Takaei Sasaki

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.

Improvement of NLD mask dry etching system

An advanced photomask dry etching system (NLDE-9035) has been evaluated. The NLD plasma has an advantage to have a capability to control the plasma distribution and density. In our previous work, it has been confirmed to obtain excellent CD uniformity, CD linearity and good pattern fidelity. To improve the CD uniformity further, the neutral loop modulation etching technique has been evaluated. As a result, a further improvement of CD uniformity has been confirmed by using neutral loop (NL) diameter modulation etching technique.

Development of a MoSi-based bilayer HT-PSM blank for ArF lithography

HT-PSM has been adopted for semiconductor industry since i-line lithography. We introduced MoSi-based HT-PSM blanks for i-line and KrF lithography. Today they have become popular material and been established mask process widely. Thus it will be convenience for many mask users that MoSi-based HT-PSM could expand to ArF lithography. We have been developing double-layer MoSi HT-PSM blanks, as same structure of KrF. We developed new sputtering method for this expansion to get smaller extinction coefficient with comparatively large refractive index at 193nm. We got following data for T6% MoSi ArF HT-PSM blanks. (1) Table 1 shows typical optical properties of T6% MoSi HT-PSM blanks for ArF. (2) Fig.1 shows a spectroscopic transmittance and reflectance properties of a sample with T=6%(at 193nm: air ref.). In this case, its transmittance of 365nm(that is a wavelength of pattern inspection) is under 40%. It shows that mask users do not need any special inspection systems. In fact, we confirmed our HT-PSM with 40% (at 365nm) was able to be inspected by a KLA-300 series UV. (3) Fig.2 shows chemical durability data. Basically MoSi film has good durability for acid (SPM: 80C H2SO4+H2O2 4:1), and slightly poor durability for alkaline (SC-1: RT. NH4OH+H2O2+H2O 1:1:4). However this 6% film has good enough durability for alkaline, as seen in Fig.2, it changed less than +/- 0.05% of transmittance (at 193nm) and -0.5 degree of phase value (at 365nm). It is evaluated same durability as our HT-PSM for KrF. (4) Table 2 shows ArF laser irradiation durability. In the air, after 10 kjoule/cm2 irradiation (estimated for one year exposure in an ArF stepper), transmittance changed less than -0.3% and phase value less than -2 degree. It seems good enough irradiation durability. (5) Fig.3 shows a typical pattern profile of the T6% MoSi ArF HT-PSM. It was processed by MERIE system (ULCOAT Dry Etcher: MEPS-6025) with CF4+O2 at 6.8Pa, 100W(0.11W/cm2), 80Gauss rotating magnetic field. The profile has more than 85 degree without

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.

Photomask blank shelf-life study on e-beam chemically amplified resists

Fabrication of 130nm and below technology node photomasks favors EBeam chemically amplified resist (CAR) due to its higher sensitivity, contrast and resolution. However, chemically amplified resist is in general much more sensitive to the environment compared to conventional resists such as PBS and ZEP7000. Coated CAR blank shelf life will have a major impact on CD control of high-end photomask manufacturing especially for extended delay situations. This paper presents blank supplier packaging methods and rawstock storage conditions and their impact on CAR blank shelf life in the photomask fabrication facility. We selected one of the top chemically amplified e-beam resists for this study.

Fabrication of MoSiON halftone masks using ZEP7000 for MEBES 4500

Halftone (HT) masks are a well-accepted method of manufacturing Phase Shift Masks (PSM). Recently, investigations of the suitability of HT masks for manufacturing have shifted from contact layers to gate devices. A regular supply of MoSiON-shifter HT mask blanks was obtained for this study. The MEBES 4500 pattern generator has been used for the electron beam writing of 250 nm design rule masks. However, this writing tool has sufficient performance to use in the next generation of masks. We have investigated the fabrication of MoSiON-HT mask using MEBES 4500. In general, because MoSiON is a very low conducting material, there are issues with pattern placement errors caused by charging. This charging effect can be reduced by utilizing an electrical conducting polymer (aquaSAVE) coated on the ZEP resist surface. The resulting registration error is corrected to the same level as that of conventional chrome blanks. Moreover we manufactured KrF-HT masks with contact-type patterns using HT blanks which were coated with electrical conducing polymer on the resist surface. From the results, we determined that we could manufacture production masks without any serious issues.

Dry etching with consideration to thicker reticle size

Studies of dry etching in consideration of thicker reticle size which was expected to be adopted for next reticle size were investigated with simulated plates. CD variation due to blanks thickness was evaluated in both of an electron beam and a laser beam reticle process with MoSiON embedded phase shift mask blanks by using a modifying magnetically enhanced RIE system (MEPS-6025) based on a method to predict surface voltage (Fig. 2). As blanks thickness increased up to 12.7 mm, CD variations were changed respectively (Fig. 5 and 6) along with surface bias voltage of blanks in discharge (Fig. 4). It was found that a bias voltage contribution between center and corner of the plate became closer corresponding to thickness of reticles size. Under this condition, 9 mm in thickness was found to be acceptable for dry etching process, because the effect of thickness may make discharge localize near by the substrate surface but any reason to deteriorate CDs could not appear in this feasibility study.