E. Lane

Properties of titanium nitride thin films deposited by rapid‐thermal‐low‐pressure‐metalorganic‐chemical‐vapor‐deposition technique using tetrakis (dimethylamido) titanium precursor

Titanium nitride (TiNx) thin films were deposited onto InP by means of the rapid‐thermal‐low‐pressure‐chemical‐vapor‐deposition (RT‐LPMOCVD) technique, using the tetrakis (dimethylamido) titanium (Ti(NMe2)4 or DMATi) complex as the precursor. Depositions were successfully carried out at temperatures below 550 °C, pressure range of 5–20 Torr and duration of 50 to 90 s, to give layer thicknesses up to 200 nm and growth rates in the range of 0.8 to 4.5 nm/s. These films had a stoichiometric structure and contained nitrogen and titanium in a ratio close to unity, but also contained a significant amount of carbon and oxygen. The elements were spread uniformly through the films, the nitrogen was Ti bounded, and the carbon was partially titanium bonded and organic bonded as well. The film resistivity was in the range of 400–800 μΩ cm−2; the stress was always compressive, in the range of − 0.5 × 109 to − 2 × 1010 dyne cm−2, and the film had a good morphology. These layers performed as an ohmic contact while depos...

Study of Ni as a barrier metal in AuSn soldering application for laser chip/submount assembly

The possibility of replacing Pt in the Ti/Pt/Au base and traditionally used metallurgical structure by Ni, while bonding InP laser chip to a submount with AuSn (80% Au) solder, has been investigated. Various Ni‐based metal alloys have been prepared by evaporation. Reflow experiments were conducted in a chamber under forming gas‐controlled ambient. The Ti/Ni/AuSn system provided much longer surface local freezing duration compared to the Ti/Pt/AuSn system. Scanning electron microscopy analysis revealed a smoother surface morphology for the Ti/Ni/AuSn system after the metal refroze. Auger electron spectroscopy depth profiles indicated the formation of a Ni‐Sn‐Au interacted layer. The interaction took place in two steps: the first stage was the dissolution of Ni into the Au‐Sn liquid followed by precipitation of a Ni‐Sn‐Au intermetallic compound; the second stage was a solid‐state interdiffusion of Sn, Au, and Ni which occured in the interacted layer and in the original Ni layer. The latter step was a diffus...

Reactive ion etching of GaAs with CCl2F2:O2: Etch rates, surface chemistry, and residual damage

The reactive ion etching of GaAs with a CCl2F2:O2 discharge was investigated as a function of gas flow rate (10–60 sccm), total pressure (2–50 mTorr), power density (0.25–1.31 W cm−2), gas composition (0%–70% O2), and etch time (1–64 min). The etch rate decreases with increasing gas flow rate, increases with increasing power density, and goes through a maximum at a gas composition of 75:25 CCl2F2:O2 under our conditions. After etching at low‐power densities (0.56 W cm−2) and for high CCl2F2 ratios (19:1 to O2), carbon and chlorine could be detected in the GaAs to a depth of less than 15 A by x‐ray photoelectron spectroscopy. Under these conditions there was a Ga deficiency to a depth of ∼100 A, which we ascribe to surface roughening and the preferential vaporization of As2O3 over Ga2O3. At high‐power densities (1.31 W cm−2) a polymeric layer several hundred angstroms thick containing CCl and CF bonds was observed on the GaAs surface. Etching under O2‐rich conditions did not lead to any additional creation...

Characteristics of III‐V Dry Etching In HBr ‐ Based Discharges

Electron cyclotron resonance (ECR) discharges of HBr/Ar, HBr/H 2 , or HBr/CH 4 were used for dry etching of Ga-based (GaAs, GaSb, and AlGaAs) and In-based (InP, InAs, InSb, InGaAs, and InAlAs) III-V semiconductors. The effects of variations in pressure (1-20 mTorr), gas composition, and additional RF-induced bias on the sample were examined. At least -100 V of dc bias is required to initiate etching under all conditions, with the etch rates found to be fastest with CH 4 addition, followed by H 2 and then Ar

The influence of ammonia on rapid‐thermal low‐pressure metalorganic chemical vapor deposited TiNx films from tetrakis (dimethylamido) titanium precursor onto InP

The process kinetics, chemical composition, morphology, microstructures, and stress of rapid‐thermal low pressure metalorganic chemical vapor deposited (RT‐LPMOCVD) TiNx films on InP, using a combined reactive chemistry of ammonia (NH3) gas and tetrakis (dimethylamido) titanium (DMATi) liquid precursors, were studied. Enhanced deposition rates of 1–3 nm s−1 at total chamber pressures in the range of 3–10 Torr and temperatures of 300 °C–350 °C at a NH3:DMATi flow rate ratio of 1:8 to 1:15 were achieved. Stoichiometric film compositions were obtained, with carbon and oxygen impurity concentrations as low as 5%. Transmission electron microscopy analysis identified the deposited films as TiN with some epitaxial relationship to the underlying (001) InP substrate. This process provides a superior film to the preview RT‐LPMOCVD TiNx film deposited using only the DMATi precursor.

Bonding of InP laser diodes by Au-Sn solder and tungsten-based barrier metallization schemes

Ti/W/Au-Sn and Ti/WxMy/Au-Sn schemes were studied as alternative metallization schemes to the traditionally used Ti/Pt/Au-Sn system for the bonding of InP laser diodes to heatsinks, and in particular to CVD diamond parts. The study comprised the Ti/W, Ti/W1(Au-Sn) and Ti/W1(Ni-Sn) barrier metal schemes, co-deposited in between the Au-Sn solder and the submount. In particular, reactivity and thermodynamic stability of the systems, acid the integrity of the barrier metal to the AuSn solder interface through the thermal bonding refreezing and reflow cycles were tracked. Premature freezing of the solder through the bonding cycles was attributed to the intermixing of the underlying barrier metal and the solder, suggesting an insufficient thermodynamic stability. Dewetting of the solder from the barrier metals through the reflowing cycle, subsequent to the completion of the bonding cycle, occurs due to the excellent inert nature of the solder to the barrier system, but exhibited the deficiency of poor solder to barrier metal adhesion. The TIM, system performed as an absolute inert barrier under the Au-Sn solder, in which no premature freezing phenomena were observed through the bonding cycle, resulting, however, in a delamination of the solder from the Ti/W, while reflown both under flux and forming-gas. In order to maintain the stable nature of this system, but to improve the barrier-solder interfacial integrity, W-Au, W-AuSn and W-NiSn co-deposited intermediate adhesion layers were introduced in between the W layer and the Au-Sn solder. As a result, the adhesion of the solder to the barrier metal improved, while the most stable performance was observed while applying the W/W(NiSn) barrier system under the Au-Sn solder. The first local freezing phenomenon of the bonding solder, while using this system, was observed only after heating the sample to 320 degrees C for more than 3 min and more than 1 h was needed to completely freeze the entire solder. in addition, an excellent solder to metal interfacial integrity was observed through the gas and flux reflow cycle. Thus, the W/W(NiSn) barrier metallization is recommended as a superior scheme to replace the traditionally used Ti/Pi system for bonding laser diodes to any type of submount using Au-Sn solder.

Temperature dependence of reactive ion etching of GaAs with CCl2F2:O2

The etch rate of GaAs during reactive ion etching (RIE) in a CCl2F2:O2 discharge (4 mTorr, 0.56 W cm−2) shows a strong temperature dependence, increasing from ∼500 A min−1 at 50 °C to 2800 A min−1 at 400 °C. Arrhenius plots of the etch rate show two activation energies (0.17 eV from 50 to 150 °C and 0.11 eV from 150 to 400 °C). There is no significant plasma power density dependence of the etch rate at elevated temperatures (≥100 °C) in contrast to the strong dependence at 50 °C. The surface morphology undergoes smooth‐to‐rough‐to‐smooth‐to‐rough transitions at ∼150, 250, and 400 °C, respectively, although TiPtAu Schottky diodes exhibit near‐ideal behavior on GaAs etched at 150 °C. The As‐to‐Ga ratio in the first 100 A from the surface increases with increasing RIE temperature, with chloride residues absent above 150 °C. Fluorocarbon residues were present on all samples, but were limited to the first 10–15 A. As determined by x‐ray photoelectron spectroscopy, fluorine was present almost exclusively as met...

Tantalum nitride films as resistors on chemical vapor deposited diamond substrates

Tantalum nitride films were reactive sputter deposited onto chemical vapor deposited (CVD)‐diamond self‐standing thick layers, to be used as resistors for microelectronic applications. The TaN films had excellent morphology and were very stable through heating cycles at temperatures up to 400 °C for a few hours. Post‐deposition sintering of the films at temperatures up to 300 °C stabilized the film resistance at values in the range of 75–85 Ω. The deposited film was later patterned with photoresist and dry etched, at rates of up to 70 nm min−1 and the resulting features served as masks for further self‐aligned etching processes of the underlying CVD‐diamond layer.

W(Zn) selectively deposited and locally diffused ohmic contacts to p-InGaAs/InP formed by rapid thermal low pressure metalorganic chemical vapor deposition

Self‐aligned, locally diffused W(Zn) contacts to InGaAs/InP structures were fabricated by means of rapid thermal low pressure metalorganic chemical vapor deposition (RT‐LPMOCVD), using a reactive gas mixture that contained diethylzinc (DEZn), WF6, H2, and Ar. W(Zn) layers of about 30 nm thick were deposited at 500 °C for 20 s and at a total pressure of about 2 Torr, onto InGaAs and InP. Spontaneous formation of highly doped underlying InGaAs and InP layers about 150 nm thick with Zn concentration levels higher than 1×1018 cm−3 took place through the deposition of the W(Zn) layers. Post‐deposition, in situ annealing at temperatures of 500 °C or lower enhanced the indiffusion of Zn into the underlying semiconductor and reduced the specific resistance of the W(Zn)/InGaAs contact to a minimum value of 5×10−6 Ω cm−2.

Low resistance tungsten films on GaAs deposited by means of rapid thermal low pressure chemical vapor deposition

Low resistance tungsten (W) films were deposited onto GaAs substrates by means of rapid thermal low pressure chemical vapor deposition (RT‐LPCVD), using tungsten hexafluoride (WF6) gas reduced by hydrogen (H2). Deposition temperatures up to 550 °C for durations of up to 30 s were explored, resulting in deposition of relatively pure W films (containing less than 2% O2 and C). Post‐deposition sintering of the layers led to significant reduction of the resistivity to values as low as 50 μΩ cm. The efficiency of the deposition improved upon increasing the H2 flow rate up to 1250 sccm resulting in a deposition rate of about 10 nm/s at a total chamber pressure of 3.5 Torr and temperature of 500 °C. The films appeared to be polycrystalline with a very fine grain structure, regardless of the deposition temperature with good morphology and underwent a limited reaction with the underlying GaAs substrates.