Hellmut Ahne

Photopatternable insulating materials

Present direct photopatternable insulating materials are only available as negative working systems. In connection with the increasing requirements for resolution capability, higher processing performance and for environmental reasons, positive working systems offer significant advantages for the future. One of the most promising systems is a formulation composed of a polybenzoxazole (PBO) precursor and a diazoquinone sensitizer. Compared with the well known novolac-based positive resists which are used for fine patterning in IC manufacturing, the annealed PBO resist incorporates both resist and dielectric properties. The present paper discusses general aspects of positive and negative mode patterning with the emphasis on positive working PBO precursors which fulfill the most important future requirements.

Application aspects of the Si-CARL bilayer process

The basic chemistry and lithographic characteristics of anhydride- containing, diazo-based NUV and DUV resists as well as silylation of top resist patterns with aqueous solutions of silicon-containing diamines in the Si-CARL bilayer process (CARL: Chemical Amplification of Resist Lines) were reported recently. This paper describes technical control of the Si-CARL process for g-line and DUV in a 6 inch pilot line using automatic equipment. Linewidth uniformity of top resist patterns is not affected by silylation and is found to be 0.045 micrometers (3(sigma) ) for nominal 0.4 micrometers lines/spaces, the resolution limit of the 0.55 NA g- line stepper used. Both overexposure and linewidth increase due to silylation conditions can be used in the Si-CARL process for optimization of defocus latitudes. With the use of a 0.55 NA g-line stepper total defocus latitudes are 2.8 micrometers for 0.6 micrometers equal lines and spaces and > 3.2 micrometers for isolated 0.6 micrometers spaces. In order to meet the requirement for sufficient throughput on KrF-excimerlaser steppers the sensitivity of DUV top resists is improved by chemical variations of resist polymers. The use of maleimide-containing resist polymers with improved alkaline solubility in diazo-inhibited top resists allows resolution of 0.25 micrometers lines and spaces at 161 mJ/cm2 on a 0.37 NA KrF-excimerlaser stepper. Further considerable improvement of DUV sensitivity to 11 mJ/cm2 was achieved using an acid-catalyzed top resist based on onium-salt and a terpolymer containing N-t-BOC-maleimide-units.

High Performance Resists Tailored for 248 nm Chemical Amplification of Resist Lines Technology

Different dry developable resist systems operating in positive bilayer (Si-CARL) and negative top surface imaging (Top-CARL) modes were investigated for application in 248 nm lithography. After exposure with the KrF excimer laser projection aligner (NA=0.37), development, aqueous silylation and oxygen reactive ion etching, 0.25 µm structures were obtained as the ultimate resolution of Si-CARL with a topresist containing diazoketone photoactive compounds. The process latitudes for 0.4 µm and 0.5 µm lines and spaces amount to 25% and 30% for exposure and to 3 µm and 3.2 µm for defocus, respectively. Comparable values were determined for an alternative Si-CARL system with a new acid catalysed topresist. The required doses for zero bias exposure are 65-70 mJ/cm2 (diazoketone) and 21 mJ/cm2 (acid catalysed). The Top-CARL resist also utilizes the acid catalysed deprotection chemistry for selective silylation of the exposed areas. The preliminary formulation presented well-shaped 0.35 µm structures at 10 mJ/cm2.

Benefits and prospects of aqueous silylation for novel dry developable high resolution resists

The paper presents a novel surface imaging resist, consisting of an anhydride-containing copolymer and a diazoquinone photoactive compound (PAC). As base resin, alternating copolymers of styrene and maleic anhydride were prepared which show benefits such as high glass transition temperature (Tg = 170 °C) or low deep-UV absorbance (0.12/pm at 248 nm), in addition to the simplicity of synthesis with high yields. After imaging exposure, the exposed areas are selectively silylated in a standard puddle development track at room temperature within 90 to 120 s md. rinsing. The silylation is performed with an aqueous solution ofabis-aminosiloxane in water and a dissolution promoter and is accompanied by a film thickness increase, the extent of which depends on several factors such as exposure dose, PAC content in the resist, molecular weight of the base resin, aminosiloxane concentration and silylation time. The resist is developed through reactive ion etching in oxygen plasma, giving negative tone patterns. Lateral structure deformation has not been observed with this system since the resist is silylated far below the Tg of the base resin. The use of suitable 2-diazo-1-naphthalenone-4-sulphonic acid esters as PAC and the absence of crosslinking during deep-UV exposure offer the advantage that the same resist can be applied in the same mode (neg.) for i-line and KrF excimer laser lithography. By this means, lines and spaces down to 0.4 pm and 0.3 pm were achieved in 2 pm thick resist after exposures with an i-line (NA = 0.4) or KrF excimer laser stepper (NA =0.37), respectively.

Chemical amplification of resist lines: a novel sub-half-micron bilayer resist tehnique for NUV and deep-UV lithography

The Chemical Amplification ofResist Lines (CARL) and its practicability in a bilayer/O2RIE processing scheme (Si-CARL) is described. Novel anhydride-containing resins and photoactive compounds of the diazonaphthoquinone type are used in top resists with sub-halfmicron resolution capability in both NUV and KrF excimer laser lithography. The silylating treatment of alkaline developed, positive tone top resist patterns with aqueous solutions of bisaminoalkyl-oligodimethylsiloxanes can be performed on standard puddle development tracks at room temperature. A concomitant linewidth increase is used to reduce dimensions of resist openings, e.g. trenches or contact holes, with good process control. Equal lines and spaces were achieved by treatment of slightly overexposedtopresist patterns. Modified top resistpatterns are transferred intothe underlying 1 .3 -1.8 j.tm thick planarizing layer without linewidth variationtogive steepprofiles and high aspect ratios. Thus, 0.3 tm resolution is obtained with KrF excimer laser exposure (0.35 NA). The attained resolution of 0.3 tm features with g-line exposure (0.55 NA) represents ak-factor of 0.38, according to the Rayleigh relation. This paper discusses process and lithographic performance characteristics of the novel Si-CARL process.