Resist process challenges for 32-nm node and beyond are discussed in this paper. For line and space (L/S) logic patterns,
we examine ways to balance the requirements of resolution-enhancement techniques (RETs). In 32-nm node logic
patterning, two-dimensional (2D) layout pattern deformation becomes more severe with stronger RET (e.g., narrow
angle CQUAD illumination). Also pattern collapse more frequently happens in 2D-pattern layouts when stronger RET is
used. In contrast, milder RET (annular illumination) does not induce the severe pattern collapse in 2D-pattern layout. For
2D-pattern layouts, stronger RET seems to worsen image contrast and results in high background-light in the resist
pattern, which induces more pattern collapse. For the minimum-pitch L/S pattern in 32-nm node logic, annular
illumination is acceptable for patterning with NA1.35 scanner when high contrast resist is used. For contact/via patterns,
it is necessary to expand the overlapping CD process window. Better process margin is realized through the combination
of hole-shrink technique and precise acid-diffusion control in an ArF chemically amplified resist.
We have designed the lithography process for 28nm node logic devices using 1.35NA scanner. In the
28nm node, we face on the ultra-low k1 lithography in which dense pattern is affected by the mask
topography effect and the oblique-incidence. Using the rigorous lithography simulation considering
the electro-magnetic field, we have estimated accurately the feasibility of resolution of the minimum
pitch required in 28nm node. The optimum mask plate and illumination conditions have been
decided by simulation. The experimental results for 28nm node show that the minimum pitch
patterns and minimum SRAM cell are clearly resolved by single exposure.
We have developed the lithography process for 32nm node logic devices under the 1.35NA single-exposure conditions. In low-k1 generation, we have to consider the minimum pitch resolution and two-dimensional pattern fidelity at the same time. Although strong RET (Resonance Enhancement Technique) can achieve the high image contrast, it has negative effects like line end shortening and resist pattern collapse. Moderate RET such as annular illumination can combine the minimum pitch resolution and two-dimensional pattern fidelity with hyper NA illumination condition. The simulation and experimental results indicate that the minimum pitches should be determined as 100nm for line pattern and 110nm for contact hole pattern, respectively. The isolated contact hole needs SRAF and focus drift exposure to improve DOF. Embedded SRAM cell of 0.125&mgr;m2 area is clearly resolved across exposure and focus window.
This paper examines improvement in post-etching gate critical dimension (CD) uniformity by post exposure bake
(PEB) temperature control. Although intra-wafer and inter-wafer resist CD uniformity is improved by PEB temperature
optimization, intra-wafer gate CD uniformity after etching could not be improved due to etcher-attributed factors. To
improve these factors, we carried out two-step optimization that combines lithography CD optimization with etching CD
optimization. By using this method, the optimization strategy can clarify the targets of optimization in each step. PEB
temperature optimization was performed by two step optimization in which etcher-attributed CD variations were
canceled out, leading to 66% improvement of gate etching CD uniformity successfully. Without any changes in
modification parameter, this PEB temperature optimization proved to be applicable to several reticle patterns with
different pattern density. Moreover, this optimization method proved the applicability to the gate process for a 55nm
node logic device for the duration of five months without modification. The result proved its long-term stability and
practicality.
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