Plasma Silicon Nitride Research Articles

Recombination at the interface between silicon and stoichiometric plasma silicon nitride

The injection level dependence of the effective surface recombination velocity (Seff) for the interface between crystalline silicon and stoichiometric silicon nitride, prepared by high-frequency direct plasma enhanced chemical vapour deposition (PECVD), has been comprehensively studied. A wide variety of substrate resistivities for both n-type and p-type dopants have been investigated for minority carrier injection levels (Δn) between 1012 and 1017 cm−3. Effective lifetimes of 10 ms have been measured for high resistivity n-type and p-type silicon, the highest ever measured for silicon nitride passivated wafers, resulting in Seff values of 1 cm s−1 being unambiguously determined. The Seff(Δn) dependence is shown to be constant for n-type silicon under low injection conditions, while for p-type silicon, there is a clear minimum to Seff for injection levels close to the doping density. Further, the Seff(Δn) dependence for these stoichiometric silicon nitride films appears to be weaker than that for other high-quality, silicon-rich silicon nitride films prepared by remote PECVD.

A highly reliable ferroelectric memory technology with SrBi/sub 2/Ta/sub 2/O/sub 9/-based material and metal covering cell structure

A multilevel metal process-based highly reliable ferroelectric memory (FeRAM) has been developed. Highly reliable characteristics have been attained by two techniques. One is a newly developed ferroelectric material with mixed superlattice crystal of SrBi/sub 2/(Ta/sub x/,Nb/sub 1-x/)/sub 2/O/sub 9/ and Bi/sub 2/ (Ta/sub x/,Nb/sub 1-x/)O/sub 6/. Which provides an elevated remnant polarization while keeping a low coercive voltage. The other is a metal covering memory cell structure which makes the use of plasma silicon nitride (p-SiN) passivation possible without reduction of the ferroelectric thin film by a hydrogen plasma during p-SiN deposition, which results in no B degradation of the characteristics of cell capacitors. The FeRAM cell capacitors with the above newly developed ferroelectric material and metal covering structure have been fabricated by using a 0.6-/spl mu/ double level metal process. The fabricated cell capacitors show highly reliable characteristics such as the ensured retention of data written at a low voltage of 2.4 V and humidity resistance for 10 y under a high temperature of 70/spl deg/C, which is promising for commercialization of FeRAM and its embedded LSIs.

Surface passivation of crystalline silicon solar cells: a review

In the 1980s, advances in the passivation of both cell surfaces led to the first crystalline silicon solar cells with conversion efficiencies above 20%. With today's industry trend towards thinner wafers and higher cell efficiency, the passivation of the front and rear surfaces is now also becoming vitally important for commercial silicon cells. This paper presents a review of the surface passivation methods used since the 1970s, both on laboratory-type as well as industrial cells. Given the trend towards lower-cost (but also lower-quality) Si materials such as block-cast multicrystalline Si, ribbon Si or thin-film polycrystalline Si, the most promising surface passivation methods identified to date are the fabrication of a p–n junction and the subsequent passivation of the resulting silicon surface with plasma silicon nitride as this material, besides reducing surface recombination and reflection losses, additionally provides a very efficient passivation of bulk defects. Copyright © 2000 John Wiley & Sons, Ltd.

Surface passivation of crystalline silicon solar cells: a review

In the 1980s, advances in the passivation of both cell surfaces led to the first crystalline silicon solar cells with conversion efficiencies above 20%. With today's industry trend towards thinner wafers and higher cell efficiency, the passivation of the front and rear surfaces is now also becoming vitally important for commercial silicon cells. This paper presents a review of the surface passivation methods used since the 1970s, both on laboratory-type as well as industrial cells. Given the trend towards lower-cost (but also lower-quality) Si materials such as block-cast multicrystalline Si, ribbon Si or thin-film polycrystalline Si, the most promising surface passivation methods identified to date are the fabrication of a p–n junction and the subsequent passivation of the resulting silicon surface with plasma silicon nitride as this material, besides reducing surface recombination and reflection losses, additionally provides a very efficient passivation of bulk defects. Copyright © 2000 John Wiley & Sons, Ltd.

High Density Plasma Silicon Carbide as a Barrier/Etch Stop Film for Copper Damascene Interconnects

AbstractA low κ dielectric barrier/etch stop has been developed for use in copper damascene application. The film is deposited using methane, silane and argon as precursors in a HDP-CVD reactor. The film has a dielectric constant of 4.2 which is lower than the dielectric constant of conventional SiC or plasma silicon nitride (>7). Film characterization including physical, electrical, adhesion to ILD films, etch selectivity, and copper diffusion barrier properties show that this film is a better barrier than silicon nitride for low κ copper damascene interconnects. This film consists of a refractive index in the range of 1.7 to 1.8, a compressive stress of 1.0-1.5×109 dynes/cm2, and a leakage current of 5.0×10−10 A/cm2 at 1 MV/cm. When integrated in-situ with HDP-FSG, an effective dielectric constant of 3.5 can be achieved.

Rapid thermal processing of next generation silicon solar cells

Rapid and potentially low-cost process techniques are analysed and successfully applied towards the fabrication of high-efficiency mono-and multicrystalline Si solar cells. First, a novel dielectric passivation scheme (formed by stacking a plasma silicon nitride film on top of a rapid thermal oxide layer) is developed that serves as antireflection coating and reduces the surface recombination velocity (S{sub eff}) of the 1.3 {omega}-cm p-Si surface to approximately 10 cm/s. The essential feature of the stack passivation scheme is its ability to withstand short 700 - 850degC anneal treatments used to fire screen printed (SP) contacts, without degradation in S{sub oeff}. The stack also lowers the emitter saturation current density (J{sub oe}) of 40 and 90 {omega}/{open_square} emitters by a factor of three and 10, respectively, compared to no passivation. Next, rapid emitter formation is accomplished by diffusion under tungsten halogen lamps in both belt line and rapid thermal processing (RTP) systems (instead of in a conventional infrared furnace). Third, a combination of SP aluminium and RTP is used to form an excellent back surface field (BSF) in 2 min to achieve an effective back surface recombination velocity (S{sub eff}) of 200 cm/s on 2.3 {omega}-cm Si. Finally, the above individual processes are integrated to achieve: (1) >19% efficient solar cells with emitter and Al-BSF formed by RTP and contacts formed by vacuum evaporation and photolithography, (2) 17% efficient manufacturable cells with emitter and Al-BSF formed in a belt line furnace and contacts formed by SP. (Author)

Rapid processing of low-cost, high-efficiency silicon solar cells

Rapid and potentially low-cost processing techniques are analyzed and applied toward the fabrication of high-efficiency Si solar cells. (i) A technology that can simultaneously form the phosphorus emitter, boron BSF, andin situ oxide in a single high-temperature furnace step or: simultaneously diffused, textured, and AR coated process (STAR) is presented. (ii) A high quality screen-printed (SP) contact methodology is developed that results in fill factors of 0·785–0·790 on monocrystalline Si. (iii) Aluminum back surface field (Al-BSF) formation is studied in detail to establish the process conditions that result in optimal BSF action. (iv) Screen-printing of Al conductor paste and rapid thermal processing (RTP) are integrated into the BSF procedure, and effective recombination velocities (S eff) as low as 200 cm/s are demonstrated on 2·3 Ω-cm Si with this rapid thermal processing of screen-printed contacts, Al alloyed BSF processes. (v) A novel passivation scheme consisting of a dielectric stack (plasma silicon nitride on top of a rapid thermal oxide) is developed to reduce the surface recombination velocity (S) to ≈ 10 cm/s at the 1·3 Ω-cm Si surface. The important feature of this stack passivation scheme is its ability to withstand a high-temperature anneal (700–850°C) without degradation in surface recombination velocity. This feature is critical for most current commercial processes that utilize SP contact firing. (vi) Finally, the individual processes are integrated to form high-efficiency, manufacturable devices. Solar cell efficiencies of 17% and >19% are achieved on FZ Si with SP and evaporated (photolithography) contacts, respectively.

Understanding and implementation of rapid thermal technologies for high-efficiency silicon solar cells

Rapid and potentially low-cost process techniques are analyzed and successfully applied toward the fabrication of high-efficiency monocrystalline Si solar cells. First, a methodology for achieving high-quality screen-printed (SP) contacts is developed to achieve fill factors (FF's) of 0.785-0.795 on monocrystalline Si. Second, rapid emitter formation is accomplished by diffusion under tungsten halogen lamps in both beltline and rapid thermal processing (RTP) systems (instead of in a conventional infrared furnace). Third, a combination of SP aluminum and RTP is used to form an excellent back surface field (BSF) in 2 min to achieve an effective back surface recombination velocity (S/sub eff/) of 200 cm/s on 2.3 /spl Omega/-cm Si. Next, a novel dielectric passivation scheme (formed by stacking a plasma silicon nitride film on top of a rapid thermal oxide layer) is developed that reduces the surface recombination velocity (S) to approximately 10 cm/s on the 1.3 /spl Omega/-cm p-Si surface. The essential feature of the stack passivation scheme is its ability to withstand short 700-850/spl deg/C anneal treatments (like the ones used to fire SP contacts) without degradation in S. The stack also lowers the emitter saturation current density (J/sub oe/) of 40 and 90 /spl Omega//sq emitters by a factor of three and ten, respectively, compared to no passivation. Finally, the above individual processes are integrated to achieve (1) >19% efficient solar cells with emitter and Al-BSF formed by RTP and contacts formed by vacuum evaporation and lift-off, (2) 17% efficient manufacturable cells with emitter and Al-BSF formed in a beltline furnace and contacts formed by SP, and (3) 17% efficient gridded-back contact (bifacial) cells with surface passivation accomplished by the stack and gridded front and back contacts formed by SP and cofiring.

A new strategy for the fabrication of cost-effective silicon solar cells

Fabrication of solar cells with very high efficiencies currently requires extremely complex processing. In order to make photovoltaics an economical large scale source of energy, very high efficiencies have to be achieved by low-cost processing. The innovative approach for the cost-effective production of highly efficient silicon solar cells presented in this paper is characterised by only four simple and environmentally safe large-area fabrication steps. The basic processing sequence consists of: (i) mechanical surface grooving, (ii) simple diffusion or inversion, (iii) shallow angle metal evaporation, and (iv) plasma silicon nitride deposition. Cell design, fabrication techniques and processing sequences for metal-insulator-semiconductor contacted diffused n +-p junction (MIS-n +p) and MIS-inversion-layer (MIS-IL) silicon solar cells are outlined. The new simple approach turned out to be most successful, as demonstrated by mechanically grooved MIS-n +p silicon solar cells with efficiencies above 21% using exclusively aluminium as metallisation.

Silane consumption and conversion analysis in amorphous silicon and silicon nitride plasma deposition using in situ mass spectroscopy

In situ mass spectroscopy is used to sense plasma deposition of silicon and silicon nitride, to analyze gas phase reactant depletion, and the efficiency of silane conversion into the thin film. A double-differentially pumped quadrupole mass spectrometer was used to monitor the SiH4, Si2H6, and H2 effluent from 100% SiH4 and 2% SiH4/He silicon deposition, and SiH4/He/N2 silicon nitride deposition processes. No significant changes in gas phase nitrogen related species were observed during nitride deposition. However, the Si species show significant process dependence allowing reaction analysis. Disilane species were produced at low powers in the SiH4/He/N2 process, but no amino–silane species were observed. The silane consumption and silicon incorporation efficiency are shown to depend on gas dilution, residence time, and reactor geometry.

Effective passivation of the low resistivity silicon surface by a rapid thermal oxide/plasma silicon nitride stack

A passivation scheme involving plasma silicon nitride (PECVD SiN) deposition on top of SiO2 grown by rapid thermal oxidation is developed to attain a low surface recombination velocity (S) of nearly 10 cm/s on the 1.25 Ω cm p-type (100) silicon surface. Such low S values are achieved by the stack structure even when the rapid thermal oxide (RTO) or PECVD SiN films individually yield poorer surface passivation. Critical to achieving low S by the RTO/PECVD SiN stack is the use of a short, moderate temperature anneal (in this study 730 °C for 30 seconds) after the stack formation. This thermal treatment is believed to enhance the release and delivery of atomic hydrogen from the SiN film to the Si–SiO2 interface, thereby reducing the density of interface traps at the silicon surface. Compatibility with this post-deposition anneal makes the stack passivation scheme attractive for cost-effective solar cell production where a similar anneal is required to form screen-printed contacts.

Influence of the reactor design in the case of silicon nitride PECVD

Based on a chemical mechanism whose reliability has already been established in a previous paper, two-dimensional models for some normally employed reactors, namely, longitudinal flow, radial flow and showerhead reactors were developed in the case of silicon nitride plasma enhanced chemical vapor deposition (PECVD) from silane and ammonia mixtures. The aim of this study was to gain a new and global insight into the understanding of the overall behavior of PECVD reactors which can be useful for reactor developers and users. In this work, the reactor design and the flow distribution were shown to be determining parameters. Apart from some second-order differences, some general tendencies were brought to the fore and two groups of reactors were distinguished: the ‘localized injection reactors’ and the ‘distributed injection reactors’. In the case of the first type, the deposition rate and film composition undergo variations which can be strong, whereas in the other, the thickness uniformity and the composition uniformity of the layer are very satisfactory, even for large-size reactors. This last type of reactors was found to be all the more interesting as the film composition could be set by choosing appropriate operating conditions.

Record low surface recombination velocities on 1 Ω cm p-silicon using remote plasma silicon nitride passivation

Outstanding surface passivation of low-resistivity single-crystalline p-silicon is reported using silicon nitride fabricated at low temperature (375 °C) in a remote plasma-enhanced chemical vapor deposition system. The effective surface recombination velocity Seff is determined as a function of the bulk injection level from light-biased photoconductance decay measurements. On polished as well as chemically textured silicon wafers we find that our remote plasma silicon nitride provides better surface passivation than the best high-temperature thermal oxides ever reported. For polished 1.5 and 0.7 Ω cm p-silicon wafers, record low Seff values of 4 and 20 cm/s, respectively, are presented.

ON-LINE FIBRE OPTIC BASED INSPECTION USING CHROMATIC MODULATION FOR SEMICONDUCTOR MATERIALS PROCESSING

This contribution describes the use of chromatic sensing for monitoring and controlling the state of industrial processing plasmas and for providing an indirect but approximate indication of the quality of the end product of the process on-line. Control systems for a Silicon Nitride plasma deposition and a Reactive Ion Etching system have been developed utilising the chromaticity of the optical emissions from the plasma as a control feedback. It is shown that there is a correlation between the plasma chromaticity and the refractive index of the thin film of semiconductor being deposited so that the chromaticity parameters can be used as indicators of the film quality. This indicates that a chromaticity monitoring system may be used as the basis of an on-line intelligenl control system. It has been demonstrated that there exists potential advantages in combining such chromatic sensing with neural network methodologies to achieve significant improvements in reliability and efficiency of such approaches.

Studies on evaporated cesium incorporation in MIS inversion layer solar cells

For MIS inversion layer solar cells with plasma silicon nitride both as antireflection coating and charged dielectric, cesium was incorporated into the nitride film by thermal evaporation. Compared to the presently used technique of dipping the silicon wafer into an alcoholic solution of CsCl, cesium evaporation yields higher fixed interface charge densities resulting in a lower inversion layer sheet resistance. As a very important result, even for intense and very energetic u.v. light ( λ ⩽ 180 nm) not present in the solar spectrum, no negative effect on the cell properties could be observed. This makes it possible to fully utilize the high response of the inversion layer solar cell in the ultraviolet range.

Statistical feedback control of a plasma etch process

This paper presents the methodology developed for the automatic feedback control of a silicon nitride plasma etch process. The methodology provides an augmented level of control for semiconductor manufacturing processes, to the level that the operator inputs the required process quality characteristics (e.g. etch rate and uniformity values) instead of the desired process conditions (e.g., specific RF power, pressure, gas flows). The optimal equipment settings are determined from previously generated process/equipment models. The control algorithm is driven by the in-situ measurements, using in-line sensors monitoring each wafer. The sensor data is subjected to Statistical Quality Control (SQC) to determine if deviations from the required process observable values can be attributed to noise in the system or are due to a sustained anomalous behavior of the equipment. Once a change in equipment behavior is detected, the process/equipment models are adjusted to match the new state of the equipment. The updated models are used to run subsequent wafers until a new SQC failure is observed. The algorithms developed have been implemented and tested, and are currently being used to control the etching of wafers under standard manufacturing conditions. >

Deposited silicon nitride with low electron trapping rates

In this article, nitrogen-rich silicon nitride plasma deposited under conditions minimizing Si—H bonding is shown to possess extremely low bulk electron trapping rates which are as low or lower than plasma-deposited oxides produced using He dilution. The bulk trap density, measured by avalanche injection decreases as the rf power is decreased. The total charge trapped within these silicon nitrides reaches a saturation value determined by high field detrapping in thick nitride films.

Donor neutralization in GaAs after plasma silicon nitride deposition

Loss of conductance has been observed in Si-doped GaAs after plasma silicon nitride deposition in a 2.45 GHz electron cyclotron resonance reactor and in a 30 kHz parallel-plate reactor, but not in a 13.56 MHz parallel-plate reactor. Based on the temperature at which conductance is restored in test structures subjected to a variety of plasmas, observation of atomic hydrogen in the plasmas by optical emission, and secondary ion mass spectrometry measurement of hydrogen in the test structures, the loss of conductance appears to be from formation of the hydrogen-silicon complex. The extent of neutralization correlates with an abundance of atomic hydrogen in the plasmas and the nitride deposition rate. When the deposition rate is high, the GaAs surface is protected quickly and donor neutralization is minimized.

Fabrication of novel self-aligned metal insulator semiconductor field effect transistors (MISFETs) on InP by a S interface engineering technique

In this paper we demonstrate for the first time that self-aligned metal insulator semiconductor field effect transistors (MISFETs) can be realized on InP by incorporating an effective surface passivation technique in the fabrication process. A chemical sulfur treatment is used to passivate the InP – indirect plasma silicon nitride interface that results in interface state densities (Dit) in the low 1011/cm2 eV. It is observed that while passivated self-aligned MISFETs subjected to post-passivation high-temperature process cycles up to 700 °C exhibit acceptable transistor characteristics, unpassivated MISFETs using the same process do not show any transistor action. The passivation procedure has been successfully used to demonstrate for the first time a self-aligned InP–InGaAs–InP heterojunction insulated gate FET. We conclude from this work that interface engineering techniques like the one used in this study would be essential to realize and (or) improve the performance of self-aligned FET structures based on InP. The fabrication process described here can be directly applied to similar interface engineering techniques.

Reduced interface state densities for remote microwave plasma silicon nitride

The interface state density and fixed charge density of films of a-Si3N4:H deposited on silicon substrates by remote microwave plasma chemical vapour deposition have been studied as a function of deposition and annealing temperature. Interface state densities (Dit as low as 9 × 1010 cm−2 eV−1 have been obtained for films deposited at 215 °C and annealed for 15 min at 500 °C. The films exhibited positive fixed charge levels (QN/q)> 1013 cm−2, increasing slightly with deposition temperature and decreasing slightly with annealing at temperatures from 500 to 700 °C. Fourier transform infrared spectroscopy and Auger depth profiling were used to study the impurities in the films and at the interface. Metal–insulator–silicon field effect transistors made with these films showed room temperature effective channel hole mobilities of 37 cm2 V−1 s−1.