Dc Substrate Bias Research Articles

Field‐Aided Thermal Chemical Vapor Deposition of Copper Using Cu(I) Organometallic Precursor

A dc substrate bias which is not enough to make a plasma was applied during the chemical vapor deposition of copper to change the adsorption behavior of the reactant. Copper films were deposited on TiN and from Cu(hfac)(tmvs) with and without the substrate bias. The surface morphology, the thickness, the sheet resistance, and the purity of the films were investigated. When a negative substrate bias of −30 V was applied to the substrate, the deposition rate of copper increased both on TiN and . The substrate bias did not cause the change in the chemical composition of the deposited copper film. It was calculated that Cu(hfac) has the dipole moment whose direction is from copper to hfac. The local electric fields due to surface roughness may affect the adsorption behavior of the precursor, especially the direction of the molecular dipole moment. Resulting from the overlapping population value analysis, the improvement of deposition rate under negative substrate bias was explained as due to the adsorption of the copper atom in the Cu(hfac) species directly onto the substrate by the local electric fields applied between the substrate and the gas showerhead.

The nucleation of highly oriented diamond on silicon via an alternating current substrate bias

A new bias-enhanced nucleation method of forming highly oriented diamond on Si(100) is reported using an alternating current bias source. The percentage of aligned particles via alternating current bias-enhanced nucleation (ac BEN) was greater than 50%. This is compared to less than 10% highly oriented particles when using a conventional negative dc substrate bias. Based on previous work in this area, the peak negative voltage portion of the ac wave form is believed to be responsible for enhancing diamond nucleation. The positive and moderate negative voltage portion of the ac wave form appears to aid the process of forming the highly oriented diamond.

Electrical properties of vapor-deposited yttria-stabilized zirconia thin films

The electrical properties of rf sputter-deposited thin films of ZrO2 doped with 4 mol % of Y2O3 were examined from 296 to 773 K. The films were deposited in an Ar/O2 (80/20) atmosphere at a pressure of 2 Pa under various substrate dc bias conditions (from −30 to +20 V). A Rutherford backscattering spectroscopy technique was used to determine the thickness of the films. Results showed that the deposition rate increased with applied negative dc bias ranging from 0.0486 nm/s for films produced with +20 V to 0.0972 nm/s for films produced with −30 V. Current–time measurements as a function of temperature were made in an electric field of 103 V/mm. Distinct conduction mechanisms of the ZrO2–Y2O3 films were observed from the slope change in Arrhenius plots of dc resistivity at 523 K. At low temperatures, the conduction was due to the migration of free oxygen vacancies. At temperatures above 500 K, the conduction was governed by the dissociation of oxygen vacancies trapped by the yttrium cations resulting in a higher activation energy for conduction. The effects of thermal cycling on the electrical behavior of the thin films were also investigated.

Noncontact minority carrier lifetime measurement of Si and SiGe epilayers prepared by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition

A 70 MHz inductively coupled rf bridge probe is used to measure the minority carrier lifetime of the Si and SiGe epilayers grown by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV-ECRCVD) at temperatures below 560 °C. Proper surface treatments before HF immersion are required for the accurate measurement of the bulk minority carrier lifetime. The effects of the process parameters such as the substrate dc bias, the distance of the ECR layer from the substrate, and the substrate temperature, including in situ surface cleaning, on the minority carrier lifetime of the Si and SiGe epilayers are examined by the rf bridge probe. It is confirmed that the rf bridge probe can monitor the epitaxial quality of low temperature Si and SiGe epilayers, making it an indispensable tool for the high quality device fabrication with Si and SiGe epitaxial layers grown by low temperature UHV-ECRCVD.

Effects of process parameters on low-temperature silicon homoepitaxy by ultrahigh-vacuum electron-cyclotron-resonance chemical-vapor deposition

The effects of the process parameters on the low-temperature Si homoepitaxial growth in an ultrahigh-vacuum electron-cyclotron-resonance chemical-vapor-deposition (UHV-ECRCVD) system are examined by reflection high-energy electron diffraction and transmission electron microscopy (TEM). The substrate dc bias during plasma deposition drastically changes the crystal structure from polycrystalline silicon at negative bias to single crystalline at positive bias. The defect production during plasma deposition is mainly caused by the energetic ions impinging on the Si substrate, and it can be effectively suppressed by the proper control of the process parameters in the direction of minimizing the ion energy. The positive substrate dc bias is a prerequisite for better crystallinity of low-temperature Si, but additionally the other process parameters such as microwave power, distance of the ECR layer from the substrate, SiH4 partial pressure, and total pressure should be definitely optimized to obtain dislocation-free Si epilayers. Dislocation-free Si epilayers are successfully grown at 560 °C at the positive dc bias greater than +10 V with the optimal control of the other process parameters. At temperatures below 470 °C, a high density of defects in the Si epilayers is observed by plan-view TEM, and the growth of the single-crystalline silicon is possible even without substrate heating but with a high density of defects. It is concluded that the substrate dc bias is a critical process parameter and the other process parameters do play a small but significant role as well in determining the crystallinity of the Si epilayers grown by UHV-ECRCVD.

Bias Sputter Deposition of Dense Yttria‐Stabilized Zirconia Films on Porous Substrates

We demonstrate that completely dense yttria‐stabilized zirconia (YSZ) electrolyte films <5 μm thick can be reactively sputter deposited onto porous (∼0.5 μ pore size) substrate/electrodes. The two key factors in achieving the fully dense films were porous substrate preparation and the use of substrate bias during YSZ film deposition. Increasing the negative dc substrate bias from 0 to 300 V produced increasingly dense and flat‐surfaced films: was chosen to yield high density without excessive film compressive stresses. Solid oxide fuel cells consisting of sputtered YSZ films and a Ni‐YSZ fuel electrode on LSM exhibited open‐circuit voltage values within 5% of the theoretical values for thicknesses down to 2 μm. Cells deposited with short‐circuited at thicknesses of 12 μm or less.

Low-temperature in situ cleaning of silicon (100) surface by electron cyclotron resonance hydrogen plasma

Low-temperature, defect-free, in situ cleaning of silicon prior to homoepitaxy is successfully developed by an electron cyclotron resonance hydrogen plasma treatment in an ultrahigh vacuum chamber. The plasma potential distribution was measured by a Langmuir probe method to understand the effect of the substrate dc bias during hydrogen plasma cleaning. It changes from downhill to uphill distribution as the dc bias changes from a negative to a positive value, which leads to a decrease in the ion number density arriving at the substrate and results in the complete suppression of the defect formation in the Si substrate. In situ hydrogen plasma cleaned Si wafer always resulted in higher quality epilayers than ones cleaned only by so-called hydrogen passivation after the HF dip. We found that there is a critical dose of the hydrogen ions during in situ plasma cleaning beyond which crystalline defects are observed in the Si substrate, subsequently leading to the poor crystallinity of the epilayers. The dose of the hydrogen ions during plasma cleaning can be effectively controlled by the substrate dc bias, the microwave power, the magnet current, and the cleaning time.

Bias Effect on Compositional Separation in Sputtered Co–Cr Films

The effect of dc substrate bias on compositional separation (CS) in sputtered Co–Cr films is examined using spin-echo 59Co NMR and transmission electron microscopy. It is observed that the degree of CS decreases monotonically with increasing negative bias voltage. Slight positive bias voltage, however, is found to enhance CS, resulting in increased saturation magnetization and a higher anisotropy field. The elimination of Ar ion bombardment at the film surface during deposition is thought to be effective in enhancing CS.

Effects of substrate temperature and bias potential on hydrogen plasma etching of silicon

Si masked by patterned SiO2 was etched using an electron cyclotron resonance hydrogen plasma. The dependence of the etch rate and the etched profile on substrate temperature and dc bias potential has been investigated, and an etch mechanism has been considered. The substrate temperature was varied between room temperature and 400 °C, and a bias potential between −100 and +100 V was applied. The etch rate of Si had the highest value at the lowest substrate temperature and decreased with increasing temperature. For the bias potential, the etch rate of Si had its peak value at 0 V. It decreased with increase of the potential which was either positive or negative. Si was also etched laterally when the substrate temperature was low. For the negative bias potential, the etched Si had a terrace on the border of a SiO2 mask. It is considered that the temperature dependence of the etch rate and the etched profile is caused by the action of hydrogen atoms, and the bias potential dependence is caused by the action of hydrogen ions. Thus, we conclude that both hydrogen ions with moderate energy and hydrogen atoms play an important role in Si surface etching.

Properties of RF sputtered B4C thin films

We have studied the effect of substrate temperature and dc bias voltage on B4C thin films grown by RF sputtering on (100) Si substrates. The composition of the films is near the high carbon limit B4C (20 mol% C). Crystalline B4C films begin to grow at substrate temperatures Ts above 900°C with a (211) texture. Applying dc biased RF sputtering, the growth direction of the films changed to random orientation and a (111̄) peak appeared due to continuous bombardment with Ar ions. With bias voltage, crystalline B4C films begin to grow at a Ts of 1100°C. With increasing bias voltage, the crystallinity of the films gradually gets completely destroyed. Incorporation of Ar was observed in the sputtered films. The concentration of Ar depends on Ts and the bias voltage. The results of hardness, indentation fracture and scratch test measurements showed that the films are hard but brittle together with insufficient adhesion.

Novel YBa2Cu3O7−x and YBa2Cu3O7−x/Y4Ba3O9 multilayer films by bias-masked ‘‘on-axis’’ magnetron sputtering

In situ YBa2Cu3O7−x (YBCO) films have been fabricated on SrTiO3 (001) and LaAlO3 (001) substrates by on-axis biased-radio-frequency magnetron sputtering in Ar-10% O2 at total pressures as low as 3 Pa (3×10−2 mbar) and a deposition rate 210 nm/h. Negative oxygen ion-resputtering has been considerably reduced by introducing a biased copper mask between the substrate and target. The surface morphology and physical properties of the films are greatly improved on applying a positive dc substrate bias with respect to the grounded deposition chamber. We have obtained superconducting YBCO films with transport critical current as high as 106 A/cm2 at 77 K and low normal-state resistivity by this approach. Scanning tunneling microscopy analyses of the films with the best superconducting properties reveal a spiral growth mechanism. However, films deposited by negative dc bias under identical sputtering conditions are insulating. From x-ray θ-2θ and rocking curve measurements, we identify the insulating films to be c-axis oriented Y4Ba3O9 (YBO) films. Furthermore, YBCO films could be grown on the YBO layers without any degradation of TC and c-axis orientation. This novel bias sputtering feature gives us a unique opportunity to produce superconductor/insulator, YBCO/YBO, multilayers from a single YBCO target.

Low-temperature silicon homoepitaxy by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition

High quality silicon homoepitaxial layers are successfully grown at 560 °C by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV-ECRCVD) using a SiH4/H2 plasma. The effects of substrate dc bias on the in situ hydrogen plasma clean and the subsequent silicon epitaxial growth are examined by the reflection high-energy electron diffraction (RHEED), secondary ion mass spectroscopy (SIMS), and cross-section transmission electron microscopy (XTEM). It is observed that the substrate dc bias plays a significant role in obtaining a damage-free, clean Si substrate prior to epitaxial growth. Severe damage in the Si surface is observed by XTEM, though RHEED shows a streaky pattern, when the substrate is electrically floating, but the damage can be suppressed with +10 V dc bias to the substrate. Substrate dc bias during plasma deposition drastically changes the crystal structure from polycrystalline at −50 V to high quality epitaxial silicon at substrate biases greater than +50 V. Precise control of the ion energy during in situ cleaning and plasma deposition is very important in low-temperature Si epitaxy by UHV-ECRCVD and it is possible by proper control of the substrate dc bias.

Epitaxial growth and magnetic properties of Fe films on Si substrates

Epitaxial growth of Fe films on Si(100), Si(110), and Si(111) substrates was achieved by dc facing targets sputtering. Substrate dc bias was found to be an important parameter to achieve epitaxial growth. Epitaxial films were not obtained without a dc substrate bias except those on Si(111) substrates. In-plane anisotropy energy for Fe(110) plane was different from the bulk. Uniaxial anisotropy and magnetoelastic energy should be considered with magnetocrystalline anisotropy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Study of a rf planar magnetron sputtering discharge: Discharge characteristics and plasma diagnostics

Electrical and Langmuir probe measurements and energy analysis of the ions impinging on the substrate electrode were used to characterize a rf planar magnetron sputtering discharge. The pressure range examined was 0.26–5.33 Pa in both argon and argon-nitrogen mixtures. The electrical measurements allowed us to determine the rf target voltage V rf and the self-bias target voltage V dc as a function of rf input power, process pressure and dc substrate bias voltage. The electron density n e , the electron temperature T e and the mean plasma potential V p were measured using Langmuir probe diagnostics. These time-averaged plasma parameters were investigated as a function of rf input power, process pressure and dc substrate bias voltage. An energy electrostatic analyser was used to study the energy of ions impinging on the negatively biased substrate electrode. The energy distributions depended on the voltage drop across the substrate sheath and on the collisions in the sheath. They were broadened by the rf modulation.

Effects of platinum content and substrate bias on the structure and magnetic properties of CoCrPt/Cr thin films

The effects of the Pt content (0–40 at. %) and the developed dc substrate bias voltage (0 to −190 V) on the magnetic properties and structure of rf sputtered CoCrPt/Cr films with two different remanent magnetization-thickness products Mrδ (0.7 and 2.3 memu/cm2) were studied. It was demonstrated that a wide range of in-plane coercivities (500–3450 Oe) can be easily obtained in these films. The addition of Pt affected the magnetic properties of the films through changes of the lattice parameter, texture, and phase composition. A maximum in the in-plane coercivity exists for moderate amounts of Pt. The saturation magnetization decreased monotonically with increasing Pt content. rf substrate bias increased the in-plane coercivity and altered the character of the magnetic interactions through changes of the stress, texture and microstructure of the magnetic layer.

Growth of epitaxial TiN films on MgO(100) by high current discharge plasma

High current discharge plasma produced by the Ta-LaB6 cathode was used for ion plating of TiN films. The dependence of the deposition rate of TiN on the substrate dc bias potential was measured using the Rutherford backscattering spectrometry (RBS) method. The results indicate that the particles impinging on the substrate, i.e., vaporized particles (Ti) and reactive gases (N2), could be ionized at high efficiency of 70%. Epitaxial TiN films were grown at temperatures between 400 and 700 °C on cleaved MgO(100) substrate supplied with negative dc anf rf potential. Structures of the epitaxial film were investigated by RBS and ion channeling, and scanning tunneling microscope (STM). The minimum channeling yields for (100) and (110) axes obtained at a substrate temperature of 550 °C with the growth rate of 40 Å/s were found to be 1.4% and 2.0%, respectively, which were almost the same as that of the MgO substrate. Atomically resolved tunneling images of (100) surface of the epitaxial TiN film were observed by STM.

Stresses in sputtered tungsten thin films

Internal stresses in 0.6 μm thick tungsten RF sputtered films, deposited on silicon wafers, were investigated in connection with microstructural aspects as a function of low positive and negative DC substrate bias voltage, in the range from +30 to −60 V. The argon pressure was fixed at 1.8 Pa and the substrate temperature measured at zero bias was varied so that the microstructure of the film could be typical of zone I or zone T in Thornton's model. No variation was observed in the structural aspects or in the stress value of the film when a low positive voltage greater than +5 V was applied. With increasing bias voltage from −10 to −60 V, both stress and microstructures properties were demonstrated to follow the same evolution as with a decreasing argon pressure: (a) for initially zone I films, presenting a porous structure, stress increased from zero towards tension as voids disappeared and then abruptly decreased when the structure became dense. The more porous the structure at zero bias, the more the zone I/zone T transition shifted towards increasing negative bias; (b) for dense zone T films, stress monotonically decreased towards compression. It was confirmed that oxygen absorption in the pores of the zone I structures produced a shift of stress with time towards compression.

The influence of an external dc substrate bias on the density of states in hydrogenated amorphous silicon

We report a study of the dependence of the density of states in hydrogenated amorphous silicon produced under different dc substrate biases. A dependence of the density of states in materials deposited simultaneously onto indium-tin-oxide-coated glass and stainless steel has been found. The same is attributed to sheath plasma differences at the top surface of the growing film. The density of states was determined by the space-charge-limited current method. The universal scaling law is tested for samples having a similar density of states. Attempts were made to correlate the product of the hole mobility and the recombination time for samples deposited in conditions similar to those used in the space-charge-limited current experiments.

Transmission electron microscopy studies of brown and golden titanium nitride thin films as diffusion barriers in very large scale integrated circuits

The usefulness of reactively sputtered TiN as a diffusion barrier in the AlTiN/Ti/Si metallization scheme in very large scale integration was reported in a previous publication. Two types of TiN thin films were studied in these experiments. Depending on the applied substrate bias voltage, the resulting TiN films can have different properties. Under no-bias conditions, dark brown colored films (called B films) with low density (3.22 g/cm3), high electrical resistivity (∼400 μΩ cm), and 5%–8% O2 are obtained. A+ -75 V dc substrate bias, bright golden colored films (called G films) with high density (∼5.0 g/cm3), low resistivity (∼20 μΩ cm), and negligible O2 are obtained. Even though the B films contain more O2, the G films were found to be better diffusion barriers for silicon. To investigate the effect of film microstructure on the diffusion barriers, cross-sectional and planar transmission electron microscopy samples were used. Both, brown and golden, types of films have columnar grain structure with approximately the same size (∼400–500 Å), contrary to fine-grained structure observed for G films by some other groups. The columns in the G films increase in size with an increase in distance from the TiN/Si interface, while the grain size remains almost constant in the B films. The intergrain structure also differs considerably; the grains in G films are very closely packed while they are very loosely bound in the B films. The intergrain voids in the B films can act as an easy path for silicon diffusion. Also, these films were studied by Rutherford backscattering spectroscopy, Auger electron spectroscopy, and x-ray diffraction to understand the diffusion mechanisms.

Cross-sectional TEM characterization of low temperature (750-800°C) epitaxial silicon by very low pressure (6 mTorr) chemical vapor deposition with and without plasma enhancement

Cross-sectional transmission electron microscopy (XTEM) and high resolution transmission electron microscopy (HRTEM) were used to characterize epitaxial silicon grown by chemical vapor deposition at 750–800° C. Optimum conditions for pre-deposition argon plasma sputter cleaning were found to be -100 V dc substrate bias and 2.5 W rf power for 13 minutes at 4 m Torr and 750–800° C. No dislocations were observed by XTEM in films deposited subsequent to this plasma exposure. Analysis of the epitaxial layer/substrate interface by HRTEM indicates complete lattice registration despite the presence of a discontinuous array of defects or microprecipitates. The strain field associated with these defects is approximately 13A in width. Annealing the epitaxial layers at 1150° C inN 2 for 4 hours led to the generation of additional defects believed to be associated with carbon and oxygen clustering. Preliminary results indicate that neither temporary (30 seconds) growth interruptions nor low power (2.5 W) plasma enhancement of thedeposition process lead to the generation of defects observable by XTEM.