The drive to smaller, less expensive, and faster devices requires radical changes in material development. The increased
material requirements drive complex processes that in turn drive equipment requirements. For the photolithography area
this demand for improved materials is seen in growing requests for device level-specific tuning of organic bottom antireflective
coatings (BARCs) or photoresists for certain imaging requirements, such as numerical aperture, immersion
conditions, and optical parameters. To test and utilize the myriad of BARC materials, there is a need to install them on a
coater-track quickly and efficiently. Installation typically requires a new filter installation, dispense line cleaning, and
usually a minimum of 8-10 L of material to clear out bubbles and other nuisance defects before coating test wafers. As
the number of materials increases, the ability to quickly prime a new filter becomes increasingly important. In this
study, the Entegris IntelliGen® Mini dispense system was utilized to test various pump priming processes to ultimately
minimize the volume purged to reach a defect baseline. In addition, the impacts of the filter media and filter retention on
priming efficiency were studied. Results show that priming processes that were not matched to the filter in use could
actually cause the defects to increase during the process, thus requiring additional purging to reach baseline, and thereby
negating any time or volume savings. Properly programmed priming recipes reduced the purging time and the purging
volume by 50-70%.
Measuring coating defects on two or more blanket film layers is difficult and can be misleading due to reflectivity
changes from the bottom layer, and surface roughness not present when the substrate is only polished silicon. To
improve signal-to-noise ratio and establish a lower limit for particle size detection, polystyrene latex (PSL) spheres are
deposited on the film stack. Particles as small as 54 nm were detectable on a stack 330-nm thick using a Hitachi LS
Series Surface Scanning Inspection System (SSIS) and RS5500 Defect Review Scanning Electron Microscope
(DRSEM). These systems have advanced capabilities enabling automated detection, classification, and characterization
of defects down to 30 nm or smaller on some substrates and films. Haze wafer maps are related to surface roughness and
reflectivity and show unusual asymmetries possibly caused by dispense problems or exhaust flow patterns during baking.
These maps can be helpful to find problems in the coating system, even if film thickness is on target. Preliminary testing
results are presented for a typical trilayer pattern stack for high-resolution 193-nm patterning consisting of a silicon spinon
hardmask (HM) layer on top of a spin-on carbon (SOC) layer. The majority of the defects were caused by bubble
formation within the HM that was modulated by process conditions used for these tests. A higher spin speed for the HM
coating produced lower defects, most likely due to a thinner film with less trapped solvent during baking, but this effect
will require more study, as it could also be due to a faster evaporation rate caused by higher airflow. Pre-wet, spin time,
and bake temperature did not produce significant effects within these tests, but showed trends requiring further study.
These advanced spin-on HM materials can be applied as thin as 15 to 20 nm due to their high etch selectivity. With the use of such high-resolution defect metrology, very subtle chemical interactions and process effects can be examined to find the ideal process conditions for both the SOC and HM layers.
Maintaining low-defect spin-applied films is paramount to the success of semiconductor manufacturing.
While some spin-on films have a low number of defects as coated, defect levels can rise with the number of
wafers processed. Thin organic films may outgas or sublime during the post-coat baking process, or even
during subsequent exposures to deep or extreme ultraviolet radiation. If these outgassing components
collect on the lid of the hot plate chamber, there is an increased risk of "fall-on" defects on subsequently
processed wafers. To increase throughput, preventive maintenance and cleaning schedules are pushed to
the limit to provide maximum output from the track. New materials must be designed to produce minimal
outgassing to ensure maximum throughput without defects. Early tests for measuring outgassing provided
qualitative results gained from collecting the condensed outgassing components on a quartz wafer and
measuring the absorbance of the resulting film. A more advanced technique involves the use of a newly
designed quartz crystal microbalance (QCM) to more carefully quantify the amount of outgassing. As the
industry continues to mature, more sensitive measurements are required to design new materials with even
lower outgassing from sublimation. The inverted wafer test and the QCM techniques provide
complementary information about outgassing and together provide a better overall prediction of the defectforming
potential than either technique alone.
Minimizing defects in spin-on lithography coatings requires a careful understanding of the interactions between the spin-on
coating material and the filtration and dispense system used on the coating track. A wet-developable bottom anti-reflective
coating (BARC) was examined for its interaction with polyamide and UPE media when utilizing the Entegris IntelliGen Mini dispense system. In addition, a new method of priming the filter and pump is described which improves
the wetting of the filter media, preventing bubbles and other defect-generating air pockets within the system. The goal is
to establish plumb-on procedures that are material and hardware specific to avoid any defect problems in the coating
process, as well as to gain a better understanding of the chemical and physical interactions that lead to coating defects.
Liquid particle counts from a laboratory-based filtration stand are compared with on-wafer defects from a commercial
coating track to establish a correlation and allow better prediction of product performance. This comparison in turn will
provide valuable insight to the engineering process of product filtration and bottling at the source.
Interactions between the silicon hardmask and the photoresist have received considerable attention for
utilization of these materials in a trilayer scheme. In contrast, the interactions between the carbon layer and
the silicon hardmask have received little or no consideration. In this paper, we present the effects of these
interactions on the performance of the silicon hardmask. Poor interactions were observed to result in a more
hydrophilic surface and poor lithographic performance of the silicon hardmask. However, beneficial
interactions between the carbon layer and the silicon hardmask resulted in a silicon film that was denser with
a hydrophobic surface. The resulting denser film had a slower CF4 etch rate and produced square, clean profiles.
This paper presents robust trilayer lithography technology for cutting-edge IC fabrication and double-patterning
applications. The goal is to reduce the thickness of a silicon hardmask so that the minimum thickness of the
photoresist is not limited by the etch budget and can be optimized for lithography performance. Successful results
of pattern etching through a 300-nm carbon layer are presented to prove that a 13.5-nm silicon hardmask is thick
enough to transfer the line pattern. Another highlight of this work is the use of a simulation tool to design the stack
so that UV light is concentrated at the bottom of the trenches. This design helps to clear the resist in the trenches
and prevent resist top loss. An experiment was designed to validate the assumption with 45-nm dense lines at
various exposure doses, using an Exitech MS-193i immersion microstepper (NA = 1.3) at the SEMATECH Resist
Test Center. Results show that such a stack design obtains very wide CD processing window and is robust for 1:3
line patterning at the diffraction limit, as well as for patterning small contact holes.
The impact of bottom reflection on critical dimension (CD) processing window is intensively investigated with a
simulation using a full diffraction model (FDM) in which the effective reflectivity is calculated from standing wave
amplitude. Most importantly, the optical phase shift of the reflection is used as a design criterion and was found to be
the primary factor that affects the UV distribution, and, hence, has a strong impact on exposure latitude and depth of
focus. Foot exposure (FE) is introduced as a new metric to characterize the phase shift. Some single-layer and dual-layer
bottom anti-reflective coating (BARC) designs were implemented with an Exitech MS-193i immersion micro-stepper
(NA=1.3) for 45-nm dense lines at the Resist Test Center (RTC) at International SEMATECH, Albany, New
York. The experimental results show that FE is closely related to the CD processing window. In contrast to
conventional BARC usage, a small amount of substrate reflection with a controlled optical phase shift dramatically
improves CD processing window.
Plasma trimming is a method widely used to achieve small feature sizes beyond the capability of photolithography.
Plasma processes reduce the dimensions of photoresist, anti-reflective coating, hardmask, or device substrate
patterns with varying degrees of anisotropy. The vertical trim rate is higher than or equal to the lateral trim rate.
As a result, much of the line-edge roughness from the resist pattern remains. High aspect-ratio resist patterns
are subject to necking and collapse during this process. However, by using a developer-soluble hardmask in
place of traditional anti-reflective layers, it is possible to achieve controllable, anisotropic trim rates, as well as
reduced roughness. Moreover, the process benefits from a very thin resist, or imaging layer, instead of relying on
a thicker mask with a high aspect-ratio. The hardmask is patterned during a standard resist develop step, and
the resist may be stripped prior to substrate etching due to the high etch resistance of the hardmask. Many other
advantages have been discovered from this wet trimming process, including high resolution, extended depth of
focus, controllable trim rate, and lower cost than traditional methods.