Dry Etch Rates Research Articles

Thermal stability and etching characteristics of electron beam deposited SiO and SiO2

We have studied the thermal stability and etching characteristics of electron beam deposited SiO and SiO2. Scanning electron microscopy, Auger, atomic form microscopy, and ellipsometry were used to analyze the surface morphology, roughness, and film composition as a function of annealing temperatures. Both SiO and SiO2 showed excellent thermal stability up to 400 °C anneal and refractive index, surface morphology and pattern edge definition of both films barely changed. For higher temperature anneal, based on Auger analysis results, the ratio of Si/O of SiO2 film stayed constant after 700 °C. However, the Si/O ratio of SiO film increased from 0.54 to 0.62 due to oxygen outdiffusion. Dry etch characteristics of SiO and SiO2 were investigated using SF6 and NF3 discharges in a Plasma Therm inductively coupled plasma system. Wet etches were performed using buffered HF and HF/H2O solutions. Dry etch rates of SiO2 were comparable with that of conventional plasma enhanced chemical vapor deposition SiO2. SiO2 etched faster than SiO under all etch conditions.

Inductively Coupled Plasma Etching of Ta2 O 5

A number of different plasma chemistries were examined for dry etching of thin film . Maximum etch rates of were achieved with or discharges, while and produced rates an order of magnitude lower. The etch rates of were always slower than those for Si under the same conditions in each of the chemistries, and there was no effect of postdeposition annealing of the on the resultant dry etch rates. © 1999 The Electrochemical Society. All rights reserved.

Wet and Dry Etching Characteristics of Electron Beam Deposited SiO and SiO2

ABSTRACTWe have studied the thermal stability and etching characteristics of E-beam deposited SiO and SiO2. Dry etch rates were studied using SF6 and NF3 discharges in a Plasma Therm inductively coupled plasma system. Wet etch rates were assessed with buffered HF and HF/H2O solutions. SiO2 etched faster than SiO under all etch conditions. Dry etch rate of SiO2 was comparable with PECVD SiO2. Auger analysis indicated that SiO2 maintained excellent thermal stability after annealing to 700°C. The Si/O ratio of SiO in the film increased when annealed to 700°C. Ellipsometry also revealed greater refractive index variance across the sample for SiO, as compared to SiO2. However, thickness variation of both films was ≤ 2% across the wafer. Ellipsometry data also showed great thermal stability of SiO and SiO2. There was <4% change after 700°C annealing.

Synthesis of copolymers containing 3-hydroxycyclohexyl methacrylate and their application as ArF excimer laser resists

Copolymers containing 3-hydroxycyclohexyl methacrylate (HCMA) were synthesized as a base polymer for AIT excimer laser lithography. The dry-etching rates of these polymers for CF 4:CHF 3 mixed gas were 1.1-1.2 times that of a novolac-based resist. The adhesion properties of the polymers were also studied by estimating the work of adhesion. When the content of the HCMA unit in the polymer exceeds 60 mol%, the work of adhesion of the resist is similar to those of polyvinylphenol (PVP)-based photoresists. A 0.19 μm pattern profile was obtained using a resist based on the terpolymer containing HCMA and the conventional developer, 2.38 wt% tetramethylammonium hydroxide (TMAH) aqueous solution.

Effect of deposition condition on wet and dry etch rates of device quality inductively coupled plasma-chemically vapor deposited SiN x

Inductively coupled plasma-chemically vapor deposited (ICP-CVD) SiN x was grown on Si substrates using a SiH 4/NH 3/He chemistry at 150°C. The influence of source power, chamber pressure, rf chuck power and percentage SiH 4 on the wet (in BOE) and dry (in ICP SF 6/Ar discharges) etch rates of the SiN x was investigated. The dry etch rates are found to strongly increase with stress in the film above a threshold of ∼500 MPa, while the wet etch rates increase rapidly with source power, chamber pressure and hydrogen content.

Infrared study of Si-rich silicon oxide films deposited by plasma-enhanced chemical vapor deposition

A single chamber system for plasma-enhanced chemical vapor deposition was employed to deposit different films of SiOx:N,H with 0.85⩽x⩽1.91, which are studied here by Fourier transform infrared transmission spectroscopy. The sample composition was determined by Rutherford backscattering spectrometry, nuclear reaction, and elastic recoil detection analysis. Moreover, physical properties such as thickness uniformity, deposition rate, density, wet and dry etch rates, and stress are determined. A quantitative study of Si–OH, N–H, and Si–H bonds was performed and interpreted on the basis of the random bonding model; in addition, the presence of NH2, Si–O–Si, H2SiO2, and Si–N groups was detected. The effect of sample annealing at 600 and 900 °C was studied and two species of Si–H bonds were identified, one more stable and the other one easily releasable. A reordering effect of annealing was also detected as a reduction of the amorphous network stress and as the increase of the bond angle in the Si–O–Si groups up to the value typical of thermal SiO2.

Processing Challenges for GaN-Based Photonic and Electronic Devices

ABSTRACTThe wide gap materials SiC, GaN and to a lesser extent diamond are attracting great interest for high power/high temperature electronics. There are a host of device processing challenges presented by these materials because of their physical and chemical stability, including difficulty in achieving stable, low contact resistances, especially for one conductivity type, absence of convenient wet etch recipes, generally slow dry etch rates, the high temperatures needed for implant activation, control of suitable gate dielectrics and the lack of cheap, large diameter conducting and semi-insulating substrates. The relatively deep ionization levels of some of the common dopants (Mg in GaN; B, Al in SiC; P in diamond) means that carrier densities may be low at room temperature even if the impurity is electrically active - this problem will be reduced at elevated temperature, and thus contact resistances will be greatly improved provided the metallization is stable and reliable. Some recent work with CoSix on SiC and W-alloys on GaN show promise for improved ohmic contacts. The issue of unintentional hydrogen passivation of dopants will also be covered - this leads to strong increases in resistivity of p-SiC and GaN, but to large decreases in resistivity of diamond. Recent work on development of wet etches has found recipes for AlN (KOH), while photochemical etching of SiC and GaN has been reported. In the latter cases p-type materials is not etched, which can be a major liability in some devices. The dry etch results obtained with various novel reactors, including ICP, ECR and LE4 will be compared - the high ion densities in the former techniques produce the highest etch rates for strongly-bonded materials, but can lead to preferential loss of N from the nitrides and therefore to a highly conducting surface. This is potentially a major problem for fabrication of dry etched, recessed gate FET structures.

Patterning of LiGaO2 and LiAlO2 by Wet and Dry Etching

ABSTRACTLiGaO2 and LiAlO2 have similar lattice constants to GaN, and may prove useful as substrates for III-nitride epitaxy. We have found that these materials may be wet chemically etched in a number of acid solutions, including HF, at rates between 150–40,000 Å/min. Dry etching with SF6/Ar plasmas provides faster rates than Cl2/Ar or CH4/H2/Ar under Electron Cyclotron Resonance conditions, indicating the fluoride etch products are more volatile that their chloride or metalorganic/hydride counterparts. Dry etch rates are low ( < 2, 000 Å/min), providing high selectivity (>5) over the nitrides. The incorporation of hydrogen in these materials is also of interest because this could provide a reservoir of hydrogen that may passivate dopants in overlying nitride films. In 2H implanted samples, 50 % of the deuterium is lost by evolution from the surface by annealing at 400 °C for 20 min and all of the deuterium is gone at 700°C. The diffusivity of 2H is ∼10-13 cm2/s at 250°C in LiA1O2, approximately two orders of magnitude higher than in LiGaO2.

Comparison of ICl and IBr for Dry Etching of III-Nitrides

ABSTRACTICl/Ar ECR discharges provide the fastest dry etch rates reported for GaN, 1.3 µm/min. These rates are much higher than with Cl2/Ar, CH4/H2/Ar or other plasma chemistries. InN etch rates up to 1.15 µm/min and 0.7 µm/min for In0.5Ga0.5N are obtained, with selectivities up to 5 with no preferential loss of N at low rf powers and no significant residues remaining. The rates are much lower with IBr/Ar, ranging from 0.15 µm/min for GaN to 0.3 µm/min for InN. There is little dependence on microwave power for either chemistry because of the weakly bound nature of IC1 and IBr. In all cases the etch rates are limited by the initial bond breaking that must precede etch product formation and there is a good correlation between materials bond energy and etch rate. The fact that low microwave power can be employed is beneficial from the viewpoint that photoresist masks are stable under these conditions, and there is no need for use of silicon nitride or silicon dioxide. Selectivities for GaN over A1N with IC1 and IBr are still lower than with Cl2- only.

Relationship Between Chemical Composition and Film Properties of Organic Spin‐on Glass

Seven kinds of commercially available organic spin‐on glass (SOG) were evaluated and analyzed to reveal a relationship between film properties and their chemical composition. Film properties evaluated were shrinkage, refractive index, wet/dry etching rates, and adhesion strength. The structure of SOG solute was analyzed by 29Si‐nuclear magnetic resource (NMR) spectroscopy. Composition of the solution was assayed in terms of GC‐MS as well as 1H‐ and 13C‐NMR. The properties were widely distributed among seven SOG films, which could be explained on the basis of the concentration of Si‐C direct bond in the solute calculated from 29Si‐NMR spectroscopy. Important parameters corresponding to the film quality such as film shrinkages, wet and dry etching rates decreased, with an increase of Si‐C direct bonding. From this point of view, SOG solute having a high organic content is favorable for forming film with high cracking resistance and good planarization of the underlayer topology. The composition of the solvent appears to affect the viscosity of the solution, which dominates the properties during coating such as occurrence of striation or film thickness per coat.

Dry patterning of InGaN and InAlN

Dry etch rates of InxGa1−xN and InxAl1−xN alloys are found to increase with In mole fraction in CH4/H2 microwave (2.45 GHz) discharges, and to decrease under the same conditions in Cl2/H2 mixtures. Both plasma chemistries produce smooth anisotropic etching across the entire composition range from InN to either GaN or AlN. Addition of SF6, rather than H2, to a Cl2 discharge produces faster etch rates and retains smooth morphologies. This suggests that either atomic hydrogen or fluorine is capable of effective removal of N from the III-V nitride materials. Ar+ ion milling rates for InGaAlN alloys are found to be approximately a factor of 2 lower than for more conventional III-V semiconductors like GaAs.

Plasma‐Assisted Chemical Vapor Deposition and Characterization of Boron Nitride Films

Boron nitride films were deposited in a single‐wafer plasma enhanced chemical vapor deposition (PECVD) system using two different reactant gas chemistries: (i) dilute diborane (1% in nitrogen), nitrogen and ammonia; (ii) borazine, and nitrogen as precursor materials. Variations of deposition rates, thickness uniformities, refractive indexes, wet and plasma dry etch rates, film stress, and electrical properties were studied as a function of the corresponding deposition parameters. Several analytical methods such as Fourier transform infrared spectroscopy, x‐ray photoelectron spectroscopy, nuclear reaction analysis, elastic recoil detection analysis, scanning and transmission electron microscopy were used to study the deposited films. Electrical properties were measured using metal‐insulator‐metal and metal‐insulator‐semiconductor structures. The stable boron nitride films do not react with water vapor showing dielectric constant values between 4.0 and 4.7. These good insulators also show promising characteristics for potential applications in high‐performance ultralarge scale integration fabrication.

Ion Milling and Reactive Ion Etching of III-V Nitrides

ABSTRACTDry patterning of GaN, InN, AlN and InGaN grown by MOMBE on GaP, Al2 O3 or GaAs substrates was performed with 100–500 eV Ar+ ions at beam angles of incidence ranging from 0–75° from the normal, or with ECR discharges of BCl3/Ar, CH4/H2 or Cl2/H2. The mill rates normalized to the Ar+ beam current were typically a factor of 2 lower than for GaAs and InP (i.e. maximum values of 300–500 Å·min-1·mA-1·cm-2 at 400eV Ar+ beam energy and 60° angle with respect to the beam normal). The surface morphology of the ion milled nitrides was smooth even at 500 eV Ar+ energy, with no evidence for preferential sputtering of N as determined by AES. The ECR dry etch rates were fastest with elevated temperature Cl2/H2discharges, although both of the other chemistries investigated provide smooth, anisotropie pattern transfer. Since the ion mill rates are slow for single-crystal nitrides and less than the mill rates of common masking materials (SiO2, SiNx, photoresist) it appears this technique is useful only for shallow-mesa applications, and that dry etching methods involving an additional chemical component or ion implantation isolation are more practical alternatives for device patterning.

X-Ray Mask Fabrication Process Using Cr Mask and ITO Stopper in the Dry Etching of W Absorber

An X-ray mask fabrication technology using a tungsten (W) absorber with a chromium (Cr) mask and indium titanium oxide (ITO) stopper was developed. When SF6 was used as the dry etching gas, substantial side etching occurred because the F radical reacts with W on the sidewall. In order to prevent side etching, a SF6 and CHF3 gas mixture was applied; however, the ratio of dry etching rate of W to that of resist is low. Furthermore, the underlying layer such as that of silicon dioxide (SiO2), which was used as the etching stopper, was easily damaged. Instead of a resist mask and SiO2 stopper, a Cr layer as the etching mask and ITO layer as the stopper layer were applied. By the use of these structures and etching procedures, high aspect ratio W patterns with vertical sidewalls have been successfully fabricated.

Characterization of biased electron cyclotron resonance deposited oxides

An extensive study characterizing the properties of silicon oxide films deposited using biased electron cyclotron resonance (ECR) plasmas was performed. The ECR system provided microwave plasma excitation at 2.45 GHz, at power levels from 200 to 1000 W. Confinement of the resonant plasma was achieved using two independent current-controlled electromagnets. The deposition gases were O2, N2O, and dilute silane in Ar; process flow rate, pressure, and microwave power were held constant. Radio frequency power was applied to the substrate electrode to attain a bias that was varied from 0 to 300 V to affect film characteristics. The uniformity, refractive index, stress, and dry and wet etch rates of ECR oxides were evaluated and compared with thermal and low-pressure chemical vapor deposition oxides. In addition, infrared spectroscopy was performed to characterize ECR oxide stoichiometry. The dependence of the Si–O and O–H content of these films will be described as a function of bias voltage applied to the substrate electrode.

Wet and dry etching characteristics of Al0.5In0.5P

A selective wet chemical etching solution for removal of Al0.5In0.5P from GaAs based on HCl:H2O has been developed. Controllable etch rates from 600 Å min−1 at 1HCl:30H2O to 6000 Å min−1 at 1HCl:5H2O at 25 °C are obtained. The etch rate is thermally activated of the form R∝exp(−Ea/kT) where Ea=12.4 kCal mol−1, consistent with reaction-limited etching. Dry etch rates of AlInP in PCl3/Ar, CCl2F2/Ar, or CH4/H2/Ar electron cyclotron resonance discharges are all <300 Å min−1 for additional dc self-biases of ≤250 V. Selectivities of ≳600:1 are obtained for etching GaAs over AlInP in CCl2F2/Ar discharges for dc biases ≤150 V. The etched surface morphologies are smooth, with small quantities of Cl-containing residues remaining after PCl3/Ar exposure, and both Cl and F detectable after CCl2F2/Ar dry etching.

Dry etching rate of electron-beam-exposed negative resists

A method using oxygen plasma treatment to remove successively-electron-exposed negative resist is proposed. The change in resist thickness with plasma treatment time depends on the different doses and the method of exposure. The resulting curves are very similar to the dissolution curves of positive resist. The etching rates in the depth of the exposed resist show that the top edge of the resist is less sensitive to dose changes than the bottom edge. The theoretical models for energy distribution in the resist film support such assumptions. The experimental data could be useful for more correct modelling and profile simulation of electron-exposed negative resists.

Fast thermal kinetic growth of silicon dioxide films on InP by rapid thermal low-pressure chemical vapour deposition

Silicon dioxide films were deposited onto InP substrates in the ranges of 350-550 degrees C temperature, and 3-15 Torr pressure by means of the rapid thermal low-pressure chemical vapour deposition (RTLPCVD) technique. SiO2 films were deposited using a variety of Ox: SiH4 ratios in the range of 5:1-50:1, and deposition rates of 15-50 nm s-1. The high temperature and high rate deposition was obtained without creating any damage to the InP substrate surface, and resulted in highly densified SiO2 layers with good thickness control and low stress. The main parameters of the as-deposited and annealed films, such as deposition rate, density, refractive index, wet and dry etch rates, stresses, film microstructure, and the SiO2/InP interface quality are reported. These parameters were studied as a function of the process variables, which include deposition time, temperature, pressure, O2:SiH4 ratio, gas flow rates and chamber geometry.

Another Step in Developing a Single Wafer Integrated Process: Rapid Thermal Low Pressure Metalorganic Chemical Vapor Deposition of Local Diffused W(Zn) Contacts

ABSTRACTA selective deposition of W(Zn) metallization, for formation of diffused ohmic contacts onto InP-based material was realized by means of rapid thermal, low pressure metalorganic chemical vapor deposition (RT-LPMOCVD). The W(Zn) layers were deposited using a reactive gas mixture that contained diethylzinc (DEZn), WF6, H2 and Ar, at temperatures of 450 to 550°C and pressures in the range of 1–5 torr. Uniform andcontinuous layers of W(Zn), 30 to 120 nm thick, were obtained. These layers contained Zn at concentrations higher than 1×l018 cm−3, which was subsequentially in-diffused into the underlying semiconductor layer to form highly doped semiconductor layers as thick as 0.2μm. As a result, the specific contact resistance of the W(Zn)/ In0.53Ga0.47 As contact was reduced to minimum value of 5×l0−6 Ω·cm2. The W(Zn) film were found to be mechanically stable with a small compressive stress of 5.10−8 dyne. cm−2, and dry etch rates of up to 90 nmmin.

Dry etching and implant isolation characteristics of AlxGa1-xAs grown by metal organic molecular beam epitaxy

The authors report on the dry etching rates of highly doped, n- and p-type AlxGa1-xAs in PCl3/Ar, CCl2F2/Ar and CH4/H2/Ar electron cyclotron resonance plasmas. These etching rates are independent of doping level and conductivity type for all three gas mixtures, and a significant dependence of etch rate on AlAs mole fraction is observed only with CCl2F2/Ar. The formation of high resistivity layers by oxygen or hydrogen ion bombardment was also investigated as a function of implant dose, Al composition and post-implant annealing temperature. Approximately 10 electrons or holes were removed from the conduction process for each 120 keV O+ ion, whereas a 40 keV proton removed about 0.3 carriers per ion. Sheet resistances above 108 Omega Square Operator -1 are obtainable for heavily doped n- or p-type AlGaAs provided the oxygen or proton doses are sufficiently high.