Hole Shrink Process Research Articles

Ultrathin initiated chemical vapor deposition polymer interfacial energy control for directed self-assembly hole-shrink applications

Integrated circuit layouts consist of patterned lines and holes, where holes define the electrical contacts between adjacent layers. Block copolymer directed self-assembly (DSA) successfully shrinks the critical dimension (CD) of these contacts beyond the resolution of conventional lithography. DSA also radically improves the CD uniformity. One particularly difficult step of the DSA hole-shrink process involves establishing the correct interfacial energy throughout a lithographically templated hole to ensure good assembly. Initiated chemical vapor deposition (iCVD) is a uniform, ultrathin, ultraconformal, all-organic deposition technique that allows for precise control of the interfacial energy. In this work, the authors use iCVD of polydivinylbenzene at film thicknesses below 5 nm to blend the interfacial energy of the coated film with that of the silicon/spin-on carbon template. They fully characterize the iCVD surface by means of two liquid surface energy measurements. They further identify the interfacial energies presented by these functionalized templates through qualitative hole-island tests as well as quantitative harmonic mean estimations. In parallel, the authors run theoretically informed coarse grained simulations with the determined interaction parameters and DSA experiments and find good agreement across the range of chemistries created. Through careful control of iCVD conditions, especially filament temperature, they achieve a strong polystyrene-preferential sidewall with a nonpreferential bottom which they then demonstrate, both in the simulation and in the experiment, allows for a successful hole-shrink process across a wide range of template hole diameters.

Studying the effects of chemistry and geometry on DSA hole-shrink process in three-dimensions

Acquiring three-dimensional (3-D) information becomes increasingly important for the development of block copolymer (BCP) directed self-assembly (DSA) lithography, as two-dimensional imaging is no longer sufficient to describe the 3-D nature of DSA morphology and probe hidden structures under the surface. Using the post-DSA membrane fabrication technique and scanning transmission electron microscopy tomography, we were able to characterize the 3-D structures of BCP in graphoepitaxial DSA hole shrink process. Different DSA structures of singlets formed in templated holes with different surface chemistry and geometry were successfully captured and their 3-D shapes were reconstructed from tomography data. The results reveal that strong polystyrene-preferential sidewalls are necessary to create vertical DSA cylinders and that template size outside of process window could result in defective DSA results in 3-D. Our study as well as the established 3-D metrology would greatly help to develop a fundamental understanding of the key DSA factors for optimizing the graphoepitaxial hole shrink process.

Mechanisms of Directed Self-Assembly in Cylindrical Hole Confinements

The directed self-assembly of block copolymers in cylindrical holes is a promising technology for lithographic patterning, particularly in the context of vertical interconnect accesses. While the hole-shrink process for single cylinders has been extensively explored, the proliferation of morphological defects remains a significant technological barrier. We use a coarse-grained model to explore morphologies that form within cylindrical confinements for combinations of template surface energies. We identify metastable defect morphologies, in addition to the desired cylindrical morphology, in majority-wetting sidewall templates. We use our coarse-grained model and the string method to identify transition pathways between defective morphologies and the cylindrical morphology to elucidate the mechanism of defect annihilation within the confinements; the transition pathway from a disordered state is also identified. This work demonstrates that the minimum free energy path for the formation of a cylinder goes th...

Dry development for a directed self-assembly lithography hole-shrink process using CO / H 2 plasma

A dry development, directed self-assembly lithography (DSAL) hole-shrink process was studied, with a focus on the selectivity of the etching of poly(methyl methacrylate) (PMMA) over polystyrene (PS), and the suppression of etch stop. The highly selective etching of PMMA over PS was achieved using CO gas chemistry. However, it was found that the PMMA etching did not proceed beyond a certain depth. Scanning transmission electron microscopy and x-ray photoelectron spectroscopy analysis indicated that a deposition layer formed not only on the PS but also on the PMMA. The addition of H2 to the CO plasma was effective in controlling the thickness of the deposition layer and in suppressing the etch stop. The CO/H2 plasma process was combined with ion energy control to achieve a dry development for hole shrinkage. The dry development DSAL hole-shrink process was successfully realized by tailoring the etching gas chemistry and controlling the ion energy.

Effects of thermal fluctuations and block copolymers compositions on defects in directed self-assembly hole shrink process

We investigated the two critical defects on the directed self-assembly hole shrink process, i.e., polystyrene (PS) residue and placement error, by performing dynamic simulations with the Ohta–Kawasaki model. In the simulations, the thermal noise was added to generate stochastic variations in shape and location of the poly(methyl methacrylate) (PMMA) cylindrical domains. For the PS residue issue, we found that the volume fraction of the PMMA minor block, fPMMA, was an effective parameter, and that the PS residue could be minimized by increasing fPMMA from a conventional value of 0.30 to 0.40. On the other hand, the placement error of the PMMA cylindrical domain was affected little by the change in shape and size of the guide hole and by the connectivity to the guide bottom wall. It is speculated that the interfacial stiffness between the PMMA and PS domains would be essential to control the placement error of the PMMA cylindrical domains.

Optimization of directed self-assembly hole shrink process with simplified model

Application of the directed self-assembly of block copolymer to the hole shrink process has gained large attention because of the low cost and high potential for sublithographic patterning. In this study, we have employed a simplified model, called the Ohta-Kawasaki model to find the optimal process conditions, which minimize the morphological defects of the diblock copolymer, PS-b-PMMA. The model parameters were calibrated with cross-sectional transmission electron microscopy images. Our simulation results revealed that it is difficult to eliminate the morphological defects (i.e., PS residual layer) by only varying the shape of the guide hole. It turned out that changing the affinity of the bottom surface of the guide hole from “PMMA attractive” to “neutral” is a more effective way to obtain a reasonably wide, defect-free process window. Note that our simulations are not only computationally inexpensive, but are also comparable to the other detailed models such as the self-consistent field theory; they may also be feasible for large-scale simulations such as the hotspot analysis over a large area.

Contact hole shrink process using graphoepitaxial directed self-assembly lithography

A contact hole shrink process using directed self-assembly lithography (DSAL) for sub-30 nm contact hole patterning is reported on. DSAL using graphoepitaxy and poly (styrene-block-methyl methacrylate) (PS-b -PMMA) a block copolymer (BCP) was demonstrated and characteristics of our process are spin-on-carbon prepattern and wet development. Feasibility of DSAL for semiconductor device manufacturing was investigated in terms of DSAL process window. Wet development process was optimized first; then critical dimension (CD) tolerance of prepattern was evaluated from three different aspects, which are DSA hole CD, contact edge roughness (CER), and hole open yield. Within 70+/−5 nm hole prepattern CD, 99.3% hole open yield was obtained and CD tolerance was 10 nm. Matching between polymer size and prepattern size is critical, because thick PS residual layer appears at the hole bottom when the prepattern holes are too small or too large and results in missing holes after pattern transfer. We verified the DSAL process on a 300-mm wafer at target prepattern CD and succeeded in patterning sub-30 nm holes on center, middle, and edge of wafer. Average prepattern CD of 72 nm could be shrunk uniformly to DSA hole pattern of 28.5 nm. By the DSAL process, CD uniformity was greatly improved from 7.6 to 1.4 nm, and CER was also improved from 3.9 to 0.73 nm. Those values represent typical DSAL rectification characteristics and are significant for semiconductor manufacturing. It is clearly demonstrated that the contact hole shrink using DSAL is a promising patterning method for next-generation lithography.

Application of Directed Self-Assembly Lithography to Semiconductor Device Manufacturing Process

Directed self-assembly (DSA) lithography are recently getting in the spotlight as one of the most promising new generation lithography (NGL) candidates, which have a potential to fabricate semiconductor device patterns down to sub-30nm. In this report, latest experimental and simulation results of contact hole shrink process using the DSA are demonstrated.