Step Coverage Profiles Research Articles

Low-Temperature Deposition of High-Quality SiO2 Films with a Sloped Sidewall Profile for Vertical Step Coverage

SiO2 is one of the most widely used dielectric materials in optical and electronic devices. The Josephson voltage standard (JVS) chip fabrication process has rigorous requirements for the deposition temperature and step-coverage profiles of the SiO2 insulation layer. In this study, we deposited high-quality SiO2 insulation films at 60 °C using inductively coupled plasma-chemical vapor deposition (ICP-CVD) to fulfill these requirements and fabricate JVS chips simultaneously. SiO2 films have a high density, low compressive stress, and a sloped sidewall profile over the vertical junction steps. The sidewall profiles over the vertical junction steps can be adjusted by changing the radio frequency (RF) power, ICP power, and chamber pressure. The effects of sputtering etch and sloped step coverage were enhanced when the RF power was increased. The anisotropy ratio of the deposition rate between the sidewall and the bottom of the film was lower, and the sloped step coverage effect was enhanced when the ICP power was increased, or the deposition pressure was decreased. The effects of the RF power on the stress, density, roughness, and breakdown voltage of the SiO2 films were also investigated. Despite increased compressive stress with increasing RF power, the film stress was still low and within acceptable limits in the device. The films deposited under optimized conditions exhibited improved densities in the Fourier transform infrared spectra, buffered oxide etch rate, and breakdown voltage measurements compared with the films deposited without RF power. The roughness of the film also decreased. The step-coverage profile of the insulation layer prepared under optimized conditions was enhanced in the junction and bottom electrode regions; additionally, the performance of the device was optimized. This study holds immense significance for increasing the number of junctions in future devices.

Structure-Dependent Contact Barrier Effects in Bottom-Contact Organic Thin-Film Transistors

This paper investigates and compares the structure-dependent contact barrier effects on the electrical performance of two bottom-contact (BC) structure (staggered and inverted coplanar) organic thin-film transistors (OTFTs) by numerical simulations. The drain saturation current ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dsat</sub> ) of the staggered device is found to be more sensitive to the variation of the source/drain (S/D) electrode thickness than that of the inverted coplanar one. The inverted coplanar device shows stronger dependence of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dsat</sub> on the contact barrier than the staggered device, and the dependence is also much more affected by the step coverage profile of the semiconductor layer on top of the S/D electrodes. For the inverted coplanar structure OTFTs, a steeper step coverage profile and a lower contact barrier can help to achieve better tolerance of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dsat</sub> to the variations of the contact barrier and step profile, respectively. The gate structure (self-aligned or fully covered) does not show any influence. The study forms a clear understanding of the device-structure-dependent carrier transport mechanisms in BC OTFTs and could also provide important guidelines for optimal device structure design and related process development for BC OTFTs.

Low Temperature Chemical Vapor Deposition of Silicon-rich Tungsten Silicide Films from Tungsten Hexafluoride - Disilane Pre-activated Mixtures

Abstract Kinetics of chemical vapor deposition (CVD) of silicon-rich tungsten silicide films from WF6/Si2H6 mixtures was investigated as a function of the configuration of a hot-wall tubular reactor. The step coverage within micron-sized trenches was analyzed to determine the overall sticking probability, which is the ratio between the film-forming species deposited on a surface and the flux of that species to the surface. The overall sticking probability was found in the range 0.01 - 0.30 as the deposition temperature was varied from 120 to 360°C. The activation energy was 25 kJ/mol. These sticking probabilities were lower than those for CVD of tungsten silicide film from WF6/SiH4 mixtures, which yielded better step-coverage profiles. The extinction temperature, Tex, below which no deposition was observed, ranged from 70 ‹ Tex ‹ 80°C. Tex = 70°C corresponded to an inner reactor diameter, d, of 22 mm, and Tex = 80°C corresponded to d = 11 mm. The dependence of Tex on d strongly suggests that radical chain reactions are involved in the CVD process. The reaction producing active intermediate species occurs in the gas phase and these active species are consumed on the surface of the reactor wall. Therefore, the volume to surface ratio of the reactor may be the key factor to control Tex, and an increase in d leads to a decrease in Tex. For Tex = 80°C, pre-heating of the gas phase can be used to induce the chain reaction and increase the silicon content in the tungsten silicide films.

Kinetic modeling of tungsten silicide chemical vapor deposition from WF 6 and Si 2H 6: Determination of the reaction scheme and the gas-phase reaction rates

Kinetic studies were carried out on tungsten silicide ( WSi x ) chemical vapor deposition from WF 6/Si 2H 6 in a hot-wall type tubular reactor, focusing on the axial distributions of step coverage and composition ratio. The growth-rate profile within the tubular reactor showed exponential decay, which suggests first-order reaction kinetics. The silicon content of the film increased downstream in the reactor, but the step coverage quality was independent of axial position. The reactive sticking probabilities obtained from the step coverage profile were about 0.33. Two reaction models were investigated to explain these experimental results. The first model is a parallel deposition model, in which W-containing species and Si-containing species are depositing separately. The other model is a consecutive reaction model, in which W-species and Si-species react in the gas phase to form intermediate species containing W and Si. Considering these plausible kinetic mechanisms, consecutive reactions in the gas phase to form W and Si containing species were found to be the controlling factor in the WF 6/Si 2H 6 process. These gas-phase homogeneous reaction-rate constants of the WF 6/Si 2H 6 process were obtained from axial distribution of film composition ratio based on this kinetic model, and the activation energy is about 25 kJ/mol.

Kinetics of chemical vapor deposition of WSi x films from WF 6 and SiH 2Cl 2: Effect of added H 2, SiH 4, and Si 2H 6

This paper describes reaction kinetics of chemical vapor deposition of WSi x films from WF 6 and SiH 2Cl 2, focusing on the effect of added H 2, SiH 4, and Si 2H 6 as an active reaction initiator. Our studies indicate that the temperature at which film formation is extinguished, T ex, can be lowered by introducing H 2 instead of the standard Ar carrier gas. For a SiH 2Cl 2/WF 6 pressure ratio of 20, H 2 addition changed the deposition mode from selective W deposition to blanket WSi x deposition. The added H 2 also improved the step-coverage profile for substrate temperatures below 600 °C. Measured step coverage profiles indicate that the activation energy of deposition species was 147 kJ/mol. Adding either SiH 4 or Si 2H 6 can assist the film-forming reactions to achieve acceptable Si/W atomic composition ratios. Under these conditions, the residual fluorine concentration remained at acceptably low levels that are typical of conventional WF 6/SiH 2Cl 2 CVD processes.

Study of the step coverage and contact resistance by using two-step TiN barrier and evolve simulation

Device aspect ratios and dimensions at the contact and via levels for old and new technologies are driving PVD/WCVD-based metallization to its full limit at integrated circuits (ICs) fabrication sites (Wilson et al., 1993). Contact and via This work describes the work performed at ST Microelectronics regarding the TiN barrier film properties with respect to process variables. Single-step and dual-step TiN barrier processes were studied for contact and via step coverage profiles used for aluminum and tungsten plug technologies. Electrical contact resistance values were evaluated using single and dual step TiN barrier processes. EVOLVE, a topography simulation program was used to study the step coverages and deposited film profiles for single and dual steps TiN barrier processes. In this work we prove that dual step TiN barrier process is superior to single step TiN barrier process in terms of step coverage, current leakage, film stress and contact resistance values.

Kinetics of TiN Chemical Vapor Deposition Process using TiCl4 and NH3 for ULSI Diffusion Barrier Applications: Relationship between Step Coverage and NH3 Partial Pressure

TiN films were deposited by chemical vapor deposition (CVD) using NH3 and TiCl4 as the source precursors. The effect of partial pressures of TiCl4 (PTiCl4 ) and NH3 (PNH3 ) on the growth rate and step coverage quality of these TiN films was measured, revealing the growth rate of TiN films followed the Langmuir–Hinshelwood (L–H) type isotherm as a function of PTiCl4 . The sticking probability of film-forming species was estimated from the step coverage profile simulated by using the Monte Carlo method. The relationship between the sticking probability of Ti-containing species and PNH3 was investigated, revealing that the sticking probability in the 1st-order kinetic regime depended on PNH3 . The effect of NH3 on the growth kinetics could be expressed by G.R.×ρTiN=[ksKCTiCl4 /(1+KCTiCl4 )]·(CNH3 )2 in the wide range of PTiCl4 . The reason for 2nd-order reaction for PNH3 is not clear yet, but the rate equation suggests the complicated gas-phase and/or surface reaction chemistries to form TiN.

Evaluation of Contact and Via Step Coverage Using a Novel Two-Step Titanium Nitride Barrier Deposition Process

AbstractAluminum plug technologies are still used for many different semiconductor device applications and are cost-effective processes. However, there are some disadvantages associated with them. The key disadvantage is aluminum junction spiking caused by aluminum diffusing down into the silicon substrate and silicon diffusing up into the aluminum plug due to a poor titanium nitride (TiN) barrier [1]. The tungsten plug process is primarily used for 0.5mm and smaller technologies. Titanium nitride barrier material plays an important role as an underlayer for tungsten plugs to prevent tungsten hexafluoride (WF6) from attacking the titanium (Ti) film [2]. The role of the TiN barrier is to retard or prevent diffusion of the materials that the TiN layer separates [3]. In this work, the authors investigated the TiN barrier film properties with respect to nitrogen flows at two different power set points and argon gas flows. Different experiments were performed to understand the properties of the TiN film with respect to process variables. Single-step and dual-step TiN barrier processes were studied for contact and via step coverage profiles used for aluminum and tungsten plug technologies.

A Study of Step Coverage Morphologies of SiH4-WSix, and SiH2Cl2-WSix for Ulsi Technologies

AbstractUltrathin refractory metal silicide films, such as tungsten silicide (WSix) offer a wide range of applications in VLSI and ULSI circuits such as local interconnects, bit lines and wordlines. One practical way of depositing WSix is by a CVD technique in which WF6, is reduced by either silane (SiH4) or dichlorosilane (SiH2 Cl2 ). In this investigation, step coverage characteristics of silane based and dichlorosilane based tungsten silicide films, deposited by low pressure chemical vapour deposition method will be compared. WSix films of various thicknesses (1200–2000 Å) were deposited on topographies created by patterning poly-Si layers. WSix, step coverage was evaluated as a function of deposition temperature, poly-Si layer thickness and poly-Si line spacing. Field emisssion scanning electron microscopy was used to characterize step coverage profiles. It is clearly shown that, silane based WSix films deposited on poly-Si lines with sub 0.5 micron spacings result in poor step coverage which could lead to higher localized stress, cracking and higher line resistance. Dichlorosilane based WSix, on the other hand showed more conformal step coverage, which results in better process marhin for subsequent patterning steps. Finally, it was also observed that, the final silicide profile is highly dependent on the thickness of the underlying poly-Si layer, as well as poly patterning process margin.

Recent experience in the deposition of thick quartz films by rf magnetron sputtering

Recent results demonstrating control of the step coverage profile by means of rf bias during rf magnetron deposition of thick quartz films are reported. The source and substrate power supplies are driven by a common oscillator, which permits the relative phase between source and substrate to be controlled. This adjustment has a profound influence upon the power required on the substrate table for a fixed bias. It is found that step coverage profile is primarily a function of substrate bias and only weakly dependent on substrate power.

Improved step coverage by ion beam resputtering

Coverage of steps by ion beam sputtered SiO2 films is greatly improved by bombarding the growing film with an ion beam. Cracks are eliminated at step edges, and step coverage profiles can be controlled by varying the degree of resputtering, as has been observed in rf bias sputtering. Using an ion beam of well-defined energy, flux, and angle, the resputtering process is under direct control. In a dual ion beam system, we examined the step coverage profiles of SiO2 films deposited under 500 eV argon ion bombardment to produce resputtering fractions of 0%, 17%, and 42%. Films deposited with no resputtering show overhanging step profiles, while those deposited with 17% resputtering give smooth sloping profiles with good coverage even with film thicknesses less than the step height. Successful lift-off patterning is also achieved with 17% resputtering. Films deposited with 42% resputtering have sloping profiles but do not fully cover step edges. We conclude that step coverage can be greatly improved using resputtering fractions of less than 20%. This level of resputtering does not degrade other film properties, and is compatible with lift-off processing.

Step coverage of rf‐diode‐sputtered SiO2 films

Step coverage profile dependences of rf‐diode‐sputtered SiO2 films on deposition parameters have been examined by SEM observations. The obtained results are summarized as follows: (1) With decreased spacing between substrate and target, slope of step coverage changes from negative to positive through vertical. (2) Decreasing argon pressure improves step coverage, resulting in a positive slope. (3) Negative dc voltage application to substrate holder makes step coverage negative. On the other hand, step coverage is improved at positive dc voltage. (4) Putting shield ring on substrates, smooth and positive slopes are obtained. The obtained results are successfully explained by shadowing effect of incidence SiO2 materials by substrate step.