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Surface modification and etch product detection during reactive ion etching in InP in CH4-H-2 plasma
Plasma Sources Science and Technology
Abstract
A detailed plasma - surface interaction study has been conducted using mass spectrometry and optical emission spectroscopy for the plasma characterization, and quasi in situ XPS analyses to control the surface chemistry modifications. The experimental results clearly evidence the different etching behaviour of In and P in the - plasma environment. A signature of the In and P etching mechanisms is available from the diagnostic of the plasma phase through the detection of phosphine as the major etching product of P and of excited In atoms related to the In etching reaction. The observation of the In emission line at 451.1 nm indicates a probable decomposition in the discharge of the organoindium compound which is regarded as the etch product of the group III element. XPS reveals the presence of P - H, C - In, In - In - C and In - In - P as surface species, and allows us to quantify precisely the P surface depletion. A time dependent etching mechanism is shown, first suggested by the etched thickness measurements and further confirmed by both etch product signal intensity and surface stoichiometry evolution with the plasma exposure time. Mass spectrometric signal and emission line intensities monitored as a function of time indicate that the In etching mechanism is responsible for this situation. It is concluded that the reactive ion etching of InP is under the control of the removal mechanism of In. The combination of surface analysis and plasma diagnostics is shown to be capable of providing an understanding of the plasma - surface interaction.
... The study showed that elemental phosphorus could still be observed in the P 2p core level spectrum approximately 5 days after the etching, but this component completely disappeared from the P 2p spectrum about two months later. 12 Since the reactivity of elemental phosphorus is expected to be very high, it is worthwhile determining if phosphorus depletion from the surface as a result of PH 3 formation occurs upon exposure to ambient air and moisture, 27 which would prevent estimation of the stoichiometry of the etched surface using ex-situ XPS measurements. Figure 3 shows the In/P overall intensity ratio calculated from the integrated peak intensities in the P 2p and In 3d core level spectra, in-situ, after 10, 100, and 120 days. ...
... Peak components at 129.1 6 0.1 and 133.6 6 0.1 eV correspond to the P 2p spin-orbit doublet from InP (labeled P -In ) and surface oxide species (labeled P -ox ), respectively. 28,29 The additional doublet at 130.3 6 0.1 eV may be ascribed to elemental phosphorus [21][22][23][24][25][26][27][28][29][30] or to (In)P-Cl or (In)P-O species in which the oxidation state of phosphorus is P þ . 29 However, we do not observe any chlorine on the surface; moreover in-situ experiments carried out in the Centura platform using similar etching conditions confirm the absence of chlorine and oxygen. ...
The chemical composition of the surface of InP samples etched in Cl2 and Cl2/Ar inductively coupled plasma (ICP) is analyzed using ex-situ x-ray photoelectron spectroscopy (XPS). Comparison between ex-situ and in-situ XPS measurements shows that the stoichiometry of the etched surface can be retrieved from the ex-situ analysis provided that an adapted procedure is used. This allows for investigating the evolution of the surface stoichiometry as a function of etching parameters. The sample temperature is found to play a determining role in the top surface composition during etching. An abrupt switch from a rough and In-rich surface to a smooth and significantly P-rich surface is observed above a critical temperature and is found to depend only weakly upon the other etching parameters such as direct current bias or pressure. Ex-situ XPS measurements are used to estimate the thickness of the phosphorus layer identified on the top surface as ∼1 nm, which is consistent with the value previously derived using in-situ XPS. Finally, the stoichiometry of the InP etched sidewalls is analyzed selectively using dedicated microscale periodic patterns. The surface P-enrichment of the etched sidewalls is found to be very similar to that of the bottom etched surface. The presence of the phosphorus top layer may have an impact on the sidewall passivation mechanism during anisotropic ICP etching of InP-based heterostructures using Cl2-containing plasma chemistry.
... Indeed, while detailed studies have been devoted to the XPS analysis of chemically cleaned InP and of InP oxides, [17][18][19][20] only a few ex situ or in situ XPS studies have been reported to date on the analysis of plasma-etched InP surface. XPS and Auger electron spectroscopy (AES) have been used to characterize the effect of CH 4 -H 2 plasma chemistry on InP using conventional RIE, 21 ICP-RIE, [22][23][24] or reactive ion beam etching. 25 As a main result, this chemistry leads to a P-depleted surface with P/In ratio down to $0.6 in a wide range of CH 4 /H 2 ratio, 23 which has been attributed to the slow In removal rate by methyl radical. ...
... They are very close to the bulk ratios; this is expected if the formation of a native oxide does not eliminate P nor In atoms from the surface. Slightly P-depleted oxides have been reported, 22 which might be attributed to PH 3 formation under exposure at ambient air/moisture. ...
A Cl2-HBr-O2/Ar inductively coupled plasma (ICP) etching process has been adapted for the processing of InP-based heterostructures in a 300-mm diameter CMOS etching tool. Smooth and anisotropic InP etching is obtained at moderate etch rate (∼600 nm/min). Ex situ x-ray energy dispersive analysis of the etched sidewalls shows that the etching anisotropy is obtained through a SiOx passivation mechanism. The stoichiometry of the etched surface is analyzed in situ using angle-resolved x-ray photoelectron spectroscopy. It is observed that Cl2-based ICP etching results in a significantly P-rich surface. The phosphorous layer identified on the top surface is estimated to be ∼1–1.3-nm thick. On the other hand InP etching in HBr/Ar plasma results in a more stoichiometric surface. In contrast to the etched sidewalls, the etched surface is free from oxides with negligible traces of silicon. Exposure to ambient air of the samples submitted to Cl2-based chemistry results in the complete oxidation of the P-rich top layer. It is concluded that a post-etch treatment or a pure HBr plasma step may be necessary after Cl2-based ICP etching for the recovery of the InP material.
... As this peak appears accompanied with the appearance of the carbide peak in C 1s spectrum, we ascribed it to indium carbide, InC x [Y. Feurprier, et al. 1997, Z. Jin, et al. 2001. This peak is absent in the sample irradiated in DI water, as shown in Figure 5.5 c. ...
Photonic integrated circuits (PICs) which combine photonic devices for generation,
detection, modulation, amplification, switching and transport of light on a chip have been
reported as a significant technology innovation that simplifies optical system design, reduces space and power consumption, improves reliability. The ability of selective area modifying the bandgap for different photonic devices across the chip is the important key for PICs development. Compared with other growth methods, quantum well intermixing (QWI) has attracted amounts of interest due to its simplicity and effectiveness in tuning the bandgap in post-growth process. However, QWI has suffered problems of lack of precision in achieving targeted bandgap modification and uncontrollable up-taking of impurities during process which possibly degrade the quality of intermixed material.
In this thesis, we have employed excimer laser to create surface defects in the near surface
region (~ 10 nm) of III-V e.g. InP and GaAs, based QW microstructure and then annealing to
induce intermixing. The irradiation by ArF and KrF excimer lasers on the QW microstructure
was carried out surrounded by different environments, including air, DI water, dielectric layers
(SiO2 and Si3N4) and InOx coatings. To propose a more controllable UV laser QWI technique, we have studied surface defects generation and diffusion with various surface/interface characterization methods, like AFM, SEM, XPS and SIMS, which were used to analyse the QW surface/interface morphology and chemical modification during QWI. The quality of processed QW microstructure was represented by photoluminescence measurements and luminescence measurements of fabricated laser diodes.
The results shows that excimer laser induced amounts of surface oxides on the
InP/InGaAs/InGaAsP microstructure surface in air and the oxygen impurities from oxides
layer diffused to the active region of the QW microstructure during annealing, which enhance
intermixing but also reduce the PL intensity. When irradiated in DI water environment, no
obvious excessive oxygen impurities were found to diffuse to the active regions and the
surface stoichiometry has been restored after intermixing. InOx with large coefficient of
thermal expansion was found inside the intermixed QW microstructure, which was supposed to increase the compressive strain in active region and enhance the PL intensity to maximum 10 times on sample irradiated in DI water. On microstructure coated with dielectric layers, bandgap modifications were always found on samples whose dielectric layers were ablated and InP surface was modified by excimer laser. On sample coated with 243 nm SiO2 layer, the PL shifts were found on sample without ablation of the SiO2 layer when irradiated by KrF laser. However, the InP interface morphology was modified, interface oxides were generated and oxygen impurities have diffused inside on the irradiated sites. The enhancements of interdiffusion on both non irradiated and irradiated sites of sample coated with InOx layer have verified the importance of oxides in QWI.
The laser diodes fabricated from KrF laser intermixed material have shown comparable
threshold current density with as grown material with PL shifted by 133 nm. Combined
aluminum mask, we have created uniform 70 nm PL shifts on 40 μm x 200 μm rectangle
arrays which presents UV laser QWI potential application in PICs.
In addition, excimer lasers have been used to create self organized nano-cone structures on
the surface of InP/InGaAs/InGaAsP microstructure and enhance the PL intensity by ~1.4x.
Excimer lasers have selective area modified wettability of silicon surface based on laser
induced surface chemical modification in different liquid environments. Then the fluorescence nanospheres succeeded to specific pattern functions with silicon surface.
... Hence, charge accumulation and dissipation are strongly related to the structure of the thin surface layer. 7 To assist charge transport on polymer surfaces, surface modification methods including reactive ion etching, 8 chemical vapor deposition, 9,10 gamma ray irradiation, 11 and direct fluorination technology 12 have been employed. The introduced chemical modifications affect the surface conductivity, surface trapping, and secondary electron emission, and hence charge accumulation and transport. ...
An effective surface charge removal is critical to diverse applications of polymer and other soft organic materials in electrical devices and systems. Here, we report on the application of atmospheric pressure dielectric barrier discharge (AP-DBD) to deposit SiOx thin films to improve the surface charge dissipation on an epoxy resin surface. The SiOx nanofilms are formed at atmospheric pressure, with the replacement of organic groups (C-H, C=O and C=C) with inorganic groups (Si-O-Si and Si-OH) within the thin surface layer. After the plasma deposition, the initial surface charge decreased by 12% and the surface charge dissipation was accelerated. The flashover voltage which characterizes the insulation property of the epoxy resin is increased by 42%. These improvements are attributed to the lower density of shallow charge traps introduced by SiOx film deposition, which also corresponds to the surface conductivity increase. These results suggest that the SiOx deposition by AP-DBD is promising to accelerate surface charge dissipation. This method is generic, applicable for other types of precursors and may open new avenues for the development of next-generation organic-inorganic insulation materials with customized charge dissipation properties.
... Also, for these two samples, as illustrated in Fig. 2 a and b, an additional peak has been observed at the lowest binding energy (443.0 ± 0.2 eV). As this peak appears accompanied with the appearance of the carbide peak in C 1s spectrum, we ascribed it to indium carbide, InC x [28] [29]. This peak is absent in the sample irradiated in DI water, as shown in Fig. 2 ...
Keywords: Quantum well intermixing InP/InGaAs/InGaAsP microstructures ArF and KrF excimer laser irradiation X-ray photoelectron spectroscopy Secondary ion mass spectroscopy Indium and InP oxides a b s t r a c t Irradiation of quantum semiconductor microstructures with ultraviolet pulsed lasers could induce sur-face defects and modify chemical composition of the microstructure capping material that during high-temperature annealing leads to selected area bandgap engineering through the process known as quantum well intermixing (QWI). In this work, we investigate the role of both ArF and KrF excimer lasers in the QWI process of InP/InGaAs/InGaAsP microstructures irradiated in air and deionized (DI) water. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy analysis was employed to study the chemical composition of the irradiated surface and investigate the chemical evolution of ArF and KrF laser irradiated microstructures. The results indicate that InP x O y oxides are the dominating surface products of the ArF and KrF lasers interaction with InP. Consistent with this observation is a relatively greater bandgap blue shift of ∼130 nm found in the microstructures irradiated in air, in comparison to a maximum of 60 nm blue shift observed in the microstructures irradiated in a DI water environment.
... However, as the peak at lower binding energy (442.7±0.2eV) in In 3d 5/2 appears accompany with appearance of the carbide peak in C 1s spectrum, we ascribed these peaks as indium carbide, In-In-C. 19,20 The presence of InO x , In x (PO 4 ), In(PO 3 ) y and In(PO 3 ) 3 has been identified at higher binding energies 18,21,22 , as shown in Figure 2. The P 2p spectrum shows 2p 3/2 and 2p 1/2 doublets for each element or chemical compound (indicated in Figure 2 (b) for InP only). The doublet separation and branch ratio of P 2p 3/2 to P 2p 1/2 were fixed at 0.85 and 2.0, respectively. ...
Excimer lasers, due to their compatibility with a large-scale industrial
production, are attractive tools for precise processing of photonic and
microelectronic materials. In this article, we discuss the effect of ArF
excimer laser defect formation on the surface of InP/InGaAs/InGaAsP
quantum well (QW) microstructures irradiated in air and deionized (DI)
water environments. Structural defects on surfaces of such QW materials
have been known to induce vacancy diffusion towards the QW region and
lead to the so called quantum well intermixing (QWI) effect during the
rapid thermal annealing step. Excimer lasers have been used to create
surface defects on InP/InGaAs/InGaAsP microstructure and induce QWI
during high temperature annealing. Chemical composition of the QW
microstructures irradiated with ArF laser in air and DI water is studied
with X-ray photoelectron spectroscopy to investigate both the formation
and role of the surface defects in the laser-induced QWI process.
... Also, for these two samples, as illustrated inFig. 2 a and b, an additional peak has been observed at the lowest binding energy (443.0 ± 0.2 eV). As this peak appears accompanied with the appearance of the carbide peak in C 1s spectrum, we ascribed it to indium carbide, InC x [28,29]. This peak is absent in the sample irradiated in DI water, as shown inFig. 2 c. ...
Indium phosphide (InP) has been focused on as one of emerging materials that can be implemented in advanced semiconductor devices. We proposed optical and electrical characterization methods to evaluate plasma-induced physical damage (PPD)—ion bombardment damage—to InP substrates. By introducing a native oxide phase in an interfacial layer, we proposed an optical model of the damaged structure applicable for an in-line monitoring by spectroscopic ellipsometry. Gas species dependence was obtained, which suggested that the H 2 plasma exposure formed a thicker damaged layer than Ar. An impedance spectroscopy (IS) under various biases ( V b ) was implemented to reveal the nature of damaged structures. Capacitive and conductive components assigned by the IS were confirmed to depend on incident species from plasma, indicating the difference of the energy profile of created defects. The presented methods are useful to characterize and control PPD in designing future high-performance InP-based devices.
The etching of semiconductors and other materials has progressed largely through empirical studies. In such efforts, a given semiconductor is etched in a given reactor type with a particular etch gas or etch gas mixture. This system, comprised of semiconductor, reactor, and etch gas, is then studied as the conditions of the etch environment are indirectly altered by external control variables. The resulting etch rates and etch profiles are then mapped as a function of total pressure, plasma excitation source power, substrate or semiconductor temperature, substrate bias or “ion energy”, and inlet gas composition. Such “parameter marches” have been exercised many times and have proven adequately effective in advancing the state-of-the-art in semiconductor device processing. These “marches” are quite time-consuming as they require a fairly large number of etches and each etch must be evaluated via etch rate measurements and etched feature profile measurements. Despite the time consumption involved in such efforts, much has been learned about the interactions of the multiple control variables of modern etching reactors and the general understanding of plasma etch processing has been advanced.
The Monte Carlo method has been applied to simulate the CH4–H2 reactive ion etching process for an atomic scale InP surface. Two neutral precursor types and one ionic precursor type have been considered in the surface etching process. CH3 and H adsorbed radicals are assumed to be bonded to the surface substrate leading to the ejection of indium and phosphorous sites, respectively, whereas energetic ions induce the In(CH3)x and P(H)x(x=0,1,2,3) ejection from the surface. The model takes into account precursor and site identities, physisorption, chemisorption, migration and desorption of etchant neutrals, chemical etching, and ion preferential sputtering of sites. The chemisorption probability effects of the neutral precursors on the rms roughness, the etching rate, and the phosphorus depletion are shown. On the other hand, the increase of the ion flux allows an increase in rms roughness. By setting the available experimental data, the simulation results confirm the existence of the phosphorus depleted surface layers, which were previously observed by x-ray photoelectron spectroscopy analyses. © 1999 American Vacuum Society.
A two-dimensional simulation of reactive ion etching (RIE) of InP trench profiles is developed. The local equation of etching rate on each string is established considering the Langmuir adsorption concept. The etching rate takes into account the chemical etching on both the covered and uncovered surface fractions by the neutrals and the ion sputtering on both the covered and uncovered fraction of surface elements. Surface kinetic parameters of InP RIE process are estimated by using a minimization method to fit the experimental data of etching rate as a function of percent CH4 in the CH4–H2 plasma mixture. Such parameters are then used to simulate the etch surface profile evolution in time under the RIE process. The effect of ratio of the ion flux to the neutral flux on the anisotropy of the profiles is shown as well as the aspect ratio on the etching rate evolution in time. © 2000 American Vacuum Society.
The effects of nitrogen gas on the methane-based reactive ion beam etching (RIBE) of InP were studied in detail. The surface was very rough and covered with In droplets and heavy polymer when it was etched by the mixture of CH4/H2 without nitrogen gas. In contrast, the surface smoothness was improved markedly when nitrogen gas was added, realizing a root mean square (RMS) roughness comparable to that of the initial InP surface before etching. From the detailed X-ray photoelectron spectroscopy (XPS) analysis, it was found that the formation of P-N bonds on the surface could suppress the preferential evaporation of P atoms in the PH3 form and balance the In- and P-reactions during the etching process. This resulted in the decrease of In droplets and a smoother etched InP surface. It was also found that the rate limiting process for etching was the In-related reaction. The study of Raman scattering showed that the crystal quality of the etched surface was improved when N2 gas was added to the CH4/H2 mixture.
XPS analysis is usually limited to surfaces whose roughness is less than the inelastic mean free path of the photoelectron in the material. Furthermore, the stoichiometry of the surface to be analysed is assumed to be constant. Clearly, in many situations neither of these criteria are met. However, a model has been developed, which combines AFM and XPS techniques to allow the analysis of rougher surfaces and complex non-uniform structures. In this work, InP surfaces were processed by an RF (13.56 MHz) hydrogen plasma over a range of pressures and power densities. The higher reactivity of hydrogen with phosphorous results in preferential sputtering and therefore depletion of this element from the surface. The residual surface layer was found to consist of indium and indium oxide, with the depth of the oxide layer in the earlier stages of processing being proportional to the depth of the phosphorus-deplete region. Since the volume of the oxide is greater than the base metal, the indium oxide layer buckles as it grows, leaving a series of ‘bumps’ with cavities beneath them. This effect is exacerbated by the presence of volatile phosphorous compounds in the cavities. This complex surface was analysed by XPS and AFM. The initially spurious XPS data were re-analysed on the basis of a model developed from the AFM measurements. Together, this combined approach allowed the thickness of the indium surface oxide layer to be accurately measured using both techniques. This approach widens the application of XPS analysis to complex surfaces.
The influence of CH4-H-2 mixture composition and rf power input on the etching mechanism of InP is discussed. Argument is based on etch rate measurements, plasma diagnostics (optical emission spectroscopy and mass spectrometry) and quasi in situ x-ray photoelectron spectroscopy (XPS) surface analysis. Results show that the key mechanistic parameters are the CH3 flux density and the ion energy flux density on the InP surface. The In removal mechanism is the most important feature as it is the one which limits the effective etching and controls the surface stoichiometry. This mechanism depends mostly upon the CH3 flux but needs ion assistance. On another hand, the P removal mechanism appears to be strictly controlled by the ion energy flux. Based on these observations an analytical model is proposed to describe the etching. The mechanism can be described as an ion-assisted chemical etching mechanism. Its originality is that In and P removal mechanisms are considered separately although they are strongly interdependent as indicated by XPS. A quantitative determination of the CH3 flux and the ion energy flux density on the InP surface by means of mass spectrometry allow to show that the model is applicable in a wide range of gas mixture composition and rf power. Moreover, it gives an estimation of the number of In atom etched per incident CH3 in agreement with the generally admitted assumption that trimethylindium is the major etch product of In, and allows an estimation of the surface coverage in methyl radicals. (C) 1998 American Vacuum Society.
The plasma-surface interaction during CH4-H-2 reactive ion etching processing of InP is described in detail by means of plasma diagnostics (optical emission spectroscopy and mass spectrometry) and x-ray photoelectron spectroscopy (XPS) surface analysis. The influence of the input power is carried out for different CH4-H2 mixtures in terms of InP etch rate, etch product and CH3 radical detection and surface damage characterization. In particular detailed XPS results allow the study of the changes in the stoichiometry and amorphization of the surface with the input power. In addition, for a given power, the quality of the etched surface improves by increasing the fraction of methane in the gas mixture. As an example, the best surface stoichiometry (InP0.86) is obtained for a pure methane plasma running at a high power (300 W). In general, it is shown that the lower the P depletion, the lower the amorphization, which is indicative of a general improvement of the etched surface quality. Based on the XPS results, a three-layer model is proposed for the representation of the surface in the course of etching. The damaged layer situated over the bulk InP is composed of a superficial P-depleted layer and of a stoichiometric amorphized InP layer. Using the curve-fitting of the P 2p spectra, the thickness of the different layers is estimated. As an example, a damaged layer as low as 37 Angstrom thick is obtained for pure methane plasma at 15 mTorr and a power of 300 W, whereas our standard conditions (10% CH4-H-2, 50 mTorr, and 80 W) give a damaged layer of 90 Angstrom. The experimental observations give evidence of the need for both ion bombardment and active neutral species to obtain etching. The improvement of the etch process is then explained by an improved In removal rate which is actually the limiting step in the etching mechanism of InP. (C) 1998 American Vacuum Society.
Nowadays, plasma-etching processes are asked to produce patterns from the nanometer to the micrometer range with the same efficiency. The very severe requirements in terms of etch rate, selectivity, profile control and surface damage plasma-etching processes lead to, have been at the origin of the development of mechanistic studies by means of plasma diagnostics and surface analysis, as well as the development of new etching devices. We review here the basic concepts of plasma etching, and using examples, we describe more in details important features. We recall, in particular, the important role of the surface layer, the ion bombardment and the substrate temperature.
We report calculations of electron inelastic mean free path (IMFPs) of 50-20oO eV electrons in a group of 15 inorganic compounds (A1, and ZnS). As was found in similar calculations for a group of 27 elements, there are substantial differences in the shapes of the IMFP versus energy curves from compound to compound for energies below 200 eV; these differ-ences are associated with the different inelastic electron scattering characteristics of each material. Comparisons are made of the calculated IMFPs and tbe values calculated from the predictive IMFP formula TPP-2 developed from the IMFP calculations for the elements Deviations in this comparison are found, which correlated with uncertainties of the optical data from which the IMFPs were Calculated. The TPP-2 IMFP formula is therefore believed to be a more reliable means for determining IMFPs for these compounds than the direct calculations.
Table of Persistent Band Heads.- Individual Band Systems.- Spectra of Deuterides.- Practical Procedure and Precautions.- On the identification of bands.- Sources.- Collimation.- Comparison spectra.- Measurement.- Spurious bands.- Literature.- Description of Plates.- Author Index.
The surface chemistry of InP substrates used for the fabrication of electronic devices (MIS structures) was examined by ESCA. Spectroscopic data on related materials such as indium metal, plasma-oxidized indium metal, In2O3, InPO4(xH2O), P4O10, AlPO4, (C6H5O)3PO and (C6H5)3P were collected so as to aid the assignment of components in the spectra of as-received and etched InP surfaces on the basis of the chemical shifts and the intensity ratios. Surface features of InP substrates from several batches were examined in the as-received and the chemically etched forms. The effectiveness of several types of etchants and the features thus produced on the substrate surface were evaluated and are discussed.
The kinetics of the CCl//4 and Cl//2 plasma etching of InP, GaAs, and GaP at 300 degree C and the role of added O//2 were investigated using atomic emission as a diagnostic aid. With the exception of the CCl//4/O//2 etching of InP, the etching rates were observed to be linear functions of the emission intensity from electronically excited Cl, regardless of the feed-gas composition. InP was observed to etch significantly faster in a CCl//4 discharge than would have been expected from the Cl emission intensity alone, indicating the active involvement of CClx species. Addition of a small amount of O//2 to either CCl//4 or Cl//2 resulted in an increase in the intensity of Cl atomic emission. With feed compositions of approximately equals 40% O//2 in Cl//2(CCl//4), extremely fast etching rates of 7. 3(2. 5), 2. 4(0. 9), and 1. 6(2. 1) mu m/min were obtained for GaAs, GaP, and InP, respectively.
and etching in chlorine plasmas at 0.3 Torr follows an Arrhenius dependence on substrate temperature. Apparent activation energies, , of and , respectively, were determined from both optical emission of product species, and step height or weight change measurements. For , equals the heat of vaporization of , and the absolute etch rate (7 μm/min at 250°C) is in reasonable agreement with the predicted vaporization rate of . Hence, volatilization of is most likely the rate‐controlling step for etching . Sputter Auger analysis shows that etching in a chlorine plasma leaves multiple layer coverage of on (removable by washing with deionized water), and submonolayer levels of chlorine on . Both surfaces are rich in the group III element. The etched surface morphologies of and are strongly dependent on temperature, exhibiting a rough‐to‐smooth texture transition above ∼250° and ∼120°C, respectively.
The reactive ion etching of GaAs and GaAlAs in BCl3-Cl2 mixture has been investigated. Under anisotropic etching conditions, clean etch profiles have been obtained with etch rates as high as 0.6 mum/min for GaAs and 0.4 mum/min for Ga0.55Al0.45As. No lag time has been observed between ignition of the gas plasma and subsequent etching. The variation in etch rates from run to run is less than ± 10%. The etch rates for the organic resist (AZ-1350) are so slow that deeply etched features (4-5 mum) with vertical side-walls have been obtained using a layer of the resist thin enough to maintain its high resolution.
Hydrogen plasmas have been used to etchsurfaces of semiconducting materials (e.g., GaAs,GaSb,InP, Si), their oxides, and Si nitride. Using a combination of analytical techniques—spectroscopic ellipsometry, Auger spectroscopy, and scanning electron microscopy(SEM), the etch rates, the surface composition and morphology have been studied. It is demonstrated that the selective etching rate of hydrogen plasma for Si over SiO2 is ∠30, and that for GaAs oxide over GaAs is ∠2. It is also shown that the hydrogen plasmaetched (and air exposed) GaAssurfaces have a Ga/As concentration ratio nearly equal to that of the air cleaved GaAssurface. Similar results have also been obtained for GaSb. Hydrogen plasmaetchedInP shows surface segregation and is rich in In. The etch rates of the semiconductors and their oxides vary by several orders of magnitude from compound to compound as determined from ellipsometry and SEM. It is also demonstrated that scanning ellipsometry can be used to monitor surfaceetching processes. Some advantages and disadvantages of the use of hydrogen plasma for surface preparation and etching applications are discussed.
High-resolution gold-valence-band photoemission spectra were obtained by the use of monochromatized Al Kα radiation and a single-crystal specimen. After background and scattering corrections were made, the results were compared directly with broadened theoretical density-of-states functions. The following conclusions were drawn: (i) Relativistic band-structure calculations are required to fit the spectrum. (ii) Both the Korringa-Kohn-Rostoker calculation of Connolly and Johnson and the relativistic-augmented-plane-wave calculation by Christensen and Seraphin give density-of-states results that (after broadening) follow the experimental curve closely. (iii) Of the theoretical functions available to date, those with full Slater exchange agree best with experiment (perhaps because of a cancellation of errors). Fractional (2/3 or 5/6) exchange gives d bands that are too wide. (iv) Eastman's 40.8-eV ultraviolet photoemission spectrum is similar to the x-ray spectrum, suggesting little dependence on photon energy above 40 eV. (v) Both (ii) and (iv) imply an absence of strong matrix-element modulation in the photoemission spectrum of gold.
The reactive ion etching of chemically vapor deposited (CVD) tungsten in SF6/O2 plasma has been investigated by means of optical emission spectroscopy, mass spectrometry, and in situ x-rav photoelectron spectroscopy. This study is particularly focused on the etching Of WO3 over W, a native oxide 34-45 angstrom thick (WO3) always appearing on the CVD tungsten surface. Actinometry measurements show an excess of atomic fluorine and oxygen relative concentrations during the etching of the WO3 layer as compared to that of tungsten. Two etch products of tungsten are detected by mass spectrometry: WF6 and WOF4. In pure SF6 plasma, the main etched product Of WO3 and W is WF6. In SF6/O2 (40/60) plasma, WF6 is the dominant product of the etching of the WO3 layer and WOF4 that of W. In situ XPS analyses show the presence of fluorine, oxygen, and sulfur on the etched tungsten surface. The role of these elements in the formation of the two etch products of tungsten is discussed.
Structural and electrical damage imparted to InP and In 0.72 Ga 0.28 As 0.6 P 0.4 (λ g ≂1.3 μm) surfaces during CH 4 /H 2 reactive ion etching (RIE) have been examined. X‐ray photoelectron spectroscopy was used to monitor changes in the surface chemistry, Rutherford backscattering spectrometry was used to measure crystallographic damage, and current‐voltage and capacitance‐voltage measurements were made to examine electrically active damage and its depth. Two classes of damage are observed: crystallographic damage originating from preferential loss of P (As) and/or ion bombardment‐induced collision cascade mixing and, for p‐type material, hydrogen passivation of Zn acceptors. Etching at 13.6 MHz, 60–90 mTorr, 10% CH 4 /H 2 , and bias voltages of ∼300 V contains gross (≳1%) damage as measured by RBS to within 40 Å and electrically active damage to within 200 Å of the surface. This is a factor of 3–6 shallower than other RIE processes operated below 10 mT with comparable or higher bias voltages. Acceptor passivation of both InP and InGaAsP, arising from the association of hydrogen with Zn sites, occurs to a depth of 2000 Å after RIE and causes a decrease in carrier concentration in this layer. The effect is reversed, however, by rapid thermal processing at temperatures between 350 and 500 °C.
We studied the magnetron ion etching of GaAs in SiCl 4 /Cl 2 discharges and sidewall passivation effect which closely relates to the anisotropic dry etching. The effects of a variety of process parameters on the final via hole profiles and morphologies were also examined. Furthermore, in order to determine the surface chemistry of the residues on GaAs sidewall in magnetron plasmas, surface characterization was undertaken using scanning electron microscopy, transmission electron microscopy combined with an energy dispersive x‐ray spectrometer, and x‐ray photoelectron spectroscopy. It was confirmed that the residues, namely the sidewall protection film, consists of double layers. The aluminum content of the underlayer is four times greater than that of the upper layer. The aluminum mainly results from sputtering of the alumina cathode covers. The formation of the sidewall protection film was identified as the key factor in controlling the via hole profile for GaAs device fabrication. © 1996 American Vacuum Society
Reactive ion etching of III–V heterostructures was monitored using laser interferometry at 632.8 nm and optical emission spectroscopy (OES) between 200 and 800 nm, simultaneously. Three standard plasma chemistries were investigated: (i) CCl 2 F 2 /He for the selective etching of GaAs on AlGaAs, (ii) SiCl 4 /He for the nonselective etching of GaAs/AlGaAs heterostructures, and (iii) CH 4 /H 2 for the etching of In‐based III–V compounds. Laser interferometry provided local monitoring of etch rate, independent of etch chemistry. During GaAs and AlGaAs etching, optical emission from etch products was detected, identified, and selected to monitor etching. Using AlCl emission line at 261.4 nm, accurate etch monitoring of GaAs/AlGaAs heterostructures in SiCl 4 ‐based plasma was demonstrated. The high resolution capacity of OES thereby allowed the discrimination of AlGaAs layers as thin as 5 nm. Accurate etch monitoring of InP/In 0.53 GaAs heterostructures in CH 4 /H 2 plasma was also demonstrated using the In atomic emission line at 325.6 nm: detection of In 0.53 GaAs layers as thin as 3 nm was possible. The combination of laser interferometry and OES was shown to be a suitable tool for III–V device etching.
Reactive ion etching of InP with CH 4 /H 2 mixtures, a promising process for optoelectronic device fabrication, has been studied to understand the mechanisms of etching and anisotropy. Special attention has been paid to the polymer film that deposits on inert surfaces in the discharge; deposition rates have been used as a monitor of the discharge chemistry as well as for process optimization. Surface analysis shows that under etching conditions that maximize the InP etch rate while minimizing polymer deposition, the hydrocarbon coverage on the InP surface equals typical ‘‘adventitious’’ carbon levels, and the surface is significantly depleted of P. The etch rate here is limited by the flux to the surface of hydrocarbon reactants responsible for In desorption. The absence of a significant hydrocarbon film on the vertical‐etched surfaces under conditions of 8:1 anisotropy precludes a surface inhibitor mechanism of anisotropy, implicating instead energy deposition via ion bombardment as the major contributor to the enhanced vertical etch rate. As the feedstock methane fraction is increased, more stoichiometric surfaces are obtained, the polymer deposition rate and the abundance of gas phase hydrocarbon oligomers increases, and ultimately, polymer forms on the InP. Here the InP etch rate is limited by transport through the permeable polymer overlayer. Reactions with polymer‐coated chamber walls are important in determining InP etch and polymer deposition rates, illustrating the need for chamber seasoning to obtain reproducible results. PH 3 is identified by mass spectrometry as the primary P‐containing volatile product, while the primary In‐containing volatile product remains unidentified.
Passivating native oxide films (≊150 Å) have been prepared by anodic oxidation of InP. X‐ray photoelectron spectroscopy (XPS) chemical depth profiles reveal a double layer structure with indium‐rich oxides at the surface and phosphorous‐rich In(PO 3 ) 3 glass‐like oxides at the interface. High quality metal–insulator–semiconductor (MIS) structures are obtained after removing the semiconducting indium‐rich outer oxide layer. The passivating properties of the interfacial In(PO 3 ) 3 oxide are discussed on the basis of chemical bonding configurations in the native oxide. It is suggested that In(PO 3 ) 3 has better intrinsic passivating properties than InPO 4 .
This paper reports a detailed thermodynamic analysis of the GaAs/Cl and InP/Cl chemical systems, which are of interest in the technological processing of these III–V materials. The thermodynamically predicted dependence of the steady state chemical etching on both Cl 2 pressure and temperature is derived assuming Langmuir free evaporation from the surface. The chemical potential data base used in this thermodynamic analysis has been checked for accuracy against all available vapor pressure measurements in the literature. The thermodynamically predicted chemical etching is compared to the etching observed in a Cl 2 plasma. This approach shows promise in semiquantitative modeling of the dependence of these reactions on both the temperature and Cl 2 pressure. In addition, changes in the surface morphologies resulting from plasma etching appear to be correlated with the thermodynamically predicted transitions of various compounds on the surface.
This paper reports a reactive ion etching (RIE) technique using a Cl 2 –Ar gas mixture for anisotropic microprocessing of GaAs and AlGaAs materials and its fundamental characteristics aimed to applications to monolithic integration of optical devices. This technique allows one to realize very fine as well as deep processing perpendicular to the wafer surface with smooth side walls, independent of the crystallographic orientation of these semiconductor materials. The etching rate was found to be controllable over a wide range by suitably adjusting the gas composition and the total gas pressure in this gas mixture. We experimentally obtained the optimum condition for smooth and perpendicular etching for both the materials at the total gas pressure of 2 Pa (1.5×10<sup>-</sup><sup>2</sup> Torr) with the gas flow ratio of Cl 2 : Ar=1 : 5. Under this condition the etching rate ratio of GaAs to SiO 2 was demonstrated more than 70. The surface damage introduced by this RIE was confirmed to be comparable at least to the case of the wet chemical etching through the measurement of photoluminescence intensities from GaAs samples.
Etch rate and etch profile characteristics of (100)GaAs in SiCl 4 reactive ion etching have been studied in the pressure range of 2–110 mTorr. Pronounced crystallographic or orientation dependent etching effects were observed at moderate pressures around 20 mTorr at lower power densities. Etch profiles became vertical at lower pressures. Therefore, pattern profiles with perfectly vertical sidewalls or with sidewalls defined by crystallographic planes can be realized merely by changing the etch conditions. The addition of argon to the etch gas increased the edge sharpness of the vertical profiles and eliminated any trace of orientation dependent etching. Sawtooth gratings and submicrometer structures with high aspect ratios have been fabricated.
The reactive ion etching of GaAs has been investigated in BCl 3 plasma discharges. Etching rates have been characterized as functions of pressure (10–25 mTorr), power density (∼0.05–0.5W/cm<sup>2</sup>), and Cl 2 /BCl 3 gas compositions. Rates of ∼12–20 nm/min have been obtained, and are significantly lower than for other chlorinated plasmas. Etching profiles exhibit a high degree of anisotropy and smooth surface morphologies.
Magnetron reactive ion etching of GaAs was investigated for the first time in a SiCl 4 plasma as a function of process parameters such as pressure and power density. The etch rate of GaAs is found to be much faster than the figures reported for conventional (unmagnetized) reactive ion etching. Vertical sidewalls and smooth surface morphology were obtained under the reported experimental conditions. Schottky diodes were fabricated on etched samples to assess the extent of residual damage. The ideality factor and barrier height of the etched samples were found to be close to those of an unetched control sample. The results indicate that SiCl 4 magnetron etching has promise for use in GaAs device fabrication.
High resolution reactive ion etching of GaAs and InP is achieved using SiCl 4 as the etching gas. Etching rates and profiles are examined at pressures between 1 and 10 mTorr and power densities from 0.2 to 0.9 W/cm<sup>2</sup>. Under the proper conditions, it is possible to obtain extremely vertical etch profiles and etch ratios of GaAs relative to masking materials such as Si 3 N 4 and NiCr which exceed 10 to 1.
Hydrogen plasmas have been used to etch surfaces of semiconducting materials (e.g., GaAs, GaSb, InP, Si), their oxides, and Si nitride. Using a combination of analytical techniques—spectroscopic ellipsometry, Auger spectroscopy, and scanning electron microscopy (SEM), the etch rates, the surface composition and morphology have been studied. It is demonstrated that the selective etching rate of hydrogen plasma for Si over SiO 2 is ∼30, and that for GaAs oxide over GaAs is ∼2. It is also shown that the hydrogen plasma etched (and air exposed) GaAs surfaces have a Ga/As concentration ratio nearly equal to that of the air cleaved GaAs surface. Similar results have also been obtained for GaSb. Hydrogen plasma etched InP shows surface segregation and is rich in In. The etch rates of the semiconductors and their oxides vary by several orders of magnitude from compound to compound as determined from ellipsometry and SEM. It is also demonstrated that scanning ellipsometry can be used to monitor surface etching processes. Some advantages and disadvantages of the use of hydrogen plasma for surface preparation and etching applications are discussed.
The chemical composition of surface films formed on air exposed bromine/methanol etched InP were investigated in both the ’’as etched’’ condition and after in situ heat treatment. Both UPS and XPS spectra were obtained in order to probe at two different depths into the surface (≊5 and 15 Å, respectively). The as etched surface appears to be composed primarily of In 2 O 3 with a small concentration of a phosphate compound, presumably either InPO 4 or H 3 PO 4 . Prolonged exposure to water or water vapor causes additional film growth. The new growth increases the phosphate concentration and an In compound which, by the location the In3d 5/2 peak at 445.6 eV, indicates either InPO 4 or In(OH) 3 . Heating the as etched surface in situ also causes film growth. The phosphate is found to evaporate from the outer surface of the film but to grow underneath the In 2 O 3 skin as the substrate is heated. It is suspected that excessive H 2 O on CO background in the vacuum chamber caused a rapid oxidation of the surface as the sample was heated.
Reactive ion etching (RIE) of InAs, InP, GaAs, and GaSb using CH 4 /H 2 mixtures has been studied to determine the resulting etch profiles and surface morphologies, as well as the dependence of etch rates on cathode temperature, chamber pressure, and electrode self‐bias. These materials are found to etch slowly and controllably, with etched samples having smooth surfaces and nearly vertical sidewalls. Our results demonstrate that CH 4 /H 2 RIE is a promising technology for fabricating electronic devices using the newly emerging InAs/GaSb/AlSb material system as well as the better established InP material system.
Most algorithms for the least-squares estimation of non-linear parameters have centered about either of two approaches. On the one hand, the model may be expanded as a Taylor series and corrections to the several parameters calculated at each iteration on the assumption of local linearity. On the other hand, various modifications of the method of steepest-descent have been used. Both methods not infrequently run aground, the Taylor series method because of divergence of the successive iterates, the steepest-descent (or gradient) methods because of agonizingly slow convergence after the first few iterations. In this paper a maximum neighborhood method is developed which, in effect, performs an optimum interpolation between the Taylor series method and the gradient method, the interpolation being based upon the maximum neighborhood in which the truncated Taylor series gives an adequate representation of the nonlinear model. The results are extended to the problem of solving a set of nonlinear algebraic e