Inside an ASML disclosure: how an EUV membrane balances contamination protection, heat removal and the passage of light.
US10908496B2 · Independent PatentOracle research · 20 September 2026
A pellicle protects the mask; a separate gas-lock embodiment helps keep debris from optical components. The disclosure offers alternative placements for a membrane, each with a different protective role.
Heat-radiating material can also reflect EUV light or degrade. The proposed stack separates the compound base from protective oxide caps, then treats layer thickness as an optical design choice.
Claim 1 requires an ordered oxide-cap, compound-base, oxide-cap stack with specified relationships between its metals. Particular chemistries, sublayers and thicknesses appear in dependent claims.
The patent concerns a membrane that must transmit EUV radiation while limiting contamination damage. In a pellicle embodiment, the membrane assembly seals off the patterning device, or mask, from airborne particles and other contamination that could produce defects on the wafer. In a distinct dynamic-gas-lock embodiment, radiation passes through a membrane in a gas-flushed structure associated with the path between projection optics and the substrate, or alternatively near the intermediate focus. Those are alternative disclosed uses, not one combined installation. The technical challenge is that the membrane absorbs some EUV energy and heats. The described designs attempt to balance infrared emissivity, which is the ability to radiate heat away; EUV transmission; very low EUV reflection; mechanical strength; and resistance to oxidation and EUV-related degradation. The disclosure expressly recognizes tradeoffs: highly emissive metallic material can increase EUV reflection or oxidize, while simpler uncapped membranes may work only under more limited EUV-power conditions.
The main claimed architecture is a three-part membrane stack. In order, it has a first capping layer containing an oxide of a first metal, a base layer containing a compound of a second metal plus Si, B, C, or N, and a second capping layer containing an oxide of a third metal. The first metal differs from the base-layer metal; the third metal may be the same as or different from the first. The proposed mechanism assigns different jobs to the layers. The base material can provide the membrane’s structural and heat-radiating function. The outer oxide caps are intended to protect it. Thickness also matters optically: certain described stack dimensions are selected so EUV reflections from opposite interfaces destructively interfere, reducing total reflection. A Zr-oxide/Mo-Si/Zr-oxide combination is specifically identified, but it is a narrower claimed refinement, not the full scope of claim 1.
FIG. 1’s apparatus context is an EUV system in which illumination reaches patterning device MA, the patterned beam is reflected from MA, and projection optics image it onto wafer W. A pellicle is associated with MA and is intended to keep particles away from that patterning device. By contrast, the dynamic gas lock is described as a hollow, gas-flushed part covered by membrane assembly 80; the radiation travels through the membrane before reaching the substrate. The patent also describes an alternative gas-lock location near intermediate focus IF. In short, the membrane can protect the mask directly, or can help prevent debris from progressing toward optical components, depending on the embodiment selected.
Original FIG. 3, cropped without redrawing. Callouts identify the layers; their drawn thicknesses are not a scale specification.
Inspect original page 4 ↗In this embodiment, the upper cap contains an oxide of a metal different from the metal in the base. The caps are described as protecting the base from degradation.
The base contains a metal compound with Si, B, C or N. The described heat-radiating role must be balanced against EUV transmission and reflection.
The lower cap contains an oxide of a third metal. That metal may be the same as or different from the upper-cap metal.
Original FIG. 4. The base gains sublayers; this is a distinct arrangement from FIG. 3. FIG. 5 separately divides the caps, and FIG. 6 combines those changes.
Inspect original page 4 ↗This sublayer contains an oxide of the additional element. The disclosure says it may act as an anti-oxidation diffusion barrier.
The central sublayer retains the metal compound. Outer base sublayers 61 and 63 are described as helping protect it during use.
The lower base sublayer also contains an oxide of the additional element. It is part of base 60, separate from lower cap 80.
On figure page 4, FIG. 3 is the baseline membrane 40: upper capping layer 70, base layer 60, and lower capping layer 80. In the associated embodiment, 70 and 80 are metal oxides and 60 is the metal-plus-Si/B/C/N compound. FIG. 4 changes the base, not the caps. Base 60 contains sublayers 61, 62, and 63: compound-containing central sublayer 62 lies between sublayers 61 and 63, which are oxides of the additional element. FIG. 5 instead retains an undivided base 60 and divides each cap: upper cap 70 contains outer oxide sublayer 71 and inner deposited-oxide sublayer 72; lower cap 80 contains inner deposited-oxide sublayer 82 and outer oxide sublayer 81. FIG. 6 expressly combines the FIG. 4 base sublayers with the FIG. 5 cap sublayers. The drawing establishes ordering and reference labels, not proportional layer thicknesses.
A high-emissivity layer is intended to emit absorbed heat as infrared radiation. The patent discusses metal silicides, especially MoSi₂ and RuSi₂, as candidates that combine infrared emissivity with useful thermo-mechanical behavior. It describes silica-scale formation as thermodynamically favorable for particular silicon-containing compounds, notably MoSi₂ and RuSi₂. That scale is proposed to protect the compound-bearing layer; it should not be generalized to every listed metal compound. The outer caps have a distinct protective role. Oxygen-conductive oxides are proposed because they can accommodate changing oxygen content and can remain stable despite oxygen vacancies; zirconia is specifically described as effective. In FIG. 4, oxide sublayers 61 and 63 may act as anti-oxidation diffusion barriers. In FIG. 5, deposited oxide 72 or 82 is an alternative when a suitable native oxide does not readily form or is not stable under the intended conditions.
The disclosure says high-emissivity metallic layers can create unwanted EUV reflection. It therefore proposes refractive-index matching and destructive interference between interface reflections. For a 13.5 nm illustrative polysilicon-core design, Table 1 lists, from one side in its printed order: a B outer-layer cap of 3.0 ± 0.5 nm, a Mo emission layer of 6.0 ± 1.0 nm, a SiN barrier of 3.5 ± 0.5 nm, a Si core of 37.5 ± 2.0 nm, another SiN barrier of 3.5 ± 0.5 nm, and a B outer-layer cap of 3.0 ± 0.5 nm. The text calls the configuration symmetrical, but the printed table does not separately list a lower Mo-emission row. This example is not the oxide-capped compound-base arrangement of claim 1. Elsewhere, the patent proposes 9 nm or 16 nm base-layer thicknesses in certain stacks to produce destructive interference between reflections associated with the two capping layers.
Figure page 8 contains infrared optical plots, not a 13.5 nm EUV-transmission chart. FIG. 11 plots transmittance against wavelength in µm; FIG. 12 plots reflectance against wavelength in µm. Both vertical axes run from 0 to 1. Dashed curves 301–304 are described as theoretical results, while solid curves 311–313 are experimental results. For example, 301 is theory for 3.5 nm MoSi₂ on one side of 25 nm SiN; 302 is theory for 3.5 nm MoSi₂ on both sides of 25 nm SiN; 303 is theory for 3.5 nm MoSi₂ on both sides of 50 nm polysilicon; and 304 is theory for 31 nm MoSi₂ alone. The patent interprets this work as showing absorbance, corresponding to emissivity, of about 0.2 or higher even for thin MoSi₂ layers, and above 0.4 for thicker layers. These are described experimental and theoretical results for specified sample structures, rather than results for every claimed stack.
The patent reports example MoSi₂ membranes 1.5 cm in diameter and 20 nm thick. Their spatial EUV transmission was reported as 84% to 88%, with a most common value of about 86.5%; the examples were reported to withstand absorbed EUV powers above 2 W/cm². Those reported values concern the stated example membranes and conditions. A separate experiment illustrates why the disclosure distinguishes bare or scale-protected membranes from stacks having added protection. At absorbed EUV power of 0.65 W/cm², the silica scale was reported as stable and transmission was roughly uniform. At 1.8 W/cm², a central region showed substantially higher transmission and glowed red; the patent says this suggests protective-scale removal or damage and etching of MoSi₂. Its conditional conclusion is that the FIG. 8-style arrangement may be used for lower power, whereas added protective layers such as FIGS. 3–6 may be desirable at higher power.
Claim 1 is not directed to every EUV pellicle or every multilayer membrane. It requires a membrane for EUV lithography having, in order: a first capping layer comprising an oxide of a first metal; a base layer comprising a compound of a second metal and an additional element selected from Si, B, C, and N; and a second capping layer comprising an oxide of a third metal. The first metal must differ from the second metal. The third metal can be the same as, or different from, the first. Accordingly, claim 1 requires oxide-containing caps on both sides and the stated compound class in the base. It does not itself require ZrO₂, MoSi₂, oxide sublayers, cap thickness below 5 nm, a base at least 8 nm thick, or destructive-interference tuning.
Claim 2 narrows one or both cap metals to a specified list. Claim 3 gives alternative metal/additional-element combinations for the base. Claim 4 depends on claim 3 and selects Mo-Si or Ru-Si; claim 5 also depends on claim 3 but instead selects Mo-B or Ru-B. Claim 7 specifies Zr for both cap metals and Mo-Si for the base. Claims 9 and 10 add plural base sublayers, including a compound-bearing middle sublayer between two sublayers that comprise an oxide of the additional element. Claims 14 and 16 respectively add deposited oxide sublayers within the first and second caps. Claim 15 depends on claim 14 and specifies silicon oxide for the first deposited oxide; claim 17 depends on claim 16 and does the corresponding job for the second. Claim 18 adds cap thickness below 5 nm; claim 19 adds a base at least 8 nm thick; claim 20 depends on claim 19 and further requires selection of base thickness for destructive interference. Alternatives written within a claim are not cumulative requirements.
As a pellicle, the membrane lies over or seals off patterning device MA and is intended to protect the mask from airborne particles and other contamination that could cause wafer defects. As a dynamic-gas-lock membrane, it is part of a gas-flushed hollow structure around the radiation path. The disclosure places that structure between projection system PS and substrate W in one embodiment, and near intermediate focus IF in another. In those uses, the intended function is to reduce debris moving toward optical components. The locations are alternatives in the disclosure.
Read the patent in four passes. First, use the apparatus discussion to distinguish the mask-pellicle and gas-lock placements. Second, use FIG. 3 as the basic cap/base/cap geometry, then compare FIG. 4’s base sublayers, FIG. 5’s cap sublayers, and FIG. 6’s express combination. Third, read the 0.65 and 1.8 W/cm² observations as a source-reported, power-dependent rationale for why extra layers may be desirable, not as a universal operating limit. Fourth, read claim 1 before the dependent claims: claim 1 fixes the ordered oxide-cap/compound-base/oxide-cap arrangement, while chemistry selections, sublayers, thicknesses, and interference tuning are additional limitations. This route separates drawing geometry, proposed mechanisms, reported measurements, and claim scope. It also avoids treating the patent’s disclosure as evidence of a current commercial implementation.
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