Methods for passivating silicon devices at low temperature to achieve low interface state density and low recombination velocity while preserving carrier lifetime
- Duluth, GA
- Marietta, GA
A new process has been developed to achieve a very low SiO.sub.x /Si interface state density D.sub.it, low recombination velocity S (<2 cm/s), and high effective carrier lifetime T.sub.eff (>5 ms) for oxides deposited on silicon substrates at low temperature. The technique involves direct plasma-enhanced chemical vapor deposition (PECVD), with appropriate growth conditions, followed by a photo-assisted rapid thermal annealing (RTA) process. Approximately 500-A-thick SiO.sub.x layers are deposited on Si by PECVD at 250.degree. C. with 0.02 W/cm.sup.-2 rf power, then covered with SiN or an evaporated thin aluminum layer, and subjected to a photo-assisted anneal in forming gas ambient at 350.degree. C., resulting in an interface state density D.sub.it in the range of about 1-4.times.10.sup.10 cm.sup.-2 eV.sup.-1, which sets a record for the lowest interface state density D.sub.it for PECVD oxides fabricated to date. Detailed analysis shows that the PECVD deposition conditions, photo-assisted anneal, forming gas ambient, and the presence of an aluminum layer on top of the oxides during the anneal, all contributed to this low value of interface state density D.sub.it. Detailed metal-oxide semiconductor analysis and model calculations show that such a low recombination velocity S is the result of moderately high positive oxide charge (5.times.10.sup.11 -1.times.10.sup.12 cm.sup.-2) and relatively low midgap interface state density (1.times.10.sup.10 -4.times.10.sup.10 cm.sup.-2 eV.sup.-1). Photo-assisted anneal was found to be superior to furnace annealing, and a forming gas ambient was better than a nitrogen ambient for achieving a very low surface recombination velocity S.
- DOE Contract Number:
- E21-H21; E21-H31
- Assignee:
- Georgia Tech Research Corporation (Atlanta, GA)
- Patent Number(s):
- US 5462898
- OSTI ID:
- 870137
- Country of Publication:
- United States
- Language:
- English
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passivating
silicon
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achieve
interface
density
recombination
velocity
preserving
carrier
lifetime
process
developed
sio
cm
effective
eff
oxides
deposited
substrates
technique
involves
direct
plasma-enhanced
chemical
vapor
deposition
pecvd
appropriate
growth
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followed
photo-assisted
rapid
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annealing
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500-a-thick
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250
degree
02
-2
rf
power
covered
evaporated
aluminum
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350
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1-4
times
10
-1
sets
record
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date
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top
contributed
value
metal-oxide
semiconductor
model
calculations
result
moderately
positive
oxide
charge
11
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-4
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superior
furnace
nitrogen
achieving
surface
silicon device
enhanced chemical
aluminum layer
forming gas
thermal annealing
silicon substrates
chemical vapor
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