Low Pressure Nitrided‐Oxide as a Thin Gate Dielectric for MOSFET's

The kinetics of thermal nitridation of silicon dioxide in ammonia ambient has been studied. SiO2 films of 100-1000~ thick were thermally nitrided at 950~176 for times from 15s to 2h. Our experimental results based on etch rate and Auger electron spectroscopy measurements clearly indicate the multilayer structure of nitrided-oxide films. Nitrogenrich layers are formed at the surface and interface regions at a very early stage of the nitridation process. After a few minutes, the nitridation reaction mainly goes on in the bulk region, with the surface and interface nitrogen content remaining fairly constant. The Auger depth profiles show that the interface moves away from the nitrogen-rich layer as the nitridation proceeds. In addition, our results indicate the formation of an oxygen-rich layer underneath the nitrogenrich layer whose thickness increases with nitridation time. The formation of this oxide-like layer can be attributed to a slow oxidation of the silicon substrate at the nitroxide/silicon interface by the oxygen which is a by-product of the bulk exchange reaction between NH3 (or nitrogen containing species) and SiO2. The results of this work can be qualitatively used to explain effects such as enhanced boron and phosphorus diffusion and growth of stacking faults in the silicon substrate during nitridation of oxide.

Section: Discussionmentioning

confidence: 99%

“…Wong et al performed nitridation of 100~ oxides at relatively low temperatures (925~ and low pressures in ammonia and an ammonia plasma ambient (4). Their AES data for 100~ SiO2 nitrided at 925~ show nitrogen peaks at the surface and the interface regions, with negligible nitrogen in the bulk.…”

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confidence: 99%

Compositional Studies of Thermally Nitrided Silicon Dioxide (Nitroxide)

Moslehi

Han

Saraswat

et al. 1985

“…Thermal nitridation of SiO2 creates oxynitride films with many properties superior to their precursor oxide. Nitrided oxides can exhibit a higher dielectric constant, improved radiation hardness, and a greater resistance to contamination during subsequent VLSI processing steps (4)(5)(6)(7). Thermal nitridation is usually performed at temperatures between 800 ~ and 1200~ in ammonia containing ambients, with the extent of nitridation being proportional to the partial pressure of ammonia in the ambient (8).…”

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confidence: 99%

Properties of SiO2 on Si after Exposure to 3:1 H 2 + N 2 and NH 3

Ruggles

Koba

Tressler

1986

Thermal oxides ≃100 nm thick were exposed to 3:1 H2+N2 for 30 min at 950°C; similar films were treated in pure ammonia for 30 min at 950°C. The oxides were examined by high frequency and quasi‐static capacitance‐voltage measurements. A silicon internal reflection element (IRE) was processed in a similar manner in order to assess the effects of the thermal processing on the infrared spectrum of the thin film. The IRE was used for attenuated total reflection infrared spectroscopy, a technique that provides greater sensitivity to molecular groups such as Si‐OH, normalSi‐NHx , Si‐H, H2O , and NH3 (1, 2). Secondary ion mass spectrometry revealed the quantitative distributions of N, O, and H throughout a sample film. Ammonia exposure resulted in replacement of oxygen by nitrogen in the amorphous tetrahedral network. Films annealed in 75%H2:25%N2 (the expected dissociation products of NH3 ) were found to exhibit significantly different properties from films nitrided in NH3 , because NH3 did not attain thermodynamic equilibrium before coming in contact with the films. The H2+N2 anneal apparently increased the degree of oxygen bridging in SiO2 . Based on the IR data, a new model is proposed to explain the annealing of interface traps via H2 . Hydrogen is suspected to act as a catalyst, promoting bond rearrangement in the amorphous network. Nonbridging oxygen atoms are thought to bond to dangling silicon orbitals at the oxide/Si interface, thereby reducing the density of defects responsible for Dnormalit .

“…According to Ito et al (1), after nitridation the distribution of nitrogen in the resulting film is monotonically decreasing from the surface; however, a quite uniform distribution of nitrogen was obtained by Hayafuji and Kajiwara (2). In more recent results, there seems to be a general agreement that the nitrogen concentration in the nitrided films is higher at the surface and near the insulator (oxynitride)/ silicon interface than elsewhere (3)(4)(5)(8)(9)(10)(11)(12).…”

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confidence: 75%

“…The second difference is based on the fact that the diffusion length of nitrogen in thermally grown nitride is only several angstroms (16) and consequently the incorporation of nitrogen at the surface will influence the amount of nitrogen diffused into the bulk. On the other hand, the by-products such as oxidizing species are difficult to diffuse out of the surface because the silicon oxynitride formed in the surface region acts as a strong barrier against diffusion (1,11). These can be seen clearly in Fig.…”

Section: Kinetic Modelmentioning

confidence: 99%

The Influence of Processes on Composition of Thermally Nitrided SiO2 Film

Liu

Cheng

Liu

1988

The influence of process conditions, involving both oxidation and nitridation, on the results of nitridation of SiO2 have been investigated. The initial oxides grown by LP, dry and wet oxidations to 200-500A have been nitrided in either a directly heated reactor or an RF-heated reactor-Systematic AES analyses show that by utilizing appropriate processing techniques, different distributions of nitrogen and nitrogen-oxygen ratios can be obtained. The results demonstrate that both a low oxidation rate and a low initial nitridati0n rate will give a higher amount of nitrogen and a higher nitrogenoxygen ratio in the nitrided film. The Auger results also indicated that at the early stage of nitridation Si-O bonds were partially broken and reactions between pure and/or partially unbonded Si and nitridizing agents had occurred. The results of POSt nitridation annealing show that the nitrogen in a nitrided oxide film can be further redistributed at an elevated temperature, and the nitridation reactions in the surface and bulk regions are reversible. A multilayer model is proposed to explain the kinetics of nitridation. With this model, the different nitrogen profiles and nitrogen-oxygen ratios for different process conditions are clarified and the influence of the processes can be predicted qualitatively.