Electrical Properties of Ultra Shallow p Junction on n type Si Wafer Using Decaborane Ion Implantation
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Electrical Properties of Ultra Shallow p Junction on n type Si Wafer Using Decaborane Ion Implantation
Jae-Hoon Song, Duck-Kyun Choi1, Min-Seok Oh, and Won-Kook Choi Thin Film Technology Research Center, Korea Institute of Science and Technology P.O. Box 131, Cheongryang, Seoul 130-650, Korea 1
Department of Inorganic Materials Engineering, Hanyang University
17 Haengdang-dong, Seongdong-Gu, Seoul, 133-791, Korea ABSTRACT
The junction depth should be less than 0.05 microns to fabricate sub 0.1 micron devices. This requires implanting boron with energy of less than 1 keV. One drawback in a low energy ion source is low throughput due to low ion beam current. At present, boron known for a major ptype dopant for PMOSFET has problem to easily diffuse into Si wafer even in rapid thermal processing by high diffusivity. To resolve this problem, decaborane (B10H14) molecules are implanted to make p+/n junction on n-type Si wafers for low-energy boron dopant source. Ionized decaborane is accelerated at 1~10 kV and implanted up to dosages from 1x1012/cm2 to 5x1013/cm2. Afterwards, Decaborane implanted Si wafers were post-annealed for 10 sec at 800, 900 and 1000oC, respectively. From RBS results on as-implanted n-type Si wafer implanted at 5 kV, it is observed there are amorphous Si layers with 4 nm in depth and boron ions are implanted up to 1~5 nm in depth from SIMS analysis. The electrical properties of these p-n junctions are 127~130 Ω/sq. as sheet resistance, +0.3 V turn-on voltage and –1.1 V breakdown voltage obtained from I-V measurement.
INTRODUCTION
Evolving into sub 0.1 µm device for the improved performance and greater density, the CMOS technology requires the junctions for source and drain extensions to be below 100 nm [1,2]. However, especially for PMOSFET, there are difficulties to overcome in low-energy implantation of boron ions for source/drain extensions and suppression of boron diffusion during A3.5.1
annealing process for dopant activation. To overcome these obstacles: the drastic reduction in boron ion beam current with the acceleration voltage and the transient-enhanced diffusion and thermal diffusion for boron ions, recently an alternative approach using decaborane molecules as boron clusters has been recently proposed [3-6]. When the boron clusters impact the solid surfaces, the constituents share the kinetic energy of clusters. Thus the boron ions have one-tenth lower implantation energy than that of decaborane (B10H14), which enables to implant boron ions shallowly with a suitable beam current and high ion dosage. In this paper, p-type junctions were fabricated successfully on n-type Si with this technique.
EXPERIMENTAL PROCEDURES
A vertical type accelerator, which could be accelerated up to 30 kV, was assembled and assessed. A turbomolecular pump used for pumping and keeping a main chamber under 1x10-6 Torr as basal pressure and 1~5x10-5 Torr as working pressure. A stainless steel vessel for sublimating decaborane was attached to the main chamber via a needle valve. Electrons emitted from a
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