A thin film made of a material containing a metal and silicon is formed on a light-transmissive substrate. Then, a treatment is performed to modify a main surface of the thin film in advance so that when exposure light having a wavelength of 200 nm or less is accumulatively irradiated on a thin film pattern of a photomask to be produced by patterning the thin film, the transfer characteristic of the thin film pattern does not change more than a predetermined degree. This treatment is performed by carrying out, for example, a heat treatment in an atmosphere containing oxygen at 450° C. to 900° C.

Photomask blank manufacturing method and photomask manufacturing method

This is an experimental result for the inhibition of effects of the growing defect. Up to now, it has been considered and defined that the growing defect is an unexpected and unusual reaction by bonding impure ions existed on the mask each other. This study is not only to suppress the unexpected reaction when making the final mask but also to stabilize the surface of mask by controlling by-product occurred when stripping upper Cr layer and damaged layer from sputtering process. According to the analysis of the surface roughness stemming from each process (from wet etching to cleaning Process) of MoSi layer, the surface still comes to be rough when a mask is done through all process. So, heat treatment was performed and surface roughness was measured to figure out how much the surface condition would be improved and how many remaining SO4, NH4 Ions on the surface after cleaning process reduced. This study shows the major factor causing plasma damage is a dry etcher, a way to control the damaged layer of MoSi at PR strip process, the level of stabilization of mask surface through cleaning process and a clue to be able to prove the stabilization by adding specific process. Analysis tools for this study are as follows. AFM (for checking the roughness of surface), TEM (for checking cross-section) and IC (Ion chromatography)analysis equipment.

The surface treatment for prevention of growing defect

A light pattern exposure method is by irradiating ArF excimer laser light to a resist film through a photomask. The photomask includes a transparent substrate and a pattern of optical film of a material comprising a transition metal, silicon, nitrogen and oxygen, with contents thereof falling in a specific range. The photomask may be irradiated with ArF excimer laser light in a cumulative dose of at least 10 kJ/cm2.

Light pattern exposure method, photomask, and photomask blank

In semiconductor fabrication industries, photomask cleaning with no pattern damage is a critical issue, especially for advanced technology nodes. Thus, optimization of cleaning techniques adopted for photomask cleaning or development of new cleaning technique is always of great interest to meet process requirements. In this book chapter, the sources of contaminants on photomask and their impact on imprinted images are first discussed. Then a critical review is presented on the wide spectrum of cleaning techniques and strategies that are adopted for the removal of particulate contaminants and organics from the photomask. The applicability of each technique and its limitations are also examined. Because extreme ultraviolet lithography (EUVL) is considered to be a next-generation lithography, a separate section is devoted to EUVL mask-cleaning techniques.

Contamination Removal From UV and EUV Photomasks

Existing cleaning technology using sulfuric acid based chemistry has served the mask industry quite well over the years. However, the existence of residue on mask surfaces is becoming more and more of a problem at the high energy wavelengths used in lithography tool for wafer manufacturing. This is evident by the emergence of sub-pellicle defect growth and backside hazing issues. A large source of residual contamination on the surface of masks is from the mask manufacturing process, particularly the cleaning portion involving sulfuric acid. Cleaning strategies can be developed that eliminate the use of sulfuric acid in the cleaning process for advanced photomasks and alternative processes can be used for cleaning masks at various stages of the manufacturing process. Implementation of these new technologies into manufacturing will be discussed as will the resulting improvements, advantages, and disadvantages over pre-existing mask cleaning processes.

Sulfur-free cleaning strategy for advanced mask manufacturing

Disclosed is a phase shift mask. Residual ions, which are considered a factor of occurrence of haze which is a growth defect of a surface of a photomask during a photolithography step of a wafer process, are controlled in order to change the content of a surface of the phase shift mask. Diffusion of the residual ions into the surface of the mask is suppressed during a photomask wet cleaning process in order to prevent the haze.

Phase shift mask for preventing haze

We choose thermal treatment as part of a methodology to remove chemical residue on the surface of a mask. This new step of thermal treatment is inserted into our standard cleaning process for embedded attenuate phase shift masks (EAPSMs). The treatment is carried out in a modified hot plate system at various temperatures and times. After thermal treatment, ion chromatography measures the residual ions on a given surface. The thermal treatment is found to considerably reduce residual sulfate ions on the mask surface. The remaining sulfate ions on the mask are <0.18 ng/cm2 using thermal treatment.

Control of chemical residue on photomasks using thermal treatment

We have chosen a combination of thermal treatment and hot D.I water rinsing as a part of methodologies to remove chemical residuals on mask surface. A new step of thermal treatment has been inserted in our standard manufacturing procedure for EAPSM. After thermal treatment, Ion Chromatography (IC) methods are used to confirm the surface cleanliness. As a result of our study, thermal treatment can considerably reduce residuals (e.g. ammonium, sulfuric and others) on mask surface. So, it could be suggested that the thermal treatment is an effective way to minimize residual ions. Also, in order to understand on haze source and mechanism, we investigated on artificial acceleration method for haze formation. We preceded haze acceleration test by using modified haze acceleration system (UV 172nm light). From the acceleration test, we found that humidity, irradiation energy, concentration of chemical residuals are dominant factors of haze formation.

A study for the control of chemical residuals on photomasks by using a thermal treatment for 65-nm node

In recent years, organic compounds have been clarified as one of major root causes of the haze, and carbon and amine components are major of them to organize. Therefore, both two should be controlled simultaneously for preventing haze defects on photomask. It is well known that UV/O 3 treatment has a strong efficiency of removing organic matters 1 . For that reason, we have inserted it into our cleaning process, especially for EA.PSMs. And the surface variation of mask, after UV/O 3 treatment, has been confirmed by the change of surface free energy on it. And organic matters remaining on mask surface have been identified by Gas Chromatography Mass Spectrometry (GC MS) with two different sample preparation methods: Thermal Desorption (TD) and direct extraction. As a result of UV/O 3 treatment, we confirmed that it has an excellent removing efficiency of aromatic compounds and semi-volatile organics on mask surface. Finally, through the haze accelerating tests, we have known that conventional SPM/SC-1 cleaning with UV/ O 3 treatment has been having a much higher threshold energy value in terms of causing haze defects on masks about 20 times higher than that of the cleaning with just SPM/SC-1.

A study of organic contamination control on photomask surface for 65nm tech node

As feature sizes of phase shift mask (PSM) have dropped below half-micron, resist adhesion have become a more critical issue, especially during second level lithography. Second writing process requires special consideration, because the resist's mechanical strength of resists on patterned chrome and patterned glass is smaller in comparison to that on the un-patterned chrome blank. If the adhesion strength is not sufficient to withstand the stress during subsequent processes, patterns will be damaged during second level lithography. Resists stress at pattern edges that subsequent processes, pattern will be damaged during second level lithography. Resist stress at pattern edges that weaken its adhesive property, together with the low mechanical strength of resists on glass, creates ample probability for the unwanted phenomenon in PSM process. In this paper, we investigate the effects of property and adhesive strength of resists on surfaces at different treatment before resist coating process, and observe the defects generation after different treatment.

Yong-Dae Kim

Papers

Phase shift mask for preventing haze

Control of chemical residue on photomasks using thermal treatment

A study for the control of chemical residuals on photomasks by using a thermal treatment for 65-nm node

A study of organic contamination control on photomask surface for 65nm tech node

Dehydration bake effects with UV/O3 treatment for 130-nm node PSM processing