Manoj K. Jain

STEP COVERAGE PREDICTIONS USING COMBINED REACTOR SCALE AND FEATURE SCALE MODELS FOR BLANKET TUNGSTEN LPCVD

A reactor scale model (RSM) for a stagnation point, single wafer reactor for blanket tungsten LPCVD is used to calculate concentrations at the wafer surface. These concentrations and the wafer temperature, which is assumed to be measurable, are needed to determine the local tungsten deposition rate on the wafer and local film conformality (step coverage) in features on patterned wafers. Two feature scale models (FSMs) are used to determine step coverages in infinite trenches which have rectangular initial cross sections and an aspect ratio of five, as a function of reactor operating conditions; 1. a continuum-like diffusion-reaction model (DRM) for simultaneous Knudsen diffusion and heterogeneous surface reactions, and 2. a flux based model which includes ballistic transport of molecules and heterogeneous surface reactions (BTRM).|The RSM establishes “boundary conditions” for the feature scale models, by providing the flux of each species to the local wafer surface. Step coverages predicted using the FSMs...

Step coverage of tungsten silicide films deposited bylow pressure dichlorosilane reduction of tungsten hexafluoride

Dichlorosilane reduction of tungsten hexafluoride was used to deposit tungstensilicide (WSix, x = 1−2.4) in rectangular trenches on patterned wafers at various temperatures using a commercial-scale Spectrum chemical vapour deposition cold wall single-wafer reactor. Step coverages of the as-deposited films determined using cross-sectional scanning electron micrographs were in qualitative agreement with predictions of a continuum diffusion-reaction model of deposition within the features. The model correctly predicts the observed trend that step coverage degrades with increasing wafer temperature. Particularly poor step coverages are realized for conditions in which the reactor is feed rate limited, or starved, for tungsten hexafluoride. Moreover, the model also predicts that under certain conditions significant film composition variation may exist along the sidewalls within a given feature. We have confirmed this behavior using careful Auger analysis of the film deposited on the sidewalls.

Model for surface diffusion of aluminum-(1.5%) copper during sputter deposition

Surface diffusion plays a critical role in improving the step coverage of sputter deposited aluminum–copper (Al–Cu) films, which are widely used in the microelectronics industry. Unfortunately, values of surface diffusivity as a function of temperature have not been published for aluminum copper films commonly used. We present a model for surface diffusion during sputter deposition of Al–Cu films and show that semiquantitative agreement with experimental Al–(1.5%)Cu film profiles can be obtained. This modeling and experimental work is a step toward developing a method to estimate diffusivity values using films deposited in process equipment, which would prove useful in process design. Al–(1.5%)Cu films were deposited at 303, 423, 523, and 623 K, into ‘‘infinite’’ trenches which have a variety of initial aspect ratios. No substrate bias was applied in order to minimize resputtering of deposited material. Surface diffusivity as a function of temperature was estimated by comparing experimental film profiles ...

Maximizing step coverage during blanket tungsten low pressure chemical vapor deposition

Abstract A significant range of step coverages can be realized in the low pressure chemical vapor deposition of blanket tungsten films by either hydrogen reduction or silane reduction of tungsten hexafluoride, at a specified deposition rate. The step coverage realized in a single-wafer reactor (SWR) depends on the operating conditions used, e.g. feed flow rate ratios and reactant conversion level. The pseudosteady state approximation to the diffusion-reaction model is used to select the partial pressure ratios at the wafer surface which lead to a balance between reactant availability and consumption. The complete transient model is then used to demonstrate that the reactant pressure ratio obtained using this “availability analysis” maximizes the step coverage at a specified deposition rate. The reactant pressure ratio at the feature mouth is related to the inlet feed rate ratio and reactor conversion level for an SWR, assuming a well-mixed reactor. Guidelines for SWR operation are given to obtain the maximum step coverage for each system. In well-mixed reactors, the optimum feed ratio is a linear function of conversion, and approaches the stoichiometric ratio as the conversion approaches unity.

Deposition rate dependence of step coverage of sputter deposited aluminum-(1.5%) copper films

Al-(1.5%) Cu films were deposited at selected temperatures and rates into trenches on patterned wafers in order to study the deposition rate dependence of film step coverage. No substrate bias was applied to minimize resputtering of deposited material. Step coverage improves with increasing temperature and decreasing deposition rates. EVOLVE, a physically based low pressure deposition process simulator that incorporates curvature driven surface diffusion of adsorbed species, yields simulated film profiles in good agreement with experimental profiles. The results demonstrate that diffusion is a rate process critical to improving step coverage.

A general model for PVD aluminum deposition

A model for free molecular transport, surface diffusion and heterogeneous reactions in features during low pressure deposition processes is specialized to simulate film profile evolution during sputtered Al PVD. The dimensionless parameter which results from nondimensionalizing the governing equation dictates film profiles. Feature size dependent step coverages are demonstrated in trenches of aspect ratio one.<<ETX>>

Deposition of Tungsten Silicide Barrier Layers and Tungsten in Rectangular Vias

Diffusion-reaction analysis of a two step process in which a tungsten silicide barrier layer is deposited in a rectangular trench by low pressure dichlorosilane reduction of tungsten hexafluoride followed by a complete tungsten fill by low pressure hydrogen reduction of tungsten hexafluoride reveals that high step coverage and high deposition rate can be readily achieved with logical selection of process parameters. This fact, coupled with the potential for accomplishing these deposition steps in the same single wafer reactor, suggests that this two step process may offer a high throughput alternative to blanket tungsten deposition by silane reduction.