Stencil mask with barriers

Abstract

The invention regards a stencil mask for defining a pattern on a substrate during evaporation of material from an evaporation source, the stencil mask comprising, a membrane having a top surface and bottom surface defining a first thickness of the membrane, at least one barrier projecting from the bottom surface of the membrane, each barrier defining a second thickness of the membrane between the top surface of the membrane and a lower surface of the barrier, such that the second thickness of the membrane is larger than the first thickness of the membrane for each barrier, and at least one slit extending from the top surface of the membrane to a lower surface of a barrier, such that the barrier forms a downwardly projecting edge of the slit, wherein an aspect ratio between the first thickness of the membrane or the second thickness of the membrane, and the width of the slit, is at least 2.

Description

[0001] Stencil mask with barriers

[0002] The present disclosure relates to a stencil mask and a method for defining patterns on a substrate for the fabrication of nanoscale device, semiconductor devices, biological applications, flexible electronics or photonics.

[0003] Background

[0004] Developments in nanofabrication tools have contributed to the major leaps in the semiconductor device manufacturing. Solid state quantum computation relies heavily in the reproducible fabrication of devices and its development is also tightly correlated to the improvement of the nanofabrication techniques being used in the process. Cleaner, faster and more precise nanofabrication processes have been demonstrated to improve the performance of the resulting devices.

[0005] The fabrication of quantum bits “qubits”, require the use of extremely controlled environments in terms of cleanliness and temperature. Ultra-high vacuum (UHV) systems with a high control of temperature and pressures are used for the fabrication of qubits due to the high vacuum levels achieved and the control of temperature along a range of hundreds of °C.

[0006] Performing as many qubit fabrication steps as possible inside UHV systems have been demonstrated to improve the qubit performance and reproducibility during quantum transport experiments. Stencil mask fabrication of qubit devices inside UHV systems is a technique that has gained attention during the recent years due to their ability of imprint devices on substrates inside UHV. The use of stencil masks overrides the necessity of extracting substrates from the UHV material growth systems and performing depositions in ex-situ systems, thus maintaining the pristine conditions of the fabricated samples and devices.

[0007] However, the state of the art in stencil mask lithography techniques involves masks that introduce a large gap between the stencil and the substrate, thus leading to imperfections in the deposition of material, such as effective broadening of features. For example, WO 2018 / 058521 relates to a metallic mask for evaporation of OLED displays. Nevertheless, the gap formed by the disclosed metallic mask would not be suitable for the design of nanoelectronic structures, as it would lead to a substantial broadening of the evaporated materials, leading to imprecise features. Effective broadening refers to a specific phenomenon that occurs when a material is deposited through a shadow mask aperture from an evaporation source. This source, due to its physical dimensions, does not emit material in a perfectly collimated (parallel) beam. Instead, the emitted particles diverge as they travel from the source to the substrate. As these particles pass through the mask aperture, they are not confined to a single trajectory. Due to the divergence, the particles spread out, causing a broadening effect when they reach the substrate. This broadening is more pronounced for particles that travel a longer distance from the aperture to the substrate. The result is that the deposited material forms a pattern on the substrate which can be larger than the actual aperture size.

[0008] Stencil masks are disclosed in pending applications PCT / EP2023 / 066468 and PCT / EP2023 / 066474 by the same applicant. These applications are hereby incorporated by reference in their entirety.

[0009] Hence, the need of a new stencil solution is required, that can lead to fabricating nanostructures with a minimum effective broadening, enabling the production of patterns with high precision and quality, crucial for the manufacturing of advanced (quantum) electronic devices.

[0010] Summary

[0011] One objective of the present disclosure is to provide a solution to the common problem of feature broadening when evaporating a material on a substrate through a mask. Therefore, the present disclosure relates to a stencil mask for defining a pattern on a substrate during evaporation of material from an evaporation source. In the preferred embodiment the stencil mask, preferably a thick stencil mask, comprises a membrane having a top surface and bottom surface defining a first thickness of the membrane, at least one barrier projecting from the bottom surface of the membrane, each barrier defining a second thickness of the membrane between the top surface of the membrane and a lower surface of the barrier, preferably such that the second thickness of the membrane is larger than the first thickness of the membrane for each barrier. At least one slit may be provided extending from the top surface of the membrane to a lower surface of a barrier. Preferably such that the barrier forms a downwardly projecting edge of the slit. The stencil mask may be configured, such that an aspect ratio between the first thickness of the membrane or the second thickness of the membrane, and the width of the slit is at least 2. One key advantage of a large aspect ratio between the first thickness of the membrane or the second thickness, and the width of the slit, is the enablement of nanostructure fabrication with minimized effective broadening, as the particles that pass through the mask can be confined to a single trajectory.

[0012] As described in the background, one common problem during evaporation through stencil masks is that due to the significant distance between the stencil mask and the substrate, the evaporated features acquire a certain effective broadening. Figure 10 illustrates the problem of effective broadening (1000) when evaporating a material through a mask (1001) on a substrate (1002). A broadened area (1003) compared to the intended area to be deposited (1004) is formed, causing not only geometrical problems due to the extended deposition, but also decreasing the quality of the evaporated material. Figure 11 shows two schematics showing the dependence of the effective broadening (1100) to the mask thickness (1101), slit aperture (1102) and distance between the mask and the substrate (1103). An upper bound on the effective broadening is estimated where g is the distance between the mask and the aperture, T is the mask thickness, a is the slit aperture, L is the distance between the evaporation source (1005) and the substrate and rsis the aperture of the evaporation source.

[0013] As a result, by forming downwardly projecting barriers as described above, it is possible to extend the thickness of the mask, framing areas of interest, resulting in the reduction of effective broadening. Figure 1 illustrates an example of a stencil mask

[0014] (100) comprising two barriers (101), where the stencil mask comprises a slit (102). The stencil mask has a top surface (106) and a bottom surface (107), and each barrier

[0015] (101) has a lower surface (108). The stencil mask defines a first thickness (109) and a second thickness (110). The stencil mask (100) is positioned on a substrate (103) below an evaporation source (104). In the absence of the barriers, the thickness of the mask at the edges (105) of the slit would be smaller, leading to broadening of the evaporated features. Employing such barriers (101) allows any evaporated material that would contribute to effective broadening to be deposited on the barriers (101) of the stencil mask (100), leading to a less broadened evaporated feature. In an embodiment, the first thickness of the membrane is at least 200 nm, preferably at least 500 nm, more preferably at least 1 pm, even more preferably at least 3 pm, most preferably at least 5 pm. I.e. defining a “thick” stencil mask as used herein. In addition, the second thickness of the membrane can be at least 200 nm, preferably at least 500 nm, more preferably at least 1 pm, even more preferably at least 3 pm, most preferably at least 5 pm. In contrast to “thin” stencil masks with thicknesses in the order of 100 nm, “thick” stencil masks as used herein hold certain advantages. For example, the edges of a stencil mask adjacent to a slit introduce constraints on the incoming flux beam of the evaporation source. Hence, flux can bounce off these edges, resulting in refocusing of the flux towards the center line. As a result, the quality of the evaporated material can be enhanced using thick membranes compared to thin membranes. In addition, it is important that the membrane is sufficiently thick, in order to allow the fabrication of bridges connecting two parts of the stencil mask above a slit.

[0016] Moreover, the stencil mask can comprise a plurality of parallel bridges forming a plurality of spacings in a slit. Such bridges can be utilized to evaporate specific patterns on a substrate, and depending on the angle of evaporation, the same stencil mask can be used to design different sets of features. An example of such a structure can be seen in Fig. 2A, where a plurality of bridges (200) form a plurality of spacings in a slit. The thickness of the bridges (201) can be adjusted depending on the needs of the experiment, and the type of evaporation.

[0017] In another embodiment, it can be advantageous that the stencil mask allows for directional flux selectivity. Directional flux selectivity relates to the ability of permitting or locally obstructing the flux from an evaporation source, by for example utilizing periodic stabilizer bridges. Therefore, the stencil mask can comprise a second pattern comprising a plurality of parallel bridges defining a thickness of the membrane, extending from the top surface of the bridges to the bottom surface of the bridges. An example of such a structure is shown in Fig. 3A, where a top view of a stencil mask is shown. A first set of parallel bridges (300) is intertwined with a second set (301) of parallel bridges. Figure 3B shows a side view of intertwined set of bridges along the B dashed line if Fig. 3A, where the two sets of parallel bridges have different thickness, resulting in different distances from the bottom of the bridges to a substrate (302, 303). The sets of parallel bridges have a thickness (304, 305) defined from the top surface of the bridges to the lower surface of bridges. Different bridge thicknesses can be engineered according to the needs of each material evaporation, and the specific type of pattern that is to be designed. One can utilize different bridge thicknesses with a certain evaporation angle in order to block flux from being deposited on the substrate along a direction, while allowing other patterns to be deposited. Such techniques are disclosed in further details in pending applications PCT / EP2023 / 066468 and PCT / EP2023 / 066474, which are incorporated by reference in their entirety.

[0018] The present disclosure further relates to a method for defining a pattern on a substrate by evaporating from one or more evaporation sources using different evaporation materials, the method comprising the steps of providing a substrate comprising a surface, providing a stencil mask according to the features described herein, locating the bottom surface of the mask at a distance from the surface of the substrate, defining a first gap between the bottom surface of the mask and the substrate and a second gap between the at least one barrier and the substrate, and evaporating one or more materials over the mask. Further details regarding this method for defining a pattern on a substrate are provided in the detailed description of the application.

[0019] Description of the drawings

[0020] Various embodiments are described hereinafter with reference to the drawings. The drawings are examples of embodiments and are intended to illustrate some of the features of the presently disclosed stencil mask with barriers and are not limiting to the presently disclosed device and method.

[0021] Fig. 1 shows a schematic view of a stencil mask comprising two barriers.

[0022] Figs. 2 A, B show schematic views of a stencil masks comprising a plurality of bridges. Figs. 3 A, B show a top view and a side view of a stencil mask comprising two steps of parallel bridges.

[0023] Fig. 4 A, B shows a side view and a perspective view of a stencil masks, having perpendicular and angled barriers respectively.

[0024] Fig. 5 A, B shows two schematics of a stencil mask with different barrier width.

[0025] Fig. 6 shows the method steps for defining a pattern on a substrate by evaporating from one or more evaporation sources.

[0026] Fig. 7 shows the fabrication steps on a silicon-on-insulator substrate to define the thickness of the stencil mask. Fig. 8 shows the steps of a fabrication process on a silicon-on-insulator substrate to define a plurality of bridges in the stencil mask.

[0027] Fig. 9 shows an example of a stencil mask design.

[0028] Fig. 10 shows a schematic illustrating the deposition of an evaporated material to a substrate through a stencil mask.

[0029] Fig. 11 shows two schematics illustrating the effective broadening of features as a function of slit aperture, distance between the mask and the substrate, and mask thickness.

[0030] Fig. 12 shows a stencil mask comprising a set of nano-pillars.

[0031] Detailed description

[0032] As described in the summary, one of the main objectives of the present disclosure is to employ a unique stencil mask configuration with multiple variable thicknesses, which can be translated to different gap distances between the stencil mask and a substrate. These gaps are pivotal in controlling the deposition of materials onto surfaces, enabling the creation of more precise and complex designs than before.

[0033] A preferred embodiment relates to a stencil mask for defining a pattern on a substrate during evaporation of material from an evaporation source. The stencil mask comprises, a membrane having a top surface and bottom surface defining a first thickness of the membrane, at least one barrier projecting from the bottom surface of the membrane, each barrier defining a second thickness of the membrane between the top surface of the membrane and a lower surface of the barrier, such that the second thickness of the membrane is larger than the first thickness of the membrane for each barrier, and at least one slit extending from the top surface of the membrane to a lower surface of a barrier, such that the barrier forms a downwardly projecting edge of the slit. The stencil mask may be configured, such that an aspect ratio between the first thickness of the membrane or the second thickness of the membrane, and the width of the slit is at least 2. As also described in the summary, a key advantage of the large aspect ratio between the first thickness or the second thickness, and the width of the slit, is the enablement of nanostructure fabrication with minimized effective broadening, as the particles that pass through the mask can be confined to a single trajectory. The aspect ratio may also be designed to be larger than 2, such as 5 or 50. Depending on the type of application and the accuracy required for the deposited nanostructures, different types of stencil mask can be fabricated to suit the needs of each application. Further details about the aspect ratio are available in the following sections of the present disclosure.

[0034] Pending application PCT / EP2023 / 066468 discloses a stencil mask, which can also be considered to be thick. This pending application discloses embodiments of a stencil mask which also applies to the present disclosed stencil mask. For example a stencil mask for manufacturing at least one nanoscale device on a substrate, the stencil mask comprising a membrane having a top surface and a bottom surface and a thickness therebetween, preferably of at least 500 nm, a predefined pattern of slits extending through the membrane, each slit having a width and a length in the top surface of the membrane, wherein at least the width and / or the length of one of said slits preferably is less than 100 nm, each slit defined by inner sidewalls extending between the top surface and the bottom surface of the membrane. A set of separating nanostructures may be provided on the top surface of the membrane for separating the top surface of the membrane from a top surface of the substrate. This embodiment of the stencil mask applies also in the present disclosure, in combination with all the same features as disclosed in here.

[0035] In pending application PCT / EP2023 / 066468, the term “slit” was written as “aperture”. The terms slit and aperture substantially describe the same feature, and may be used interchangeably herein. In addition, in pending application PCT / EP2023 / 066468, the term “top surface of the membrane” is used, but in the present disclosure this is referred to as “bottom surface of the membrane” and vice versa. The reasoning behind this “opposite” notation between the present disclosure and PCT / EP2023 / 066468, was that in the membrane fabrication process disclosed in pending application PCT / EP2023 / 066468, the membranes are formed upside down, compared to the orientation that they would finally be positioned on a substrate. Therefore, in PCT / EP2023 / 066468 the top surface of the membrane would be in contact with the top surface of the substrate by using the structural element(s) for separating the top surface of the membrane from a top surface of the substrate. Figure 12 shows an example of this, using to the notation of the present disclosure, where the bottom surface (1203) of the stencil mask is separated from the top surface of the substrate (1204) by a set of nano-pillars (1200).

[0036] Specifications of the stencil mask The presently disclosed stencil mask can be configured such that at least one slit is embedded between a first of said at least one barrier and a second of said at least one barrier. A schematic of an example of a slit embedded between two barriers can be seen in Fig. 1. Such a design can be beneficial to reduce effective broadening in both parts of a deposited structure. These barriers effectively form a reduced stencilsubstrate interface and thus reduce the chance for trapping particles between the stencil and the substrate. For example, when depositing an electrode along the strip (102) shown in Fig. 1 , by introducing a barrier on each edge of the strip, it is possible to reduce the effective broadening of the deposited material in both edges. As a result, the deposited material can have the originally designed shape, by minimizing any possible broadening. It should be noted that the reduction of effective broadening is not simply a geometrical advantage that leads to the formation of patterns with optimal widths or lengths. By controlling the effective broadening, the quality of certain deposited materials may be increased, such as semiconductors and superconductors. Therefore, by introducing barriers projecting from the bottom surface of a membrane guarantees an increased quality of deposited material in the substrate.

[0037] In an embodiment, the barrier surface can be perpendicular to the top surface and to the bottom surface of the stencil mask, as shown in Fig. 1 and in Fig. 4A (401). In certain cases, it can be advantageous that the barriers are tilted, forming a valley shape, as seen in Fig. 4B (400). Figure 4A shows a side view and a perspective view of a stencil mask having perpendicular barriers (401). Figure 4B shows a side view and a perspective view where the barriers (400) are fabricated such that they form a non- orthogonal angle with the top surface of the stencil mask.

[0038] One purpose of designing a plurality of slits is to allow for selectivity based on beam direction relative to the orientation of the slits. This requires deposition at non-normal incidence, where normal incidence can be considered depositing material from an evaporation source, where the evaporation source is parallel to the substrate. For a stencil of finite thickness, a non-normal incidence creates two broadenings: one at the “front” where the beam is cut off by the top of the stencil, and another at the “back” where the beam is cut off by the stencil bottom. Angled barriers provide a wider range of freedom for choosing beam angles and mitigating different broadening phenomena. Ideally, the angle of the barriers and slit walls at least match the incidence angle of evaporation, removing the “front” side shadow phenomenon. Angled walls may also prove beneficial, as a very sharp stencil edge may be easier to achieve with the angles such as in Figure 4B rather than vertical edges as shown in figure 4A.

[0039] In another embodiment, the length of the barrier can be extended (500), as shown in Fig. 5. Fig. 5A shows a barrier with a thinner barrier length (500), while Fig. 5 B shows a barrier with an extended barrier length (501). Such a modification reduces the stencil fabrication complexity and may further increase the support of the stencil mask. Combinations of extended barrier lengths with shorter barrier lengths can be engineered in the same stencil mask, allowing the fabrication of different patterns in a single substrate.

[0040] Moreover, the stencil mask can be configured, such that the at least one slit has a length larger than 100 nm, or at least 500 nm, possibly up to 5000 pm. Depending on the object that is to be deposited on a substrate, different slit lengths can be fabricated to accommodate for each specific element of the design. For example, for the fabrication of a 10 pm long electrode, a stencil mask with a slit having a length of 10 pm can be utilized, while for a shorter electrode, a slit having the corresponding length can be used.

[0041] In another embodiment, the at least one slit in the stencil mask can have a width of more than 10 nm, and less than 1 pm. As described above, depending on the type of structures that are to be deposited in a substrate, different slit widths can be designed, in order to accommodate for each fabrication design.

[0042] The stencil mask can be configured, such that an aspect ratio between the first thickness or the second thickness of the membrane, and the width of the slit is at least 2, preferably at least 5, more preferably at least 10, even more preferably at least 50, most preferably at least 100, possibly up to 200 or even above. The aspect ratio is the ratio of first thickness (109) or the second thickness (110) of the membrane, over the width of the slit (102). A main advantage of the presently disclosed stencil mask is the thickness the membrane, which can be at least an order of magnitude higher than membranes in usual stencil masks disclosed in the prior art, and still be used for accurately defining apertures extending through the membrane. Thereby the obtainable aspect ratio of slit width vs. membrane is very high. In an embodiment, the stencil mask comprises one or more structural elements for separating the top surface of the membrane from a top surface of the substrate. Specifically, the stencil mask can be configured such that a set of separating nanostructures are configured to separate the lower surface of a barrier a fixed distance from the surface of the substrate. Such nanostructures can have the form on pillars, which are positioned at large distances from the slits, such as 100 pm or even more. Those pillars provide both stability for the stencil mask, and they assist in defining a fixed distance between the barriers, and the substrate. Depending on the type of deposition, a different height of pillars can be chosen, in order to modify the distance between the substrate and the stencil mask. Such separating nanostructures can comprise a set of nano-pillars, preferably arranged homogeneously on the bottom surface of the membrane. In another embodiment, the set of separating nanostructures are separated at least 1 m from any slit of the membrane. An example of separating nanostructures can be seen in Fig. 12, where a set of nano-pillars (1200) is fabricated on the bottom surface of the stencil mask, providing stability and a fixed distance between the barriers (1201) and the surface of the substrate (1202).

[0043] Bridge structures in the stencil mask

[0044] In addition, the stencil mask can be configured, such that it comprises a plurality of parallel bridges forming a plurality of spacings in a slit. For example, as seen in Fig. 2A, a plurality of bridges (200) can be fabricated in a stencil mask, having certain thickness (201) and defining a spacing (202) which reflects the distance between two bridges. The combination of spacing and bridge thickness can be utilized along with the angle of evaporation from a source, in order to define certain structures inside the slit. Combining the above with the sharp edges of the barriers (203) enables a consistent flux and ensures the fabrication of sharp, well-defined features inside the slit. In another embodiment, the bridges can be used both for defining certain features, or for stabilizing another set of bridges, in order to prevent the bridges from clamping together.

[0045] Moreover, the stencil mask can be configured, such that the bridges are perpendicular to said slit. For example, as seen in Fig. 3A, a first set of bridges (300) is designed to be perpendicular to the longitudinal axis of the slit. In other scenarios, it may be useful that the bridges are non-orthogonal to the longitudinal axis of the slit, or they may also be parallel to the slit, as the second set of parallel bridges (301). The choice of angles depends on the design and type of evaporated material that is to be fabricated.

[0046] In an embodiment, the stencil mask can be configured such that the pattern of parallel bridges defines a third thickness of the membrane, extending from the top surface of the membrane to a bottom surface of the bridges, wherein the third thickness is different from the first thickness and the second thickness of the membrane. As shown in Fig. 3B, one set of parallel bridges defines a thickness (304) of the membrane. In another embodiment, the first pattern comprising a plurality of bridges is intertwined by a second pattern comprising a plurality of bridges. Such an example is shown in Fig. 3A, where a set of parallel bridges (300) is intertwined by a second set of parallel bridges (301).

[0047] In addition, the stencil mask can be configured, such that the second pattern comprising a plurality of parallel bridges defines a thickness of the membrane, extending from the top surface of the bridges to the bottom surface of the bridges, such that said thickness is smaller than the thickness of the first pattern of parallel bridges. For example, in Fig. 3B a second pattern comprising a plurality of parallel bridges defines a thickness (305) being smaller than the thickness (304) of the first pattern comprising a plurality of parallel bridges. However, the second set of parallel bridges can have the same, or different thickness compared to the thickness of the first set of parallel bridges. Such thickness modifications depend on the use of such bridges. For instance, if the main purpose of one pattern of bridges is to stabilize the first pattern of bridges, then their thickness can be smaller than the first pattern of bridges. On other hand, two pattern of bridges can be intertwined in order to be used for different angle evaporations using the same stencil mask on the same fabrication step. In such a case, depending on the design that is to be fabricated, the bridge thicknesses can be designed accordingly.

[0048] Furthermore, the stencil mask can be configured, such that the first and second patterns are perpendicularly intertwined. For example, Fig. 3A shows a top view of a stencil mask, where a first pattern comprising a plurality of parallel bridges (300) is perpendicularly intertwined to a second pattern comprising a plurality of parallel bridges (301). As described above, different angles may also be utilized, depending on the type of fabrication that is required. Following the above reasoning, it may be beneficial in certain fabrication steps to have a stencil mask with a plurality of different patterns, each comprising a plurality of parallel bridges. For complex nanoelectronic devices, it may be that four or more different patterns are designed above a slit in a stencil mask, to be used for angle evaporation, or for stabilizing purposes.

[0049] Composition of the barrier

[0050] The stencil mask can be further configured, such that the at least one barrier is comprised of a same material than the membrane, such as SiN, Si, SiC, SiGe, Ge, Al, AIOx, Cr, Au, In or other ultra-high vacuum, high vacuum or vacuum compatible materials. In another embodiment, the stencil mask can be configured such that the at least one barrier is comprised of a different material than the membrane.

[0051] Method for defining a pattern on a substrate

[0052] One significant advantage of the present disclosure over prior art, is that it enables multiple, locally tailored gaps between the stencil mask and a substrate. Such a design facilitates independent and precise adjustments of both the flux distribution and the broadening of evaporated features — a significant leap forward from existing methods where these two aspects are tightly intertwined and difficult to control separately.

[0053] Specifically, the present disclosure relates to a method for defining a pattern on a substrate by evaporating from one or more evaporation sources using different evaporation materials. Figure 6 presents the steps of the method (600). The method comprises the steps of: providing a substrate comprising a surface (601), providing a stencil mask according to any of the features described above (602), locating the bottom surface of the mask at a distance from the surface of the substrate, defining a first gap between the bottom surface of the mask and the substrate and a second gap between the at least one barrier and the substrate (603), and evaporating one or more materials over the mask (604). For example, Fig. 2B shows a stencil mask comprising two barriers (207) and a plurality of bridges (208), as seen from a side view. The mask defines a first gap (204) between the bottom surface of the mask and the top surface of the substrate, each barrier defines a second gap (205) between the lower surface of each barrier and top surface of the substrate, and the bridges define a third gap (206) between the bottom surface of the bridges and the top surface of the substrate. Naturally, if a stencil mask is fabricated to have more patterns of parallel bridges, then each pattern of parallel bridges define an additional gap between their bottom surface and the top surface of the substrate. In an embodiment, the bottom surface of the mask can either have a finite distance from the surface of the substrate, or it may also have a minimal distance from the surface of the substrate, such that the bottom surface of the mask or the barrier is in contact with the surface of the substrate.

[0054] By controlling the relation between these three gaps, it is possible to fine-tune the stencil mask, and optimize the flux through a slit while at the same time minimizing any possible broadening of features in unwanted areas of the substrate.

[0055] Another advantage of the presently disclosed stencil mask is that the stencil mask may be reversibly attached to the substrate, and that the evaporated deposition material can be removed from the stencil mask such that the stencil mask is reusable. The evaporated deposition material on the mask can for example be removed via selective wet etch. The deposition of materials may be performed in a series of steps ordered such that the removal of remaining material can be done by etching techniques. The deposition of materials may be performed at a deposition rate, temperature and vacuum chamber pressure such that the removal of remaining material is performed by etching or thermal annealing processes.

[0056] A spatial positioning of at least one source of the at least first and / or second deposition material may be controlled to define a deposition material angle with respect to the bottom surface of the membrane. In that regard, the deposition material angle may at least partly define the at least one nanoscale device pattern deposited through the pattern of slits (or apertures) in the membrane.

[0057] An angular dispersion of the evaporated deposition material on the top surface of the substrate may be determined by the aspect ratio between the thickness of the membrane of the stencil mask, the width of the slits in the pattern and the separation distance between the top surface of the membrane and the top surface of the substrate. In addition, the angular dispersion of the evaporated deposition material may be determined by the height of the nano-pillars located in the substrate proximal surface, wherein an increase of the height induce a higher angular dispersion of the deposition material. At a height of the nano-pillars equal to 0 nm, the angular dispersion is supressed and the defined pattern is directly imprinted onto the surface of the substrate.

[0058] Fabrication of a stencil mask

[0059] The fabrication process of a stencil mask is according to the fabrication methods provided in pending applications PCT / EP2023 / 066468 and PCT / EP2023 / 066474. Specifically, one possible fabrication method of a Si membrane is to be fabricated using silicon on insulator (SOI) wafers, where an insulating layer acts as a stopping layer for the etch processes. The individual steps of the process can be seen in Fig. 7 and Fig. 8. The fabrication process starts with a SOI wafer (700) which is covered with a SiN layer using low pressure chemical vapor deposition (LPCVD) (701). On the backside of the substrate (702), openings in the SiN layer can be patterned (703), using UV lithography, followed by submerging the substrate in a potassium hydroxide (KOH) solution. KOH etches Si anisotropically, and creates angles in the substrate as it etches into it (704). That is a controlled process, which allows a user to control the size of the membrane. The SiO2 acts as a stopping layer, having good selectivity to Si in a KOH solution, so the etch will naturally slow down when reaching that layer. That allows a user to control the thickness of the membrane. The SiN layer can be removed (705) in a H3PO4 solution.

[0060] The fabrication of a multi-gap shadow mask begins with a Si membrane (800), fabricated according to Fig. 7 and Fig. 8. For the current fabrication recipe, the membrane is sufficiently thick, ranging from 7 pm to 10 pm, allowing a plurality of bridges to be fabricated. Electron beam lithography (EBL) and etching techniques is utilized, to form the bridge structure of the stencil mask. Specifically, a chromium layer is deposited on the top surface of the substrate (801), followed by selective etching of the chromium (802). A subsequent etching step in a deep reactive ion etch (DRIE) is performed, where a recipe for high aspect ratio processes is developed, known as the CORE process. The width of the bridges is typically at the 100 nm scale, while the etching depth is larger than 2 pm, resulting to the high aspect ratio etch process. After etching down (803), the layer of chromium is removed, before depositing a new layer of chromium (804). The new layer covers the surface and the bottom of the etched-out trenches. A subsequent EBL step is performed, in order to form a mask to etch the surrounding features of the bridges (805). The CORE process is utilized, in order to etch past the bridges (806) up until the SiO2 layer. The chromium layer is then removed, and the SiO2 layer can be etched using HF. The resulting bridge structure is complete (807). In case of a stencil mask comprising a plurality of different parallel bridges, the above description of etching out the bridges can be repeated as many times as the number of different thicknesses of bridges.

[0061] One of the advantages of using the CORE process, is that he stencil mask can be configured, such that the surface roughness of the downwardly projecting edge of at least one barriers may be below 10 nm, preferably below 5 nm, most preferably below 1 nm. Surface roughness is understood here as either the maximum extension of the surface variation or the average extension of the surface variation. Scallop roughness is a known effect in this technical field and it may happen during known dry etching processes, wherein the inner sidewalls of defined apertures such as slits, develop inner protrusions of nanometric size towards the inside of the of the substrate inside the aperture. The presently disclosed stencil mask can be realized with slits with substantially scallop free downwardly projecting edges, even for thinner range of widths described before.

[0062] Examples

[0063] An example of a stencil mask design combining barriers projecting from the bottom surface of the membrane, slits, and bridges can be seen in Fig. 9. In this design, the purpose is to evaporate two channels of a material along the two slits (900). The barriers (901) are designed accordingly in order to limit the feature broadening of the evaporated material. Using the set of bridges (902), it is possible to deposit material in the slits using a first evaporation angle, blocking the deposition of material in the two slits for a second angle, thereby allowing the fabrication of multiple independent selective depositions using the same stencil mask, without removing the substrate from UHV.

[0064] Items

[0065] 1. A stencil mask for defining a pattern on a substrate during evaporation of material from an evaporation source, the stencil mask comprising, a membrane having a top surface and bottom surface defining a first thickness of the membrane, at least one barrier projecting from the bottom surface of the membrane, each barrier defining a second thickness of the membrane between the top surface of the membrane and a lower surface of the barrier, such that the second thickness of the membrane is larger than the first thickness of the membrane for each barrier, and at least one slit extending from the top surface of the membrane to a lower surface of a barrier, such that the barrier forms a downwardly projecting edge of the slit.

[0066] 2. The stencil mask according to item 1 , wherein the first thickness of the membrane is at least 200 nm, preferably at least 500 nm, more preferably at least 1 pm, even more preferably at least 3 pm, most preferably at least 5 pm.

[0067] 3. The stencil mask according to any of the preceding items, wherein the second thickness of the membrane is at least 200 nm, preferably at least 500 nm, more preferably at least 1 pm, even more preferably at least 3 pm, most preferably at least 5 pm.

[0068] 4. The stencil mask according to any one of the preceding items, wherein the at least one slit has a length larger than 100 nm, or at least 500 nm, possibly up to 5000pm.

[0069] 5. The stencil mask according to any one of the preceding items, wherein at least one slit is embedded between a first of said at least one barrier and a second of said at least one barrier.

[0070] 6. The stencil mask according to item 5, wherein said slit has a width of more than 10 nm, and less than 1 pm.

[0071] 7. The stencil mask according to any of the preceding items, comprising a plurality of parallel bridges forming a plurality of spacings in a slit.

[0072] 8. The stencil mask according to item 7, wherein said bridges are perpendicular to said slit.

[0073] 9. The stencil mask according to any of the preceding items, wherein a pattern of parallel bridges defines a third thickness of the membrane, extending from the top surface of the membrane to a bottom surface of the bridges, wherein the third thickness is different from the first thickness and the second thickness of the membrane.

[0074] 10. The stencil mask according to any of the preceding items, wherein a first pattern comprising a plurality of bridges is intertwined by a second pattern comprising a plurality of bridges.

[0075] 11. The stencil mask according to any one of the preceding items, wherein a second pattern comprising a plurality of parallel bridges defines a thickness of the membrane, extending from the top surface of the bridges to the bottom surface of the bridges, such that said thickness is smaller than the thickness of the first pattern of parallel bridges.

[0076] 12. The stencil mask according to item 10, wherein the third thickness of the first pattern is equal to the third thickness of the second pattern.

[0077] 13. The stencil mask according to item 10, wherein the third thickness of the first pattern is different to the third thickness of the second pattern.

[0078] 14. The stencil mask according to any of the preceding items, wherein the first and second patterns are perpendicularly intertwined.

[0079] 15. The stencil mask according to any of the preceding items, wherein the at least one barrier is comprised of a same material than the membrane, such as Si N , Si, SiC, SiGe, Ge, Al, AIOx, Cr, Au, In or ceramics.

[0080] 16. The stencil mask according to any of the preceding items, wherein the at least one barrier is comprised of a different material than the membrane.

[0081] 17. The stencil mask according to any one of the preceding items, wherein an aspect ratio between the first thickness or the second thickness of the membrane, and the width of the slit is at least 2, preferably at least 5, more preferably at least 10, even more preferably at least 50, most preferably at least 100. 18. The stencil mask according to any one of the preceding items, wherein a surface roughness of the downwardly projecting edge of at least one barriers is below 5 nm.

[0082] 19. The stencil mask according to any of the preceding items, wherein the set of separating nanostructures are configured to separate the lower surface of a barrier a fixed distance from the surface of the substrate.

[0083] 20. A method for defining a pattern on a substrate by evaporating from one or more evaporation sources using different evaporation materials, the method comprising the steps of a. providing a substrate comprising a surface, b. providing a stencil mask according to any one of the preceding items, c. locating the bottom surface of the mask at a distance from the surface of the substrate, defining a first gap between the bottom surface of the mask and the substrate and a second gap between the at least one barrier and the substrate, and d. evaporating one or more materials over the mask.

[0084] 21. The method according to item 20, wherein the stencil mask further comprises a plurality of parallel bridges, each set of parallel bridges defining a gap between the bottom surface of the bridges and the substrate.

[0085] 22. The method according to items 20-21, further comprising a step of removing the evaporated material from the stencil mask such that the stencil mask is reusable.

[0086] 23. The method according to items 20-22, wherein a spatial positioning of at least one source of the at least first and / or second deposition material is controlled to define a deposition material angle with respect to the bottom surface of the membrane.

[0087] 24. The method according to any of items 20-23, wherein an angular dispersion of the evaporated deposition material on the top surface of the substrate is determined by the aspect ratio between the thickness of the membrane of the stencil mask, the width of the slits (or apertures) in the pattern and the separation distance between the top surface of the membrane and the top surface of the substrate.

Claims

Claims1. A stencil mask for defining a pattern on a substrate during evaporation of material from an evaporation source, the stencil mask comprising, a membrane having a top surface and bottom surface defining a first thickness of the membrane, at least one barrier projecting from the bottom surface of the membrane, each barrier defining a second thickness of the membrane between the top surface of the membrane and a lower surface of the barrier, such that the second thickness of the membrane is larger than the first thickness of the membrane for each barrier, and at least one slit extending from the top surface of the membrane to a lower surface of a barrier, such that the barrier forms a downwardly projecting edge of the slit, wherein an aspect ratio between the first thickness of the membrane or the second thickness of the membrane, and the width of the slit, is at least 2.

2. The stencil mask according to claim 1 , wherein the first thickness of the membrane is at least 200 nm, preferably at least 500 nm, more preferably at least 1 pm, even more preferably at least 3 pm, most preferably at least 5 pm.

3. The stencil mask according to any of the preceding claims, wherein the second thickness of the membrane is at least 200 nm, preferably at least 500 nm, more preferably at least 1 pm, even more preferably at least 3 pm, most preferably at least 5 pm.

4. The stencil mask according to any one of the preceding claims, wherein the at least one slit has a length larger than 100 nm, or at least 500 nm, possibly up to 5000 pm.

5. The stencil mask according to any one of the preceding claims, wherein at least one slit is embedded between a first of said at least one barrier and a second of said at least one barrier.

6. The stencil mask according to claim 5, wherein said slit has a width of more than 10 nm, and less than 1 pm.

7. The stencil mask according to any of the preceding claims, comprising a plurality of parallel bridges forming a plurality of spacings in a slit.

8. The stencil mask according to claim 7, wherein said bridges are perpendicular to said slit.

9. The stencil mask according to any of the preceding claims, wherein a pattern of parallel bridges defines a third thickness of the membrane, extending from the top surface of the membrane to a bottom surface of the bridges, wherein the third thickness is different from the first thickness and the second thickness of the membrane.

10. The stencil mask according to any of the preceding claims, wherein a first pattern comprising a plurality of bridges is intertwined by a second pattern comprising a plurality of bridges.

11. The stencil mask according to any one of the preceding claims, wherein a second pattern comprising a plurality of parallel bridges defines a thickness of the membrane, extending from the top surface of the bridges to the bottom surface of the bridges, such that said thickness is smaller than the thickness of the first pattern of parallel bridges.

12. The stencil mask according to claim 10, wherein the third thickness of the first pattern is equal to the third thickness of the second pattern.

13. The stencil mask according to claim 10, wherein the third thickness of the first pattern is different to the third thickness of the second pattern.

14. The stencil mask according to any of the preceding claims, wherein the first and second patterns are perpendicularly intertwined.

15. The stencil mask according to any of the preceding claims, wherein the at least one barrier is comprised of a same material than the membrane, such as Si N , Si, SiC, SiGe, Ge, Al, AIOx, Cr, Au, In or ceramics.

16. The stencil mask according to any of the preceding claims, wherein the at least one barrier is comprised of a different material than the membrane.

17. The stencil mask according to any one of the preceding claims, wherein the aspect ratio between the first thickness or the second thickness of the membrane, and the width of the slit is at least 5, preferably at least 10, more preferably at least 50, even more preferably at least 100.

18. The stencil mask according to any one of the preceding claims, wherein a surface roughness of the downwardly projecting edge of at least one barriers is below 5 nm.

19. The stencil mask according to any of the preceding claims, wherein the set of separating nanostructures are configured to separate the lower surface of a barrier a fixed distance from the surface of the substrate.

20. A method for defining a pattern on a substrate by evaporating from one or more evaporation sources using different evaporation materials, the method comprising the steps of a. providing a substrate comprising a surface, b. providing a stencil mask according to any one of the preceding claims, c. locating the bottom surface of the mask at a distance from the surface of the substrate, defining a first gap between the bottom surface of the mask and the substrate and a second gap between the at least one barrier and the substrate, and d. evaporating one or more materials over the mask.

21. The method according to claim 20, wherein the stencil mask further comprises a plurality of parallel bridges, each set of parallel bridges defining a gapbetween the bottom surface of the bridges and the substrate.

22. The method according to claims 20-21, further comprising a step of removing the evaporated material from the stencil mask such that the stencil mask is reusable.

23. The method according to claims 20-22, wherein a spatial positioning of at least one source of the at least first and / or second deposition material is controlled to define a deposition material angle with respect to the bottom surface of the membrane.

24. The method according to any of claims 20-23, wherein an angular dispersion of the evaporated deposition material on the top surface of the substrate is determined by the aspect ratio between the thickness of the membrane of the stencil mask, the width of the slits (or apertures) in the pattern and the separation distance between the top surface of the membrane and the top surface of the substrate.

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