispersibility and wear ratio(1) Low dispersibility

Grinding wheel service life, index

Figure 5 shows the results from observation of thegrinding wheel surface in each dispersion condition witha laser microscope, and the changes in spindle current
during grinding. With low dispersibility structures (1) and(2), there are clumps of abrasive grains and bonding agent
within the grinding layer structure, resulting in unstablespindle current during grinding. On the other hand, inthe high dispersibility structure (3), the grinding wheel
constituent elements are evenly distributed on the surfaceof the grinding wheel, and the spindle current is alsostable during grinding.
Based on the results shown in Fig. 4 and Fig. 5,
localized loads were applied during grinding at the parts
where there were uneven clumps of abrasive grains andbonding agent on the grinding wheel surface, and startingfrom these points, the surrounding structures which wereunable to withstand the load fell off over a broad range.
As a result, this produced problems such as unstablespindle current during grinding, and an increase ingrinding wheel wear. However in the structure with highdispersibility, the load was applied evenly over the entire
grinding wheel surface. There was no large falling-off ofstructures, spindle current was stable, and low wear wasachieved.

250

2.3× longer service life

200
150
100
500

Conventional productnanoVi®
(developed product)

Fig. 6 Comparison between service lives of existing wheels
and nanoVi®

(2) Low dispersibility(3) High dispersibility120 mGrinding wheelsurface
Results fromobservation bylaser microscope

60 m0 m

0200
Grinding time, s400

13119753

Unstable spindle current

0200

400

Grinding time, sSpindle current, A

Unstable spindle current

Spindle current, A

Spindle current, A

Changes inspindle current
during grinding

13119753100 m100 m100 m13119753

Stable spindle current

0200

Clumps of bonding agent
and abrasive grains
Concentration of pores

400

Grinding time, sFig. 5 Relation between dispersibility and current of grinding wheel spindle motor

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JTEKT ENGINEERING JOURNAL English Edition No. 1020E (2024)®

−Development of Grinding Wheel with Extended Service Life (nanoVi ) for SiC Power-semiconductor Wafers — Optimization of Wheel Components — −5. Conclusions
This development investigated the correlation functions
between the ratios of grinding layer constituent elements
and grinding performance in wheels used for grinding SiC
power semiconductor wafers, and determined a material
compounding ratio which produced both high cutting
quality and long service life. In addition, the dispersibilityof the constituent elements affected the spindle current
during grinding, which is an indicator of cutting quality,
as well as the wear rate, which is an indicator of grinding
wheel service life. Higher dispersibility produced morestable spindle current during grinding and a lower wearrate.
Based on the above technologies, the newly developed
high-strength bonding agent was used to develop thegrinding wheel nanoVi®.

6. Acknowledgements
The developed product nanoVi ® was developedwith the cooperation of the Tsukuba Power Electronics
Constellations (TPEC) led by the National Institute ofAdvanced Industrial Science and Technology.
We are deeply grateful for Professor Kato from theNational Institute of Advanced Industrial Science andTechnology and everyone on the Wafer Process Team fortheir great advice and cooperation.

K. MINESHIMA* S. SHIMADA*T. KOJIMA*T. KATO*****JTEKT ENGINEERING JOURNAL English Edition No. 1020E (2024)

Development Dept., JTEKT GRINDING TOOLSCORPORATION
National Institute of Advanced Industrial Science andTechnology (AIST)103