Yuheng Wang

Multiple-image encryption by space multiplexing based on compressive sensing and the double-random phase-encoding technique

In this paper, a new multiple-image encryption and decryption technique that utilizes the compressive sensing (CS) concept along with a double-random phase encryption (DRPE) has been proposed. The space multiplexing method is employed for integrating multiple-image data. The method, which results in a nonlinear encryption system, is able to overcome the vulnerability of classical DRPE. The CS technique and space multiplexing are able to provide additional key space in the proposed method. A numerical experiment of the proposed method is implemented and the results show that the proposed method has good accuracy and is more robust than classical DRPE. The proposed system is also employed against chosen-plaintext attacks and it is found that the inclusion of compressive sensing enhances robustness against the attacks.

Equipment Design and Control of Advanced Thermal-Processing Module in Lithography

A programmable multizone thermal-processing module is developed to achieve wafer-temperature uniformity during the thermal-cycling process in lithography. The bake and chill steps are conducted sequentially within the same module without any substrate movement. An array of thermoelectric devices (TEDs) is used to provide a distributed heating to the substrate for uniformity and transient temperature control. The TEDs also provide active cooling for chilling the substrate to a temperature suitable for subsequent processing steps. This design is an improvement of a previous work, eliminating the need of a mica heater. The system is designed via detailed modeling and simulations based on first-principle heat-transfer analysis. Experimental results on the prototype demonstrate about ±0.4°C spatial uniformity during the entire thermal cycle.

Equipment design and control of advanced thermal processing system in lithography

A programmable multizone thermal processing module is developed to achieve temperature uniformity of a silicon wafer during the thermal cycling process in lithography. In the proposed unit, the bake and chill steps are conducted sequentially within the same module without any substrate movement. The unit includes two heating sources. The first is a mica heater which serves as the dominant means for heat transfer. The second is a set of thermoelectric devices (TEDs) which are used to provide a distributed amount of heat to the substrate for uniformity and transient temperature control. The TEDs also provide active cooling for chilling the substrate to a temperature suitable for subsequent processing steps. The system is designed via detailed modeling and simulations based on first principle heat transfer analysis. Experimental results on initial prototype demonstrates less than 0.1degC spatial uniformity during the entire thermal cycle.

Integrated bake/chill system for across-wafer temperature uniformity control in photoresist processing

An integrated bake/chill thermal processing module is developed and experimentally evaluated to achieve spatial temperature uniformity of a silicon wafer throughout the entire processing temperature cycle of ramp, hold, and quench in lithography. The module uses a set of thermoelectric devices which are used to provide distributed heating and cooling to the substrate for uniformity and transient temperature control. The experimental results demonstrate that the wafer spatial temperature uniformity is within ±0.3 and ±0.1°C during transient and steady-state thermal processing, respectively.

Direct measurement of beam size in a spectroscopic ellipsometry setup

Spectroscopic ellipsometry signals used in thin film analysis are dependent on the beam probe size. In this work, we report a technique to determine the beam size that uses the existing detection facilities in a spectroscopic ellipsometry setup without the need to rearrange the optical components. The intensity signal recorded with the technique comprises a coupled boundary diffraction and knife edge wave that can be isolated using nonlinear fitting. This then permitted an accurate measurement of the beam size with the stronger knife edge component. The technique has the added advantage of picking up chromatic aberration in the probing lens which may be a factor in ellipsometry measurement.

In-situ Real-time Temperature Control of Baking Systems in Lithography

We proposed an in-situ method to control the wafer spatial temperature uniformity during thermal cycling of silicon substrate in the lithography sequence. These thermal steps are usually conducted by the placement of the substrate on the heating plate for a given period of time. We have previously proposed an approach for controling the steady-state wafer temperature uniformity in steady-state. In this paper, we extend the approach by considering the dynamic properties of the system. A detailed physical model of the thermal system is first developed by considering energy balances on the system. Next, by monitoring the bake-plate temperature and fitting the data into the model, the temperature of the wafer can be estimated and controlled in real-time. This is useful as production wafers usually do not have temperature sensors embedded on it, these bake-plates are usually calibrated based on test wafers with embedded sensors. However, as processes are subjected to process drifts, disturbances, and wafer warpages, real-time correction of the bake-plate temperatures to achieve uniform wafer temperature is not possible in current baking systems. Any correction is done based on run-to-run control techniques which depends on the sampling frequency of the wafers. Our approach is real-time and can correct for any variations in the desired wafer temperature performance during both transient and steady state. Experimental results demonstrate the feasibility of the approach.

Temperature Cycling for Photoresist Processing

Abstract A programmable multizone thermal processing module together with a model-based feedback control method are developed to achieve temperature uniformity of a silicon wafer throughout the processing temperature cycle of ramp, hold and quench in post-exposure bake (PEB) step of lithography. The module comprises of numerous small thermoelectric devices (TEDs) capable of precise substrate spatial temperature control. The detailed thermal modeling of the module is presented and the simulation results are compared with the experimental results to verify its feasibility. A model-based PID feedback control method is employed to minimize temperature nonuniformity across the wafer. With the method, temperature nonuniformity could be controlled less than 0.1°C throughout the entire thermal cycle. Advanced applications are enabled due to the proposed system.

A heater plate assisted integrated bake/chill system for photoresist processing

A thermal processing module, which consists of a dense distribution of multivariate controlled heat/chill elements, is developed to achieve temperature uniformity of a silicon wafer throughout the processing temperature cycle of ramp, hold and quench in microlithography. In the proposed unit, the bake and chill steps are conducted sequentially within the same module without any substrate movement. The unit includes two heating sources. The first is a mica heater which serves as the dominant means for heat transfer. The second is a set of thermoelectric devices (TEDs) which are used to provide a distributed amount of heat to the substrate for uniformity and transient temperature control. The TEDs also provide active cooling for chilling the substrate to a temperature suitable for subsequent processing steps. The feasibility of a practical system is demonstrated via detailed modeling and simulations based on first principle heat transfer analysis.

A lamp thermoelectricity based integrated bake/chill system for advanced photoresist processing

The design of an integrated bake/chill module for photoresist processing in microlithography is presented, with emphasis on the spatial and temporal temperature uniformity of the substrate. The system consists of multiple radiant heating zones for heating the substrate, coupled with an array of thermoelectric devices (TEDs) which provide real-time dynamic and spatial control of the substrate temperature. The TEDs also provide active cooling for chilling the substrate to a temperature suitable for subsequent processing steps. The use of lamp for radiative heating also provide fast ramp-up and ramp-down rates during thermal cycling operations. The feasibility of the proposed approach is demonstrate via simulations based on first principle heat transfer modeling. The distributed nature of the design also means that a simple decentralized control scheme can be used to achieve tight spatial and temporal temperature uniformity specifications.