Selective Deposition Process Research Articles

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.

Selective Electroless Metal Deposition for Via Hole Filling in VLSI Multilevel Interconnection Structures

Selective electroless metal deposition process is investigated for via hole filling to provide a planar surface for the fabrication of high density multilevel interconnections. The substrates used in this work consisted of a 1.0 μm thick Al layer covered with 1.0–1.5 μm thick CVD silicon dioxide layer. Via holes of 1.5 μm nominal size are formed in the oxide layer by plasma etching. Selective deposition of Ni is achieved by first activating the Al surface in a Pd solution, Ni is then deposited on the activated surface from an aqueous solution using dimethylamineborane or hypophosphite as reducing agents. Pd can be selectively deposited directly on the Al surface without the need of surface activation. Either hypophosphite or hydrazine is used as the reducing agent in the Pd deposition solution. Cobalt can also be selectively deposited to fill the via holes. The filled via holes can have almost perfectly planar surface. Good contact resistance has been obtained by measuring the via chain resistance.

Selective deposition of thin films by substrate argon ion bombardment

As an alternative to normal patterning in sub-micron integrated circuit technology, selective processes have gained in interest. One fairly well known process is the thermally activated decomposition of WF 6 to deposit selectively a thin tungsten film onto silicon areas of patterned wafers. Some problems with the thermal decomposition technique are the need for a specific metal carrying gas and an elevated process temperature. In a series of articles we have presented a completely new process for selective deposition, using high bias sputtering in an argon atmosphere. If the substrate bias is increased to the point where the net deposition rate becomes almost zero, substrate-dependent effects such as different sputtering yields (because of the difference in binding energy to different substrate atoms) and sticking coefficients for different surfaces come into action. On a patterned silicon wafer, it is thus possible to deposit material on silicon areas but not on the oxide (or vice versa), without the use of any photoresist masking. To make the mathematical model describing this selective process more comprehensible, we have developed a graphical method using a nomogram, that simplifies the prediction of selectivity between various materials. To further point out the possibilities of this selective method, results from ion beam selective deposition of platinum onto patterned silicon wafers are also presented.

Low-temperature (250 °C) selective epitaxy of GaAs films and p-n junction by laser-assisted metalorganic chemical vapor deposition

Low-temperature selective epitaxial growth of device quality GaAs has been achieved by laser-assisted chemical vapor deposition (LCVD). GaAs substrates thermally biased to temperatures in the range 250–500 °C were irradiated by an Ar ion laser to induce localized deposition of GaAs. Carefully selected growth conditions resulted in growth rates as low as a monolayer per second at 250 °C. This is the lowest substrate temperature for epitaxial GaAs with optical and structural quality comparable to those achieved in conventionally metalorganic chemical vapor deposition grown GaAs. Also reported is the first p-n junction by LCVD technique using zinc as the p-type dopant. This new low-temperature selective deposition process can lead to maskless fabrication of multicomponent devices on the same wafer.

Thermochemical modeling of interfacial reactions and selective deposition at growth from the vapor

Advances in various computational techniques for chemical equilibria now enable complex multicomponent chemical vapor deposition systems to be analyzed. The results obtained from the thermodynamical calculations can be used to construct ‘‘road maps’’ indicating how changes in the experimental parameters can affect deposition conditions. In this paper, thermochemical modeling and its use are discussed for two major areas: (i) Interfacial reactions at the initial stages of growth. These reactions influence adhesion, autodoping, grain size, and topography of the interface. (ii) Selective deposition processes based on differences in chemical reactivity between different substrate areas. Parameters for prediction of selectivity and for identification of selectivity modifiers are introduced.

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.

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.

Selective deposition of tungsten—prediction of selectivity

Preferential or selective chemical vapor deposition to a substrate region is based on a difference in thermochemical stability between different substrate regions. The higher this difference is, the higher selectivity is expected. In this paper a thermodynamic analysis of selective deposition of tungsten from H2 and WF6 on silicon regions in the presence of silicon dioxide is presented. At the initial stages of growth—silicon present in the vapor—the selectivity is favored by a low temperature, a low total pressure and a high WF6 concentration in the vapor. For the continuation—growth on the deposited tungsten—a low total pressure, a low WF6 concentration in the vapor and a higher temperature than that used initially should be chosen for highest selectivity. From the analysis it is also seen that simultaneous etching and tungsten oxide/tungsten deposition may occur on the silicon dioxide. The technique used to analyze the selective tungsten deposition process seems to be a useful tool for optimizing the selectivity in a given system and for reducing or eliminating undesired side reactions.

Interfacial Structure of Tungsten Layers Formed by Selective Low Pressure Chemical Vapor Deposition

We have analyzed the interfacial structure of selectively deposited LPCVD tungsten on monocrystalline silicon, polycrystalline silicon, and polycrystalline aluminum substrates. Cross‐sectional specimens were examined by transmission electron microscopy to determine the amount of substrate consumed by the selective deposition process and to assess the degree of lateral encroachment under masking layers for different conditions of deposition and surface preparation. The tungsten‐silicon interfacial structure was found to depend strongly on the initial surface preparation. Immersion in a dilute solution resulted in a smooth interface, while a glow‐discharge treatment led to highly irregular interfaces, which, in extreme cases, contained tunnels extending 1 μm or more into the silicon substrate. Layers formed in plus were found to consist of two layers, of which the lower layer is formed by the substrate reduction of .