George Patrick Watson

Space charge effects in projection charged particle lithography systems

Charged particle image projection lithography systems have been proposed and are currently under development for design rules of 0.18 μm and below. Although charged particle projection lithography systems do not suffer from diffraction as a limit to spatial resolution as in photolithography, image degradation due to the effects of mutual repulsion of particles in the beam, space charge, will ultimately limit the performance of these systems. Space charge effects increase with increasing beam current. The uncorrectable image blur caused by space charge effectively reduces the dose latitude in projection charged particle lithography and therefore limits the ultimate throughput of such systems. We will describe the effects of space charge in charged particle projection lithography systems using a model we have previously developed. We will compare the predictions of the model with experimental data for an ion projection system and predict the performance of electron and ion beam systems under development. Th...

Comparison of tilting and piston mirror elements for 65nm node spatial light modulator optical maskless lithography

Spatial light modulator (SLM) maskless lithography, an optical technology that replaces photomasks with an adjustable array of microelectromechanical mirrors can potentially complement conventional, mask-based, lithography. The usefulness of this technology depends on whether it can print features at least as well as conventional tools and can keep pace with the International Technology Roadmap for Semiconductors. In particular, any SLM-based tool developed now must be capable of printing 50nm or smaller gates and 130nm pitch lines and spaces using 193nm light as is being planned for the 65nm half-pitch node. SLM mirrors may be designed to tilt or shift in depth (piston). Aerial image simulations presented here show that 65nm node features formed by piston mirrors have the same process latitude as tilt mirrors with a numerical aperture (NA) of 1.1. In addition, piston mirrors exhibit the added benefit that they may be arranged to mimic alternating aperture phase shift photomasks. Isolated and dense featur...

Writing an arbitrary non-periodic pattern using interference lithography

Abstract We propose a technique to write non-periodic patterns using interference lithography. Arbitrary patterns in one and two dimension are constructed by continuous scanning of multiple coherent sources at various incident angles and intensities.

Linewidth reduction using liquid ashing for sub-100 nm critical dimensions with 248 nm lithography

The need for sub-100 nm semiconductor devices has driven our industry to develop new resists, exposure tools (248 nm, 193 nm, extreme ultraviolet, SCALPEL, etc.), mask technologies, and processing procedures. An enormous amount of research has gone into every aspect of the semiconductor device fabrication process and new techniques to further reduce the critical dimensions need to be investigated. The work that is reported on in this article identifies a process that is referred to as liquid ashing. Liquid ashing is a novel approach to linewidth reduction of resist features patterned with positive 248 nm deep-ultraviolet (DUV) resists. The lashing process reduces linewidth through the use of a second wet development step. This process is isotropic and can be continued once started. A bake prior to the second development improves process control. Various types of phase-shifted patterns have been measured and evaluated to determine the effectiveness of this process. This process has been exercised using dif...

Focus drilling and attenuated phase shift mask for subwavelength contact window printing using positive and negative resists

We have investigated the process latitude and resolution limit of printing contact windows using a high numerical aperture KrF stepper and attenuated phase shift mask (APSM). We show that both positive and negative resists can be used depending on the size of the window on the mask. The advantages and disadvantages of using the positive and negative resists are presented. A combination of APSM and focus drilling are shown to extend the focus latitude of subwavelength window printing.

Photon tunneling microscopy of latent resist images

The ability to examine latent resist images can provide a means of separating out the influences of the exposure itself from the subsequent postexposure bake and from the development process in determining the form of the final developed image. We describe the technique of photon tunneling microscopy (PTM) and its application to examining latent resist features. The PTM is based upon the concept of frustrated total internal reflection, and can give information on latent images that is highly sensitive to both changes in topography as small as 1 nm and refractive index changes on the order of 10−2–10−3. Preliminary modeling shows how this technique can give quantitative information about the progress of the radiation induced chemistry in resist. Experimental data for two positive-tone, chemically amplified materials, ARCH2 and CAMP1 illustrate the potential of the technique.

Implementing advanced lithography technology: A 100 MHz, 1 V digital signal processor fabricated with phase shifted gates

To demonstrate the effectiveness of alternating aperture phase shift lithography for integrated circuit manufacturing, a demonstration device was designed and processed. A 2 million transistor integrated circuit was processed with a phase shifted gate level using 248 nm wavelength lithography. The lithographic results were confirmed by careful feature size measurements throughout the process sequence and finally by the performance of the devices themselves. Gate lengths were reduced from 240 to 120 nm, resulting in fully functional chips with 100 MHz circuit speed at 1.0 V operation, more than a two-fold speed improvement and a record for communication circuits of this type at a low supply voltage.

Macro- and Micro-Scale Probing of the Mechanical Properties of DNA-Crosslinked Gels Using Embedded Inclusions

Mechanical properties of a class of self-assembling hydrogels based on DNA hybridization were studied using rigid, embedded inclusions. Because inclusions can be deflected without direct contact with a manipulator (e.g., magnet) once they are embedded within the subject material, the measurement technique is well suited for monitoring instantaneous and time-varying changes in the mechanical properties of active materials as they respond to external stimuli. In gels crosslinked with complementary strands of oligonucleotides, hybridization chemistry and strand displacement mechanisms allow reversible assembly, shape change, and large changes in compliance through the application of particular strands of DNA. In earlier work using large (diameter ∼0.8 mm) magnetic beads, the scaling behavior of the global elastic modulus with crosslink density was determined. More recently, it was shown that a threefold increase in stiffness was possible by generating prestress in the DNA-crosslinked gel network. Currently, the gels are functionalized to support cell attachment and embedded with micro-fabricated nickel bars. Through the measurement of local elastic and shear moduli as well as Poisson’s ratios, cell-substrate interactions can be used as a means of evaluating the potential of DNA-crosslinked gels as active cellular engineering substrates and tissue engineering scaffolds.