D. W. Hess

A mathematical model for spin coating of polymer resists

The success of lithographic processes in microelectronics fabrication depends on the reproducible generation of desired polymer resist film thickness and profile uniformity. Numerous process variables affect the outcome of spin coating of resists on wafers. A thorough understanding of the intricate interdependence of process parameters is essential to guide future process design and improvement. A mathematical model is derived to elucidate the dominant mechanisms governing film formation. The non‐Newtonian character of the resist solution is taken into account, as well as the changes in resist viscosity and solvent diffusivity with changing polymer concentration. Results obtained from this model show that polymer film thickness is controlled by convective radial flow of the resist solution and solvent evaporation. The former process governs film thickness during the early stages of the process, while the latter becomes significant in later stages. The model accurately describes the experimentally observed...

Oxygen plasma etching for resist stripping and multilayer lithography

Oxygen‐based plasmas commonly used in resist stripping and multilayer resist patterning are contrasted to highlight the differences involved in these applications. Mechanisms for polymer etching are reviewed, with particular emphasis on silicon‐containing resists proposed for bilayer lithography. While silicon‐containing materials offer a simpler process than trilayer schemes for improving lithographic resolution, considerable differences in etch behavior among these materials have been observed. Further characterization and fundamental understanding are required before widespread acceptance of silicon‐containing resists is achieved.

Oxidation of silicon in an electron cyclotron resonance oxygen plasma: Kinetics, physicochemical, and electrical properties

An electron cyclotron resonance (ECR) plasma system was used to oxidize single‐crystal silicon. Two distinct oxidation processes were observed, one of which was ion flux controlled. Oxidation of trench structures confirmed the existence of these two oxidation regimes. Kinetic rate studies indicated that the effective activation energies for both oxidation processes were substantially lower than the activation energy of atmospheric pressure steam or dry oxygen oxidation. The Deal–Grove linear‐parabolic rate law can be used to describe long‐time ion‐controlled oxidation rates, although the theory of Wolters–Zegers‐van Duynhoven best described the observed oxidation rates. Oxides grown in the ion flux controlled regime had growth rates and physicochemical properties nearly identical to thermal oxides grown at atmospheric pressure and above 1123 K, whereas oxides grown outside this regime were self‐limiting (≊100 A) in thickness and of poorer dielectric quality unless subjected to a post oxidation anneal. Cap...

Effects of dc bias on the kinetics and electrical properties of silicon dioxide grown in an electron cyclotron resonance plasma

Thin (3–300‐nm) oxides were grown on single‐crystal silicon substrates at temperatures from 523 to 673 K in a low‐pressure electron cyclotron resonance (ECR) oxygen plasma. Oxides were grown under floating, anodic or cathodic bias conditions, although only the oxides grown under floating or anodic bias conditions are acceptable for use as gate dielectrics in metal‐oxide‐semiconductor technology. Oxide thickness uniformity as measured by ellipsometry decreased with increasing oxidation time for all bias conditions. Oxidation kinetics under anodic conditions can be explained by negatively charged atomic oxygen, O−, transport limited growth. Constant current anodizations yielded three regions of growth: (1) a concentration gradient dominated regime for oxides thinner than 10 nm, (2) a field dominated regime with ohmic charged oxidant transport for oxide thickness in the range of 10 nm to approximately 100 nm, and (3) a space‐charge limited regime for films thicker than approximately 100 nm. The relationship ...

Correlation of chemical and electrical properties of plasma‐deposited tetramethylsilane films

Thin films of tetramethylsilane (TMS) were formed using rf‐glow‐discharge polymerization. The films were found to be pinhole free, chemically resistant, and adherent to silicon, aluminum, and glass substrates. Electron microprobe analyses and IR Fourier transform spectroscopy (FTS) demonstrated that small concentrations of oxygen (2–6 at. %) were always incorporated into the polymer structure. Film density, refractive index, and dielectric constant were correlated with the chemical composition of the films. Capacitance‐voltage studies of metal‐polymer‐silicon structures indicated that charge trapping and polarization instabilities existed in the films, and FTS suggests that these charge effects originated at SiO and C = 0 sites. The polymer films were found to be sensitive to moisture and to oxygen. Electron transport was enhanced in films which were exposed to water vapor.

Ion transit through capacitively coupled Ar sheaths: Ion current and energy distribution

The ion current and ion energy distribution (IED) of Ar+ and ArH+ impinging on a grounded surface immersed in capacitively coupled Ar plasmas have been measured as a function of pressure, applied rf voltage amplitude (Vrf), interelectrode gap, and sampling orifice size. A maximum in ion current occurs at high Vrf and intermediate electrode spacing. rf modulation of the collisionless IED occurs at high pressure and high Vrf and is caused by reduction of the sheath dimension under these conditions. Collisional shift to lower ion energy is also noted at high pressure. A low‐energy peak at ∼10 eV is observed under high pressure and ion current conditions. Larger orifice sizes increase the collisions occurring downstream from the orifice as indicated by collisional energy shifts in the IED and a decrease in ion current density.

Plasma etch chemistry of aluminum and aluminum alloy films

The chemistry occurring in glow discharges used to etch aluminum and aluminum alloy films is examined and is related to recurring problms such as initiation and reproducibility of etching, polymer or residue formation, photoresist degradation, aluminum corrosion, and safety aspects. The relative effects of different etch gases on these problems is discussed in light of aluminum surface chemistry and gas-phase plasma chemistry.

Reaction of atomic and molecular chlorine with aluminum

In order to quantify the contributions of atomic and molecular chlorine during the plasma etching of aluminum, a discharge‐flow system was used to generate chlorine atoms upstream of a parallel‐plate reactor in which aluminum samples were etched with the afterglow. Molecular dissociation in excess of 70% was achieved. Dissociation was measured in the parallel‐plate reactor by gas‐phase titration of the chlorine atoms with NOC1 using the chemiluminescent emission resulting from atom recombination as an end point indicator. Molecules etched aluminum at least four times faster than atoms and displayed an activation energy near zero (0.02–0.04 eV/molecule) between 35 and 150 °C. Below 25 °C etching was quenched due to the inability of products and/or contaminants to desorb. The higher molecular etch rate is believed to be the result of an enhanced sticking coefficient on the chlorinated surface. Calculation of molecular sticking coefficients based on the assumption of adsorption‐limited etching are in good ag...

Measurement of rotational temperature and dissociation in N2O glow discharges using in situ Fourier transform infrared spectroscopy

The technique of in situ Fourier transform infrared (FTIR) absorption spectroscopy has been used to determine rotational temperatures and the extent of dissociation of N2 O in a radio‐frequency (rf) glow discharge. Measurements were made at 0.65 cm−1 resolution on 13.56‐MHz plasmas at 500 mTorr, with an input flowrate of 40 sccm, and powers of 10 and 30 W. Temperature and dissociation information estimates are based upon analysis of P branch rotational lines of the 2ν1 harmonic and ν1 +ν3 combination band of the molecule. Line intensities are corrected for instrument‐induced distortion. Under the conditions investigated, rotational temperatures are between 335 and 420 K, and dissociation ranges from 45% to 75%. Both rotational temperature and dissociation increase with rf power.

Kinetics of photoresist etching in an electron cyclotron resonance plasma

An electron cyclotron resonance plasma processing system was used to etch hardbaked KTI‐820 photoresist from single crystal silicon wafers, silicon dioxide films and patterned multilayer structures. Etch rates of 1500 nm/minute were observed at a substrate temperature below 373 K in a Pforward=750 W, 0.13‐Pa ECR oxygen plasma with no applied substrate bias. The etch rate increased linearly with increasing power from Pforward=300–750 W. Etch rate was a complicated function of pressure and residence time, but a modified adsorption‐reaction‐ion‐stimulated desorption rate expression could be used to fit the data. Etch rates decreased for increasing oxygen residence time at low operating pressures due to a combination of polymeric film formation of reaction products and reactant (atomic oxygen) depletion. Maximum etch rates were observed at approximately 0.13 Pa for all residence times. Multilayer photoresist structures were etched at various pressures as well as at a 45° angle to the incident plasma stream. E...