This PDF file contains the editorial “Multimedia in JM3 is a Win-Win for Authors and Subscribers” for JM3 Vol. 6 Issue 02

We present a systematic robustness analysis for several feedback controllers used in photolithographic critical dimension (CD) control in semiconductor manufacturing. Our study includes several controllers based on either the exponentially weighted moving average (EWMA) estimation or Kalman filters. The robustness is characterized by two features, namely the controller's stability margin in the presence of model mismatch and the controller's sensitivity to unknown noise. Simulations on the closed-loop control system are shown for the performance comparison. Both the analysis and the simulations prove that the multiple-dimensional feedback controller developed in this paper using the average of previous inputs and outputs outperforms the other controllers in the group.

The National Institute of Standards and Technology (NIST) and SEMATECH are working to address traceability issues in semiconductor dimensional metrology. In semiconductor manufacturing, many of the measurements made in the fab are not traceable to the SI unit of length. This is because a greater emphasis is often placed on precision and tool matching than on accuracy. Furthermore, the fast pace of development in the industry makes it difficult to introduce suitable traceable standard artifacts in a timely manner. To address this issue, NIST and SEMATECH implemented a critical-dimension atomic-force-microscope-based reference measurement system (RMS). The system is calibrated for height, pitch, and width, and has traceability to the SI definition of length in all three axes. Because the RMS is expected to function at a higher level of performance than inline tools, the level of characterization and handling of uncertain sources is on a level usually seen in instruments at national measurement institutes. In this work, we discuss recent progress in reducing the uncertainty of the instrument as well as details of a newly implemented performance monitoring system. We also present an example of how the RMS concept can be used in a semiconductor manufacturing environment.

Liquid loss occurs at the receding contact line that forms when a substrate is withdrawn from a liquid. This behavior, often called film pulling, is fundamental to coating and cleaning processes, as well as other systems. There has been substantial prior work relative to understanding the static and dynamic behavior of the receding contact line and film pulling, but this work has focused primarily on operating conditions where the interfacial and viscous forces dominate. In the current work, experimental investigations are presented that identify a second regime, where inertial forces are dominant. These results are used to develop a semiempirical model for predicting the velocity at which an arbitrary liquid is deposited onto an arbitrary smooth substrate from the receding meniscus. The model is verified for a range of fluid properties and is accurate to within 20% mean average error.

In 1981 A. N. Broers suggested that the spatial limit of direct writing electron beam lithography (DWEBL) would be limited to ~10 nm by the laterally scattered fast secondary electrons (FSE) even in atomically thin resist. One possible solution to this restriction would be to use low- or ultralow-energy electrons. Experiments and simulations have been carried out to quantify the contribution of FSE to the energy deposition that results in exposure of the resist over high-beam energies. To examine the effects of FSE on low-voltage operations, studies of electron-beam lithography (EBL) in the low- to ultralow-energy range, employing commonly used resists such as PMMA, were performed, and the results were compared to those from conventional high-voltage processing. DWEBL was performed in a Schottky field emission gun scanning electron microscope (SEM), used in cathode-lens mode for ultralow-voltage operation. The exposure characteristics and sensitivity of the system at these energies have been investigated using Monte Carlo simulation methods. Saturation doses were calculated at low energies, which would give a useful condition to target for routine exposure because it ensures the critical dimensions will not be affected by any random changes in beam intensity.

One of the critical issues within extreme ultraviolet lithography is mirror lifetime and the degradation due to debris from the pinch. This research investigated and showed the efficacy of using a helium secondary plasma and heat for removal of Li debris from collecting on the surface of collector optics. A He helicon plasma, which minimizes self-biasing and sputtering, has good extreme ultraviolet (EUV) photon wavelength transmission and preferential sputtering of lithium compared to other collector optics material. Through the combined use of heating and a He secondary plasma, EUV collector sample surface roughness and surface composition was able to be maintained near as-received status. The use of the He secondary plasma while the collector optics sample is exposed to Li debris shows promise as an in situ cleaning process for collector optics and can extend the lifetime of collector optics.

The paper presents a simulation approach for mask proximity printing. The simulation steps include image formation in air and in photoresist, post-exposure bake, and chemical development and analysis of resist profiles. The intensity distribution in air and in resist in proximity distance from the mask is described by a fast frequency domain method that is based on scalar diffraction analysis. The accuracy and the performance of the method are compared with rigorous electromagnetic field computations that take mask topography effects and the finite conductivity of absorber materials into account. The computed intensity distributions inside the resist are coupled to an established standard simulation flow, which is also used in the simulation of projection printing. The resulting resist profiles can be evaluated in terms of linewidth, sidewalls, and other parameters. Finally, an application of the simulation procedure for the simulation of process windows and optimization of linewidth biasing is shown.

We present a one-step replication technique for optical gratings that allows the control of the corrugation height and period. By using an ink that slowly condenses into a multilayer polymer, it is possible to control the corrugation height by changing the condensation time. In addition, by applying a mechanical strain on the stamp, it is also possible to change the period of the grating. The combination of these two features added to the ease of use and low cost of this technique makes it very attractive for the fast prototyping of optical gratings for applications such as the measurement of surface plasmon band gaps. Corrugation heights in the range of 100 to 250 nm and period variations up to 10% are achieved.

Authors have demonstrated that by controlling the mixing ratio of polydimethylsiloxane's (PDMS's) two components-base polymer (part A) and a curing agent (part B)-different mechanical properties of PDMS can be achieved. Test results show that the Young's modulus decreases as the increasing of mixing ratios (A:B). However, there is a transitional mixing ratio (part A:part B=10) after which the Young's modulus is almost independent of the mixing ratio. The PDMS's thickness plays an important role in determining the mechanical properties. The results show that the thinner the PDMS, the stiffer it behaves. The bonding strength between two cured PDMS parts with different mixing ratios shows that it depends on the mixing ratio. A maximum bonding strength of 130 kPa occurs on a bonded couple with mixing ratios of 30A:1B and 3A:1B, respectively. The fracture on bonded specimens does not occur at the bonding interfaces. Instead it occurs at the side with a larger portion of part A. The intermediate material property formed at the interface is attributed to the diffusion layer formed.

Multicontact MEMS relays laterally actuated using electrostatic comb-drive actuators are reported. The relay consists of a movable main beam anchored to the substrate using two identical folded suspension springs. Multicontact RF ports consist of five movable fingers connected to the movable main beam and six fixed fingers anchored to the substrate. Comb-drive actuators located at the top and bottom ends of the main beam enable bidirectional actuation of the RF contacts. The MEMS relays were fabricated using the MetalMUMPs process, which uses 20-μm-thick electroplated nickel as the structural layer. A 3-μm-thick gold layer was electroplated at the electrical contact surfaces. An example MEMS relay with planar contacts of area 80 μm×20 μm and a spacing of 10 μm between the movable and fixed contacting surfaces is discussed. The overall size of the relay is approximately 3 mm×3 mm. "Resistance versus applied voltage" characteristics of the MEMS relay have been measured for applied DC bias voltages in the range of 172 V to 220 V. A multiscale rough surface contact model was used to estimate the actual electrical contact resistance versus applied force curve of these devices. The multiscale model showed good qualitative agreement with the experimental measurements but requires more refinement to achieve good quantitative agreement.

A novel, electromagnetically driven variable fiber optic attenuator based on micro-electromechanical system (MEMS) technology is described. The attenuation level is adjusted by changing the microshutter position in the optical path. A new technique, termed "nonsilicon surface micromachining," is used to fabricate the shutter, in which a copper layer was used as the sacrificial layer, and the electroplated FeNi as the structure layer. This scheme provides another way to fabricate the optical microstructure. The optical characteristics of the attenuator are theoretically analyzed, and the result is verified by experiments. The MEMS attenuator has fiber-to-fiber insertion loss less than 3 dB at 1550-nm wavelength, dynamic range greater than 40 dB, 0.2-dB repeatability, and return loss better than 40 dB.

Tunable optical filters are key components for dense wavelength-division-multiplexed (DWDM) optical networks. One of the successful mechanisms to realize the wavelength tunability is by utilizing micro-electromechanical systems (MEMS) technology. The tuning mechanism works by applying a voltage between the top mirror and the bottom electrode. Micromechanically actuated optical filters are desirable because of their wide tuning range and process compatibility with other optoelectronic devices. Modeling and simulation play important roles in the MEMS domain. In this paper, we present four different mirror models. A detailed theoretical analysis including both static and dynamic aspects was developed on the four mirror models. A record tuning range of 149 nm with a very small actuation voltage of 2.5 V is achieved for the MEMS-based tunable optical filter.

Nanopatterning of polymer thin films is the basis for the vast majority of current microlithography processes used in integrated circuit manufacturing. Future scaling of such polymer patterning methods will require innovative solutions to overcome the prohibitively high tool and mask costs associated with current optical lithography methods, which will prevent their use in many applications. Scanning probe-based methods for surface modification are desirable in that they offer high resolution patterning while also offering the ability to perform in situ metrology. We report a new scanning probe lithography method that uses heated atomic force microscope cantilevers to achieve nanoscale patterning in thin polymer films via the local thermal decomposition of the polymer and in situ postdecomposition metrology. Specifically, cross-linked polycarbonate thin films are developed in this work and are shown to be excellent writing media for this process. This new method has the advantage that the tip can be heated and cooled on microsecond time scales and thus material can be removed and patterned without need for the disengagement of the tip from the polymer surface. This ability to write while the tip is constantly engaged to the surface offers significantly higher writing speeds for discontinuous patterns relative to other scanning probe techniques.