Chemical Shrink Research Articles

Extension of 193nm Lithography by Chemical Shrink Process

Extension of 193nm Lithography by Chemical Shrink Process

Parallelizable Simulation of Material Effects of Chemical Shrink Process of Nanolithography

A parallelizable simulator of the chemical shrink process of nanolithography is developed to investigate the process dependence on material properties. The chemical shrink process model employed for the simulator includes the cross-linking reaction of the resolution enhancement of lithography assisted by chemical shrink (RELACS) material, the inhibitor deprotection reaction of the chemically amplified (CA) resist, and the photoacid diffusion and trapping in the CA resist and RELACS material. It is found that, in the descending order of their effectiveness on amount of shrinkage, the photoacid trapping and diffusion mechanisms of the RELACS are the most effective ones, the photoacid trapping mechanism of the CA resist is second, the photoacid diffusion mechanism of the CA resist and the cross-linking reaction of the RELACS are third, and the deprotection reaction of the CA resist is the least effective. The interpretations of the dependence of the shrinkage amounts on these mechanisms are also provided on the basis of the simulations.

Newly Developed Resolution Enhancement Lithography Assisted by Chemical Shrink Process and Materials for Next-Generation Devices

We have newly developed a resolution enhancement lithography assisted by chemical shrink (RELACS) material for ArF lithography. Several process performances were evaluated for 65 nm nodes and next-generation devices. The principle and procedure of the RELACS process is similar to those developed previously for KrF lithography. The extent of cross-linking reaction and the mobility balance of chemical components at the boundary between the resist and RELACS film is adjusted to ArF resist chemistry. The novel RELACS material causes variation in shrinkage from 10 to 50 nm by controlling process conditions. The shrinkage amount is independent of pattern pitch and lithography conditions, i.e., dose and focus. We confirmed that the pattern profile, lithography margin, critical dimension (CD) uniformity, etching resistance, and pattern defects were not deteriorated by the RELACS process with distilled water. We believe that the novel RELACS process and materials are extremely useful for 65 nm nodes and next-generation devices.

Reaction-diffusion mechanisms for the chemical shrink process of nanofabrication

The effectiveness of reaction-diffusion mechanisms on the formation of nanoscale polymer films in the chemical shrink process is investigated by a two-dimensional model. The model includes three mechanisms: the catalytic cross-linking reaction of water-soluble polymers and cross-linkers, the diffusion of photoacids, and the trapping of photoacids by the cross-linked polymers. It is found that, although the cross-linking reaction is the vital mechanism for the chemical shrink process, it is much less effective on the formation of nanoscale polymer films than the photoacids diffusion and trapping mechanisms.

Temporal Saturation Effects of Nanoscale Contact Holes Fabricated by Chemical Shrink Techniques

The temporal saturation effects of the critical dimensions of nanoscale contact holes are investigated by a two-dimensional reaction–diffusion simulator for the chemical shrink techniques of nanolithography. Models included with the simulator are the crosslinking reaction of water-soluble polymers and crosslinkers, the diffusion of photoacids, and the inactivation of photoacids. Within the the statistical errors of the experimental data, the simulation critical dimensions agree with the experiment for baking temperatures over 105°C and for all baking times. It is found that the temporal saturation of the contact holes' critical dimensions can be explained by the photoacid inactivating reaction included in the simulator.

Fabrication of sub-60-nm contact holes in silicon dioxide layers

We have developed a fabrication technique, comprising electron-beam writing, chemical shrinking, and silicon dioxide etching, for the fabrication of sub-60-nm contact holes. The dimensions of the contact holes after the electron-beam writing, chemical shrinkage, and plasma etching steps were 140, 93, and 53 nm, respectively. We carefully evaluated the critical process parameters, such as mixing-bake temperature, mixing-bake time, plasma etch selectivity, and the profile shapes. A higher mixing-bake temperature led to an overhang of the contact hole in the resist; the optimal mixing-bake conditions occur when heating at 110 °C for 70 s. A fluorinated mixture of gases (CHF3/CF4=1:1) was used to etch the nano-scale contact holes in the silicon dioxide layer. The formation of side-wall polymers during the plasma etch phase contributed further to the contact hole shrinkage in addition to resist chemical shrinkage. The ratio of the hole's perimeter to its area affects the shrinkage dimensions of the etch process, especially for smaller contact holes. The pattern reduction due to side-wall polymer deposition in etch process has the inverse relationship with the diameter of contact hole.

Most Efficient Alternative Manner of Patterning sub-80 nm Contact Holes and Trenches with 193 nm Lithography

The patterning of sub-80 nm contact holes and trenches by ArF lithography is very challenging. To solve this problem, several technologies have been proposed, including thermal flow, resolution enhancement of lithography assisted by chemical shrink (RELACS), and shrink assist film for enhanced resolution (SAFIER). In this paper, we compare these processes in order to determine the advantages and disadvantages, and to gain an understanding on their mechanism on the basis of the performances of each process. Thermal flow shows a strong advantage in terms of simplicity, but it shows several disadvantages in terms of layout dependence, mask error enhancement factor (MEEF), and process window. RELACS is proven to be the most reliable, since there is a small shrink amount dependence on layout and temperature, but the limitation of shrink amount is an obstacle. Finally, SAFIER shows strong advantages in low MEEF, wide process window, and enhanced uniformity, with a weakness of the deformation in asymmetric pattern. It is considered that such performances are strongly related to the mechanism of each process, and therefore, the process should be used according to its own performances and mechanism. On the basis of the properties and relationship with the mechanism, the appropriate applications are recommended for each process.

Fabrication of 65-nm Holes for 157-nm Lithography

We investigated the use of hole shrink processes along with a bilayer process as a fine-hole-pattern replication technique for 157-nm lithography. A siloxane-type resist and an organic underlayer were used in the bilayer process. The lithographic resolution limit was 90 nm in diameter with a 0.85-numerical-aperture 157-nm microstepper using an attenuated phase-shift mask. Using the bilayer process, we successfully transferred 85-nm-diameter hole patterns in the resist into a 400-nm-thick tetraethylorthosilicate (TEOS) layer. A thermal flow process and the Resolution Enhancement Lithography Assisted by Chemical Shrink (RELACS) process were used as the hole shrink processes to enhance the resolution. The 120-nm-diameter hole patterns in the resist were shrunk to 80 nm by the thermal flow process and to 65 nm by the RELACS process. In the RELACS process, the diameters of the shrunk hole were less dependent on the hole pitch than in the thermal flow process.

Fabrication of sub-60-nm contact holes in silicon dioxide layers

We have developed a fabrication technique, comprising electron-beam writing, chemical shrinking, and silicon dioxide etching, for the fabrication of sub-60-nm contact holes. The dimensions of the contact holes after the electron-beam writing, chemical shrinkage, and plasma etching steps were 140, 93, and 53 nm, respectively. We carefully evaluated the critical process parameters, such as mixing-bake temperature, mixing-bake time, plasma etch selectivity, and the profile shapes. A higher mixing-bake temperature led to an overhang of the contact hole in the resist; the optimal mixing-bake conditions occur when heating at 110 °C for 70 s. A fluorinated mixture of gases (CHF 3/CF 4=1:1) was used to etch the nano-scale contact holes in the silicon dioxide layer. The formation of side-wall polymers during the plasma etch phase contributed further to the contact hole shrinkage in addition to resist chemical shrinkage. The ratio of the hole's perimeter to its area affects the shrinkage dimensions of the etch process, especially for smaller contact holes. The pattern reduction due to side-wall polymer deposition in etch process has the inverse relationship with the diameter of contact hole.

Contact Hole Resist Solutions for 45-90nm Node Design Rules

Target contact hole (C/H) CD sizes for 45-90nm node design rules range from 70 to 130nm with defect levels of one failure per billion contacts. Achieving these C/H design rule targets is a challenging task for the lithographers and the resist chemists. The issue is lack of high resolution and DoF especially for the 65 and 45nm node targets, low depth of focus (DoF) for the isolated contacts even for the 90nm node targets (hence the loss of desired overlap process windows) and high mark error factor (MEF) for the dense contacts. Several resolution enhancement techniques (RETs) such as chromeless phase lithography (CPL), double exposure technique IDEAL and IDEAL-Smile, use of high transmission attPSM have been proposed but none of them have been proven in real production and comes with compromises. The best option and expectation is 193nm resist formulations to deliver the desired targets. While improvements in resolution and process margins are seen and more progress will come as the maturity of the 193nm resists continue, use of resist flow process (RFP) and chemical shrink processes are also being considered at least for the 65nm node and above. Undoubtedly, the resist flow process is the easiest one to implement but it is pitch dependent and therefore does not find global acceptance. Shrink processes such as Resolution Enhancement of Lithography Assisted by Chemical Shrink (RELACSTM in combination of a high performance 193nm resist offers the best promise for the 65-45nm node targets and may be extendable to beyond 45nm node design targets. This paper provides the current status and performance of advanced 193nm single layer resist and the developments in the RELACSTM.

Thermal Flow and Chemical Shrink Techniques for Sub-100 nm Contact Hole Fabrication in Electron Beam Lithography

The application of high-resolution electron beam lithography to positive chemically amplified deep ultraviolet (UV) and electron beam resists has been developed. In general, deep UV resists are not suitable for resolving sub-100 nm problems except for the case of strict process control. We demonstrated thermal flow and chemical shrink techniques for sub-100 nm contact hole fabrication in electron beam lithography. The 200 nm contact hole resist patterns could easily be shrunk to less than 80 nm after a simple thermal flow procedure on a hot plate. The effects of thermal flow temperature and time period were evaluated. For the chemical shrink method, critical parameters of greatest influence, such as mixing bake temperature, baking time and initial hole size were discussed. After suitable chemical shrink, a hole dimension of 75 nm was obtained. The thermal process window for the thermal flow method was narrower than that for the chemical shrink method for sub-100 nm contact hole fabrication by electron beam lithography.

Below 100-nm Hole Pattern Formation Using Resolution Enhancement Lithography Assisted by Chemical Shrink (RELACS).

Below 100-nm Hole Pattern Formation Using Resolution Enhancement Lithography Assisted by Chemical Shrink (RELACS).

Advanced Micro-Lithography Process for i-line Lithography

In our previous paper [Jpn. J. Appl. Phys. 40 (2001) 419], we reported the development of an advanced micro-lithographic process for producing 0.1 µm contact holes by KrF excimer laser (248 nm) lithography. This chemical shrinkage technology, called resolution enhancement lithography assisted by chemical shrink (RELACS), utilizes the cross-linking reaction catalyzed by the acid component remaining in a predefined resist pattern. We report herein the results of the application of RELACS to i-line (365 nm) lithography. The properties of RELACS for i-line lithography were very different from those for KrF lithography. This is due to the difference in chemical mechanism between i-line and KrF resists. The characteristics of the application of RELACS to i-line lithography were studied by conducting basic experiments on the addition of a photo-acid generator (PAG) to an i-line resist and investigating the property of the cross-linking reactions involved in the pre-doping of various acids to RELACS film. Finally, we optimized RELACS materials to match i-line resist and realized the fabrication of contact holes less than 0.2 µm diameter by i-line lithography.

Advanced Micro-Lithography Process with Chemical Shrink Technology

We have developed an advanced micro-lithographic process for producing 0.1 µm contact holes (CH). A chemical shrink technology, resolution enhancement lithography assisted by chemical shrink (RELACS) utilizes the cross-linking reaction catalyzed by the acid component existing in a predefined resist pattern. This “RELACS” process is a hole shrinking procedure that includes simple coating, baking, and rinse steps applied after conventional photolithography. We evaluated the dependency of CH shrinkage on resist formulation. Though the acetal type KrF positive resist (low activation energy system) can achieve around 0.1 µm CH after RELACS processing under the optimized condition, the acrylate type positive resist (high activation energy system) showed less shrinkage under the same process condition. The shrinkage performance of the RELACS process largely depends on the resist chemistry used as the underlying layer. The results of these studies are discussed in terms of the influence of the base polymer on shrinkage performance and tendency.

Implementation of COMA type ArF Resist for Sub-100nm Patterning.

To accomplish sub-100nm minimum feature size to sub 100nm, new light sources for photolithography are emerging, such as ArF(λ=193nm), F2(λ=157nm), EPL(E-beam Project Lithography) and EUV(Extremely Ultraviolet, 13nm). Among these lithography technologies, ArF lithography will be used for sub 100nm lithography at first. For a few years, ArF resist development has been the key issue for the success of ArF lithography. For this ArF lithography, we have developed COMA (cyclo-olefin/maleic anhydride) type ArF resists in which the base resin consists of cycloolefin and maleic anhydride. Now, this COMA type resist is strong candidate for primary ArF resist. From the patterning results, we can say that the ArF resist is enough to start real device production except contact hole patterning. For the sub 100nm contact hole patterning, more intensive research must be performed in the field of RFP (Resist Flow Process) or RELACS (Resolution Enhancement Lithography Assisted by Chemical Shrink). From the etch resistance point of view, COMA type ArF resists have some problems under oxide etch condition. To solve this oxide etch problem, additional E-beam curing is required. For the more fundamental solution for the oxide etch, new etch equipment or hard mask must be developed for implementation of ArF process. E-beam curing also solves the line slimming due to E-beam attack during SEM measurement.

Corrosion and strength degradation of Si3N4 and sialons in K2CO3 and K2SO4 melts

Si3N4-based ceramics, such as hot isostatically pressed Si3N4, hot-pressed Si3N4, hot-pressed sialons containing 0, 30, 60 and 100% a phase, were corroded by K2SO4 and K2CO3 melts at 1150 to 1300 and 925 to 1150° C, respectively. The surface chemical reaction-controlled shrinking core model adequately described the relationship between the weight loss of the specimen and time for the corrosion reactions in both K2SO4 and K2CO3 melts, and the apparent activation energies were 380 to 608 and 157 to 344 kJ mol−1, respectively. The corrosion rate in K2CO3 melt decreased with increasing content of aluminium and yttrium ions in the specimens, but no systematic relation was observed for the reaction in K2SO4 melts. The fracture strength of the specimens corroded by K2SO4 and K2CO3 melts degraded to 2/3 to 2/5 of the original values up to a 2% weight loss, and then was almost constant up to 30% weight loss.

Machine-Washable, Water- and Oil-Repellent, Flame-Retardant Wool

Shrink-resist treatments based on chemical degradative processes and the chlorine/Hercosett treatment, while compatible with the Zirpro flame-retardant treatment, decrease the water-repellency of wool. Addition of fluorocarbons improved the water-repellency of chlorine/Hercosett- and Zirpro- treated wool, but this was inferior to fluorocarbon-treated Zirpro wool without a chemical shrink- resist treatment, particularly after washing. Chemical shrink-resist treatments, in the absence of Hercosett, decreased the fastness of oil-repellent treatments to washing. Application of fluorocarbons by the exhaustion technique with Zirpro produced a higher degree of water-repellency than application by padding. Application of chlorine/Hercosett by the exhaustion technique to wool in fabric form was successfully followed by the Zirpro treatment without intermediate drying, indicating insolubilization of the polyamide-epichlorhydrin resin on the wool fiber, after exhaustion in alkaline conditions. When an untreated fabric, dimensionally stable to washing, was treated with the Zirpro treatment, this was fast to at least 20 washes at 60°C. Several multipurpose finishes avoiding the use of chemical degrada tive shrink-resist treatments were evaluated. Wool fabric construction and weight influence the effectiveness of a flame-retardant multipurpose finish, particularly after washing.