Dry Etching Method Research Articles

Low damage dry etching of III–V compound semiconductors using electron cyclotron resonance discharges

Electron cyclotron resonance (ECR) discharges are characterized by low ion energies ( ≤ 15 eV) and high densities of active species. This makes them excellent candidates for high rate, low damage dry etching of III–V semiconductors. We have investigated the use of ECR discharges of CH 4/H 2/Ar for etching InP, InGaAs, AlInAs and GaAs as a function of additional rf biasing of the sample, and in this article present the InP results. In contrast to the results with conventional reactive ion etching (RIE), ECR discharges lead to very shallow (~ 20 Å) damaged layers on these materials and much less disruption of the electrical quality of the etched surface. For example, RIE of InP leads to nonstoichiometric, In-rich surfaces to which one cannot make a Schottky contact. Removal of at least 150 Å of material is required before the integrity of the surface is restored. We have been able to achieve excellent rectifying contacts on ECR-etched InP without the need for wet chemical treatment of the surface. Optical and chemical analysis of the ECR etching shows that it clearly is a low damage process relative to the more conventional dry etch methods.

Chemical Etching of Thermally Oxidized Silicon Nitride: Comparison of Wet and Dry Etching Methods

The ability to etch silicon nitride changes after this material is exposed to a wet oxygen ambient, as a result of the partial oxidation of the silicon nitride to form a silicon oxynitride. We have measured the etch rate of silicon nitride exposed to different oxidation temperatures and pressures, to determine how these parameters affect the mask removal step needed in the local oxidation of silicon‐based processing sequence. Both wet (hydrofluoric acid and phosphoric acid) and dry ( remote plasma) isotropic etch methods are described, and correlated to Rutherford backscattering and ellipsometric measurements. Our results show the presence of an oxidized layer which increased in thickness with oxidation temperature and pressure. Process modifications must comprehend the altered silicon nitride surface in order to adequately strip this film.

Flux pinning in thin films of YBa 2Cu 3O 7-x

Thin films of YBa 2Cu 3O 7-x are deposited on MgO substrates via dc magnetron sputter technic. The thicknesses varry between 10nm and 500nm. The films are patterned by dry etching method. Narrow stripes with widths down to 1 μm are obtained without serious degradation, e.g. T c,off > 85K and T c < 1.5K. The critical properties of the bridges are determined by resistive measurements. The upper critical field, B c2(T), and the irreversibility line, B c2 [starf](T), are derived from the resistive transition in fields up to 14 Tesla and from extrapolation of the pinning data, respectively. The volume flux-pinning force F p=J c·B is measured as a function of temperature, and applied magnetic induction. A strong increase of the critical current density with decreasing width of the bridges was found. A discussion of the flux pinning data in the context of the flux-line shear model is given.

The impact of poly-removal techniques on thin thermal oxide property in poly-buffer LOCOS technology

The authors used both oxidation and dry-etching methods for removing the sandwiched polysilicon used as a stress-relief film in the poly-buffer local oxidation of silicon (LOCOS) process. The impact on thin thermal oxide (125 AA) grown after PBL-LOCOS was examined by using both time-zero and time-dependent dielectric-breakdown I-V techniques. The results of the time-zero breakdown tests show no difference in oxide-breakdown strength with respect to both methods employed in the poly-removal sequence. A very tight distribution in time-zero breakdown-field in the vicinity of 10 MV/cm was obtained for both oxidation and dry-etching cases. The high-voltage time-dependent dielectric-breakdown tests, carried out at oxide fields of 11-12 MV/cm, however, detected a marked difference in the endurance of high oxide field before the catastrophic damage occurs. In the case of samples using dry-etching poly, the mean-time-before-failure (MTBF) is approximately 6 s in comparison to 200 s measured in the samples in which the poly-film was removed by oxidation. The degradation of thin thermal oxide with respect to high-voltage time-dependent dielectric-breakdown endurance in the case of dry etching is attributed to the plasma damage and/or ion contamination such as carbon/fluorine during the poly dry etching.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Loss in heterostructure waveguide bends formed on a patterned substrate

An experimental comparison is made of the loss of Al/sub x/Ga/sub 1-x/As heterostructure waveguide routing geometries at approximately 860 nm that were patterned by two methods: Zn-impurity-induced layer disordering and native growth on a patterned substrate. Two multimode geometries were investigated: a raised cosine s-bend and a modified abrupt bend as described by T. Shiina et al. (Opt. Lett., vol.11, p.736-8, 1986). The measured transition distance for 3-dB loss was approximately 300 mu m for 100- mu m offset guides in the s-bend geometry for the patterned substrate samples using wet and dry etching methods. For the so-called Shiina bend, the measured angle corresponding to the 3-dB loss was about 13 degrees for both etching methods.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Observation of Aharonov-Bohm magnetoresistance oscillations in selectively doped GaAs-AlGaAs submicron structures

Aharonov-Bohm magnetoresistance oscillations are investigated in a selectively doped GaAs-AlGaAs submicron ring with a width of 0.35μm and a diameter of 1μm. The ring is fabricated from a MBE grown film making use of electron beam lithography and dry etching methods. A wire with submicron width and several micron length, which is fabricated for comparison, shows only aperiodic fluctuations with an average period much larger than h/e. However, the ring shows the MR oscillations with the period of h/e due to AB effect, superimposed on aperiodic fluctuations.

Novel process for emitter-base-collector self-aligned heterojunction bipolar transistor using a pattern-inversion method

A process for base-emitter-collector self-aligned HBTs using a pattern-inversion method is presented. A fabricated HBT has an emitter with a size of 1.5 × 10μm2 realised by employing a dry-etching method. Typical current gain for the fabricated HBT is 26.

Plasma cleaning in an a-Si:H deposition chamber

Reactors can be cleaned of precipitations resulting from the deposition of a-Si:H films by chemical wet-etching or plasma dry-etching with fluorine-containing gases. Acidic etchants, alkaline solutions and the gases CF 4, NF 3 and SF 6 are compared with respect to ease of application and efficiency. The dry-etching method with flourine-containing gases seems favourable. However, adsorbed products of the dry-etching process, mainly fluorine and its compounds, have to be controlled carefully, as they may influence film properties in subsequent deposition runs. To reduce impurity incorporation in a-Si:H films, a glow discharge of Ar or O 2 is advisable after the etch process.

Pattern transfer

A discussion is presented of the current status of pattern transfer in microfabrication. Additive methods are summarized briefly and emphasis is placed on dry etching methods employing either rf glow discharges or wide-area ion beams, namely: glow discharge sputter etching, plasma etching, reactive ion etching, ion milling, reactive ion beam etching and chemically assisted ion milling. A summary of the etching mechanisms is given and some of the factors which should be considered when selecting a dry etching process are summarized.

Dry Etching of Nb and Fabrication of Nb Variable-Thickness-Bridges

Several reactive dry etching methods; ion etching, sputter etching and plasma etching, were studied in order to fabricate a niobium variable-thickness type thin film bridge (VTB). Niobium was etched by CF4 reactive sputter etching with submicron accuracy and no significant influence on the superconducting transition temperature except very near the surface (<200 Å). The niobium VTB behaved as an S-S'-S bridge, and a reduced self-heating effect was realized by a variable-thickness geometry. The DC Josephson effect was observed in the temperature range without thermal hysteresis. The quality factor of the IcRn product obtained was at least 0.42 mV.

Dry etching for pattern transfer

Dry etching or plasma-assisted etching (ion beam milling, plasma etching and reactive sputter etching) has become an indispensable preparation technique for high resolution pattern transfer in IC manufacturing and other areas of microfabrication. Etching can either be due to the purely physical process of momentum transfer from ions to the solid surface (e.g. inert ion etching) or due to chemical reactions of reactive species, produced in the plasma, with the solid surface resulting in a volatile reaction product (e.g. plasma etching in a barrel reactor). However, in most dry etching methods both effects play a major role and it is possible to optimize etch selectivity and the shape of the etched profile by a proper choice of parameters.