Image reversal trilayer (IRT) combines three lithographic patterning enhancement approaches: image reversal, spin on
hard masks, and shrink for recess types of features. With IRT, photoresist imaging is done directly on top of the carbon
underlayer. Thick IRT-Carbon Hard Masks (CHM) films provide effective antireflection with high NA lithography and
are more etch resistant than common photoresist. IRT-Silicon Hard Masks (SiHM) can be coated over the resist patterns
in the lithography track. IRT etching reverses the resist pattern into the IRT-SiHM and transfers this image to the IRTCHM.
The recessed patterns in the IRT-CHM are smaller than the CD of the photoresist feature from an inherent
shrinking capability of the IRT-SiHM.
Continuous improvements to both IRT-SiHM and IRT-CHM have been made. Silicon contents in IRT-SiHM have been
pushed as high as possible while not impacting other important properties such as stability, coating quality and resist
compatibility. Newer polysiloxane IRT-SiHM no longer require resist freezing prior to coating. Carbon contents in IRTCHM
have been pushed as high as possible while maintaining solubility and a low absorption which is important when
resist imaging is done directly on top of the IRT-CHM.
Feasibility of this image reversal trilayer process was previously demonstrated on L/S and pillar gratings. Recent work
focused on nonsymmetrical 2D gratings and simultaneous patterning of L/S gratings at different pattern densities.
Particular emphasis is given to pattern density effects which are applicable to any top-coating image reversal process.
This paper describes the lithography, pattern transfer process and 2nd generation hard mask materials developed for IRT
Cost-effective approaches to double patterning are currently an area of intense interest. This paper describes an
update on the progress of AZ's Vapor Reaction Chamber (VRC) freeze approach to double patterning. Swift integration
of the VRC process will depend on whether or not a commercial prime chamber can function as a VRC chamber without
modifications. Procedures for testing this were developed and applied to a lab VRC and 2 AHD modules. Results
demonstrate that for the 8in ADH the across wafer freeze uniformity is within the experimental error of the FT-IR
measurements used to evaluate the process, but that some slight variation was seen for the 12in ADH.
In addition, progress has been made in improving double imaging profiles over earlier work which used the same
resist in both exposures on ArF 1C5D substrates. This work looked at the benefits of using different substrates, establish
a suitable resist for each exposure, and using substrate treatments to improve profiles.
Conventional trilayer schemes alleviate the decreasing photoresist budgets as well as satisfy the antireflection issues
associated with high NA imaging. However, a number of challenges still exist with standard trilayer processing, most
notable among which is the lack of broad resist compatibility and trade-offs associated with improving Si content, such
as stability and lithography performance. One way to circumvent these issues is to use a silicon hard mask coated over a
photoresist image of reverse tone to the desired pattern. Feasibility of this image reversal trilayer process was
demonstrated by patterning of trenches and contact holes in a carbon hard mask from line and pillar photoresist images,
respectively. This paper describes the lithography, pattern transfer process and materials developed for the image
reversal trilayer processing.
Trilayer stacks with alternating etch selectivity were developed and extensively investigated
for high NA immersion lithography at 32nm node and beyond. This paper discusses the
fundamental aspects of the Si-containing BARC (Si-BARC) materials with ultra-high silicon
content and carbon-rich underlayers that we developed. Designing of materials at a molecular level
is presented. It was demonstrated that this fundamental understanding assisted in achieving
satisfactory shelf life and excellent coating defect results.
Prolith® simulations using trilayer stacks showed superior reflectivity control for hyper-NA
immersion lithography. The impact of high incident angles on substrate reflectivity was analyzed
and this paper demonstrated that trilayer scheme provides wider process windows and is more
tolerant to topography than conventional single layer BARC. Extensive resist compatibility
investigation was conducted and the root causes for poor lithography results were investigated.
Excellent 45nm dense lines performance employing the spin-on trilayer stack on a 1.2 NA
immersion scanner is reported. In addition, pattern transfers were successfully carried out and the
Si-BARC with high silicon content demonstrated outstanding masking property. In comparison to
the theoretical %Si values, better correlation with etch selectivity was observed with
experimental %Si. Furthermore, this paper addresses the wet rework of trilayer materials and
results using Piranha rework are presented. Clean 12in wafers were obtained after reworking
trilayer stacks, as evidenced by defect analysis.
Spin-on trilayer materials are increasingly being integrated in high density microfabrication that use high NA ArF
lithography due to dwindling photoresist film thicknesses, lower integration cost and reduced complexity compared to
analogous CVD stacks. To guide our development in spin-on trilayer materials we have established etch conditions on an
ISM etcher for pattern transfer through trilayer hard masks. We report here a range of etch process variables and their
impact on after-etch profiles and etch selectivity with AZ trilayer hard mask materials. Trilayer pattern transfer is
demonstrated using 1st and 2nd minimum stacks with various pattern types. Etch recipes are then applied to blanket
coated wafers to make comparisons between etch selectivities derived from patterned and blanket coated wafers.
Substrate reflectivity control plays an important role in immersion lithography. Multilayer
bottom anti-reflective coatings (B.A.R.C.s) become necessary. This paper will focus on the
recent development in organic ArF B.A.R.C. for immersion lithography. Single layer low k ArF
B.A.R.C.s in conjunction with multilayer CVD hard mask and dual layer organic ArF B.A.R.C.
application will be discussed. High NA dry and wet lithography data will be presented. We will
also present the etch rate data, defect data and out-gassing property of these new B.A.R.C.
New challenges face ArF bottom antireflection coatings (BARCs) with the implementation
of high NA lithography and the concurrent increase use of spin-on hard masks. To achieve superior
reflectivity control with high NA at least two semi-transparent ARC layers, with distinct optical
indices, are necessary to effectively lower substrate reflectivity through a full range of incident
angles. To achieve successful pattern transfer, these layers in conjunction with the organic resist,
should be stacked with an alternating elemental composition to amplify vertical resolution during
etch. This will circumvent the inherent low etch resistance of ArF resist and the decreasing film
thicknesses that accompanies increasing NA. Thus, incorporating hard mask properties and
antireflection properties in the same two layer system facilitates pattern transfer as a whole rather
than just enhancing lithography. As with any material expected to exhibit multiple roles there is a
delicate balance between optimizing materials with respect to one of its roles while not impairing its
other roles. We will discuss some of these conflicts and present Si-BARCs and carbon rich
underlayers which aim to balance these conflicts. In this paper we will explore simulations aimed at
finding the best film thicknesses and optical indices, etch rate selectivity, and lithographic
performance of high silicon content and high carbon content BARC materials designed to meet the
demands of both high NA lithography and trilayer processing.
As the feature sizes of integrated circuits shrink, highly anisotropic etching process (i.e., ion-assisted plasma etch, or reactive ion etch (RIE)), becomes even more essential for successful pattern transfer in the fabrication of semiconductor devices. The stringent 193 nm lithography process necessitates the use of bottom anti-reflective coating (BARC) for controlling reflections and improving swing ratios. Prior to RIE of a patterned wafer, the BARC layer must first be opened to allow pattern transfer from the resist mask to the underlying films. As we enter the era of sub-90nm imaging, minimum loss of the photoresist during the BARC open step is becoming more critical, since the demand for higher optical resolution dictates the use of ever thinner resist films. This in turn requires higher etch rate of BARC materials. In this paper we report on the impact of etching gas chemistries on the etch rates of BARC materials. The correlation between the etch chemistry and BARC products will be discussed. Reactive ion etch rates for blanket BARC coatings and BARCs under resist patterns were measured. Etch rates of BARC products of various material compositions were measured with a typical ArF resist as reference. It is well known that the chemical composition and structure of organic materials essentially determine the etch rates under certain etch process conditions. The correlations between etch rates and BARC polymer chemistry are reported. Etch chemistries, (i.e. the chemical interaction of plasma reactive ions with BARC materials), may also have profound effects on etch rates. Here we report on results obtained using four etching gas chemistries to study how oxygen contents, polymerizing gases, and inert gas effect the etch rates of different ArF BARC products.
We will describe our barrier coat approach for use in immersion 193 nm lithography. These barrier coats may act as either simple barriers providing protection against loss of resist components into water or in the case of one type of these formulations which have a refractive index at 193 nm which is the geometric mean between that of the resist and water provide, also top antireflective properties. Either type of barrier coat can be applied with a simple spinning process compatible with PGMEA based resin employing standard solvents such as alcohols and be removed during the usual resist development process with aqueous 0.26 N TMAH. We will discuss both imaging results with these materials on acrylate type 193 nm resists and also show some fundamental studies we have done to understand the function of the barrier coat and the role of differing spinning solvents and resins. We will show LS (55 nm) and Contact Hole (80 nm) resolved with a 193 nm resist exposed with the interferometric tool at the University of New Mexico (213 nm) with and without the use of a barrier coat.
Extending the resolution capability of 193nm lithography through the implementation of immersion has created new challenges for ArF B.A.R.C.s. The biggest of which will be controlling reflectivity over a wider range of incident angles of the incoming imaging rays. An optimum B.A.R.C. thickness will depend on the angle of incidence of the light in the B.A.R.C. and will increase as the angle increases. At high angles different polarization have different optimum thicknesses. These confounding effects will make it increasingly difficult to control reflectivity over a range of angles through interference effects within a single homogenous B.A.R.C. Unlike single layer B.A.R.C.s, multilayer B.A.R.C.s are capable of suppressing reflectivity through a wide range of incident angles. In fact, remarkable improvements in antireflective properties can be achieved with respect to CD control and through angle performance with the simplest form of a multilayer B.A.R.C., a dual layer. Here we discuss the attributes of an all organic dual layer B.A.R.C. through simulations and preliminary experiments. One attribute of an organic over inorganic B.A.R.C. in high-NA lithography is its ability to planarize topography. ArF scanners designed to meet the needs of the 45nm node will have a very small depth-of-focus (DOF) which will require planar surfaces.
The leaching of ionic PAGs from model resist films into a static water volume is shown to follow first order kinetics. From the saturation concentration and the leaching time constant, the leaching rate at time zero is obtained which is a highly relevant parameter for evaluating lens contamination potential. The levels of leaching seen in the model resists generally exceed both static and rate-based dynamic leaching specifications. The dependence of leaching on anion structure shows that more hydrophobic anions have lower saturation concentration; however, the time constant of leaching increases with anion chain length. Thus in our model system, the initial leaching rates of nonaflate and PFOS anions are identical. Investigation of a water pre-rinse process unexpectedly showed that some PAG can still be leached from the surface although the pre-rinse times greatly exceeded the times required for saturation of the leaching phenomenon, which are expected to correspond to complete depletion of leachable PAG from the surface. A model is proposed to explain this phenomenon through re-organization of the surface as the surface energy changes during the air/water/air contact sequence of the pre-rinse process.
As the semiconductor industry sails into the 100nm node and beyond, enabled by the integration of ArF lithography, new Bottom Antireflective Coatings (B.A.R.C.s) are required to address challenges associated with this new technology. Of these challenges, higher etch rates and better compatibility with the over coated resist are of central importance. New polymer platforms and additives in B.A.R.C. formulations will be required to overcome these challenges. The intent of this publication is to introduce our newly developed B.A.R.C.s designed to addresses the challenges of ArF lithography. All are currently available for integration into mass production of sub 100nm integrated circuit devices.