DIU No. 216 

DRD NO. SE-2 

DOB/JPL 956 831-1 

Distribution Category UC-63 

PULSED EXCIHBR LASER PROGgSSIX 

FOR COST-EFFECTIVE SOLAR CELLS 

Quarterly Report No. 1 

Hay - July 1984 

Prepared By 

D. Wong 

Principal Investiga 

Approved By - 

Program Manager 

ARC0 Solar, Inc. 

P. 0. Box 2105 

Chatsworth, California 91311 

The JPL Plat-Plate Solar Array Project is sponsored by the U.S. 

Department of Energy and forms part of the solar Photovoltaic 

Conversiori Program to initiate a major effort toward the 

development of low-cost solar arrays. This work was performed 

for the Jet Prcpulsion Laboratory, California Institute of 

Technology, by agreement between NASA and DOE. 
This work was performed for the Jet Propulsion Laboratory, 

California Institute of Technology, and vas sponsored by the U.S. 

Department of Energy through an agreement with the National 

Aeronautics and Space Administration. 

This report was prepared as an account of work sponsored by an 

agency of the United States Government. Neither the United 

States Government nor any agency thereof, nor any ot their 

employees, makes any warranty, express or implied, or assumes any 

legal liability or responsibility for the accuracy, completeness 

or usefulness of any information, apparatus, product or process 

disclosed, or represents that its use would not infringe 

privately owned rights. 

Reference herein to any specific commercial product, process, or 

service by trade rime, trademark manufacturer, or otherwise, does 

not necessarily constitute or imply its endorsement, 

recomendatim, or favoring by the United States Government or 

any agency thereof. The views and opinions of authors expressed 

herein do not necessarily state or reflect thcse of the United 

State6 Government or any agency thereof. 

- il - 
The objective of this contract is to develop a solar cell process 

sequence that incorporates three process steps which use pulsed excimer lasers, to verify that this sequence yields high 

efficiency cells at a low cost, and to document the feasibility 

of carrying this technology from the laboratory bench scale to 

factory size. The three process steps are: junction formation, 

surface passivation, and front metallization. The effort is to 

take place during a one-year period. 

During this reporting period, a series of annealing experiments 

were conducted. Parameter variations included beam energy 

density, percentage of beam overlap, sources of diffusant, and 

different surface conditions such as chemical-mechanical 

polisnea, caustic etchea, and textured. Diff usant deposition 

included spin-on liquid dopant and ion implant. 

Due to the lower surface reflectivity 2nd the "wetting" erfect by 

the spin-on source, textured wafers experienced more surface 

dazage and stress than polished wafers. Maximum cell efficiency 

obtained for Cz polished wafers was 9% and for Cz textured wafers 

was 11.5% (no WR). Surface damage limited the cell efficiency. 

Laser annealing on ioc-implanted wafers was conducted with 

phosphorus implant with acceleration energy of 10 keV at fluences 

of l-SxlO15 atom/crn2. Haximum cell efficiency was less than 8% 

(no A/R coating). Low JSC, VOC, and fill factor suggested 

incomplete implant damage removal. 

Decreasing the implant voltage from 10 keV to 5 keV and 

increasing laser energy to above 0.9 J/cm2, some cell 

efficiencies over 9.4% before A/R. The goal of producing cells 

of 16.5% has not materialized due to problems in ion implant 

uniformity, unavailable low keV ion implant, and laser beam 

inhomogeneity. 

During the next period, work will focus on developing a 1 keV 

glow discharge capability and on fabrication of Boron implanted 

junctions on n type wafers, 

- iii - 
1.0 Introduction and Sullll(lary .................................. 1 

2.0 Progress .................................................. 3 

2.1 Development of Process Sequence Selection ............ 3 

2.2 Laser Equi~ent ...................................... 4 

2.2.1 Small Scale Laser .............................. 4 

2.2.1.1 Optical System ........................ 4 

2.2.1.2 Computer Control System ............... 9 

2.2.1.3 Optical Diagnostics ................... 9 

2.2.2 High Energy Excimer Laser (Lucy) .............. 9 

2.2.2.1 Motion Control and Laser Firing ....... 11 

2.2.2.2 Optical Diagnostics ................... 13 

2.2.3 Reticon Array for Beam Profiling .............. 13 

2.3 Quarterly Activities ................................. 23 

3.0 Significant Experimental Results .......................... 29 

3.1 Liquid Dopant ........................................ 29 

3.1.1 Textured Surface .............................. 29 

3.1.2 Chemically Polished Surface ................... 31 

3.2 Ion Impanted Emitter ................................. 34 

4.0 Discussion of Experimental Results ........................ 45 

5.0 Target Process Selection Report ........................... 49 

5.1 Process Selection .................................... 49 

5.1.3 Baseline Prices ............................... 49 

5.1.2 Description of the preliminary laser process .. 51 

5.2 Economic Analysis .................................... 53 

5.2.1 Approach ...................................... 53 

5.2.2 Results ....................................... 54 

Excimer Laser Applications ........... 58 

5.2.2.1 Discussion of Cost Elements of 

5.2.3 IPEG Analysis of Specific Laser Processes ..... 58 

6.0 Program Status and Plans .................................. 63 

References .................................................... .67 
CO~loTs (continued) 

Tables 

1. Excimer laser annealing parameters........................25 

2. Textured Cz p-type war'er with spin-on source laser 

annealed: 

a. 

b. 

c. 

at 0.4 J/cmZ with 70% overlap. ........................ 29 

at 0.4 J/cm2 with 70% over-lap followed by furnace 

heat treatment at 65OOC for 30 minutes................31 

at 0.7 J/cmZ with 50% overlap. ........................ 31 

3. Cells fabricated from polished Cz p-type wafer with 

spin-on source, laser annealed at energies: 0.9, 1.2 

and 1.6 J/cm2... ......................................... 32 

4. Cell performance of thermally diffused wafers, 

caustic polished with spin-on source as dopant ........... 34 

5. Results of laser annealing for caustic olish, 10 keV 

ion implant with dosage 5x1015 and 1x10 Y 5 

5 keV ion implanted with 2.5~1015 atom/ca s dosage. . . . . . . .37 

atoms/cm2, respectively. ................................ -34 

6. Results of laser annealing for chem-mech olished wafers 

7. First experimental result with the large laser, "Lucy", 

at density 1.4 and 1.6 J/cm2, respectively.. ............. 39 

8. Results of annealing by large laser with lower 

energy density and overlap %.............................41 

9. Laser annealing for wafer with thermal N+ deposition. 

Control cells were thermally diffused. All cells 

without A/R..................*..........................,42 

10. Cost Summary - JPL Sample Sequence ....................... 55 

11. Cost Summary - Proposed Laser Process....................56 

1. Laser annealing processe sequences for 

the First Quarter........................................ 3 

2. Second phase process sequence............................ 4 

3. Laboratory arrangement for excimer laser processing 

of silicon solar cells................................... 6 

4. Excimer laser annealing facility... ............. ......... 7 

5. Typical laser pulse shapes used in laser annealing 

process studies.......................~.................... 8 

- vi - 
cOWl%llTS (continued) 

6 . 

7 . 

8 . 

9 . 

10 . 

11 . 

12 . 

13 . 

14 . 

15 . 

16 . 

17a . 

17b . 

18a . 

18b . 

19 . 

20 

Scan patterns ............................................ 10 

Laboratory layout for large excimer annealing process .... 12 

Intensity vs . time from large x-ray preionized 

excimer laser using XeCl (308 nm) ........................ 14 

Input He-Ne beam used for testing kaleidoscope 

beam homogenizer ......................................... 16 

Optical set-up for kaleidoscope testing .................. 17 

f/4 oPtics ............................................... 19 

Beam profile demagnified 2x and reimaged ................. 20 

Beam profile at exit plane of kaleidoscope using 

Beam profile at exit plane of kaleidoscope using 

Profile of excimer output beam ........................... 22 

f/6 input optics ......................................... 21 

Quartery Activities ...................................... 23 

500x SEM of textured surface (with spin-on li uid 

(b) 0.7 J/cm2 and (c) 1.2 J/cm2 .......................... 31 

dopant) after laser annealing at (a) 0.4 J/cm 9 ........... 30 

Laser annealing (B7-3F) at 0.9 J/cmZ on caustic 

polished surface with spin-on liquid dopant source . Heavy melting and surface damage are clearly shown ....... 33 

Pimple t pe crater defects on surface annealed at 

1.2 J/cm 3 ................................................ 33 

Electrical characteristics of a thermally diffused N+ 

spin-on liquid source on p substrates. light I-V ......... 35 

Electrical characteristics of a thermally diffused N+ 

spin-on liquid source on p substrates. dark I-V .......... 36 

Baseline material characterization of PZ wafers 

by thermal (POCl3) diffusion . Spin-on A/R coating ....... 38 

Laser annealing on 5 KeV. 2.5 x 1015 atom/cd ion 

implanted surfaces at 1.3 J/cm2. with 70% overlap 

pulse duration estimated 6ns (B-9) ....................... 40 

. vii . 
COIUTBNTS (continued) 

21a. 

21b. 

22 . 

23 . 

24. 

25. 

26 . 

27 . 

Light and dark I-V curves for typical cells from 

thermal N+ deposition and diffusion......................43 

Light and dark I-V curves for typical cells from 

thermal N+ deposition and laser drive at 1.25 J/cm*, 

10% overlap ............................................ ..44 

SIMS depth profile for 31p+ ion implanted at 5 KeV, 

2.5 x 1015 atom per cm2. 

-0.3 

Substrate resistivity 

ohms-cm boron doped ................................ -46 

Laser scanning of hi hly damaged surface laser 

annealed at 1.3 J/cm%, 70% overlap factor 

(B9-#4). Heavy recombination at the center of 

overlapped area is clearly revealed..................-...47 

Baseline process. 5.2" diameter, p type (boron 

doped) 0.3 ohm-cm Cz silicon.............................50 

Preliminary laser process. 5.2" diameterr n tyke (phosphorus doped) 0.3 ohm-cm Cz silicon.............. .. .52 

IPEG coefficients for JPL sample process sequence.. ..... -57 

Program schedule.............................~...........64 

- viii - 
The objective of this Contract is to develop a solar cell process 

sequence that incorporates three process steps which use pulsed excimer lasers, to verify that this sequence yields high 

efficiency cells at a low cost, and to document the feasibility 

of carrying this technology from the laboratory bench scale to 

factory size. The three process steps are: junction formation, 

surface passivation, and front metallization. This effort is to 

take place during a one-year period. The first quarter 

accomplisnment targets the completion of 25 2x2 cm2 cells of 

16.5% efficiency measured at AH1.5 insolation. 

This quarterly report summarizes the technical progress made 

since the contract initiation date of Hay 4, 1984. 

During this reporting period, a series of annealing experiments 

were conaucted. Parameter variations included beam energy 

density, percentage of beam overlap, 8ources of diffusant, and 

various surface conditions including chemical-mechanical polish, caustic etch, and texture. Diffusant deposition included spin-on 

liquid dopant and ion implant. 

Due to the lower surface reflectivity and the 'wetting' erfect by 

the spin-on source, textured wafers are believed to experience 

more surface damage and stress than polished wafers. !hXiRlUh 

ceil efficiency chained for Cz polished wafers was 9% and for Cz 

textured wafers was 11.5%, without anitreflection (A/R) coating. Surface damaop appears to limit the cell efficiency in both 

cases. 

Laser annealing of ion-implante? wafers wae first conducted for 

phosphorlis implants with acceleration energy of 10 keV at 

f luence8 of l.-5xl0~~atom/cia~. Maximum cell efficiency obtained 

had heen less than 8% (50 A/R coating). The low Jsc, Voc, and 

fi1.I factor suggested incomplete implant c'.amage removal. 

By decreasing rhs implant voltage from 10 keV to 5;keV while 

increasing laser energy to above 0.9 J/cm2, cell efficiency over 

9.4% was obt.rined before AIR (13.7% after A/R). The goal of 

producing cells of 16.5% has not materialized due to problems of 

ion implant nonuniformity, unavailable low keV ion implant 

sources, and laser beam inhomogeneity. 

Ion implantation as the dopant source is still being investigated 

to produce hiqh-efficiency cells because of its potential for a 

high purity, tailored junction. 

This quarterly report includes work tor both ion-implanted and 

spin-on dopant sources. The two important factors for 

experimentatim are laser energy density and overlap. The set of 

variables and their permutat' sns to be investigated originally included surface conditions \texture vs. chemical polish), dopant 

sources, laser energy density, and overlap ratio, none of which 

-1- 
is independent of the others. 

As yet, neither a comprehensive model nor a complete experimental 

matrix has been established that covers all of the issues that 

must be addressed in developing a viable low cost, high 

efficiency solar cell. At this stage we will draw on relevant 

segments of the literature combined with our results to piece 

together an empirical model that explains and wil serve to guide 

the laser annealing experiments being conducted. 

-2- 
2.0 PBOGRESS 

2.1 DEVELOPHBNT OF PROCESS SEQUENCE SELECTION 

The laser process sequences investigated in the first part of the 

program are schematically shown in Fig. 1. 

NaOH Etch NaOH Etch 

Ion Implant Spin 0; Dopant 

1 Laser Anneal 1 L;lser Anneal 

1 

Me tal 1 ize 

1 

Test 

I 

Met a1 1 iz e 

I 

Test 

Fig. 1. Laser annealing process sequences for the First Quarter. 

There were two parallel processes in the early stage of the 

program: one with ion implantation as the dopant source, the 

other with spin-on liquid dopant. P-type substrates grown by 

ARC0 Solar were predominantly used because of their availability 

and their well-characterized properties. Both n-type and p-type 

Czochralski substrates were used based on 3-in. and 4-in. round 

slices as well as 4-in. squares. Floatzoned mciterial had also 

been used as control samples occasionally. 

After a series of experiments using liquid dopant sources without 

promising results, the process was discontinued. Instead, ion 

implantation has been substituted for N+ deposition on 

mechanically polished wafers as baseline experiments. 

Optimizea laser annealing parameters have been derived by an 

iterative method. Variables include energy density, pulse duration time, beam uniformity, and substrate temperature. Wafer 

cleaning ana cell fabrication follow conventional methods, such 

as organic solution rinses, acid rinsing, and evaporated 

contacts . In the later stages of the program, laser-assisted pattern 

writing for front grid lines and surface oxide growth for 

passivation will be investigated. The second phase of the laser 

annealing process is shown in Fig. 2. 

-3- 
NaOg Etch 

Dopant Incorporation 

Laser Anneal 

Surf ace Passivation 

(i) Laser Assisted 

(ii) Thermal Oxidation 

Fine Gridline Metallization 

(i) Laser Assisted 

(i i) Lithographic 

1 

I 

1 

1 

* Test 

Fig. 2. Second phase process sequence. 

2.2.1 

2.2.1.1 Optical System 

The optical system used for laser annealing of silicon wafers by 

the small scale EXCI-LITE-1 laser is zhown in Fig. 3. The laser 

source, optical train components, x-y motorized stage, and 

ancillary components are located on a 3x6-ft tab,e with magnetic 

top surface. The optical component holders are secured to the 

table with magnetic bases. 

The laser source is an EXCI-LITE-1 excimer laser which produces 

4-20 nsec (EWH) wide output pulses with repetition rates of up to 

200 Hz. The present output wavelength is 308 run and the average 

laser output energy pr pulse is 13-20 mJ. No pulse drop-outs 

have been observed in over 106 shots. The output beam has a 

square cross section of 0.8 x 0.6 mm. The light output is 

essentially incoherent and thus interference effects at the work 

surface are absent. The beam divergence is approximately 10 mrad 

full angle. 

Adjustment of the pulse output duration was achieved by variation 

of the gas mixture. Figure 5n shows the temporal pulse profile using a gas mix of 0.2% Xe, 0.015% HCl with a buffer gas of He at 

-4- 
50 psig. A width of approximately 6 ns is observed. Upon 

substitution of Ne for He, the double pulse shown in Fig. 5b is 

observed. Such a pulse format will affect the surface annealing 

process more like a long pulse of duration -20 ns. 

The output beam is steered to the proper height with the beam 

elevator consisting of mirrors M1 and M2 shown in Fig. 4. The 

mirrors are coated with a dielectric multilayer stack selected 

for high reflectivity and independence of reflectivity with 

polarization at the design wavelength and angle of incidence 

(45O). Thus the originally unpolarized light remains 

unpolarized. An optional square aperture may be placed between 

the laser and the subsequent optical elements to create an image 

at the work surface with sharp edges. Aperture insertion loss is 

20-50%, depending on aperture size. The light is directed to an 

overhead support stand (not shown) which holds lenses L1 (focal 

length If.11 = 35 cm) and 12 (f.1 = 10 cm) as well as tne 90' 

bending mirror M3. The sy*cing between L3 and L2 may be varied, 

thus changing the effectivt focal length of the combination. The 

distance of L2 from the work surface can be adjusted, which 

allows variation of the image size at the work surface and 

permits variation of the energy density of the laser. This 

density may also be varied in a controlled manner by inserting neutral density filters (not shown). Lens L2 is moved axially in 

a coarse manner along tracks cut into the support stand, and is 

mounted on a precision translation stage to permit fine fccal 

length adjustments. The overhead 90' bending mirror M3 is also 

angularly adjustable to ailow proper centration of the light 

through L2 and ensure that the light is normal to the wafer 

surface. After proper alignment and positioning of all optical 

components the optical throughput is -66% (without aperture), the 

main losses occurring at the four uncoated surfaces of lenses L1 

and L2. The overhead support structure includes two separate, 

independent stations for steering mirrors and lenses. The second 

station (not shown) can hold optics for a second laser annealing 

stat ion. 

The two-stage motorized x-y annealing platform is located 

directly beneath the overhead optical support stand. It may be 

positioned below either of the two optical stations using a 

unislide. The mot-rrized stages execute excursions up to 6 in. 

and 4 in. respectively in the x-y directions at table speeds of 

up to 1 in./sec. The wafer is held securly in place with an 

aspirator-based vacuum chuck system. Vapor and dust from the 

annealing process are removed by a vacuum system. The glass 

plate is used as the top surface on the wafer holder table and 

used for processing wafers up to and including the edge, thus 

eliminating any wasted mate,ial. The entire x-y stage and wafer 

holder are enclosed in a Plexiglas box to exclude dust during the 

processing. A gas purge of the wafer surface is employed duriag 

the processing to reduce the chance of foreign material being 

deposited on the surface during annealing. 

-5- 
X-Y TRANSLATCP. 

I 

1-1 ANhEALXNG FACILITY 

7 

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GAS 

CAB I hTT 

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GAS PROCESS CWBER 

OFTXCAL TABLE 

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EXCXMER LASER PHOT3DEPOS:TIOK 

FACILITY 

C XTROL 

COh'SCiE 

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WET 

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10 nsec/Div 

Long Pulse Using Neon Di luent 

Fig. 5. Typical Laser Pulse Shapes Used in Laser Annealing 

Process Studies. 

- 8- 
2 . 2 . 1 . 2 Computer Control System 

Both stepper motor controlled stages and the stepper motor 

sequencer and power supply were supplied by Daedal and were 

automated using an LSI-11 based computer as master coctroller, 

and appropriate electronics for control of laser triggering and 

table motion. The control program uses the parallel interface 

for 110 control of the sequence and laser firing. The control 

program was written in Macro-11 assembly language to optimize 

timing and execution speed. 

The control program is capable of executing several distinct scan 

patterns designed arou: A the two wafer geometrics which were 

laser annealed during this reporting period. The first pattern 

is a standard raster scan with user selectable pulse overlap in 

both directions. Both table speed and wafer size are also 

selectable. Based upon the input values of effective spot size 

and table speed, the computer controls and fires the laser at the 

correct frequency and allows for table acceleration time. The 

total number of scan lines required to cover a given annealed 

area is also computed and used to control the scan. User input 

to the program is over the serial interface to the terminal Shawn 

in Pig. 4. A given scan may also be aborted from the keyboard if 

desired. The annealed area resulting from the first scan pattern 

is square or rectangular. For circular wafers, to anneal as 

large an area as possible, a diagonal type annealing pattern 

(shown in Fig. 6) is employed. Such a pattern allows nearly the 

entire surface area of a round wafer to be lised for solar cell 

fabrication. Control of all experiment parameters is available 

through the terminal. The control signals sent by the computer 

to the sequencer are shown in Fig. 4. A single power supply is 

used for both motors by multiplexing the sequencer output using relays in the control box. The current scan patterns do not 

require that both motors be operated concurrently, so this scheme 

is quite satisfactory. 

2.2.1.3 Optical Diagnostics 

Average energy measurements of the laser output as a function of 

repetition rate have been performed using a Scientech 

calorimetric type power meter. Temporal pulse width measurements 

were performed with a fast PIN photodiode and a 1 GHz bandwidth 

oscilloscope. Both widths and amplitudes showed very little 

pulse-to-pulse variation. A roush measurement of the transverse 

spatial profile using a PIN detector and a small pinhole which 

was moved across the beam gave qualitative results indicating non-uniformity of the transverse energy profile. More refined 

beam profile equipment is being developed to improve the latter 

diagnostic (see Section 2.2.3) . 

A 

2.2.2 

second 

* 

laboratory contains a high energy x-ray preionized 

excimer laser that also is being used for experiments on laser 

- 9- 
c 

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e 

m 

P 

a 

a 

4 
annealed junction formation. The laser was designed for 

experimental research on various excimer lasers, and has been 

adapted to the present laser annealing experiments with minimal 

changes . The laboratory set-up is shown schematically in Fig. 7. The 

laser and energy storage supplies occupy the central area of the 

rocm, The control panels and screen room for diagnostics are 

located well away from the regions of high voltage, high gas 

pressure, and high laser intensity. Regular monitoring of the 

x-ray generation by the device is done in order to maintain a 

safe working environment for personnel. The output of the laser 

is reimaged on the x-y trarAslation table through a reflective 

mirror that permits passage and return of the Be-Ne alignment laser. 

The excimer laser discharge chamber is made of Lucite with 

aluminum electrodes, One of the electrodes is milled very thin 

and transmits x-rays with very little loss. An x-ray collimator 

is also used to provide good spatial uniformity of the x-ray flux 

over the full aperture of the source. The x-ray generator is a 

broad area, high voltage electron gun operating at about 250 kV 

for 500 nsec. The electrodes are pulse charged to just below the 

self-break voltage, and the x-ray preionizer acts as the switch, 

ionizing the laser gas and causing voltage breakdown, A 

dielectric pulse forming line then provides current to the 

discharge at its self-sustaining voltage for about 75 nsec. 

The discharge volume is 75 cm long by 4 cm between electrodes by 

3.5 cm wide. The laser chamber includes 4 in. diameter A/R 

coated windows at each end. An external 20 meter radius of 

curvature total reflector and a 30% reflective flat output 

coupler form the optical cavity, To provide sharp beam edges, a 

rectangular aperture is included in the cavity just inside the 

output coupler. A He-Ne laser is used to establish good alignment of the cavity mirrors with each other and with the 

optical axis defined by the electrodes and the rectangular optical aperture. The focusing lens is positioned to form an 

image of the laser aperture at the wafer, and to provide a size 

reduction of about 3 to 1. The lens can be adjusted axially to 

vary the spot size, thereby providing variation in energy density 

on the wafer, 

Since the large laser was originally fabricated for single pulse 

experiments, the construction materials limit the gas lifetime. 

To reduce the interaction between the laser gas and Lucite walls, 

a Teflon liner was introduced. At present the laser output remains constant (within 10%) for about 30 pulses before 

requiring replacement of a portion of the gas to bring the energy 

back to its original value. 

2.2.2.1 Motion Control and Laser Firing 

The large laser processing station consists of the beam transport 

- 11 - 
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optics as previously described and a two-axis, DC motor-driven 

table supplied by Aerotech. The table position is sensed by an 

integrated shaft encoder and direction, speed (feedrate) and 

position are determined by a programmable Aerotech motion 

controller, the Unidex 111. Currently the motion controller is 

not interfacec'! to an external computer as in the case of the 

small excimer laser processing station, and both positioning and 

firing of the large laser are performed manually. To avoid the 

possibility of electronic damage to the controller during the 

high voltage electrical discharge of the large laser, the 

controller is turned off during laser firing. The battery backed-up internal memory of the controller permits the operator 

to return the table to the last position processed and then to 

advance to the next area to be annealed. It should be noted that 

in the future these steps could be automated as in the case of 

the small laser processing station described in Section 2.2.1. 

2.2.2.2 Optical Diagnostics 

A volume absorption calorimeter is used to determine pulse energy 

from the laser. The intensity distribution and spot size are 

determined by using photosensitive paper and by examining the 

surface of wafers that have been processed by a single spot. The 

pulse duration is monitored on each pulse by a fast response 

photodetector viewing the signal transmitted by the total 

reflector. A typical pulse is shown in Fig. 8. 

2.2.3 e Profilina 

During this quarter a reticon array with associated frame 

digitizing features was developed, tested, and used to determine 

the characteristics of two optical beam homogenizers. In the 

current configuration, the reticon diagnostic digitizes and 

stores light intensity data at the rate of -400 kHz. The array 

is designed to be used to characterize short time duration 

(compared with the frame time) pulses typical of excimer lasers 

used for laser annealing. These arrays are particularly useful 

for studying light intensity distributions in the W regime since 

they possess a quartz window and adequate wavelength response to 

0.2 pm. This is in contrast to their major competitor, CCD 

arrays? which typically respond only to wavelengths greater than 

0.4 pm. 

The array consists of 32x32 individual pixels spaced on 100 pm 

centers. Each individual photodiode current is stored on an 

integrated capacitor and read out (through an integrated shift 

register) every 4 msec, thus zeroing the array. By initiating the triggering of the excimer laser on the end-of-frame signal 

provided by the reticon array, a single shot of video 

information, representing the laser pulse, may be colleccted. 

Since the PDP-11 computer cannot digitize and store information 

at the high speeds required to minimize array dark count, a 

special timing and digitizing board was designed around an 

AMD6108 8-bit A/D (1 MHz maximum rate) and fast (150 nsec) video 

- 13 - 
25 50 75 100 125 150 175 

TI=, nsec 

Fig. 8. Intensity Versus Time From Large X-Ray Preionized 

Excimer Laser Using XeC1 at 308 nm. 

- 14 - 
memory. The current amount of video memory is sufficient to 

store 8 successive frames of spatial intensity information. The 

individual photodiodes have a dynamic range (nanufacturer's data) 

of nearly 2000:l; thus the sensitivity of the array is limited by 

the 1 bit quantization error (measured) of the A/D converter. 

Thus -0.501% sensitivity is possible. 

During the testing phase of the array, dark count data were 

collected and stored jn a data file. These data were then 

averaged and used to subtract the dark count from the actual 

laser beam intensity profile. The pixel-to-pixel variation in 

response was tested by uniformly illuminating the array with a 

diffuse light source. The resulting variation was less than 5%. 

These data were also stored to provide appropriate response scaling if desired. This information is then transferred to a 

PDP-11 computer and saved in a diskette data file. The 

information is then transferred to a VAX 111780 computer where a 

Gaussian curve fit routine may be used to extract pertinent 

information on the spatial size and ellipticity of the pulse. 

Also, a contour plotting routine may be employed to give direct 

visual information concerning the two dimensional energy 

distribution. Such information is shown in Fig. 9 which is the 

output of a small BeNe laser. The output is Gaussian as 

expected, and the profile was found to be slightly elliptical. 

To characterize the optical kaleidoscope to be used for beam 

homogenization of the EXCI-LITE-1 laser, the same HeNe beam was 

used to test the performance of the kaleidoscope, as well as the 

influence of the f/# (which determines the number of internal 

reflections) of the input optics on the uniformity of the output 

beam. The first optical set-up is shown in Fig. 10. To closely 

approximate the behavior of the excimer laser, the small HeNe (W 

= 0.45 mm) beam was expanded in the telescope consisting of a 2 

mm lens followed by a 250 mm lens. The resulting beam was then 

focused into the kaleidoscope using the 40 mm lens shown. The 

f/4 input optics resulted in the fairly uniform beam shown in 

Fig. 11. This profile was taken at the output of the 

kaleidoscope and measured 3x3 mm. To test our ability to reduce 

this object size to ar! image size compatible with our desired 

energy density at the work surface, an f/l optic was used at a 

2:l conjugate ratio with the resulting image shown in Fig. 12. 

The image is both square and possesses a rapid drop-off in 

intensity at the edges. The uniformity of the beam could be 

improved over that shown in Figs. 11 and 12 if the input and 

output faces of the kaleidoscope were better polished. An 

imperfection in at least one of the faces was observed to lead to 

spurious light scattering. The conclusion from this experiment is that f/4 input optics are sufficient to homogenize the beam to 

the 27% level. Figure 12 indicates that beam overlapping of 

100-200 m at the work surface should be sufficient. 

! 

In another series of experiments the 5x5 mrn kaleidoscope was used 

with the identical optical train. The resulting output was too 

large to record in a single shot on the reticon, but by scanning 

- 15 - 
0 0 

3200 

RELATIVE 

INTENSITY 

Fig. 9. Input He-Ne Beam Used for Testing Kaleidoscope Beam 

Homogenizer . 

- 16 - 
'A 

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the array across the optical field the output (using f/4 input 

optics) was found to be as uniform as that shown in Fig. 8 for 

the 3x3 mm kaleidoscope. The difficulty with the 5x5 mm 

kaleidoscope stems from the large size reduction ratio required 

to achieve energy densities of -1.2 J/cm2 at the work surface. 

Thus, although the 5x5 mm kaleidoscope is of superior optical quality, it is not suitable for the EXCI-LITE-1 at present. 

Recently three 2~2x100 mm kaleidoscopes of better optical quality 

were ordered. f/l optics will be used to reduce the image size 

to about 1 mm square. The new kaleidoscopes will have beveled 

edges to prevent chipping during the polishing process, and will 

have a high polish on all six surfaces. This will then require a 

laser energy of 12 mJ at the work surface. Since 60-70% of the 

input light is present at the kaleidoscope output, the required laser output energy is -20 m~. 

It was found that with careful alignment and optimization using 

the reticon array diagnostic, even fewer internal reflections 

(such as provided by f/6 optics) can yield sharp edges and good 

beam uniformity (see Fig. 13). The picture in Fig. 11 was taken 

with the image slightly offset from the center of the reticon to 

illustrate the sharp intensity gradient at the edges. This is an 

obviously desirable characteristic with regard to successful 

laser annealing of silicon wafers. 

In a recent set of experiments, the actual output beam (suitably 

attenuated) of the small excimer laser previously described in 

Section 3.1 was characterized by the reticon array. Figure 14 

shows the resulting profile of the beam. The intensity was 

reduced 107 using N.D. filters and then the spot was reduced to 

-2x2 mn using a single simple 250 nun lens. In addition, several 

other independent profiles at the identical image plane were taken to determine shot to shot variation in energy distribution. 

It was found that although the energy centroid remained 

approximately constant, intensity spikes occurred which are 

undesired, and will be removed by beam homogenization. 

- 18 - 
RE L AT WE 

INTENSITY 

3200 

Fig. 11. Beam Profile at Exit Plane of Kaleidoscope Usfng f/4 

Input Optics. 

- 19 = 
RELATIVE 

INTENSITY 

C 

3200 

Fig. 12. Beam Profile Demagnified 2x and Reimaged. 

- 20 - 
RELATIVE 

INTENSITY 

3200 

Fig. 13. Beam Profile at Exit Plane of Kaleidoscope Using f/6 

Input Optics. 

- 21 - 
FIEC AT IVE 

INTENSITY 

0 

3200 

Fig. 14. Profile of Excimer Output Beam. 

- 22 - 
2.3 QUARTERLY ACTIVITIES 

Figure 15 describes the quarterly activity. 

I As Sawn I 

I Wafers I 

I PtYpe 1 

I Cbem-Mech I PZ I I 

--I Polish I I cz 

II I 

I I NaOe 209 I 

I 111 1 I I I I 

I'~P+ Ion Implant1 I I I I 

I 5 keV I 

li) 1 I 1015 I ITexture I I Spin-on I lPJ1 Ion Implant I lP3I 1.1 1 

tii) 2.5 x 1015 I 12% raoe I I (1 250) I I 10 keV I I 10 keV I 

I 11 11 I1 i 1015 I I 5 10151 

I I I I II I 

I I I I I 

I I I I I 

I I I 

ti) EXCI-LITE I I ISpin-On I I I I Furnace II 

I 20 ns I It1 250) I I 1-1 Diffusion II 

I II I I I 82OoC, 1.5 hr I I 

lii) 4J Laser I I I I II 

I 80-90 ns I I I I II 

I I I I I 

I I I 

I I ILaser Anneal EXCI-LITE I I I 

I I I 1) 6 ns (sing!e pulse) I- I 

I I 2) 20 ns (double pulse) I 

I I I 

I I 

I i 

I 

I (Ifla I (11)b I (I)a I (I)b 

I Furnace I 

I I I Stress-Relieve1 

I Ratallization I,--I 63OOC for I 

I I I 1.5 hours I 

I I I 

I 

I Cell Test I 

I I 

i) Starting material included Cz, both texturized and caustic 

ii) Emitter dopants of spin-on source were Emulsitone N250 and 

iii) 31P+ ion implantation at 10 keV and 5 keV with 1, 5, 

etched, and PZ which was chem-mechanically polished. 

Allied Chemical PX-IO respectively. 

2.5~1015 atoms/cd f luence respectively. 

iv) Laser used had been EXCI-LITE 1 (small XeCl laser) and 

"Lucy" (large 4 J laser). 

v) Metallization has been by shadow mask evaporation method, 

with 92% active area. Lithography will be applied in the 

2nd quarter. 

- 23 - 
vi) Cells were tested at direct AM1.5 with SERI calibrated cell 

Y128 which was found identical with the reference cell 

provided by JPL #MT-472. 

vii) Sequence of experiments with various laser parameters and 

implantation are summarized in Table 1. 

- 24 - 
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Results 

e 

can be separated into two major categories, spin-on 

dopant source and ion implantation. All annealing experiments for liquid dopants were conducted with the EXCI-LITE laser with a 

beam spot of approximately 0.6x0.8 mm. In the early stage of 

annealing ion implanted wafers, the EXCI-LITE laser was also 

used. However, in order to obtain minimum overlap percentage and 

to get the best uniformity available, a more powerful 45 laser 

was used. 

3.1 LIQUID DOPANT 

The annealing experiment was started using a phosphxus spin-on 

dopant source on p-type Cz wafers of 0.7 ohm-cm base resistivity. 

Surface conditions included chemical polish and texture. 

Threshold laser energy was found to be different for the two due 

to differencss in surface reflectivity as expected. 

3.1.1 

Energy density as low as 0.4 J/cm2 (70% overlap) was found 

sufficient to melt the texturized surface. However, cells were 

almost all badly shunted (Table 2a). A sister wafer (2x4 in.) 

that had been laser annealed at the same settings went through an 

additional furnace heat treatment at 65OOC for 30 minutes betore 

metallization. This cell had its efficiency improved to as high 

as 11.7% (Table 2b). Such low temperature heat treatment is 

believed to stress-relieve the melt-recrystallized surface. 

Cell performance of 0.7 J/cm2 annealing with 50% overlap shawed 

further improvement. Highest cell efficiency was about i1.6% 

before A/R coating (Table 2c). Heat treatment to the 0.7 J/cm2 

annealed wafer did not show obvious imprwement. A possible 

explanation could be that 0.7 J/cm2was sufficient to cause more 

complete surface regrowth with less relievable stress. In fact, 

SEM photographs of these two samples indicated much more surface 

resolidification with 0.7 J/cm2 than with 0.4 J’cm2 (Fig. 16). 

Table 2. Textured Cz p-type wafer with spin-on source laser 

annealed : 

a. At 0.4 J/d with 70% overlap. 

Cell I Voc, I J c, I FF, I Eff, 

ID I V I mA7cm2 I % I % 

B5B 1 I 0.429 I 28.32 I 59.60 1-7.24 

2 I 0.406 I 28.26 I 57.30 I 6.56 

3 I 0.399 I 28.24 I 55.40 I 6.25 

4 I 0.434 I 27.89 I 57.60 I 6.97 

b. At 0.4 J/cm2 with 70% overlap followed by 

furnace heat treatment at 65OOC for 30 minutes. 

Cell I Voc, I Jsc, I FF, I Eft, 

ID I V I mA/cm2 I % I % 

B5BT 1 I 0.555 I 28.95 I 69.50 I 11.18 

2 I 0.560 I 29.04 1 67.40 I 10.96 

3 I 0.563 I 28.54 I 69.10 I 11.10 

4 I 0.560 I 28.90 ! 68.90 I 11.15 

5 I 0.573 I 28.66 I 71.40 I 11.73 

6 I 0.544 I 29.08 I 65.00 I 10.27 

C. At 0.7 J/cm2 with 50% overlap. 

Cell 1 Voc, I Jsc, I FF, I Eff, 

ID I V I mA/cm2 I % I % 

B5A 1 I 0.534 I 29.94 I 69.30 I 11.08 

2 I 0.536 I 29.56 I 68.60 I 10.87 

31 

4 I 0.459 I 26.34 I 63.00 I 7.74 

51 

6 I 0.549 I 30.43 I 69.66 I 11.64 

Dead Cell - - - 

Dead Cell - - - 

--- 

--- 

High energy density, e.g. at 1.2 J/cm2, yielded lower cell 

efficiency (-8.7%) due to severe reduction in Jsc (21 mA/cm2) 

because of loss in texturing. SEM photos (Fig. 15c) also 

revealea that heavy melting-resolidification took place after 

such high energy density annealing. The effective energy density 

at the surface was increased at least by 40% due to the second 

reflection from the textured surface. 

3.1.2 -v Powd Surface 

In parallel with the textured wafer experiment, 20% NaOH etched 

wafers (Cz 0.7 ohm-cm p-type base) had spin-on liquid dopant followed by laser annealing at energy densities of 0.9 J/cm2, 1.2 

J/cm2, and 1.6 J/cm2 with 50% overlap. Results are summarized in 

Table 3. The data represent the average cell efficiency weighted 

over 4 samples in each case. Also included in Table 3 are the 

results of post furnace annealing at 65OOC for 30 minutes to test 

for a stress relief effect. 

- 31 - 
Table 3. Cells fabricated from polished Cz p-type wafer with 

spin-on source laser annealed at energies 0.9, 1.2, and 1.6 

JICd . 

I I Control I 65OOC Funace Annealed 

Cell I ~aser l----------------------------l-------------------~-------- 

ID IEnerq, I VG~, I JSC, I FF, I Eff, I VoC, I Jsc, I FF, I Eff, 

I J/cm I ImWcm2l % I % I v ImA/cm2I % I % 

B7-I I I I I I I I I I 

(1F) I 1.2 I 0.586 I 20.65 I 75.3 I 9.1 I 0.587 I 19-90 I 76.0 I 8.9 

I I I I I I I I 1 

B7-I11 I I I I I I I I I 

(2F) I 0.9 I 0.582 I 21.15 I 68.8 I 8.5 I 0.589 I 20.54 I 73.0 I 8.8 

I I I I I I I I 1 

B7-XI I I ! I 1 I I I I 

(3F) I 1.6 I 0.588 I 19.40 I 75.9 I 8.6 I 0.587 1 18.60 I 79.7 I 8.5 

As indicated by the data, the shallow junction formed by 

annealing at 0.9 J/cm2 on these reflective surface wafers 

improved the Jsc in comparison with other groups (Hovel, 1975). 

However, the fill factor was lowered as a result of increased 

series resistance. Deeper junctions of groups I and I1 had much 

better fill factor yet lower Jsc, confirming the statement above. 

It is interesting to notice that 1.2 J/cm2 energy density had 

yielded the highest efficiency cell, which is consistent with 

other published erticles. However, surface damage due to the 

'wetting" effect of the spin-on coating was most severe at 1.2 

J/cm2. Flow ot aolten silicon was obvious at 0.9 J/cm2 (Fig. 

17a). "Crater" defects were found on the 1.2 J/crnZ annealed 

surface (Pig. 17b). 

Furnace annealing at 65OOC for 30 minutes (before metallization) 

improved the fill factor slightly, especially on group I (0.9 

J/cm2), but degraded the JSC by approximately 3-4%. The results 

suggest that thermal stress relief appears effective only for low 

laser energy density annealed surfaces, which is similar to the 

observation for the textured surface. 

For control purposes, liquid dopant on caustic etched wafers were 

subjected to thermal diffusion at 82OOC for 1.5 hours. Results 

are summarized in Table 4. 

- 32 - 

Table 4. 

polished witb spin-on source as dopant. 

Cell performance of thermally diffused wafer of caustic 

5 

BB 5 

1 

LB 1 

"F 

.p 

#4 

Cell ID I Vocr I J cr I FF, I Effa I 

(Cz 1 I V I mA7cm2 I % I % 1 

0.581 I 18.7 I 67.0 I 7.3 I 33 

0.516 18.7 

90 

8.4 0.479 19.8 68.3 I 6.5 87 

:::: I ::: 31 

(50k6.L. 1 I 

0.4 

(708 . ye !do 1 

0.389 20.4 (50 0.L.) 

(70% 0.L.) 

Spin on B5-C I I I I I 

(1 1 I 0.531 I 22.87 I 64.4 I 7.8 I 

(2) I 0.563 I 23.33 I 71.1 I 9.3 I 

(3) I 0.559 I 23.43 I 71.8 I 9.4 I 

(4) I 0.585 I 22.43 I 60.2 I 7.9 1 

(5) I 0.540 I 23.00 I 71.4 I 8.9 I 

Cell efficiency of the thermally diffused wafers on average was 

better than those laser annealed due to higher Jsc, suggesting 

that the junction depth of thermally diffused cells with spin-on dopant was even shallower (Fig. 18a). The lower Voc was probably 

due to high recombination in the junction as indicated by the 

dark I-V (Fig. 18b). In fact, all cells with emitters diffusert 

both thermally or laser assisted with liquid dopant had high dark 

recombination current. One of the possible sources of 

recombination centers could be from the liquid dopant, as one of 

the supplier's analytical data showed impurity levels were as 

high as 0.5 ppm. The usage of liquid dopant was then halted. 

In the early stage of the programr ion implants were processed 

for 4-in. diameter p-type caustic polished Cz (-0.33 ohm-cm! 

wafers at 10 keV with dosage of 5x1015 atoms/cm2 and 1x1013 

stoms/cm2 respectively. Laser energy density (EXCI-LITE-1) was 

set at 0.4 J/cm2 and 0.7 J/cm2, respectively, with pulse duration 

4-6 ns. Cell characterization indicated low Jsc, Voc, and fill 

factor as the result or insufficient implant damage removal by 

low laser energy density that was too low. Typical results are 

listed in Table 5. 

Table 5. Results of laser annealin in caustic lished, 10 keV 

respectively. 

ion implant witb dosage 5x101s and 1x10 p" 5 ators/cr2, 

I 10 kev ILaser Energy I I I I I 

VoC, I JSC, I FF, I Eff, ISheef, I v I mA/cm2I % I a I Rho, 

I I I I ohm/sq 
C 

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The extremely low Voc on L5A #7 wis due to insufficient surface 

concentration which also atfected the sheet rho uniformity across 

the surface causing leakage as revealed by reverse dark I-V 

measurement. 

The poor result with caustic polished Cz wafers suggested the use 

of chem-mechanically polished FZ of 0.3 ohm-cm p-type wafers as a 

baseline experiment. The material had been well characterized by 

conventional thermal diffusion that yielded efficiency of 16% at 

AIYl.5 with simple spin-on A/R coating for cells of 25 cm2 total 

area (Fig. 18). 

Material from this batch was sent for ion implantation with 31P+ 

at 5 keV of dosage 1x1015, 2.5~1015 and 5x1015 atoms/cm2, 

respectively. Laser energy varied from 0.90 to 1.30 J/cm2, with 

overlay from 20% to 70%. Pulse duration time was extended from 6 

ns to 50 ns (double pulse shape). The reason for overlap was to 

compensate beam non-uniformity. As beam quality was 

progressively improving, the overlap factor was decreasing 

proportionally. Results are summarized in Table 6. 

Table 6. Results of laser annealing on chem-aech polished wafers 

5 keV ion implanted with 1x1015 and 2.5.1015 ators/d dosage, 

respectively. 

I 5 keV I Laser i I I I I I 

Cell IIon Dosage, I Energy [Over- I V,, I Jsc, I FF, I Eff, ISheet 

ID I 1015 I Density, I lap, I V I mWcm2 I % I % I Rho, 

(FZ) I atom/cm2 I J/c~Z I % 1 I I I I owsq 

I 1.30 I 70 I 0.554 I 18.23 I 75.00 I 7.58 

I 1.30 I 70 I 0.552 I 18.22 I 75.70 I 7.62 I B&.l I 2.5 

2.5 

Wf 73 00 I 67:~ 1 kB I %83 tj I 2.5 0.555 

I!! I $:l 1 k# t t 8:5%4 1 18.33 71.72 7.14 I 40-45 

B9-2 

I1 I 2.5 21.36 48.13 50-5 

I 2.5 

(4 I 2.5 

2.5 I 8:88 I '8 1 8:# I 21.13 I 55.92 I 65:% I 50-53 

I 0.90 I 70 I 0.531 I 21.17 I 60.21 I 6.77 I 50-55 

I 0.90 I 70 i 0.593 I 21.12 I 67.20 I 8.42 I 50-55 

B10-1 

I 0.90 I 30 I 0.534 I 21.74 I 70.24 I 7.70 I 65-74 

1 1 8:8 I 8 1 0.552 1 1 68.97 I 8.51 I 66gTt 

0.90 30 0.548 22.64 70.74 8.78 65-74 

0.553 72.17 9.01 

1. 5 0.569 21.77 70.68 60- I 21 I 0.572 I 21.96 I 70.67 I 8:87 

0.577 21.95 I 71.32 I 8.83 I 60-JS 

t5 I 1 I 1.25 I 20 I 0.573 I 21.59 I 72.12 I 8.92 I 60-72 

I 60-7 

In experiment B9-1 where laser energy density was as high as 1.3 

J/cm2 with 70% overlap, both current density and Voc were very low. The latter was probably due to excessive surface damage, 

- 37 - 
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especially at the center of overlap (Fig. 20). The former was 

due to the deep junction characteristic that limited the JSC to 

less than 18.5 mAlcm2. Eowever, the deep junction helped to 

improve the fill factor on average. 

All cells annealed at 0.9 J/cm2 (B9-2) had high leakage current 

and low shunt resistance that affected the fill factor. 

The general trend of the above experiments suggested that 

reduction in overlap % (to the limit where beam uniformity fails 

to anneal the whole area), the better the cell performance. There was not much effect due to dosage difference from 1x1015 to 

2.5~1015 atoms/cm2. Also, examination of literature data 

suggested that a minimum of overlap is required to obtain the 

highest efficiencies. As a result, the start-up and use of a 

higher power, larger beam size (spot size 2 0.7 cm2) laser, at 

MSNW was initiated. Two initial experi.ments were conducted. 

Result& obtained were encouraging. 

Table 7. First experimental result with the larger laser, at 

density 1.4 and 1.6 J/cd respectively. 

(See Table 7.) 

- -- 

Cell1 5 keV IEnergy lover-I Pulse I I I I 1 Sheet 

ID I Dosa e, IDensity, llap, IDurationl VoC, I Jsc 1 FF, I Eff, I Rho, 

(FZ) I x1d I J/m2 1 % 1 ns I v ta-5 I % I % lohm/sq 

B-11 

#l I 2.5 I 1.3 I 20 I 80 I 0.569 I 21.47 I 67.951 8.311 46-65 

#2 I 2.5 I 1.3 I 20 I 80 I 0.581 I 21.06 I 62.151 7.6CI 46-65 

(4 I 2.5 I 1.3 I 20 I 80 I 0.587 I 21.53 I 74.181 9.371 46-65 

115 I 2.5 I 1.3 I 20 I 80 I 0.583 I 21.36 I 67.561 8.411 46-65 

B-12-2.5E 

#1 I 2.5 I 1.6 I 8 I 80-90 I 0.593 I 20.14 I 78.501 9.381 40-53 

#2 I 2.5 I 1.6 I 8 I 80-90 I 0.580 I 20.02 I 71.171 8.261 40-53 

B-12-5E 

#l I 5 I 1.6 I 8 I 80-90 I 0.593 I 20.40 I 70.621 8.551 26-32 

#2 I 5 I 1.6 I 8 I 80-90 i 0.593 I 20.54 I 73.891 9.011 26-32 

Although the junctions formed here were deeper than previous 

experiments, as indicated by the lawer sheet resistivities, both 

the Voc and JSC were.comparatively higher on average. A fill 

factor as high as 78*.5% was also obtained (B-12-2.5E #I). 

Results suggested the advantage of a more powerful laser of 

larger beam size with more output uniformity that allowed less 

total overlap. 

Two more experiments with different combinations of energy and % 

of overlap were then immediately conducted: 0.95 J/cmz with 9% 

overlap and 1.1 J/cmZwith 7% overlap, respectively. Results are 

summarized in Table 8. 

- 39 - 
Pig, 20, Laser Annealing on 5 KeV, 2.5 x 1015 atom/cm2 Ion 

Implanted Surfaces at 1.3 J/cm*, With 70% Overlap Pulse 

Duration Estimated 6ns (B-9) 

- 40 - 
Table 8. Results of annealing by the larger laser with lower 

energy density and overlap %. 

_-_-e-_- .-___---”----- - -- 

Cell I 5 keV I Energy I Over- I I I I I Sheet 

ID i *sa e, I Density, I lap, I Voc, I Jsc, I FF, I Eff, I Rho, 

(FZ) I ~1012 I J/mZ I % I V I mWcm2 I % I % I ohrn/sq 

B-13 

111 I 5 I 0.95 I 9 I 0.495 I 21.30 I 49.93 I 5.26 I >lo0 

12 I 5 I 0.95 I 9 I 0.531 I 20.80 I 52.29 I 5.78 I >lo0 

(4 I 5 I 0.95 I 9 I 0.425 I 21-81 I 41.87 I 3.88 I >lo0 

#5 I 5 I 0.95 I 9 I 0.554 I 21.54 I 52.80 I 6.30 I >lo0 

s-li 

#1 I 5 I 1.10 I 7 I 0.531 I 22.71 I 58.78 I 7.09 I 68-80 

#2 I 5 I 1.10 I 7 I 0.533 I 22.99 I 58.80 I 7.20 I 68-80 

#4 I 5 I 1-10 I 7 I 0.477 I 20.37 I 44.59 I 4.33 I 68-80 

83 I 5 I 1.10 I 7 I 0.512 I 22.69 I 53.58 I 6.23 I 68-80 

All cells showed high series resistance and high shunt 

conductivity due to shallow junction as well as insufficient 

overlap. The other factor considered to be contributing to the 

low VO, was the presence of ion implantation damage that was not 

removed at such low energy densities. 

In order to isolate the effects of ion implantation shh as 

nonuniformity and lattice damage, a special experiment was 

conducted in which Cz polished wafers (0.7 ohm-cml were subjected 

to N+ deposition at 83OOC using POCl3 as the dopant source. 

Sheet rho after the phosphorus glass was removed was about 200 

ohms/sq. A wafer with the phosphorus glass still remaining was 

then laser annealed at 1.25 J/cmZ with 10% overlap. Sheet 

resistivity after annealing was as low as 15 ohms/sq. Cells were 

fabricated only after etching back to 60 ohms/sq. Highest efficiency was 10% without A/R. In parallel to the laser 

annealing, control cells were made from similar wafers that had 

been subjected to thermal diffusion. As shown in Table 9, 

results of the laser annealed and that of the thermally diffused 

were quite alike. 

- 41 - 
Table 9- Laser annealing for wafer with thermal N+ deposition. 

Control cells were thermally diffused. All cells without A/R- 

~ ~~ 

cell I N+ I Laser I Over- I I I I I Sheet 

ID IDepositionl Energy 1 lap, 1 Voc, I Jsc, I FF, I Eff, I Rho on 

(Cz) I Temp (OC) I Density I % I v I m~/cm21 % I % I Cells 

B-15 

--- 

#l I 830 I 1.25 I 10 I 0.588 I 22.15 I 76.89 110.011 60-65 

#2 I 830 I 1.25 I 10 I 0.587 I 21.82 I 76.36 I 9.781 60-65 

(3 I 830 I 1.25 I 10 I 0.568 I 21.04 I 76.37 I 9.121 60-65 

#4 I 830 I 1.25 I 10 I 0.588 I 21.82 I 76.49 I 9.811 60-65 

Contrcrl 

Special 

B-15 I Thermal I I I I I I 

#I I 830 I Diffuse I -- I 0.586 I 21.64 I 74.02 I 9.381 60-70 

82 I 830 I -- I -- 1 0.593 1 22.54 1 75.97 110.141 60-70 

#3 I 830 I -- I -- I 0.592 I 22.37 I 77.58 110.281 60-70 

c4 I 830 I -- I -- I 0.592 I 22.00 I 77.93 110.161 60-70 

In fact, the dark and light I-V curves of the typical cell in 

each group were almost identical (Fig. 21). 

- 42 - 
CZ, THEPPML GEPOS!TIOl4 

COOLED. OROUE-IN @ 530 FOR 30 :Ill( 

SINlERED 

L -2 

0 

G 

c -3 U 

R 

R 

E -4 N 

1 

-5 E 

I4 

S 

-6 

Y 

-7 

Pn: 8.011 (uotts) 

CIf: 77.93 r. 

Eff: 10.16 2 

CZ. lMLRNdL OEPOC,lTlON 

SINVERED 

COOLED. tPouE-iN e 830 FOR 30 HIn 

Pig. 21a. Light and Dark I-V Curves for Typical Cells From 

Thermal N+ Deposition and Diffusion. 

- 43 - 
n 

C 

1 

f 20 

C 

R 

E 

; 21 

n ' 14 

b 

E 

n 

5- 

I' 

e 

-I 

L -2 

c -3 

0 

C 

U 

D 

R 

E -4 

n 

T 

D -5 

E 

n 

5 

r 

; -6 

-a 

lor: B.002 (ami 

Jon: 20.4s cna'soi 

Uon: 0.498 (roltsi 

Pr: 0.B40 (matts) 

ti): 76.89 :: 

€66: 10.01 :: 

Pig. 21b. Light and Dark I-V Curves for Typical Cells From 

Thermal N+ deposition and Laser Driven In at 1.25 

J/cm2, 10% Overlap. 

- 44 - 
The 

4.0 

laser 

a 

annealing experiment started with spin-on liquid dopant 

for convenience and for economic reasons. Surface conditions 

included sodium hydroxide texture and polish. Due to the 

increase in absorption, spin-on dopant caused more surface damage than expected, especially at the overlap area where melting was 

more severe. 

Damage on a textured surface with spin-on coating was even 

greater. Because of the pyramid surface structure, 0.4 J/cm2 was 

found sufficient to cause melting. The degree of melting at 

different energy densities can be visualized trom Figure 16. At 

1.2 J/cm2, the surface was almost recrystallized, losing most of 

the texturing property. Spin-on dopant on either polished or 

textured wafers tor laser annealing requires more 

experimentation. 

Laser annealing of phasphorus ion implanted wafers was also 

extensively investigated. Results were far from ideal. Two of 

the most important factors were the beam uniformity and high 

implantation energy. 

Model calculations of the depth and duration of pulsed excimer 

laser melting as a function of energy density predicted the 

threshold of 0.9 J/cm2 for surface melting, 1.5 J/cm2 to a depth 

of 0.166 pm and 1.75 J/cmZ to a depth of 0.266 pm (Young, 1982). 

The SIMS depth profile for a 5 keV phosphorus ion implant sample 

(Fig. 21) suggested the ion channeling distance was almost 0.16 

pm. Both the calculated melt depth and ion channeling distance 

suggested that the threshold energy required to completely remove 

lattice damage caused by a 5 keV implant would be at least 1.5 

J/cm2 (90 ns pulse). Experiment B-9-1 was conducted at 1.3 J/cm2 

with the small laser. However, the 70% overlap caused severe 

surface damage (Fig. 20) that limited the Voc to less than 0.56 

V. Current recombination at the damaged areas are clearly shown 

by the laser scan photo (Fig. 23). 

By using the larger laser (5 J max power) with greater uniformity 

and area coverage, less overlapping was necessary. Maximum cell 

efficienc of 9.4% without A/R (13.7 with A/R) was obtained with 

all experiments. Results were in agreement with the calculated 

melt depth and lattice damage by ion implant described above. 

1.6 J/cm r energy density. Voc on average was the highest among 

The effect of unremoved lattice damage was further demonstrated 

indirectly by laser annealing a thermal N+ deposition wafer. 10% 

maximum cell efficiency was the result for a Cz wafer. Had the 

phosphorus glass been thinner before annealing, higher cell 

efficiencies would be obtained. The VOC was still comparatively lower (5-8 mV) than thermally diffused cells. This is believed 

to be due to recombination at the overlap boundaries. 

- 45 - 
n 

0 

0 

\ 

E 

0 

3 

0 

e 

u 

PROCESSED DATA + 

OEFTH PROFILE 

6)P)SI SKeV 2.5e15 

1P t 

Depth profile for 31?+ ion inplanted 

e 5 KeV. 2.5x1~15 atoms per cm 2 I 1P 

S 

c 

1020\ 5 

lo'* 

SL 

h 

?i.bbhp 

101° i I 

0 0.00 0.16 0.24 0.32 0.40 

DE?TH (mxcrone) 

Pig. 22. SIMS Uepth Profile for 31P+ Ion Implanted at 5 keV, 2.5 

x 101sAtom per cm2. Substrate Resistivity -0.3 ohms-cm 

Boron Doped. 

- 46 - 

5.0 

5.1 PROCBSP SELECTION 

A description of the selected baseline and excimer laser process 

sequence follows. 

5.1.1 

The baseline process is essentially the same as the JPL 

state-of-the-art process. The only difference beicg the absence 

of a back surface formation step and the use of plasma etching. 

This operation has been amenable to higher throughput than the 

ir.dividualized laser scribing trchnique. A flow diagram of the 

baseline process is shown in Figure 24. The process utilizes 

CzochralsKi grown p-type (Boron doped) (1-0-0) wafers of 5.2" 

diameter and nominal resistivity ef 0.3 ohm-cm. The nominal 

wafer thickness is 400pm. 

A sodium hydroxide (NaOH) etch is used to remove the damaged 

surface layer (sawing damage). This etching step removes 50-75 

m of the surface layer. The etched surface is then subjected to 

an anisotrophic texturin2 etch utilizing dilute (2%) NaOH 

solution. Dilute NaOH preferentially etches (100) 

crystallographic planes more rapidly than the (111) plane leading 

to a surface finish that consists of tetrahedrons projecting 

upwards from the silicon surface. These tetrahedrons act as very efficient light traps. The texturea surface is then cleaned in a 

dilute H2s04 acid solution and is rinsed in deionized water and 

dried. 

The textured surface is then subjected to a ditfusion step to 

form the p-n junction. Phosphorous oxychloride is used in a gas diffusion tube to deposit a phosphorus rich n-layer on the p-type 

wafer. The phosphorus is then driven into the silicon to form 

the p-n junction. This diffusion/drive-in proczss is carried out 

at a high temperature (85OOC) . The resulting junction is 

typically 0.3 pm deep. The sheet resistance of the diffused 

surface region ranges between 35-40 ohms per square. To remove 

any shunting path between the front and back surface of the cell, 

the edges of the diffused cell are etched in a plasma etcher 

tJsing a f luorocarbon-oxygen mixture. Ohmic contacts to ishe cell 

ax made by screen printing a grid pattern of silver paste on the 

fro,.t and back surface of the cell. The contacts are dried and 

then sintered in a conveyor fed infrared furnace. This 

processing sequence typically yields cells with the following 

par ame te r s 

JSC = 30 mA/cm2r VOC = 585 mV; ff = 

The fabricated cells are then assembled and laminated into 

modules using the JPL state-of-the-art process. 

0.74; EFF = 13.0% 

PRl?CEDIXG PAGE BLANK NOT FEW,D - 49 - 
L 303 NaOH Etch Print Ag 

FrontlDry 

2% NaOH 

Texturing Etch 

Dilute H SO4 

Ri nse/Dr$ 

I 

Contact Firiyg 

- 

To Module 

Ass zrnb 1 y 

Fig. 24. Baseline Process. 5.2" Diameter, P Type (Boron Doped) 

0.3 ohm-cm Cz Silicon. 

- 50 - 
5.1.2 -of the Prv PA schematic of the selected laser processing sequence for the 

fabrication of solar cells is shown in Figure 25. Phosphorus doped n type Czochralski grown silicon (100) wafers of 5.2" 

diameter and nominal resistivity of 0.3 ohm-cm will be used 

(range 0.1 - 0.3 ohm-cm). The nominal wafer thickness will be 

400 pm. A sodium hydroxide etch will be used to etch the wafer 

surface to remove the damaged surface layer (50-75pm). The 

etched surface will be subjected to an anistropic etch (2% NaOH) 

to texture it. The textured surface will then be cleaned in 

dilute H2S04 solution. The surface is rinsed in deionized water 

and dried. 

The textured surface is then subjected to an ion implantation 

process as a first step towards a p-n junction formation. The 

front surface of the cell will be implanted with Boron (IlB) at 

an energy of 5 keV and to a dose of 6 x 1015 atoms/cm2. A Spire 

Inc. continuous ion implanter is an example of the equipment to 

carry out this implant. After ion implantation, the samples will 

be cleaned with acetone, methanol, H202:H2S04(1:l), 

BN03:E2S04(1:1) and €iF:H20(1:10) to remove any organic and 

metallic contaminants prior to laser annealing. 

The annealing of the boron implanted region would be carried cut 

using a high power excimer laser such as the XMR XL-150. This 

laser has a wavelength of 308 nm when operated using XeCl gas. A 

beam energy density or 1.2 J/cm2 will be utilized at the work 

surface. The laser will be pulsed at 500 Hz. The pulse width of 

the laser is 50-80 nsec. A beam width of 0.35 x 0.35 cm2 will be 

utilized. The annealing will be done in air. One pulse per 

0.125 cm2 area will be required. Overlap is assumed to be 

minimal, below 5%. The annealing process will require about 1025 

laser pulses to cover the surface. The time to carry out the 

annealing will be about 3 seconds including wafer tramport time. 

The laser is expected to melt the silicon surface to a depth of 

approximately 0.3 - 0.5 Frn and result in a junction depth in the 

0.15 - 0.2 pm range. The laser annealed samples will be cleaned 

in a HF:H2C(1:10) solution, rinsed with deionized water and 

dried. The back surface of the cell will be metallized with an 

2000A thick layer of nickel phosphide. 

The front surfsce of the solar cell will have an intentionally 

grown passivating thin oxide layer to minimize the carrier 

recombination along the cell top surface. The oxide has to be 

thin (-15-20A) so that carriers can tunnel through it and to be 

efficiently collected by the front grid pattern. This technique 

has yieldea cells with high open circuit voltage and consequently higher efficiency. A laser assisted process will be used to grow 

this thin oxide. The oxide growth will be carried out in a 

N20/SiHq ambient at a pressure of 6 torr and at a substrate 

temperature of <3COoC. The laser used for this process will be 

Bn excimer AsP laser (193 nm). Deposition rates in the 600 wmin 

to 800 Airbin have been observed using these deposition 

- 51 - 
- 

2: NaOH 

Texturing Etch 

6 Ion Implant "B" 

- 

Front 

Metal lization 

-1 

Test a Sort 

h 

t 

Etch Dilute HF 

Back Contact 

Metallization 

~~ 

Front Passivation 

Lase r Ass i s t ed 

Oxide Growth 

Buildup of Front 

Passivating Oxide 

I 

To Module 

As senb 1 y 

Fig, 25, Preliminary Laser Process. 5.2" Diameter, N Type (Phosphorus Doped) 0.3 ohm-cm Cz Silicon. 

- 52 - 
conditions. Depositlm rates in this range are appropriate for 

achieving goo2 control of the oxide thickness in the desired 

rnage (15-20 3). The properties of these laser grown oxides have 

been shown to be comparable to oxides grown using plasma enhanced 

and mercury photosensitized chemical vapor deposition. 

The passivated cells will be coated with gridlines on the front 

surface using laser assisted pattern writing on semiconductors. 

This deposition will be carried out to a thickness of 2000A of 

aluminum so that the buildup of the gridline thickness using 

electroplatirg is possible. The laser beam will be optically configured to write thin narrow lines. The laser energy density 

has to be low enough so as not to damage the p-n junction formed 

during the laser anneal but still has to high enough to provide 

metal deposition rates that are meaningful for scale-up of this 

process (i.e. a 1000 umin rate at the minimum). 

After gridline deposition, the cell front surface will be 

subjected to a second oxide growth step to provide passivation of 

the front surface in between the gridlines. Oxide growth will be 

carried out in a fashion similar to the one discussed above. 

However, the oxide will be grown to a greater thickness C-lOOA). 

This thickness of the intergrid oxide has been demonstrated to 

provide good passivation of the front surface leading to high 

open circuit voltage. Once the front surface passivation has 

been carried out, the thickness of the gridlines and the back 

cmtact will be increased to 7 pm by utilizing electrochemical 

techniques to plate nickel phosphide on the gridlines to incnease 

their electrical conductivity and thereby increase their ability 

efficiently to extract the photogenerated current. The cells 

then are encapsulated using the JPL baseline process. 

5.2 ECOWMIC AMALYSIS 

5.2.1 ApDroach 

Development of a simplified methodology which permits increased 

flexibility in performing price estimation of individual process elements was described by (Aster, 1980) with the publication of 

the Improved Price Estimation Guidelines (IPEGI . The equation and coefficients whicn were generated at that time provided 

closer agreement with SAMIS results than the earlier versions. 

An IPEG calculation for each process step has been prepared. 

Changes from the baseline process were substituted into the 

baseline and the module final cost recalculated. These estimates 

employ the recently revised IPEG coefficiente listed in Table 9. 

The baseline sequence is called the JPL Sample Process. 

In order to perform an estimate, the cost elements required for 

the IPEG calculation have been individually developed for each 

process step. The following sections discuss the assumptions 

associated with the required process equipment and its 

installation, operation and maintenance scenarios. Based on 

throughput and use factor estimates, the required iabor, 

- 53 - 
materials, and utilities to maintain an annual production capacity or 5 MW were developed for each of the propose2 

processes . 5.2.2 Results 

Tables 10 and 11 provide a direct corayarison of costs for the 

baseline process, and the proposed laser process sequence. The 

calculated baseline cost estimate is 52.98; using an asscmsd cell 

efficiency of 13%. Table B indicates a cumulative potential cost 

reduction of $0.66 per peak watt if the proposed laser methods 

are fully implemented. 

When comparing costs to the JPL Sample Process sequence, it is 

necessary to consider the resultant cell @utFut and mDdule 

efficiency (taken as 9.6% for the sample sequence), and the 

effect or expected improved cell efficiency and larger wafer size 

on the number of units processed anually to achieve req~ired 

production volumes. If the predicted improved efficiency of 176 

is achieved, and the 5.2 inch wafers can be processed at the 

predicted yields, then the module efficiency at the stated 

conditions (NOC) will approach 11.7%. This will reduce the costs 

of subsequent process steps by virtue of fabrication of 21% fewer 

modules/year. For example, if a module geometry of 0.6 x 1.2 m 

is chosen as the design point, a total of 908422 modules are 

required to be equivalent to five megawatt for d 9.6% efficiency 

(at NOCi module design. However, using 17% efficient cells 

(which yield a module efficiency of approximately 11.7%) only 

74,192 modules were required. Immediately obvious benefits from 

this reduced build-requirement are proportional reductions in the 

labox content of all process steps and, for those steps which are 

assembly or test sequences, the entire cost will be reduced 

substantially (e.g. cell layup, haterial preparation, layup trim 

seal test and package module). Attendent to these reductions are 

similar reductions in material usage. For example, the total 

area of glass superstrate is reduced by 11,685 m2. At a 1983 

quantity price of $9.92/m2 quoted by glass manufacturers for 118" 

tempered low-iron AR treated glass, a cost reduction can be 

calculated (using the IPEG materials coefficient of 1.17) as: 

Similar reductions in other module direct materials requirements 

such as encapsulant, substrates and frames have been calculated. 

Additionally, process yields were estimated for the laser process 

sequence which result in a net cumulative process sequence yield 

equivalent to the JPL sample process. Impiementation of the 

proposed laser process will employ relatively "cold" methods 

including the use of a handling pallet which positions and 

supports the wafers through the majority of tne cell 

manufacturing steps. Thus, the incidence of yield losses due to 

mechanical breakage, will be significantly reduced. 

- 54 - 
a, 

E 

4 I rl 

5 

ma, 

H 0 * 0 

pc 0 

H 

0 

co 

3 

r( I (I, 

s 

3 

!E I 

I 

w 

to 

3 

E 

IC 

n 

II 

m 

d 

I H 

I 

I 

I 

m 

In 

I 
pi 

w 

B 

Lo 

w 

z I 

I 

I 

I 

I 

I 

I 

1 

I 

1 

1 

1 I 1 

I 

I 

12 

IE 

I2 

G 

w 

W 

4 

d 

Er 

X 

rl 

IO 

I4 

.. 

E2 

4E.c 

bW 

A ZZ 

I 

I 

I 

I 

I 

I 

1 

1 

I 

1 

I 

I 

I 

I 

I 

1 

I 

I 
JPL has documented this sample process sequence with a complete 

set of SAHICS Format A forms and performed a computer SAWIS run 

to calculate these costs. As a result of the detailed computer 

runr IPEG coefficients have been calculated. These are: 

c1 = 0.59 for annual equipment cost (EQPT) 

c2 = 136 for annual factory area cost (FT~) 

c3 = 2.02 for annual direct labor cost (DLAB) 

c4 = 1.17 for annual material cost (MATS) 

c5 = 1.17 for annual utilities cost (UTILI 

Pig. 25. IPEG Coefficients for JPL Sample Process Sequence. 

- 57 - 
5.2.2.1 Discussion of Cost Blements of Excimer Laser 

Applications 

(a) -nt 

The initial cost of present commercial excimer lasers ranges from 

$10-15K for lower power devices (5 watt) to $40-50K for the 

highest power devices (20-30 watts). The higher power devices 

that are anticipated (50-200 watts) will range in cost from 

$100-400. Thus the normalized cost of near term excimer laser 

equipment is approximately $2500/watt in the 10 to 200 watt 

range. The wavelengths available are 193, 248, 308, and 351 nm. 

(b) user Cosfs 

There are three principal cost elements associated with excimer 

lasers; the consumption of excimer laser gas, the use of 

electricity and other utilities, and scheduled maintenance to 

replace or repair short lifetime components. Typical costs per watt-hour of excimer laser output are $0.05 (ArF or XeC1) to $5.0 

(KrF) for laser gas, $0.02 to $0.05 for electricity, and $0.2 to 

$2.0 for scheduled maintenance. Reduction of gas consumption and 

maintenance costs is one of the critical development steps 

required for the successful application of excimer laser 

technology to solar cell fabrication. 

Recent promising developments in the United Kingdom in the area 

of excimer gas on-line reprocessing have demonstrated significant reductions in gas replenishment frequency, especially for ArF. A 

reduction of 20:l in gas consumption is assumed in this cost 

estimate. 

In the area of maintenance, the principle driving costs involve 

frequent refurbishment and replacement of internal parts affected 

by the excimer gas and the high switching pulse loads on the 

thyratron. In particular, efficient laser operation requires 

complete teatdowc of the laser optical system about every 1 x 108 

shots. This is approximately once a week for the proposed ArF 

laser . An advantage of the XMR XeCl high power laser is that it does not 

use thyratrons for pulse switching so the maintenance cost is 

much reduced from the ArF laser as can be seen in the detailed 

par a gr a ph s . 5.2.3 ec Laser PrEach IPEG cost elements is discussed below on a 

process-by-process basis. The following assumptions, consistent 

with IPEG procedures, were used throughout the analysis: 

- 58 - 
I. 

2. 

3. 

4. 

5. 

6. 

(b) 

1. 

2. 

3. 

Equipment Capital Costs (-1 include installation and 

Lirst year's major component spares, reduced by salvage and 

removal value. 

Equipment has a 7 year life and uses straightline depreciation. 

Facility Area (FT2) includes equipment footprint area and 

required working space for normal operation. 

Direct Labor (-1 includes, as applicable, factory manufacturing and maintenance personnel at the following hourly direct rates (excluding fringes): 

Technician/Operator - $ 6 

Senior Processor -$8 

Maintenance - $10 

Process Engineer - $12 

Direct Material Costs (MATLS) are based on best estimates 

from actual laser operating experience and include scheduled 

maintenance materials. 

Utility Cost (-1 is based on $0.75/KWHR rate. KWHR 

demand is calculated on basis of operation for estimated 

equipment availability factor of 0.85. 

- Process rates require one XeCl laser system operating 

at 55% capacity thus, a spare system would not be required. Wafer transportation is assumed to be cassette-to-cassette. 

1 XC-150 XeCl laser 

1 precision N/C table 

1 microprocessor 

1 gas reprocessor 

1 K-bottle/manifold bank 

1 wafer transport system Installation - 2 man mos 

Less salvage @ :O,OOO 

EQPT TOTAL 

- 232,000 

- 10,000 

- 3,000 

- 35,000 

- 2,000 

- 2,000 

- 8,160 

-_10.000 

= 302,160 

E&- Approximate area for laser and associated equipment is: 

PT2 total = 14' x 10' = 140 FT2 

DLAB - The laser anneal facility is operated for 2300 hours 

by one technician. All scheduled/routine maintenance is 

performed by skilled electro-mechanical maintenance 

technicians: 

Operation 2300/yr @ $6 = $13,860 

- 59 - 
Maintenance 300/yr @ $10 - 9 ?,OM 

DLAB TOTAL $16,80G 

4. MAI'Ls - Principal direct costs are the replacement parts for 

the laser systems. Gas consumption assumes that the gas 

reprocessor can achieve a 16:l extension of gas life. 

o Gas consumption, annual * 88,680 

WTLS TOTAL = 88,680 

53 hours/fill; 2300 hours/year; 200 $/fill 

5. lJTIL - Estimated electric deEand for the laser anneal 

facility includes cell transport and location at 0.5 Kw; 

control electronics at 0.2 Kw; and laser power requirement of 15.8 Kw. 

Annual KWER = 837,950 

Rate = . 075 

UTIL TOTAL = 2,900 

(c) Laser Front 

1. EOPT - Based on rates described, two ArF lasers operating 

one microprocessor, one gas reprocessor, reactant gas pumping and reclaim system, and wafer transport and locating equipment for the laser writing are required: 

2 EXC-2 ArF lasers @ 27,000 = $ 54,000 

1 gas reprocessor @ 10,000 = 10,000 

2 N/C tables @ 10,000 = 20,000 

1 microprocessor @ 3,000 s 3,000 

1/2 K-bottle bank @ 1,000 = 1,000 

2 wafer transport systems @ 5,000 = 10,000 

1 tri methylaluminum gas @ 100,000 = 100,000 

Salvage value =o 

(shared with other ArF processes) 

transport and recovery/scrubber system Installation s 8,000 

EQPT TOTAL =$ 203,000 

2. FT2 - Based on a preliminary estimate of 30 PT2 for the 

scrubber system, total facility area = 138 FT2. 

3. - Maintenance for the two lasers is based on required thyratron replacement, with an additional two hr/week 

devoted to the reactant gas scrubber. Facility operation is 

assigned to one full time operator per shift: 

Operation = 4160/yr Q 86 * $ 24,960 

Maintenance = 740 hr/yr @ $10 = 8 7=40Q 

DLAB TOTAL = $ 32,360 

4. MATL8 - Replacement parts for the two lasers are based on 

thyratron replacement and weekly parts refurbishment 

- 60 - 
previously described. Excimer gas consumption with the gas scrubber was calculi ‘ed at slightly less than S0.05/hr. 

Preliminary calculations of reactant gas consumption, 

assuming thqt N2 is used as the carrier, show insignificant 

usage. Calculated material costs are: 

Gas consumption, annual (ArF) -$ 173 

Weekly part refurbish @ cost of Sll7/laser (2) = $ 5,136 

Part replacement monthly @ cost of $1250/laser = $-3Q&QQ 

Thyratron replacement @ 6 week intervals: = $ 38,280 

2 lasers x 8.7/yr @ $2,200 

MATLS TOTAL = $ 73,589 

5- UTIL - Annual KWHRs for equipment were estimated at: 

Wafer transport = 1,768 KWHR 

Thyratron s = 10,404 KWHR 

Gas ieprocessing - 6 94 

Scrubber I1.768 

UTIL TOTAL @ $0.075/KWHR = S 1,097 

- 

.. . (d) mer Wde Peon -nd wde Gr1- EOPT - Two racility setups are required using identical 

lasers but operating at different rates due to process dwell 

time to control the oxide thickness. One setup deposits 

only 15 to 20A and accomplishes the requireil crepoGition 

rates/wafer with only one ArF laser. Second stage, 

performed subsequent to the laser metallization process described above produces oxides grown to approximate19 751( 

and hence requires proportionally longer process times. 

Equipment types for the two facilities is identical varying only in that there are two lasers employed in the growth 

step. The gas processor, source gas scrubber and K-bottle 

bank costs are split on a 30:70 basis between the 

facilities : 

For oxide passivation: 

1 EXC-2 laser - $27,000 

1 N/C table = 10,000 

1 Microprocessor = 3,000 

3/10 scrubber = 30,000 

3/10 gas reprocess = 3,000 

Cell transport 7,500 

K-bottle farm =1,00[! 

PASSIVATION EQPT TOTAL = $81,500 

For oxide growth equipment cost8 are: 

2 EXC-2 ArF lasers = 8 54,000 

7/10 gas processor = 7,000 

1 microprocessor P 3,000 

2 N/C tables = 10,000 

- 61 - 
K-bottle bank X 1,000 

7/10 source gas scrubber = 70,OQO 

OXIDE GROWTH EQPT TOTAL = $1558000 

2. E&- An additional 20 FT2 of facilities area is required dGe to the second laser. The passivation process is 

allocated 78 PT2 and the growth step. 98 FT2. 

3. - The passivation facility operates at only 1.3 

shifts/day to achieve the 650 wafer/hour rate. Maintenance 

labor is assumed to be required at 67% of the normal rate 

for full shift operation. For this step, the direct labor 

is: 

Operators 1.3 shifts x 2080 Br @ $6 = $ 16,224 

Maintenance = 175 Hr/Yr @ $10 =J&zsQ PASSIVATION DLAB TOTAL = $17,974 

By contrast, to achieve 650 wafers per hour, the oxide 

growth facility has 1.5 operators assigned full time for two 

shifts. Maintenance labor is equal to that of the laser 

metallization process: 

1 Operatorlshift @ $6 = $ 24,960 

1/2 Sr. Processor/shift @ $8 = 16,640 

Maintenance 740 Hr/Yr @ $10 - 7.40Q 

OXIDE GROWTH DLAB TOTAL = 848,000 

4. - Direct materials costs for these two similar 

processes are assumed to be proportional to the laser front 

contact metallization at directly and by twofold 

respectively. 

5. nTlL - The KWHR estimates for both processes were based on 

predicted rates for the lasdr metallization process adjusted 

for relative cost sharing. 

- 62 - 
The project goal :c produce 16.5% cells has not yet materialized. 

Major problem8 are believed to be beam nonuniformity and the deep channeling distance of 31P+ ions, even at 5 keV. Improvemeat to 

the beam uniformity is in progress by installation of a 

kaileaoscope 6s described in Section 4.2. Low keV ion 

implantation would reduce the ion channeling distance which 

requires lower annealing energy, leaving the surface less damaged 

at the overlap area. However, at the time of this report, the 

lowest kev available is 5 keV. 

An alternate approach is to use an n-type substrate with a boron 

ion implant which will nave lower penetration depth and has been 

reported to produce 16.5% efficiency (R. Young, App. Phys. Lett. 

1983) on 1x2 cm2 cell area. 

During the next quarter work will focus on developing the laser 

annealing process €or boron ion implantation and developing a 

capability for uniforni dopant incorporation. 

Figure 27 shows the program status. 

- 63 - 
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Hovel, Harold. Semiconductors and Materials, Vol. 2, p. 40, 1975 

Young, R.T., Van der Leeden, G-A., Narayan, J.# Christie, #.Hef 

Wood, R.F., Rothe, D.G., and Levanther, J.I. IBEB Electron 

Device Letters, Vol. EDL-3, No. 10, 1982. 

Lockheed Quarterly Report No. 2, JPL Contract 955696, 1980. 

Young, R.T., Van der Leeden, G.A., Wood, R.F. and Westbrook, ROD. 

Applied Physics Letters, 43 (71, p. 666, 1983. 

i’UXEDING PAGE BLANK KOT FEWTD 

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