DRL 175 DOE/JPL-956205-84/8Distribution Category UC-63

Quarterly Technical Progress Report

No. 6329-27

on the

DEVELOPMENT OF METALLIZATION PROCESS

FSA Project, Cell and Module Formation Research Area

For the Period Ending

June 30, 1984

Contract 956205

Prepared by:

Alexander Garcia III

Approved by :

Nick MardesichManager , Advanced Programs

SPECTROLAB, INC.12500 Gladstone Avenue

Sylmar, California 91342

July 1984

The JPL Flat Plate Solar Array Project is sponsored by theU.S. Department of Energy and forms part of the Solar Photo-voltaic Conversion Program to initiate a major effort towardthe development of low-cost solar arrays. This work was per-formed for the Jet Propulsion Laboratory, California Instituteof Technology by agreement between NASA and DOE.

https://ntrs.nasa.gov/search.jsp?R=19840025959 2018-08-09T09:28:56+00:00Z

This report was prepared as an account of work sponsoredby the United States Government. Neither the UnitedStates nor the United States Department of Energy, norany of their employees, nor any of their contractors,subcontractors, or their employees., makes any warranty,express or implied, or assumes any legal usefulnessof any information, apparatus, product or process dis-closed, or represents that its use would not infringeprivately-owned rights.

ABSTRACT/SUMMARY

New pastes were evaluated that contained additives to aid in the

silicon-to-metallization contact. None were completely success-

ful. A reevaluation of the molybdenum oxide paste and the two-

step screen printing process was done. The oxide paste did not

show promise. The two-step process enabled soldering of the

cells but the cells still had a high series resistance. Pastes

are on order from a different manufacturer.

TABLE OF CONTENTS

Section Title Paqe

ABSTRACT/SUMMARY i

1.0 INTRODUCTION 1

2.0 TECHNICAL DISCUSSION 2

3.0. CONCLUSION AND RECOMMENDATIONS 12

4.0 ACTIVITIES PROJECTION 12

-11-

Section 1.0

INTRODUCTION

The objective of this contract is the optimization, evaluation,

and demonstration of a novel metallization applied by a screen

printing process. The process will be evaluated on both CZ

and non-CZ silicon wafers.

-1-

Section 2.0

TECHNICAL DISCUSSION

Based upon the SEM work done on the heated stage at Mircoscopy

Research Laboratories, Inc. a set of experiments was done using

the L paste and sintering for long periods of time at lower

temperatures without drying. It was hoped that the nonwetting

of the molten tin particles was caused by an oxide which would

be broken down in time by reaction with hydrogen. Cells were

printed, dryed and placed in the sintering furnace under H- at

400°C. After 4 hours in the furnace cells did not show signs

of sintering. Two new pastes were procured from Electrink.

Table 1 shows the formulations. These formulations were based

on experience at Electrink on silver inks. Paste S is similar

to Paste J with silver flake added and Paste T has bismith

added. The printed cells were sintered at temperatures of up

to 650°C but did not show good curve shape. Typical light and

dark curves are shown in Figures 1 and 2. Higher temperatures

and longer times produced low shunt resistances. Both S and T

behaved in a similar fashion.

More experimentation was done on the molybdenum oxide paste

(Paste M). Sintering temperatures up to 825°C under H2 were

used. The best cell IV curves are shown in Figures 3 and 4.

Cells fired at higher temperatures showed severe shunts. The

low short circuit current is difficult to explain and may be

due to an opaquing layer forming on the cell surface. Cells

fired at temperatures of 825 and 850°C showed metallic-like

-2-

Table 1

PRODUCT INFORMATION

Formulation % by Weight

Item F-86 . F-87

Vehicle Formulation

Item • V-38

a-terpineol . 43.62

Butyl Carbitol Acetate 43.62

Ethyl Cellulose N-14 . 9.76

Thixatrol ST 3.00

Titanium Hydride (TiH2) .55 .55

Molybdenum Powder 14.40 14.40

Tin Powder 57.60 57.60

Frit L1571A 4.45 4.45

Silver Flake Type C ' 8.00

Bismuth Powder - 8.00

Vehicle V-38 15.00 15.00

Identification S • T

-3-

Table 1 (continued)

Frit Composition - % by Weight

Item Frit L1571A

PbO

B2°3

sio2

60

30

10

Material

Titanium Hydride (TiH2)

Silver Flake

Molybenum Powder

Tin Power 325 Mesh

Frit No. L1571A

a-terpineol

Butyl Carbitol Acetate

Ethyl Cellulose

Thixatrol (thickner)

Elvacite (acrylic resin)

Bismuth Powder

Materials Sources

Designation

77113

C

Source

Alfa-Ventron, Danvers, MA

Metz Meta-lurgical, Plainfield,Nj

280/325 GTE Sylvania, Towanda, PA

00352 Alfa-Ventron, Danvers, MA

L1571A . Americal Porcelain Enamel Co.Muskegan, Mich.

TX 75 MCB Chem. Cincinnati, OH

BX 1722 MCB Chem. Cincinnati, OH

N-14 Hercules, Wilmington, DE

ST NL Industries, Hightstown, NJ

2042 Dupont, Wilmington, DE

00046 Alfa-Ventron, Danvers, MA

-4-

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grid patterns which were solderable. However, none of the

solderable cells had measurable IV curves. Spectrolab has

been unable to reproduce earlier research done on this paste

system.

The use of a two-step screen printing sequence was reexamined.

Cells were first printed with J and E pastes, and prefired at

600°C. The pattern left the soldering pad bare. Silver paste

was then printed over the solder pad area overlapping onto the

Mo/Sn metallization. The cell was then fired in air at 750°C

(48"/min., 24" zone at 400°C and 18" zone at 750°C). The cells

were sintered in H- for 5-30 min. at 600-650°C. The best cell

is shown in Figures 5 and 6. There is good continuity between

the ohmic pad and the rest of the metallization but series

resistance is too high.

The problems of this experiment may be due to the paste used.

Earlier work was done using Thick Film Systems' Paste F-503.

The two pastes used here are Electrink equivalents. To ensure

reproducibility an order has been placed for the Thick Film

Systems' F-503 paste. Paste F-503 will be used exclusively in

further work on the two-step process.

-9-

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Section 3.0

CONCLUSION AND RECOMMENDATIONS

There are no conclusions or recommendations to report for the

period.

Section 4.0

ACTIVITIES PROJECTION

During the next quarter additional pastes will be evaluated.

Work on the two-step process will continue with the new paste.

Economic analyses of the processes will be done using an IPEG

analysis. The program will be concluded in this quarter.

-12-