Ajit Paranjpe

Atomic Layer Deposition of AlO x for Thin Film Head Gap Applications

A 150-200°C atomic layer deposition (ALD) process has been developed for advanced gap and tunnel junction applications for thin films heads. The primary advantage of the ALD process is the near 100% step coverage with properties that are uniform along the sidewall. This process provides smooth (R a ≃ 2 A), pure (impurities <2 atom %), AlO x films with excellent breakdown strength (9-10 MV/cm). The process uses trimethylaluminum (TMA) as the aluminum source and water as the oxidant. The optimal precursor/oxidant delivery methods for high breakdown strengths were found to be vapor draw for the TMA and a bubbler for the water. For both reagents, a sweep gas is used to reduce the transit time to the wafer. The ALD AlO x films are continuous and exhibit excellent insulating characteristics even down to 5-10 A making them a potential candidate for tunnel barriers for magnetic tunnel junctions. By plasma annealing the films in situ every 25-50 A, the as-deposited tensile stress becomes slightly compressive and the breakdown field exceeds 10 MV/cm. ALD provides a relatively low deposition rate of 0.8 A/cycle. A small chamber volume that allows the cycle time of 5 s is the key to meeting production throughput requirements of 4-6 w h -1 for a 100 A film.

Ultralarge scale integrated metallization and interconnects

The use of copper interconnects enables higher speed, enhanced electromigration lifetime reliability, reduced power consumption, and ultimately reduced manufacturing cost for silicon integrated circuits. The formation of planarized inlaid copper interconnects requires sequential deposition of a continuous diffusion barrier layer followed by copper seed/fill deposition and chemical-mechanical polishing (CMP). In this article we present a vacuum-integrated cluster tool technology for deposition of a TaN barrier and copper seed/fill layers using metalorganic chemical vapor deposition (MOCVD). The MOCVD-based TaN layers deposited at substrate temperatures below 430 °C are highly conformal, have 800–1000 μΩ cm resistivity, have satisfactory adhesion to silicon dioxide, and provide superior diffusion barrier properties compared to Ta and TaN layers deposited by physical vapor deposition. The cluster MOCVD-Cu process is capable of depositing conformal and low-resistivity copper seed layers with satisfactory adhe...

Use of a TiN cap to attain low sheet resistance for scaled TiSi 2 on sub-half-micrometer polysilicon lines

A new process technology has been demonstrated that successfully addresses an urgent challenge in silicide technology scaling: the formation of low-resistivity TiSi/sub 2/ on sub-half-micrometer polysilicon lines. The key idea is the use of a TiN cap during the silicide process to minimize contaminants and stress in the film. No complex process steps have been added, and the thermal budget actually has been reduced, allowing for easy integration into standard CMOS technology. The new technology enables low sheet resistance values to be attained for scaled-down TiSi/sub 2/ thicknesses on sub-half-micrometer geometries, and thus, is eminently suited for scaling TiSi/sub 2/ technology.

Meeting the process challenges for spin-valve fabrication on an industrial scale

We investigated industrial deposition processes for spin-valve giant magneto resistance (GMR) multilayers. We compared rf diode with dc magnetron deposited films, as well as films deposited in a cluster tool equipped with single target process modules and a multitarget module. It is found that the best MR response is obtained by using dc magnetron deposition in a multitarget process module, as this minimizes contamination by background gas atoms and interface mixing due to self-biasing of the substrate. Furthermore, dc magnetron deposition allows accurate control of the deposition time, and thus the thickness of 10–100 A films. Applying this method to spin-valve deposition results in a controllability of 0.5 A, a uniformity around 1% (=1σ) over 150 mm wafers and repeatability around 1%. This implies that this process meets the requirements for production of GMR magnetic read heads.

A statistical approach to optimization of alumina etching in a high density plasma

Inductively coupled plasma (ICP) reactive ion etching of Al2O3 with fluorine-based gas chemistry in a high density plasma reactor was carried out in an initial investigation aimed at data storage applications. A statistical design of experiments was implemented to optimize etch performance with respect to process variables such as ICP power, platen power, direct current (dc) bias, and pressure. Both soft photoresist masks and hard metal masks were investigated in terms of etch selectivity and surface properties. The reverse power dependence of dc bias on the ratio of ICP to platen power was elucidated. Etch mechanisms in terms of physical and ion enhanced chemical etchings were discussed. The F-based chemistry greatly enhances the etch rate of alumina compared to purely physical processes such as ion milling. Etch rates as high as 150 nm/min were achieved using this process. A practical process window was developed for high etch rates, with reasonable selectivity to hard masks, with the desired profile, a...

Modeling the uniformity in a magnetron etching system

Magnetically enhanced reactive ion etch (MERIE) systems are increasingly popular for etching applications which demand high anisotropy and high etch rates without sacrificing etch selectivity. Conventional planar magnetron etch systems in which the magnetic fields are radial, exhibit a nonuniform race track etch. We report on an adjustable, rotating field, planar MERIE system. An etch uniformity of ±5% (6 in. wafer diameter) for resist etching in an O2 plasma has been obtained over a wide range of conditions. The impact of magnetic field adjustment and contoured electrodes on resist etch uniformity is characterized. An equivalent circuit model coupled with a diffusion model, and a Monte Carlo simulation of secondary electron transport have been used to predict the spatial distribution of plasma parameters in an Ar plasma sustained between planar electrodes. The measured magnetic field distribution, radio‐frequency power, current, and voltage are used as inputs to the model. The spatial distribution of the...

Ion Beam Patterning of High-Density STT-RAM Devices

Dependence on ion beam energy, ion species, and incidence angles is investigated to reduce sidewall re-deposition on the magnetic tunnel junction barrier. Experimental and simulated etch data, for a representative spin-torque transfer random access memory structure with 40 nm critical dimension and 150 nm pitch, indicated a reduction in the sidewall re-deposition when operating at: high angle, high voltage, and with Xe as the source gas. The Monte Carlo binary collision model simulations showed re-deposition thickness reduced by ~75% with Xe versus Ar at 1 kV beam energy and 30° incidence angle.