Papers by Keyword: Lift-Off

Abstract: With the rising need for power devices suitable for harsh environment conditions like high temperature applications, contact materials and packaging of the devices have become critical factors in device fabrication [1, 2]. Therefore, a contact metal stack containing silver and titanium nitride which can be used at elevated temperatures under oxygen atmosphere was investigated. For patterning of the approx. 2 µm thick sputter-deposited metal stack on the wafer front side, a lift-off process using a negative photoresist was established. Characterization of the photoresist sidewall shape was performed by cross-sectional views prepared with SEM and top view images taken on a microscope. It was found that for a successful lift-off, a distinct undercut is needed so no metal is deposited at the downside of the undercut, ensuring a metal-free surface for the solvent to reach the photoresist. To obtain this, most influencing factors are exposure dose and development time, which were optimized considering the undercut shape as well as pattern fidelity. Lift-off with acetone proved to be good for the fabricated 4H-SiC MOSFET devices.

Abstract: Semiconductor component and microelectromechanical system manufacturing requires metal patterning in an integrated circuit (IC), using the photoresist lift-Off process. Ideal advantages like cost-effectiveness, reduction of complexity and process maturity are associated with the lift-Off process. Alternatively, the choice of photoresist relies on factors such as cost, initial photoresist thickness and reliable processing parameters extraction. However, the availability of the cheap photoresist is still at question. For the case of the underlying study, a highly cheap photoresist E8015 of thickness 38-micrometer was developed for the purpose of edge profiling. Desirable extraction of the useful parameter range for dry resist processing is performed. Parameter variation like exposure energy and development time led to a successful undercut angle of 66° to 73°, while the straight edge profile of 90° was realized at various parameter combinations. Eventually, a metallic multilayer of 10-micrometer thickness is successfully lifted off on plain silicon. Controlled self-propagating reaction within these structured metallic layers may be employed for IC packaging hereafter.

Abstract: Lift-off process is a critical combined process in semiconductor manufacturing field. However, traditional methods of lift-off process can hardly be carried out in Ultraviolet Nanoimprint Lithography due to the poor solubility of ultraviolet imprint resist. In this paper, a modified lift-off process using a multi-layer transfer method has been introduced to solve this problem. More importantly, this method could bring an improved result even if the aspect ratio of hard stamp is small. By applying this method, we succeeded in fabricating pillar photonic crystal stamp using hole pattern mother stamp and using the newly defined stamp to fabricate nanopattern sapphire substrate. Depth of the nanopattern is 250nm and the profile of the pattern is pyramid type which is very suitable for subsequent epitaxy.

Abstract: Eddy current testing technique has been widely used in a variety of fields, many researches have been done in quantitative estimation in conductive structure. In the actual use of ECT system, lift-off effect is an inevitable factor which is still a challenging task. Hence, the objectives of this study are to introduce a novel model-free method Support Vector Regression optimized by Particle Swarm Optimization (PSO-SVR) to estimate the surface defect with variable lift-off. Experimental validation carried out that the proposed method had a good performance in surface defect estimation with lift-off effect.

Abstract: The lift-off problem is a very important problem in eddy current testing, which will influence the measurement accuracy. This paper proposes a novel technique for eliminating the probe lift-off in eddy current nondestructive testing. Firstly, the basic principles and characteristics of eddy current testing were introduced. Secondly, this paper analyzed and studied the coil impedance responses caused by the variations of the probe lift-off. Based on simulation results, this paper presents that choosing proper probe excitation frequency can eliminate the disturbance of coil impedance caused by the lift-off, and obtains better results.

Abstract: Thin film patterning by a lift-off method is effective from the viewpoint of cost performance and environmental issues. As a solution to the problems of conventional lift-off methods, the inversely-tapered resist profile with interstice was proposed and its fundamental feasibility was experimenatally proved. The resist profile still needed to be designed properly to solve the problems completely, and therefore a design method was also suggested. The method presupposes that conditions of deposition process have been already determined. However, actually, the conditions relate closely to the design of resist profile and wrong conditions may result in undesirable or infeasible design result. This paper proposes an integrated design method of the thin film patterning process considering design of both resist profile and deposition conditions.

Abstract: In this Paper, we Propose an Alignment Method for Lift-Off on Shallow Grooves in Transparent Substrates without an Extra Mask. An Assistant Metal Layer Was Deposited on the Glass Substrate with Grooves to Increase the Reflectance, and then a Layer of Photoresist for Lift-Off Process Was Coated and Patterned Aligning with the Shallow Grooves. We Compared the Effect of Aluminum and Chromium Films with Different Thickness as Reflecting Layers. an Aluminum or Chromium Film with the Thickness Larger than 10nm Provides High Enough Image Contrast of Profile of the Alignment Marks Beneath the Photoresist. the Image Contrast of Contour Profile of the Marks Was Enhanced as the Thickness Increased. Lift-Off Process Was then Implemented on the Assistant Reflecting Layer. With a 20nm Cr Layer, we Successfully Did Lithography and Finished the Lift-Off Process to Pattern a Cr/Au Layer on Shallow Grooves in a Glass Wafer. Finally, the Assistant Cr Layer Was Removed Using Dry Etching. the Assistant Metal Layer Has No Undesirable Influence on the Following Process and the Device Property.

Abstract: This paper describes a simple and effective lift-off method that relies upon a single layer of positive photoresist and lithography technology. We have succeeded in patterning narrow lines in a photoresist film by image reversal process. Image reversal with AZ 5214-E resist is characterized by contact lithography. A process of patterning different line widths was developed based on image reversal technology, using AZ5214-E, followed by pre-bake, exposure, reversal bake, flood exposure and development. We could obtain very neat patterns with 2-5μm dimensions and their relative features have been supported by scanning electron microscope (SEM) pictures. The application of the proposed process is suitable for the electrode fabrication in MEMS SAW devices.

Abstract: This paper presents an enhanced lift-off process for forming side electrode on the quartz –based double-ended tuning fork (DETF) resonator. In the case of fabricating quartz-based DETF, electrode pattern design is an important issue. Taking advantage of the piezoelectricity effect, a simple surface electrode can excite the flexural motion of the DETF, however it suffers from the large motional resistance. Proposed lift-off process can pattern excitation electrode on the side wall without using special photolithograph equipments. Experimental results demonstrated that the motional resistance can be reduced by several times by forming side electrode using proposed process.

Abstract: Recent developments in producing large single crystal CVD diamond plates are reviewed. The developments consist of synthesis of large single crystal diamond and production of single crystal diamond plates from the bulk diamond by the lift-off process. Combining these developments, half-inch single crystal CVD diamond plates have been successfully produced.