Epoxy-novolak thick film resists are of interest for applications where the resist pattern remains in the device serving as
mechanical alignment aids, micro channels or protection layers. For these applications, good mechanical properties are of
interest. Unfortunately mechanical strength comes with high cross-linking density and, therefore, high tensile stress. We
report here on a comparison of three commercially available thick film resists with respect to the following criteria:
thickness and uniformity on high topography wafers, i-line photo speed, adhesion on Si<sub>3</sub>N<sub>4</sub>, hardness and plasticity, glass
transition temperature and wafer warp. The three resists (2 types of SU-8 [MicroChem Corp.] and one type of TMMR
[Tokyo Ohka Co., LTD]) show different behavior as a result of the different solvent, photo-acid-generator (PAG) and
polymer properties, and trade-offs have to be made depending on the applications.
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.
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.
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