Gregory M. Wells

Beryllium window and acoustic delay line design for x-ray lithography beam lines at the university of Wisconsin center for x-ray lithography

X‐ray lithography systems require sample chambers that can perform exposures in helium gas at atmospheric pressure. The interface between the experimental chamber and the beamline is critical for x‐ray lithography and the storage ring. It must allow a high x‐ray flux throughput while providing a vacuum barrier so that helium gas does not leak into the beam line and the storage ring. The beam line must also be designed to have protection in the case that a window does fail in order to minimize adverse effects to the ring and other systems. The details of the design for the vacuum system used on beam lines for the Center for X‐ray Lithography at the University of Wisconsin Synchrotron Radiation Center 1‐GeV electron storage ring are reported. Curved beryllium windows with a 1×5‐cm2 aperture and 13 μm thick that have a leak rate less than 10−10 Torr l/s have been successfully used at the experimental chamber beam‐line interface. This thin flat beryllium foil is mounted in a curved housing with a wire seal to...

Accelerated radiation damage testing of x-ray mask membrane materials

An accelerated test method and resulting metrology data are presented to show the effects of x- ray radiation on various x-ray mask membrane materials. A focused x-ray beam effectively reduces the radiation time to 1/5 of that required by normal exposure beam flux. Absolute image displacement results determined by this method indicate imperceptible movement for boron-doped silicon and silicon carbide membranes at a total incident dose of 500 KJ/cm2, while image displacement for diamond is 50 nm at 150 KJ/cm2 and silicon nitride is 70 nm at 36 KJ/cm2. Studies of temperature rise during the radiation test and effects of the high flux radiation, i.e., reciprocity tests, demonstrate the validity of this test method.

Beamline and irradiation chamber for dosimetry and biology studies using synchrotron radiation

Ultrasoft x rays are a useful probe for mechanistic studies of radiation damage in living cells. The highly localized energy deposition from a low energy x‐ray occurs in a volume comparable to the sensitive biological targets within a cell, so that these low‐energy x rays can be used as a tool to investigate radiation effects on the subcellular level. In the ultrasoft x‐ray energy region the bright intensity and tunable energy selection of synchrotron radiation is unmatched by conventional sources. A beamline and irradiation chamber for dosimetry and radiation biology studies has been set up at the ES‐0 exposure station of the Center for X‐ray Lithography at Aladdin. The beamline includes a 10‐μm‐thick Be entrance window and a combination filter and single synthetically fabricated multilayer mirror for energy selection. The irradiation chamber contains another Mylar window for isolation, a two‐dimensional scanning system allowing a 400‐cm2 exposure area with scanning rates up to 3.5 cm/s, a rotating feedt...

Effects of intense x-ray radiation on polycapillary fiber performance

Several applications of Kumakhov polycapillary optics require extended exposure to intense x- ray radiation. No degradation of performance has been observed when using polycapillary x- ray optics with laboratory sources. As part of an ongoing study to develop an understanding of damage mechanisms and performance limitations, borosilicate glass polycapillaries have been exposed to white beam bending magnet synchrotron radiation with peak energies of 5 and 11 keV, and focused broad band energy centered at 1.4 keV synchrotron radiation. In situ and ex situ measurements of degradation of x-ray transport efficiency have been performed at doses up to 1.8 MJ/cm2 at ambient and elevated temperatures. No decrease in transmission was observed for in situ measurement of fibers exposed to 1.4 keV photons at doses up to 1.4 MJ/cm2. Ambient temperature exposure to higher photon energies causes degradation that can be recovered by low temperature annealing. Exposure at elevated temperatures prevented any measurable damage to rigid fibers, at doses up to 800 kj/cm2.

X-ray mask fabrication process

The Center for X-ray Lithography (CXrL) has developed an x-ray mask fabrication process based on silicon nitride membranes and gold absorber. The LPCVD conditions for the growth of the nitride film produce 2 micrometers thick films with low tensile stress and an optical transmission sufficient for optical alignment. The membranes are formed with an reactive ion etch of the membrane window on the backside nitride, followed by a KOH etch of the silicon wafer. A plating base of 100 angstrom chrome followed by 200 angstrom gold is evaporated on the wafers. The wafer is then mounted on a glass ring using either adhesive or anodic bonding. The absorber pattern is delineated via e-beam lithography into either PMMA or SAL 601. Following resist development and an oxygen plasma cleaning, gold plating is used to produce features of the desired thickness.

Amorphous stuctured Ta4B absorber on SiC membrane for x-ray mask

Stress controllability, stress distribution and radiation stability of Ta4B absorber film on SiC membrane were investigated in detail. A low stress Ta4B film was deposited on as-deposited SiC membrane with excellent reproducibility by an rf magnetron sputtering using Ar gas. Ta4B film with very low stress below 10 MPa and high thermal stability have been obtained by annealing. The film has amorphous structure and uniform stress distribution of +/- 2.5 MPa in a window area of 28 mm square. The Ta4B film has been found to show high durability against SR irradiation. SR-induced displacement (3(sigma) ) of 0.8-micrometers -thick Ta4B film on SiC membrane were X equals 29 and Y equals 24 nm after irradiation of 531 kJ/cm2, which were within the measurement error of 30 nm.

The center for X-ray lithography facility status and beamlines development

Abstract The University of Wisconsin-Madison Center for X-ray Lithography (CXrL) is a national facility for basic and applied research in the field of X-ray lithography operating five beamlines dedicated to X-ray lithography at the University of Wisconsin-Madison Aladdin storage ring. In addition to the beamlines, support facilities for lithographic processing are available. A recent development program with ARPA and Motorola has led to a large increase in the processing and methological facilities available at CXrL. CXrL is in the process of upgrading several key aspects of the facility to accommodate the new equipment and research initiatives. A description of the facility upgrades and a summary of beamlines capabilities, research activities and support facilities is provided.

Performance of the Modified Suss XRS 200/2M X-Ray Stepper at CXrL.

An XRS 200 model 2M X-ray stepper has been installed at the Center for X-ray Lithography. This paper describes the capability of the machine and its installation. Of greater interest is the performance the stepper gives with respect to the dose control and the mask/wafer alignment. How robust a process is depends on the latitude of each process parameter and the control tolerance accorded the machines and materials that affect each one. The dose repeatabillty and uniformity is determined by the optical elements in the beamline, the helium delivery system, and the accuracy of the scanning stage. Test results are reported for dose control using three separate methods. The scan speed is measured using Suss supplied equipment and is verified separately by CXrLs own technique. The dose delivered is analysed by the response of radiachromic film. Also important is the behavior and performance of the ALX-100 alignment system. The optical set-up is described as a model that includes the ALX hardware and illumination as well as the mask and wafer. The signal and contrast from the mask and wafer are compared to data for several substrates. A figure of merit is discussed for determining which membranes will give the best overlay.

Parametric studies and characterization measurements of x-ray lithography mask membranes

The techniques used in the experimental characterization of thin membranes are considered for their potential use as mask blanks for x-ray lithography. Among the parameters of interest for this evaluation are the films stress, fracture strength, uniformity of thickness, absorption in the x-ray and visible spectral regions and the modulus and grain structure of the material. The experimental techniques used for measuring these properties are described. The accuracy and applicability of the assumptions used to derive the formulas that relate the experimental measurements to the parameters of interest are considered. Experimental results for silicon carbide and diamond films are provided. Another characteristic needed for an x-ray mask carrier is radiation stability. The number of x-ray exposures expected to be performed in the lifetime of an x-ray mask on a production line is on the order of 107. The dimensional stability requirements placed on the membranes during this period are discussed. Interferometric techniques that provide sufficient sensitivity for these stability measurements are described. A comparison is made between the different techniques that have been developed in term of the information that each technique provides, the accuracy of the various techniques, and the implementation issues that are involved with each technique.

Installation and initial operation of the Suss Advanced Lithography Model 4 X‐ray Stepper (abstract)

A Suss Advanced Lithography X‐ray Stepper designed as a production tool for high throughput in the sub‐quarter‐micron device range has been installed and is being commissioned at the University of Wisconsin’s Center for X‐ray Lithography (CXrL). Illumination for the stepper is provided by a scanning beamline designed and constructed at CXrL. The beamline optical components are a gold‐coated plane mirror, a 1‐micron‐thick silicon carbide window, and a 25‐micron‐thick beryllium exit window. Beamline features include synchronized scanning of the mirror and exit window, variable scan velocity to compensate for reflectivity changes as a function of incident angle, and a horizontal oscillation of the beryllium window during vertical scanning to average the effects of nonuniform beryllium window transmission. A helium purged snout transports the x‐rays from the beamline exit window, to the exposure plane in the stepper. This snout is retractable to allow for the loading and unloading of masks into the stepper. T...