The automation of the slicing system utilizing internal-diameter saws for the production of the silicon wafers used in solar arrays is discussed. It is argued that saw productivity can be increased by reducing silicon waste, decreasing usage of consumables, keeping the saw slicing, and increasing the cutting speed. Several machine enhancements utilizing automatic control are discussed. The need for record keeping to anticipate maintenance operations is noted, and a digital serial communication interface with the microprocessor-based saws is recommended. Distributed control of the manufacturing process is discussed in detail, and is recommended as a method for increasing productivity

Lewandowski, T.

English

NASA Technical Reports Server

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I.D. SLICING AND THE AUTOMATED FACTORY 
T. LEWANDOWSKI 
SILICON TECHNOLOGY CORPORATION 
OAKLAND, NEW JERSEY 07436 
1' 
Silicon wafering in the semiconductor industry today is 
done almost exclusFvely on I.D. saws operating semiautomatically. 
One machine operator is reqcired for support of every four to 
ten saws. The exacting cost goal of the Low-Cost Solar Array 
Project demands a much higher level of automation. The I.D. saw 
of today must be enhanced to operate with less human 
intervention. This improved saw must be integrated into a 
slicing system which makes maximum use of each individual saw. 
The slicing system, in turn, must be controlled by some central 
intelligence so it can meet the demands of the 01-era11 
manufacturing process. 
The objective of automation is, of course, increased 
productivity. The ratio of process output to resource input 
must be increased while the desired production rates are 
maintained. The output of a solar array factory is measured as 
peak output power of the finished product. The measure of 
resources used is the cost of materials, capital equipment, 
laboy, and consumables. 
The saw productivity can be increased by reducing silicon 
waste, decreasing usage of ccnsumables, keeping the saw slicing, 
and increasing the cutting speed. These variables are strongly 
interrelated. An improvement in one may adversely affect others. 
Since the saw improvements which follow are evaluated 
qualitatively only, a net productivity gain is possible only if 
no negative effects are likely. 
The I.D. saw as it exists today is capable of cutting a 
number of wafers automatically. The desired number is entered 
manually from the machine control panel, and operation is 
initiated. When the correct number of wafers is completed, 
operation stops. The machine now sits idle until the operator 
removes the wafers and restarts the slicing operation. An 
automatic wafer removal system would eliminate the need for 
manual intervention. The unpredictable human response is 
eliminated enabling the saw to spend more time slicing and 
thereby reducing idle time. 
Another area which requires action by the operator is 
blade dressing. Blade deflection monitors are widely used to 
determine when a blade neede service. If axial blade deflection 
exceeds a preset limit during a slice, the slice is completed 
https://ntrs.nasa.gov/search.jsp?R=19820015796 2020-03-21T17:00:21+00:00Z
and the saw is stopped before a new slice is started. An alarm 
light alerts the operator who must manually dress the blade. A 
strip chart recorder maintains a record of deflection versus 
time which can be used to determine what part of the blade needs 
dressing. 
Blade dressing affects blade life, wafer quality, kerf loss, 
and slicing speed. Proper blade dressing is a necessity for 
high productivity. An automatic system which can interpret 
blade derlection data and can respond with the correct dressing 
action is an important machine enhancement. Excess blade 
deflection can also be caused by loss of blade tension. When 
dressing does not restore correct cutting action, retensioning 
is usually necessary. Early detection of tension loss would 
permit corrective action before blade damage occurs and would 
eliminate unnecessary blade dressing. 
Occasionally, a wafer will stick to the back of the blade 
and, if not removed, will break subsequent wafers. Corrective 
action is to shut down the saw and to flush out the wafer or 
the pieces with a water stream. Detection oi this condition is 
important because saw operation will be largely unattended and 
loss of a considerable number of wafers could result. 
A portion of potential productivity is lost because of the 
compromise necessary in cutting speed. High cutting speed will 
cause edge chipping on entry and exit. A fixed speed system 
must be o~erated at a speed slow enough to limit edgs chipping. 
This spet is lower than is possible in the bulk of the material; 
therefore, total cycle time is increased. Programmed feed 
enters the ingot slowly to prevent edge chipping and then 
increases speed in the center to the highest value consistent 
with acceptable wafer quality. The cutting speed is decreased 
again at the end of the cut. The net rssult is a higher average 
cutting sseed. Programmed feed rate increases saw productivity 
by increasing average slicing speed. 
After a slice has been completed, the blade must be 
withdrawn before another slice can tte started. Withdrawal time 
can be reduced considerably with simple saw modifications. 
Decreasing the blade withdrawal time reduces the tine the saw 
is not cutting. 
The goal of most of the aforementioned machine enhancements 
has been to reduce the necessity for human intervention with 
machine operation. A large slicing operation may involve 
dozens or possibly hundreds of saws. Because human presence on 
the production floor is limited, alarm conditions indicated on 
the individual machines can be overlooked, thus reducing 
productivity. 
There is also a need for record keeping to anticipate 
reloading of silicon, blade changes, and other maintenance 
operations. Since the controls on newly designed saws are 
microprocessor based, a digital serial communication interface 
can easily be added witn the necessary firmware to send needed 
information to a central point. 
This central monitoring point would have to receive data 
from a large number of saws, store the data, and display the 
inlormation to the operator. The basic data received from the 
machines would be their state (i.e. cutting, idle, or alarmed) 
and an indication of a wafer being completed. The central 
monitoring system must have enough intelligence to act as a 
controller on a communication link with many stations and to 
operate on the data provided so that it can be presented in a 
usable manner to the operator. 
The most likely configuration for interface with an operator 
is a CRT and a keyboard. Alarm data would be displayed 
automatically. Display of other data could be requested using 
the keyboard. 
Distributed control is a concept that has been used for 
several years now and is becoming more popular in the process 
control industry. The system intelligence is distributed as is 
the system hariware. Intelligence is placed close to the source 
of data or point of control. Various intelligent components 
communicate over a "data highway." They can pass data among 
themselves and pool their computational power to control the 
system. 
The data highway is the key element of the system. It 
permits high speed communication among system elements. In 
situations where there are many system components which do not 
need to send or to receive large volumes of data, the components 
are connected via a low speed bus to a data concentrator. This 
concentrator assembles and disassembles the message to be sent 
or to be received on the data highway. 
Careful examinati~ of the slicing system with central 
monitoring reveals many of the features of distributed control. 
Each saw is a data source and control point which communicates 
with a central monitoring point over a low speed serial data 
bus. If the central monitoring point is used as a data 
concentrator and connected to a data highway, a distributed 
control system is created. 
The primary function of this control system is to 
coordinate the activities of the entirc system and to insure 
that each element is operating near its maximum capacity. Many 
elements in solar array processing are sirnilar to the slicing 
element in that they are made up of many conponents (saws) 
operating in parallel. If the control system can keep each 
component ~perating near capacity, the total number of components 
can be reduced from the number required for ac uncontrolled 
system. Efficient control should reduce capital equipment 
requirements. 
A secondary function of the control system is excnange of 
information among system elements. This can be used by the 
destination element to improve its operation; for example, the 
results of product inspection can be fed back to the slicing 
element for possible corrective action. 
Data fed back to the slicing process wculd L,e uselF--s 
unless the identity of the saw which produced th, 
off-specification product is known. This could be accomplished 
by adding a wafer marking operation after slicing. A less 
expensive alternative would be to add intelligence to the wafer 
transport element and to use the data highway to pass the 
desired source and destination information. This is another 
area where equipment cost may be reduced. 
Another important feature of a distributed control system 
is its ability to log data on its own operatioll. This data 
base can be used for off-line analyses to test schemes for 
improving process performance. 
Distributed control simplifies interfacing equipment built 
by different manufacturers because standardization is required 
only at the data highway level. Equipment can be built with 
hardware and software designed to interface with the data 
highway. System design would then require system software 
only. 
Application of distributed control will improve 
productivity by reducing material waste and lowering capital 
expenditures. Successful integration of an I.D. saw into an 
automated factory requires the enhancements described in order 
to improve productivity and to minimize the amount of human 
intervention necessary to operate the entire system. The human 
element is not removed; its focus is merely shifted from dull, 
repetitive jobs to the more demanding tasks of system 
optimiz7tion. 
DISCUSSION: 
YOO: For  real .  s u c c e s s  i n  au toma t ion ,  I t h i n k  t h a t  one of t h e  most impor t an t  
f a c t o r s  is  ho-1 a c c u r a t e l y  you monl t o r  t h e  b l a d e  c o n d i t i o n .  You mentioned 
checking  t h e  b l ade  c o n d t t i o n  by b l ade  d e f l e c t i o n  o n l y .  Maybe t h e r e  a r e  
some o t h e r  f a c t o r s  t h a t  i n f l u e n c e  t h e  r e a l  q u a l i t y  of  t h e  b l a d e  o t h e r  t h a n  
b l ade  d e f l e c t i o n .  I n  o t h e r  words,  p o s s i b l y ,  mon i to r ing  t h e  c e n t e r  of t h e  
I D  b l a d e ,  e t c .  
LEWANDOWSKI: Cen te r ing  of t h e  I D  b l a d e  is  u s u a l l y  a s e t u p  p rocedure .  I imagine 
t h e r e  i s  a  p o s s i b i l i t y  t h a t  i t  would s h i f t  i n  o p e r a t i o n ,  bu t  I have n e v e r  
hea rd  anyone complain about  t h a t  happening.  A s  f o r  mori l tor ing o t h e r  
v a r i a b l e s  t o  de t e rmine  t h e  c o n d i t i o n  of t h e  b l a d e ,  y e s ,  t h e r e  a r e  o t h e r  
v a r i a b l e s  t h a t  a r e  impor t an t .  One t h a t  we worked w i t h  t o  some e x t e n t  I s  
b l a d e  to rque .  We f i n d  a  c l e a r  c o r r e l a t i o n  between s l i c e  q u a l i t y  ana  t h e  
amount of t o rque  r e q u i r e d  by t h e  s l i c i n g  p r o c e s s .  We have done some work 
on measuring t h e  f o r c e  r e q u i r e d  a t  t h e  c u t t i n g  b l a d e .  The paper  t h a t  was 
p r e s e n t e d  on Monday, t h e  s o u r c e  of d a t a  was STC and i.t goes  back a  number 
of y e a r s  where we had o r i g i n a l l y  done work i n  t h i s  a r e a .  We a r e  a c t i v e  i n  
t h i s  a r e a  now and we a r e  aware of o t h e r  p a r a m e t e r s  t h a t  may he u s e f u l  i n  
de t e rmin ing  b l a d e  c o n d i t i o n ,  and we i n t e n d  t o  make use  of  them. 
DAUD: Could you g i v e  u s  a  p r i c e  e s t i m a t e  a s  t o  how much I t  w i l l  i n c r e a s e  t h e  
saw p r i c e ?  
LEWANDOWSKI: No. As yo11 g e t  t o  a  h i g h e r  l e v e l  of au toma t ion  t h e r e  h a s  been 
l e s s  work done. Many of  t h e  machine implavements  t h a t  I t a l k  abou, do 
e x i s t  o r  a r e  Jn t h e  d e s i g n  s t a g e s  and we can  g i v e  you a  p r i c e  on them i f  
you a r e  i n t e r e s t e d .  The r e a l  g a i n s  t h a t  you a r e  going  t o  s e e  from 
au toma t ion  a r e  no t  a t  t h e  machine l e v e l .  They a r e  go ing  t o  be a t  t h e  
sys tem l e v e l  and t h e y  a r e  go ing  t o  make u s e  of t h e  a b i l i t y  t o  communicate 
fzom SUJ  rsL...n. When ycu put  a  s e n s o r  on t h e  saw i t  o n l y  b e n e f i t s  you i f  
i t  is  on Every saw. I f  you pu t  i t  i n  a n o t h e r  subsystem I t  can  be used t o  
a  g r e a t e r  e x t e n t ,  more e f f i c i e n t l y ,  and i t  would r e s u l t  i n  l e s s  o v e r a l l  
c a p i t a l  e x p e n d i t u r e .  The system l e v e l  i s  where au tomat ion  i s  r e a l l y  go ing  
t r  pay o f f  . It h a s  b e n e f i t s  on t h e  saw l e v e l ,  t h e  enhancements  I t a l k e d  
about  t o  i n c r e a s e  p r o d u c t i v i t y  f o r  example,  bu t  t h e  b i g  g a i n s  w i l l  be s e e n  
a t  t h e  sys tem l e v e l  and t h e r e  r e a l l y  h a s n ' t  been a l l  t h a t  much work done 
on t h a t  y e t .  
LIU: You mentioned t h a t  one of  t h e  i t e m s  t h a t  you w i l l  be m o n j t o r i n g  on your  
automated sys tem would be t h e  t e n s i o n i n g  of t h e  b l a d e .  I assume what you 
meant by t h a t  you would be a ' l e  t o  mon i to r  t h e  a c t u a l  t e n s i o n  of t h e  b l a d e  
i n  s i t u  w h i l e  i t ' s  w a f e r i n g .  Is t h a t  what you meant? 
-- -
LEWANDOWSKI: When you s t a r t  l o s i n g  h y d r a u l i c  p r e s s u r e  t h e  f o r c e  you a r e  
a p p l y i n g  t o  t h e  b l a d e  i s  reduced ,  t h e r e f o r e  t h e  h l a d e  becomes more 
f l e x i b l e  . 
KACHAJIAN: I n  f u r t h e r  r e sponse  t., t h a t  q u e s t i o n ,  we w i l l  a l s o  i n  t ime be 
mon i to r ing  t h e  c u t t i n g  f o r c e  a t  t h e  p o i n t  of  c o n t a c t  w i t h  t h e  workpiece .  
Toge the r  w i t h  t h e  a c t u a l  b l a d e  d e f l e c t i o n  and t h e  measur ing  of  t h e  c u t t i n g  
force we can determine if the cutting force increases or decreases and 
that could be a function of the loss of tension in the blade. If the 
blade is not tensioned properly it will not be cutting properly, and that 
will show up as an increased force. 
LIU- Are you saying that we are losing tensioning on the blade because we are 
losing the hydraulic pressure itself, or is it just an indication of the 
blade being stretched during the wafering? 
LEWANWWSKI: Both. You can be losing hydraulic pressure; you do lose some 
tension because of biade yielding. You can retension, up to a point of 
course, and still cut effectively even though you have less tension due to 
yielding. 
KACHAJLAN: The only time you can not recover really is when the ccre has been 
rcbbed, and the steel has yielded dramatically in m e  direction. Then 
, s 
tnere is hardly anything you can do. 
MORRISON: I suggest that you ndght monitor concentricity o; .ically; a continu- 
ous monitoring might indicate whether you are getting a slip of tension or 
distortion of the blade. 
I understand you people are building a multi-saw laboracory in-house and I 
am wondering how much of the type of systems you describeu i- your 
presentation we can expect to see there and on what kind of a schedule. 
LEWANDOWSKI: Saws that go into that laboratory will be equipped with just about 
all of the enhancements ;hat are available today. We hope to have 
requirements for the centralized monitoring system defined by the end of 
the ysar and would be going into design at the beginning of next year. 
Again, tk.is device is kind of a tricky one because we are selling to two 
different markets with widely varying requirements. Semiconductor is more 
of a batch-type process. They are cutting many different specifications on 
a slicing operation and they may have more of a need for this thing 
j.nitially as strictly a monitoring type of device. In solar, I believe its 
real use will come when we are talking about integrating into a completely 
automated factory. 
KACHAJIAN: The saws, unautomated, but ready for automation and design, will 
be in place by the third quarter of this year (and that is more than 10). 
ILES: There is an old-fashioned way of dressing which I think involves mounting 
the ingots on a surface--a sort of a poor man's dressing--and as the blade 
came through each time, it at least cleaned the debris. IS that idea 
completely slipped away now or is it still an option? 
LEWANDOKSKI: 1 would say that it is not an option simply because one of the 
thin~s yo& want to avoid is excessive dreaslng. This is detrimentai to 
bladelife. That is why it is important to develop a sensor or sensors 
that can tell you when the blade needs to be dressed, and dress it only 
when it needs to be dressed. The manner in which you dress it makes a big 
diffcrence. If the blr ,e is deflecting during a slice one way or another 
it indicates that it should be dressed on the opposite side and not on 
both sides. What you are suggesting would dress it both sides every time 
t hrcug h. 


ID slicing and the automated factory

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