G. K. Reeves

Ion beam etching of CVD diamond film in Ar, Ar/O2 and Ar/CF4 gas mixtures

The Ar + ion beam etching of diamond in the presence of O 2 or CF 4 gases was examined as a function of ion energy and gas composition. The details of etch rate and the structural features of the etched surfaces have been interpreted in terms of the mechanism of etching. In all cases, the etch rate has shown a square root dependence on ion energy, E 1/2 i . The etching of the diamond film in Ar/O 2 gases was characterised by a moderate etch rate (12-20 nm/min) dependent on the percentage of O 2 and has been attributed to ion-enhanced chemical etching. In comparison, the etching with Ar + ions or Ar + in the presence of CF 4 has shown a low etch rate (8-10 nm/min) which was insensitive to variation in CF 4 percentage indicative of sputter etching.

Error correction for finite semiconductor resistivity in Kelvin test structures

The Cross Bridge Kelvin Resistor structure is a commonly used test structure for the extraction of the specific contact resistance of ohmic contacts. Analyses using this structure are generally based on a two-dimensional model which assumes zero voltage drop in the semiconductor layer (in the direction normal to the plane of the contact). This paper uses a three-dimensional analysis to show the magnitude of the errors introduced by this assumption, and illustrates the conditions under which a three-dimensional analysis should be used.

Graphitic Schottky Contacts to Si formed by Energetic Deposition

Carbon films deposited by filtered cathodic vacuum arc have been used to form high quality Schottky diodes on p-Si. Energetic deposition with an applied substrate bias of -1 kV and with a substrate temperature of 100 °C has produced carbon diodes with rectification ratios of ~ 3 × 106, saturation currents of ~0.02 nA and ideality factors close to unity (n = 1.05). Simulations were used to estimate the effective work function and the thickness of an interfacial mixed (C/SiO2) layer from the current/voltage characteristics of the diodes.

Thermal Stability in Pd-Based Contacts to p-Type In 0.53 Ga 0.47 as Characterized by Rbs

The resistivity and interfacial characteristics of Pd/Zn/Pd/Au and Pd/Zn/Au/LaBd 6 /Au contacts to p-In 0.53 Ga 0.47 As have been investigated. Annealing of the contacts at 375–425°C yielded a minimum in specific contact resistance, p,, of 2 × 10 -7 Δ cm 2 for the Pd/Zn/Pd/Au contacts and 1 Δ cm 2 for the Pd/Zn/Au/LaB 6 /Au configuration. This is the lowest reported measurement of p c for an ohmic contact to p-In 0.53 Ga 0.47 As doped to ≤1 × 10 19 cm −3 . In the Pd/Zn/Au/LaB 6 /Au scheme, the minimum in p c was the same irrespective of whether the Zn was incorporated as a structural layer or as Zn ions implanted into the interfacial Pd prior to metallization. The effect of thickness of the Zn layer on pc has been determined for the Pd/Zn/Au/LaB 6 /Au scheme. RBS measurements have shown that during annealing, the LaB 6 layer acted as a barrier to the indiffusion of Au and to the degradation of the In 0.53 Ga 0.47 As substrate.

Pd/Zn/Pd/Au and Pd/Zn/Au/LaB6/Au ohmic contacts to p‐type In0.53Ga0.47As

The resistivity and interfacial characteristics of Pd/Zn/Pd/Au and Pd/Zn/Au/LaB6/Au contacts to p‐In0.53Ga0.47As have been investigated. Annealing of the contacts at 375–425 °C yielded a minimum in specific contact resistance, ρc, of 2×10−7 Ω cm2 for the Pd/Zn/Pd/Au contacts and 1×10−6 Ω cm2 for the Pd/Zn/Au/LaB6/Au configuration. The measurement of ρc for the Pd/Zn/Pd/Au system is the lowest reported for an ohmic contact to p‐In0.53Ga0.47As doped to ≤1×1019 cm−3. In the Pd/Zn/Au/LaB6/Au scheme, the minimum in ρc was the same whether the Zn was incorporated as a structural layer or as Zn ions implanted into the interfacial Pd. At ≥375 °C, the LaB6 layer limited the indiffusion of Au and the degradation of the In0.53Ga0.47As substrate.

The Stability to Ageing of Pd/Zn and Pt-Based Ohmic Contacts to p-InGaAs/InP

Pd/Zn/Au contacts to p-In 0.53 Ga 0.47 As/InP with various barrier layers (Pd, Pt or LaB,) to the indiffusion of Au have been examined by Rutherford Backscattering Spectrometry (RBS). For the metallisations with a barrier layer of Pd, the ageing of the contacts at 400°C for 20 h produced a widespread indiffusion of Au. In comparison, the incorporation of a layer of Pt or amorphous LaB 6 prevented an indiffusion of Au and significantly reduced any outdiffusion of the semiconductor elements. The presence of the barrier layer of Pt or LaB 6 produced little or no detrimental increase in specific contact resistance, ρ c , for this contact system. Values of ρ c in the range 8–10 × 10 −6 Ω cm 2 were obtained for all of the contacts based on Pd/Zn/Au after annealing at 500°C. A comparison has been made with the characteristics of Pt/Ti/Pt/Au contacts to p-In 0.53 Ga 0.47 As/ InP which were shown as stable against the indiffusion of Au.

The Study of Morphological Structure and Raman Spectra of 3C-SiC Membranes

In this paper, membranes of 3C-SiC with dimensions up to 10 mm x 15 mm2 have been fabricated in epitaxial 3C-SiC/ Si wafers by the means of photolithography, reactive ion etching of 3C-SiC and wet etching of Si. Scanning electron microscope (SEM) micrographs were used to observe the structure of the membrane and the wall formed by the Si wet etching. The quality of the 3C-SiC membranes were observed using Raman Spectroscopy. The remains of <111> Si substrate which was unetched during the Si wet etching were presented with the formation of microstructure defects which showed distinct peaks in comparison to the high quality 3C-SiC membranes at different position. Here, the effect of the membrane fabrication procedures to the 3C-SiC membrane properties especially the morphological structure and its Raman characteristics is discussed in detail.

Reactive ion etching of TiN, TiAlN, CrN and TiCN Films in CF 4 /O 2 and CHF 3 /O 2 Plasmas

The reactive ion etching of a range of hard coatings (TiN, TiCN, CrN and TiAlN) has been examined as a function of rf power, flow rate and pressure. The films were deposited by filtered arc deposition (TiN, TiAlN and CrN) or low energy electron beam (TiCN) on polished disc substrates of M2 tool steel. The flat surfaces were lithographically patterned with a grating structure (∼1 μm pitch). The TiN and TiCN layers have shown significantly higher etch rates (100-250 nm/min) than the CrN and TiAlN (∼5 nm/min) coatings. These regimes of higher and low etch rate were identified as ion-enhanced chemical etching and physical sputtering, respectively. In CF 4 /O 2 plasma, the etch rate of the TiN and TiCN layers increased with rf power, flow rate and pressure which were parameters known to enhance the density of active fluorine species. The etch rates of TiN and TiCN layers were higher in CF 4 /O 2 plasma than in CHF 3 /O 2 gases in which polymer deposition was produced at pressure ≥ 35 mTorr.

Shallow and Low-Resistive Ohmic Contacts to p-In 0.53 Ga 0. 47 As Based on Pd/Au and Pd/Sb Metallizations

InP/In 0.53 Ga 0.47 As heterojunction bipolar transistors with high current gain for optoelectronic applications place stringent requirements on the ohmic contact to the base layer of moderately doped (p 19 cm −3 ) In 0.53 Ga 0.47 As. Contact resistivity should be −6 Ωcm 2 and low depth of penetration is necessary considering the small base thickness of approximately 100 nm. The authors have recently presented data on Pd/Zn/Au/LaB 6 /Au contacts on p-In 0.53 Ga 0.47 As (doped to 4×10 18 cm −3 ) with low contact resistivities of l×10 −6 Ωcm 2 . In this paper, details are given on the optimization of the contact composition and annealing conditions of the metallization that resulted in shallow and low-resistive contacts. Alternatively, it is shown that Au-free Pd/Zn/Sb/Pd contacts on p-In 0.53 Ga 0.47 As have exhibited even lower resistivities, i.e. 3-6×10 −7 Ωcm 2 . Backside SIMS measurements revealed a depth of penetration as low as 20 nm for this contact scheme. Aging tests at temperatures of 300 - 400 °C have demonstrated that the electrical characteristics of both types of metallization were sufficiently stable to withstand the typical processing steps for device passivation.

Dry Etching of Indium Phosphide

Indium Phosphide (InP) based multilayer structures are becoming increasingly important in the semiconductor industry with optoelectronic applications being the main growth area. Mesa type structures with finely controlled width and etch angle, often form the building blocks for many of these photonic devices. Traditional wet etching techniques have often proved to be inadequate for the required anisotropie removal of material. This paper presents the results of etching semi-insulating InP (100) using a combination of an Argon ion beam and a reactive gas, CCl 2 F 2 (Freon 12). It was found that the etch rate was enhanced by increasing the ion energy and by the addition of CCl 2 F 2 . Auger electron spectroscopy revealed that the increased etch rate was accompanied by an increase in the surface indium concentration and at low ion beam energies carbon build-up retarded the etch rate. The optimum etch angle to fabricate 3μm waveguides was found to be 22° to the surface normal, however Schottky contacts to these structures were unsuccessful.