Klaus Edinger

e-beam induced EUV photomask repair ― a perfect match

Due to the updated ITRS roadmap EUV might enter the market as a productive solution for the 32 nm node1. Since the EUV-photomask is used as mirror and no longer as transitive device the severity of different defect types has changed significantly. Furthermore the EUV-photomask material stack is much more complex than the conventional 193nm photomask materials which expand the field of critical defect types even further. In this paper we will show, that classical 193 mask repair processes cannot be applied to EUV material. We will show the performance of a new repair process based on the novel ebeam repair tool MeRiT® HR 32. Furthermore this process will be applied on real EUV mask defects and the success of these repairs confirmed by wafer prints.

EUV and non-EUV inspection of reticle defect repair sites

We report the actinic (EUV wavelength) and non-actinic inspection of a multilayer-coated mask blank containing an array of open-field defect repair sites created in different ways. The comparison of actinic brightfield and darkfield measurements shows the importance of having both local reflectivity and scattering measurements. Although effective mask blank repair capabilities have not been adequately demonstrated, the data acquired in this experiment have been very instructive. Correlation with non-actinic inspection methods shows the difficulty of establishing a successful predictive model of the EUV response without EUV cross-comparison. The defect repair sites were also evaluated with SEM, AFM, and 488-nm-wavelength confocal microscopy. The data raise important questions about mask quality specifications and the requirements of future commercial actinic inspection tools.

Bringing mask repair to the next level

Mask repair is an essential step in the mask manufacturing process as the extension of 193nm technology and the insertion of EUV are drivers for mask complexity and cost. The ability to repair all types of defects on all mask blank materials is crucial for the economic success of a mask shop operation. In the future mask repair is facing several challenges. The mask minimum features sizes are shrinking and require a higher resolution repair tool. At the same time mask blanks with different new mask materials are introduced to optimize optical performance and long term durability. For EUV masks new classes of defects like multilayer and phase defects are entering the stage. In order to achieve a high yield, mask repair has to cover etch and deposition capabilities and must not damage the mask. These challenges require sophisticated technologies to bring mask repair to the next level. For high end masks ion-beam based and e-based repair technologies are the obvious choice when it comes to the repair of small features. Both technologies have their pro and cons. The scope of this paper is to review and compare the performance of ion-beam based mask repair to e-beam based mask repair. We will analyze the limits of both technologies theoretically and experimentally and show mask repair related performance data. Based on this data, we will give an outlook to future mask repair tools.

Increasing mask yield through repair yield enhancement utilizing the MeRiT

The push toward smaller feature size at 193 nm exposure has been enabled by resolution enhancement techniques (RET) such as phase shifting technologies and optical proximity correction (OPC) which require more costly and time intensive resources to fabricate. This leads to a higher overall cost associated with each mask, making it more important than ever for the mask shop to fully utilize and improve its repair capabilities as the presence of defects on the final product is the major yield reducing factor. An increase in repair capability leads to a direct enhancement in repair yield which translates to an improvement in overall mask yield and a reduction in cycle time. The Carl Zeiss MeRiT® MG 45 provides numerous benefits over other techniques that can lead to an increase in repair yield. This paper focuses on methods utilizing the MeRiT® MG 45 that can be employed in a production environment in order to increase mask repair yield. The capability to perform multiple repairs at a single site without optical degradation enables defects that were not successfully repaired the first time to be corrected on a subsequent attempt. This not only provides operator mistakes and inexperience to be corrected for, but eliminates the need to hold up production in order to start a new mask which can cause a cascading effect down the line. Combining techniques to approach difficult partial height and combination defects that may have previously been classified as non-repairable is presented in an attempt to enable a wider range of defects to be repaired. Finally, these techniques are validated by investigating their impact in a production environment in order to increase overall mask yield and decrease cycle time.

High-resolution e-beam repair for nanoimprint templates

UV nanoimprint lithography (UV-NIL) is a high-throughput and cost-effective patterning technique for complex nanoscale features and is considered a candidate for CMOS manufacturing at the 22nm node and beyond. To achieve this target a complete template fabrication infrastructure including inspection and repair is needed. Due to the 1X magnification factor of imprint lithography the requirements for these steps are more challenging compared to those for 4X photomasks. E-beam repair is a very promising repair technology for high-resolution imprint templates. It combines the advantages of precise beam placement using fine resolution images and damage free repair by electron beam induced chemical reactions. In this work we performed template repair using a new test stand with improved beam and stage stability. Repeatability of 3D pattern reconstruction with main focus on shrunk lateral repair dimensions and height control was investigated. The evaluation was done on various features in a 40nm half pitch design. Additionally, the resolution capability of the new hardware was examined on selected programmed defects in a 32nm half pitch design. A first qualitative examination of the repaired template was done using top-view SEM images taken from the test stand before and after repair. The repaired template was then imprinted on 300mm silicon wafers, and the imprinted repaired defects were analyzed using a SEM Zeiss Ultra 60.

Electron beam directed repair of fused silica imprint templates

Imprint lithography has been shown to be an effective method for replication of nanometer-scale structures from a template mold. Step-and-Flash Imprint Lithography (S-FILTM) employs a UV-photocurable imprint liquid, which enables imprint processing at ambient temperature and pressure. The use of a transparent fused silica template facilitates precise overlay. With this combination of capabilities, NIL is a multi-node technique that is suitable for advanced prototyping of processes and devices to meet the anticipated needs of the semiconductor industry. However, since the technology is 1X, it is critical to address the infrastructure associated with the fabrication of templates. An essential part of this infrastructure is the capability to identify and repair template defects. Fused silica imprint templates are typically produced from photomask substrates, and it is straightforward to make use of the tools and processes that have been developed to repair commercial photomasks. However, the optical properties of the repaired region are of secondary importance because S-FIL patterning is based on direct transfer of topography (rather than indirect transfer of an optical image). As in conventional photolithography, both additive and subtractive repairs are required to correct a variety of defect types. Repair techniques that are based on electron-beam induced chemical reactions have demonstrated the capability to perform both additive (deposition) and subtractive (etching) processes at high resolution. This work is a demonstration that electron-beam directed additive repair is capable of repairing fused silica template structures with sub-100 nm resolution.