Electrical Characteristics of Ultra-Thin Multi-Layers of Poly-Si and Silicon Dioxide
- PDF / 1,015,203 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 93 Downloads / 172 Views
KEVIN K. CHAN, YOUNG H. LEE, AND CAROL L. STANIS IBM Research Division, Thomas J. Watson Research Center, Yorktown Heights, NY 10598
ABSTRACT Rough-surface polycrystalline silicon films have been used for fabrication of electrically erasable-programmabe read-only-memories (EEPROM). Silicon-Rich Oxides (SRO), also known as semi-insulating polycrystalline silicon (SIPOS), have been recommended for use as electron injectors. The advantage of SRO as injectors is that both the bottom and top surfaces of the filn can be used to obtain high field enhancement. An ultra-thin multi-layer structure of silicon and silicon dioxide has been fabricated by low pressure chemical vapor deposition (LPCVD). High resolution TEM shows alternating layers of 50 A thick Si0 2 and polycrystalline Si (grain size ,-, 80
A) films were deposited and MOS capacitors using this multilayer dielectric were studied to understand their electrical characteristics.
Both I-V and C-V measurements show that the Fowler-
Nordheim tunneling current is proportional to the number of polycrystalline layers. The "turn-on" voltage of the tunneling current is determined by the thickness of first SiO2 layer, and the effective dielectric constant varies from 3.9 to 9.1, proportional to the number of poly-Si layers within the multi-layer structure (MLS). 0
For a 350 A stack (7 layers), the interface trap density, Dl,, was
2
3x101 traps/cm , and the effective dielectric constant was roughly 9.
INTRODUCTION: Rough-surface polycrystalline silicon films have been used for fabrication of EEPROM cells. These poly-Si films, consisting of bumps 1000 A in diameter, are thermally oxidized at high temperature to form polyoxide'. The entire structure of rough poly-Si and polyoxide may be used as an efficient electron injector for the EEPROM cells. However, these polyoxides suffer from a high 2
rate of electron trapping which reduces the number of erase/write cycles . Silicon-rich oxide (SRO) has also been recommended as an electron injector because the operating voltage for both the
845 Mat. Res. Soc. Symp. Proc. Vol. 358 01995 Materials Research Society
write/erase operation is significantly reduced due to the enhanced electron injection from the higher electric field at the surface of the silicon islands within the SRO network3 . In this study, we have synthesized a new dielectric structure by alternating layers of poly-Si and SiO 2 deposited in a conventional low pressure chemical vapor deposition (LPCVD) system. Tlhis poly-Si/SiO 2 multilayer structure (MLS) exhibits a regular array of poly-Si grains scparated by an ultra-thin Si'
2 film
and
shows an enhancement of tunneling current which is similar to the characteristics of an SRO film.
EXPERIMENTAL N-type, < 100 > -oriented, 2 to 5 tl-cm silicon wafers were used as substrates. After RCA cleaning, substrates were placed immediately inside the LI'CVD furnace at 700 °C to grow 30
A
of SiO 2 at 0.4 torr in O0ambient. Then, the multi-layer structure (MLS) was deposited by alternately depositing 75 A of poly-Si
Data Loading...
