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193nm binary photomasks are still used in the semiconductor industry for the lithography of some critical layers for the nodes 90nm and 65nm, with high volumes and over long periods. However, these 193nm binary photomasks can be impacted by a phenomenon of chrome oxidation leading to critical dimensions uniformity (CDU) degradation with a pronounced radial signature. If not detected early enough, this CDU degradation may cause defectivity issues and lower yield on wafers. Fortunately, a standard cleaning and repellicle service at the mask shop has been demonstrated as efficient to remove the grown materials and get the photomask CD back on target.Some detection methods have been already described in literature, such as wafer CD intrafield monitoring (ACLV), giving reliable results but also consuming additional SEM time with less precision than direct photomask measurement. In this paper, we propose another approach, by monitoring the CDU directly on the photomask, concurrently with defect inspection for regular requalification to production for wafer fabs. For this study, we focused on a Metal layer in a 90nm technology node. Wafers have been exposed with production conditions and then measured by SEM-CD. Afterwards, this photomask has been measured with a SEM-CD in mask shop and also inspected on a KLA-Tencor X5.2 inspection system, with pixels 125 and 90nm, to evaluate the Intensity based Critical Dimension Uniformity (iCDU) option. iCDU was firstly developed to provide feed-forward CDU maps for scanner intrafield corrections, from arrayed dense structures on memory photomasks. Due to layout complexity and differing feature types, CDU monitoring on logic photomasks used to pose unique challenges.The selection of suitable feature types for CDU monitoring on logic photomasks is no longer an issue, since the transmitted intensity map gives all the needed information, as shown in this paper. In this study, the photomask was heavily degraded after more than 18,000 300mm wafers exposed and the cleaning brought it back almost to its original state after manufacture. Wafer CD, photomask CD and iCDU results can be compared, before and after a standard mask shop cleaning. Measurement points have be chosen in logic areas and SRAM areas, so that their respective behaviours can be studied separately. Transmitted maps before and after cleaning were analysed in terms of CD shift and CDU degradation. The delta map shows a nice correlation with photomask CD shift. iCDU demonstrated the capability to detect a reliable CD range degradation of 5nm on photomask by a comparison between a reference inspection and the current inspection. Die to die inspection mode provides also valuable data, highlighting the degraded chrome sidewalls, more in the photomask centre than on the edges. Ultimately, these results would enable to trigger the preventive cleanings rather than on predefined thresholds. The expected gains for wafer fabs are cost savings (adapted cleanings frequency), increased photomask availability for production, longer photomask lifetime, no additional SEM time neither for photomask nor on wafer.

The aim of this study is to determine the different types of haze contamination that occur in industrial conditions, using direct physico-chemical analyses on full 6'' masks leaving their pellicle intact. Contaminated masks coming from end users (ST - France) or masks fab (Toppan Photomask) have been analysed. First, references XPS analyses on specially designed blanks from Toppan have been performed. Four references have been studied by angle resolved XPS. These studies show the absence of nitrogen and sulphur contamination on SiO"2 side for the four references. On Cr side, a weak residual sulfur contamination has been observed as well as a very significant nitrogen concentration for the masks treated with a standard process. Concerning the masks treated with a sulfate free process, on Cr side, no residual sulfur has been detected by XPS, whereas few trace of nitrogen amount has been detected. Then a mask coming from the ST fab contaminated in real industrial conditions has been studied with several complementary characterisation techniques such as XPS, SEM, Raman and Tof-Sims. Theses analyses confirm that the back glass haze on the mask is on a particle form. Two types of defects have been found: small particles (a few @mm size), having a stick shape, with a very typical form indicating a crystal growth mechanism, and big particles (a few [email protected] size). The detailed physico-chemical results show the composition of the particles. Raman and Tof-Sims clearly show that small particle (with a stick form) are made of ammonium sulphate (NH"4)"2SO"4 crystals. XPS, Raman and Tof-Sims indicate that big particles are a nitrogen containing polymer with a weak sulphate contamination.

193nm binary photomasks are still used in the semiconductor industry for the lithography of some critical layers for the nodes 90nm and 65nm, with high volumes and over long period. These 193nm binary masks seem to be well-known but recent studies have shown surprising degrading effects, like Electric Field induced chromium Migration (EFM) [1] or chromium migration [2] [3] . Phase shift Masks (PSM) or Opaque MoSi On Glass (OMOG) might not be concerned by these effects [4] [6] under certain conditions. In this paper, we will focus our study on two layers gate and metal lines. We will detail the effects of mask aging, with SEM top view pictures revealing a degraded chromium edge profile and TEM chemical analyses demonstrating the growth of a chromium oxide on the sidewall. SEMCD measurements after volume production indicated a modified CD with respect to initial CD data after manufacture. A regression analysis of these CD measurements shows a radial effect, a die effect and an isolated-dense effect. Mask cleaning effectiveness has also been investigated, with sulphate or ozone cleans, to recover the mask quality in terms of CD. In complement, wafer intrafield CD measurements have been performed on the most sensitive structure to monitor the evolution of the aging effect on mask CD uniformity. Mask CD drift have been correlated with exposure dose drift and isolated-dense bias CD drift on wafers. In the end, we will try to propose a physical explanation of this aging phenomenon and a solution to prevent from it occurring.

The aim of this study is to determine the different types of haze contamination that occur in industrial conditions, using direct physico-chemical analyses on full 6" masks leaving their pellicle intact. Contaminated masks coming from end users (ST - France) or masks fab (Toppan Photomask) have been analysed. First, references XPS analyses on specially designed blanks from Toppan have been performed. Four references have been studied by angle resolved XPS. These studies show the absence of nitrogen and sulfur contamination on SiO 2 side for the four references. On Cr side, a weak residual sulfur contamination has been observed as well as a very significant nitrogen concentration for the masks treated with a standard process. Concerning the masks treated with a sulfate free process, on Cr side, no residual sulfur has been detected by XPS, whereas few trace of nitrogen amount has been detected. Then a mask coming from the ST fab contaminated in real industrial conditions has been studied with several complementary characterisation techniques such as XPS, SEM, Raman and Tof-SIMS. Theses analyses confirm that the back glass haze on the mask is on a particle form. Two types of defects have been found: small particles (a few μm size), having a stick shape, with a very typical form indicating a crystal growth mechanism, and big particles (a few 10 μm size).The detailed physico-chemical results show the composition of the particles. Raman and Tof-Sims clearly show that small particle (with a stick form) are made of ammonium sulfate (NH 4 ) 2 SO 4 crystals. XPS, Raman and Tof-Sims indicate that big particles are a nitrogen containing polymer with a weak sulphate contamination.

In microelectronic industry, mainly from the 65nm node, phase shift photomasks (PSM) are increasingly used for critical layers, optical properties of the shifter (MoSi) giving a better control of critical dimensions (CD) in photoresist. Fabusers and maskshops have committed on specifications that restrict phase and transmission variations within certain limits. The goal of this study is to validate and/or update these previously admitted limits. A specific test reticle has been jointly designed with several structures representative of 65nm and 45nm nodes and then manufactured with a specific process in order to voluntarily degrade the phase and transmission uniformity within the mask. Knowing all CD and their related phase and transmission on mask, CD variations seen on wafers have been directly linked to phase and transmission variations. In parallel, rigorous simulations have been performed using Panoramic software in order to predict effects of phase and transmission variations on wafer. This reticle has been also used for early studies to evaluate the impact of phase and transmission variations on optical proximity correction (OPC) model.

With the optimization of sulfate-free cleaning the issue of haze under pellicle was almost eliminated. In consequence, current reasons for mask repelliclization needs are moving from pattern issues to more gross problems on back glass. Moreover, the longer life of photomasks allows a new problem to appear as growing defects on back glass, commonly ascribed to environmental conditions at user's site. The commonality of these problems is being independent on mask complexity and substrate. In order to avoid the criticalities of pellicle removal and cleaning treatment as well as the cost of necessary inspection after new pellicle application, the best solution is cleaning only the backside of the mask, provided that integrity of pellicle and pattern on front side are preserved In this article we present the results obtained by the use of the Mask cleaner DE050019TM on several cases. The efficiency of the treatment was assessed in terms if removal capability on different kinds of contaminations, either from use or mask aging. Pattern inspections were conducted in order to assess ESD robustness. Ionic residues were checked by IC aimed to compare with standard cleanings. This methodology demonstrated to be capable of maintaining a Particle Removal Efficiency>97% on all kinds of contaminations, without any damage to pellicle or harm to patterns, still maintaining residual ions at the same level as after cleaning by standard tools.

Within the frame of the European R&D project the so called "HYMNE" project, lead by STM, advanced vacuum decontamination processes had been demonstrated to be efficient on wafer substrates in order to remove airborne molecular contamination (moisture, VOC..), to avoid crystalline defects after dry etching process and to improve yield for sub 90 nm technologies. Further to these significant results on wafers, a pool of partners investigated new methods and processes based on vacuum technology for photomask decontamination. These studies were carried out in the frame of the European R&D CRYSTAL project, focusing on photomask defect reduction. Today, vacuum process is not very widespread in photomask environment: in fab environment nor in mask manufacturing cycle. However such vacuum substrate decontamination could be also efficiently applied in order to reduce AMC contamination, which is one of the root causes of haze and crystalline defects. In this paper, we report for the first time, vacuum process investigations on pellicled photomasks that could be applied in fab environment, as well as vacuum process investigations on patterned blank that could be integrated into mask manufacturing cycle. First, vacuum process had been investigated on pellicled photomasks, including parameter influences. Goal is to renew and replace the environment under the pellicle by clean environment. During the process, specific care has to be taken on pellicle behavior under vacuum. The challenge is indeed to manage the pellicle during the vacuum process without damaging it, especially after several decontamination cycles. Finally, repeatability tests have also been successfully carried out and will be reported. We also report advanced vacuum process on patterned blank that could be integrated into mask manufacturing flow. Such procedure is an efficient complementary process in order to outgas contaminants from photomasks, and in order to reduce AMC residues (especially sulfate) in mask manufacturing cycle. Experimental results will be reported.

Contamination and especially Airbone Molecular Contamination (AMC) is a critical issue for mask material flow with a severe and fairly unpredictable risk of induced contamination and damages especially for 193 nm lithography. It is therefore essential to measure, to understand and then try to reduce AMC in mask environment. Results and assessment of mask pod environment in term of molecular contamination was presented in a first step (1 1 ). Then in second step further studies was carried out within European CRYSTAL project in order to reduce mask pod influence and contamination due to material out gassing. Results are shown here. These studies were carried out in the frame of the European R&D project, the so called "CRYSTAL" project, focusing on photomask defect reduction.

The paper describes a new approach of evaluating isolated opaque defects, as well as CD-like defects on hole layer, using features available on the inspection tool. This eliminates further verifications on specific tools, which would result in their overloading and in time consuming, with a potential negative impact on the delivery time of any product going through such processes. In the first case the method consists of associating the effect of a cluster of assist bars to that of isolated opaque defects, considering their size and position on the layout of the mask. In case of CD-like defects on holes the evaluation is based on a thorough characterization of the performance of the Litho2 detector of the Terascan T576 and its further verification with the AIMS readings.

Context/ study Motivation: Contamination and especially Airbone Molecular Contamination (AMC) is a critical issue for mask material flow with a severe and fairly unpredictable risk of induced contamination and damages especially for 193 nm lithography. It is therefore essential to measure, to understand and then try to reduce AMC in mask environment. Mask material flow was studied in a global approach by a pool of European partners, especially within the frame of European MEDEA+ project, so called "MUSCLE". This paper deals with results and assessment of mask pod environment in term of molecular contamination in a first step, then in a second step preliminary studies to reduce mask pod influence and contamination due to material out gassing. Approach and techniques: A specific assessment of environmental / molecular contamination along the supply chain was performed by all partners. After previous work presented at EMLC 07, further studies were performed on real time contamination measurement pod at different sites locations (including Mask manufacturing site, blank manufacturing sites, IC fab). Studies were linked to the main critical issues: cleaning, storage, handling, materials and processes. Contamination measurement campaigns were carried out along the mask supply chain using specific Adixen analyzer in order to monitor in real time organic contaminants (ppb level) in mask pods. Key results would be presented: VOC, AMC and humidity level on different kinds of mask carriers, impact of basic cleaning on pod outgassing measurement (VOC, NH3), and process influence on pod contamination... In a second step, preliminary specific pod conditioning studies for better pod environment were performed based on Adixen vacuum process. Process influence had been experimentally measured in term of molecular outgassing from mask pods. Different AMC experimental characterization methods had been carried out leading to results on a wide range of organic and inorganic contaminants: by inline techniques based on Adixen humidity, also VOC and organic sensors, together by off-line techniques already used in the extensive previous mask pods benchmark (TD-GCMS & Ionic Chromatography). Humidity and VOC levels from mask carriers had shown significant reduction after Adixen pod conditioning process. Focus had been made on optimized vacuum step (for AMC) after particles carrier cleaning cycle. Based upon these key results new procedures, as well as guidelines for mask carrier cleaning optimization are proposed to improve pod contamination control. Summary results/next steps: This paper reports molecular contamination measurement campaigns performed by a pool of European partners along the mask supply chain. It allows us to investigate, identify and quantify critical molecular contamination in mask pod, as well as VOC and humidity, issues depending on locations, uses, and carrier's type. Preliminary studies highlight initial process solutions for pods conditioning that are being used for short term industrialization and further industrialized.

Crystal growth on advanced reticles is currently a world wide industrial problem in high end semiconductor production environment, crystals are mainly found on reticles that use high energy photons at 193nm wavelength. The most common crystals to be found on masks are ammonium sulphate, a combination of sulphate, from maskshop residues after clean, pellicle materials and storage conditions and amines from clean room, tool and storage environments. High energy photons act as a catalyst to form crystals on both the pattern side as well as the backglass surface. After a number of exposures crystals can grow in size and eventually become printable. In order to detect HAZE before critical dimensions have been reached suitable detection methods need to be implemented to ensure image integrity. These detection methods are different and complementary depending on the surface to be inspected. Once crystals have started growing, the only method to regain mask quality is to clean the mask at the manufacturers site. This brings with it several undesirable situations, not only is the mask unavailable for production but the cleaning of a mask leads to a potential risk of damaging the mask especially for sub resolution patterns such as scatter bars and phase and transmission changes for eaPSM (Embedded Attenuated Phase Shift Mask) masks. This paper will discuss the initial haze issues seen in a 300mm wafer fab and actions put in place to address the problem. An explanation of results gained from haze reduction actions implemented in a wafer fab will be given. Haze seen by reticle inspection and surface analysis tools can be characterised by typical contamination patterns. These signatures appear after a certain number of wafers exposed depending on several reticle variables such as transmission, Binary, eaPSM, Pellicle. Details will be given of how reticles are managed to ensure minimum impact to a production environment with an appropriate reticle control plan. AMC (Airborne Molecular Contamination) in wafer fab and equipment environment is a key factor for crystal growth. The type of filtration installed to reduce AMC and method of atmospheric monitoring for critical areas will be explained. Choice of reticle storage conditions and materials used for transport during the life of the reticle will be included. Improvements in maskshop cleaning processes, reticle materials and environmental control have lead to extended mask lifetime in the wafer fab of more than 20 times. The fundamental differences and relative monitoring will be described and gain from implemented actions will be presented Once crystals have started growing, the only method to regain mask quality is to clean the mask at the manufacturers site. This brings with it several undesirable situations, not only is the mask unavailable for production but the cleaning of a mask leads to a potential risk of damaging the mask especially for sub resolution patterns such as scatter bars and phase and transmission changes for eaPSM (Embedded Attenuated Phase Shift Mask) masks. This paper will discuss the initial haze issues seen in a 300mm wafer fab and actions put in place to address the problem. An explanation of results gained from haze reduction actions implemented in a wafer fab will be given. Haze seen by reticle inspection and surface analysis tools can be characterised by typical contamination patterns. These signatures appear after a certain number of wafers exposed depending on several reticle variables such as transmission, Binary, eaPSM, Pellicle. Details will be given of how reticles are managed to ensure minimum impact to a production environment with an appropriate reticle control plan. AMC (Airborne Molecular Contamination) in wafer fab and equipment environment is a key factor for crystal growth. The type of filtration installed to reduce AMC and method of atmospheric monitoring for critical areas will be explained. Choice of reticle storage conditions and materials used for transport during the life of the reticle will be included. Improvements in maskshop cleaning processes, reticle materials and environmental control have lead to extended mask lifetime in the wafer fab of more than 20 times. The fundamental differences and relative monitoring will be described and gain from implemented actions will be presented