The first quarter of a one-year program to investigate the production of patterned etch resistant wax coatings on solar cell substrates by printing is reported. Master molds for printing plates were produced for the plates. The resist wax is being studied to determine its relevant physical properties. A printing device is currently in design, and material costs are being compiled as first step in a cost analysis task. All phases of the project are proceeding according to schedule. No specific phases are yet completed

Pastirik, E.

English

NASA Technical Reports Server

(NASA-CB-158563) THE DEVELOPlENP CF A U79-23527 
HBTBQL OF P B O D U C I I G  PTCB BESISTANT O A X  
PATTEBlS 01 SOLAR CELLS Cuarterly Technical 
DRL N O -  97 Bepoct, 17 Jan, - 31  ~ar, 1979 (lotorola, Unclas 
Inc.) 13 p HC AOZ/MF A01 CSCI 10A G 3 / O U  25196 
DRD N O -  S E - 4  
THE DEVELOPHENT OF A WETHOD OF PRODUCING ETCH RESISTANT  
WAX PATTERNS ON SOLAR C E L L S  
QUARTERLY T E C H N I C A L  REPORT NO 1 
MOTOROLA REPORT N O -  2 3 6 5 / 1  
DRD N O -  SE-4  
17 JANUARY 1979 - 31 MARCH - 1979 
J P L  CONTRACT N O -  955324 
PREPARED B Y  
E -  P A S T I R I K  
MOTOROLA I N C  SEMICONDUCTOR GROUP 
5 0 0 5  EAST MCDOWELL ROAD 
PHOENIX, ARIZONA 85005 
THE J P L  LOW-COST SOLAR ARRAY PROJECT I S  SPONSORED B Y  THE 
U S DEPARTMENT OF ENERGY AND FORMS PART OF THE SOLAR 
PHOTOVOLTAIC CONVERSI ON PROGRAM TO I N I T I A T E  A MAJOR EFFORT 
T W A R D  THE LOW-COST SOLAR ARRAYS-  T H I S  WORK WAS PEHFORMEl) 
FOR THE JET PROPULSION LABORATORY, C A L I F O R N I A  I t i S T I T U T E  OF 
TECHNOLOGY B Y  AGKEEMENT BETWEEN NASA AND DOE 
PROJECT fJO 2365 
https://ntrs.nasa.gov/search.jsp?R=19790015356 2020-03-21T23:50:58+00:00Z
THIS REPORT MAS PREPARED AS AN ACCOUNT OF WORK 
SPOISOREO BY THE UNITED STATES GOVERNMENT. 
NEITHER THE UNITED STATES NOR THE UNITED 
STATES DEPARTMENT OF ENERGY, NOR ANY OF THEIR 
EMPLOYEES,NOR ANY OF THEIR CONTRACTORS, 
SUBCONTRACTORS, OR THEIR EMPLOYEES, MAKES ANY 
YARRAMTY, EXPRESS OR IMPLIED, OR ASSUMES ANY 
LEGAL L I A B I L I T Y  OR RESPONSIBILITY FOR THE 
ACCURACY, COMPLETENESS OR USEFULNESS OF AMY 
IWFOR~ATION, APPARATUS, PRODUCT OR PROCESS 
DISCLOSED, OR REPRESENTS THAT I T S  USE MOULD 
NOT INFRINGE PRIVATELY OYNEO RIGHTS. 
D I S T R I B U T I O N  CATEGORY U C - 6 3  
DRL  NO 9 7  
DRD NO S E - 4  
THE DEVELOPMENT OF A METHOD OF PRODUCING ETCH R E S I S T A N T  
WAX PATTERNS ON SOLAR C E L L S  
QUARTERLY TECHNICAL  REPORT NO 1 
MOTOROLA REPORT N O -  2365/1 
DRD N O -  SE-4  
17 JANUARY 1979 - 31 MARCH 1979 
J P L  CONTRACT N O -  955324 
PREPARED BY  
E -  P A S T I R I K  
MOTOROLA I N C  SEMICONDUCTOR GROUP 
5005 E A S T  MCDOUELL ROAD 
PHOEN I X, AR I Z ONA 85005 
THE J P L  LOU-COST SOLAR ARRAY PROJECT I S  SPONSORED BY THE 
U S *  DEPARTMENT OF ENERGY AND FORMS PART OF THE SOLAR 
PHOI  OVOLTAIC CONVERSI ON PROGRAM TO I N I T I A T E  A MAJOR EFFORT 
TOWARD THE LOW-COST SOLAR ARRAYS-  T H I S  WORK WAS PERFORMEi) 
FOR THE J E T  PR3PULS ION LABORATORY, C A L I F O R N I A  I N S T I T U T E  OF 
TECHNOLOGY B Y  AGREEMENT BETWEEN NASA AND DOE. 
PROJECT N O *  2365 
TABLE OF CONTENTS 
SECT l ON 
1 .O 
2.0 
3.0 
4.0 
5.0 
6.0 
7 -0 
8.0 
9.0 
T l TLE 
-
Sumnary statement 
Introduction 
Technical Discussion 
Projected Activities for the Next Three Months 
Recomnendat i ons 
Current Problems 
Work Plan Status 
Action Items 
New Technology 
Program and Documentation Milestones 
PAGE 
-
1 
1 
1 
5 
5 
6 
6 
6 
7 
7 
1 .O SUIJMARY STATWENT 
This report covers the f i r s t  quarter of a one-year program t o  investigate the 
production of patterned etch resistant  wax coatings on solar  c e l l  substrates 
by pr int ing.  
Master molds fo r  p r in t ing  plates have been produced for  the plates. The 
res is t  wax i s  being studied t o  determine i t s  relevant physical properties. A 
p r in t ing  device i s  current ly i n  design, and material costs are being compiled 
as a f i r s t  step i n  a cost analysis task. 
A l l  phases of the project  are proceeding according t o  schedule. No speci f ic  
phases have yet been completed. 
2.0 l NTRODUCT l ON 
The aim o f  'his project  i s  t o  research an al ternate t o  photoresist process- 
ing as presently practiced and applied t o  the production o f  photovoltaic devices. 
The alternate method, p r in t ing  o f  a wax r e s i s t  pattern, i s  designed t o  o f fer  advan- 
tages of  low cost an? high production rates, along wi th the poss ib i l i t y  of recycle 
of used materi a I .  
3.0 TECWICAL DISCUSSION 
3.1 PROBLEMS ASSOCIATE9 WITH CURRENT TECHNOLOGY 
Present solar-cel! processing makes use o f  photoresist (PR), a l ight-sensi t ive 
material, t o  produce etch-resistant, patterned coatings on the cal I substrate 
material. Subsequent operations etch the c e i l  o r  some overlying material - e.9. 
s i l i con  oxide, s i l i con  n i t r i d e  - t o  provide openings fo r  metal l izat ion, de f in i -  
t i o n  o f  mesa areas, etc. The photoresist i s  then removed and discarded along 
with the chemicals used fo r  i t s  development and removal. 
The use of photoresist presents a number o f  problems. The material i t s e l f  
i s  expensive. Being l i g h t  sensitive, PR processing areas must be il luminated by 
yellow safety l i g h t  and must also be carefu l ly  temperature- and humidity-controlled. 
The photographic process by which the PR i s  patterned i s  time consuming, and 
c a l l s  for  expensive exposure equipment and carefu l ly  prepared photographic glass 
plates bearing the Intended pattern image (or  i t s  photographic negative 1. More- 
over, the PR mixtures avai lable are non-reuseable. Once applied and processed, 
the PR undergoes i r revers ib le  chemical a l te ra t ion  and must be chemically destroyed 
i n  order t o  e f fec t  removal from the substrate surface. Other disadvantages 
are also encountered. PR contains organic solvents, such as xylene, which are 
released t o  the atmosphere during use; some PR mixtures generate gas during 
storage, causing pressure build-up i n  the container and causing the container t o  
burst; and v i r t u a l l y  a l l  have l imi ted shelf l i f e .  
The purpose of t h i s  project  i s  t o  investigate the replacement o f  PR use and 
processing by an al ternate method - the use o f  an iner t  wax as an etch res is t  t o  
be applied t o  solar c e l l  substrates i n  patterned form by mans of  a p r in t ing  
technique. The time-consuming exposure o f  PR can thus be eliminated, along wi th 
the requirements for  temperature and humidity control, safety i l lumination, and 
the expense o f  the PR i t se l f .  If i n  addit ion the wax can be recyclable, the 
qdantity (and expense) o f  waste materials w i l l  be greatly reduced. 
3.2 SPECIFIC AREAS OF PROGRESS 
The work done t o  date involves i n i t i a l  preparation o f  materials and acqui- 
s i t i o n  of supplies, as well as progress i n  the fol lowing tasks: Master Mold 
Development, Wax Physical Properties Research, Pr in t ing Device Design, Cost 
Analysis. 
3.2.1 MASTER MOLD DEVELOPMENT 
Master molds f o r  p r i n t i n g  p la tes  have been produced by a Motorola metal etch 
fac i  I i ty. A t  present, copper, steel,  and aluminum m s t e r s  have been prepared i n  
both p o s i t i v e  (pat tern areas ra ised 1 and negati ve (non- image areas ra  i sed) ver- 
sions. Glass master p la tes  are  now i n  preparation. The p la tes  prepared from the  
masters w i l l  be used i n  a p r i n t i n g  method known as le t te rse t ,  i n  which ra ised 
areas o f  the p l a t e  w i l l  bear wax which w i l l  be t ransferred t o  the  c e l l  substrate 
on contact (Figure 1 1. The p r i n t i n g  p la tes  themselves w i l l  be produced by molding 
a substance such as s i l i c o n e  rubber t o  t h e  surface o f  the  master and then separ- 
a t i n g  the molded p l a t e  from i t s  master (Figure 2 ) .  
Also o r i g i n a l l y  planned f o r  study was i n t a g l i o  pr in t ing ,  i n  which wax i s  
borne by depressions i n  the  plate, the  ra ised p l a t e  areas being res i s tan t  t o  wax 
wetting. Surface tension o f  the  wax would cause "beading*' o f  the  wax i n  the  
depressions, resu l t i ng  i n  wax protruding above the ra ised p la te  areas (Figure 3 ) .  
T r i a l s  o f  t h i s  techniq-e showed t h a t  t h e  masking wax had i n s u f f i c i e n t  surface 
tension t o  cause the  required beading. I n  addit ion, a durable wax ant iwet t ing  
agent f o r  the ra ised p l a t e  por t ions was not  found. Stray droplets of wax on 
ra ised p l a t e  por t ions a l so  contr ibuted t o  the  problems associated w i th  t h i s  
method. In  view o f  the  imprac t i ca l i t i es  involved, the  i n t a g l i o  technique has 
been dropped from fur ther  consideration. 
An a l te rnate  metnod o f  l i thographic p r i n t i n g  i s  being investigated. This 
involves the use o f  p r i n t i n g  p lates constructed o f  metals which are se lec t i ve l y  
wet w i th  o i l y  o r  aqueous solutions, thus a l lowing a f l a t  p l a t e  t o  p ick  up wax 
only i n  designated areas. The p l a t e  preparat ion i s  rather  involved and t h i s  
study i s  being pursued as one o f  secondary importance. 
Figure 1 
LETTERF'RESS PRINTING TECHNIOUE 
- 
PRINTING PLATE WITH WAX TRANSFER 
- 
PATTERNED MASKED 
ADHERENT WAX ON CONTACT SUBSTRATE 
W l TH SUBSTRATE 
Figure 2 
PRINTING PLATE PRODUCTION 
MASTER MOLD MASTER W l TH 
CURABLE PR l NT I NG 
PLATE MATER l A L 
F i g u r e  3 
INTAGLIO PRINTING TECHNIQUE 
P!?INTING PLATE 
SEPARATED FROM 
MASTER 
PLATE WITH 
WAX-F I LLED 
DEPRESSIONS 
WAX TRANSFER PATTERNED 
ON CONTACT MASKED SUBSTRATE 
W l TH SUBSTRATE 
3.2.2 WAX PHYS l CAL PROPERT I ES RESEARCH 
Studies fo r  t h e  determination o f  wax physical p roper t ies  are  continuing. 
The f i r s t  inves t iga t ion  i s  on wax adhesion t o  wafer surfaces. This  study i s  
incomplete but suggests t h a t  wax creep may be a problem on textured bare 
s i l i c o n  wafers. The problem may have a so lu t i on  by the  add i t i on  o f  f i l l e r s  
or  thickeners t o  the wax. A search f o r  an e f f e c t i v e  f i l l e r  i s  under way. 
The wax selected f o r  use i n  solvent-wax masking solut ions, Multiwax 
195F4, melts a t  9g0c, forming a low v i s c o s i t y  l i q u i d  which i s  e a s i l y  handled. 
The a v a i l a b i l i t y  o f  inexpensive equipment t o  a t t a i n  and maintain the  modest 
mel t ing temperature of t h i s  wax i s  an add i t iona l  advantage. 
The problem o f  wax removal from wafer surfaces has a l s o  been addressed. 
It has been found t h a t  wax can be removed from c e l l  surfaces by i m e r s i o n  
of the  c e l l s  i n  hot water, during which the wax melts and f l o a t s  t o  the  
surface i n  an eas i l y  removed layer. The process i s  incomplete when pure 
water a t  i t s  boi l i ng po in t  i s  used; aboul 705 o f  t he  app l ied wax i s  removed. 
Addit ion o f  dense s a l t s  such as ammonium s u l f a t e  t o  the  water ra ises  the  
b o i l i n g  temperature and densi ty  o f  t he  water so t h a t  more complete removal 
resul ts .  k!ax removed i n  t h i s  way can be separated from the  water and 
reused. Removal by organic solvents i s  a l s o  pcssible. I f  desired, wax can 
be recovered, and the  solvent pur i f ied ,  f o r  reuse by simple d i s t i l l a t i o n .  
3.2.3 PRINTIN5 DEVICE DESIGN 
The design of a p r i n t i n g  press has begun. The f i r s t  ~ d e l  i s  intended 
t o  be o f  simple form, a l low ing evaluat ion of  p l a t e  performance without 
unnecessary mechanical complication. 
I n  i t s  e a r l i e s t  forn, t he  device w i l l  consis t  of  a vacuum wafer chuck 
over which i s  suspended the  p r i n t i n g  p late.  Contact between the  p l a t e  and 
wafer w i l l  be made by lowering the p l a t e  by means o f  a screw dr ive.  I n i t i a l  
t e s t i n q  o f  the  performance o f  d i f f e r e n t  p l a t e  mater ia ls  w i l l  be made using 
t h i s  device. Modi f icat ions which are necessary t o  increase convenience o r  
u t i l i t y  w i l l  be incorporated i n t o  the  design o f  improved models a t  a l a te r  
date. 
3.2.4 COST ANALY S I S 
Material  costs are being compiled fo r  l a te r  use i n  the  analysis. 
4.0 PROJEC-TED ACT t V  l T l  ES FOR THE P.IEXT THREE !40?!1iiS 
The production o f  master molds fo r  p r i n t i n g  p la tes  i s  expected t o  be 
completed w i th in  the  next few days. Candidate materials f o r  p r i n t i n g  p la tes  
have been and are being selected and p r i n t i n g  p la te  production w i l l  begin. 
Wax physical propert ies are s t i l l  being determined. Addit ional work 
w i l l  be permormed on the  a l t e r a t i o n  o f  wax propert ies through the use of 
f i l l e r s  and thickeners i n  the  wax nix. These e f f o r t s  need t o  be done on the  
basis of information gained i n  p r i n t i n g  t r i a l s  which are scheduled t o  begin 
i n  one mnth .  
Wax r e s i s t  performance w i l l  a lso begin i n  one month. The wax w i l l  be 
applied t o  commonly used s i l i c o n  wafers, and wafers bearing oxide and n i t r i d e  
layers. Both polished and pyramidally textured wafers w i l l  be used. The 
masked wafers w i l l  then be exposed t o  a l l  common etchants and the  masking 
performance noted. 
Cost analys is  w i l l  continue. Further material  costs w i l l  be tabulated, 
along wi th  the  costs f o r  t he  photoresist methods now i n  use. 
5.0 RECOttlMENDAT l ONS 
No recommendat ions are necessary. 
6.0 CURRENT PROBLEMS 
Other than the discovery that intagllo prlnting i s  unsuitable for wax 
* 
printing, no problems have been encountered. 
7.0 WORK PLAN STATUS 
Work is on schedule. 
8.0 ACTION ITEMS 
No urgent action is required on any item. 
9.0 NEW TECHNOLOGY 
No reportable items of new technology have been identified, as yet. 
10.0 PROGRAM AND DOCUMENTATION MILESTONES 
Activities associated with the total program are shown in the Program 
and Documentation Miiestone Charts Figure I and 2 contained in Appendix 1. 
APPENDIX 1 

DOCUMENTATION MILESTONE' CHART 
Monthly F i  nsnc i a  1 Management Report  
- 
Technical L e t t e r  Progress Report 
Quar te r ly  Technical  Report 
D r a f t  F i n a l  Report 
Final Report 
Program Plan 
Basel ine  Cost Est imate  
Manufacturing Process S p e c i f i c a t i o n  
Chemica1/Procc~ss/Equipment Cost Analysis 
L 
MONTH 
1979 
FEB 
--- 
MAR 
A 
- -- 
(Ir 
A 
APR AUG 
A A A A A A A A A  
A 
> 
MAY 
A 
SEP 
A  
JUN 
A 
4 
JUL OCT 
A 
NOV 
A 
I 
DEC 
A  
A 
A 
1980 
JAN 
A 
FEB 
A 
i 
A 


The Development of a Method of Producing Etch Resistant Wax Patterns on Solar Cells

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server