Ultra Shallow Incorporation of Nitrogen into Gate Dielectrics by Pulse Time Modulated Plasma
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Ultra Shallow Incorporation of Nitrogen into Gate Dielectrics by Pulse Time Modulated Plasma Seiichi Fukuda, Yoshimune Suzuki, Tomoyuki Hirano, Takayoshi Kato, Akihide Kashiwagi, Masaki Saito, Shingo Kadomura, Youichi Minemura1 and Seiji Samukawa1 Semiconductor Technology Development Group, Semiconductor Solutions Network Company, Sony Corporation, 4-14-1 Asahi-cho, Atsugi-shi, Kanagawa, 240-0014 Japan 1 Intelligent Nano-Process Laboratory, Institute of Fluid Science, Tohoku University, 2-1-1 Katahira Aoba-ku Sendai-shi, Miyagi, 980-8577 Japan ABSTRACT In order to obtain a controllability in the nitrogen depth profile in the oxy-nitride gate dielectrics which has been known to have a strong effect on MOS reliability, micro second ordered pulse was used for the inductive coupled plasma source in our pulse time modulated plasma. The radio frequency (RF) of source plasma and pulse frequency were 12.56 MHz and 10 kHz (100 micro second), respectively. Pulse duty ratio was varied from 20 to 100 %. 1.7nm thick thermal silicon dioxide films were subjected to the pulse time modulated plasma and analyzed by SIMS to see the depth profile of nitrogen. A new finding is that both the concentration and the peak position of nitrogen atoms in silicon dioxide films depend on the pulse duty ratio and plasma radiation time. NBTI lifetime was improved with decreased interface state density. We also used this technique to high-k material and investigated process characteristics of nitridation INTRODUCTION In the device below 90 nm generation, utilization of the plasma nitridation techniques for gate oxide films progresses quickly and many developments are tried. It is becoming impossible to disregard the problem of NBT lifetime degradation with thinner gate oxide films which met scaling. In addition, the device technology of the reduction in power consumption makes the problem of NBT lifetime degradation more serious [1-3]. For example, in order to reduce the Ioff leak current of transistor, when making Vth high, since Ids is prescribed by Vg-Vth, it is expected that degradation of Ids becomes severer. Anyway, it assumed that one of the causes of NBT degradation originated in the nitrogen injected into transistor channel part of silicon substrate as pointed out in many papers, and how to improve NBT was examined, without affecting the amount of incorporated nitrogen to gate oxide films and EOT scaling [4]. In order to improve NBT, you have to reduce the nitrogen injected into transistor channel of silicon substrates. That is, it is required to control the nitrogen profile in an oxide film to a surface side [5-7]. Although plasma nitridation is influenced with supplied power to the source of plasma, or the pressure of a reactor, it is difficult to control the energy and density of a nitrogen particle independently. In this paper, pulse time modulated plasma technique was applied to plasma nitridation, and it was shown by carrying out precision control of the energy of nitrogen injection that the improvement of NBT degradation and
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