In low pressure, radio frequency (RF) discharges of the type used in plasma processing of semiconductor materials, the rate of electron impact excitation and energy transfer processes depends upon both the phase of the RF excitation and position in the discharge. Electron impact collisions create radicals that diffuse or drift to the surfaces of interest where they are adsorbed or otherwise react. To the extent that these radicals have a finite lifetime, their transport time from point of creation to surface of interest is an important parameter. The spatial dependence of the rate of the initial electron impact collisions is therefore also an important parameter. The power that sustains the discharge is coupled into the system by two mechanisms: a high energy “e-beam” component of the electron distribution resulting from electrons falling through or being accelerated by the sheaths, and by “joule heating” in the body of the plasma. In this paper, we will discuss the spatial dependence of excitation rates and the method of power deposition in RF discharges of the type used for plasma processing. The basis of that discussion will be results from a Monte-Carlo plasma simulation code for RF discharges. Preliminary results from a model for the etching of silicon in SF6 /O2 plasmas will be presented and evidence for long term changes in the manner of energy deposition will be discussed.

A simple convenient technique is described for fabricating 25-5,000Å sized microstructures which are suitable for use as thin sections in transmission electron microscopy. Microstructures are produced by reactive ion beam etching (RIBE) a submonolayer colloidal particle mask, and several effects seen in RIBE are discussed. In particular, it is shown that polymeric deposits formed on vertical side walls can be imaged and etch rates near the surface of some materials can differ substantially from the bulk. The microfabrication technique affords a simple method to study the internal structure of thin deposited films and use of the technique is illustrated with structural studies of amorphous semiconductor superl atti ces.

The analysis of plasma etching processes has been explored for the etching of polysilicon films with CF3Cl/Ar discharges. The etching rate is well fit as a function of the macroscopic plasma parameters (power input, pressure, and composition) using Response Surface Methodology. The parametric expression obtained can be used to examine the sensitivity of the process to the operating conditions, and to optimize the process. The parametric expression also permits comparison of the experimental data with physically meaningful kinetic models.

The Response Surface Method allows characterization of a wide parameter space with few experiments. The design of the experimental set is critical to the success of the parametric fit. The parametric expression must account for interactions between parameters, and the expected curvature of the response surface will dictate the required number of data points.

The fundamental plasma kinetics of chlorofluorocarbon discharges have been studied experimentally and modeled. Electrical impedance analysis of the plasma discharge during the etching process was used to estimate the average electron energy and the electron concentration. Assuming the electron-impact generation of reactant species is the rate limiting step, the etching rate of polysilicon etching was modeled using a simplified expression for the electron-impact rate coefficient for dissociation and the experimentally estimated electron densities and electron energies. Dissociative electron attachment should play a significant role in the production of etchant species at low electron energies. The lower threshold energy and the larger cross-section (σ) for dissociative attachment of chlorofluorocarbons (σmax,∼6×10-18 cm2 at ∼ 3 eV for CF3Cl) in coomprpsanrtison to that of fluorocarbons (σmax ∼0.8×10-18 cm2 at ∼7 eV for CF4 ), increases the significance of this machanism in chlorofluorocarbon discharges. In addition, the production of appreciable concentrations of C1- could influence the transport of positive ions to the electrode surfaces.

The etching of polysilicon and polycide films requires both profile control and selectivity control. The use of a dual frequency tri-electrode system combined with a chlorine based chemistry have produced useful results.

Conventional integrated circuit fabrication is currently making the transition from wet to dry etching in the effort to shrink feature sizes to about 1 micron. These plasma etching techniques, though, are not limited to micron dimensions; devices and structures smaller than 100 nm can be made. Using e-beam lithography and reactive ion etching, patterns down to about 20 nm have been made in tri-level stencils and in semiconductor substrates. Working silicon MOSFETs with gate widths down to about 30 nm have also been made. These MOSFET devices are so small that individual electron trapping events can be observed. These devices are being studied to give a better understanding of the physics of electronic conduction in small devices and better define the limits of microfabrication.

We report on process characterization of contact hole etching in a load-locked, hexa-gonal reactive ion etching system. Contact holes were etched in silicon dioxide and phos-phosilicate glass (PSG) with emphasis on wall profile control and selectivity to the underlayer of either single crystal silicon, polysilicon, or aluminum.

To achieve these requirements, a two stage etch process was developed. In the first stage, controlled wall taper is obtained with a mixture of CHF3 and O2. The second stage utilizes a mixture of CHF3 and a small amount of CO2 to obtain high selectivity to the underlying material. Evaluation of the effects of chamber pressure, RF power, and gas mixture on taper angle, selectivity, resist erosion, and etch rates is presented.

In addition, evidence which suggests that the reproducibility of optimum etch condi-tions can be enhanced by the use of a continuously pumped process chamber will be dis-cussed.

The application of reactive ion etching to oxide films on 150mm sub-strates was studied. Etch rates of greater than 450 Å/min for thermal oxide with overall uniformities of less than ±5% have been observed. Selectivity of thermal oxide to polysilicon (20ω per square) has been observed to be in the range of 14:1 to 17:1.

A new method has been developed which allows submicron patterns to be rapidly copied from a master into an inorganic substrate. Physical repli-cation and lithographic pattern transfer are combined to produce a wide variety of surface textures on large area substrates. Physical replication techniques are used to create a polymeric intermediate transfer mask which is then used as an etch mask on the substrate. Both positive and negative copies of the original pattern can be created using this process. Final pattern transfer is accomplished by dry processing, allowing precisely controlled alterations of the aspect ratios in the original pattern. Using this process it is possible to fabricate extremely large area submicron sized surface textures (such as diffraction gratings) which are useful in many areas of science and technology.

Redeposition-free patterns have been etched in 3000Å thick permalloy films using the technique of chemically assisted sputter-etching. This technique involves the simultaneous adsorption of a reactant gas from a molecular beam source and normally incident argon ion bombardment. Experimental conditions with Cl2 adsorption can be maintained to etch the permalloy at 80Å/min and to etch positive photoresist at 110Å/min. These etch rates are not significantly different from rates obtained with argon ion milling, even though the permalloy surface is known to incorporate Cl2. Re-deposited material observed with Cl2 chemically assisted sputtering has been shown to be water soluble, and can be completely removed from feature side-walls prior to stripping the resist. Linewidth measurements show that no feature broadening occurs on 2 micron line and space patterns, within the precision of the measurement (±0.2 micron).

The excited states of He-5 % SiH4 PECVD have been analysed by emission and absorption spectroscopy.

Variations of spectral line intensities and He(23S) metastable densities have been correlated to the SiH over SiH2 bond ratio and to the deposition speed.

The best correlation has been found with the He excited states, specially He(23S) metastables : SiH films without SiH2 bonds have been obtained when the He(23S) densities reach a minimum value.

Thin layers (100Å) of SiO were deposited at room temperature in a RF glow discharge in a nitrous oxige – silane ambient. Surface properties of the deposit were studied using quantitative and qualitative XPS and AES. Abrupt changes in the energy difference between the O 1s and Si 2p photoelectron peaks, the O/Si stoichiometric ratio, and nitrogen incorporation are observed with varying amounts of silane in the gas ambient (for a fixed nitrous oxide flow). The abrupt change in binding energy difference correlates with the presence of free oxygen in the glow discharge as measured by in-situ mass spectrometry. At silane flows below the abrupt change, nitrogen is excluded from the deposit and the surfaces appear to be chemically silicon dioxide with a O/Si ratio of 2.1 as determined from quantitative XPS analysis. Above the abrupt change, the films exhibit a surface composition of less than 2.0.

Sputtered amorphous germanium films have been examined by spectroscopic ellipsometry. a technique known to yield the void fraction in the bulk of the film,. (and hence a measure of density, ρcalc) with a high degree of precision, Considering the commonly accepted values of the dielectric function and the directly measured density, ρexpt, of Paul, Connell and Tomkin (1973), as the reference data, we reportf that ρcalc for some a-Ge films can be greater than that of crystalline Ge. Examination of the top surface of the sputter deposited films indicates that the highest densities are achieved under conditions of high energy ion bombardment of the film. This study indicates that a more detailed microscopic model of the structure of a-Ge must be considered.

We have measured core-, valence-, and conduction band densities of states of amorphous hydrogenated (a-SiNx:H) and unhydrogenated (a-SiNx) silicon nitride with x varying between 0 and 2. From an analysis of the Si 2p core level spectra in terms of five chemically shifted components the number of Si-N bonds is calculated and compared to the total nitrogen concentration. Above x ≈ 0.8 the average silicon coordination of nitrogen starts to deviate from three. The addition of hydrogen increases this deviation because N-H bonds are favored over N-Si bonds accounting thus for the excess nitrogen concentration (x ≥ 1.33) found in hydrogenated samples. A band of N2p lone pair states is identified at the top of the valence bands in stoichiometric Si3N4. This band determines the character and position of the valence band maximum (VBM) above x = 1.1. Below x = 1.1 Si-Si bonding states mark the VBM. The conduction band minimum (CBM) is determined by Si-Si antibonding states up to x = 1.25 and its position relative to the core levels is virtually unaffected by the presence of nitrogen or hydrogen. Above x = 1.25 a percolation-like transition to Si-N antibonding states occurs which is accompanied by a sharp recession of the CBM. The position of the Fermi level within the gap is investigated as a function of x and hydrogen content. Si-H and N-H bonding states are identified at 6.3 and 9.8 eV below the VBM in nearly stoichiometric a-Si3N4. Si-Si bonding defect states lie 0.5 to 1.0 eV above the VBM and the corresponding antibonding states (3.0 ± 0.3) eV above the VBM.

Plasma-enhanced CVD (PECVD) has been widely used for the deposition of insulating and semiconducting thin films. In recent years, interest has arisen in the use of PECVD to form metal layers for barrier, contact, and interconnect applications. Plasma deposition conditions that result in the formation of conducting films of transition metals, transition metal silicides, and transition metal nitrides are discussed. Particular attention is given to the as-deposited resistivities of these films, and their relationship to the gas phase reactants. The effects of postdeposition heat treatments are also discussed.

Amorphous carbon films deposited by sputtering or ion-beam techniques, as well as a-C:H films produced by glow discharge in hydrocarbon vapor, can exhibit interesting and desirable properties such as hardness, wide optical gap, high resistivity and chemical inertness. A critical parameter common to all methods for producing such films appears to be kinetic energy of the ions or atoms incident on the growing film. We report an investigation of laser-produced carbon plasmas as a deposition source which can supply ions and atoms having energies requisite for the production of hard carbon films. The plasmas were generated by focusing 1.06 μm radiation from a Q-switched Nd:YAG laser onto a carbon rod which could be rotated within the vacuum chamber to present a fresh surface for each shot. Plasma temperature, varied as a function of laser pulse energy, was monitored by recording X-UV plasma emission spectra during deposition. Films having thicknesses up to ˜0.5 μm were deposited on various substrates and were evaluated by microscopic inspection, thickness profiling, optical transmission measurements and hardness testing. Hardness increased significantly with plasma temperature, from about 3 to over 7 on the Mohs scale. There was no corresponding increase in optical gap, which remained near 0.4 eV for all films.

Rapid solidification, sputtering and electroless chemical deposition have been used to produce amorphous metal alloys which possess excellent corrosion and abrasion resistance. This paper discusses a new technique for obtaining amorphous metal alloy coatings. This technique consists of dissociating mixtures of organometallics (metal carbonyls) and metalloid hydrides in a hydrogen carrier gas using a radio-frequency discharge. In particular, the formation of Ni-P alloys is discussed.

Plasma decomposition of Ni(CO)4 and PH3 in argon and hydrogen carrier gases [Ni(CO) 4/PH3˜8/l] yielded films that were black and silver, respectively, in appearance. Both films were amorphous as determined by transmission electron microscopy. Films deposited using a hydroqen carrier gas were three orders of magnitude more conductive than those deposited using an argon carrier gas. Analysis of both films using electron microprohe analysis and inductively-coupled plasma spectroscony showed an enrichment of P in the films over the P content in the plasma qas mixtures. Reducinq the P content of the plasma gas mixture [Ni(CO)4/PH3˜17/Il yielded crystalline films with no P enrichment. The grain size in these films was ˜Å as determined by x-ray line-broadeninq.

Using Auger electron spectroscopy, films deposited using hydroqen and argon carrier gases were determined to have, in addition to Ni and P, small amounts of carbon (8–12 at%) and oxygen (1–4 at%). Infrared spectra of both crystalline and amorphous films showed chemisorhed CO.

A series of amorphous silicon/carbon films were deposited from an RF glow discharge in silane-phenylsilane feed gas mixtures with the (ΦSiH3 content varying from 0 to 100 %. The films were characterized with optical and electrical measurements. While the structure of the films deposited from the mixtures contains carbon in more than one configuration the amount of pendant phenyl groups increases as the phenylsilane content of the feed gas is increased. The optical gap, derived from Tauc plots of the absorption spectra, ranges from 1.7 to 2.9 eV, while the refractive index obtained from ellipsometry, ranges from 3.7 to 1.8. The optical gap was found to vary linearly with the carbon atomic fraction in the feed gas, independent of the configuration of carbon atoms in the solid. The refractivity, (n2− 1)/(n2 + 2) , was found to exhibit a similar composition dependence. The room temperature resistivity was observed to increase sharply with increasing carbon content, rising from 107 ohm-cm to 1016 ohm-cm as the ΦSiH3 content of the feed gas was increased from 0 to 25 per cent.

A sputtering method to prepare amorphous polyphosphide thin films has been investigated. The method consists of sputtering from a polyphosphide (KP15) target and plasma cracking of a P4 vapor stream injected into the plasma from an external phosphorus source. From the deposition rates of KP15 thin films, we determine that the plasma cracking efficiency of the P4 molecule into reactive P species required for compound growth is significantly higher than thermal cracking efficiency. We conclude that this method is applicable to other compound semiconductors (InP) and that the P4 delivery system used here should be useful in other techniques such as MBE or OMCVD

SiO2 and Si3N4 thin films have been deposited at a substrate temperature of 350° using a glow discharge electron beam irradiating perpendicular to the wafer surface. Deposition rates up to 1000 Å/min and 250 Å/min respectively have been obtained. Films deposited over 4 inch diameter silicon wafers show uniformity of 5 percent. The deposition conditions and film properties are discussed.