Improve Thickness Uniformity Research Articles

Communication—Effects of DC-Bias Voltage on Piezoelectric and Dielectric Properties of Li-Doped ZnO Thin Film

Highly (002)-oriented 3 at% Li-doped zinc oxide (LZO) thin films are fabricated using a radio frequency magnetron sputtering technique with synchronous DC-bias voltages ranging from 0 ∼ 25 V. The DC-bias voltage modifies the microstructure and thickness uniformity of the films, and therefore changes their piezoelectric and dielectric properties. The optimal values of the effective piezoelectric coefficient (19.42 pm/V) and dielectric constant (17.75) are obtained using DC-bias voltages of 20 and 25 V, respectively. The superior piezoelectric performance is due to an improved crystallization of the LZO film, while the superior dielectric performance is owing to an improved thickness uniformity.

A technology to improve formability for rectangular cross section component hydroforming

In order to overcome difficulties in non-uniform thickness distribution and cracking failure during rectangular tube quasi-static hydroforming, a new forming technology, named as electromagnetically assisted hydroforming, is put forward. Both experiment and finite element method were conducted to investigate corner deformability and deformation pattern and its effect mechanisms. Results indicate that both corner deformability and thickness distribution are improved greatly under electromagnetic-assisted hydroforming. The reason is that deformation behavior changed after electromagnetic force application. As electromagnetic force is applied, tine petal cross sections are periodically produced and flattened. Thus, petal-like preform continues to generate and play a useful role in corner filling. Such deformation pattern overcomes friction holding back defect and results in stress state going over from tensile stress to compressive stress, which helps to avoid cracking failure and greatly improve thickness uniformity. At the same time, it also contributes to improve surface quality and decrease forming pressure simultaneously.

Improvement of thickness uniformity and elements distribution homogeneity for multicomponent films prepared by coaxial scanning pulsed laser deposition technique

In conventional pulsed laser deposition (PLD) technique, plume deflection and composition distribution change with the laser incident direction and pulse energy, then causing uneven film thickness and composition distribution for a multicomponent film and eventually leading to low device quality and low rate of final products. We present a novel method based on PLD for depositing large CIGS films with uniform thickness and stoichiometry. By oscillating a mirror placed coaxially with the incident laser beam, the laser's focus is scanned across the rotating target surface. This arrangement maintains a constant reflectance and optical distance, ensuring that a consistent energy density is delivered to the target surface by each laser pulse. Scanning the laser spot across the target suppresses the formation of micro-columns, and thus the plume deflection effect that reduces film uniformity in conventional PLD technique is eliminated. This coaxial scanning PLD method is used to deposit a CIGS film, 500 nm thick, with thickness uniformity exceeding ±3% within a 5 cm diameter, and exhibiting a highly homogeneous elemental distribution.

Optimization of thickness uniformity of coatings on spherical substrates using shadow masks in a planetary rotation system

A model is developed to improve thickness uniformity of coatings on spherical substrates rapidly and automatically using fixed shadow masks in a planetary rotation system. The coating thickness is accurately represented by a function composed of basic thickness, self-shadow effect, and shadow mask function. A type of mask with parabolic contours is proposed, and the thickness uniformity of coatings on spherical substrates can be improved in a large range of ratios of clear aperture (CA) to radius of curvature (RoC) by optimizing shadow masks using a numerical optimization algorithm. Theoretically, the thickness uniformity improves to more than 97.5% of CA/RoC from -1.9 to 1.9. Experimentally, the thickness uniformities of coatings on a convex spherical substrate (CA/RoC = 1.53) and on a concave spherical substrate (CA/RoC=-1.65) improve to be better than 98.5% after corrected by the shadow masks.

An Approach to Improve Thickness Uniformity of TA15 Tubular Part Formed by Gas Bulging Process

Gas bulging with local-stretching preforming is presented to form titanium alloy tubular part with small radius. In ordinary gas bulging process, local thinning occurs at the corners with small radius and produces dangerous position of the component. In the paper, a preforming process so-called local-stretching is applied before gas bulging. Finite element simulation and experiments were carried out to verify the effectiveness of the preforming and gas bulging process for the tubular component of titanium alloy TA15. During the local-stretching preforming, the material near the corner was kept almost rigid, but the material far away from the corner experienced stretching deformation and thickness thinning. Then, during gas bulging, the material near the corner experienced thinning deformation. So, the thickness uniformity of the final component was improved effectively.

An approach to improve thickness uniformity within tailor-welded tube hydroforming

Both experimental and simulation studies were run to investigate the effects of deformation sequence on stress and strain states and thickness distribution during tailor-welded tube hydroforming. The effects of geometrical boundary condition were also studied. Then, an approach to improve thickness uniformity was put forward. Both stress and strain histories indicate that the deformation states of thinner and thicker tubes were obviously different duo to the difference in thickness during tailor-welded tube hydroforming. These induce tensile strain concentrates to happen near weld seam on thinner tube, but compressive strain on thicker tube, which lead to strain mutation around weld seam on tailor-welded tube components. As result, bigger thinning takes place on thinner tube. The difference in thinning ratio between thinner and thicker tubes reaches about 6.6%. By deformation sequence optimization, thickness distribution uniformity can be improved obviously. When deformation sequence altered from thicker tube to thinner tube, the difference in thinning ratio between two segments can be decreased to 1.5%. At last, the effects of geometrical parameters of preform component were analyzed and the suitable parameters were given.

Improvement in Thickness Uniformity of Thick SOI by Numerically Controlled Local Wet Etching

Silicon-on-insulator (SOI) wafers are promising semiconductor materials for high-speed LSIs, low-power-consumption electric devices and micro electro mechanical systems (MEMS). The thickness distribution of an SOI causes the variation of threshold voltage in electronic devices manufactured on the SOI wafer. The thickness distribution of a thin SOI, which is manufactured by applying a smart cut technique, is comparatively uniform. On the other hand, a thick SOI has a large thickness distribution because a bonded wafer is thinned by conventional grinding and polishing. For a thick SOI wafer with a thickness of 1 microm, it is required that the tolerance of thickness variation is less than 50 nm. However, improving the thickness uniformity of a thick SOI layer to a tolerance of +/- 5% is difficult by conventional machining because of the fundamental limitations of these techniques. We have developed numerically controlled local wet etching (NC-LWE) technique as a novel deterministic subaperture figuring and finishing technique, which utilizes a localized chemical reaction between the etchant and the surface of the workpiece. We demonstrated an improvement in the thickness distribution of a thick SOI by NC-LWE using an HF/HNO3 mixture, and thickness variation improved from 480 nm to 200 nm within a diameter of 170 mm.

Optimization of a Concentrated Chloride-Based CVD Process for 4H–SiC Epilayers

Concentrated homoepitaxial growths of 4H–SiC was performed using a chloride-based chemical vapor deposition (CVD) process on different off-angle substrates (on-axis, 4 and 8° off-axis toward the direction). A suitable combination of gas flow and process pressure is needed to produce the gas speed that yields an optimum cracking of the precursors and a uniform gas distribution for deposition over large areas. The use of low pressure and the addition of chlorinated precursors bring the added benefit of achieving higher growth rates. A systematic study of the gas speed’s effect on the growth rate, uniformity, and morphology on the 4H–SiC epitaxial layers was performed. Growth rates in excess of were achieved on 50 mm diameter wafers with excellent thickness uniformity (below 2% σ/mean without rotation of the substrate) and smooth morphology using only 1/10 of the typical gas carrier flow and process pressure demonstrating the feasibility of a concentrated chloride-based CVD process for 4H–SiC. Thermodynamic calculations showed that the improved thickness uniformity could be due to a more uniform gas phase composition of the silicon intermediates. The concentration of the intermediate increases by a factor of 8 at a reduced carrier flow, while all the other hydrogenated silicon intermediates decrease.

Enhancement of optical properties for CdTe absorber through improving thickness uniformity by CMP process

The enhanced optical properties including absorbance of cadmium telluride (CdTe) thin film as an absorber in heterojunctioned solar cells were experimentally obtained by the chemical mechanical planarisation (CMP) process after sputtering deposition, which had been caused by improving the thickness uniformity of the as-deposited CdTe thin film.

Engineering polycrystalline Ni films to improve thickness uniformity of thechemical-vapor-deposition-grown graphene films

It has been shown that few-layer graphene films can be grown byatmospheric chemical vapor deposition using deposited Ni thin films onSiO2/Si substrates. In this paper we report the correlation between the thickness variations of thegraphene film with the grain size of the Ni film. Further investigations were carried outto increase the grain size of a polycrystalline nickel film. It was found that theminimization of the internal stress not only promotes the growth of the grains with (111)orientation in the Ni film, but it also increases their grain size. Different types ofSiO2 substrates also affect the grain size development. Based upon these observations, anannealing method was used to promote large grain growth while maintaining the continuityof the nickel film. Graphene films grown from Ni films with large versus small grains werecompared for confirmation.

Observation of Self-limiting Regime in the Atomic Layer Deposition of ZnO Films using Nitrous Oxide as the Oxygen Supply

We report the observation of self-limiting process in the atomic layer deposition (ALD) of zinc oxide (ZnO) films on (0001) sapphire substrates at low temperatures using diethylzinc (DeZn) and nitrous oxide (N2O). I was found that a monolayer-by- monolayer growth regime occurred in a range of DeZn flow rates from 5.7 to 8.7 μmole/min. Furthermore, the temperature window for the self-limiting process of the ALD-grown ZnO films was also observed ranging from 290 to 310 °. The transmission and absorption spectra of the ZnO films prepared in the self-limiting regime show good optical characteristics with tramsmittance being more than 80% in the visible light region. Experimental results indicate that ZnO films grown in the self-limitng regime all exhibit improved materials characteristics and thickness uniformity.

Improvement of Thickness Uniformity of Bulk Silicon Wafer by Numerically Controlled Local Wet Etching

We have developed numerically controlled local wet etching (NC-LWE) as a novel deterministic subaperture figuring and finishing technique, which is suitable for fabricating various optical components and finishing functional materials. In this technique, a chemical reaction between the etchant and the surface of the workpiece removes the surface without causing the degradation of the physical properties of the workpiece material. Furthermore, the processing properties of NC-LWE are insensitive to external disturbances, such as the vibration or thermal deformation of the machine or the workpiece, because of its noncontact removal mechanism. By applying the NC-LWE process using HF/HNO3 mixtures to etch the silicon, we corrected the thickness distribution of the bulk silicon wafer with a diameter of 200 mm and achieved the total thickness variation of less than 0.23 µm within the diameter of 190 mm.

Improvement of Thickness Uniformity of Bulk Silicon Wafer by Numerically Controlled Local Wet Etching

Improvement of Thickness Uniformity of Bulk Silicon Wafer by Numerically Controlled Local Wet Etching

Effect of the Thickness Uniformity in Micro-Electroforming Process by Dividing Conductive Zone on Cathode

In this paper, an effective method is presented to improve thickness uniformity in nickel electroforming process. In most electroforming processes, thickness ratio of edge to center is 2.5~4 and the shape of the electroforming zone is naturally a concave. Dividing conductive zone of electroforming structure to redistribute current density was applied to improve electroforming uniformity. Theoretical analysis and experimental results verify that a proper dividing method can improve the electroforming uniformity effectively. In the experiment, the thickness ratio of edge to center decreases from 2.91 to 1.88.

59.4: A Novel Route for Thinning of LCD Glass Substrates

The present work describes methods to reduce the thickness of glass substrate used in a liquid crystal display (LCD). Reduction of the thickness improves a thin and ligh-weight performance of LCDs. For this purpose, a fluoride-base chemical was introduced as an etchant of the LCD glass. The new etchant was tested and evaluated by comparing it with the conventional etchant, hydrofluoric acid. An apparatus was also introduced. In the apparatus, rollers were used to remove the reaction products of the etchant and glass. Operation of a pilot-scale equipment showed that the total thickness variation and surface roughness, Ra, was less than 1.0 μm and 0.01 μm, respectively, when the LCD glass plate of 550×650mm was thinned from 0.8 mm to 0.61 mm. This indicates that the thinning process developed in the present work can be directly applied to make small-sized LCD modules such as PDAs, cellular phones, digital cameras, etc., using the 0.6 mm thick glass without any additional process like polishing. Improvement of yield is expected due to remarkable improvement of thickness uniformity. Modification of the present process is needed for making large-sized LCD modules for notebook computers using the 0.4 mm or thinner glass.

Improvement of thickness uniformity and crystallinity of AlN films prepared by off-axis sputtering

We improved both the thickness uniformity and crystallinity of Aluminum nitride (AlN) films deposited by off-axis sputtering. The results in thickness uniformity and X-ray rocking curve full-width at half-maximum (FWHM) of AlN (0 0 0 2) are achieved to be ±0.2% and 1.4°, respectively on a 100 mm Si (1 0 0) substrate. The residual stress can be controlled from tensile to compressive by varying sputtering parameters such as gas pressure, RF power and DC bias voltage applied to a substrate without degradation in the crystallinity and thickness uniformity.

Epoxy/BaTiO/sub 3/ composite films and pastes for high dielectric constant and low-tolerance embedded capacitors fabrication in organic substrates

Epoxy/BaTiO/sub 3/ composite embedded capacitor films (ECFs) were newly designed for high dielectric constant and low-tolerance (less than /spl plusmn/5%) embedded capacitor fabrication for organic substrates. In terms of material formulation, ECFs are composed of a specially formulated epoxy resin and latent curing agent, and in terms of a coating process, a comma roll coating method is used for uniform film thickness in large area. The dielectric constant of ECF in high frequency range (0.5/spl sim/3 GHz) is measured using the cavity resonance method. In order to estimate dielectric constant, the reflection coefficient is measured with a network analyzer. The dielectric constant is calculated by observing the frequencies of the resonant cavity modes. Calculated dielectric constants in this frequency range are about 3/4 of the dielectric constants at 1 MHz. This difference is due to the decrease of the dielectric constant of the epoxy matrix. The dielectric relaxation of barium titanate (BaTiO/sub 3/: BT) powder is not observed within measured frequency. An alternative material for embedded capacitor fabrication is epoxy/BaTiO/sub 3/ composite embedded capacitor paste (ECP). It uses similar materials formulation like ECF and a screen printing method for film coating. The screen printing method has the advantage of forming a capacitor partially in the desired part. However, the screen printing makes surface irregularities during mask peel-off. Surface flatness is significantly improved by adding some additives and by applying pressure during curing. As a result, a dielectric layer with improved thickness uniformity is successfully demonstrated. Using epoxy/BaTiO/sub 3/ composite ECP, a dielectric constant of 63 and specific capacitance of 5.1 nF/cm/sup 2/ were achieved.

Method for improving thickness uniformity of deposited ozone-TEOS silicate glass layers

The ability of the atomic force microscope (AFM) technique to detect and to characterize surface roughness of as-deposited and thermally annealed borophosphosilicate glass (BPSG) films, deposited using atmospheric and sub-atmospheric pressure TEOS-ozone based chemical vapor deposition (CVD) as well as atmospheric and low pressure silane-based CVD, have been demonstrated. The as-deposited BPSG films processed under atmospheric pressure conditions produced higher surface roughness than BPSG films deposited at a reduced pressure. Thermal treatment of BPSG glass films smoothened the film surface roughness. However, the liquid defects on the film surface were found to affect the accuracy of the roughness measurements. The AFM demonstrated to be a quick and non-destructive technique for the characterization of BPSG planarization in terms of flow angle on the step model of integrated semiconductor circuit devices. The correlation between AFM flow angle and scanning electron microscopic analysis of the same device areas showed a linear dependency for angles less than 80°.

数値制御プラズマCVMによる水晶ウエハの高精度加工に関する研究

数値制御プラズマCVMによる水晶ウエハの高精度加工に関する研究

Effects of Heater Surface Precoating and Plasma Treatment on Deposited TiN Film Thickness

Titanium nitride (TiN) films are widely used in integrated circuits as diffusion barrier and adhesion layer materials. Process kits in the chemical vapour deposition (CVD) chamber, which have been in service for a long time, become coated with a thick TiN film and must be replaced with new or recycled parts during chamber preventive maintenance. However, after the replacement of the process kits and the chamber preventive maintenance, it is difficult to achieve the required uniformity and thickness and this results in a delay before the chamber can be released for production. The present paper evaluates the effects of two methods: heater surface precoating and plasma treatment. Experimental results show that these two methods are useful and effective in controlling the deposition rate and improving thickness uniformity in the TiN CVD process. The recovery time after preventive maintenance can also be shortened, improving chamber utilisation and reducing costs.