Resist reflow techniques have widely been adopted for lithography in resolution limited region. During the reflow process, resist patterns are heated over its glass temperature through number of temperature steps. Early works have focused how the temperature steps during heat-up process can be effectively controlled for critical dimension (CD) and the pattern profile after reflow. However, for a specific application that needs moderate CD and profile change, adjusting heat-up parameters would not be sufficient to achieve good CD and profile control and additional relevant parameters should be accounted.
In this paper, we count surface treatment condition on reflow process as an additional control parameter. We measured CDs with varying surface treatment parameters of substrate on square arrays of resist islands with 300 nm island-to-island gap space. We found that the amount of after develop CD to after reflow CD bias decreases as contact angles of substrates increases. In conclusion, we prove the resist reflow CD can be controlled precisely by adjusting the substrate coverage of hydroxyl groups during adhesion treatments in addition to the temperatures for the resist reflow process.
Sub-resolution assistance feature (SRAF) has become one of popular resolution enhancement technique because it is
the most easily applicable technique that can be adopted for sub-65 nm node technology. The SRAF can be realized, for
example, by locating lines having width below resolution limit around isolated feature. With the SRAF, intensity profile
of the isolated feature will be modified to dense-like one and, as a result, focus response of the isolated feature can be
improved up to dense feature level. Previous works on SRAF have focused mainly on the critical dimension (CD) margin
window. However, CD margin window is not sufficient to evaluate optimum SRAF configuration because process
margin degradation due to irregular pattern profile such as line edge roughness (LER) would become more prominent as
technology node goes beyond sub-65nm node. Therefore, appropriate methodology to optimize SRAF configuration both
for CD margin window and pattern profile is indispensable for those applications.
In this paper, we focus on the impact of SRAF configuration to pattern profile as well as CD margin window. The
SRAF configuration was adjusted by varying assistance feature to main feature distance and pitch of the assistance
features at mask level. Pattern profile was investigated by measuring LER with varying assistance feature parameters
quantitatively. From the results, we prove the impact of SRAF configuration both on pattern profile and CD margin
window. We also show that the experimental data can easily be predicted by calibrating aerial image simulation results to
measured LER. As a conclusion, we suggest methodology to set up optimum SRAF configuration with regard to both
CD margin window and pattern profile.
With the development of a CMOS Image Sensor (CIS), the pixel size of a CIS is continuously decreasing. It makes the
photo diode smaller and smaller in the unit pixel and, as a result, the sensitivity is reduced at the same time. A micro lens
(ML) is added to improve the sensitivity of CIS. The size of ML is reduced with the pixel size and it almost arrived at the
limitation of the size which is governed by diffraction. In this paper, we simulate the diffraction feature of a ML with an
electro-magnetic wave simulation. The efficiency and the crosstalk of some ML which have a size near the diffraction
limit are calculated and compared. From the simulation result, we suggest a guide line of the ML design.
The pattern deformation such as photoresist lifting after lithography due to not enough
photoresist adhesion to substrate is become critical issue when aspect ratio is much higher than
what photoresist adhesion can support. This aspect ratio is getting higher when our design rule
of device requests smaller feature size in lithography process. The BARC (Bottom Antireflective
Coating), which advanced lithography is using, is very good layer to improve adhesion of
photoresist since they are same kind of chemical. However, BARC needs extra etching process
before main etching which is step to remove substrate. Sometimes, this BARC etching step
generated defects which makes yield loss. Especially, lithography step for metallization with
aluminum likes without BARC process to be free from those defect. We think that adhesion of
photoresist on metal substrate such as aluminum or TiN is very important to develop lithography
process without BARC. The adhesion change between photoresist and metal substrate will be
changed as function of how we apply pretreatments for metal substrate. The typical
pretreatments before patterning are dry ash, wet cleaning and HMDS treatment.
In this paper, we study that adhesion changes as function of pretreatments and their
mechanism. To understand the interaction between photoresist and substrate, we analyze
surface change of wafers which prepared with several different experimental conditions using
XPS (X-ray photoelectron spectroscopy) and Dynamic Contact Angle Analyzer. The results will
explain how photoresist adhesion may be changed with different pretreatment conditions and
how we can optimize process condition to improve photoresist adhesion without BARC.
We discussed to KrF process extension for 90 nm technology node. The continuous shrinkage of critical dimensions on
sub 130 nm devices becomes a key point to improve process margin with pattern resolution problem for lithography.
Recently, according to development demand of high density and high integration device, it is tendency that the shrink
rate of design rule is gradually accelerated. It is difficult to develop with image contrast problem around k1=0.25 which
is a theoretical process limit region. We need to technology development which is available to having resolution for sub
90nm line and space by using KrF lithography not by using ArF lithography.
In generally, KrF have not been used in nano-process such as 90nm technology. In this study, however, we can apply
the KrF in 90nm technology by means of minimizing the error range in the nano-process, optimizing the process, and
extending the process margin. This Application of KrF in 90nm technology results in elimination of additional
investment for development of 90nm technology.
Finally, we will show which simulation and experimental results such as normalized image log slope, pupil plane,
image of focus variation, process window, top view image, photo resist and etch profile, and pitch linearity.
In resolution limited lithography process, the image deformation is getting severer. This is very important area where
we need to fully understand and improved since the image deformation is directly giving poor CD control effect.
Especially, contact hole image will be more sensitive since it has lower k1 factor that line and spaced pattern. This image
deformation of contact hole can give some severe electrical fail due to not opened contact. In our case, we observed
some critical failure mode of diagonal induced by abnormal contact hole shape of rough edge.
In this paper, we investigate how deformed contact hole image impacted on degradation of device performance in
electrical properties and yield and how we can improve it. To quantitatively analyze image deformation of contact hole,
we recommend new measurement method first. This new measurement gives exact image deformation amount at
different experimental conditions.
Finally, we will show how experimental conditions such as soft bake temperature, post expose bake temperature,
hardening bake temperature, illumination condition and mask bias change image deformation of contact hole.
Flare has been important variable to achieve good CD control in low k1 lithography. Early works on flare
have focused on long-range DC and local flare, with an attention on how to measure flare and how flare
impact on CD control within theoretical model for ideal situation. As pattern size decreases below 100 nm,
however, short-range flare begins to appear prominently beyond that technology node. It has been pointed
out that process conditions such as photo resist thickness, substrate film stacks, and even some times
photo masks can be important variables for short-range flare but impact of process variables on flare at
illumination level has less been understood yet. Recently, Yun et al. have shown that the illumination
conditions such as coherence factor and illumination aperture shapes also give impact on short-range flare.
They found that the amount of short-range flare, the additional portion of the diffraction image to the
ideal one, increases as the illumination aperture size increases but inner radius of the annular illumination
apertures affect little on the amount of the short-range flare.
In this paper, as the series of the experiments by Yun et al., we will prove detailed relation between
illumination aperture shapes and the short range flare by exploring its impact with number of off-axis
illumination apertures including multi-pole illumination apertures, in addition to the previous data on
partially coherent conventional and simple annular illumination apertures. We utilize the 193-nm scan-and-step exposure tool and evaluate the short-range flare by measuring CD on the 100 nm lines surrounded by clear window having various open ratios. The extended data on various off-axis
illumination apertures reveal clarify the impact of illumination aperture shape on the short-range flare.
Flare has been important variable to obtain good CD control in the resolution limited lithography area such as sub-90 nm node. So far, many papers have been reported about how to measure flare and how flare impact on CD control. And some papers have tried to understand theoretical mechanism of flare. However, we expect that the illumination apertures such as the partial coherence factors or the modified illumination aperture shapes would also give impact on the flare. The short-range flare is changing as the open ratio variation on the mask. We assume that the illumination aperture shape change will also give similar effect as the open ratio variation on the mask. In this paper, we will show how the illumination aperture shapes give effect on short-range flare. Experiments were done for 100 nm lines surrounded by clear window having different width from 1 μm to 20 μm. We utilized the 193 nm scan-and-step exposure tool with the partially coherent conventional and off-axis illuminations apertures. In conclusion, we will prove the relationship between flare and illumination apertures.