Noriyuki Harashima

Evaluation of loading effect of NLD dry etching

Recently, loading effect is becoming a great issue in mask dry etching process. It is well known that the effect is affected by pattern density. To improve the issue, an advanced mask dry etching system using neutral loop discharge was applied for next generation mask fabrication, because the tool make is possible to get high plasma density and low gas pressure.

Advanced NLD mask dry etching system for 90-nm node technology

Front-end semiconductor lithography demands smaller size of patterns for 90 nm node and beyond, on both Si wafers and photomasks. In dry etching for photomasks, it needs tighter CD uniformity and loading effect. For meeting these demands the advanced NLD (magnetic Neutral Loop Discharge) mask etcher has been developed, because it could operate at lower pressure for reducing loading effect than conventional ICP etchers, due to the magnetic confinement of electron in plasma generation. In the NLD mask etcher, the configuration of plasma source was investigated for better performance and the etching condition was re-optimized for improving selectivity. Consequently, the selectivity of Cr/resist (ZEP-7000) was more than 1.6, compared with 0.95 in the previous condition. And also, the CD uniformity in Cr etching was improved to meet our target 6 nm (3 sigma) around 0.68 Pa. However, in the view of reducing loading effect, other condition that is lower pressure than 0.68Pa and adding Helium (HE) showed smaller global loading. Therefore, making a balance of uniformity and loading is necessary to get better performance in mask process. We also propose a basic condition using the advanced NLD mask etcher for dry etching a MoSiON shifter of atenuated PSM in this paper.

Quartz 9-inch size mask blanks for ArF PSM (Phase Shift Mask)

Semiconductor technology nodes are steadily miniaturizing. On the other hand, various efforts have been made to reduce costs, mass production lines have shifted from 200 mmφ of Si wafer to 300 mmφ, and technology development of Si wafer 450 mmφ is also in progress. As a photomask, 6-inch size binary Cr mask has been used for many years, but in recent years, the use of 9-inch binary Cr masks for Proximity Lithography Process in automotive applications, MEMS, packages, etc. has increased, and cost reduction has been taken. Since the miniaturization will progress in the above applications in the future, products corresponding to miniaturization are also desired in 9-inch photomasks. The high grade Cr - binary mask blanks used in proximity exposure process, there is a prospect of being able to use it by ULVAC COATING CORPORATIONs tireless research. As further demands for miniaturization, KrF and ArF Lithography Process, which are used for steppers and scanners , there are also a demand for 9-inch size Mask Blanks. In ULVAC COATING CORPORATION, we developed a 9 - inch size KrF PSM mask Blanks prototype in 2016 and proposed a new high grade 9 - inch photomask. This time, we have further investigated and developed 9-inch size ArF PSM Mask Blanks corresponding to ArF Lithography Process, so we report it.

Prototyping 9-inch size PSM mask blanks for 450mm wafer process (2016)

6-inch size (known as 6025QZ) binary Cr mask is widely used in the semiconductor lithography for over 20years. Recently for the 450mm wafer process, high grade 9-inch size mask is expected. For this application, we have studied and developed prototyping 9-inch size PSM KrF and ArF mask blanks. This time we will explain these PSM mask blanks status.

New grade of 9-inch size mask blanks for 450mm wafer process (2015)

6-inch size (known as 6025QZ) binary Cr mask is widely used in the semiconductor lithography for over 20years. Recently for the 450mm wafer process, high grade 9-inch size mask is expected. For this application, we have studied and developed new grade 9-inch size mask blanks for recent 450mm wafer process requirement. There are three types of glass substrates material use and select as 9inch size mask blanks and for required applications by the users. Each glass material has advantage and disadvantage for lithography process as well as wafer process. By knowing the each glass substrate material characteristics and quality level the users enable to select the proper 9inch mask blanks for their targeting applications. At present, ULCOAT has produced 9-inch size mask blanks by the most advanced chrome sputtering equipment use for 6025QZ.

The possibility of CrOx as the top coating material on a MoSi HT

A binary Cr is widely used material as the top coating on a MoSi HT. Generally, a binary Cr mask has larger GL(Global loading) than a MoSi HT by dry etching process. Now we are using a binary Cr as the masking material for a MoSi HT. So if we want to make a MoSi HT pattern with smaller CD variation, we have to make a smaller CD variation for Cr pattern. Two layers, that is, a metal Cr film and a CrOx film, make a binary Cr. GL is one of the source of a CD variation on a MoSi HT. In our investigation, a binary Cr GL is caused by a metal Cr GL. In order to make a MoSi HT with smaller CD variation, we examined monolayer CrOx film, which has a shorter dry etching time and a smaller GL property. As the result, we conformed the optimized monolayer CrOx film can be used as a good masking material for MoSi HT production. We improved GL by the monolayer CrOx film and we found it has a proper OD(Optical Density) and a excellent electric conductivity on a MoSi HT.

New structure of ArF high-transmittance attenuated phase-shifting mask with dry etching process

ULVAC Coating Corporation proposes a new ArF high transmittance attenuated mask which consists of a thin MoSiON film and a quartz trench. We made an appropriate thickness MoSiON film and found a proper dry etching condition to dig a quartz trench by a NLD dry etcher. The etched quartz trench had very smooth bottom and correct depth. It is very difficult to make ArF high transmittance attenuated mask with perfectly satisfy the transmittance and phase shift angle because of characteristics of MoSiON film. PSM with MoSiON film has been used commercially under 248nm and 193nm wavelength. If it is possible to use the current MoSiON film also for ArF high transmittance attenuated mask making, it would be very convenient for mask makers. This report will show our investigation results in regards to the possibility of making ArF high transmittance attenuated mask by using current MoSiON film with setting the transmittance of 15% at 193nm wavelength and setting the phase shift angle of 180 degree by MoSiON film and quartz trench etching. NLD (Magnetic Neutral Loop Discharge) mask etcher was used for this investigation. At conventional conditions, a large side etch was observed on the MoSiON film as a result of the etching process. We checked correlation between gas pressure and side etch, and found lower pressure resulted in smaller side etch. As the further low pressure, appearance of sub-trench were observed. By adding a CxFy gas with CF4-base etching gas for the dry etching process, we are able to improve the side etching and also sub-trench.

Improvement of NLD mask dry etching system for 100nm node technology

The advanced photomask dry etching system using neutral loop discharge (NLD) has been thought as a promising candidate for the next generation technology, because the NLD plasma has a capability to control the plasma distribution and density. In previous work, we improved CD uniformity for 130nm node technology using the neutral loop modulation etching technique. However, 100nm node lithography requires tighter specification, thus we set a target to achieve CD accuracy of 6nm (3 sigma) by improving CD uniformity and loading effect of the NLD dry etching system. First, we changed the system configuration: exhaust place, reactor size, and electrode shape. Especially, by optimizing the antenna configuration, we improved the unevenly distributed plasma. Additionally, we introduced a new etching technique to reduce CD shift from resist profiles by enhancing Cr/Resist sensitivity. Consequently, the NLD dry etching system for 100nm node technology was confirmed the effectiveness to improve CD performance using the above techniques.