A non-topcoat (non-TC) resist is a photoresist that contains a hydrophobic additive, which segregates to the surface and
forms a layer to minimize surface free energy. The improvement of surface hydrophobicity and the suppression of resist
component leaching were confirmed by using this segregation layer. Compared to conventional topcoat process, it is
speculated that the use of non-TC resist will reduce the cost of lithographic materials, improve throughput, and will be
compatible for the scanning speed improvement of immersion scanners. One issue for the non-TC resist is the possibility
of increased defect generation compared to processes using topcoats. It is assumed that the high resist surface
hydrophobicity and the developer insolubility of the hydrophobic additive are main factors causing the increase in defect.
Therefore, it is important to work out solutions for reducing these defects to realize the non-TC resists. A process of
selectively removing the hydrophobic additive between exposure and development process for the purpose of defective
reduction of non-TC resist was investigated. Specifically, wet processing was performed to the wafer after exposure
using an organic solvent to dissolve the hydrophobic additive. As a result, defect count was reduced to less than 1/1000
with the effective removal of the segregation layer without affecting pattern size. These results prove the effectiveness of
the proposed process named 'selective segregation removal (SSR)' treatment in reducing defects for non-TC resists.
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.
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.
A dynamic receding contact angle (RCA) is a well-known guideline to estimate the degree of watermark (WM)
defects, which shapes circle and bridges inside of the defect and reduces with enlarging the RCA of topcoat (TC).
However, our recent investigation revealed the occurrence of the circular shape defects in spite of using the TC with a
large RCA, bringing about a change of line and space pattern pitch. In this paper, we clarify the origin of these defects
and propose a new key factor of the dynamic surface properties of immersion-specific defects. It was found that the
pitch-change defect is caused by the lens effect of the air bubbles embedded between advancing water meniscus and the
TC. To well understand generation of the bubble defects, we defined the "effective" hysteresis (EH) as the hysteresis of
dynamic contact angle taken the effects of water-absorption into account. An analysis with the EH indicates that the
bubble defect arises from not only to the large ACA but also small amount of water uptake and the amount of
water-absorption could be substituted by the dissolution rate of TC. It was demonstrated that the EH proposed is a new
key factor for estimating the number of bubble defects. The EH is very useful for analyzing the bubble defects in
immersion lithography. The characteristics of the bubble defect are also discussed with a focus on the structure of the
polymer attached to water.
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.
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.
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.
The critical dimensions (CD) change by the process delay is the most critical issue to apply the chemically amplified resists (CAR) for photomask fabrication. In the photomask fabrication processes, the resist should have both post coating delay (PCD) and post exposure delay (PED) stability, while keeping higher sensitivity. To achieve this requirement, overcoat process has been examined for the purpose of CD stabilization in CAR process for photomask manufacture. The material, which consists of hydrophobic polymer and PAG, was used for the overcoat in this study. Consequently, it has become clear that pattern formations have been possible without unnecessary thickness loss. Moreover, it has been proved that the overcoat shows the effect of controlling CD change and improvement of CD uniformity. From these results, it is thought that the overcoat process is promising for the size stabilization in photomask manufacture for devices less than 90 nm.
The critical dimensions (CD) change by the process delay is the most critical issue to use the chemically amplified resists (CAR) for photomask fabrication. In the photo-mask fabrication processes, the resist should have both post coating delay (PCD) and post exposure delay (PED) stability, while keeping higher sensitivity. To achieve this requirement, overcoat process has been examined for the purpose of CD stabilization in CAR process for photomask manufacture. The material, which consists of hydrophobic polymer and photo acid generator (PAG), was used for the overcoat in this study. It has been proved that the overcoat shows the effect of controlling CD change, and applying the overcoat does not generate a fatal number of defects and pinholes. From these results, it is thought that the overcoat process is promising for the size stabilization in photomask manufacture for 100 nm devices.
We have investigated the ZEP resist characteristics of stress relaxation and reduction by applying some additives to the ZEP resist. The stress of the resist film was significantly reduced in ZEP resist with (beta) -Carotene. Without an additive, the stress of the ZEP resist film reduced from 30 MPa to 25 MPa as a result of the delay time after resist coating. On the other hand, with the addition of 5 wt% (beta) - Carotene, the stress of the resist film just after coated was almost same to that of the resist film without an additive. The stress, however, decreased to 15 MPa for one month. The stress change caused by deep UV exposure in the (beta) - Carotene additive system became one-third of that in the non- additive system. This system had a similar pattern replication quality to the original ZEP resist. It is considered that this system is useful for improving the image placement accuracy in EB writing on the membrane such as an x-ray mask.
Acrylic polymers are used for the ArF resists due to their high transparency. The development behaviors of the resists remarkably differ from that of conventional phenol resists. We investigated the influence of the ions in the developer and rinse to the development. The behaviors are explained clearly by considering the salting out effect. An exposed resist does not dissolve completely and forms gel by the salting out effect during the development, especially when the exposure is insufficient. This gel is dissolved by the rinse in which the salting out effect is very weak. The salting out effect also has influence to the unexposed resist. During the development, the diffusion of TMAH into the resist film occurs, while the swelling of the resist is inhibited by the salting out effect. The removal of the resist is observed occasionally during the rinse. A molecule of the ArF resists contains highly hydrophilic parts with the photogenerated carboxylic acid and hydrophobic parts. This type of molecule easily makes gel during the dissolution because the hydrophilic parts introduces the water and the hydrophobic parts make crosslinks of hydrophobic bonds. The hydrophobic bonds are influenced by the ions. This is because the acrylic resists are easy to be influenced by the salting out effect.
The resists for SR lithography require higher contrast (gamma value) for the current weak ability of the masks to cutoff x- ray beam as well as the high sensitivity for improving of throughput. Unfortunately, gamma values have not been estimated invariably because the method to obtain a quantitative gamma value has not been established. Little attention has been paid to the acquirement of the accurate gamma value of the resist. We have formed a fitting equation to the sensitivity curve to quantitatively investigate the resist contrast. We have evaluated tert-Butoxycarbonyl (tBOC) based chemically amplified resist. This resist showed good resolution but low gamma value. This result is due to the incomplete tBOC elimination during exposure and post exposure baking (PEB) process. We have simulated the amount of chemical reaction in the resist and the sensitivity curves. From these results, it is concluded that the most effective way to achieve a high gamma value is not only to increase the reactivity of decomposition reaction with an acid catalyst but also to augment the initial substitution ratio.
The chemical amplification resist system composed of partially tBOC-protected PVP, a dissolution inhibitor, and an acid generator are investigated as EB resists. As dissolution inhibitors, hydroquinone protected with tert-butoxycarbonyl group (B-HQ) and isophthalic acid protected with tert-butyl group (B-IP) are utilized. It is found that dissolution rate of the resist consisting of B-IP is faster than that of B-HQ in the exposed area. B-HQ and B-IP as dissolution inhibitors convert into HQ and IP as dissolution promoters after exposure, respectively. The pKa of IP is smaller than that of HQ. It is considered that the acidity of IP is higher than that of HQ, so the ability of the dissolution promotion of IP is much larger than that of HQ. IP enhances the solubility of the matrix resin to the alkaline developer larger than HQ. The resist consisting of B-IP has a high dissolution rate ratio between the exposed and unexposed areas, so it is considered that it results in a much improved patten profile. A 0.14 micrometers lines-and-spaces pattern is successfully fabricated at 17.5 (mu) C/cm2 using 50 keV. EB.
Most positive chemical amplification resists do not have enough stability to process delay. It has been claimed that airborne contaminants neutralize acids from photo-acid generators. It has been found by means of x-ray photoelectron spectroscopy that an onium salt used as a photo-acid generator is deficient at the surface of the prebaked resist film. The over-top coating using water-soluble polymers with organic acids has been investigated in order to not only separate the resist surface from airborne contaminants but also supply acids to the resist surface. We have succeeded in the suppression of the surface insoluble layer generation and of the pattern size change for more than 8 hours.