Via-first Dual Damascene Process Research Articles

CORRELATION BETWEEN SIMULATION AND EXPERIMENT USING UV CURABLE GAP FILL MATERIALS FOR GLOBAL PLANARIZATION

This study focuses on the correlation between simulation and experiment using UV curable gap fill materials for global planarization in advanced lithographic and nanoimprinting techniques. A novel gap fill material has been optimized and developed for global planarization properties. Gap fill materials planarize irregular substrates such as patterned steps, vias, and trenches to increase depth of focus and patterning resolution. After planarizing the substrate surface, the gap fill materials provide dry etching selectivity to the under-layer to avoid damaging the dielectric materials. In the characterization of UV curable gap fill materials, two key factors were identified. The factors were the specific dependence of planarization on the spin speed and film thickness. By optimizing these factors, an appreciable reduction in via topography was realized. An array of 1.1 μm deep, 300 nm diameter holes was planarized to 10 nm thickness bias with a 380 nm thick planarizing film. In addition of global planarization, a final design consideration was to reduce the amount of outgassing during the process. UV curable gap fill material was optimized for sublimate reduction resulting in a defect-free coating. The sublimate produced from the developed gap fill material during baking was significantly decreased when compared with that produced from a thermal curable material. And, the third evaluation of UV curable gap fill materials was reported, to avoid resist poisoning issues in an advanced via-first dual damascene process. The resist poisoning properties in UV curable gap fill material were observed better performance than that of thermal curable material. The resulting UV curable gap fill materials based on this study will be extremely useful for lithographic and nanoimprinting techniques.

Resist Poisoning Studies of Gap Fill Materials for Patterning Metal Trenches in Via-First Dual Damascene Process

The via-first dual damascene process is the current manufacturing technology for copper/low-k interconnect fabrication. In the conventional via-first dual damascene process, metal trench patterning lithography is applied after filling the vias with sacrificial organic materials under the resist, such as gap fill materials and bottom antireflective coating. Resist poisoning has become a serious problem for the 65 nm technology node and beyond owing to the use of porous low-k dielectric materials. This study describes the newest method of evaluating resist poisoning. The dependence of film thickness on resist poisoning was observed, and the effects of the gap fill materials with different polymers were also clarified. One gap fill material was found to have an excellent resist poisoning blocking property as determined from the bias of trench patterning size between the center and edge areas. In addition, to evaluate the resist poisoning in lithography, a chemical approach using the developed gap fill materials can potentially allow the skipping of the additional thermal annealing process and achieve high throughput wafer processing by only coating the gap fill material on the substrates that generate resist poisoning. Continuing the via-first dual damascene process using porous low-k dielectric materials in an advanced lithography will be valuable in future studies based on this evaluation method, compared with the trench-first dual damascene process owing to the higher cost of the latter.

Development of Developer-Soluble Gap Fill Materials for Planarization in Via-First Dual Damascene Process

Gap fill materials and planar-type bottom antireflective coating are needed for patterning metal trenches in the via-first dual damascene process. We have already reported on thermal cross-link gap fill materials and bottom antireflective coating as planarizing layers under a resist that can be spin-coated and etched faster than resists. In this study, developer-soluble gap fill materials were optimized in order to obtain excellent planarization, simplify the process, and increase wafer throughput. The developer-soluble gap fill materials using poly(4-hydroxystyrene) derivatives developed by an approach of the via-first dual damascene process was obtained by optimizing the concentration of the phenol group with solubility in the alkaline developer (0.26 N tetramethylammonium hydroxide, TMAH) and by thermal cross-link reaction. In addition to a superior via-filling performance, developer-soluble gap fill materials using poly(4-hydroxystyrene) derivatives showed a wide process window of prebake temperature, the controllable dissolution rate for the etch-back process, and a good CF4 etch rate of 1.4 times higher than that of a resist for etching the substrate. These results were attributed to the polymer structures of poly(4-hydroxystyrene) derivatives. Both dry plasma cleaning and wet developer cleaning can be used to remove residual gap fill materials after processing. This novel approach using developer-soluble gap fill materials as a new type of sacrificial material in an advanced lithography process makes this solution convenient for planarizing surfaces and is economically favorable owing to high throughput.

Gap Fill Materials Using Cyclodextrin Derivatives in ArF Lithography

High planarizing gap fill materials based on β-cyclodextrin in ArF photoresist under-layer materials have been developed for fast etching in CF4 gas. Gap fill materials used in the via-first dual damascene process need to have high etch rates to prevent crowning or fencing on top of the trench after etching and a small thickness bias between the dense and blanket areas to minimize issues observed during trench lithography by narrowing the process latitude. Cyclodextrin is a circular oligomer with a nanoscale porous structure that has a high number of oxygen atoms, as calculated using the Ohnishi parameter, providing high etch rates. Additionally, since gap fill materials using cyclodextrin derivatives have low viscosities and molecular weights, they are expected to exhibit excellent flow properties and minimal thermal shrinkage during baking. In this paper, we describe the composition and basic film properties of gap fill materials; planarization in the via-first dual damascene process and etch rates in CF4 gas compared with dextrin with α-glycoside bonds in polysaccharide, poly(2-hydroxypropyl methacrylate) and poly(4-hydroxystyrene). The β-cyclodextrin used in this study was obtained by esterifying the hydroxyl groups of dextrin resulting in improved wettability on via substrates and solubility in photoresist solvents such as propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate and ethyl lactate. Gap fill materials using cyclodextrin derivatives showed good planarization and via filling performance without observing voids in via holes. In addition to superior via filling performance, the etch rate of gap fill materials using β-cyclodextrin derivatives was 2.8–2.9 times higher than that of an ArF photoresist, evaluated under CF4 gas conditions by reactive ion etching. These results were attributed to the combination of both nanoscale porous structures and a high density of oxygen atoms in our gap fill materials using cyclodextrin derivatives. The cyclodextrin derivatives may be applicable as a new type of sacrificial material under the photoresist in ArF lithography.

Ultraviolet Cross-Link Gap Fill Materials and Planarization Applications for Patterning Metal Trenches in 32–45 nm Via First Dual Damascene Process

In the dual damascene (DD) process using the via-first trench-last approach, a planarizing thermally cured material is used to minimize thickness variation across the vias. The coating planarization is followed by photoresist application and lithography on vias. The major problem with this process is the large thickness bias observed as via pattern pitch and density change across the wafer. The thickness bias between the open field and dense via arrays is not acceptable for advanced lithography and leads to narrow process windows and problems during the subsequent trench etch steps. In this study, UV-cured gap fill materials are proposed as planarizing layers under a photoresist. UV-cured gap fill materials show good planarization, via fill properties (no voids), etch selectivity, minimal outgassing during curing, excellent resistance to solvents and photoresist intermixing when compared with thermally cured films. This novel method using UV curing to reduce thickness bias in gap fill materials is one of the most promising processes ready to be incorporated into the mass production of patterning metal trenches by the 32–45 nm via-first DD process.

Study of Self Cross-Link Bottom Antireflective Coating and Gap Fill Materials for Sublimate Defect Reduction in ArF Lithography

Sublimate reduction from the new bottom antireflective coating (BARC) and gap fill materials in bake process was investigated by means of absorption spectroscopy and the quantitative analysis of sublimation using the quartz crystal microbalance (QCM) sensing element. The small molecular components in BARC and gap fill materials were found to be related to a decrease in the number of sublimate defect. The application of the newly developed BARC and gap fill materials of the polymers with a self cross-link reaction system showed lower sublimate amount. In addition, good resist profiles and 130 nm via fill performance in the via-first dual damascene process were achieved using this self cross-link polymer system. This new system is one of the most promising systems ready to be tested for the mass production of 32–45 nm node IC devices and beyond.

Process sensitivity and robustness analysis of via-first dual-damascene process

Sacrificial layer (SACL) coating had been proposed to protect the sealing layer of underlying copper lines during trench etching as the via-first scheme is employed for dual-damascene patterning. Because the coated SACL thickness depends on via size and via density, the process window is hard to identify. In this paper, the criteria for a successful SACL process are derived. A four-step procedure for SACL process development is also proposed. It is suggested that shallow trench depth and medium etch rate selectivity between the inter-metal-dielectric and SACL material are preferred. The SACL thickness in the via can be adjusted by adjusting the overetching percentage at the SACL breakthrough step so that the criteria are satisfied. The validity of the proposed criteria is proved by the very high yield of via chains with via size ranging from 0.27 to 0.16 /spl mu/m. It is concluded that the SACL process can be robust and can be employed to reduce the thickness of the capping layer effectively even beyond the 0.13-/spl mu/m technology node.

Dual Damascene Etching Process Using Sacrificial Spin-on-Glass Film

The dual damascene (DD) formation process for sub 0.2 µm feature size devices has been investigated. The via-first DD process, where via holes are first formed, followed by trench formation, used the antireflection film in via holes after the trench pattern lithography process. In subsequential trench etch process, crownlike etch residues of SiO2 were formed around via holes due to etch inhibiting effect of antireflection films in via holes. A spin-on-glass (SOG) film is filled in via holes as a sacrificial film before trench pattern lithography was used. It could eliminate the crownlike etch residues because of the absence of an antireflection film in via holes. Moreover, it could give via holes a rounded profile at their top edges. This DD process used for fabricating films with no etch residues and rounded via holes reduces the aspect ratio of via holes and was confirmed to be effective for subsequential metal filling process.