Naresh C. Saha

Titanium nitride oxidation chemistry: An x‐ray photoelectron spectroscopy study

We report a study of the oxidation of TiN. In previous work, the oxidation kinetics for 350–450 °C were reported and an initiation time prior to fast oxidation was identified. In this study, x‐ray photoelectron spectroscopy was used to investigate the oxidation mechanisms at 350 °C during this initiation time period. The oxide thickness increases slowly with oxidation time and the film appears to change from an amorphous TiO2 layer to a crystalline TiO2 layer. Spectral features which are intermediate between TiO2 and TiN are reported and a model involving grain boundary oxidation is proposed. One of the thicker oxides studied was annealed in vacuum to 700 °C. Following oxidation, some of the capping oxide and much of the intermediate material is no longer in the analysis volume and we suggest that the oxygen and nitrogen is being dissolved into the bulk in much the same way that nonevaporable getters are activated before use.

Role of native oxide in the activation of implanted Si in GaAs

We have investigated the effect of oxygen plasma treatment on GaAs surface prior to plasma enhanced chemical vapor deposition of silicon nitride cap on the activation efficiency of implanted Si in GaAs. The oxygen plasma treatment improved the activation efficiency by ∼35% over (1:10) NH4OH:H2O treatment. In addition, the oxygen plasma treated samples had uniform sheet resistance across the wafer with minimum wafer‐to‐wafer variations. X‐ray photoelectron spectroscopy analysis of oxygen plasma treated GaAs surface indicated the formation of ∼25‐A‐thick oxide layer consisting of Ga2O3, As2O3, As2O5, and elemental As. During the activation anneal, the arsenic‐containing oxides react with the GaAs substrate to form Ga2O3 and elemental As which increases the probability that the implanted Si incorporates in the Ga sites over the As sites, and thereby improves the activation efficiency. This surface related mechanism suggests that the variation in activation efficiency is mostly attributed to variation in surf...

UV-radiation-induced degradation of fluorinated polyimide films

Abstract Fully cured fluorinated polyimide (FPI) films with low dielectric constants (⩽3.0) have been found to be chemically altered when exposed to UV radiation during a process integration study. This chemical modification is manifested in the loss of film thickness after it is subjected to UV radiation followed by photoresist stripping. The UV-radiation-induced surface modifications of the FPI film have been characterized by X-ray photoelectron spectroscopy (XPS). The XPS data show the presence of C=0 and COO-sites in the FPI molecule following UV exposure. Under prolonged UV exposure in a stepper, the FPI film acts as positive working photoresist. However, a 2kA plasma enhanced chemically vapor-deposited oxide mask and/or a typical 12 kA photoresit mask effectively shields the FPI from UV-radiation-induced degradation. The effects of FPI on UV radiation present during other normal wafer processing steps such as plasma deposition and reactive ion-etching were also studied and found to be negligible.

Chemical Stability of Reactively Sputtered AlN with Plasma Enhanced Chemical Vapor Deposited SiO 2 and SiN x

We have studied the chemical stability of reactively sputtered aluminum nitride film with plasma-enhanced chemical vapor deposited SiO 2 and SiN x films. It was found that the PECVD SiO 2 film reacted with A1N to form aluminosilicate (3Al 2 O 3 ·2SiO 2 ) at the SiO 2 /A1N interface after annealing above 550°C. The presence of Al-0 bonds at the SiO 2 /AlN interface was verified with x-ray photoelectron spectroscopy and x-ray induced Auger electron spectroscopy. The formation of aluminosilicate resulted in significant decrease in the wet etch rate of A1N layer. For SiN x /AlN/Si layered structure, no interfacial reactions were detected at the SiN x /AlN interface after annealing up to 850°C. These results confirm the thermodynamic predictions on the mutual stability of SiN x /AlN and SiO 2 /AlN.

Doping of GaAs using SF6 plasma treatment

We propose a new method of making heavily doped n‐type GaAs to a very shallow depth using sulfur hexafluoride (SF6) plasma treatment of the GaAs surface. Semi‐insulating GaAs substrate implanted with Si was exposed to a sulfur containing SF6 plasma and capped with silicon nitride anneal cap. During a subsequent anneal step at an elevated temperature to electrically activate the implanted Si, the sulfur diffused into GaAs to a shallow depth of ∼600 A resulting in further enhancement of net carrier concentration. With this technique the carrier concentration near the surface region was almost doubled compared to samples with Si implantation only. The enhanced carrier concentration improved the wafer‐scale variation of ohmic contact resistance using AuGeNi contact metals from 0.089±0.073 to 0.049±0.017 Ω mm. The surface chemistry of SF6 plasma treated GaAs surface was characterized by x‐ray photoelectron spectroscopy and Auger electron spectroscopy, and the results were compared with the carrier‐concentratio...

Oxygen Plasma Treatment of Fluorinated Polyimide: An X-Ray Photoelectron Spectroscopy Study

The oxygen plasma induced surface modifications of a fluorinated and conventional polyimide were studied by X-ray Photoelectron Spectroscopy. The interaction between polyimides and oxygen plasma resulted in the formation of carbonyl (>C=O) and carboxylic acid (-COOH) sites in both types of polyimides. In the fluorinated polyimide, -CF3 containing polymeric residues were also detected. The plasma induced residues were loosely bound to the polyimide surface and could be removed by vacuum annealing of the plasma treated surfaces restoring the as-cured polyimide surface chemistry in both types of polyimides. The mechanism of interaction of oxygen plasma with both polyimides leading to the observed surface modifications is discussed.

Aluminum Metallization of Polyimide Substrate

This paper discusses the effects of different pre-metal treatments of polyimide on adhesion between aluminum metallization and Du Pont 2555 polyimide. The interaction of oxygen plasma with poly imide resulted in the formation of carbonyl (>C=O) and carboxylic acid ( -COOH) sites on the polyimide surface and enhanced aluminum to polyimide adhesion. Heating of the oxygen plasma treated polyimide substrate in vacuum resulted in the gradual loss of carbonyl and carboxylic acid active sites, and delamination of aluminum film occurred when it was deposited onto these substrates.