During the past ten years electron cyclotron resonance (ECR) plasma-processing technology has matured into a diverse assortment of ECR plasma reactor and plasma source design concepts and has been extensively applied to numerous low-pressure plasma processing applications. This paper reviews the substantial progress made in the design and application of ECR plasma technology in recent years. Five representative ECR reactor/source designs from large-area 450-cm/sup 2/ discharges to compact plasma sources inserted into molecular-beam epitaxy (MBE) machines are described in detail. The performance of these ECR devices is evaluated by computing performance figures of merit from the available experimental data. These calculations are then compared with the behavior as predicted from a global model of the discharge. This comparison suggests that global plasma models can be employed as an approximate method for ECR reactor design. More extensive diagnostics and numerical models that investigate the spatial variation of ion density and ion energy distributions are also presented. Several illustrative ECR plasma-processing applications are discussed. These include submicron etching of silicon, etching of III-V and II-VI electronic and photonic devices, and the epitaxial growth of GaN. The variety and the sophistication of these applications demonstrate that low-pressure high-density ECR plasma processing technology has evolved into a very useful, versatile group of plasma-processing machines.

The design and application of electron cyclotron resonance discharges

Changes in the sheet resistance of doped epitaxial layers of InP and In0.53Ga0.47As exposed to microwave Ar or H2 discharges were measured as a function of the exposure time (1–20 min), plasma pressure (1–20 mTorr) and the additional rf‐induced negative dc bias (50–400 V) on the sample. Changes in sheet resistance of ≤10% are only obtained for low dc biases (≤−75 V) or short exposures for either type of discharge. Hydrogen plasmas led to more substantial resistance changes than argon plasmas under all conditions, with the amount of damage introduction or hydrogen passivation being strongly dependent on dc bias and exposure time, but weakly dependent on pressure. The results indicate that high density, low pressure plasmas with low dc biases are capable of causing minimal disruption to InP‐based materials during dry etching for device fabrication.

Damage introduction in InP and InGaAs during Ar and H2 plasma exposure

Electron cyclotron resonance (ECR) discharges are characterized by high ion densities (<or approximately=1012 cm-3) at low pressure ( approximately 1 mTorr) and by low ion energies (<or=15 eV). They are ideally suited for dry etching of III-V semiconductor devices, particularly when combined with additional RF biasing of the sample. In this paper the authors give examples of the use of this hybrid ECR-RF approach for etching of InP based devices in CH4/H2 plasmas and GaAs-based devices in CCl2F2 or PCl3 plasmas. The systematics of damage introduction into HEMTs and HBTs using these mixtures have been studied and the authors slow that it is possible to dry etch such devices without creating ion-induced surface damage. A feature of ECR etching is the highly anisotropic nature of the pattern transfer. The role of the masking material in the subsequent morphology of the sidewall is also discussed.

https://iopscience.iop.org/article/10.1088/0963-0252/1/1/004/pdf

III-V semiconductor device dry etching using ECR discharges

A review is given of dry etching of III-V semiconductors. Gas chemistries based on chlorine have traditionally been used for plasma etching of these materials due to the volatilities of both group III and group V chlorides. Recent work on the use of iodine- or bromine-based discharges has shown promising results, although the corrosiveness of the feedstock gases is of concern. For indium-containing III-V semiconductors, CH4/H2 plasmas have produced smooth anisotropic etching at relatively low rates. In applications requiring etch rates near 1 μm min−1, Cl2/CH4/H2 electron cyclotron resonance discharges have proved effective. Examples are given of the structural and chemical changes induced in the semiconductor as a result of dry etching, due to the combined effects of energetic ion bombardment and preferential removal of one of the lattice constituents. Applications for dry etching in modern microelectronic fabrication range from shallow (∼30 nm) mesa formation to creation of through-wafer via holes typically ∼100 μm deep.

Science of dry etching of III-V materials

Plasma etching of III-V semiconductor thin films

A dry etch fabrication technology for high‐speed AlInAs/InGaAs heterojunction bipolar transistors (HBTs) utilizing low‐damage electron cyclotron resonance (ECR) CH4/H2/Ar plasma etching is detailed. Small‐area (2×4 to 3×9 μm2 ) devices demonstrated current gains up to 160, unity gain cutoff frequency ( fT) of 57 GHz and a maximum oscillation frequency ( fmax) of 35 GHz. The dry etch process uses triple self‐alignment of the emitter and base metals and the base mesa, minimizing the base‐collector capacitance (CBC). These results represent the first report of a truly scalable process for In‐based HBTs and demonstrate the ability of ECR plasma etching to provide smooth, degradation‐free etching of III–V semiconductors.

K. F. Kopf

Papers

AlInAs/InGaAs based heterojunction bipolar transistors fabricated by electron cyclotron resonance etch