Douglas Charles Latulipe

Three-dimensional wafer stacking using Cu TSV integrated with 45nm high performance SOI-CMOS embedded DRAM technology

For high-volume production of 3D-stacked chips with through-silicon-via (TSVs), wafer-scale bonding offers lower production cost compared with bump bond technology [1][2][3] and is promising for interconnect pitch <;= 5μ range using available tooling. Prior work [3] has presented wafer-scale integration with tungsten TSV for low-power applications. This paper reports the first use of low-temperature oxide bonding and copper TSV to stack high performance cache cores manufactured in 45nm SOI-CMOS embedded DRAM (EDRAM) having 12 to 13 copper wiring levels per strata. A key feature of this process is its compatibility with the existing high performance POWER7™ EDRAM core [4] requiring neither re-design nor modification of the existing CMOS fabrication process. Hardware measurements show no significant impact on device drive and off-current. Functional test at wafer level confirms 1.48GHz 3D stacked EDRAM operation.

High-resolution 248-nm bilayer resist

Bilayer thin film imaging is one approach to extend 248 nm optical lithography to 150 nm regime and beyond. In this paper, we report our progress in the development of a positive-tone bilayer resist system consisting of a thin silicon containing imaging layer over a recently developed crosslinked polymeric underlayer. The chemically amplified imaging layer resist is based on a novel dual-functional silicon containing monomer, tris(trimethylsilyl)silylethyl methacrylate, which in addition to providing etch resistance, also functions as the acid sensitive functionality. The stabilization of (beta) -silyl carboncation by silicon allows this moiety to serve as an acid sensitive protecting group. Thus high silicon content and high resist contrast are achieved simultaneously. Lithographic evaluation of the bilayer resist with a 0.63 NA and a 0.68 NA 248 nm exposure tool has demonstrated resolution down to 125 nm equal line/space features with a dose latitude of 16 percent and depth of focus (DOF) of 0.6 um. The dose latitude and DOF for 150 nm equal line/space features are 22 percent and 1.2 um, respectively. Finally, residue-free, ultra-high aspect ratio resist features have been obtained by O2 or O2/SO2 reactive ion etching using a high-density plasma etch system. The resist design, deprotection chemistry, lithographic and etch characteristics of the top layer, as well as the design of the new underlay, will be discussed.

Extension of 248-nm optical lithography: a thin film imaging approach

A negative-tone bilayer thin film imaged (TFI) resist has been developed for extension of 248 nm optical lithography to sub-150 nm regime. The bilayer TFI resist system consists of a thin (0.2 um) silicon containing top imaging layer and a thick (0.7 - 0.8 um) highly absorbing organic underlayer. The chemically amplified negative-tone top layer resist comprises of three major components: an aqueous base soluble silicon containing polymer, poly(hydroxybenzylsilsesquioxane); a crosslinking agent; and a photoacid generator. The highly absorptive underlayer is a hard baked novolak resist or a DUV ARC. Imaging of the top layer resist has shown resolutions down to 137.5 nm for line/space features and 130 nm for isolated features with 248 nm exposure tools and chrome on glass masks. The O2 reactive ion etch (RIE) selectively of the top layers versus a novolak underlayer is more than 25:1 as a result of the high silicon content in the silicon containing polymer. Furthermore, residue-free and nearly vertical wall profile image transfer to the underlayer has been achieved with RIE. Application of the negative-tone bilayer resist to 150 nm Gbit DRAM critical level lithography has been demonstrated. Resist line edge roughness is also discussed.

Comparison of liquid- and vapor-phase silylation processes for 193-nm positive-tone lithography

Liquid- and vapor-phase silylation processes are compared for a 193-nm positive-tone lithographic process using polyvinylphenol as a resist. The liquid-phase process, using a mixture of xylene, hexamethylcyclotrisilazane, and propylene glycol methyl ether acetate, was found to have higher silylation contrast, better sensitivity, and a smaller proximity effect (a decrease in silylation depth for smaller feature sizes). These factors result in a larger exposure latitude, particularly at feature sizes below 0.5 μm. These advantages are greatly offset, however, by the increased chemical costs, which are estimated to be more than 100 times greater than for the vapor-phase process.

Impact of attenuated mask topography on lithographic performance

Experimental evaluations were used in conjunction with rigorous electromagnetic simulations to evaluate the affect of attenuated phase-shifting mask (PSM) fabrication processes on lithographic performance. Three attenuated PSMs were fabricated including a normal leaky- chrome reticle and two novel approaches: a recessed leaky-chrome reticle for reduction of edge scattering and a single-layer reticle employing a hydrogenated amorphous carbon film. Direct aerial image measurements with the Aerial Image Measurement System (AIMSTM), exposures on an SVGL Micrascan 92 deep-UV stepper, and TEMPEST simulations were used to explore the effects of edge-scattering phenomena for the different mask topographies. For each reticle, the process window at a feature size of 0.25 micrometers was evaluated for four basic feature types: nested lines, isolated lines, isolated spaces, and contact holes. Further evaluation of the sidewall profiles and the image size on the mask are required to address these discrepancies.

Effects of underlayer on performance of bilayer resists for 248-nm lithography

Thin film interference plays an important role in critical dimension control of single layer resists causing large changes in the effective exposure dose due to small changes in optical phase. To overcome these problems bilayer resists have been proposed. Advantages to such systems include enhanced process latitude, enhanced resolution, and improved critical dimension control due to minimization of substrate reflectivity. In this paper, we have investigated the effects of the underlayer with respect to the optical properties as well as the chemical composition on the performance of bilayer resists for 248 nm lithography. The optimum optical constants (index of refraction n((lambda) ) and extinction coefficient k((lambda) )) of the underlayer were deduced by simulations. It was also found that with some underlayers, the optical properties could be tuned by controlling the processing conditions. Novolaks have been found to interact with the resist resulting in significant residue limiting the resolution of the 248 nm bilayer resist to 150 nm. Properly designing the underlayer with suitable optical constants and preventing resist/underlayer interaction resulted in 125 nm resolution with a 248 nm bilayer resist. We also investigated the use of an amorphous diamond-like carbon film as an underlayer material. Thin films, deposited by plasma enhanced chemical vapor deposition, offers advantages over spin on hard baked polymers because it can be deposited conformally with high optical purity. Furthermore, the composition and optical properties can be fine-tuned by changing the process parameters.

0.25-μm lithography development using positive mode top surface imaging photoresist

As design rules for ULSI chip sets continue to require sub-O.3j.un resolution for high density patterns the drive toward shorter wavelength (248nm), and higher numerical aperture (<O.5NA) steppers will continue. Process development on these advanced lithography systems is made difficult for a variety of reasons. The first of these is cost, the most modem steppers available today can cost <

Diamond-like carbon films from a hydrocarbon helium plasma

5 million per system making it necessary to keep manufacturing cost in check by extending life times to more than one generation chip set. Secondly, working at 248nm and high numerical aperture tends to reduce process latitudes making manufacturing processes inherently more difficult to control. Last but not least, photoresist and antireflective coatings needed for even the simplest processes historically have had major environmental sensitivity problems or material compatibility problems associated with them. These issues have been addressed by such developments as phase shift masks, off axis illumination techniques, and major advances in resist technology. So far these types of cures have proven to be both costly and extremely complicated to implement in a manufacturing environment.