Jan Van Hoeymissen

Etching of Thermal SiO2 in Supercritical CO2

Supercritical CO2 (SCCO2) processing has been proposed for several IC manufacturing applications like low-k repair, post etch residue removal, photo resist stripping or metal deposition [1]. SCCO2 presents excellent properties (liquid-like density, low viscosity and negligible surface tension) that make SCCO2 a good candidate for several FEOL and BEOL processing steps. Aqueous HF is widely used in semiconductor processing (etching, polymer removal, surface preparation ...). Anhydrous HF in SCCO2 can be used as an alternative etching process, e.g. for sacrificial SiO2 etching for MEMS or DRAM manufacturing, thus avoiding pattern collapse issues. In particular, SCCO2/HF/pyridine etching can offer good etch selectivity of SiO2 towards other materials like high-k dielectrics. Low HF concentration in SCCO2 can also be used for BEOL post etch residue removal (PERR) [2]. However, the chemical reaction mechanisms occurring during the etching of SiO2 with HF/pyridine complex in SCCO2 are basically unknown. In this paper, the etching of thermal SiO2 using HF/pyridine in SCCO2 has been studied in detail. The impact of various processing parameters (processing temperature, HF concentration in SCCO2, etching time, ...) on the etch rate is reported. The chemical reactions, etching mechanisms and reaction product formation involved in SiO2 etching using SCCO2/HF/pyridine chemistry are also investigated.

Particle-Substrate Interaction Forces in a Non-Polar Liquid

Aqueous chemistries have been used for the past 30 years in semiconductor cleaning processes and show, amongst many benefits, good particle removal efficiency. However, water can lead to pattern collapse during drying, corrosion of metal layers, inefficiency in cleaning hydrophobic surfaces and in removing polymer residues. With the planned down-scaling to sub-45 nm devices, and the continuous introduction of new materials, industry requirements are becoming stricter and all these inconveniences must be overcome. Water-based chemistries are thus being pushed to their limits and non-aqueous solvents are being investigated as a possible replacement for some specific applications. In aqueous media, surface groups of solid surfaces are highly dissociated and counterions in solution give origin to a diffused electrical double layer [1]. When a particle comes into the vicinity of a surface, the two double layers overlap causing electrostatic repulsion. Playing with the pH of aqueous solutions it is possible to improve the repulsion, thus preventing particles to deposit onto the surface. This scenario gets worse in non-aqueous solvents: most common solvents are less polar than water, thus suspended solid surfaces are weakly dissociated. Consequently, the diffused double layer is weaker and particles may adhere to the wafer surface because of insufficient electrostatic repulsion [2]. For this reason, a fundamental study of particle-substrate interactions in low-polar solvents was started [3]. In anhydrous alcohols (13< εR <32), it was shown that the silicasilica interface is always repulsive, and the magnitude of repulsion decreases with the relative permittivity of the alcohol.

Recovery of Tungsten from the Exhaust of a Tungsten Chemical Vapor Deposition Tool

An ETC Dry Scrub plasma scrubber has been successfully tested for the capturing and recovery of metallic tungsten from the exhaust of a W chemical vapor deposition (CVD) tool. The scrubber operation was completely transparent to the upstream CVD process. The WF 6 destruction removal efficiency of the scrubber was determined with a quadrupole mass spectrometer. The system had been tested with two different plasma frequencies: 100 and 40 kHz. With the 100 kHz frequency, the destruction efficiency of WF 6 reached an initial value of 98% at a nominal dissipated power of 1200 W. However, the layer of W deposited on the scrubber electrodes contained hydrates of tungsten oxides. Moreover, the destruction efficiency of WF 6 dropped to less than 70% after eight consecutively processed wafers (memory effect). Introducing an intermediate H 2 plasma treatment ensured a continuously high efficiency, and improved significantly the purity of the deposited W layer in the scrubber With the 40 kHz power supply, the maximum efficiency reached is more than 99% from a nominal dissipated power of 1100 W on. The purity of the deposited W layer is high (>99%). No memory effect was observed. Successful marathon runs have been performed with each tested frequency.

Metal Contamination on Silicon Surfaces from Solvents

Introduction The use of organic solvents is well established in semiconductor manufacturing. With the development of advanced cleaning methods, using e.g. CO2, solvents will become even more important. The impurity level in solvents is typically 50ppb or better. This is of the same order as the impurity level in aqueous chemicals. In contrast to DI water, however, the effects of impurities in solvents are not well known. In previous publications, contamination in photoresists has been discussed [1,2]. Photoresists are complex blends of solvents and photoactive polymers. During spinon, the solvents evaporate, leaving behind the polymers and possibly contamination. However, interactions between substrate and contaminants in the liquid solvent phase can not be excluded. As a first step in a more systematic approach, we studied silicon surface contamination from pure organic solvents.