Beam Shaping for CW Laser Recrystallization of Polysilicon Films
- PDF / 2,747,321 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 4 Downloads / 197 Views
BEAM SHAPING FOR CWLASER RECRYSTALLIZATION OF POLYSILICON FILMS P. ZORABEDIAN, C.I. DROWLEY, T.I. KAMINS, AND T.R. CASS Hewlett-Packard Laboratories, 3500 Deer Creek Road, Palo Alto, CA
94304
ABSTRACT A shaped laser beam has been used for laterally seeded recrystallization of polysilicon films over oxide. Direct maps of the shaped-beam intensity distribution in the wafer plane are correlated with the grain structure of the recrystallized polysilicon. Using 60% overlapping of shapedbeam scans along directions, we have obtained seeded areas one mm wide and 50 to 500pm long. These consist of 40Pm-wide adjacent single-crystal strips regularly separated by low-angle grain boundaries extending laterally away from the seed openings. The spacing between grain boundaries is equal to the scan spacing, providing a means for controlling the location of grain boundaries in otherwise defect-free, single-crystal films. INTRODUCTION Single-crystal silicon films which are free of all grain boundaries are desirable for the application of recrystallized silicon-on-insulator structures to VLSI. Energy-beam shaping can be used to prevent heterogeneous nucleation and promote growth of long individual grains. The cw Ar-ion laser offers the potential for good control over the recrystallization process because of the ability to produce a narrow molten zone and to shape the beam with a variety of optical techniques. Recent work with argon lasers has concentrated on shaping the laser spot either by inserting masks in the TEMo0 (Gaussian) mode [1] or by forcing the laser to run in the TEMOI* mode [2]. In those experiments the shape of the beam at the wafer was inferred, but was not directly observed. In our experiment the beam was shaped by using a 900 metal wedge to mask the trailing edge of a TEMo 1* beam, and the intensity distribution at the wafer surface was directly mapped with a computer-controlled photodiode system L3]. This correlation was useful because the heat diffusion time is much less than the laser dwell time for the spot sizes and scan speeds typically used for recrystallization [4]. Therefore, the local temperature responds to the local laser intensity as the beam is swept across the polysilicon, and the details of the intensity distribution in the laser spot strongly affect the recrystallization process. In the first part of this study, the beam-shaping technique was characterized by correlating the grain structure of isolated scans with the experimental shaped-beam intensity distributions. Subsequently, the shaped beam was used for laterally seeded recrystallization. MATERIALS and APPARATUS A Coherent System 5000 laser annealer was used, with modifications for mapping and masking the beam. In this system, the beam size at the wafer surface is adjusted by varying the working distance between the lens and the wafer. The samples studied were three-inch wafers containing a O.55pm LPCVD polysilicon layer over a 1. 4 pm Si0 2 film on a (100)-oriented silicon substrate. Mat.
Res.
Soc.
Symp.
Proc. Vol.
13 (1983) ®Elsevier
Data Loading...
