Reactive Sputter Etching And Its Applications

AbstractThe requirements for high-fidelity, anisotropic etching are discussed. A brief discuss­ ion on the various dry etch techniques available is followed by a description of a batch reactive sputter etch system that fulfills all patterning requirements. Examples of results obtained with this system are given and demonstrated with SEM photographs.IntroductionWith the progress of the I. C. industry toward the VLSI regime, many methods of device processing used previously are being extended to their limits as feature size shrinks toward ly. It is well known that photolithograpic techniques capable of generating such features became available in recent years. In order to transfer these fine patterns into underlying substrate materials with the maximum amount of pattern fidelity, a method of well controlled anisotropic etching is required. Conventional pattern transfer by wet etchants is unable to provide this and, in general, has found its application limited to 4 ym and above features. Dry processes, such as sputtering, ion milling, plasma chemical etching and reactive sputter etching, have become increasingly attractive due to their better resolution, and increased dimensional and etch profile control. Of these, reactive sputter etching has shown itself to be capable of providing the best overall etch results.This paper will review the requirements of pattern transfer for VLSI applications, summarize the advantages and limitations of various dry etching techniques and describe the results obtained with a new batch reactive sputter etch system.Pattern transfer requirementsIn order to achieve higher packing density and better circuit performance future VLSI devices will have features in the micron and sub-micron range. The transfer of these patterns into the underlying layers will require the dry etch process and reactor design to produce the following results in order to provide a high yield:1. Controlled profile of etch features from highly anisotropic to a tapered profile.2. High selectivity in etching relative to masking materials, substrate and exposed surfaces of system.3. Minimal damage of masking materials to allow use of soft-baked resist without reticula­ tion. .4. High uniformity of etching - both etch rate and finished linewidth.5. A clean and smooth etched surface - no trenching, surface roughness, or surface deposits.6. No radiation damage or metal contamination.7. No loading effects - neither reactor nor proximity.8. Sequential etching - the ability to change or alter etch gases and/or operatingconditions during one etch run. 9 0 Reproducibility of etch results and reliability of etch results combined with highthroughput of reactor operation as well as minimum maintenance.Characteristics of reactive sputter etchingDry etching generally involves the creation of a glow discharge by the application of an electric field (DC or AC) between two electrodes in a partially evacuated chamber. The various techniques can be divided into three groups: ion etching (ion milling and sputter etching), chemical plasma etching, and reactive sputter etching.Ion etching involves the creation and subsequent acceleration of inert ions toward the sample to be etched. Etching takes place purely by physical means - momentum transfer between the energetic ion and the material being etched. The technique offers high re­ solution but suffers from low etch rates, poor selectivity, faceting, trenching, redeposition and low efficiency.