Kenji Sugishima

Improvements of stress controllability and radiation resistance by adding carbon to boron-nitride

The addition of an atom having different bonding radii to a matrix film is an effective method for changing the stress of the film. In a plasma-enhanced CVD of BN, it is difficult to obtain tensile stress except for extremely boron-rich films. The controllability of tensile stress in BN film was improved by introducing a small amount of carbon into the BN matrix, using plasma-enhanced CVD between 400{degrees} and 500{degrees}C. The authors have obtained transparent films with high Youngs modulus and tensile stress. They report that the radiation resistance of BNC deposited at 400{degrees}C was improved five times better than that of BN deposited by low-pressure CVD at similar temperatures.

Stress stabilization of β‐tantalum and its crystal structure

We studied the relationship between Ta crystal structures and the stress stability of Ta under heating. The stress in Ta which was sputter deposited on SiC was unstable and changed more than 2×109 dyn/cm2 to the compressive side during heating at 200 °C for 30 min in air. In contrast, the stress in Ta which was sputter deposited on SiC whose surface was modified by Ar sputtering was very stable, and the stress change was less than 1.5×108 dyn/cm2 even after 6 h of heating at 200 °C. The x‐ray diffraction patterns of the Ta revealed that stable Ta was strongly (002) oriented β‐Ta, and that unstable Ta was randomly oriented β‐Ta with some α‐Ta. We found that amorphizing the SiC surface or inserting a thin amorphous interlayer enhanced growth of strongly (002) oriented β‐Ta.

An Etching Mechanism of Ta by Chlorine‐Based Plasmas

Ta is easily etched by chlorine plasmas in spite of the low vapor pressure of the reaction product, i.e. Ta-chloride. In order to clarify the etching mechanism of Ta in relatively low temperature conditions below 25°C, optical emissions were monitored. Contrary to the case of Al etching, the emission intensity of atomic chlorine, which is assumed to be an active etching species, becomes stronger during Ta etching as if it is a reaction product itself. This suggests that molecular chlorine reacts with Ta as strong as atomic chlorine, and that the reaction, especially the desorption process of the reaction product, is strongly assisted by ion bombardment, and that the reaction product, TaCl x , is sputtered off the surface to form partly as decomposed TaCl x−1 and atomic chlorine

Precise Reactive Ion Etching of Ta Absorber on X-Ray Masks

We investigated the reactive ion etching (RIE) of the Ta absorber on X-ray masks using a mixture of chlorine (Cl2) and chloroform (CHCl3) gases. To improve the pattern profiles, we used a gas mixture of chlorine (Cl2) and chloroform (CHCl3) which enhances deposition and protects side wall. We consistently obtained vertical side walls (90°±3°) with a Ta-to-resist etch-rate ratio (selectivity) of 7 and pattern edge roughness below 0.02 µm. The transfer accuracy was 0.00±0.04 µm (3 sigma) using 40% CHCl3 and Cl2 with a gas pressure of 0.2 Torr and power density of 0.8 W/cm2.

Effects of X-ray mask structures and processes on X-ray mask distortion

Abstract We measured the distortion of 0.8 μm thick Ta absorbers patterned on 2 μm thick SiC membranes. The maximum membrane diameter was 60 mm, and the largest field-window was 40 × 40 mm. This paper describes the relationship between the distortion and the shape of the blocker pattern. We got a distortion less than 0.10 μm using a parallel-cross blocker and filling the area outside the blocker pattern with dummy patterns with the same pattern density as the cell region.

Lithography for micro-electronics

Abstract Synchrotron-radiation-based X-ray lithography has been studied for more than 15 years as an alternative to conventional UV lithography. Storage rings, beamlines, X-ray masks, X-ray steppers and other components have been developed and optimized for X-ray lithography. Compact rings have therefore become commercially available, beamlines have been optimized for practical use, and test devices can now be fabricated because of improved total accuracy in the X-ray masks and steppers. This report discusses the status of key techniques involving synchrotron radiation sources, beamlines, X-ray masks, and X-ray steppers.

Stress stabilization of tantalum absorbers on x-ray masks

Abstract We developed a new technique for stabilizing the stress in Ta sputter deposited over epitaxially grown SiC. The technique is to modify the SiC surface before deposition by bombardment with Ar ions. The stress in the Ta deposited over the SiC treated in Ar plasma was much more stable than that of Ta deposited on as-prepared SiC, and its change due to heating for 6.5 hours at 200°C in air was less than 1.5 × 10 8 dyn/cm 2 . Structure analysis of Ta using X-ray diffraction revealed that the more stable Ta has a β -phase structure with strong (002) orientation.

0.35-um rule, high-density, full-chip x-ray mask patterning

We study the dimensional and placement accuracies of masks for X-ray lithography, using a 64 Mbit DRAM as an example. We describe a way to stabilize and control X-ray absorber, and reduce stress induced distortion to within 0.03 micrometers . We improve the accuracy of e- beam writing which takes several hours by automatically calibrating the e-beam deflector periodically and by using a ceramic mask-holder. Placement accuracy was within 0.1 micrometers over a 40 mm square with a 2 hour exposure. We demonstrated that in chip areas with highly regular size and periodicity, we can correct for the proximity effect using only size shifts. In chip areas without high regularity, we used dose correction based on a double-gaussian proximity effect function and improved dimensional accuracy.

Anomalous Etching Residues of Sputter-Deposited Ta upon Reactive Ion Etching Using Chlorine-Based Plasmas

Anomalous etching of Ta which is sputter-deposited on silicon carbide (SiC) films is observed upon reactive ion etching (RIE) using a gas mixture of chlorine and chloroform. We find that α-Ta is hardly etched off by either chlorine-based plasmas or aqueous hydrofluoric acids (HF), while β-Ta is easily etched off by the same methods. The extent of α-Ta depends on the surface treatment of SiC. The difference in chemical reactivity between the α phase and β phase is discussed using photoemission spectroscopy.