Monte A. Douglas

Ultrathin nitrogen-profile engineered gate dielectric films

A simple and novel scheme is presented for the formation of /spl sim/4 nm gate dielectric films with nitrogen at the top (gate electrode/dielectric) interface. It consists of low-temperature, remote, high-density N/sub 2/-plasma nitridation of thermal SiO/sub 2/, followed by a post-nitridation anneal. The key results are: (a) high N concentrations (10-20 at.%) incorporated uniformly within /spl sim/0.7 nm of the oxide surface, (b) little V/sub fb/-shift and no significant variation in midgap-D/sub it/ from that of control oxide, (c) suppression of B-penetration for high B levels and for high thermal budgets including a hydrogen ambient, and (d) no evidence of damage to the oxide.

VLSI Local interconnect level using titanium nitride

A local interconnect technology has been developed for VLSI CMOS applications using a titanium nitride layer. The technology has been realized by utilizing the titanium nitride layer that forms during the self-aligned titanium silicide process: which is used to simultanously reduce gate and junction sheet resistances to < 1 ohm/sq. Normally the TiN layer is discarded, but in this process the 0.1µm thick TiN layer is patterned and etched to provide local connections between gates and N+ and P+ junctions, with a sheet resistance of < 10 ohm/sq. This is accomplished without area consuming contacts or metal straps, and without any additional deposition steps, in addition to providing a VLSI version of the buried contact process, the technology results in self-aligned contacts and minimum geometry junctions, for reduced capacitance. The technology has been demonstrated by the fabrication of a CMOS VLSI memory with nearly half a million 1µm transistors.

Modeling and Optimization of Oxynitride Gate Dielectrics Formation by Remote Plasma Nitridation of Silicon Dioxide

The process of remote plasma nitridation of ultrathin gate dielectrics was modeled and optimized using response surface models and physical-based models. Nitrogen profiles in SiO 2 were obtained by time of flight secondary ion mass spectroscopy (SIMS), and models were developed to predict the total nitrogen dose, top surface (SiO 2 -polysilicon) nitrogen concentration, and bottom interface (Si-SiO 2 ) nitrogen concentration. Models were also developed to predict the resulting decrease in effective electrical oxide thickness. These models were used for gate dielectric engineering by optimizing the nitrogen profile in SiO 2 dielectric for (i) maximizing the nitrogen concentration at the top surface and the total integrated nitrogen dose (for prevention of boron penetration) and (ii) minimizing nitrogen concentration at the bottom Si-SiO 2 interface (for minimum degradation to metal oxide semiconductor field effect transistor transconductance).

Depth Profile Analysis of Ultrathin Silicon Oxynitride Films by ToF‐SIMS

A new method to depth profile N and O concentrations through sub-30 A silicon oxynitride films by time-of-flight secondary ion mass spectrometry (ToF-SIMS) is examined. Using secondary Si + matrix ions to cationize neutral molecular and elemental species, quantitative N and O concentration (concn) data are obtained through sub-30 A films with N concns of 12 atom % or less. Concentration depth profiles through 10 A thick silicon oxide films are achieved. Isobaric mass interference with the Si 2 N + peak at unit atomic mass resolution elevates the N background concn to 0.25 atom % at a 5 A depth. At higher mass resolution (m/Δm = 5,500 full width at half-maximum), the N background is less than 0.1 atom % at 1 A, achieving a baseline level of 0.015 atom % after 10 A. Using a reference sample, variation in O and N depths and concentrations over several months is less than 2% relative standard deviation.

Silicon diffusion characteristics of different surface imaging resists

This paper describes a study of the silylation characteristics of different resists that are suitable for single-layer, surface-imaging patterning applications. In particular, the effect of different process parameters on the silicon diffusion in UCBs Plasmask®resist is discussed. The diffusion profile of silicon in the resist is decorated by a staining technique followed by SEM analysis. This allows for two-dimensional resolution of the diffusion profiles and the observation of other process attributes. Links are established among exposure, silylation and etch by observing silylated profiles. It is shown that the silylation profile characteristics are dominated by the resist image created during exposure. Also, the effects of post-exposure bake and silylating agent temperature are presented. Diffusion profiles for MacDermids PR1024 are also shown.

Photo-stimulated removal of trace metals

Generally, and in one form of the invention, a method is presented for the photo-stimulated removal of trace metals 16 from a surface 11, comprising the steps of covering the surface 11 with an ambient species 14, exciting the trace metals 16 and/or the ambient species 14 by photo-stimulation sufficiently to allow reaction of the trace metals with the ambient species to form metal products, and removing the ambient species 14 and the metal products from the surface 11. Other methods are also disclosed.

Effect of Ar Sputter Etch on the Texture of Ti and Al/TiN/Ti Metal Stack

The effects of Ar sputter etch and Ti deposition temperature on the crystalline orientation of Ti films deposited by long-throw sputtering geometry are reported. Both Ar sputter etch and high Ti deposition temperature degraded the Ti microstructure from highly (002) Ti textured to mixed (002) Ti and (011) Ti. This degradation produced a wide distribution in the crystalline orientation of Al grains in the Al/TiN/Ti stack. A mechanism based on the effects of Ar sputter etch on the oxide surface roughness and surface chemistry was proposed to explain the effect of Ar etch on the crystalline texture of Ti and Al in the Al/TiN/Ti stack.

Submicron Single-Layer Lithography Using Reactive Ion Etching

This paper describes the application of reactive ion etching to submicron single-layer lithography. It is shown that the etch selectivity of silicon containing resists is a strong function of the ion energy; that is, the selectivity increases for low ion energies. That supports the use of magnetically enhanced ion etchers for the development of single-layer silylated photoresists since the ion energy in these reactors is low for most process conditions. This paper shows that by a proper design of the reactor and the process good selectivity can also be achieved in a reactive ion etcher. This allows for the use of a simple reactor for some dry-develop lithography applications. The conditions leading to good selectivity as well as several submicron applications are described in this paper.