Mamoru Terai

Newly developed RELACS materials and process for 65 nm nodes

We have developed a new ArF-RELACS (Resolution Enhancement Lithography Assisted by Chemical Shrink) material called AZ-LExp.R720. The principle and process procedure of LExp.R720 are almost identical to those previously developed with KrF lithography. The extent of crosslinking reactions and the mobility balance of chemical components at the boundary between resist and the RELACS film is adjusted to ArF resist chemistry. LExp.R720 can vary shrinkage from 10 to 40nm by controlling the process conditions, mainly the mixing bake temperature. The amount of shrinkage is independent of pattern pitch and focus. We confirmed that pattern profile, lithography margin, CD uniformity, etching resistance, and pattern defects were not deteriorated by the RELACS process with deionized water development. L.ExpR720 was able to get an amount of shrinkage with several of ArF resists, which has commercial applications. In conclusion, we believe that LExp.R720 is extremely useful for 65 nm node and next generation devices.

Below 70-nm contact hole pattern with RELACS process on ArF resist

A chemical shrink technology, RELACS (Resolution Enhancement Lithography Assisted by Chemical Shrink), 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 rinsing applied after conventional photolithography. Our target is realize of sub-70nm hole pattern formation by using new RELACS for ArF resist. At present, RELACS process is introduced to mass production of KrF lithography by using AZ R200 (Product name of Clariant) mainly. Then first of all we reported process performance of conventional RELACS material, AZ R200 with ArF resist. However AZ R200 does not show satisfactory shrinkage on ArF resist. Thereupon, we started on the development of new RELACS corresponding to ArF resist. As the result, we developed new RELACS material including Cross Linking Accelerator (CLA). It was found that CLA is able to improve reactivity of RELACS with ArF-resist. By using this new RELACS, It is Realized sub-70nm hole pattern formation with ArF-Ex lithography and It is able to Control of hole size by mixing bake (MB) temperature and additive ratio of CLA. Moreover this process was realized that thickness of shrunk hole is increased.

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.

Immersion-Specific Defects of High-Receding-Angle Topcoat

Dynamic receding contact angle (RCA) is a well-known parameter for estimating the degree of immersion-specific defects that have mainly circular and bridge shapes. In general, these defects decrease in number with increasing RCA of the topcoat (TC). However, we found the occurrence of circular defects despite using the TC with a large RCA. In this study, we analyzed the relationship between the physical properties of TC to reduce the number of defects. The result shows that the number of defects depends not only on a large RCA but also on a small amount of water uptake of TC. To understand well the degree of defects, the effective hysteresis (EH) is defined in terms of the RCA, the advancing contact angle (ACA) and the water absorption of TC. EH will be a useful way of explaining the circular defects. The characteristics of the defects are also discussed with a focus on the structure of the polymer attached to water.

Double Patterning Using Multilayer Hard Mask Process with Perhydropolysilazane

A new technology called the double patterning (DP) process with ArF immersion lithography is one of the candidate fabrication technologies for 32-nm-node devices. Over the past few years, many studies have been conducted on techniques of the DP process. Among these technologies, the double Si hard mask (HM) process is thought to be the most applicable technology from the viewpoint of high technical applicability to 32-nm-node device fabrication. However, this process has a disadvantage in terms of cost performance compared with other DP technologies since these HMs are formed by the chemical vacuum deposition (CVD) method. In this study, we examined the DP process using a dual spin-on Si-containing layer without using the CVD method to improve process cost and process applicability. Perhydropolysilazane (PSZ) was used as one of the middle layers (MLs). PSZ changes to SiO2 through reaction with water by the catalytic action of amine in the baking step. Using PSZ and Si-BARC as MLs, we succeeded in fabricating a fine pattern by this novel DP technique. In this paper, the issues and countermeasures of the double HM technique using spin-on Si-containing layers will be reported.

Improvements of adhesion and hydrophobicity of wafer bevel in water immersion lithography

In this study, we focus on the controllability of a wafer bevel from adhesion and hydrophobicity viewpoints in order to solve the problems of film peeling and microdroplet formation around wafer bevels, which result in pattern defects. Hexamethyldisilazane (HMDS) treatment is a common solution to these problems. We examine a novel wafer bevel treatment utilizing silane coupling agents (SCAs) for obtaining high adhesion and hydrophobicity. SCAs comprise trimethoxysilanol and organic functional groups. These groups react with inorganic substrates and films just over the surface subjected to a novel chemical treatment (NCT), respectively. Several organic functional groups both with and without fluorine are examined. The hydrophobicity is estimated from the static and receding contact angles of water. The adhesion strength is measured from the stress required for pulling the topcoat film away from the substrate subjected to the NCT. The coating performance of chemicals on the surface by the NCT and the aging stability of the formulated solution of the SCAs are examined for optimizing the composition of the NCT solution. Further, we verify the film peeling behavior and water leakage in wafers having a topcoat, ArF resist, and bottom antireflective coating (BARC) using a quasi-immersion exposure stage.

Double patterning using dual spin-on Si containing layers with multilayer hard mask process

A new technology called the double patterning (DP) process with ArF immersion lithography is one of the candidate fabrication technologies for 32 nm-node devices. Over the past few years, many studies have been conducted on techniques for the DP process. Among these technologies, we thought that the double Si hard mask (HM) process is the most applicable technology from the viewpoint of high technical applicability to 32 nm-node device fabrication. However, this process has a disadvantage in the cost performance compared with other DP technologies since these HMs are formed by the chemical vacuum deposition (CVD) method. In this paper, we studied the DP process using a dual spin-on Si containing layer without using the CVD method to improve process cost and process applicability. Perhydropolysilazane (PSZ) was used as one of the middle layers (MLs). PSZ changes to SiO2 through the reaction with water by the catalytic action of amine in the baking step. Using PSZ and Si-BARC as MLs, we succeeded in making a fine pattern by this novel DP technique. In this paper, the issues and countermeasures of the double HM technique using spin-on Si containing layers will be reported.

Studies on immersion defects using mimic immersion experiments

Top coat process is required for immersion lithography in order to prevent both the chemical contamination of scanner optics with eluted chemicals from resist material and the formation of residual droplet under the immersion exposure with high scanning speed. However, defect density of ArF immersion lithography with alkaline developer soluble type top coat material is much higher than that of ArF dry lithography. Mimic immersion experiments comprised of soaking of exposed conventional dry ArF resist with purified water followed by drying step were performed in order to study the immersion specific defects. It was suggested that the origin of immersion specific defects with alkaline developer soluble type top coat was the remaining water on and in the permeable top coat layer that might interfere the desired deprotection reaction of resist during post exposure bake (PEB). Therefore, application of post exposure rinse process that can eliminate the impact of the residual micro water droplets before PEB is indispensable for defect reduction. Post exposure rinse with optimized purified water dispense sequence was noticed to be valid for defect reduction in mimic immersion lithography, probably in actual immersion lithography.

Studies of the mechanism for immersion specific defects

In the past several years, ArF immersion lithography has been developed rapidly for practical applications. One of the most important topics is the elucidation of a mechanism and its solution of immersion specific defects. In this paper, we report several analytical results of immersion specific defects. First, we classify several possible origins of specific defects that are proposed based on our experiment on the actual immersion process and previous literature. We focused on a droplet of immersion water that was the origin of circular and deformed circular-type defects. Further, a watermark (WM) was created on some types of film stacks with or without the topcoat (TC) on the resist. We observed that all samples exhibited the trace of the WM. From chemical surface analyses, we obtained different types of components in the residue of the WM, which dried spontaneously. These components depended on the tested film stack. Some types were not always derived from leaching materials in the resist. Some components in the residue appeared to be airborne contaminants that were unregulated in machines used in the photolithography process. Based on the results of these tests, we discussed some methods for avoiding defects according to the droplet WM.