Shingo Kanamitsu

Prospect of EUV mask repair technology using e-beam tool

Currently, repair machines used for advanced photomasks utilize principle method like as FIB, AFM, and EB. There are specific characteristic respectively, thus they have an opportunity to be used in suitable situation. But when it comes to EUV generation, pattern size is so small highly expected as under 80nm that higher image resolution and repair accuracy is needed for its machines. Because FIB machine has intrinsic damage problem induced by Ga ion and AFM machine has critical tip size issue, those machines are basically difficult to be applied for EUV generation. Consequently, we focused on EB repair tool for research work. EB repair tool has undergone practical milestone about MoSi based masks. We have applied same process which is used for MoSi to EUV blank and confirmed its reaction. Then we found some severe problems which show uncontrollable feature due to its enormously strong reaction between etching gas and absorber material. Though we could etch opaque defect with conventional method and get the edge shaped straight by top-down SEM viewing, there were problems like as sidewall undercut or local erosion depending on defect shape. In order to cope with these problems, the tool vender has developed a new process and reported it through an international conference [1]. We have evaluated the new process mentioned above in detail. In this paper, we will bring the results of those evaluations. Several experiments for repair accuracy, process stability, and other items have been done under estimation of practical condition assuming diversified size and shape defects. A series of actual printability tests will be also included. On the basis of these experiments, we consider the possibility of EB-repair application for 20nm pattern.

Application of EB repair for high durable MoSi PSM

Recently there has been a demand for high durability MoSi masks. There are some candidates for MoSi mask materials. They are preferable for both mask user and mask manufacture because they show not only high durability against exposure or cleaning process but also process compatibility in production line[1]. They are gaining momentum to practical application. However, there is a drawback for manufacturing regarding the mask repair process. Because ebeam repair employs pure chemical reaction, it faces severe etching difficulty due to higher chemical stability. Meanwhile, the tool supplier has looked into that chemical reaction in detail since the problem was unveiled. They developed a dedicated etching process for high durable materials. It’s so important for the mask manufacturer to evaluate this process properly before they transfer conventional MoSi to new high durability MoSi. A comprehensive understanding of this new process should be acquired by trying several kinds of etching tests. In this paper we will report the results ranging from basic etching rate, selectivity, repair accuracy to flexibility for complicated shaped defects. This data tells us a lot about if it can be applied for practical use. The experiment was performed with e-beam repair tool “MeRiTⓇ”, which was released as the latest version from ZEISS last year. An improved new etching process was applied to “A6L2” type high durable blanks provided by HOYA corporation. A wide variety of programmed defects were arranged on a line and space featured test mask. These programmed defects were repaired with the procedure developed by ZEISS. After repair, printed image was evaluated by AIMSTM system. This paper will discuss the initial results of these first steps into the uncharted territory of high durability MoSi repair.

A photomask defect evaluation system

Photomasks are currently inspected based on the standard of defect size. A shortcoming of this standard is that the type of defects which do not impact on a wafer, could be detected as impermissible defects. All of them are subject to repair works and some of them require further inspection by AIMS. This is one of the factors that are pushing down the yield and the turnaround time (TAT) of mask manufacturing. An effective way to improve this situation will be to do the repair works selectively on the defects that are predicted to inflict a functional damage on a wafer. In this report, we will propose a defect evaluation system named ADRES (Advanced Photomask Defect Repair Evaluation System), featuring a function to extract edges from a mask SEM image to be passed on to a litho-simulation. A distinctive point of our system is the use of a mask SEM image with a high resolution.

Future Application of e-Beam Repair Tool Beyond 3X Generation

Currently, repair technology is one of the key factors in mask making process regarding TAT reduction and yield level enhancement. Since its commercial release EB repair tool has been commonly used for production line and contributed to high quality repair. But it is not guaranteed whether those conventional machines can keep up with future pattern reduction trend or not. In 2Xnm generation node some advanced exposure techniques seem to be adopted and that will inevitably require higher specification of repair machine. A simple lithography simulation predicts 5nm of indispensable repair accuracy for 2Xnm generation pattern. This number implies the necessity of upper class machine. Generally, the error budget of EB repair tool is composed of three to four components, stated another way mechanical stability, electrical (charging) uniformity, process stability, and graphical quality including software ability. If errors from those components are reduced, overall repair accuracy could be better. A suggestion which can improve those errors was issued last year from tool vender including new machine concept. We have conducted several kind of experiment in order to confirm the performance of new machine. In this paper, we will report the result of experiment and consider which part can effectively contribute to repair accuracy. And we have also evaluated its practical utility value for 2Xnm node by verifying actual application of some 3Xnm production masks.

A noble evaluation method for repaired area utilizing SEM images

In general photomask defect repair process flow, repaired portion is evaluated with AIMSTM and if AIMSTMs result is out of specification, the repaired portion must be re-repaired. With shrinking pattern on device, tighter specification is required. Therefore re-repair cycle time increases and turn around time of defect repair process becomes much longer. To solve this problem, we propose a noble evaluation method that enables us to judge without using AIMSTM with repair tool images. Images of EB repair tool is available for our propose because EB repair tool dose not give any damage on substrate and the resolution of image is quite high compared to other repair tools, FIB and Nanomachining tool. We made lithography simulation and practical experiments with line & space pattern of ArFatt. PSM with programmed defects. Consequently, we can predict AIMS-Results immediately after repair and there is a possibility to reduce the turn around time of defect repair process.

Application of EB Repair Tool for 45nm Generation Photomasks

Although photomask defect repair tools based on FIB, AFM and pulsed laser are mainly used in current production lines, there is a possibility they will not meet the requirements of 45nm generation photomasks. The EB repair tool is one of the candidates that has a possibility of meeting those requirements. The EB repair tool, MeRiT-MGTM, has already been announced by Carl Zeiss GmbH. The basic performance of this tool has been reported.1) Recently MoSi mask is most commonly used in leading edge devices, and defects are mainly opaque type. For this reason, the performance of EB-repair tool for MoSi etching should be investigated. In this paper, we will report the evaluation results of MeRiT-MGTM and consider whether this tool has a possibility of meeting the requirements of 45nm generation photomasks. In order to evaluate the performance of MeRiT-MGTM, we prepared 180nm half pitch line & space pattern of ArFatt. PSM with programmed defects. These programmed defects are not only simple extrusion shape but also of various shapes and sizes. By using these defects, we made practical experiment which would happen in real production line.

Improvement of sub-20nm pattern quality with dose modulation technique for NIL template production

Nanoimprint lithography (NIL) technology is in the spotlight as a next-generation semiconductor manufacturing technique for integrated circuits at 22 nm and beyond. NIL is the unmagnified lithography technique using template which is replicated from master templates. On the other hand, master templates are currently fabricated by electron-beam (EB) lithography[1]. In near future, finer patterns less than 15nm will be required on master template and EB data volume increases exponentially. So, we confront with a difficult challenge. A higher resolution EB mask writer and a high performance fabrication process will be required. In our previous study, we investigated a potential of photomask fabrication process for finer patterning and achieved 15.5nm line and space (L/S) pattern on template by using VSB (Variable Shaped Beam) type EB mask writer and chemically amplified resist. In contrast, we found that a contrast loss by backscattering decreases the performance of finer patterning. For semiconductor devices manufacturing, we must fabricate complicated patterns which includes high and low density simultaneously except for consecutive L/S pattern. Then it’s quite important to develop a technique to make various size or coverage patterns all at once. In this study, a small feature pattern was experimentally formed on master template with dose modulation technique. This technique makes it possible to apply the appropriate exposure dose for each pattern size. As a result, we succeed to improve the performance of finer patterning in bright field area. These results show that the performance of current EB lithography process have a potential to fabricate NIL template.

High-performance fabrication process for 2xnm hole-NIL template production

UV nano imprint lithography (UV-NIL) has high-throughput and cost-effective for complex nano-scale patterns and is considered as a candidate for next generation lithography tool. In addition, NIL is the unmagnified lithography and contact transfer technique using template. Therefore, the lithography performance depends greatly on the quality of the template pattern. According to ITRS 2013, the minimum half pitch size of Line and Space (LS) pattern will reach 1x nm level within next five years. On the other hand, in hole pattern, half pith of 2x nm level will be required in five years. Pattern shrink rate of hole pattern size is slower than LS pattern, but shot counts increase explosively compared to LS pattern due to its data volume. Therefore, high throughput and high resolution EB lithography process is required. In previous study, we reported the result of hole patterning on master template which has high resolution resist material and etching process. This study indicated the potential for fabricating 2xnm hole master template [1]. After above study, we aim at fabricating the good quality of 2xnm master template which is assured about defect, CD uniformity(CDU), and Image placement(IP). To product high quality master template, we develop not only high resolution patterning process but also high accuracy quality assurance technology. We report the development progress about hole master template production.

High resolution hole patterning with EB lithography for NIL template production

Nano imprint lithography (NIL) is one to one lithography and contact transfer technique using template. Therefore, the lithography performance depends greatly on the quality of the template pattern. In this study, we investigated the resolution and the defect level for hole patterning using chemical amplified resists (CAR) and VSB type EB writer, EBM9000. To form smaller pattern with high quality, high resolution resist process and high sensitivity etching process are needed. After these elements were optimized, we succeeded to form 24 nm dense hole pattern on template. In general, it is difficult to suppress the defect density in a large area because of fogging effect and process loading and so forth. However, from the view point of defect quality, 26 nm hole pattern is achieved to form with practical level in a large area. Therefore, we indicate the capability of forming 26 nm hole master template which will be required in 2019 from ITRS2013. These results show that this process is possible to obtain less than 30 nm hole pattern without enormous writing time. As future work, we will imprint master to replica template and check the printability.

Defect printability of advanced binary film photomask

Based on an acceptable wafer critical dimension (CD) variation that takes device performance into consideration, we presented a methodology for deriving an acceptable mask defect size using defect printability [1]-[3]. The defect printability is measurable by Aerial Image Measurement System (AIMSTM) and simulated by lithography simulation without exposure. However, the defect printability of these tools is not always the same as the actual one. Therefore, the accuracy of these tools is confirmed by fabricating the programmed defect mask and exposing this mask on wafer. Advanced Binary Film (ABF) photomask has recently been studied as a substitute for the conventional MoSi phase shift mask. For ABF photomask fabrication, mask performance for process and guarantee for mask defects by repair and inspection are important. With regard to the mask performance, the ABF photomask has high performance in terms of resolution of pattern making, placement accuracy, and cleaning durability [4]. With regard to the guarantee for mask defects, it has already been confirmed that the defect on the ABF photomask is repairable for both clear and opaque defects. However, it has not been evaluated for inspection yet. Therefore, it is necessary to evaluate the defect printability, to derive the acceptable mask defect size, and to confirm the sensitivity of mask inspection tool. In this paper, the defect printability of the ABF photomask was investigated by the following process. Firstly, for opaque and clear defects, sizes and locations were designed as parameters for memory cell patterns. Secondly, the ABF programmed defect mask was fabricated and exposed. Thirdly, mask defect sizes on the ABF programmed defect mask and line CD variations on the exposed wafer were measured with CD-SEM. Finally, the defect printability was evaluated by comparing the correlation between the mask defect sizes and the wafer line CD variations with that of the AIMSTM and the lithography simulation. From these results, the defect printability of AIMSTM was almost the same as the actual one. On the other hand, the defect printability of the lithography simulation was relaxed from the actual one for the isolated defect types for both clear and opaque defects, though the defect printability for the edge defect types was almost the same. Additionally, the acceptable mask defect size based on the actual defect printability was derived and the sensitivity of the mask inspection tool (NPI-7000) was evaluated. Consequently, the sensitivity of the NPI-7000 was detectable for the derived acceptable mask defect size. Therefore, it was confirmed that the ABF photomask could be guaranteed for mask defects.