The Effect of Channel-Protect Oxide on Laser Recrystallized Silicon-on-insulator MOS devices.
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THE EFFECT OF CHANNEL-PROTECT OXIDE ON LASER RECRYSTALLIZED SILICON-ON-INSULATOR MOS DEVICES.
S. Sritharan, G. J. Collins, J. Fukumoto , N. Szluk M. M. Al-Jassim** Colorado State University, Fort Collins, C080523.
,
K. M. Jones
and
NCR Microelectronics, Ft Collins, C080525. **SERI, Golden, C080401.
ABSTRACT Latchup free lateral CMOS transistors with PMOS devices in the laser recrystallized silicon and the 140S devices in the bulk silicon were fabricated. One micron thick field oxide isolates the PMOS devices in the recrystallized silicon from the NMOS devices in the bulk wafer. The seed area for recrystallization was used for the fabrication of the NMOS devices. An oxide layer of 0.1um thickness was used to protect the channel region of the NMOS devices during the laser recrystallization. The effect of this channel protect-oxide is discussed and the characteristics of the NMOS devices with and without the channel protect oxide are compared. INTRODUCTION Many techniques have been used to achieve Silicon-On-Insulator (SOI) structures. Among them graphite strip heater recrystallization [1], electron beam recrystallization (2] and laser recrystallization [3] can be categorized as melt grown SOI techniques. In these techniques, a layer of polysilicon film deposited on thermally grown oxide on silicon is melted by a heat source and the recrystallization front is propagated in a lateral direction from side to side.
Grain and subgrain boundaries are for-med
during the propagation and seed patterns on the oxide layer have been used to suppress these boundaries. The integrity of the bulk silicon wafer in seed region will be affected during the recrystallization and this inturn will degrade the properties of the devices fabricated in the seed region. We have fabricated CMOS devices called bi-layer lateral CMOS and the properties of these devices have been discussed earlier [4]. These devices consist of PMOS devices fabricated in the recrystallized silicon layer and the NMOS devices fabricated in the bulk substrate in the seed region. A layer of thin oxide called CHannel-Protect OXide (CHPOX) was grown in the seed region and localized to the channel region of the NMOS transistors to protect the channel region during the laser recrystallization. The effect of CHPOX will be disscused in this paper. PROCESS
One micron thick thermal oxide was grown with patterned line seed holes. One thousand angstroms of CHPOX was thermally grown and localized to the channel region of the NMOS transistors to be fabricated in the seed region and 0.5 um polysilicon was deposited by LPCVD method. Two hundred angstroms thick oxide was thermally grown and 500 X thick silicon nitride was deposited to act as capping layer. A sequentially raster scanning argon ion beam of 9.5 W power and 50 um diameter was used with 55 cm/s scan speed to recrystallize this structure.
The cap layer was stripped off after
Mat. Res. Soc. Symp. Proc. Vol. 74. e1987 Materials Research Society
622
recrystallization and phosphorus was blanket implanted over the
r
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