ICP Source Power Research Articles

Effect of Dry Etching to Improve Ohmic Contacts on Bulk, Lightly-Doped β-Ga2O3

Ti/Au is a typical Ohmic metal contact stack to n-type β-Ga2O3 but there have been few systematic studies of the use of pre-exposure of the surface to plasmas prior to metal deposition in order to lower the contact resistance. The effects of Cl2/Ar Inductively Coupled Plasma exposure of Ga2O3 surfaces prior to deposition of Ti/Au (20/80 nm) contacts were examined through circular transfer length method (CTLM) measurements to determine both the contact resistance and specific contact resistivity. ICP source power, which controls ion density in the plasma is found to be more important than ion energy (∼165–490 eV in these experiments). The plasma exposure improved specific contact resistivity by more than a factor of 2 in all cases for lightly n-type (1017 cm−3) Ga2O3 and a minimum value of 2 × 10−4 Ω.cm2 was obtained after heating at 550 °C.

The Role of Oxygen on Anisotropy in Chromium Oxide Hard Mask Etching for Sub-Micron Fabrication

Chromium and its oxides have been playing a vital role in the fabrication of micro- and nano-scale structures in numerous applications for several decades. Controllable, robust and anisotropically dry-etched hard masks and their optimal etch recipes are required in state-of-the-art device fabrication techniques. In terms of manufacturability and repeatability, a mechanistic understanding of the plasma-etching process of chromium oxide (Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) is necessary for its adoption as a hard mask. We present a systematic investigation of plasma etching of chromium oxide films via an inductively coupled plasma-reactive ion etching (ICP-RIE) system in nanoscale. The effects of plasma composition, ICP source power and HF platen power on the etch rate, sidewall profile, surface morphology, and dc-bias have been methodically investigated. We paid particular attention to studying how oxygen content can be used to control the etch profile of nano trenches using chlorine/oxygen gas mixtures, including extremes of very low and very high oxygen content. It was found that chromium oxide etch mechanisms are dependent strongly on the oxygen level. We achieved desirable vertical sidewalls with reasonable etch rates when the oxygen content is in the range 10-40% in the plasma. Oxygen content below 10% resulted in positively tapered etch profiles with low etch rates. On the other hand, bowl-like etch profiles with undercut formation was observed at high oxygen content above 40%, caused by re-emission of the reactive species at this regime. As a hard mask material, patterning Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films compared to Cr metal is advantageous in terms of etch uniformity and reproducibility. Contrary to Cr, Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> is not as sensitive to chamber wall conditions.

Etch Characteristics of Micrometer-Scale Masked Cu Thin Films Using Inductively Coupled Plasma of H₂/Ar.

Inductively coupled plasma reactive ion etching (ICPRIE) of copper thin films masked with photoresist (PR) and SiO₂ thin films was performed in H₂/Ar gas. As the H₂ concentration increased, the etch rates of copper films significantly decreased. The etch profiles show heavy redeposition on the sidewall of the etched films in low H₂ concentration but steep etch profiles without redeposition and etch by-product were obtained in high H₂ concentration. The systematic variation of the etch parameter such as ICP source power, dc-bias voltage to substrate, and process pressure was carried out to characterize the copper etching in H₂/Ar gas. Based on the etch characteristics of copper films, Langmuir prove analysis, and X-ray photoelectron spectroscopy, it was revealed the physical sputtering by ions and the formation of the volatile copper compound and the protection layer had great influence on achieving a good etch profile.

Inductively coupled plasma etch damage in (-201) Ga2O3 Schottky diodes

Bulk, single-crystal Ga2O3 was etched in BCl3/Ar inductively coupled plasmas as a function of ion impact energy. For pure Ar, the etch rate (R) was found to increase with ion energy (E) as predicted from a model of ion enhanced sputtering by a collision-cascade process, R ∝(E0.5 – ETH0.5), where the threshold energy for Ga2O3, ETH, was experimentally determined to be ∼75 eV. When BCl3 was added, the complexity of the ion energy distribution precluded, obtaining an equivalent threshold. Electrically active damage introduced during etching was quantified using Schottky barrier height and diode ideality factor measurements obtained by evaporating Ni/Au rectifying contacts through stencil masks onto the etched surfaces. For low etch rate conditions (∼120 Å min−1) at low powers (150 W of the 2 MHz ICP source power and 15 W rf of 13.56 MHz chuck power), there was only a small decrease in reverse breakdown voltage (∼6%), while the barrier height decreased from 1.2 eV to 1.01 eV and the ideality factor increased from 1.00 to 1.06. Under higher etch rate (∼700 Å min−1) and power (400 W ICP and 200 W rf) conditions, the damage was more significant, with the reverse breakdown voltage decreasing by ∼35%, the barrier height was reduced to 0.86 eV, and the ideality factor increased to 1.2. This shows that there is a trade-off between the etch rate and near-surface damage.

Atomic scale study of InP etching by Cl2-Ar ICP plasma discharge

A gas phase kinetic model combined to a 3D atomic etching model have been developed to study the etching process of InP under Cl 2 -Ar ICP plasma discharge. A gas phase global kinetic model is used to calculate the reactive particle fluxes implied in the etching mechanisms. The 3D atomic InP etching model is based on the Monte Carlo kinetic approach where the plasma surface interactions are described in the probability way. The coupling between the plasma chemistry model and the surface etching model is an interesting approach to predict the etched surface properties in terms of the etch rate, the surface roughness and surface steochiometry as a function of the operating conditions. A satisfactory agreement is obtained by comparing the experimental and the simulation results concerning the evolution of the main plasma discharge parameters such as the electron density and temperature versus the ICP source power for a surface recombination coefficient of atomic chlorine fixed at γ Cl = 0.04. On the other hand, simulation results show the effect of the operating conditions on the etched surface roughness and the etch rate evolutions with time in the early stage. Moreover, the simulation results show the correlation between the decrease of the ion to chlorine flux ratio and the decrease of the RRMS as a function of the pressure.

High Density Plasma Etching of Platinum Films in BCl3/Ar and CF4/Ar Inductively Coupled Plasmas

The etch characteristics of platinum films and the etch selectivities for platinum over the mask materials in BCl3/Ar and CF4/Ar ICP discharges have been investigated to establish a process window for the thick platinum structure formation in MEMS devices. Maximum etch rates of ≈1800 A/minute and ≈1200 A/minute were obtained at a moderate ICP source power (750 W) and a relatively high rf chuck power (400 W) condition for CF4/Ar and BCl3/Ar ICP discharges, respectively. Maximum etch selectivities of ≈2.6 for platinum over Al and of ≈2.1 for platinum over ZnO were obtained. CF4/Ar ICP etching with aluminum mask layer seems to be a very attractive tool for the fabrication of MEMS devices containing a thick platinum structure layer.

Preparation of Phosphorus Doped Hydrogenated Microcrystalline Silicon Thin Films by Inductively Coupled Plasma Chemical Vapor Deposition and Their Characteristics for Solar Cell Applications

Intrinsic and phosphorus-doped hydrogenated microcrystalline silicon (microc-Si:H) films were prepared using inductively coupled plasma chemical vapor deposition (ICP-CVD) method. Structural, electrical and optical properties of these films were studied as a function of silane concentration, ICP source power and PH3/SiH4 gas ratio. Characterization of these films from Raman spectroscopy and X-ray diffraction revealed that the conductive film exists in microcrystalline phase embedded in an amorphous network. The condition of electrical properties (sigma(d): approximately 10(-7) S/cm, sigma(ph): approximately 10(-4) S/cm) and activation energy (0.55 eV), satisfied with properties of intrinsic microc-Si:H, was obtained at 1200 W of ICP power and 2% of silane concentration, respectively. At PH3/SiH4 gas ratio of 0.09%, dark conductivity has a maximum value of approximately 18.5 S/cm and optical bandgap also a maximum value of approximately 2.39 eV. The deposition rate was not satisfactory (4.9 angstroms/s) at same condition.

Study of Selective Etching of GaAs over AlGaAs and InGaP Semiconductors in High Density Planar Inductively Coupled BCl3/SF6 Plasmas

We investigated selective dry etching of GaAs over AlGaAs and InGaP in high density planar inductively coupled <TEX>$BCl_3/SF_6$</TEX> plasmas. The process parameters were ICP source power (0-500 W), RE chuck power (0-30W) and gas composition <TEX>$(60-100\%\;BCl_3\;in\;BCl_3/SF_6)$</TEX>. The process results were characterized in terms of etch rate, selectivities of GaAs over AlGaAs and InGaP, surface morphology, surface roughness and residues after etching. <TEX>$BCl_3/SF_6$</TEX> selective etching of GaAs showed quite good results in this study. Selectivities of GaAs <TEX>$(GaAs:AlGaAs\~36:1,\;GaAs:InGaP\~45:1)$</TEX> were superior at <TEX>$18BCl_3/2SF_6$</TEX>, 20 W RF chuck power, 300 W ICP source power and 7.5 mTorr. Addition of <TEX>$(5-15\%)SF_6\;to\;BCl_3$</TEX> produced relatively high selectivities of GaAs over AlGaAs and InGaP during etching due to decrease of etch rates of AlGaAs and InGaP (boiling points of etch products: <TEX>$AlF_3\~1300^{\circ}C,\;InF_3>1200^{\circ}C$</TEX> at atmosphere) at the condition. SEM and AFM data showed slightly sloped sidewall and somewhat rough surface<TEX>$(RMS\~9nm)$</TEX>. XPS study on the surface of processed GaAs proved a very clean surface after dry etching. It shows that planar inductively coupled <TEX>$BCl_3/SF_6$</TEX> plasmas could be a good candidate for selective dry etching of GaAs over AlGaAs and InGaP.

Inductively coupled plasma etching of Ta, Co, Fe, NiFe, NiFeCo, and MnNi with Cl2/Ar discharges

Dry etching of the magnetic thin films such as Ta, Fe, Co, NiFe, NiFeCo, and MnNi was carried out in inductively coupled plasmas of Cl2/Ar mixture. All the magnetic materials went through a maximum etch rate at 25% Cl2. The effects of the ICP source power and the rf chuck power on the etch rate and the surface roughness were quite dependent of the materials. An ion-enhanced chemical etch mechanism was important for the magnetic films. The surface roughness of the etched samples was relatively constant of the rf chuck power up to 200 W, but a rougher surface at a higher rf power was obtained. Post-etch cleaning of the etched samples in de-ionized water reduced the chlorine residues substantially.

Dry Etching of GaAs and AlGaAs Semiconductor Materials in High Density BCl3 And BCl3/Ar Inductively coupled Plasmas

We investigated dry etching of GaAs and AiGaAs in a high density planar inductively coupled plasma system with BCland BCl/Ar gas chemistry. A detailed etch process study of GaAs and ALGaAs was peformed as functions of ICP source power, RIE chuck power and mixing ratio of and Ar. Chamber process pressure was fixed at 7.5 mTorr in this study. The ICP source power and RIE chuck power were varied from 0 to 500 W and from 0 to 150 W, respectively. GaAs etch rate increased with the increase of ICP source power and RIE chuck power. It was also found that etch rates of GaAs in /5Ar plasmas were relatively high with applied RIE chuck power compared to pure 20 sccm plasmas. The result was the same as AlGaAs. We expect that high ion-assisted effect in /Ar plasma increased etch rates of both materials. The GaAs and AlGaAs features etched at 20 sccm and /5Ar with 300 W ICP source power, 100 W RIE chuck power and 7.5 mTorr showed very smooth surfaces(RMS roughness

Inductively coupled plasma etching of HgCdTe

The high-density inductively coupled plasma (ICP) etching technique has been applied to HgCdTe. The HgCdTe etch rate was studied as a function of key process variables commonly used in high-density plasma etching: chamber pressure, direct current (DC) bias, and ICP-source power. Mesa profiles were characterized using scanning electron microscopy (SEM), and the profiles for the process conditions used were found to be compatible with fabrication procedures for HgCdTe infrared focal-plane arrays (FPAs). The etch uniformity was measured to be better than 5% over a diameter of 6-in.

Dry Etching of GaAs in a Planar Inductively Coupled BCI3 Plasma

We studied BCl<TEX>$_3$</TEX> dry etching of GaAs in a planar inductively coupled plasma system. The investigated process parameters were planar ICP source power, chamber pressure, RIE chuck power and gas flow rate. The ICP source power was varied from 0 to 500 W. Chamber pressure, RIE chuck power and gas flow rate were controlled from 5 to 15 mTorr, 0 to 150 W and 10 to 40 sccm, respectively. We found that a process condition at 20 sccm <TEX>$BCl_3$</TEX> 300 W ICP, 100 W RIE and 7.5 mTorr chamber pressure gave an excellent etch result. The etched GaAs feature depicted extremely smooth surface (RMS roughness < 1 nm), vertical sidewall, relatively fast etch rate (> <TEX>$3000\AA$</TEX>/min) and good selectivity to a photoresist (> 3 : 1). XPS study indicated a very clean surface of the material after dry etching of GaAs. We also noticed that our planar ICP source was successfully ignited both with and without RIE chuck power, which was generally not the case with a typical cylindrical ICP source, where assistance of RIE chuck power was required for turning on a plasma and maintaining it. It demonstrated that the planar ICP source could be a very versatile tool for advanced dry etching of damage-sensitive compound semiconductors.

Inductively coupled plasma etching of GaN and its effect on electrical characteristics

Dry etch behavior in the inductively coupled plasma processing of GaN using SF6/N2 plasma has been found to be highly ion induced with an ion energy threshold of about 100 eV. Temperature dependence of the etch rate indicates a small kinetic component. Maximum etch rate of 67 nm/min and good anisotropy have been demonstrated. The most efficient etch regime is observed for an ICP source power between 500–1000 W where the etch mechanism is ion limited. In contrast to reactive ion etching induced damage behavior, almost ideal diodes are obtained at the higher dc bias condition (300 V). X-ray photoelectron spectroscopy and atomic force microscopy studies indicate that smooth surface with minimal surface contamination, coupled with the incorporation of N on the substrate surface help to produce ideal diodes on surfaces etched at 300 V. Sidewall depletion is found to be in the range of 65 nm at the given SF6/N2 plasma process conditions.

A unified global self-consistent model of a capacitively and inductively coupled plasma etching system

Based on the concept of independent control of ion flux and ion-bombardment energy, a global selfconsistent model was proposed for etching in a high-density plasma reactor. This model takes account of the effect on the plasma behavior of separate rf chuck power in an Inductively Coupled Plasma etching system. Model predictions showed that the chuck power controls the ion bombardment energy but also slightly increases the ion density entering the sheath layer, resulting in an increase in etch rate (or etch yield) with increasing this rf chuck power. The contribution of the capacitive discharge to total ion flux in the ICP etching process is less than about 6% at rf chuck powers lower than 250 W. As a model system, etching of InN was investigated. The etch yield increased monotonically with increasing the rf chuck power, and was substantially affected by the ICP source power and pressure. The ion flux increased monotonically with increasing the source power, while the dc-bias voltage showed the reverse trend.

Low Temperature Silicon Nitride and Silicon Dioxide Film Processing by Inductively Coupled Plasma Chemical Vapor Deposition

High‐density plasma technology is becoming increasingly attractive for the deposition of dielectric films such as silicon nitride and silicon dioxide. In particular, inductively coupled plasma chemical vapor deposition (ICPCVD) offers a great advantage for low‐temperature processing over plasma‐enhanced chemical vapor deposition (PECVD) for a range of devices including compound semiconductors and magnetic heads. In this paper, the development of low temperature (<200°C) silicon nitride and silicon dioxide films utilizing ICP technology is discussed. The material properties of these films have been investigated as a function of ICP source power, radio‐frequency chuck power, chamber pressure, gas chemistry, and temperature. The ICPCVD films are compared to PECVD films in terms of wet etch rate, stress, and other film characteristics. Two different gas chemistries, and , were explored for the deposition of ICPCVD silicon nitride. The ICPCVD silicon dioxide films were prepared from . The wet etch rates of both silicon nitride and silicon dioxide films are significantly lower than films prepared by conventional PECVD. This implies that ICPCVD films prepared at these low temperatures are of higher quality. The advanced ICPCVD technology can also be used for efficient void‐free filling of high aspect ratio (3:1) sub‐micrometer trenches. © 2000 The Electrochemical Society. All rights reserved.

Inductively Coupled Plasma Etching of III-Nitrides in Cl2/Xe, Cl2/Ar and Cl2/He

The role of additive noble gases He, Ar and Xe to Cl2-based Inductively Coupled Plasmas for etching of GaN, AlN and InN were examined. The etch rates were a strong function of chlorine concentration, rf chuck power and ICP source power. The highest etch rates for InN were obtained with Cl2/Xe, while the highest rates for AlN and GaN were obtained with Cl2/He. Efficient breaking of the III-nitrogen bond is crucial for attaining high etch rates. The InN etching was dominated by physical sputtering, in contrast to GaN and AlN. In the latter cases, the etch rates were limited by initial breaking of the III-nitrogen bond. Maximum selectivities of ∼ 80 for InN to GaN and InN to AlN were obtained.

Group-III Nitride ETCH Selectivity IN BCl /Cl ICP Plasmas

Patterning the group-III nitrides has been challenging due to their strong bond energies and relatively inert chemical nature as compared to other compound semiconductors. Plasma etch processes have been used almost exclusively to pattern these films. The use of high-density plasma etch systems, including inductively coupled plasmas (ICP), has resulted in relatively high etch rates (often greater than 1.0 µm/min) with anisotropic profiles and smooth etch morphologies. However, the etch mechanism is often dominated by high ion bombardment energies which can minimize etch selectivity. The use of an ICP-generated BCl3 /Cl2 plasma has yielded a highly versatile GaN etch process with rates ranging from 100 to 8000 Å/min making this plasma chemistry a prime candidate for optimization of etch selectivity. In this study, we will report ICP etch rates and selectivities for GaN, AlN, and InN as a function of BCl3/Cl2 flow ratios, cathode rf-power, and ICP-source power. GaN:InN and GaN:AlN etch selectivities were typically less than 7:1 and showed the strongest dependence on flow ratio. This trend may be attributed to faster GaN etch rates observed at higher concentrations of atomic Cl which was monitored using optical emission spectroscopy (OES).

Development of Low Temperature Silicon Nitride and Silicon Dioxide Films by Inductively-Coupled Plasma Chemical Vapor Deposition

ABSTRACTHigh-density plasma technology is becoming increasingly attractive for the deposition of dielectric films such as silicon nitride and silicon dioxide. In particular, inductively-coupled plasma chemical vapor deposition (ICPCVD) offers a great advantage for low temperature processing over plasma-enhanced chemical vapor deposition (PECVD) for a range of devices including compound semiconductors. In this paper, the development of low temperature (&lt; 200°C) silicon nitride and silicon dioxide films utilizing ICP technology will be discussed. The material properties of these films have been investigated as a function of ICP source power, rf chuck power, chamber pressure, gas chemistry, and temperature. The ICPCVD films will be compared to PECVD films in terms of wet etch rate, stress, and other film characteristics. Two different gas chemistries, SiH4/N2/Ar and SiH4/NH3/He, were explored for the deposition of ICPCVD silicon nitride. The ICPCVD silicon dioxide films were prepared from SiH4/O2/Ar. The wet etch rates of both silicon nitride and silicon dioxide films are significantly lower than films prepared by conventional PECVD. This implies that ICPCVD films prepared at these low temperatures are of higher quality. The advanced ICPCVD technology can also be used for efficient void-free filling of high aspect ratio (3:1) sub-micron trenches.

High-density plasma etch selectivity for the III–V nitrides

High-density plasma etching has been an effective patterning technique for the group-III nitrides due to ion fluxes which are 2–4 orders of magnitude higher than more conventional reactive ion etch (RIE) systems. GaN etch rates exceeding 0.68 μm/min have been reported in Cl 2/H 2/Ar inductively coupled plasmas (ICP) at −280 V dc-bias. Under these conditions, the etch mechanism is dominated by ion bombardment energies which can induce damage and minimize etch selectivity. High selectivity etch processes are often necessary for heterostructure devices which are becoming more prominent as growth techniques improve. In this study, we will report high-density ICP etch rates and selectivities for GaN, AlN, and InN as a function of plasma chemistry, cathode rf-power, ICP-source power, and chamber pressure. GaN:AlN selectivities >8:1 were observed in a Cl 2/Ar plasma at 10 mTorr pressure, 500 W ICP-source power, and 130 W cathode rf-power, while the GaN:InN selectivity was optimized at ∼6.5:1 at 5 mTorr, 500 W ICP-source power, and 130 W cathode rf-power.

Cl 2-based dry etching of the AlGaInN system in inductively coupled plasmas

Cl 2-Based inductively coupled plasmas with low additional d.c. self-biases (−100 V) produce convenient etch rates (500–1500 Å·min −1) for GaN, AlN, InN, InAlN and InGaN. A systematic study of the effects of additive gas (Ar, N 2, H 2), discharge composition and ICP source power and chuck power on etch rate and surface morphology has been performed. The general trends are to go through a maximum in etch rate with percent Cl 2 in the discharge for all three mixtures and to have an increase (decrease) in etch rate with source power (pressure). Since the etching is strongly ion-assisted, anisotropic pattern transfer is readily achieved. Maximum etch selectivities of approximately 6 for InN over the other nitrides were obtained.