Influence of Pre-Gate Cleaning ON Si/SiO 2 Interface and Electrical Performance of Cmos Gate Oxide
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INFLUENCE OF PRE-GATE CLEANING ON Si/SiO2 INTERFACE AND ELECTRICAL PERFORMANCE OF CMOS GATE OXIDE X. DUAN
a, b
a
a
, K. KISSLINGER , L. MAYES , S. RUBY
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a
AND J. BARRETT ,
a. National Semiconductor Corp., South Portland, ME 04106; b. MIT, Dept. of Materials Science and Engineering, Cambridge, MA 02139
ABSTRACT The Si/SiO2 interface is attracting new interest as gate dielectrics in MOS devices become ultra thin. In this paper, the impact of pre-gate cleaning on the morphology of the Si/SiO2 interface and the electrical performance of CMOS gate oxides has been systematically investigated. Using the High-Resolution Transmission Electron Microscopy (HRTEM) technique, we observed the Si/SiO2 interface at an atomic level. We have found a direct experimental relationship between the pre-gate cleaning scheme, Si/SiO2 interface morphology, and the electrical properties of CMOS gate oxides. When the ratio of H2O2:NH4OH ≥ 1.45, the roughness of the Si/SiO2 interface was dramatically improved, which, in turn, increased the Charge-to-Breakdown to an ideal value.
1. INTRODUCTION The Si/SiO2 interface arouses broad interest since it directly controls gate oxide quality; the charges and traps in the Si/SiO2 interface would produce critical effects on the gate performance of CMOS devices. The Si/SiO2 interface becomes more critical in the technologies for CMOS below 0.18µm generations as the gate dielectrics in CMOS devices become ultra thin [1]. Numerous studies have been performed to study the effect of Si/SiO2 interface on the electrical properties of CMOS devices [1 - 5], and a great amount of effort has been made to improve the Si/SiO2 interface via pre-gate cleaning. It is well known that there are four continuous steps in pre-gate cleaning procedure (RCA method) [6]. During pre-gate cleaning processes, several chemicals, such as HCl, H2SO4, H2O2, HF and NH4OH, are widely involved. Each chemical has its positive effects and negative influences. Certain chemical reactions will take place when some chemicals are intermixed. A lot of studies have been performed with the purpose of modifying However, no the Si/SiO2 interfaces via controlling the HF-based chemical mixtures [7 - 9]. systematic studies of the effect of other HF-free chemical solutions on Si/SiO2 interfaces in pregate cleaning processes have been reported yet.
AA3.43.1 1
In this paper, we have systematically investigated the effect of the SC1 chemical solution (H2O + H2O2 + NH4OH) in pre-gate cleaning on the morphology of the Si/SiO2 interface and the electrical performance of CMOS gate oxides. We directly observed the atomic structure of the Si/SiO2 interface via using the High-Resolution Transmission Electron Microscopy (HRTEM) technique, and established a relationship between the pre-gate cleaning SC1 chemistry, the morphology of the Si/SiO2 interface and the gate oxides, as well as the electrical properties of CMOS capacitors. The mechanisms for the effect of SC1 chemical solutions on the morphology of the Si/SiO2 interface and the electrical perform
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