We have developed a compact and inexpensive laser direct writing system, based on the 796 nm radiation of a 1 W diode laser array for the deposition of tungsten silicides. The laser power incident on TiN substrates varies between 50 and 550 mW. Lines are deposited from a gas mixture of WF6 and SiH4, whose total pressure is kept below 15 Torr to avoid uncontrolled reactions. Experiments are performed in a static reactor with WF6/SiH4 ratios varying from 0.2 to 10. Lines written at speeds ranging from 2 to 100 μm/s have typical thicknesses and widths varying from 30 to 1000 μm and from 4 to 15 μm respectively. Auger Electron Spectroscopy (AES) shows that no fluorine is incorporated in the WSix film, within the limit of detection. Moreover, no oxygen, carbon or nitrogen are detected in the bulk, although some surface contamination is present. From AES measurements, the W/Si ratio is estimated to be between 1.1 and 1.4 for a reactive gas mixture of WF6: SiH4 (1: 3).

We have studied the thermal and photoinduced dissociation pathway of AsH3 on the Ga-rich GaAs(100) surface. Arsine adsorbs molecularly at 115 K and dissociates upon either heating to above 140 K or upon irradiation with 3.5 - 6.4 eV photons. The decomposition of arsine is accompanied by the formation of surface Ga-H species, which are thermally and photochemically more stable than surface AsHx. A comparison of the wavelength dependence for adsorbed and gas phase arsine reveals that the excitation mechanism of the AsH3 surface photochemistry is substrate mediated, which probably involves a charge transfer between surface states and the adsorbate.

Maskless etching of single crystalline Mn-Zn ferrite (MnO: ZnO: Fe2O3 = 31:17:52) has been investigated in a SiCl4 atmosphere by Ar+ laser irradiation. The ferrite substrate can be thermochemically etched by a single scan of a laser beam. Silicon oxide was deposited simultaneously in the etched groove. The deposited silicon oxide lines were investigated by AES, XPS and RBS. It is found that the deposited lines were stoichiometric SiO2 under specific conditions. The etching and deposition process can be controlled by changing the SiCl4 gas pressure. A planarized SiO2 layer buried in ferrite was found not to affect the magnetic characteristics of the ferrite layer.

Buried quantum well structures have been fabricated in GaAs/AIGaAs system using an in situ lithography process. The process utilizes an ultrathin oxide layer formed in situ on a GaAs surface as a mask against Cl2 gas etching. An electron beam (EB)-induced Cl2 gas etching is used to locally remove the oxide mask for positive-type lithography. For negativetype lithography, the oxide mask is selectively formed on a GaAs surface by EB-stimulated oxidation. Subsequent Cl2 gas etching results in the formation of isolated quantum wells. After removing the oxide mask, overgrowth using molecular beam epitaxy is successfully carried out on the patterned surface. The cathodoluminescence image of the buried quantum well demonstrates the high quality of the resulting structure formed by this “in situ EB lithography” process. The photoluminescence intensity from the quantum well of the processed sample is proved to be the same order of magnitude compared with that from a successively grown sample, showing that the use of the oxide mask causes no serious degradation in the processed interface.

The scanning tunnelling microscope (STM) can be used to selectively deposit material from a gaseous precursor compound. Ultrasmall (less than a 100 nm across) spatial dimensions for selective area deposition may be achieved by this means. In this paper we outline a scheme forselecting and designing main group cluster compounds and organometallics for this type of selective area deposition using nido-decaborane(14) as an example.

GaAs etching with Cl2 gas is studied with a scanning tunneling microscope (STM). Both Cl2 gas and tunnel electron assist etching occur under the tip during scanning and the etching profile is found to depend on the gas flow time. GaAs and Si patterns with nanometer dimensions are fabricated by STM assist etching with a very low voltage (-IV). Also atomic layer etching of GaAs is demonstrated by STM assist-etching using a Cl adlayer.

A focused electron beam has been used to selectively decompose sub micron thick films of palladium acetate, Pd(OOCCH3)2, resulting in the formation of <0.1μm wide Pd rich features. Resistivity of the palladium acetate film decreased when exposed to doses above 500μC/cm2. Annealing to 160°C further reduces the resistivity of the exposed areas to as low as 100μΔcm. XPS analysis of the exposed areas indicate that the Pd is reduced to a metallic state and that the ratio of C and 0 to Pd drops to 1.5 and 0.6, respectively, after exposure. Residual gas analysis during exposure indicates that CO2 and CH3 are the primary volatile products of the decomposition.

We have produced nanometer scale patterning (nanostructures) by metal shadowing of two-dimensional protein crystals (S-layers), followed by milling with ions or fast atoms. In this parallel process, the metal overlayer is formed into a metal screen consisting of hexagonal arrays of 10 nm size holes with a 20 nm periodicity. We have studied the time evolution of the milling process, and temperature effects. Nanostructure formation may be due to preferential sputtering of the troughs relative to the crests of the metallized S-layer. The effect of temperature on pattern formation indicates that thermal diffusion is also important.

Exposing a Si(100) surface to a pulsed beam of neutral Cl2 with high translational energy results in etching at a rate faster than that seen with chlorine at thermal energies. The Cl2 beam used in these experiments is produced by laser vaporization of cryogenic films. It has a broad energy distribution which can be varied by changing laser energy and film thickness. Beams with mean energies as low as 0.4 eV result in etching =10 times faster than etching by thermal Cl2. When Cl2 beams are used which have considerable flux above 3 eV, the etching rate increases by a further factor of 3.6 ± 0.6. This rate increase, which occurs at energies just above the Si-Si bond energy, suggests that kinetic energy can be efficiently utilized to break surface bonds.

Perpendicular etching profiles of n+-Si(100) are obtained with a supersonic Cl2 beam at substrate temperature of 900°C. Although small undercuts are observed just below the SiO2 mask, the side wall etching caused by the background Cl2 is almost negligible. An aspect ratio of greater than 6 and selectivity of greater than 8000 are obtained with 0.5 μm line & space mask pattern. From Arrhenius plots of etch rates, an effective activation energy of the nozzle beam etching is determined to 0.53 eV. Assuming that the reaction product is SiCl2, the reaction probability is estimated to be 19% at 900°C. Highly anisotropic etching of the Si(100) obtained here is due to the large reaction probability.

Downstream oxygen plasmas are used routinely to etch and strip resist materials in integrated circuit (IC) process sequences. Differences in the electrical damage incurred in thin (26 nm) silicon dioxide films on silicon due to the afterglow of rf and microwave oxygen plasmas appear to be due to higher energy VUV emission and to a greater density of positive ions in the case of rf excitation at downstream distances less than 35 cm. The high flux of oxygen ions in electron cyclotron resonance (ECR) plasmas also permits reasonable silicon oxidation rates at low temperature. Oxidation rates ofsilicon in ECR oxygen plasmas at temperatures between 250 and 450 C are comparable to those obtained for thermal oxidation in dry oxygen at temperatures above 850 C. Although oxidation rates are adequate under floating, anodic or cathodic bias conditions, only oxides grown under floating or anodic conditions display comparable chemical, physical and electrical properties to those of thermal oxides.

The etching of a novolak-based positive photoresist was studied downstream of O2/CF4 and Ar/O2/CF4 plasmas. Gas phase electron resonance was used to quantitatively track the two primary etchant species, atomic oxygen and atomic fluorine. These species were then correlated to etch rates as determined by laser interferometry. In addition to being industrially relevant, the downstream reactor allows the influence of neutral chemistry and surface activation to be deconvoluted from that of ion bombardment and strong electric fields, which traditionally make processes occurring in the body of the plasma so difficult to understand. The maximum in etch rate with respect to CF4 addition to an oxygen plasma yields an optimum ratio of O/F of 20 at 150 °C. The addition of argon to the O2/CF4 gas mixture unexpectedly leads to an increase in etch rate by a factor of at least two. Moreover, the optimum O/F ratio decreases by a factor of three and, correspondingly, the optimum CF4 mole fraction decieases. Analysis of oxygen and fluorine densities suggests argon metastables alter the homogeneous chemistry for fluorine atom production as well as the heterogeneous chemistry of photoresist chain scission. Overall activation energies are 10.6, 10.8, 4.1 and 0.7 kcal/mole for O2, Ar/O2, O2/CF4 and Ar/O2/CF4 mixtures, respectively. The optimal CF4 mole fraction increases with increasing substrate temperature. A Hougen-Watson model for the heterogeneous chemistry on the wafer surface reproduces the data very well.

The formation of rugged surface polycrystalline silicon (poly-Si) using Cl2/O2 plasmas in which O2 concentration is 0-10 % has been investigated. Phosphorus doped poly-Si (n+ poly-Si) surface is rugged by the plasma etching under the condition that O2 concentration are 1-5 % at 10 Pa, but is not rugged at 1.3 Pa. On the other hand, undoped poly-Si surface is not rugged in Cl2 /0-10 %O2 plasmas at 10 Pa. Oxygen and phosphorus play an important role in the ruggedness of n+ poly-Si. The ruggedness mechanism has been investigated using scanning electron microscope, optical emission spectroscopy and mass spectrometry. The ruggedness mechanism is suggested that in Cl2 plasmas added a small amount of oxygen, n+ poly-Si is etched selectively at the grain boundaries which contain more phosphorus than in grains. The Cl emission intensity and n+ poly-Si etch rate reach maximum in Cl2/3 %O2 plasma at 1.3 Pa. Oxygen has a possibility of promoting SiCIx dissociation and increasing Cl radicals.

Silicon single crystal wafers are lithographically patterned and etched for via holes by means of RIBE, RIE and ECR based techniques. The damage introduced by etching is analyzed using charge collection microscopy. This technique probes sensitively the occurrence of electrically active defects due to their altered electron hole recombination properties compared to the bulk material. Furthermore, investigations of the temperature dependence of the EBIC contrast give informations about the physical mechanisms for the recombination. The experiments revealed a substantial increase [several %] of the EBIC contrast in the etched part of the pattern, i.e. electrically active damage is introduced by the etching technique, giving rise to enhanced recombination. Measurements of the diffusion length in etched and unetched areas of the specimen reveal identical values, i.e. the damage is confined close to the surface. Using the different etching methods quantitatively different defect levels are found. Measurements of the temperature dependence of the EBIC contrast aimed to reveal the physical nature of the defects show a drastic increase of the contrast with decreasing temperature. This increase can be described by two regimes in an Arrhenius plot with a linear characteristic of different slopes.

The effects of P2S5 surface passivation treatments on damage caused by chemically assisted ion beam (CAIBE) etching of GaAs have been examined using ex-situ photoreflectance. Epitaxially grown undoped GaAs on heavily doped GaAs substrates were used to determine surface electric fields. The etching process is observed to decrease surface electric fields, produce subsurface damage and to reduce surface photovoltages. Post-etching treatments with P2S5 are observed to increase surface photovoltages, but have no significant effect on the surface fields or subsurface damage. That the surface field is unaffected suggests that in etched materials the Fermi level pinning is not solely determined by the surface and that the near surface regions are important. We also find that samples pretreated with P2S5 exhibit more etch damage than those which are only degreased.

Although the directed energy and chemical reactivity of dry etching permits the fabrication of nanostructures with precise geometries, it also causes unwanted electrical and optical changes to the surface, changes generally referred to as “damage”.

This paper discusses the extent and the impact of dry-etching damage on rI-V and I[-VI compound semiconductors as assessed by a very wide range of techniques: the performance of devices such as MESFETs, and measurements of other properties - surface uniformly and precisely, Schottky junction characteristics, cut-off of epitaxial wire conductance, integrated photoluminescence, X-ray reflectivity, DLTS, TEM imaging and Raman scattering.

We distinguish an important difference between the nature of damage on sidewalls and on surfaces normal to the directed ions, and report on progress towards establishing a model of the nature of dry etching damage. This model is applied to indicate what kinds of processes are likely to give etching with low damage.

The production of surface defects by low energy 4He and Xe ions incident on very smooth Ge(001)2x1 surfaces is reported. Roughening at -50°C by 100-500 eV ions is measured by RHEED in real-time using the intensity of the out-of-phase specular beam. For He, the surface displacements per ion range from 0.05 to 0.3 and are comparable to our binary collision calculated surface vacancy production rate for a displacement threshold energy of 11 eV (3/4 of bulk value). For Xe, the displacement rate ranges from 2 to 10 (∼30x higher) and falls between the calculated total vacancy and total defect (vacancy + interstitial) production rates.

A highly sensitive laser probe for photo-acoustic displacement(PAD) has been developed and applied to the monitoring of low-level lattice damage in semiconductors. Since a photodisplacement laser probe with the sensitivity of 0.1 picometers is employed in this measurement, lower density damage for instance, formed by 50 keV B+ implantation with a dose of 5X109 ions/cm2 can be detected. Correlation of the PAD with damage density was obtained in B+ implantation. Therefore, quantitative damage density can be obtained from the relation for lightly damaged layers, such as formed by chemomechanical polishing and by electron cyclotron resonance plasma etching. This technique is useful-for monitoring of low damage density surface.

Molecular dynamics simulations are used to investigate the formation of deep crystalline damage during the low-energy ion bombardment of semiconductor crystals. The trajectories of primary ions are calculated as they propagated through a model crystal lattice. Energy losses by nuclear recoil and and by electronic excitation are included. For beams of heavy ions at energies below 1 keV, the average penetration range of the simulated trajectories is only a few nanometers. However, a small, but, significant fraction of the ions are found to scatter into <011= axial channels through which they propagate tens of nm below the surface. This effect is used to explain high-resolution secondary ion mass spectrometry and photoluminescence data which reveal deep ion penetration and optical damage on the same length scale. Our results suggest that unintentional ion channeling is a major factor in the extensive degradation of optical and electrical properties of semiconductor surfaces which are exposed to low energy ion bombardment during device fabrication.

This paper describes a laboratory built ion beam etching system and its performance when used for etching Hg1-xCdxTe, GaAs and InP. The etching system provides a means for forming device mesas on a wide range of semiconductors without having to resort to wet chemical etches. The system uses a Kaufmann ion source, a rotating platform and two flow controllers to allow the variation of gas ratios and flows.