Selective Tungsten Deposition Research Articles

Selective Tungsten Chemical Vapor Deposition with High Deposition Rate for ULSI Application

For the application of selective tungsten chemical vapor deposition (CVD) on ULSI device fabrication, two serious problems still remain: loss of selectivity and damage on devices. Selective tungsten deposition with the high rate of 1 µm/min has been achieved by a new CVD system having a cold susceptor, where the high selectivity has been well maintained continuously. We have also found that the tungsten-Si contacts with good performance of low contact resistance and no device damage can be formed by controlling the initial growth of tungsten.

Use of Selective CVD‐W with a Polyimide Mask for Local Interconnects

The use of selective chemically vapor deposited tungsten with a polyimide (P.I.) mask for local interconnects has been demonstrated with a sheet resistance of 0.60 Ω/□. The selective tungsten deposition conditions were examined. The growth rate (22–85 nm/min) was proportional to the partial pressure (0.15–0.60 mTorr). The W resistivity (14–26 μΩ‐cm) and stress (, in large features) decreased as the deposition temperature (300–360°C) was increased. The selectivity was worse at higher deposition temperatures and improved for high ratio. Loss of selectivity (stray W nuclei) was removed when the P.I. was plasma stripped. The process stability was examined (with a sheet resistance of 0.60 Ω/□) the overall standard deviation of the sheet resistance (wafer to wafer and within wafer) was 7.6%.

Characterization of Encroachment of Selective Chemical Vapor Deposition of Tungsten at the Edge of Contacts

The encroachment of selective chemical vapor deposition of tungsten at the edge of contacts has been examined with RBS, SEM, stylus height measurements, and TEM. Encroachment is minimized by using reduction instead of reduction, a deposition temperature of 340°C or less, an in situ plasma clean, and a flow ratio ≥0.1. Use of a plasma clean can reduce the W grain size by a factor of four and reduce nonuniform consumption of the polysilicon. The improvements using a plasma clean are associated with an increase in the density of chemical vapor deposition of tungsten nucleation sites.

Equipment Simulation of Selective Tungsten Deposition

This paper presents the numerical modeling of a cold wall reactor for selective tungsten chemical vapor deposition. In a two dimensional simulation the mass and heat transfer equations were solved considering the five chemical species ,, , , and . Detailed models for multicomponent diffusion and for the autocatalytic tungsten nucleation process were implemented. Model results are in good agreement with experimental findings. The simulations are used to study the impact of reactor design on selectivity.

Reactor Issues Important for the Deposition of Selective Tungsten by Chemical Vapor Deposition Using the SiH4 Reduction of WF6

ABSTRACTWe have analyzed a single-wafer chemical vapor deposition (CVD) reactor used for the selective deposition of tungsten (W) by the silanc (SiH4) reduction of tungsten hcxafluoride (WF6). Results from a reactor model, which incorporates simplified heterogeneous reaction chemistry, arc compared to experimental data obtained from the same reactor to provide insight and understanding into reactor performance and define some of the trade-offs in the design of the reactor. A reactor for this process must provide: acold-wall temperature to suppress homogeneous reactions, a uniform wafer temperature to ensure uniform stress and resistivity in deposited films, and a uniform flux of SiH4 to the wafer surface to ensure uniform thickness of films. Maintaining a small internal volume in the reaction chamber was found to be beneficial for reducing both the quantity of rcactant gas at elevated temperatures and the residence time of the gas in the reactor, both of which lead to improved selectivity.

Study on mechanism of selective chemical vapor deposition of tungsten using in situ infrared spectroscopy and Auger electron spectroscopy

Selective chemical vapor deposition (CVD) of tungsten (W) using tungsten hexafluoride (WF6) and monosilane (SiH4) is investigated by in situ infrared spectroscopy and Auger electron spectroscopy. The infrared spectra show that trifluorosilane (SiHF3) is the main by-product species, and that silicon-tetrafluoride (SiF4) is less than 20%–25% of SiHF3 in partial pressure. The main chemical reaction involved in selective W CVD can be expressed as WF6+2SiH4→W+2SiHF3+3H2. Based on our experimental results, a new mechanism of selective W CVD, which notes hydrogen dissociation having a central role in this process, is proposed. It disproves the widely accepted model, which is based on the assumption that SiF4 is the major reaction product.

Experimental and thermodynamical investigation of selective low pressure chemical vapour deposition of tungsten using WCl 6 as tungsten source

Selective low pressure chemical vapour deposition of tungsten using WCl 6 as the tungsten source was investigated both experimentally and thermodynamically. The process was found to be very sensitive to the thickness of the native oxide, thus making it difficult to obtain good reproducibility. The selectivity of the chloride process was good for both Ar-WCl 6 and H 2-WCl 6 reaction gas mixtures. Tungsten layers thicker than 2000 Å were occasionally deposited from the Ar-WCl 6 reaction gas mixture. This is explained by the porosity of the coatings, allowing for WCl 6 diffusion through the tungsten layer and permitting continued tungsten growth. Channel-like growth of tungsten into the silicon windows of patterned Si/SiO 2 was also observed when the Ar-WCl 6 gas mixture was employed. It is suggested that oxygen-containing species from the simultaneous etching of SiO 2 may promote the formation of channels.

Some considerations of the thermodynamics and kinetics of the chemical vapour deposition of tungsten

Abstract The possibility of the chemical vapour deposition of tungsten for metallisation for microelectronic applications has been considered and investigated for about twenty years, but the process still remains problematical and has serious limitations. Many of the difficulties arise from a lack of a good understanding of the chemistry of the processes and on the effect of that chemistry on layer properties and characteristics. In particular, the very limited information about the thermodynamics and kinetics of the processes allows little more than an empirical approach to the control of reaction parameters or reactor design. In this paper we review the two predominant reactions of silicon and hydrogen reduction of tungsten hexafluoride and we make some observations and comments on the thermodynamics and kinetics of the two reactions. We also review the chemistry of selective deposition of tungsten. However, in order to fully exploit the chemistry of the deposition processes it is pointed out that for both basic studies and applications it is necessary to make use of high vacuum technology in order to minimise the effect of atmospheric impurities, particularly water, and reaction by-products.

SATPOLY: a self-aligned tungsten on polysilicon process for CMOS VLSI applications

The use of complementarily doped n/sup +/ and p/sup +/ polysilicon has been proposed for future generations of CMOS technology. The implementation of this technology requires low-resistance shunts both to reduce the overall resistance of the gate level interconnections and to short out the polysilicon p-n junctions. A process in which tungsten is chosen to provide the low-resistance shunts, with the necessary gate sidewall spacers formed before the selective deposition of tungsten, is described. A nonselective tungsten deposition process, originally developed explicitly for the implementation of direct tungsten gate MOS technology, is a key step in the formation of the spacers in the SATPOLY (self-aligned tungsten on polysilicon) process. The work function stability and the adhesion of the tungsten-polysilicon double-layer structure as a function of the polysilicon glue layer thickness have also been investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Selective Electroless Metal Deposition for Integrated Circuit Fabrication

Selective electroless metal deposition process was studied for its applications in integrated circuit fabrication. Compared to selective metal deposition by CVD process, such as the selective tungsten deposition process, the selective electroless deposition process is more attractive due to its simplicity as well as process flexibility. A variety of material such as Ni, Co, Pd, and Cu were studied for contact filling, via filling, and for conductor patterns. These materials were selectively deposited on a variety of surfaces such as silicon, silicide, Al‐Si, through patterned CVD silicon dioxide, CVD silicon oxynitride, and photoresist. Although this process is still in its early stage of development, very promising results have already been achieved. The experimental conditions and results for selectively filled contact holes, via holes, and conductor patterns are described using actual examples.

Application of selective CVD tungsten for low contact resistance via filling to aluminum multilayer interconnection

Process parameters for selective chemical vapor deposition of tungsten to fill vias between aluminum or aluminum alloy multilevel metallization have been identified and demonstrated. By controlling two competing parallel reactions: Aluminum and hydrogen reductions of tungsten hexafluoride in one reduction step process, the specific contact resistivity was found to be in the range of 2.5 to 8.0 x 10−9 ohm-cm2 for 1.8 micron diameter vias. This is at least one order of magnitude lower than the values reported by the previous workers. It was also observed that alloying the aluminum did not appear to affect the contact resistance significantly. In this experiment one cold wall experimental reactor, two cold wall production systems of two different models and one hot wall tube furnace were used to deposit selective CVD tungsten on aluminum or aluminum with 1% silicon first level metal. As a consequence of these findings, problems associated with filling straight wall vias of high aspect ratio in VLSI multilevel interconnection (i.e., high contact resistance, poor step coverage, electromigration, etc.) can now be alleviated or resolved. Therefore, the use of selective CVD tungsten in the existing aluminum IC metallization becomes very attractive and feasible.

Evaluation of the Selective Tungsten Deposition Process for VLSI Circuit Applications

Tungsten films have been selectively deposited on oxide‐patterned silicon wafers using two successive deposition steps, i.e., the Si reduction of followed by the reduction of . The deposition process was performed in a horizontal hot wall LPCVD reactor. In this reactor, the surface of vertical wafers was parallel to the axis of the quartz tube. The thickness of W films obtained for a given deposition time was found to be dependent on the “history” (or the cleanliness) of the CVD reactor. The thickness uniformity across a wafer and from wafer to wafer was determined as a function of the wafer position in the CVD reactor. The selectivity of the process was evaluated by measuring the W nuclei density on the oxide (PSG) mask as a function of the thickness of W films. During the validity period of the CVD reactor, tungsten films of 220 nm in thickness were produced on 12 wafers per run with undetectable W nuclei on the mask (perfect selectivity). The CVD reactor appears to be suitable for selective deposition of W films used as diffusion barriers in Al/W/Si contact structures.

Thermodynamic investigation of selective tungsten chemical vapour deposition: Influence of growth conditions and gas additives on the selectivity in the fluoride process

Two steps in the fluoride-based selective tungsten deposition process were analysed thermodynamically: the initial step which is the silicon reduction of WF 6 and the continuation step which is H 2 reduction. The tendency of selective deposition was analysed from the calculated driving force values for the initial step, while chemical potentials were used for selectivity predictions for the continuation step. Three reaction gas mixtures were analysed: H 2-WF 6, H 2-WF 6-SiH 4 and H 2-WF 6-SiF 4. The results of the thermodynamic analysis were in good agreement with experiments. The predicted drastic increase in selectivity in addition of SiH 4 to the H 2-WF 6 gas mixture was attributed to compositional changes of the vapour. SiF 4 had only a minor influence on the selectivity but a reduced enroachment can be expected with the addition of SiF 4 to the H 2-WF 6 gas mixture. This investigation indicates that thermodynamics can be used to optimize selectivity as well as to select selectivity modifiers for chemical vapour deposition.

A comparison of tungsten film deposition techniques for very large scale integration technology

Tungsten films have long been considered as a metallization candidate for integrated circuits because of their relatively low electrical resistivity, freedom from electromigration and mid-range work function. Initial work in the early 1970s employed electron gun evaporation at high substrate temperatures in order to improved adhesion, to lower resistivity and to control the high stress present in refractory metal films. Planar diode sputtering was not widely used because of radiation damage caused by the high target voltage and the slow deposition rate. Progress in magnetically enhanced plasma technology led to the development of magnetron sputtering, and this resulted in a higher deposition rate at much lower ion energies. The high stress ever present in refractory metal films has almost been eliminated by the use of a high sputtering pressure. By contrast with evaporation, films with reasonably low resistivity in the range 10–11 μΩ cm can be routinely deposited by magnetron sputtering onto unheated substrates with excellent adhesion and reproducibilty. Successful application of magnetron-sputtered tungsten films in metal/oxide/semiconductor (MOS) devices was reported recently. In the meantime new applications of tungsten films prepared by chemical vapor deposition in very large scale integration technology are emerging. The selective tungsten deposition process, in which the desired film grows on silicon and other metals and alloys, but not on oxides and nitrides, appears to be very attractive for contact metallization in MOS devices because of the process simplicity, although there seem to be some problems associated with this process: encroachment and tunneling. The same selective tungsten films are also ideally suited to via-hole filling, contact metallization and upper level wiring. The non-selective chemically vapor- deposited tungsten films may also find applications in upper-level wiring because of their resistance to electromigration.

Formation of MOS Gates by rapid thermal/microwave remote-plasma multiprocessing

A novel cold-wall single-wafer lamp-heated rapid thermal/ microwave remote-plasma multiprocessing (RTMRPM) reactor has been developed for multilayer in-situ growth and deposition of dielectrics, silicon, and metals. This equipment is the result of an attempt to enhance semiconductor processing equipment versatility, to improve process reproducibility and uniformity, to increase growth and deposition rates at reduced processing temperatures, and to achieve in-situ processing. For high-performance MOS VLSI applications, a variety of selective and nonselective tungsten deposition processes were investigated in this work. The tungsten-gate MOS devices fabricated using the remote-plasma multiprocessing techniques exhibited negligible plasma damage and near-ideal electrical characteristics. The flexibility of the reactor allows independent optimization of each process step yet permits multiprocessing.

Achieving Low Contact Resistance to Aluminum with Selective Tungsten Deposition

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New insights on nucleation of tungsten on insulators during selective chemical vapor deposition

Selective deposition of tungsten on metals and silicon in the presence of insulators is important in several very large scale integrated circuit applications. The results of experiments investigating this selectivity are reported. The influence of the total area and composition of the selective growth surface on the nucleation of tungsten on adjacent insulators are illustrated. Specifically, nucleation is shown to occur preferentially in close proximity to the area of tungsten growth. The extent of nucleation on silicon dioxide compared to silicon nitride or phosphorus-doped glass is dependent on the composition of the surface on which the initial selective tungsten growth occurs. The qualitative observations presented here form the basis for further quantitative investigations.

Microwave Plasma LPCVD of Tungsten in a Cold-Wall Lamp-Heated Rapid Thermal Processor

ABSTRACTA novel cold-wall single-wafer lamp-heated Rapid Thermal/Microwave Remote Plasma Multiprocessing (RTMRPM) reactor has been developed for multilayer in-situ growth and deposition of dielectrics, silicon, and metals. This equipment is the result of an attempt to enhance semiconductor processing equipment versatility, to improve process reproducibility and uniformity, to increase growth and deposition rates at reduced processing temperatures, and to achieve in-situ multiprocessing in conjunction with real-time process monitoring and automation. For high-performance MOS VLSI applications, a variety of selective and nonselective tungsten deposition processes were investigated in this work. The tungsten gate MOS devices fabricated using the remote plasma multiprocessing techniques exhibited negligible plasma damage and near-ideal electrical characteristics. The flexibility of the reactor allows optimization of each process step yet allows multiprocessing.

ChemInform Abstract: Growth of Selective Tungsten on Self‐Aligned Ti and PtNi Silicides by Low Pressure Chemical Vapor Deposition.

AbstractThe Selective deposition of tungsten (WF6 source) onto TiSi2 results in the consumption of Si from the upper 40‐50 nm of the substrate.

Rapid low-resistance interconnects by selective tungsten deposition on laser-direct-written polysilicon

Polysilicon interconnections were locally deposited on oxide-covered silicon wafers by pyrolysis of silane using a scanned Ar+-laser spot. The 2-µm-wide interconnects, written at scan speeds of 2.5 mm/s, have a 500-µΩ.cm resistivity and exhibit low contact resistance to underlying Al and Al/Si structures. These films were subsequently reacted with WF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> vapor to form a tungsten-silicon composite interconnect by the silicon reduction of WF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> . Electrical tests show that the conductivity of 0.4-µm-thick conductors is enhanced up to 20-fold, by formation of a surface metallic layer having conductivity characteristic of pure thin-film tungsten. Auger and Rutherford backscattering spectra (RBS) confirm the purity and selectivity of the surface tungsten layer formed at temperatures compatible with preexisting aluminum metallization. The tungsten-polysilicon composite interconnects have applications as rapidly written discretionary metallization for prototyping and in situ analysis of integrated circuits.