Raul E. Acosta

B-Si masks for storage ring X-ray lithography

The fabrication of masks used in storage ring X-ray lithography is described. These masks consist of a gold absorber electroplated over a substrate formed by a thin boron-doped silicon membrane covered by a layer of polyimide. Measurement of the properties of the materials which are of concern in this application is also described.

Fabrication challenges for next-generation devices: Microelectromechanical systems for radio-frequency wireless communications

With wireless communications becoming an important technology and growth engine for the semiconductor industry, many semiconductor companies are developing technologies to differentiate themselves in this area. One means of accomplishing this goal is to find a way to integrate passive components, which currently make up more than 70% of the discrete components in a wireless handset, directly on-chip thereby greatly simplifying handsets. While a number of technologies are being investigated to allow on-chip integration, microelectromechanical systems technologies are an important part of this development effort. They have been used to create switches, filters, local oscillators, variable capacitors, and high-quality inductors, to name a few examples. The lithography requirements for these devices are very different than those found in standard semiconductor fabrication with the most important involving patterning over extreme topography. We discuss some of the fabrication challenges for these devices as well as some approaches that have been demonstrated to satisfy them.

Distortion of masks for X-ray lithography

Abstract Experimental and theoretical results are presented on the determination of distortion induced during the process of fabrication of X-ray lithography masks. The studies were performed on B-doped Si and on B-N-H mask substrates.

Pellicles for x-ray lithography masks

The feasibility of using thin films of organic material as a protective cover for x-ray lithography masks has been demonstrated. A pellicle structure that fits unobtrusively inside the mask-wafer gap and on the x-ray lithography NIST standard ring was developed. The pellicle solves several problems: 1) protects the mask absorber from direct contact to external sources of possible damage without itself contacting the absorber, 2) allows effective cleaning of the x-ray mask by preventing dust or debris particles from getting imbedded in the absorber pattern, 3) reduces contamination of the stepper and wafers by absorber metal debris in the event of catastrophic breakage of the mask membrane, 4) reduces contamination of the absorber pattern by debris generated by the resist or the stepper environment during x-ray exposure, and 5) reduces photoelectrons generated by the absorber during x-ray exposure from reaching the resist. Furthermore, pellicles may offer inspection advantages by providing a flat surface without absorber topography. Several approaches for the fabrication of suitable pellicles using organic and inorganic films will be presented in this paper. Pellicles have been successfully tested in the SVGL and SUSS steppers in the IBM Advanced Lithography Facility in the East Fishkill, NY. Results on pellicles performance together with radiation damage measurements to estimate a pellicles lifetime are presented in this paper.

X-ray mask distortion due to radiation damage

Abstract During use X-ray masks will receive very large accumulated doses, perhaps as high as 0.5 MJ/cm 2 . Because the allowed mask distortion for 0.25 μm ground rules is of the order of 0.075 μm, the permissible radiation-induced distortion is ⋍ 0.025 μm, thus requiring substrate materials with negligible distortion when subjected to large radiation doses. The in-plane distortion of various X-ray mask substrate candidates when subjected to large accumulated doses, up to 51,000 J/cm 2 , is reported.

Annealing behavior of gold absorber in x-ray masks

Abstract The stress of gold electrodeposited on membranes of Si, SiC, SiN, and BN was measured using a high precision resonant frequency technique. Measurements were made at room temperature (RT) and between 20 and 350 °C. After annealing, the RT stress was always more tensile than the as deposited stress. This is caused by plastic deformation of the gold at high temperature, resulting from its higher expansion coefficient relative to the substrate.

Fully scaled 0.5μm MOS circuits by synchrotron radiation X-ray lithography: Mask fabrication and chraterization

Abstract Full sets (8 levels each) of X-ray masks have been made and characterized for overlay, resolution and line- width control. These mask sets have been successfully used to fabricate fully scaled 0.5 μm MOS circuits. The mask absorber included, in addition to the device pattern, test patterns and fiducials. A multilevel resist system was used to pattern the critical levels of the mask set. The precision of the mask set has been characterized by measuring more than 600 fiducials on each mask. Analysis of this data shows a level to level overlay error of less than 0.12 μm (3 σ) including measurement error. SEM measurements show a line-width controlled to within 250 A (1 σ). Details of the device masks and their characteristics are discussed in this paper.

Characterization of stress in the absorber of X-ray masks using a holographic technique

Abstract The distortion of X-ray masks is directly related to the stress of the absorber used. Because of this, it is very important be able to determine the value of the absorber stress in order to be able to control, or reduce, the distortion of the masks. A simple technique, double exposure holographic interferometry, is described. Its application in measuring the stress of electrodeposited gold films, and the effect that several deposition parameters have on the gold stress are described.

Fabrication challenges for next-generation devices: MEMS for rf wireless communications

With wireless communications becoming an important technology and growth engine for the semiconductor industry, many semiconductor companies are developing technologies that differentiate themselves in this space. One means of accomplishing this goal is to find a way to integrate passive components, which currently make up over 70 percent of the discrete components in a wireless handset today, directly on-chip thereby greatly simplifying handsets. While a number of technologies are being investigated to allow on- chip integration, MEMS technologies are an important part of this development effort. They have been used to create switches, filters, local oscillators, variable capacitors and high quality factor inductors to name a few examples. The lithography requirements for these devices are very different than those found in standard semiconductor fabrication with the most importatnt involving pattern over extreme topography. In this paper, we discuss some of the fabrication challenges for these devices as well as some approaches that have been demonstrated to satisfy them.

Micromachining using Helios

Micromachining using Deep Etch Lithography (the LIGA process) has been the subject of intensive research since the 1980s. Efforts are underway to produce a wide variety of microstructure products, from fuel injectors in the automobile industry to micropumps for high precision fluid delivery in the medical industry. This paper describes a successful demonstration of the patterning step of this process that was recently performed at the IBM Advanced Lithography Facility, East Fishkill, on Helios, the Oxford Instruments 0.7 GeV compact synchrotron. A number of test microstructures were produced in PMMA resist, including waveguides, micromotor components and miniature optical components. The critical dimensions in some of these test samples were below 2 micrometers . The required exposure times ranged from a few minutes for small areas, to a few hours for the largest areas (60 X 100 mm2) and thickest resists (500 micrometers ). The spectral requirements for achieving the desired results in varying thickness resists are discussed. The demonstration showed that Helios is well-suited as a source for micromachining, despite the fact that it was designed as an optimized source for conventional x-ray lithography, which requires a lower x-ray energy.