Low-temperature Microwave Plasma Research Articles

Plasma Parameters for Fast Deposition of Highly Crystallized Microcrystalline Silicon Films Using High-Density Microwave Plasma

We have studied microcrystalline silicon (µc-Si) film growth using a high-density, low-temperature microwave plasma (MWP) of a SiH4–H2 mixture for fast deposition of highly crystallized µc-Si films with low defect density. A very high deposition rate of ∼65 Å/s has been achieved at a SiH4 concentration of 67% diluted by H2 with a high Raman crystallinity of Ic/Ia>3 and a low defect density of (1–2)×1016 cm-3 by adjusting the plasma condition. In contrast to the case of a conventional rf plasma, the defect density of the µc-Si films strongly depends on substrate temperature, Ts, increasing with Ts even at a Ts below 300°C. This suggests that the real surface temperature at the growing surface was higher than the monitored value. A sufficient supply of deposition precursors, such as SiH3, at the growth surface under an appropriate ion bombardment was effective for the fast deposition of highly crystallized µc-Si films as well as for the suppression of the incubation and transition layers at the initial growth stage.

Fast Deposition of Highly Crystallized Microcrystalline Si Films Utilizing a High-Density Microwave Plasma Source for Si Thin Film Solar Cells

AbstractIn this work, we investigate the influences of source gas supply method and dc substrate bias on the deposition rate as well as structural properties of μc-Si films and demonstrate the high rate synthesis of highly crystallized μc-Si films with improved film density by using a high-density and low-temperature microwave plasma source. A high flux of SiH3 and atomic hydrogen on film growing surface achieved through adjusting SiH4 gas supply configuration is effective for the fast deposition of highly crystallized μc-Si films and for the improvement of film mass density. Appropriate ion bombardment under moderate negative dc substrate bias along with the suppression of contributions of detrimental species to film growth also account for the improvement in properties of resulting films. As a consequence, a very fast deposition rate of ~65 Å/s was achieved with a high Raman crystallinity Ic/Ia>3 and a low defect density of (1-2)×1016 cm-3 despite a high silane concentration of 67%.

Polymerization-like grafting of thermoplastic polyurethane by microwave plasma treatment

In this study, the low temperature microwave plasma was used to activate the surface of thermoplastic polyurethane (TPU). Sequentially, grafting with acrylic acid (AA) can be achieved. To immobilize collagen, the coupling reactions between carboxylic group of AA and amino group of protein formed by the assistance of 1-ethyl-3-(-dimethylaminopropyl) carbodiimide. Under controlled plasma parameters, hydrophilic property can be improved for grafted and immobilized TPU. The optimized plasma parameter was using 40 W oxygen plasma under a vacuum of 0.1 Torr for 30 s. Collagen was immobilized successfully on the AA-grafted TPU and confirmed by the Coomassie brilliant blue G test.

Aerosol Plasma Deposition Method for Preparation of Lead Zirconate Titanate Thick Films

Lead zirconate titanate (PZT) thick films were grown by a novel aerosol plasma deposition (APD) method, which combines aerosol deposition (AD) and low-temperature microwave plasma. In our set-up, the deposition rate used in the APD method was about one order of magnitude higher than that in the AD method, which can be attributed to the charging and decomposition effects of the plasma on moving agglomerates to form a trapped jet. While an as-grown APD film deposited at 200°C with a thickness of ∼10 µm showed no ferroelectric hysteresis loop, a PZT film annealed at 600°C showed a remanent polarization of ∼26 µC/cm2 and a coercive field of ∼110 kV/cm.

Optical properties of diamond films deposited by low temperature microwave plasma CVD from camphor

Diamond films were deposited on quartz and Si substrates at a relatively low substrate temperature (∼623 K) by microwave plasma CVD technique using camphor as the precursor. The films were characterized by optical and microstructural (SEM) studies. The film quality was found to be dependent on the sp 3/sp 2 ratio. FTIR studies revealed the ratio of sp 3/sp 2 to vary within 1.7–5.67.

Gate dielectrics on strained-Si/SiGe heterolayers

The purpose of this article is to report on the recent developments on the gate dielectric formation on strained-Si/SiGe heterolayers. In the first part, growth of a high quality strained-Si layer on a relaxed, linear or step-graded SiGe buffer layer and SiGe-free strained-Si on Silicon-on-Insulator (SSOI) is briefly reviewed. Characterization results of strained-Si films using atomic force microscopy (AFM), transmission electron microscopy (TEM) and Raman spectroscopy are then presented. In the second part, the processing issues of gate dielectric formation on strained-Si films are critically examined and the thermal oxidation of strained-Si layers are discussed. Low thermal budget processing, such as rapid thermal oxidation (RTO) and low temperature microwave plasma oxidation and nitridation of strained-Si layers are discussed in the third part. Microwave plasma deposition of various high- k gate dielectrics, such as ZrO 2, Ta 2O 5, and TiO 2 on strained-Si, their electrical properties and the current conduction mechanisms are also discussed.

Relationship between microstructure and photovoltaic performance in microcrystalline silicon film solar cells fabricated by a high-density microwave plasma

Microcrystalline silicon (μc-Si) films have been prepared by a high-density, low-temperature microwave plasma for higher throughput of p–i–n junction solar cells. The correlations among plasma state, film microstructure and photovoltaic performance are investigated as functions of deposition parameters such as axial distance Z from the quartz glass plate, pressure and flow rate ratio of H 2 to SiH 4 r=Fr(H 2)/Fr(SiH 4). Relatively, a high deposition rate of 13 Å/s is achieved with I (2 2 0) / I (1 1 1) of 1.7 at r=3 and 80 mTorr pressure. Solar cells using a μc-Si photovoltaic layer show a relatively high short circuit current, J sc of 18 mA/cm 2, strongly dependent on film microstructure. The correlation among plasma state, microstructure and photovoltaic performance are discussed.

多結晶Ｓｉ薄膜トランジスタ製作へのプラズマ技術の応用 高密度マイクロ波プラズマによるシリコンネットワーク構造の制御

The high-density and low-temperature microwave plasma (2.45 GHz) utilizing a spoke antenna was applied for fast deposition of hydrogenated microcrystalline silicon (μc-Si : H) film. Highly crystallized and photoconductive, μc-Si : H film was fabricated under the plasma condition that the electron density ne show the maximum together with the minimum of the “hot electron population”. The precise control of the ion beam energy impinging to the growing surface was very effective for the promotion of the film crystallinity. High rate deposition of μc-Si : Hfilm was also achieved at 47 A/s from the 30 sccm SiH4 plasma. This high-density microwave plasma has a high potential not only for etching but also for the large-area thin film deposition processes such as solar cell and thin film transistors (TFTs).

Fast Deposition of Microcrystalline Silicon Films Using The High-Density Microwave Plasma Utilizing a Spokewise Antenna

ABSTRACTThe high-density and low temperature microwave plasma utilizing a spokewise antenna was successfully applied to fast deposition of highly crystallized and photconductive microcrystalline silicon (μ-Si:H) films at low temperatures. The deposition rate and film crytstallinity significantly depend on the axial distribution of the plasma parameters. Best crystallinity was obtained at the axial distance Z from the quartz glass plate, where the spread of the ion beam energy impinging to the growing surface was minimum. By optimizing the axial distance Z and total pressure, highly crystallized μ-Si:H films could be fabricated with a high deposition rate of ∼47Å/s in the SiH4 and Ar mixture plasma with no use of the H2 dilution. An intentional control of the ion beam energy is also attempted using a mesh grid electrode to suppress the ion bombardment to the growing surface.

The control of the high-density microwave plasma for large-area electronics

A uniform, low-temperature, and high-density microwave plasma (2.45 GHz) is produced without magnetic field, utilizing a spokewise antenna. The plasma maintains a uniform state in Ar low pressure of several 10 mTorr with high electron density, >10 11 cm − 3, and a temperature less than 2.5 eV within ±6% over 16 cm in diameter. Highly crystallized and photoconductive, hydrogenated microcrystalline silicon (μc-Si:H) film is produced from dichlorosilane (SiH 2Cl 2), H 2 and Ar mixture at high deposition rate of more than 5 Å/s. This low-temperature and high-density microwave plasma source has a high potential not only for etching but for future large-area film deposition processes.

MOS capacitor characteristics of plasma oxide on partially strained SiGeC films

Low temperature microwave plasma oxidation of UHV CVD grown partially strain compensated Si1−x−yGexCy (Ge/C=20:1 and 40:1) with and without a Si cap layer is reported. The electrical properties of grown oxides have been characterized using C–V, G–V, J–E and constant current stressing of metal-oxide-semiconductor capacitors. Fixed oxide charge density and mid-gap interface trap density are found to be 2.9×1011cm−2 and 8.8×1011cm−2/eV, respectively, for directly oxidized Si0.79Ge0.2C0.01 films. The oxide on samples with C concentration of 0.5% exhibits hole trapping, whereas electron trapping is observed for oxides on alloys containing 1.0% carbon.

Surface modification of an aramid fibre treated in a low-temperature microwave plasma

The surface modification of an aramid fibre treated in a low-temperature microwave (mw) plasma was investigated. Three different plasma gases, oxygen, argon and ammonia, were used to achieve different surface modifications during fibre treatment. The modification of the fibre surface was analysed with electron spectroscopy and electron microscopy. The influence of the surface modification on the fibre-matrix interaction was inspected by measuring the interlamellar shear strength of the composites and the pull-out strength of a fibre bundle in model composites. The process gas and thus the kind of plasma has no significant influence on the fibre modification resulting from plasma treatment. It was shown that a fibre cleaning with subsequent surface ablation is the dominate modification process during mw plasma treatment, independent of the process gas. The degree of surface cleaning and removal of a contamination layer strongly depended on the treatment range. No incorporation of oxygen or nitrogen containing functional groups was observed. This was explained with the composition of the process gas. The improvements of the composite properties demonstrate the advantage of the mw plasma treatment as a fast, environmentprotected, cost-efficient process for fibre modification.

Surface modification of polyethylene fibers treated in an oxygen microwave plasma

AbstractThe surface modification of a commercial polyethylene fiber treated in an oxygen low temperature microwave plasma was investigated. The change in surface chemistry was analyzed with electron spectroscopy for chemical analysis. A controlled state of oxidation of the fiber surface was reached by variation of gas flux, process pressure and microwave energy. The oxygen was incorporated into the fiber surface in the form of functional groups. In the determined treatment range, a change in surface morphology as a result of the plasma treatment was not observed with electron microscopy. The higher oxygen content in the fiber surface increased the fiber‐matrix adhesion as shown by mechanical tests.

Low-Temperature Microwave Plasma Etching of Crystalline Silicon

Low-temperature microwave plasma etching of crystalline silicons is described. Vertical and lateral etch rates of Si and the selectivities of Si to photoresist are measured as a function of water temperature within a range of -150 to +30° for SF6, and (3) the selectivities become high at low temperatures (e.g., >40 at -90°C and 2.3 Pa). This etching enables highly anisotropic Si etching at a high etch rate and high selectivity with fluoride gases. Less-polymerizing-type gases can provide high etch rates. An etching model of the ion-bombarded surfaces in discussed. The model implies that separate control of the side wall reaction and the horizontal surface reaction is archived by the low-temperature etching.

Low-Temperature Etching for Deep-Submicron Trilayer Resist

The effects of Cl2 addition to O2 plasma used for deep-submicron trilayer resist etching are investigated. The bottom-layer organic resist is etched using a low-temperature microwave plasma etcher. With O2+Cl2 etching gas, highly anisotropic etching is achieved at higher temperatures than with pure O2. Cl2 concentrations above 25% reduce resist selectivity relative to the SOG intermediate layer. Vertical 0.1-µm-wide resist patterns are achieved with O2+25% Cl2 at -60°C. Broadened resist patterns with tapered side walls are produced at lower temperatures and at higher Cl2 concentrations; this is thought to be caused by chlorine passivation and polymer deposition on the side walls.

Mechanism of Radiation Damage in SiO2/Si Induced by vuv Photons

The generation yield (Rf) of effective positive charges at an SiO2/Si interface, induced by a vacuum ultraviolet (vuv) photon, is measured as a function of the substrate temperature by a low-temperature microwave plasma etching apparatus. The Rf decreases monotonously with decreasing temperatures from 300 K down to 120 K. The model is verified by analyzing the experimental results according to the effective positive charge generation model previously proposed. From this analysis, it is proposed that an ultra low-damage plasma process becomes possible by eliminating the holes generated by the vuv photons from the SiO2 film keeping the specimens at low temperatures.

Low-temperature reactive ion etching and microwave plasma etching of silicon

A new low-temperature reactive ion etching and microwave plasma etching method is described. Highly anisotropic silicon etching with extremely small width shifts has been performed with high selectivities of 30 for organic resist films. High etch rates of 500 and 1000 nm/min by reactive ion etching and microwave plasma etching, respectively, were achieved with a SF6 gas plasma at low wafer temperatures from −130 to −100 °C. It is concluded that lower temperatures during plasma treatment yield lower side etching and increase the dry etch resistance of organic masks.