T. F. Deutsch

Laser photodeposition of metal films with microscopic features

Metal deposits with features smaller than 2 μm have been produced by the uv laser‐induced photodissociation of organometallic compounds. Such laser‐induced heterogeneous photochemical processes may have application in several areas of microelectronics including metallization, etching, and growth of semiconductor films.

Laser chemical technique for rapid direct writing of surface relief in silicon

High‐resolution etching of single‐crystal and polycrystalline silicon has been demonstrated using an argon‐ion laser to control microscopic chemical reactions. Gas‐phase Cl2 or HCl is used in reactions initiated both by surface heating and by molecular photolysis. Features smaller than 5 μm and etch rates greater than 6 μm/s have been obtained. The process seems immediately suitable for a variety of problems in integrated‐circuit fabrication.

Laser microphotochemistry for use in solid-state electronics

A focused, ultraviolet (UV) laser beam has been used to produce micrometer-sized chemical processes on solid surfaces. These processes are initiated by the photodissociatlon of a molecular gas in the vicinity of the gas-solid interface. Depending on whether the active photofragment reacts with or is adsorbed on the solid, microetching or microdeposition occurs. Both the surface properties of the solid and the gas-phase kinetics contribute to the process localization. Metal alkyls and methyl halides have been used as parent molecules for deposition and etching, respectively. A focused, 3 mW UV laser is sufficiently intense to produce satisfactory rates for both processes. Several applications of this small-scale photochemistry to microelectronics have been investigated.

Laser‐induced microscopic etching of GaAs and InP

Ultraviolet laser photolysis of methyl‐halides has been used to produce localized photoetching of GaAs and InP. A spatial resolution of ≃1μm has been achieved and an etch rate ≳104 times that of the dark reaction demonstrated. A chemical mechanism is proposed and the observed resolution is explained by a simple physical model.

Spatially delineated growth of metal films via photochemical prenucleation

Photodissociation of a thin surface layer of metal‐alkyl molecules with a UV laser is shown to be an effective technique for predisposing the irradiated region to subsequent film growth. The efficacy of this technique, termed ’’prenucleation,’’ can be understood using a simple mathematical model for the early stages of thin‐film formation. The technique has applications in direct writing of microstructures.

Efficient Si solar cells by laser photochemical doping

An ArF excimer laser has been used to form p‐n junctions in Si. The laser produces dopant molecules by gas‐phase photolysis of an organometallic molecule and simultaneously heats the substrate to allow incorporation of the dopant. Solar cells having conversion efficiencies of 9.6% at AM1 without the use of antireflection coatings have been fabricated from these junctions.

Synthesis of metastable, semiconducting Ge‐Sn alloys by pulsed UV laser crystallization

Thin microcrystalline films of the metastable semiconducting alloy Ge1−xSnx (x≊0.22) have been formed using excimer laser radiation to crystallize amorphous sputtered films on glass and semiconducting crystalline substrates. X‐ray diffraction, electroreflectance, and Raman spectroscopy have been used to characterize the semiconducting material which is stable to at least 200 °C. The study demonstrates the possibility of extending earlier studies of amorphous Ge1−xSnx alloys into a crystalline regime with a direct band‐gap variable with x from 0 up to about 0.5 eV. The crystallization technique is potentially applicable to the formation of other metastable semiconducting compounds of device potential.

Infrared laser photochemistry of silane

The infrared photochemistry of silane has been investigated using CO2 TEA laser excitation. Energy deposition measurements show that only 1.5 photons/molecule are absorbed at a pressure of 1 Torr and a P (20) fluence of 0.8 J/cm2, while at 10 Torr 7.5 photons/molecule are absorbed. The visible luminescence that accompanies the dissociation of silane is due to molecular and atomic hydrogen. The thresholds for both luminescence and dissociation increase sharply as the pressure drops below 5 Torr, indicating that dissociation is a collisional process. Silane d1 and d2 have been produced by irradiating silane–deuterium mixes.

Laser microreaction for deposition of doped silicon films

An Ar‐ion laser has been used to activate surface pyrolytic deposition of polycrystalline Si in a several micrometer reaction zone. Controlled doping with boron during deposition allows one‐step direct writing of highly conducting Si lines with linewidths as small as 1 μm. An unexpectedly fast deposition rate is associated with changes in the reaction kinetics as the dimensions of the reaction volume are reduced to microscopic lengths.

Self‐developing resist with submicrometer resolution and processing stability

Nitrocellulose films have been shown to function as self‐developing resist layers that are sensitive to both low‐energy ( 25:1 have been demonstrated using a stencil mask and an argon ion beam; the resolution obtained was mask limited. The sensitivity of the resist to 2‐keV Ar+ ions is 36 μm/min at beam currents of 1 mA/cm2, allowing exposure times of 1 s for 0.5 μm of resist. The material is capable of functioning as a mask material for typical semiconductor dry etching processes.