Kuniaki Yamazaki

Development of heavy ion beam sputtering method for long-lived carbon stripper foils

Abstract A heavy noble gas ion beam sputtering (HIBS) technique was developed to prepare carbon stripper foils with a characteristic of long lifetime. The dependence of lifetimes on the mass of noble gas was also investigated. Compared with foils made by lighter ions such as Ne and Ar, the foils made by Kr and Xe noble gases were not so much stronger mechanically, but were long-lived under bombardment with a 3.2 MeV Ne+ ion beam 3 μA in intensity and 3.5 mm in diameter. The mean lifetime in the case of Kr sputtering gas was around 51 mC, 20 times longer than that of commercially available foils. The key point in producing long-lived foils with Kr or Xe noble gas ions was found to be to decrease the amount of oxygen contaminants as much as possible.

Nitrided carbon foils as long-lived charge strippers

Abstract Nitrided carbon stripper foils with excellent lifetimes and mechanical properties have been made by a new method based on reactive nitrogen-ion-beam sputtering. The foils showed no shrinkage and maintained mechanical flexibility during long periods of irradiation by ion beams. The average integrated current stripped by such foils before breakage was 75 mC using a 3.2 MeV Ne+ beam flux of 4 μA, 3.5 mm in diameter. This capability is about 30 times greater than commercially available carbon stripper foils. Details are given for the method of preparation and the compositions of the foils produced.

Nanometer scattered-light alignment system using SiC x-ray masks with low optical transparency

Previously we described a video-based scattered-light alignment (SLA) system, capable of nanometer-scale alignment accuracy. In order to meet highly accurate alignment with low optical transparency in x-ray masks, we performed the modifications of alignment marks and an optical microscope imaging system on the conventional SLA system. The advanced SLA system has achieved a high alignment accuracy of 10.2–15.7 nm (|mean|+3σ) using a silicon carbide (SiC) x-ray mask of 18% optical transparency, coated with 5 nm thick chrome (Cr) film as an etching stop, with four different processed wafers: nitride, oxide, poly-Si, and aluminum. The different SiC membranes of 2–5 μm in thickness did not have an effect on the alignment accuracy in the nitride wafer.

Evaluation of alignment accuracy in processed wafers and SiC masks on a scattered-light alignment system for x-ray aligners

The alignment performances of the video-based scattered-light alignment (SLA) system for 0.1 μm lithography are described in this article. The SLA system has high sensitivity to the silicon carbide (SiC) mask without an antireflection coating (ARC). This article especially focuses on the alignment accuracy in processed wafers and the dependency of the alignment accuracy on the SiC membrane thickness. A series of alignment tests was done on a lab-based vertical wafer stage using the SiC masks. In order to evaluate the alignment accuracy in processed wafers, we prepared four processed wafer types: nitride, oxide, poly-Si, and aluminum. The high position sensing repeatability in the range of 4.8–6.4 nm (3σ) was obtained using the combination of the four processed wafers and a 2-μm-thick SiC membrane without the ARC. We also obtained the alignment accuracy using the wafer alignment marks only, resulting in an alignment accuracy of 10.0, 8.8, 9.1, and 35.7 nm (3σ) for the nitride, oxide, poly-si, and aluminum ...

Scattered-light alignment system using SiC mask for x-ray lithography

We propose a novel alignment method using scattered-light, which has high sensitivity to a silicon carbide x-ray mask without coating antireflection films and opaque film. The scattered-light alignment system is a video-based alignment utilizing the white-light (lambda equals 400 - 700 nm in wavelength) scatted on pattern edge of the alignment marks. A two dimensional periodic array is used for both mask and wafer marks. The scattered-light are focused onto field charge coupled devices camera through lenses by a magnification of 100 times. The alignment optical unit equipped with the field camera is located out of x-ray exposure field. Mask to wafer displacement is detected by means of video image processing. We have obtained position-sensing repeatability of 4.8 nm (3 sigma) by using combination between the polished silicon carbide mask and nitride processed wafer. The alignment signal indicated a high signal to noise ratio of 41.9 and 33.4 dB for the mask and wafer marks, respectively.

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.

Accelerated radiation damage studies of antireflection materials on SiC x‐ray mask membrane

The effect of antireflection (AR) coating on optical transparency for SiC membrane and the accelerated radiation damage of thicker AR film of 0.4 μm in thickness on a 2‐μm‐thick SiC membrane have been investigated in detail using SiO2, Al2O3, and ITO (indium tin oxide) films. SiO2, Al2O3, and ITO films were suitable for obtaining higher optical transparency and reducing the amplitude of interference fringes. The transmittance above 80% at 633 nm was achieved for 1‐μm‐thick as‐deposited SiC membrane with these AR films on both sides. AR films showed film stress change toward the compressive direction by synchrotron radiation (SR) irradiation. ITO film was found to have the strongest durability against SR irradiation among the AR films studied. The measured maximum and 3σ values for X and Y coordinates of the SR‐induced displacement of the SiC membrane with 0.4‐μm‐thick ITO film on one side were 30 nm and X=11 and Y=39 nm, respectively, after irradiation of 191 kJ/cm2. Optical transparency of the mask membr...

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.

Impact Of Metallization Films On Scattered-Light Alignment For X-Ray Lithography

The degradation of overlay accuracy due to metallization (i.e., aluminum copper physical vapor deposition (PVD) process) on electronics devices is reported. In a video-based scattered-light alignment (SLA) system for X-ray lithography, the metal layer on the alignment mark structure affects the alignment signal quality. In this paper, we specifically focus on the significant effects of aluminum (AL) metallization on the performance of the scattered-light alignment (SLA) system. The SLA system demonstrated an overlay accuracy of 10.1 nm or less smaller (mean + 3σ) for Al films of 0.1, 0.2, 0.3 and 0.4 µm thickness. Only the 1-µm-thick Al-sputtered wafer showed a significantly poor performance of 44.4 nm error (mean + 3σ). The SLA system employs two different types of alignment marks: one type uses narrow edges, while the other types uses wide edges. We estimated the mark-related alignment error using the two different types of alignment marks. The results showed that the narrow edges of the alignment marks had the advantage of smaller mean shift error compared to the wide edges of the alignment marks. Furthermore, we discuss an asymmetry-induced error in thick Al metallization.

Synchrotron radiation x‐ray lithography beamline optics alignment using the Hartmann method

This article studies the effect of mirror misalignment on run‐out overlay errors in a synchrotron radiation based x‐ray lithography system. Using the ES‐5 beam‐line installation at the CXrL as an example, we found that the current beamline mirror alignment method, which relies on the final beam shape and orientation at the mask‐wafer plane, is insensitive to the mirror grazing incident angle alignment. Simulations using the ray‐tracing program shadow indicate that a smaller than ±0.5‐mrad mirror grazing angle misalignment consumes the required run‐out overlay error budget of the beamline. A direct beamline run‐out overlay measurement technique based on the Hartmann method was developed for the beamline mirror alignment. This measurement technique was applied to our ES‐5 beamline mirror alignment procedure. The measurement results show that the beamline induced run‐out error of the installed ES‐5 beamline is less than 0.014 μm in both horizontal and vertical direction for a 25‐mm exposure field with a mask...