Hideyuki Jinbo

0.2 mu m or less i-line lithography by phase-shifting-mask technology

A novel phase-shifting technology has been developed for improving resolution of isolated patterns. A phase-shifter edge line (PEL) is used as an opaque mask instead of a chrome pattern. The intensity distribution of the PEL is sharper than those of chrome patterns under the same illumination conditions. 0.15 mu m wide space patterns in LMR-UV (negative resist) are delineated in the focus range of more than 1.5 mu m by using a PEL-mask and an i-line stepper. In the same manner, 0.15 mu m wide line patterns are clearly formed by use of PFR-TT15 (positive resist). In addition, a new modification adapted to hole or pillar patterns has been developed by applying double exposure with a pair of PEL-masks. By this method 0.2 mu m hole patterns in LMR-UV are successfully delineated in a wide focus latitude of 1.5 mu m.<<ETX>>

Sub-Half-Micron i-Line Lithography by Use of LMR-UV Resist

Negative photoresist, LMR-UV, has been developed for i-line lithography. It resolves isolated 0.3 µm space and 0.35 µm hole patterns of 1.0 µm thickness by using a 0.42-numerical-aperture i-line reduction projection aligner. LMR-UV gives overhung profiles because of its large absorption coefficient of 3.8 µm-1 at the i-line. New phase-shifting mask patterns which are adapted to isolated space and hole patterns for negative resist have been developed. By use of this mask, LMR-UV clearly resolves 0.25 µm space and 0.3 µm hole patterns by using the i-line aligner. This phase-shifting mask improves both resolution and focus margin.

Poly(siloxane)-Based Chemically Amplified Resist Convertible into Silicate Glass

A novel poly(siloxane)-based chemically amplified resist has been developed. The polymer is a glass precursor, and it can be converted to silicate glass through merely a lithographic procedure. The developed resist has a high sensitivity of 1.3 µC/cm2 and a high resolution of 0.1 µm lines and spaces. Simple and highly selective etching processes using the silicate glass mask obtained from this resist system have been proposed, which is substantiated in the bilevel resist process and tungsten-etching process.

Subhalf‐micron patterning of negative working resist by using new phase‐shifting masks

A lithographic technique using phase‐shifting masks combined with i‐line reduction projection printing in negative working results has been evaluated for subhalf‐micron patterning. The combination of a ‘‘standard’’ phase‐shifting mask and image reversal resist, AZ 5214E (from Hoechst), makes it possible to resolve 0.3‐μm line and space patterns with practically enough focus latitude on a 0.42 numerical aperture i‐line aligner (σ:0.5). New phase‐shifting masks which are adapted to isolated spaces and holes for negative working resist have been developed. Of these new masks, a mask whose patterns consist of only shifter film gives excellent results. By using this mask and the i‐line aligner, 0.3‐μm hole patterns are clearly resolved in LMR‐UV (low‐molecular‐weight resist for UV lithography resist) film.

Sub-Quarter-Micron Gate Fabrication Process Using Phase-Shifting Mask for Microwave GaAs Devices

A phase-shifting mask technique using an i-line stepper was applied to the gate formation process of AlGaAs/GaAs high electron mobility transistors (HEMTs). To obtain a fine gate pattern of less than a quarter micron, the phase-shifter edge-line mask, which has the highest resolution and wide focus margin for an isolated pattern, was used and the double exposure process was developed to form a real gate pattern. The controllable gate length was in the range of 0.50-0.15 µm. By using this technique, 0.18 µm-gate HEMTs with good and uniform microwave performances in a 3-inch wafer were obtained. This technique has great advantages for applications to microwave GaAs devices and ultrahigh-speed GaAs LSIs.

A novel technique for shifter void defect repair by a focused ion beam tool

A new phase‐shifting mask repair concept, transferred image correction (TRIC), for repairing shifter void defects is proposed. TRIC repair fills shifter voids with an opaque material by focused ion beam (FIB) deposition, in which a FIB tool is used to partially remove Cr adjacent to the void. The transferred image of a TRIC‐repaired mask pattern corresponds to that of the original mask pattern with no defects.

Asymmetric overhung resist profile fabricated by optical lithography

We propose a new and simple fabrication technique for resist patterns of asymmetric overhung profiles. This technique uses an asymmetric blind phase edge line (AB PEL) mask and a negative photoresist which has a large absorption coefficient. The AB PEL mask has repeated chrome line patterns, called blind patterns, to reduce light intensity at large undercut overhangs of resist space. The bottom part of the resist film under the blind area is not sufficiently irradiated to become insoluble in the developer. An asymmetric overhung profile with 0.25 μm space width at the resist top is fabricated. This profile enables fabrication of asymmetric gate recesses for field‐effect transistors in compound semiconductors.

Application of conventional defect repair technique to phase-shifting masks

We studied phase shifter defect repair techniques which use conventional mask repair tools. This paper describes two repair techniques applicable to phase shifter residue defects on the etch-stop layer of a quartz substrate. These new techniques, which use a conventional Nd:YAG laser and a Focused Ion Beam (FIB) are beam-on-edge and absorber implantation. Beam-on-edge repair removes phase shifter pin-dots by optimally applying an Nd:YAG laser under conventional mask repair conditions. Absorber implantation repair optimizes phase shifter form combining FIB and Nd:YAG laser tools.

Evaluation of shifter edge shape on attenuated phase-shifting mask

The influence of edge taper angle and edge roughness on transferred wafer image was investigated by computer simulation for sub-half-micron space and hole patterns on the wafer. The exposure latitude for a 0.3- micrometers space pattern on the wafer is almost unchanged for angles exceeding 60 degrees. The exposure latitude for 0.3-, 0.35-, and 0.4- micrometers hole patterns remains almost unchanged unless the edge roughness exceeds 0.04 micrometers . However, when shifter thickness on the pattern edge decreases 50%, a particularly bad case, and edge roughness of 0.01 micrometers results in 25% degradation of exposure latitude. Taking simulation results into consideration, we optimized the mask manufacturing process using wet etching for CrO-based phase shifters and obtained an edge roughness of approximately 0.01 micrometers and an edge taper angle greater than 60 degrees. Experiment showed that wet-etched mask performance is equivalent to that of the dry-etched mask.

Chemically amplified resist convertible into inorganic silicate glass (GPR)

We have developed a unique chemically amplified negative-type resist composed of poly(t- butoxysiloxane) and photoacid generator, the GPR (glass precursor resist), which can be converted into inorganic silicate glass. Poly(t-butoxysiloxane) is a specially designed SiO2 precursor masked by t-butoxyl groups. To confirm the mechanism of condensation to SiO2 an intermediate trapping experiment was carried out. GPR exposed at a low dose is fully developed by alkaline solution to give a positive tone; on the other hand, high-dosage GPR gives negative tone by means of organic solvent development. They correspond to the formation of poly(hydroxysilane) and SiO2 respectively. Deprotection proceeds readily even at low temperature, whereas condensation requires thermal assistance. Decreasing the content of t-butoxyl groups enhances the sensitivities to electron beam exposure. Precursor polymers with several degrees of branching were synthesized. The high-branching polymer provides high sensitivity because its network grows abruptly with condensation. GPR has high resolution and high sensitivity. The fine patterns can be resolved with the practical dose latitude using an electron beam direct-writing system.