BI Dan-dan, ZHANG Li-chao, SHI Guang
(1.Engineering Research Center of Extreme Precision Optics,Changchun Institute ofOptics,Fine Mechanics and Physics,Chinese Academy of Sciences,Changchun 130039,China;2.University of Chinese Academic of Sciences,Beijing 100049,China;3.Changchun National Extreme Precision Optics Co. Ltd.,Changchun 130039,China)
Abstract: The deep ultraviolet lithography is currently a main method for integrated circuit manufacture. The immersive projection objective must be used to increase resolution of the optical system for realization of smaller component feature dimensions. Therefore a number of rigorous requirements for optical coating component are put forward. In this paper we present designs of the film material and film system applicable to immersive lithographical system as well as the large angle polarization-maintaining film system required for optical systems at high NA. Key issues about immersion environment adaptability, hydrophobicity and anti-contamination of the immersion coating most critical to the objective are discussed. Laser irradiation lifetime of the coated components especially in the immersion environment that is an important factor to evaluate performance of the immersive lithographical system is analyzed.
Key words: immersion lithography;optical coatings;coating system design;environmental adaptability;lifetime under laser irradiation
引 言
New process nodes need to be reached according to Moore′s Law to increase integration of the integrated circuit components involved in the semiconductor technology. Its key issue lies in how to improve the lithographical resolution. In consideration of the fact that the resolution of lithographical projection objective is directly proportional to the exposure wavelengthλand the process factorkand inversely proportional to the numerical aperture of lithographical projection objective NA[1], the value of objective NA can be increased to improve the lithographical resolution only with full immersion between the last objective component and the silicon wafer in case that the main exposure wavelength is fixed as 193 nm and the process factor has been minimized[2].
在半導體技術中,為增加集成電路器件的集成度,需要按照摩爾定律不斷推進到新的工藝節(jié)點,其核心問題在于如何提升光刻分辨率??紤]到光刻投影物鏡的分辨率與曝光波長λ及工藝因子k成正比,并與投影光刻物鏡的數(shù)值孔徑NA成反比[1],在主流曝光波長固定在193 nm,工藝因子已經(jīng)縮小到極限的情況下,只能通過將物鏡最后一片元件與硅片之間充滿浸液的方式來提高物鏡的NA值,進而提高光刻分辨率[2]。
The value of projection objective NA can be increased to 1.3-1.4[3]with objective immersion to meet the requirement 10x nodes. But the application of the objective immersion technology makes the corresponding optical design and manufacture processes face more rigorous technology issues, and even thin-film optical components of the objective have to face a number of issues such as realization of optical indices, adaptability to the immersion environment and security of the laser irradiation lifetime. The objective specifications such as component transmittance and polarization aberration[4]must be strictly met. Design and preparation of the large angle polarization-maintaining film system will face extreme challenges[5]. The last system component has to be immersed into a liquid environment for years, and its characteristics such as anti-etching[6]and hydrophobicity[7]represent particular requirements that regular optical coatings have never faced. At the same time, film-coated components need to maintain optical capabilities in a liquid immersion environment and under the laser irradiation for years[8].
通過物鏡浸液的方式,可以使投影物鏡的NA值增大到1.3~1.4[3],滿足十幾納米光刻技術節(jié)點的要求,但應用物鏡浸液技術使得相應的光學設計與制造面臨更多苛刻的技術難題。而物鏡中的薄膜光學元件,更面臨著光學指標的實現(xiàn)、浸液環(huán)境的適應、激光輻照壽命的保障等眾多問題:物鏡中元件的透過率、偏振像差[4]等指標必須得到嚴格滿足,其大角度保偏膜系設計及制備將面臨極大挑戰(zhàn)[5];系統(tǒng)最后一片元件需數(shù)年浸泡在液體環(huán)境下,其防刻蝕[6]、疏水[7]等特性是常規(guī)光學薄膜未面臨的特殊要求;同時,鍍膜元件需在浸液環(huán)境以及長達數(shù)年的激光輻照環(huán)境下保持光學性能[8]。
The above issues relate to the fields of optics, chemistry, materials science,etc. They can be solved systematically only through the multi-disciplinary technical cooperation. To this end, systematic researches on the lithography were carried out began from end of the last century, under the leadership of the research of integrated circuit manufacturing technology, the lithography machine and the projection objective manufacturer as the main force, with the cooperation of optical materials manufacturers and related universities and research institutes. The optical capability, liquid immersion and irradiation lifetime of mask aligner, particularly immersion projection objective provide severe limitation of the overall design and operation stability. Therefore, mask aligner suppliers such as ASML and Nikon are dedicated to solving the contamination in an objective application environment and building up Marathon test devices for evaluation of the long-term irradiation lifetime of components and thin films[9]. Material suppliers such as Corning and Heraeus have commenced the long-term testing to evaluate the laser irradiation lifetime of optical materials such as fused quartz and calcium fluoride, and also created foundational damage models to evaluate the long-term practicability[10]. Furthermore, some research institutes have also conducted continual in-depth investigations under organizing by industry unions such as SEMATECH in United States and ASET in Japan[11]. For example, Lincoln Laboratory at MIT has conducted systematic researches on DUV(193 nm)/VUV(157 nm) laser irradiation and liquid immersion lifetime of optical materials and thin films[8]. In addition, projection objective manufactures such as Zeiss and Nikon are dedicated to researches on security of optical capability of high NA projection objectives, control of the polarization aberration and manufacture of extremely high-precision coated optical components[5,12]. Layout of the above multi-level researches has effectively supported fundamental and applied studies on the immersive lithographical objective. Capabilities of the immersive mask aligner that first emerged since 2004(ASML-XT1250i) have been constantly improved and now can meet the requirement for 1Xnm nodes.
上述問題涉及光學、化學、材料學等領域,需要跨學科技術協(xié)作才能夠獲得系統(tǒng)解決。為此,自上世紀末起,在集成電路制造技術研發(fā)需求的牽引下,以光刻機與投影物鏡制造商為主力,在光學材料廠商以及各相關大學、研究所的協(xié)同配合下,開展了光刻機的系統(tǒng)研究工作。光刻機尤其是浸沒式投影物鏡的光學性能、浸液和輻照壽命嚴重限制了整機的設計及使用穩(wěn)定性,因此ASML、尼康等光刻機供應商主要致力于解決物鏡應用環(huán)境下的污染問題,并搭建馬拉松實驗裝置來評價元件、薄膜的長期輻照壽命[9]??祵帯①R利氏等材料供應商則開展了長期實驗,對融石英、氟化鈣等光學材料進行激光輻照壽命評估,建立基礎損傷模型以評價其長期實用性[10]。另外,在美國SEMATECH和日本ASET等產(chǎn)業(yè)聯(lián)盟的組織下,一些研究機構也進行了持續(xù)的深入研究[11],例如MIT林肯實驗室在十余年的時間內(nèi),針對DUV(193 nm)/VUV(157 nm)光學材料、薄膜進行了激光輻照、浸液環(huán)境壽命的系統(tǒng)研究[8]。另外,蔡司、尼康等投影物鏡制造商致力于高NA投影物鏡光學性能保障、偏振像差的控制以及極高精度薄膜光學元件制造等方面的研究[5,12]。上述多層次研究布局有效支撐了浸液光刻物鏡的基礎及應用研究,自2004年首次問世以來(ASML-XT1250i),浸沒式光刻機的性能不斷得到提升,目前已滿足1Xnm節(jié)點需求。
Chinese studies in this field began from 2007. Changchun Institute of Optics, Fine Mechanics and Physics carried out research and development of the lithographical projection objective technology towards than 90 nm[13]nodes and much smaller nodes. Systematic research progresses in terms of ArF laser irradiation lifetime of thin-film components and immersive material protection interface have been obtained[14-16]to provide a good foundation for further apply of the projection objective.
該領域的研究在我國始于2007年。在國家科技重大專項的支持下,長春光機所開展了面向90 nm[13]及以下節(jié)點的光刻投影物鏡技術研發(fā),在薄膜元件ArF激光輻照壽命、浸液材料防護界面等研究方面取得了很大進展[14-16],為投影物鏡的進一步實用化奠定了良好基礎。
浸沒式光刻物鏡元件的大角度膜系設計及實現(xiàn)途徑
寬角度減反(BAAR)膜系的設計
There are two particular difficulties for the immersive projection objective. First, a high NA causes increase of the light incidence angle on the component surface. NA1.35 can be used as an example the water refraction index is 1.437 corresponding to the objective system NA0.94. In such case, some components need to reduce the residual reflectance within 0-70°[17]. The optical coating for immersive projection objective faces severer issues in terms of the large angle incidence than those for dry objective(NA0.75). In addition and from the view of film system design, film systems designed with materials such as MgF2, AlF3, LaF3, GdF3and SiO2[18-19]prepared in traditional thermal evaporation and ion beam sputtering methods are insufficient to ensure the extremely low residual reflectance and S/P polarization split at a large angle incidence, when an ArF excimer light source with the operating wavelength of 193nm is used. Some common methods that eliminate the polarization[20-21]cannot be compatible with the requirement for large angle incidence and need to pursue better solutions.
對浸沒式投影物鏡來說,存在兩個特殊的難題:首先,高NA導致了光線在元件表面入射角的增加,以NA1.35為例,水的折射率為1.437,相當于物鏡系統(tǒng)NA0.94,這種情況下,部分元件需要在0~70°[17]范圍內(nèi)減少剩余反射,相對干式物鏡(NA0.75)而言,浸沒式投影物鏡光學薄膜面臨的大角度入射問題更加嚴峻。另外,從膜系設計的角度考慮,當工作波長為193 nm的ArF準分子光源時,使用傳統(tǒng)熱蒸發(fā)和離子束濺射方法制備的MgF2、AlF3、LaF3、GdF3和SiO2[18-19]材料所設計的膜系很難保證在大角度入射時仍具有極低的剩余反射和S/P偏振分離,另外一些常見消偏振方法[20-21]無法兼顧大角度入射需求,需要尋求更好的解決辦法。
From the view of film system design, the above broad angle antireflection(BAAR) film system can be realized with two ideas. On one hand, the best solution of a film system design depends on materials with high/low refraction indices known from the maximum value principle in mathematics. The larger refraction index difference results in better optical capabilities of a film system[22]. The BAAR film system with more superior capabilities can be designed with importing film layers that have a lower refraction index. As shown in Fig.1, lower the refractive index of the outermost material in the design, the smaller the residual reflectance and polarization separation when the film is incident at a large angle. On the other hand, a film system design within 0-70° has approached to the so-called “omni-directional antireflection film”. An ideal solution uses the film system where the refraction index is shaded from the substrate to the air side, which has no interface and reflection and can effectively eliminate the polarization split[23-24]. However, an ideal film system with shaded refraction index is hard to be realized. The film system with shaded refraction index can be substituted approximately with the film system that has a gradient refraction index only according to the principle of Snell′s Law and following the rule that the film system interface with a smaller refraction index variation results in a larger initial incidence angle that begins to cause the polarization split. To realize both the above ideas, many possible attempts have been made in practice to prepare film layers with extremely low and adjustable refraction indices[25-26].
從膜系設計的角度看,可以通過兩種思路實現(xiàn)上述寬角度減反(Broad Angle Anti-Reflection,BAAR)膜系:一方面,由數(shù)學上的極大值原理可知,一個膜系設計的最優(yōu)解由高/低折射率材料所決定,其折射率差值越大,膜系的光學性能越好[22],因此可以通過引入折射率更低的膜層設計出性能更加優(yōu)異的BAAR膜系,如圖1所示,在設計中最外層材料折射率越低,膜系大角度入射時的剩余反射率和偏振分離越??;另一方面,0~70°的膜系設計已接近所謂的“全向減反膜”,理想的解決方案是采用從基底到空氣端折射率漸變的膜系,這樣的膜系無界面、無反射,能夠有效消除偏振分裂[23-24],然而理想的折射率漸變膜系很難實現(xiàn),只能根據(jù)斯涅耳定律的原理,遵循膜系界面折射率突變越小發(fā)生偏振分離的起始入射角越大的規(guī)律,采用梯度折射率膜系近似替代折射率漸變膜系。為實現(xiàn)以上兩種思路,制備出超低折射率膜層和折射率可調的膜層,人們在實踐中嘗試了多種可能[25-26]。
BAAR膜層材料的實現(xiàn)途徑
2.2.1Filmlayerwithanextremelylowrefractionindexpreparedinthesol-gelmethod
溶膠-凝膠法制備超低折射率膜層
Among regular film-coated materials, MgF2and cryolite have the lowest refraction index. MgF2has the refraction index of approximately 1.44 at 193 nm. The cryolite has a lower refraction index, but it is not suitable for use in the objective due to its worse environmental adaptability. In addition, traditional PVD processes are not convenient to realize the refraction index adjustment. Thus only other methods can be pursued to realize an extremely low refraction index. It can be known from the equivalent medium approximation(EMA) model that a pore structure needs to be introduced into the film layer to reduce the film layer refraction index. Main methods to prepare film layers with an extremely low refraction index include template and sol-gel methods. In recent years, many technologies to prepare thin films with the template method use copolymer as the template where film layers with the refraction index of 1.11 in a visible range as well as a certain anti-friction capability can be prepared. But the high-temperature calcination at more than 450 ℃ shall be used for this method. It is insufficient to meet the requirement on film-coated component surface shape index for the lithographical objective(less than 1 nm for a single component). Compared with the template method, the sol-gel method has been widely used in recent years due to its simple reaction principle, relatively low preparation temperature(~200 ℃), and favorable surface hydrophobic modification[27-28].
在常規(guī)鍍膜材料中,MgF2和冰晶石具有最低的折射率,其中MgF2在193 nm處的折射率約為1.44,冰晶石雖然具有更低的折射率,但由于其環(huán)境適應性較差而不適合在物鏡中使用。另外,傳統(tǒng)PVD工藝不便于實現(xiàn)折射率的調控,因此超低折射率的實現(xiàn)只能尋求其他方法。由等效介質近似(EMA)模型可知,為降低膜層折射率,需要在膜層內(nèi)引入孔隙結構,主流的超低折射率膜層制備方法有模板法和溶膠-凝膠法。近年來模板法制備薄膜的技術多采用異量分子聚合物(copolymer)為模板,可以制備出可見范圍內(nèi)折射率1.11的膜層,并且具有一定的抗摩擦性能,但該方法在工藝上需采用450 ℃以上的高溫煅燒工藝,很難保障光刻物鏡對鍍膜元件面形指標的要求(單個元件1 nm以下)。相對于模板法,溶膠-凝膠法因其反應原理簡單、制備溫度(~200 ℃)相對較低、利于進行表面疏水修飾的工藝優(yōu)勢,近年來被廣泛采用[27-28]。
For optical coatings on the lithographical objective, the regular sol-gel method uses MgF2as a base material to prepare materials with an extremely low refraction index. Different reaction paths can be adopted in realization[29]. But the essential idea is basically consistent. The MgF2sol material is obtained through reaction between the weak acidic salt or alcoholate that contains magnesium and the fluoric acid. Generally this material consists of self-organized nanometer particles that can form the MgF2bubble structure after treatment with an autoclave or aging treatment. In addition, the catenulate tree structure is formed through hydrolytic polycondensation of TEOS. It wraps the bubble MgF2particles to constitute an irregular tree structure. The sol sample obtained is used for thin film preparation through Czochralski method[30]or the spin-coating method. Finally pore film layers are prepared to realize a refraction index lower than that of the lumpy MgF2. The refraction index of film layers obtained finally can be adjusted with parameters in the reaction. The lowest refraction index that can be realized with this method is slightly more than 1.1, but the mechanical strength of film layers is frequently low. To solve this problem, Ishizawaetal.[31]use the viscous SiO2solution for spinning on the MgF2film layer prepared and heat to 100-200 ℃ to form the amorphous SiO2between MgF2particles, which makes mechanical strength of the film layer increase from approximately 25 MPa to about 135 MPa. In addition to the extremely low refraction index of the sol-gel film layer, its another advantage lies in a high resistance to laser damage that makes the film layer maintain integrity after exposure to the ArF laser irradiation at 5×107pulses and the energy density of 600 mJ/cm2/pulse[32].
對于光刻物鏡光學薄膜,為制備出超低折射率材料,常規(guī)的溶膠-凝膠方法均以MgF2為基礎材料,可以采用不同的反應路徑[29],但其本質思路基本一致:通過含鎂的弱酸鹽或醇鹽與含氟酸反應獲得MgF2溶膠原材料,這種材料通常是自組織的納米顆粒,通過高壓釜處理或老化處理形成MgF2水泡結構,另外,通過TEOS的水解縮聚反應,形成鏈狀的樹形結構,并將水泡狀MgF2顆粒包裹其中,成為無規(guī)則的樹狀結構。得到的溶膠樣品通過提拉法[30]或旋涂法制備薄膜,最終制備出含孔隙的膜層,實現(xiàn)了低于塊狀MgF2的折射率,最終獲得的膜層折射率可由反應過程中的各參數(shù)進行調控來獲得。采用該方法可實現(xiàn)的最低折射率略大于1.1,但通常膜層機械強度較低,為解決這一問題,Ishizawa等人[31]在制備完成的MgF2膜層上,用SiO2粘合溶液甩膠并加溫100~200 ℃,使MgF2粒子之間形成了非晶SiO2,將膜層的機械強度由~25 MPa提升至~135 MPa。溶膠-凝膠膜層除了具有超低折射率,另一優(yōu)勢在于其具有較高的抗激光損傷能力,在能量密度為600 mJ/cm2/pulse的條件下經(jīng)歷5×107脈沖的ArF激光輻照后,膜層仍然保持完好[32]。
As shown in Fig.1, the MgF2antireflection film prepared with the sol-gel method or traditional PVD film system with the sol-gel coated MgF2film layer has good optical capacities at the vacuum ultraviolet waveband and deep ultraviolet waveband.
如圖1所示,溶膠-凝膠方法所制備的MgF2減反膜,或在傳統(tǒng)PVD膜系上增鍍?nèi)苣z-凝膠MgF2膜層,在真空紫外與深紫外波段,都有良好的光學性能。
2.2.2Mixedfilmlayermaterial
混合膜層材料
When the two materials of high/low refractive index are co-evaporated, a specific refractive index film layer between the two materials can be realized by adjusting the ratio of the two materials. Realization can be made with two methods. One is the gaseous phase mixture method where two separate evaporation sources each evaporate one material and the required proportions are obtained by changing deposition rates of both materials. The other one is used to directly mix materials as per designated proportions in one evaporation source for evaporation, which is called the liquid phase mixture. The former is flexible for refraction index adjustment and is more applicable to cases where continuous adjustment of the refraction index is required. But its defects are also evident. Proportions of two materials are different in space distribution. Thus it is not suitable for the preparation of large diameter components. The latter can be used only to realize particular proportions of materials, but it can be used for large-caliber components with curved surface and is applicable more extensively.
當高/低折射率的兩種材料共同蒸發(fā)時,可以通過調控兩種材料的配比,實現(xiàn)介于兩種材料之間的特定折射率膜層。具體實現(xiàn)可以采用兩種方法:一種是氣相混合,即兩個獨立的蒸發(fā)源各自蒸發(fā)一種材料,通過改變兩種材料的沉積速率獲得所需的配比;另一種是直接按照指定配比將材料混合在同一蒸發(fā)源中再蒸發(fā),即所謂的液相混合。其中前一種方法對折射率的調整較為靈活,更適用于需要連續(xù)調節(jié)折射率的情形,但其缺陷也比較明顯,即兩種材料的配比具有空間分布的差異性,因此無法實現(xiàn)大口徑元件的制備;后一種方法只能實現(xiàn)特定材料配比,但可用于具有曲面形狀的大口徑元件,具有更廣泛的適用性。
What needs to be pointed out specifically is that any refraction index between 1.20 and 1.44 can be realized with the aforesaid sol-gel method where the molar ratio between Si and Mg in two sols of MgF2and SiO2are controlled. The schematic diagram for mixture of two sols in different proportions and the corresponding refraction index are shown in Fig.2. Recently, Xu Yaoetal.[33-34]have prepared the antireflection film system with a gradient refraction index by controlling the molar ratio between mixed materials, which is potential to meet broad wavebands or the demand for broad angle antireflection.
另外需要特殊指出的是,在前面所述的溶膠-凝膠法中,通過控制MgF2和SiO2兩種溶膠Si和Mg的摩爾比,也可以實現(xiàn)折射率從1.20到1.44的任意折射率,圖2為兩種溶膠不同比例混合示意圖及其對應折射率。最近,徐耀等人[33-34]通過控制混合材料摩爾比制備出了梯度折射率減反射膜系,具有滿足寬波段或寬角度減反需求的潛力。
Fig.2 Realization of the adjustable refraction index with mixture of two sols(MgF2 and SiO2) at different Si/Mg molar ratios 圖2 兩種溶膠(MgF2和SiO2)不同Si/Mg摩爾比混合實現(xiàn)可調折射率
BAAR膜系對物鏡系統(tǒng)級指標的保障
Design and realization approach of the BAAR film system have been presented in the above. Now indices of objectives NA0.75 and NA1.35 are used as an example to explain how to evaluate objective system indices. Impact of the objective on the incident light can be expressed with Jones Matrix. The pupil expressed with Jones Matrix is called Jones Pupil, components of which are not certain in physical significance. It is not easy to distinguish indices because of combination of different influence factors. Thus it is broken down into the form of physical pupil, components of which are independent from each other and certain in physical significance. They can be expressed with parameterization in the directional Zernike Polynomials. The objective′s Jones Pupil can be described with five pupil functions that have certain physical significances after simplification and decomposition:
上述內(nèi)容介紹了BAAR膜系的設計及實現(xiàn)途徑。現(xiàn)以NA0.75和NA1.35物鏡的指標為例,說明物鏡系統(tǒng)級指標如何評估。物鏡對入射光的影響可用瓊斯矩陣表示,用瓊斯矩陣表示的光瞳稱為瓊斯光瞳。瓊斯光瞳各個分量的物理意義不明確,不同影響因素交織在一起,不易進行具體指標的劃分,因此將其分解成物理光瞳的形式。物理光瞳的各分量相互獨立且物理意義明確,并可用方向澤尼克多項式進行參數(shù)化表征。通過簡化與分解,物鏡的瓊斯光瞳可以由5 個具有明確物理意義的光瞳函數(shù)進行描述:
J≈t·ei·Φ·Jdia(d,θ)·
Jrot(α)·Jret(φ,β)
The diattenuationJdiaand the retardationJretare two main influence factors of the polarization aberration, which correspond respectively to amplitude and phase splits. Generally it is required in the immersive projection objective with NA1.35 that the diattenuation is less than 0.5% and the retardation is less than 2 nm. It is also required that the apodization uniformity corresponding to each viewing field of the system is not less than 90% and the transmittance is not less than 60%.
式中,二次衰減(diattenuation,Jdia)和延遲(retardation,Jret)為偏振像差的兩個主要影響因素,分別對應振幅分離和相位分離,在NA1.35的浸沒式投影物鏡中,一般要求其二次衰減<0.5%,延遲<2 nm。另外要求系統(tǒng)各個視場對應的切趾均勻性(apodization uniformity,t)≥90%,透過率≥60%。
Impact of the polarization aberration caused by film system on the imaging cannot be ignored at a certain extent of the objective numerical aperture. Shang Hongboetal. use the objective system with NA0.75 for studies on the intensive lines imaging at 90 nm intervals and the imaging contrast. It is found through comparison between common and BAAR film systems in terms of diattenuation, retardation, apodization uniformity, transmittance and intensive line contrast at 90 nm intervals that the system retardation has been reduced significantly from 1.55 nm to 1.2 nm after use of the BAAR film system. In addition, the intensive line contrast at 90 nm intervals in the objective is increased from 0.08 to 0.89 by adjusting the objective system design simultaneously[35].
當物鏡數(shù)值孔徑達到一定程度時,膜系所引起的偏振像差對成像的影響不容忽視。尚紅波等采用NA0.75物鏡系統(tǒng)對90 nm密集線條成像,并對成像的對比度進行研究,通過對比普通膜系和BAAR膜系對應的二次衰減、延遲、切趾均勻性、透過率和90 nm密集線條對比度等指標,發(fā)現(xiàn)采用BAAR膜系后,系統(tǒng)的延遲顯著降低,由1.55 nm降到1.2 nm。另外,通過調整物鏡系統(tǒng)設計,使物鏡90 nm密集線條對比度由0.08提升至0.89[35]。
The film system has a bigger impact on the polarization aberration in an immersive objective with higher numerical aperture. System indices corresponding to different film systems such as regular film system, combined film system and combined BAAR film system that includes film layers with an extremely low refraction index are shown in Tab.1.
在數(shù)值孔徑更高的浸沒式物鏡中,膜系對偏振像差的影響更大。表1是不同膜系對應的系統(tǒng)指標,一種是常規(guī)膜系,一種是組合膜系,另一種是應用超低折射率膜層構成的組合BAAR膜系。
Tab.1 System indices corresponding to different schemes 表1 不同方案對應的系統(tǒng)指標
It can be seen from the table that retardation, apodization uniformity and transmittance of the film system have been increased significantly after use of film layers with the extremely low refraction index of 1.1 and the requirement for objective system indices can be met.
從表中可以看出,膜系中應用折射率為1.1的超低折射率膜層后,系統(tǒng)延遲、切趾均勻性和透過率均有較大提升,能夠滿足物鏡系統(tǒng)級指標要求。
浸液工況環(huán)境下的鍍膜元件壽命
The practice used to increase numerical aperture of an optical system with immersion of the last component has a long history. For example, this method has been being used in a high-NA microscopic objective. Use of the dry lens cannot realize the system-required imaging resolution at the minimum optical exposure image resolution of a mask aligner that is less than 45 nm. Therefore the immersion lithography is naturally put forward. The system resolution at 193 nm can be increased by 44.3% through objective immersion when other conditions of the objective system are not changed. However, use of the immersion lithography technology will make the last component of the objective be immerged in water for a long term. Service lifetime of the immerged component must be fully considered.
通過對最后一片元件進行浸液可以提高光學系統(tǒng)數(shù)值孔徑,這種做法由來已久,例如高NA顯微物鏡一直采用這種方法。當光刻機光學曝光的最小圖形分辨率達到45 nm以下時,采用干式鏡頭已無法實現(xiàn)系統(tǒng)要求的成像分辨率,浸沒式光刻由此自然而然地被提出。在193 nm處,在物鏡系統(tǒng)其它條件不變的情況下,僅通過將物鏡浸液的方式就可將系統(tǒng)分辨率提升44.3%。然而如果采用浸沒式光刻技術,物鏡最后一個元件需要長時間浸沒在水中,必須充分考慮浸沒元件的使用壽命。
下窗口元件的防水性能
The objective immersion is realized by adding an immersion liquid supply and recovery device between the last-window objective component and the silicon wafer, which will continuously inject fresh water into the gap between last window and silicon wafer and recover it. Thus the last-window component has to be continuously subjected to washing by the immersion liquid when the objective is operating. The requirement for anti-etching and hydrophobicity is put forward therefrom.
物鏡浸液通過在物鏡下窗口元件與硅片之間增設浸液供給與回收裝置提供,該裝置將持續(xù)不斷地向下窗口與硅片之間的間隙處注入新鮮的純水并回收。因此在物鏡工作期間,下窗口元件將會持續(xù)承受浸液的沖刷,由此對元件產(chǎn)生了防刻蝕與疏水的要求。
The objective itself does not move together with the silicon wafer workbench during exposure. The flow field on the last window surface forms a nearly lateral flow at approximately 60 mm/s. The component will be subjected to the shearing force and etched constantly. Anti-etching characteristics of the component depend mainly on the material itself at the pure water condition. Use of CaF2as the last-window component material will result in its un-ignorable dissolution in water, and it will be etched easier at a certain flow field. Thus coating of a protective film system is required in use. The fused quartz material is much solider than it. Weissenriederetal[6]have carried out a detailed research on material etching and given reference indices. The dissolution/etching rate of the surface exposed to immersion liquid(that may be the non-film coated optical material or outermost layer of film layer material) in an immersion environment shall be less than 0.01 mg/(cm2·day) or even less than 0.005 mg/(cm2·day) or 0.002 mg/(cm2·day). The film system for immerged component must contain protective film layers including the barrier layer and wearing layer. The barrier layer does not have pores that penetrate film layers, and there is at least one layer that cannot be permeated by the immersion liquid. The wearing layer is outermost layer exposed to the immersion liquid, which shall have a sufficiently low etching rate.
由于物鏡本身在曝光期間并不隨硅片工件臺移動,下窗口表面上的流場為~60 mm/s的近橫向流動,元件將承受剪切力而被不斷刻蝕。在純水的條件下,元件防刻蝕特性主要取決于材料本身:如果采用CaF2作為下窗口元件材料,其在水中會發(fā)生不可忽視的溶解,在一定的流場下則更易被刻蝕,因此使用時需要增鍍保護膜系。相對而言,融石英材料則堅固得多。Weissenrieder等人[6]對材料的刻蝕情況進行了詳細的研究,給出了參考指標:與浸液接觸的表面(可能是未鍍膜的光學材料或是膜層材料的最外層)在浸液環(huán)境下的溶解/刻蝕速率應當小于0.01 mg/(cm2·day),甚至小于0.005 mg/(cm2·day)或0.002 mg/(cm2·day),并且浸液元件的膜系必須包含具有保護功能的膜層,包括阻擋層和磨損層,其中阻擋層不含有貫穿膜層的孔隙,并至少有一層無法被浸液滲透,磨損層為與浸液接觸的最外層,應具有足夠低的刻蝕速率。
In practice, the barrier layer in a protective film system can be prepared with the plasma enhanced chemical vapor deposition(PECVD) method. Generally it consists of pore-free SiO2film layers. It must be ensured that overall optical capabilities of the film system do not vary with thickness of the wearing layer gradually reduced over time. The wearing layer can use a protective flat panel consisting of body material(e.g. fused quartz). The barrier layer can be prepared with hydrophobic material, e.g. Merck′s WR series materials or polytetrafluoroethylene(PTFE). The film system with protective layers can be also applied. The liquid material or lubricating material is applied together with the flat panel made of body material. Bai Jingjianetal.[36]have investigated solubility of various materials in water(the flow field in this test is not provided at the lithographical condition, so the test result shall be static solubility of the material). It is found that thicknesses of the SiO2film layer and the LaF3film layer prepared on crystal surface of the CaF2substrate (111) are not changed. The index at which solubility of the film layer in the pure water shall be less than 2×10-12g/mL is given. Burnetal.[37]have summarized the index from the view of practice, at which thickness reduction of the anti-corrosion coating at operating conditions shall be less than 10-5/h and indicated possible materials including SiO2, ITO, polymer and non-sensitive resin for photoresist.
在實踐中,保護膜系中的阻擋層可以采用等離子體增強化學氣相沉積(PECVD)方法來制備,一般為無孔的SiO2膜層。對于磨損層,由于其膜厚隨時間逐漸減小,必須保證膜系的整體光學性能不因磨損層厚度而變化,磨損層可以采用由體材料構成的保護平板(例如融石英)。阻擋層可以利用具有疏水性的材料制備,如默克的WR系列材料或聚四氟乙烯(PTFE),還可以應用保護層膜系,即液體材料或具有潤滑性的材料與體材料平板配合應用。白井健等人[36]考察了各種材料在水中的溶解度(在該實驗中未按光刻工況提供流場,所以測試結果應為材料的靜態(tài)溶解度),發(fā)現(xiàn)在70 ℃恒溫的純水中浸泡3 h前后,SiO2膜層與CaF2基底(111)晶面的上制備的LaF3膜層的厚度均未發(fā)生改變,并給出膜層對純水的溶解度應小于2×10-12g/mL的指標。Burn等人[37]也從實踐角度總結出抗腐蝕膜系(Anti-Corrosion Coating,ACC)在工況下厚度的減少量需要低于10-5/h的指標,并指出了可能的材料,包括SiO2、ITO、聚合物和光致抗蝕劑的非感光樹脂。
Some solutions for preparation of the pore-free optical coating are provided. Pazidisetal.[38]use SiO2prepared through chemical reaction to fill or partially fill pores in the film layer. The reaction substance can be trimethylfluorosilane, hexamethyldisilazane, hydroxytrimethylsilane or hexamethylcyclotrisiloxane. Bai Jingjianetal.[36]use high homogeneity and backfilling of the wet film forming method to fill pores in the film layer for increase of the anti-permeation ability of the film-coated component. In addition, there are also solutions to address the problem with film-coating and polishing cycles[6]. The first coated film layer is polished to remove a part of thickness and then the removed thickness with polishing is compensated through subsequent coating. The probability that defects are generated at the same location in two times of coating is relatively small. Pores that penetrate film layers can be removed completely through a number of coating and polishing cycles to realize waterproofness of film layers.
針對如何制備出無孔隙的光學薄膜,人們也提出了一些方案:Pazidis等人[38]采用化學反應制備出的SiO2來填充或部分填充膜層中的孔隙,其反應原料可以是三甲基氟硅烷、六甲基二硅氮烷、三甲基硅醇或者六甲基環(huán)丙硅烷;白井健等人[36]利用濕式成膜法的高均質性和高填埋性來填充膜層中的孔隙,以提高鍍膜元件的抗浸透能力;另外,還有采用鍍膜-拋光循環(huán)流程[6]解決問題的方案,即當首層薄膜鍍制后,對其拋光去除一部分厚度,然后再通過后續(xù)鍍膜補足被拋光去除的厚度,由于兩次鍍膜時缺陷生長在同一位置的幾率相對較小,通過若干次鍍膜-拋光循環(huán)就可以完全去除貫穿膜層的孔隙,實現(xiàn)膜層的防水。
浸液元件的浸析污染與疏水特性
The silicon wafer with coated photoresist needs to be exposed and etched repetitively for manufacture of devices on the mask aligner. There will be many contamination factors in more than 100 manufacture processes, which lead to defective devices that make the transmittance fall down. Furthermore in comparison with the dry lithographical technology, the possibility for contamination of the last window on the immersive objective is extremely increased due to continuous flow of the immersion liquid between the last window and the silicon wafer. Thus the immersive lithographical objective must meet the anti-contamination and superficial hydrophobicity requirements.
在光刻機制造器件時,需要對涂布光刻膠的硅片進行反復曝光-刻蝕,在上百道制造流程中會存在眾多引起污染的因素,這將導致器件出現(xiàn)缺陷而透過率下降。另外,與干式光刻工藝相比,由于浸液在下窗口與硅片之間持續(xù)流動,極大增加了浸沒式物鏡下窗口被污染的可能性。因此浸沒式光刻物鏡必須同時滿足防污染與表面疏水要求。
Contamination of the last window on objective results mainly from leaching[39-40]and viscosity[41]of the photoresist. It is very possible for photo-acid generator(PAG), quencher and small-molecule group in the photoresist that are dissolved in the immersion liquid to adhere to the last surface of objective window at the flow field. Accumulation of these leached substances with a very small amount in years of the operating period will lead to lens hazing[42]on the objective that increases system stray lights and decreases the transmittance.
對于物鏡下窗口,污染主要來自于光刻膠的浸析(leaching)[39-40]和粘附性狀態(tài)[41],光刻膠中的光酸產(chǎn)生劑(PAG)、猝滅劑(quencher)和小分子基團等溶解于浸液,在流場中極有可能吸附到物鏡窗口的下表面。雖然這些浸析物的劑量非常微小,但在長達數(shù)年的使用期內(nèi)積累在下窗口表面,將使物鏡產(chǎn)生“鏡頭起霧(lens hazing)”[42]問題,導致系統(tǒng)雜散光增加、透過率下降。
The immersive lithographical contamination can be eliminated by increasing the contact angle of the objective last-window component surface, which needs to be controlled at the minimum of approximately 70°[43]for restraint of the defect quantity within an allowable range and prevention of contaminants from adherence to the component surface along with water flow. The result of contact angle measurement for common last-window components and film layer materials is shown in Fig.3. The contact angle of SiO2[44], Al2O3, MgF2and LaF3film layers is less than 50°. It is mush insufficient to meet operating requirements.
浸沒式光刻污染問題可以通過提高物鏡下窗口元件表面的接觸角解決。在浸液高速流動的情況下,為將缺陷數(shù)量限制在允許范圍內(nèi),接觸角至少需要控制在~70°[43],防止污染物隨水的流動在元件表面附著。圖3顯示常用下窗口元件及膜層材料的接觸角測量結果,SiO2[44]、Al2O3、MgF2、LaF3膜層的接觸角均小于50°,遠遠不能滿足使用要求。
Fig.3 (a)Last optical element of the lithography objective; (b)Contact angle of the film layer material 圖3 (a)常用光刻物鏡下窗口元件;(b)膜層材料的接觸角
To solve this problem, it is necessary to modify the surface of the coated component to increase the contact angle by using last surface energy group, such as the small molecule fluoride, methyl or the like. This case is exhibited in Fig.4. Contact angle of the film surface can be increased to approximately 110° with surface modifying, which meets the hydrophobicity requirement. But the contact angle may be decreased to a certain extent during the long-term laser irradiation[45]. Therefore, it is worthy to further study stability of the film layer surface hydrophobicity at the laser irradiation condition.
Fig.4 Increase of the material surface hydrophobicity with surface trimming 圖4 通過表面修飾提高材料表面疏水性能
為解決這一問題,需要對鍍膜元件的表面進行修飾,通過增加小分子氟化物、甲基等表面能較低的基團來提高接觸角。圖4展示了這種情況:通過表面修飾,可使薄膜表面的接觸角提升到~110°,滿足疏水性的要求。但其在長期激光輻照過程中,接觸角可能發(fā)生一定程度的降低[45],因此膜層表面疏水性能在激光輻照條件下的穩(wěn)定性問題值得進一步研究。
薄膜光學元件的激光輻照壽命
Optical film components of the lithographical objective need to withstand several ten billion pulses in operating period of the mask aligner that is 7-10 years. Repetitive frequency of a laser source is 4-6 kHz[46]. Energy density of a single pulse is between 0.1 mJ/cm2and several mJ/cm2. The energy density at this extent is 2-3 magnitudes lower than the classical laser induced damage threshold(LIDT)[47]of optical coatings. But the long-term laser irradiation will still result in absorption, adherence and optical thinning of the film-coated component[11]and even a combined variation brought by both the laser irradiation and the immersion environment.
在光刻機7~10年的使用周期內(nèi),光刻物鏡中的光學薄膜元件需要承受數(shù)百億個脈沖,并且激光光源的重復頻率在4~6 kHz之間[46],單脈沖能量密度在0.1 mJ/cm2至數(shù)個mJ/cm2之間。雖然這種程度的能量密度較光學薄膜的經(jīng)典激光損傷閾值(Laser Induced Damage Threshold,LIDT)[47]低2~3個數(shù)量級,但是長期激光輻照仍然會使鍍膜元件產(chǎn)生吸收、粘附性和光致變薄的問題[11],甚至產(chǎn)生激光輻照與浸液環(huán)境共同作用所帶來的復合變化。
深紫外薄膜光學元件的激光輻照壽命
Optical path of the basic test device for online monitoring of continuous variation of the component transmittance during irradiation is as shown in Fig.5. In addition, accessories can be added into the evaluation device to detect the sample's laser-induced fluorescence(LIF) spectrum or perform the online/offline ellipsometric measurement. These results together with the online transmittance result are used for comprehensive evaluation of the irradiation lifetime.
用于在線監(jiān)測元件透過率在輻照過程中持續(xù)變化的基本實驗裝置光路如圖5所示。除此之外,還可以在評估裝置內(nèi)增加附件,檢測樣品激光誘導熒光光譜(LIF),或對樣品進行在線/離線橢偏參量測量,利用這些結果與在線透過率結果進行輻照壽命的綜合評估。
Fig.5 Optical path of in-situ transmission measurement while laser irradiation 圖5 激光輻照過程中在線透過率檢測光路圖
There is a non-linear relationship between the extinction coefficient of Al2O3film subjected to asynchronous excitation of the laser at 193 nm and the repetitive laser frequency[48]. Thus what needs to be first considered in the laser irradiation lifetime evaluation is impact of the repetitive frequency on the component lifetime. So far, similar phenomena have not been found in fluoride materials(including the fluoride film), and the single photon absorption mode is still presented. Thus the value of irreversible component damage(the increased absorption) is linearly correlated to the repetitive frequency and energy density, as shown in Fig.6.
鑒于193 nm激光對Al2O3薄膜產(chǎn)生異步激勵影響,使其消光系數(shù)與激光重復頻率之間呈現(xiàn)非線性關系[48]。因此,激光輻照壽命評估中首先需要考慮的是重復頻率對元件壽命的影響。迄今為止,尚未在氟化物材料(包括氟化物薄膜)中發(fā)現(xiàn)類似的現(xiàn)象,仍顯示為單光子吸收模式,因此元件不可逆損傷(吸收的增加)的數(shù)值與重復頻率、能量密度都呈線性關系,如圖6所示。
Fig.6 Relationship between the value of irreversible component damage and the repetitive frequency and energy density 圖6 元件不可逆損傷的數(shù)值與重復頻率、能量密度的關系
Intuitive recognition of the component damage progress can be based on online tracking and measurement of the component's wide-spectrum ellipsometric parameters. Mapping distribution of ellipsometric parameters that were initiatively not featured tends gradually to be same as the irradiation facula shape along with dose accumulation in the irradiation. As shown in Fig.7, variation of a film system can be fit dynamically by using changes ofΔandΨover time. Liberman et al have created the dynamic film layer thinning model based on the assumption of surface film-layer laser irradiation densification in accordance with the film system fitting result, assuming that the film thickness changes continuously at a constant rate in the irradiation environment. This model agrees very well with the online film-system transmittance fitting results[8], as shown in Fig.8.
通過對元件的寬光譜橢偏參量進行在線跟蹤測試,可以對元件的損傷歷程建立直觀認識:在輻照過程中,隨著劑量的累積,原本無特征的橢偏參量mapping分布逐漸與輻照光斑形狀趨同,如圖7所示,利用Δ和Ψ隨時間的變化可以動態(tài)擬合膜系的變化。Liberman等跟據(jù)膜系擬合結果,基于“表面膜層激光輻照致密化”的假設,建立了膜層動態(tài)減薄模型,假設薄膜的厚度在輻照環(huán)境下持續(xù)發(fā)生變化,并且變化速度是恒量,這種模型與膜系在線透過率擬合結果吻合得非常好[8],如圖8所示。
Fig.7 (a)Delta space distribution for the film-coated component after laser irradiation; (b)Laser irradiation sample 圖7 (a)鍍膜元件在激光輻照后的空間Delta分布;(b)激光輻照樣品
Fig.8 Relationship between the transmittance(solid lines) in dynamic film-layer thinning model and the transmittance(scattered points) measured actually during irradiation 圖8 膜層動態(tài)減薄模型透過率(實線)與輻照過程中實測透過率(散點)關系
浸液環(huán)境下的元件激光輻照壽命
The last-window surface exposed to water in the immersive lithographical projection objective is subjected to both the immersion liquid and the laser irradiation. Its service lifetime is different from that in the pure immersion or laser irradiation. Liberman et al had evaluated the laser irradiation lifetime of products provide by main suppliers of lithographical film-coated components and obtained the result showing multiple degenerations including film dissolution, film layer falloff, complete transmittance disappearance in a un-irradiated area, surface roughness increase, film layer thickening/densification, film blackening and discoloration in an irradiated area that can be found only at the reflective observation condition[49].
在浸沒式光刻投影物鏡中,與水接觸的下窗口表面同時受浸液與激光輻照的雙重影響,其使用壽命有別于單純的浸液或激光輻照。Liberman等人曾對主流光刻鍍膜元件供應商的產(chǎn)品進行激光輻照壽命的評估,結果顯示了多種退化現(xiàn)象,包括薄膜溶解、膜層脫落、未輻照區(qū)域透過率完全消失、表面粗糙度增加、膜層變薄/致密、薄膜發(fā)黑、僅在反射觀察條件下能夠發(fā)現(xiàn)的輻照區(qū)域變色等[49]。
The above result has shown complication of the issue. Immersion irradiation lifetime of the component is closely related to the immersion environment(including contamination) and irradiation condition. The water quality and leaching contamination have a considerable impact. Liberman el al have built up an ultrapure water treatment cycle system to strictly control indices in the part of immersion liquid in contact with component surface including conductivity(>18 MΩ) and total carbon content(<2×10-9g/mL)[8], and further studied contamination effects at different doses brought by contaminants such as isopropanol, acetone, methylbenzene and silicone on the above basis. Contaminants at the content of several ppb to more than one hundred ppm are injected into the immersion liquid and cycled for observation of immersion irradiation characteristics of the fused quartz substrate[50]. Surprisingly, film layers that can be considered as contaminants and have a refraction index different from the substrate have not been found in all samples. The reason is explained such that a water film was formed on surface of the fused quartz to inhibit formation of surface contaminants at the interface between water and component.
上述結果顯示了問題的復雜性,元件的浸液輻照壽命與浸液環(huán)境(包括污染)、輻照條件均緊密相關,其中水質與浸析污染等具有相當大的影響。Liberman等人搭建了超純水處理循環(huán)系統(tǒng),對浸液中與元件表面接觸部分的電導率(>18 MΩ)、總碳含量(<2×10-9g/mL)等指標進行了嚴格的控制[8],并在此基礎上針對異丙醇、丙酮、甲苯、硅酮等污染物進行了不同劑量的污染效果研究,將數(shù)個ppb至上百個ppm含量的污染物注入浸液中進行循環(huán),并對融石英基底的浸液輻照特性進行了觀察[50]。令人意外的是,在所有的樣品中,都未發(fā)現(xiàn)可被視為污染物以及折射率異于基底的薄膜層。并解釋其原因為:在融石英表面形成了一層水膜,抑制了表面污染物在水/元件二者界面上的形成。
To further identify the contamination mechanism, the contaminant content and pure water flow will be strictly controlled at quasi-working conditions in the next test. Having studied the bare fused quartz substrate and film-coated CaF2sample, a more complicate anti-intuitive phenomenon is found. Samples have not been contaminated in the laser irradiation area but have been severely contaminated at upstream of the water flow outside the irradiation area, and even the transmittance disappeared completely at some locations[51]. On basis of these phenomena, Liberman et al point out that: first, the contamination shall not be a pure adherence and shall result from competition between both the adherence and cleaning mechanisms; second, the laser appears not only as a negative player but also as a participant in the complicated photochemical reaction to make foreign matters become contaminants on one hand and facilitate generation of the cleaning catalyst with water participation on the other hand, where the component surface maintains cleaned at a bigger action of the latter than the former; and finally, the severe contamination at upstream of the component and the unchanged optical capabilities at downstream can be explained as excessive intermediate products with the cleaning effect that gather at downstream along with water flow while no such products at upstream. The above result constitutes a very important reference to effectively controlling immersion irradiation lifetime of the component.
為了進一步明確污染機制,在接下來的實驗中,污染含量、純水流量等被嚴格控制于準工況下。經(jīng)過對融石英裸基底與鍍膜CaF2樣品進行研究,發(fā)現(xiàn)了更加復雜的反直覺現(xiàn)象:在激光輻照的區(qū)域內(nèi),樣品是無污染的;但在輻照區(qū)域外水流方向的上游側,則出現(xiàn)了比較嚴重的污染,某些位置甚至透過率完全消失[51]?;谶@些現(xiàn)象,Liberman等指出:首先,污染不應該是一個單純的吸附過程,而是吸附與清潔兩種機制競爭產(chǎn)生的結果;其次,激光的出現(xiàn)也不僅僅起負面作用,而是參與了復雜的光化學作用,一方面使外來雜質形成污染物,另一方面,在水的參與下促使清潔催化劑的生成,當后者的作用超過前者時,元件表面仍然呈現(xiàn)為清潔狀態(tài);最后,元件上游污染嚴重、下游光學性能未變的原因可以解釋為伴隨著水的流動,下游聚集了過多的具有清潔作用的中間產(chǎn)物,而上游則沒有。上述結果為有效控制元件的浸液輻照壽命提供了非常重要的參考依據(jù)。
5Conclusions
結 論
The immersive lithography technology represents currently the upmost optical manufacture, which imposes requirements on the thin-film mainly from two respects. Rigorous requirements such as large incidence angle and inhibition of the polarization split are brought by high numerical aperture of the projection objective. New film layer materials together with corresponding processes need to be developed to meet demands for shaded refraction index, film layer with an extremely low refraction index, etc, realize the large angle polarization-maintaining film system and satisfy the system image quality requirement. The optical coating component works at highly repetitive frequency and high cumulative energy density conditions, and even the last component needs to be immerged in the immersion environment during the full life cycle. Satisfaction of the requirements for waterproofness, hydrophobicity and resistance to laser irradiation constitutes a precondition to apply the immersive projection objective. The relevant research progresses to the above issues were presented and the relevant technologies were discussed in this paper to point out a technical direction for optical coating components to better satisfy the demand for immersive projection objective.
浸沒式光刻代表了目前光學技術的制造極限,對薄膜的要求主要來自兩方面:投影物鏡的高數(shù)值孔徑帶來了大入射角、抑制偏振分離等苛刻要求,為此需要開發(fā)新型膜層材料與配套工藝,以滿足漸變折射率、超低折射率膜層等需求,實現(xiàn)大角度保偏膜系,滿足系統(tǒng)像質要求;薄膜光學元件工作在高重頻、高能量密度的工況下,甚至最后一片元件還需在全壽命周期內(nèi)浸泡在浸液環(huán)境中,同時滿足防水、疏水、抗激光輻照的要求是浸沒式投影物鏡實際應用的前提條件。本文針對上述問題,對相關研究進展進行了介紹,對相關技術進行了討論,為薄膜光學元件更好地滿足浸沒式投影物鏡的需求指明了技術方向。