The development of EUV resists is one of the major challenges for the deployment of high-NA EUV lithography, which is on the roadmap for high-volume manufacturing of future semiconductor technology nodes. Resist performance is admittedly governed by a resolution-roughness-sensitivity (RLS) tradeoff. This study reports on the EUV resist progress achieved during the last year in the framework of the resist screening program by PSI and ASML. An extensive performance characterization of different resists was carried out using the XIL-II beamline EUV interference lithography (EUV-IL) tool at the Swiss Light Source (SLS). We present the upgraded screening metrology used in 2020 at PSI enabling increased confidence in results. We report material performance towards patterning lines/spaces features with respect to the key parameters of RLS: half-pitch (HP), dose-to-size (DtS), line-width-roughness (LWR), as well as Z-factor for overall performance consideration. General progress in EUV resist development is reviewed by considering several resist platforms available today from different vendors. Different molecular and chemically amplified resist materials are demonstrated as viable for 16 nm resolution technology nodes. One chemically-amplified resist vendor shows suitable materials for 13-nm-resolution technologies while exhibiting potential for further downscaling. We present different metal-oxide resists screening with resolutions down to 10 nm HP. We finally discuss the overall progress of materials achieved between 2019 and 2020 towards reaching high-NA.
High-NA extreme ultraviolet lithography (EUVL) is going to deliver the high-volume manufacturing (HVM) patterning for sub-3nm technology node for the semiconductor industry. One of the critical challenges is to develop suitable EUV photoresists at high resolution with high sensitivity and low line-width roughness (LWR) at reduced film thickness needed for high-NA by its reduced depth of focus (~1/NA2). The resist performance is generally limited by the resolution-LWR sensitivity (RLS) tradeoff, and it is critical to find new materials to support the future lithography nodes. EUV interference lithography (EUV-IL) is a powerful and efficient technique to test new materials at high resolution. In this work, we evaluate the performance of about 120 EUV resists, including molecular resist, inorganic resist, chemically-amplified resist (CAR), and chemically-amplified resist with a metal sensitizer (metal-CAR). Among all tested resists, we selected and compared six resists with the best performance in dose-to-size, line-width roughness, and maximal exposure latitude for 16 nm and 14 nm half-pitch (HP) lines/spaces (LS). A molecular resist showed the lowest dose to resolve HP 16 nm (29 mJ/cm2) and 14 nm (31 mJ/cm2), still featuring low LWRunbiased (2.7 nm and 3.1 nm, respectively). We observed that there is steady progress in EUV resist development: the LWR of the resists was improved in comparison with the results of the last two years as we noted that the amount of the resists within given dose and LWR threshold increased from 10 % to 33% for HP 14 nm. For contact holes, CAR gave the lowest LCDU of 2.2 nm for HP 20 nm with the lowest doses (21.1 mJ/cm2). While inorganic resists resolved pillars with highest resolution HP down to 18 nm with LCDU of 2.1 nm.
We investigated how the processing parameters, including post exposure baking (PEB), and resist film thickness (FT) influence the dose and line width roughness (LWR) of different types of EUV resists, targeted for the high-NA EUV lithography. We compared the dose and LWR of molecular, inorganic and CAR resists at half-pitch (HP) of 16 and 14 nm for different PEB temperatures. The results show that without PEB or at lower PEB temperature, resists require higher doses, as expected. We also observed the different behavior of various resist platforms in response to variation of the film thickness. The results showed that there is a room for the optimization of the processing parameters to improve dose and LWR of molecular, inorganic and CAR resists for line/space printing at high resolution.
Using high-resolution extreme ultraviolet interference lithography (EUV-IL), we investigated contact hole/pillars printing performance of several EUV resist platforms for the high-NA EUV lithography. We compared the dose and local critical dimension uniformity (LCDU) of the three chemically-amplified resists (CARs) with the best performance for printing contact holes (CHs) at half pitch (HP) of 24 and 20 nm. One of the CARs showed the lowest LCDU, 2.3 and 2.2 nm with lowest dose 16.4 and 21.1 mJ/cm2 for HP 24 and 20 nm, respectively. With the inorganic resist we obtained 38.8 mJ/cm2 with an LCDU of 1.3 nm for HP 20 nm pillars. We have also studied the effects of the resist thickness and post-exposure baking (PEB) temperature on the dose and LCDU. These results show that there are promising CAR and non-CAR resists for CH printing towards high-NA EUVL.
High-NA extreme ultraviolet lithography (EUVL) is going to deliver the high-volume manufacturing (HVM) patterning for sub-7 nm nodes for the semiconductor industry. One of the critical challenges is to develop suitable EUV resists at high resolution with high sensitivity and low line-edge roughness (LER). The resist performance is generally limited by the resolution-LER-sensitivity (RLS) tradeoff and it is critical to find new resists that have a performance beyond this tradeoff. EUV interference lithography (EUV-IL) is a powerful and efficient technique that can print high resolution: half pitch (HP) down to 6 nm nanostructures. In this work, we evaluate the performance of the EUV resists, including molecular resist, inorganic resist, chemically-amplified (CAR) and metal sensitizer chemically-amplified resist (Metal-CAR). Six resists with the best performance have been compared in dose-to-size, line-edge roughness, exposure latitude for half pitch 16 nm and 14 nm. The molecular resist A showed lowest dose to resolve HP 16 nm (35 mJ/cm2) and 14 nm (41 mJ/cm2) but with high line edge roughness (LER 3.5 nm). CAR resist C provided lowest LER 1.9 and 1.8 nm for HP 16 nm and HP 14 nm, respectively, but with higher doses 74 mJ/cm2 (HP 16 nm) and 69 mJ/cm2 (HP 14 nm). The inorganic resist showed comprehensive good performance, giving low LER of 2.1 nm with 50 mJ/cm2 and 42 mJ/cm2 for HP 16 nm and HP 14 nm, respectively. Using the simplified Z-factor model, we showed that the LER of the resists was improved over the last two years. As the inorganic resist could resolve HP 11 nm with dose 67 mJ/cm2, we conclude it to be the current best candidate to partially resolve the RLS tradeoff problem and could be the potential EUV resist for semiconductor technological node printing.
Extreme ultraviolet interference lithography (EUV-IL) is a relatively simple and inexpensive technique that can pattern high-resolution line/space and has been successfully used for the resist performance testing. While the aerial image in EUV-IL formed by two beams is straightforward to understand and has contrast of 1, the aerial image formed by four beams providing contact holes is rather complicated. The beam polarization and relative phases of the individual beams play a significant role in the aerial image formation in four-beam interference lithography. In particular, controlling the relative phase of the beams is very difficult to achieve due to short wavelength. To circumvent this problem, we propose an effective double exposure four-beam interference lithography method, by intentionally designing the grating with a slightly different pitch to create an optical path difference that is longer than the coherence length of the EUV light (13.5 nm). We numerically prove the effective double exposure four-beam interference is not sensitive to the phases difference and verify our analytical model by printing both positive tone chemically amplified resist and a negative tone inorganic resist.
For more than a decade, the semiconductor manufacturing industry has anticipated the introduction of Extreme Ultraviolet Lithography (EUVL) into high-volume manufacturing (HVM). The readiness of the supporting EUV resists is one of the requirements for HVM. While the industry is planning to introduce EUVL into HVM at 7 nm node, it is important to address the availability of the resists for future generations and in particular for the high-NA EUVL which will have the patterning capability down to 8 nm half-pitch. In this study we report on the performance of promising EUV resists evaluated by EUV interference lithography (EUV-IL) at the Swiss Light Source (SLS) at the Paul Scherrer Institut (PSI). We evaluated EUV resists that are being developed as candidate materials for future technology nodes and we assessed their potential for high-NA EUV lithography. Several new chemically-amplified resists (CARs) and non-CAR resists have been investigated with the aim to resolve patterns down to 10 nm hp. While, up to now, CARs performance reached down to 13 nm half pitch (hp) only, we report about a recent CAR that can partially resolve lines down to 11 nm hp. Moreover, some other non-CAR resists have achieved resolutions down to 10 nm. We evaluated essential parameters, such as critical dimension (CD) and line edge roughness as a function of dose and we estimated the exposure latitude (EL). Furthermore, we report on the ultimate extendibility of CAR platform materials in manufacturing, and on novel resist platforms developed to address the challenges in the patterning at hp ≤ 10 nm.
Extreme ultraviolet interference lithography (EUV-IL) is relatively simple and inexpensive technique that can pattern high resolution line/space and has been successfully used for the resist performance testing. While the aerial image in EUV-IL formed by two beams is straightforward to understand and has contrast of 1, the aerial image formed by four beams providing contact holes (CHs) is rather complicated. The phases of the interfering beams as well as by the polarization play big roles in the image of the interference pattern and its contrast. To understand thoroughly the formation of CH, we investigate theoretically polarization effect on the aerial image generated with two and four-beam interference. We show the coherent four-beam interference provides the highest contrast (1) with zero initial phase. But the interference pattern strongly depends on the phase difference and switch from one to another when the phase difference between the two pairs of gratings is π/2. Consequently, the contrast also decreases and interference pattern could end with random form when the relative phase of the beams cannot be fully controlled. We propose an incoherent four-beam interference model by intentionally designing the grating with a slightly different pitch to create an optical path difference that is longer than the coherence length of the EUV light (13.5 nm). We also discuss the polarization-induced contrast loss. We verify our analytical model by printing both positive tone chemically amplified resist (CAR) and a negative tone inorganic resist.
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