Three-dimensional structures are produced using photoresist.

Abstract

This invention relates to a method for producing three-dimensional structures using photoresist, specifically for generating stepped structures in the micrometer to millimeter range. The objective of finding new possibilities for realizing microstructures that allow for substantially free-form and high-volume production of stepped structures, enabling micromechanical and high-performance electronic structures, is achieved according to the invention by: coating (3) a copper-clad substrate (1) at least once with a first photoresist to generate at least one structural step of defined height, and coating (3) the first photoresist at least once with a second photoresist to generate at least one additional structural step of defined height, wherein the first and second photoresists have different photosensitivity and transmission properties, which, through exposure (4) with different wavelengths and radiation doses and after development (5), allow the formation of structurally forming regions (35; 36) of at least the first and second photoresists. These structurally forming regions (35; 36) at least partially overlap each other and form a stepped three-dimensional structure.

Description

Technical Field

[0001] This invention relates to a method for producing three-dimensional structures using photoresist, specifically for creating stepped structures from photoresist or for molding bodies using stepped structures in the micrometer to millimeter range. The invention is particularly applicable to the electronics industry, printed circuit board packaging and chip packaging, the semiconductor industry, and microtechnology, especially microtechnology for producing micromechanical structures. Background Technology

[0002] In existing technologies, photoresist is used for photolithographic patterning to create structures in the micrometer and submicrometer range for microelectronics and microsystems technologies. This process is typically performed by applying a photoresist layer to a substrate or an existing circuit structure layer and subsequently exposing it to areas with a negative resist that will remain as the structure surface, or to areas with a positive resist that will be ablated. The non-resist areas of the photoresist structure are removed as uncured layer components during subsequent development processes and can subsequently be filled with electronic conductor and semiconductor structures or partially occupied by gate structures.

[0003] This procedure was described by V. Papageorgiou et al. in the technical paper “Cofabrication of Planar Gunn Diode and HEMT on InP Substrate” (IEEE Transactions on Electron Devices, Vol. 61, No. 8

[2014] 2779-82784). In this context, the gate gap between the source and drain required for Gunn diodes or HEMT (High Electron Mobility Transistors) structures with widths of 1.5 μm to 2 μm is generated by an ablation photoresist structure. Because the source and drain layers are thin, only a photoresist layer of about 0.1 μm thickness is required. The photoresist used for the diode structure requires different photoresist sensitivities due to different percentages of PMMA (polymethyl methacrylate) composition in order to achieve different ablation depths. Regarding the possibility of producing structures whose midlayer thickness is on the order of or greater than the width of the structure, the aforementioned cited technical paper does not disclose any recommendations or insights on feasible greater ablation depths given the required energy and time. Summary of the Invention

[0004] The purpose of this invention is to find new possibilities for realizing microstructures of micromechanical and high-performance electronic structures, which allow for the essentially free-formation of stepped, particularly overhanging, structures, and allow for flexible, high-volume production of complex shapes for forming metallic microstructures and conductive traces.

[0005] According to the present invention, the above objective is achieved in a method for producing three-dimensional structures using photoresist, the method comprising the following steps:

[0006] - Provide a metal-clad substrate (1) to improve surface adhesion or adaptability to subsequent metal deposition and separation of the structure (6; 71) from the substrate (1);

[0007] - Coating (3) the copper-clad substrate (1) with a first photoresist at least once to create at least one structural step of a defined height, and coating (3) the first photoresist with a second photoresist at least once to create at least one additional structural step of a defined height, wherein the first photoresist and the second photoresist have different photosensitivity and transmission characteristics for patterning.

[0008] - In at least one structurally forming region (35) of the first photoresist, the first photoresist is exposed (4) with exposure radiation (41) having a first wavelength range and a first radiation dose;

[0009] - In at least one structurally forming region (36) of the second photoresist, at least the second photoresist is exposed with exposure radiation (42) having a second wavelength range and a second radiation dose, wherein at least the structurally forming regions (35; 36) of the first photoresist and the second photoresist at least partially overlap each other;

[0010] - At least one multilayer photoresist structure (6) is developed (5) from the overlapping structurally forming regions (35; 36; 37) of at least the first photoresist and the second photoresist by developing the non-structurally forming exposure regions of at least the coatings (31; 32; 33; 34) of the first photoresist and the second photoresist.

[0011] Advantageously, the coating of the first photoresist with the second photoresist is performed before the first structurally generating exposure of the first photoresist and the structurally generating exposure of the second photoresist.

[0012] Alternatively, the coating of the first photoresist with the second photoresist is performed only after the structurally generative exposure of the first photoresist, and the structurally generative exposure of the second photoresist is performed after the coating with the second photoresist.

[0013] In a further advantageous variation, the coating of the second photoresist with a third photoresist is performed only after the structurally productive exposure of the second photoresist, and the coating with a fourth photoresist or any other photoresist occurs after the structurally productive exposure of the third photoresist or any other previously applied photoresist.

[0014] In a preferred embodiment of the method, at least the first photoresist or the second photoresist or another photoresist having more than one photoresist layer is stacked and applied to each other in order to create a structural step of a desired defined height for the photoresist structure.

[0015] Furthermore, it is preferable that the first photoresist and the second photoresist are selected to have different sensitivities in each case, such that the first photoresist and the second photoresist can be cured by different exposure radiations that do not react to another corresponding photoresist.

[0016] A preferred variation is that the first photoresist is sensitive to longer wavelength exposure radiation with a higher exposure dose relative to the effective wavelength and exposure dose of the second photoresist, and is insensitive to shorter wavelength exposure radiation with a lower exposure dose that reacts with the second photoresist; and the second photoresist is transparent and insensitive to the longer wavelength exposure radiation and higher exposure dose of the first photoresist, and is sensitive to shorter wavelength exposure radiation relative to the effective wavelength and exposure dose of the first photoresist.

[0017] The different sensitivities of the first and second photoresists in the wavelength range between 375 nm and 436 nm suitably differ by more than 20 nm, preferably more than 30 nm, and differ by between 10 mJ / cm² in terms of applicable dosage. 2 With 2200mJ / cm 2 The range between them is preferably greater than 4 times.

[0018] The third or additional photoresist is advantageously selected to have a sensitivity such that, in a wavelength range between 248 nm and 436 nm, it differs from the wavelengths of the first and second photoresists by more than 20 nm, preferably more than 30 nm, and is within the range of 10 mJ / cm². 2 With 2200mJ / cm 2 Within the range between these values, the applicable dose is preferably greater than 4 times different from the applied exposure dose of the first photoresist and the second photoresist.

[0019] It has proven advantageous that, during the development of at least the first and second photoresists, a three-dimensional photoresist structure of the overlapping structurally forming regions of at least the first and second photoresists is retained on the substrate and a photoresist gap is formed between adjacent photoresist structures, the photoresist gap being usable as a cavity for filling with a moldable material.

[0020] In this regard, metal or metal alloy can be deposited into the photoresist gaps between adjacent or surrounding photoresist structures.

[0021] At least one metal or alloy thereof from the group consisting of copper, nickel, titanium, chromium, aluminum, palladium, tin, silver and gold is suitably used as the filling material for the cavity.

[0022] The photoresist structure is preferably produced in the form of a stack of elongated layers spaced apart by gaps or a stack of layers surrounded by gaps, so as to mold different molded bodies in the gaps.

[0023] After metal deposition is performed in the gap created between the photoresist structures by developing at least the first and second photoresists, the removal of the photoresist structures can be suitably performed by a resist developer, wherein the formed metal mold remains on the metal layer of the metal-clad substrate.

[0024] The metal back etching method on the substrate can be advantageously performed using a metal etchant, at least in the intermediate space between the metal structures formed by the metal deposition.

[0025] In particularly advantageous applications, the metal back etching method can continue with an etchant suitable for the metal layer of the metallized substrate until the metal layer of the substrate is completely ablated, so that the metal structure is cut into a metal molded body.

[0026] This invention demonstrates the possibility of realizing microstructures for micromechanical or high-performance microelectronic structures, which allow for the essentially free-formation of stepped, particularly overhanging, structures and enable flexible, high-volume production of complex shapes for forming metal micromolds. Attached Figure Description

[0027] The invention will be described more fully below with reference to exemplary embodiments and illustrations. The accompanying drawings show:

[0028] Figure 1 A schematic diagram of a method according to the invention for generating advantageous stepped structures with different photoresist layers is shown;

[0029] Figure 2A schematic diagram of a method according to the invention for generating an additional advantageous stepped structure with different photoresist layers is shown;

[0030] Figure 3 A schematic diagram of another embodiment of the method according to the present invention for generating a three-layer structure having at least two different photoresists is shown;

[0031] Figure 4 According to the invention, it is used for... Figure 3 A schematic diagram of a method to continue execution to produce a six-layer structure having at least three different photoresists;

[0032] Figure 5 according to Figure 3 and 4 The method according to the invention is continued, wherein the photoresist structure generated multiple times is used to produce a metal molded body, and the molded body is diced (detached from the substrate);

[0033] Figure 6 A schematic diagram of a further execution of the method according to the invention for producing a structure having at least two different photoresists, wherein in each instance, exposure is performed on each of the different photoresists before exposure with the next photoresist;

[0034] Figure 7 According to the method of the present invention, from Figure 6 The advantageous continuation, in which multiple resist structures are generated for the production of metal structures, wherein the etching back of the copper coating on the substrate can be performed only for electrically isolated individual metal structures or can be performed before the metal molded body can be cut into individual pieces (separated from the substrate);

[0035] Figure 8 A schematic diagram of a further execution of the method for producing a thick photoresist layer according to the present invention is shown, wherein separate exposures are performed on different photoresists, and the gaps in the structure are filled with copper after the resist structure is developed, so as to obtain a separated copper structure on the substrate after the metallization of the substrate (or the substrate itself) and the etching back.

[0036] Figure 9 The selection of an easily achievable cross section for the preferred photoresist structure used in the production of microstructures using a limited number of different photoresist layers produced by a single combined development step.

[0037] Symbol explanation:

[0038] 1: (Metal-clad) substrate

[0039] 2: Metal layer

[0040] 3: Coating

[0041] 31, 32, 33: Photoresist layer

[0042] 34: Final photoresist layer

[0043] 35, 36, 37, 38: Structurally Forming Regions

[0044] 4: Exposure

[0045] 41: (exposure radiation of photoresist layer 31)

[0046] 42: (exposure radiation of photoresist layer 32)

[0047] 43: Exposure radiation (of photoresist layer 33)

[0048] 44: (exposure radiation of photoresist layer 34)

[0049] 5: Development

[0050] 51: Developer

[0051] 6: Photoresist structure

[0052] 61: (Photoresist) Gap

[0053] 7: Metal deposition

[0054] 71: Metal Structure

[0055] 72: (Metal) Molded body

[0056] 8: Removal of corrosion inhibitor

[0057] 81: Resist developer (resist stripper)

[0058] 9: Metal back corrosion

[0059] 91: (For metal layer 2) Metal etchant

[0060] 92: Etching agent used for partial metal layer etching back Detailed Implementation

[0061] According to the invention, it is used in accordance with Figure 1 The method for generating microstructures with structural height (layer thickness) in the low to high micrometer range (1 μm to several hundred μm) in the basic variant includes the following steps:

[0062] - Provide a metallized substrate 1 (typically: metal cladding, PVD metallization, or metal deposition);

[0063] - A metal-clad substrate 1 is coated with a first photoresist at least once to create at least one structural step with a defined step height, and a first photoresist is coated with a second photoresist at least once to create at least one additional structural step, wherein the first and second photoresists have different photosensitivity and transmission characteristics for patterning.

[0064] - Perform first structure-generating exposure on the first photoresist using a first wavelength range and a first radiation dose;

[0065] - Second structure-generating exposure of the second photoresist using a second wavelength range and a second radiation dose 4;

[0066] -Develop the 5-step photoresist structure by ablating the non-structure-forming exposure areas of the first and second photoresists.

[0067] In this respect, there are virtually no restrictions on the types of structural configurations in terms of the number, height, and width of edges. However, to achieve the edge quality achievable at the end of the photoresist structure development process (which depends on the desired height of the structural steps), the photoresist material should be selected based on its spectral sensitivity and the absorption / transmission characteristics of the photoresist used to the processing beam. Additionally, there are the available radiation output and radiation dose to achieve structure-generating exposure within the shortest possible exposure time, within the sensitivity range of the photoresist used.

[0068] Figure 1 A schematic cross-sectional view of the layer stack produced on substrate 1 illustrates each step. Substrate 1 is in the sub- Figure 1 A metal layer 2 (metal cladding layer) is provided as the starting point for the generation of the desired microstructure. The metal layer 2 is mainly used to improve surface adhesion for additional coatings, subsequent metal deposition processes, and processes that allow the structure to detach from the substrate 1.

[0069] Figure 1 son Figure 2 The image shows a substrate 1 after being coated with a first photoresist 31 (e.g., photosensitive polymer A), the layer thickness of which is suitable for the desired height of the structure to be produced. If a defined uniform layer cannot be achieved in one step, the required layer thickness can also be achieved by applying the same photoresist 31 multiple times, as will be shown more fully later (e.g., Figure 3 and Figure 4 ).

[0070] The choice of photoresist is essentially adapted to the final shape of the structure to be produced. The characteristics of the photoresist used for processing are wavelength-dependent absorption / transparency and sensitivity (exposure dose). These characteristics must be appropriately adapted to each other for the corresponding structure.

[0071] like Figure 1 The method adopted and illustrated, for the purpose of subsequent metal forming, such as the creation of a T-structure from a polymer, requires a first photoresist (e.g., Hitachi HM-40112) as the lower photoresist layer 31. This first photoresist reacts to a relatively large wavelength (e.g., 402 nm) and requires a high exposure dose (e.g., 250 to 400 mJ / cm² at 405 nm). 2 The photoresist can be cured to the full depth of the photoresist layer 31. For example, Hitachi RY series, Hitachi HM series and DuPont WBR series, which have exposure wavelengths suitable for curing, are also suitable as the insensitive photoresists of the above types.

[0072] In contrast, when different cross-sectional and / or height dimensions are required for the final shape of the structure, the overlying photoresist layer 32 needs significantly different properties. Figure 1 The selected T-shaped protrusion shape is used for the upper photoresist layer 32. A photoresist (e.g., Kolon Industries LS-8025) is chosen that has high absorption for short wavelengths (e.g., 375 nm) and high transparency for long wavelengths used for exposure of the first photoresist layer 31, and has the lowest possible exposure dose (e.g., Kolon Industries LS-8025: 35 to 50 mJ / cm at 375 nm). 2 For example, Hitachi RD series, Hitachi SL series, Asahi Kasei AQ series, and Kolon Industries LS series are suitable for use as this type of highly sensitive photoresist.

[0073] By selecting photoresists with different parameters, the exposure process (such as the exposure of the first structurally forming region 33 of the photoresist layer 31 provided for curing) using exposure radiation 41 is made possible. Figure 4 (as shown) and the exposure process (as shown) of the second structurally forming region 34 of the photoresist layer 32 selected for curing using exposure radiation 42. Figure 5 (As shown) should be limited as much as possible to the layers targeted by the exposure process. This is important because, in particular, those portions of the structurally forming regions 33 and 34 of the photoresist layers 31 and 32 targeted by the two exposure radiations 41 and 42 are only affected by the exposure radiation 41 or 42 intended for them, so that a consistent degree of curing can be achieved in the respective structurally forming regions 33 and 34 of the first photoresist layer 31 and the second photoresist layer 32, which allows for the application of the exposure process according to the desired results. Figure 1 son Figure 6 In the subsequent development process, the uncured residues of photoresist layers 31 and 32 are subjected to edge-specific precise ablation.

[0074] For example Figure 2 The inverted T-shaped structure shown requires reversing the previous reference. Figure 1 The characteristics of the first photoresist layer 31 and the second photoresist layer 32 are described. The lower photoresist layer 31 requires a first photoresist with low exposure dose and higher sensitivity to longer wavelengths (e.g., having 30 to 50 mJ / cm at 405 nm). 2 (e.g., Hitachi SL-1338). On the other hand, the upper photoresist layer 32 should have a second photoresist for high exposure doses and high transparency to long wavelengths (e.g., having a photoresist with a strength of 180 to 300 mJ / cm at 375 nm). 2 Hitachi RY-5125).

[0075] Used to execute according to Figure 2 All other sequences of the method are with Figure 1 The first photoresist, chosen solely for the structural shape, the second photoresist conforming to the latter, and the exposure radiations 41 and 42 selected to suit the latter are changed. In principle, if the transparency of the second photoresist layer 32 within the wavelength range of the exposure radiation 41 used for the first photoresist layer 31 is permissible, then... Figure 1 The material pairing of the selected photoresist layers 31 and 32 can also be applied in the opposite manner and can be cured using an adapted model of exposure radiation 41 and 42.

[0076] Figure 1 and Figure 2 The embodiments described herein (and all examples of the embodiments below) reflect the substantial advantages and core of the method according to the invention, because the coating and exposure processes and the development process can be performed in a uniform (i.e., non-alternating) cycle, so that the coated substrate 1 does not need to be repeatedly changed to its specific processing chamber, and due to the economics of this method, a large number of desired three-dimensional microstructures can be produced at high process yields using methods known in chip manufacturing.

[0077] Figure 3 Further embodiments of the method according to the invention using a first photoresist and a second photoresist different from the first photoresist are shown. In this case, due to the desired structural height of the second photoresist, after the lower photoresist layer 31 is coated on the metal coating 2 (e.g., a copper cladding layer) on the substrate 1, as in the case of a sub-photoresist layer... Figures 1 to 4As shown in the steps, the photoresist layer 32 is applied twice. This multiple coating is typically only possible under the following conditions: both photoresist layers 32 (e.g., including Hitachi RY-5125) have sufficient transparency within the wavelength of the exposure radiation 41 (e.g., 405 nm) used for the first photoresist (e.g., Hitachi SL-1338), and the latter can be applied at low exposure doses (e.g., at 30 to 50 mJ / cm²). 2 (Below) solidification, such as child Figure 5 As illustrated. Based on Figure 3 son Figure 6 The second exposure radiation 42 (e.g., at 375 nm, with 200 to 300 mJ / cm) is utilized. 2 After the exposure process of the second photoresist (e.g., Hitachi RY-5125) on the two upper photoresist layers 32, the structure generation process and the development process (corresponding to) Figure 2 sub Figure 6 The process can end there, or, as expected in the text, more complex structures can be created using additional photoresist coatings.

[0078] Figure 4 Two additional structural steps are shown for generating the desired structure. Figure 3 The method of variation continues advantageously. The requirements may be the same when the desired structure only has a greater height. Figure 4 Reference Figure 3 consecutively numbered sub Figure 7 In this process, an additional photoresist layer 33 is applied in a dual manner to create additional edge structures (structural steps) in the absence of a prior development process on the layer stack that has been applied and exposed up to this point and includes the lower photoresist layer 31 and two upper photoresist layers 32 thereon. This is because a third photoresist with a low exposure dose (e.g., JSR THB-111N, with 25 mJ / cm² at 355 nm) is selected. 2 Therefore, multilayer coating is not determined by the desired (relatively low) structural height, but rather by the need to prevent interference with the underlying photoresist layers 31 and 32. The wavelength used to cure the third photoresist must also be selected differently than that used for the first and second photoresists. However, if the exposure dose of layer 33 is sufficiently low and the absorption is sufficiently high, the same wavelength used for layer 31 can be used. After two photoresist layers 33 have been applied, as in the case of sub-layers... Figure 9 As illustrated in one particular style, it utilizes a short wavelength and low exposure dose (e.g., 355 nm, at 25 mJ / cm²) for the third photoresist. 2(As described above) or alternatively, 375nm for the Krohne Industrial LS-8025, at 35mJ / cm 2 The exposure radiation 43 cures the two photoresist layers within the structure-forming region 35.

[0079] Furthermore, for Figure 4 The example shown assumes that the structure-forming region 38 is smaller than the structure-forming region 37 of the photoresist layer 33, so that it can be used with a third photoresist (e.g., JSR-THB-111N: [e.g., at 355 nm, 25 mJ / cm). 2 The same additional photoresist application method provides further gradation of the desired structural profile according to sub-Figure 10.

[0080] However, if the size of the final structure-forming region 38 of the photoresist layer 34 is large, that is, relative to the structure-forming region 37 ( Figure 4 If the image (not shown) has an overhang, then a fourth photoresist (e.g., JSR ARX series, at 248nm, 15mJ / cm) must be selected. 2 The fourth photoresist also has a different wavelength (at least relative to the third photoresist of layer 33) and requires a small radiation dose for curing in order to prevent damage to the underlying photoresist layers 31, 32 and 33 outside the structurally forming regions 35, 36 and 37.

[0081] Curing is performed by exposure radiation 44, which corresponds to the exposure radiation 43 of the smaller structure-forming region 38 in the first example described above (e.g., curing). Figure 4 (As shown in sub-Figure 11) After the final photoresist layer 34, the joint development process of all photoresist layers 31 to 34 is carried out according to sub-Figure 12 using a common developer 51 (e.g., an alkaline developer (sodium carbonate, potassium carbonate, potassium hydroxide, tetramethylammonium hydroxide, etc.) or an organic developer (1-methoxy-2-acetic acid propyl ester, cyclopentanone, etc.)), after which the desired structure 6 remains.

[0082] Figure 5 It is shown in accordance with Figure 3 and 4 The preferred application of the method for producing structure 6 is assumed to be that the multiple production of structure 6 is performed on substrate 1 occupied by metal layer 2. Figure 5Sub-Figure 13 illustrates such a cross-section of substrate 1, in which metal deposition 7 (e.g., copper, nickel, chromium, tin, palladium, silver, gold, or alloys thereof) is performed between two adjacent structures 6 in each case until the photoresist gap 61 is completely filled. To protect the metal deposition 7 during subsequent etching processes, it may be advantageous to select substrate 1 that is soluble in organic solvents and therefore non-corrosive to the metal of the metal deposition 7. For this purpose, it is useful to incorporate an additional thin separator layer (not shown here) made of polymer between substrate 1 and metal layer 2.

[0083] Figure 5 Sub-Figure 14 shows the exposed photoresist layers 31 to 34 (only in...) Figure 4 and Figure 5 The next step is the molding of metal deposition 7 between structures 6 (as specified in the diagram). In this case, structure 6, which serves as the negative mold for shaping the metal deposition 7, is dissolved for this purpose because the resist developer 81 acts on the structurally forming regions 35 to 38 of the photoresist layers 31 to 34 during the resist removal step, and simultaneously the photoresist structures 6 between the metal-filled photoresist gaps 61 are dissolved. Thereafter, the metal deposition 7, molded into the photoresist gaps 61 and still fixedly connected to the substrate 1 via the metal layer 2 of the substrate 1, remains on the metal-clad substrate 1.

[0084] If the metal deposition 7, which is the metal structure 71 (specified only in sub-Figure 16), remains fixedly bonded to the substrate 1 but electrically isolated from each other, then metal back etching 9 is performed to a limited extent, such that only the metal cladding layer of the substrate 1 is ablated by the resist developer 81 (e.g., ferric chloride (III) or copper chloride (II) with hydrogen peroxide for copper, ferric chloride (III) or nitric acid with hydrochloric acid for nickel, ammonium hydroxide with hydrogen peroxide and methanol for silver, dilute nitric acid for tin, etc.). Figure 5 Subfigure 15 schematically illustrates the results.

[0085] If a single-cut metal structure 71 is desired, the metal etch-back process 9 is prolonged and / or continued with an etchant (as described above) specifically suited to the metal layer 2 of the substrate 1, until the metal structure 71 is detached from the substrate 1 as a single metal molded body 72, as shown in sub-Figure 16.

[0086] In the six subgraphs, Figure 6 Another example of producing a simple photoresist structure 6 is shown, in which only two photoresist layers 31 and 32 are required to produce a T-structure 6 having the following dimensions: width b: 100 μm, height h: 83 μm, support width s: 50 μm, and support height (ht): 45 μm.

[0087] The procedure and according to Figure 1and Figure 2 The difference in the embodiments is that, according to the sub Figure 2 After coating with a first photoresist (e.g., DuPont Hitachi RY-5545 optimized for a relatively short wavelength of 365 nm [i-line of a mercury vapor lamp]), the process is performed with a second photoresist sensitive to a relatively large wavelength (e.g., Hitachi SL-1333 at 405 nm) according to the sub-... Figure 4 Before coating 3, in the corresponding sub Figure 3 The resulting photoresist layer 31 is exposed in the structurally forming region 35 (e.g., first with an exposure radiation 41 adapted to it [e.g., at 375 nm, 240 mJ / cm²). 2 ]).

[0088] If photoresist layer 32 is applied, then according to the sub- Figure 5 It is then exposed to irradiation 42 (e.g., at 405 nm, 30 mJ / cm) in the structurally forming region 36. 2 Exposure. Subsequently, a combined development process 5 is performed using the selected resist developer 81 (e.g., an alkaline solution based on sodium carbonate, sodium hydroxide, potassium carbonate, or potassium hydroxide).

[0089] To achieve a particularly high width b while maintaining a small support width s, a photoresist layer 31 with exceptionally high sensitivity may be required. An example of such a photoresist is AZ 125nXT, which requires 1500 mJ / cm² for thicker layers starting from 70 μm. 2 Up to 2200mJ / cm 2 The upper photoresist layer 32 can be cured with a dosage that is four times smaller but significantly higher than usual, thus enhancing its stability and enabling greater overhang than the lower photoresist layer 31. In this example, the structure-forming region 36 (formed by Hitachi SL-1333 resist) can be cured at approximately 150 mJ / cm². 2 Instead of 30mJ / cm 2 Exposure. In contrast, the dose used to expose the lower photoresist layer 31 is ten to almost fifteen times its amount, so that a dose less than one-tenth of the dose used for the upper photoresist layer 32 has no significant effect on the unexposed areas of the lower photoresist layer 31 (outside the structure-forming region 35).

[0090] In each case, the exposure doses of the lower to upper photoresist layers 31, 33 and 32, 34 should differ by a factor of four or more. This prevents unwanted exposure of the corresponding other photoresist layers 32, 34 and 31, 33 outside the already exposed structurally forming regions 35, 36. Since the exposure dose is essentially determined by the sensitivity of the selected resist, the smaller the factor of dose difference can be chosen, the farther apart the wavelengths that the corresponding resists are sensitive to.

[0091] Figure 7 It shows Figure 6 Continuing the method, which is used to produce a metal structure 72 on a substrate 1, for producing robust conductive traces for power electronic devices or delicate conductive traces with enhanced mechanical stability. However, the intersecting photoresist structures 6 on the substrate can also be cured by exposure, such that gaps 61 are released by intersecting structure-forming regions 35 and 36 for metal deposition 71 having a base area ranging from square, rectangular, parallelogram, elongated rhombus, hexagonal, or elliptical to circular.

[0092] To illustrate an embodiment of this method, sub Figure 7 A cross-section of a metal-clad substrate 1 with a metal layer 2 (e.g., copper) is shown. The metal (as a layer of, for example, copper, nickel, chromium, tin, palladium, silver, gold, or an alloy thereof) is deposited in the gaps 61, according to… Figure 6 son Figure 6 The gaps are created between the photoresist structures 6. Therefore, the gaps 61 are completely filled, and thus the metal deposition 7 is correspondingly molded by utilizing the structure of the gaps 61 as a preform. According to the sub- Figure 8 During resist removal 8, the photoresist structure 6 is completely dissolved by resist developer 81 (e.g., potassium carbonate), and then metal etching 9 is performed on the metal layer 2 by applying etchant 92 (as described above), which is suitably adapted to partially etch back the metal of the metal layer 2 between the metal structures 71. Thus, the substrate 1 retains the metal structures 71 of a specific shape and the remainder of the metal layer 2 serving as an adhesion promoter.

[0093] exist Figure 8 In the illustrated method variation, a significant feature of the resulting structure is the formation of a particularly tall T-shaped photoresist structure 6, where the ratio of the support height (ht) to the total height h is approximately one. Consequently, an overhang of the structure-forming region 36 of the second photoresist is formed over the structure-forming region 35 of the first photoresist. Furthermore, to save time, the photoresist structure 6 is produced with as few photoresist layers 31 and 32 as possible. In this example, the dimensions of the stepped T-shaped photoresist structure 6 are assumed to be h = 155 μm, b = 90 μm, s = 60 μm, and (ht) = 75 μm.

[0094] For this purpose, a photoresist layer 31 generated by a first photosensitive polymer (e.g., DuPont WBR-2075 or Hitachi HM-40112) is used (with a relatively large wavelength (e.g., 405 nm) and a high exposure dose (e.g., 350 mJ / cm). 2 The photoresist layer 32 is applied to the metal layer 2 of the metal-clad substrate 1 at 405 nm. For the second overhanging structure step, two identical photoresist layers 32 are required for coating 3, and a second photoresist (e.g., Asahi Kasei AQ-4088) is used. This second photoresist has high absorption for short wavelengths (e.g., 365 nm) and high transparency for long wavelengths used for exposure of the first photoresist layer 31, and has the lowest possible exposure dose (e.g., 80 mJ / cm²). 2 (At 375nm). Wavelength pairing of 405nm and 355nm can also be used, provided a suitable light source is available in the exposure apparatus (not shown), in which case, for example, JSR THB-111N (with 25mJ / cm² at 355nm). 2 (A small exposure dose) can be used as a second resist.

[0095] Like a child Figure 1 As shown, after coating 3 with the lower photoresist layer 31, in this case, the process is performed using two similar photoresist layers 32 (according to the sub-layer). Figure 3 and 4 Before the second and third coatings (including the second photoresist), an exposure radiation 41 suitable for the first photoresist is applied to the desired structurally forming region 35 (sub-photoresist). Figure 2 Similarly, exposure 4 is performed in (). According to Figure 8 son Figure 5 Then, exposure 4 is performed in the provided structurally forming region 36 using exposure radiation 42 suitable for the second photoresist. Next is the joint development 5 of all photoresist layers 31 and 32. Figure 6 (See the previous examples for reference.) Figure 5 and 7 As described, metal deposition 7 is performed in the gaps 61 between the photoresist structures 6, thereby molding metal structures 71 (e.g., layers comprising copper, nickel, chromium, tin, palladium, silver, gold, or alloys thereof) at the photoresist structures 6. After resist removal 8 by means of a resist stripping solution 81 (e.g., by means of a 10% potassium hydroxide solution), conductive connections formed by the metal layer 2 of the substrate 1 are retained between the metal structures 71 (according to the description). Figure 8To remove the latter and obtain a metal structure 71 as a fixed structure on substrate 1, metal back etching 9 (sub-etching) is performed using an etchant 92 specifically suitable for metal layer 2 (e.g., copper(II) chloride with hydrogen peroxide for Cu; a mixture of 5% nitric acid / 65% phosphoric acid / 5% acetic acid and water for Al; dilute nitric acid for Sn). Figure 9 ), to be used for partially ablation of the metal layer 2 only between the desired metal structures 71.

[0096] Figure 9 A specific advantageous photoresist structure 6 according to the method steps of development 5 is shown again. To illustrate the example already described above, in the sub- Figure 1 The instructions specify the dimensions to be adjusted.

[0097] Figure 9 son Figure 1 The photoresist structure 6 shown is preferably designed to produce a metal structure 71 or a metal molded body 72, and typically has dimensions of h = 30-1000 μm and (ht) = 10 μm-900 μm, wherein its width b and support width s can be optionally selected, but in each case depends on the height and spacing of the structure and on the stability of the resist. When only two different photoresists are used, producing multiple similar layers 31 and 32 respectively allows the structural height of each structural step to increase to a maximum of 1000 μm. Individual photoresist layers 31, 32 can sometimes have significantly smaller heights (e.g., up to 76 μm for Hitachi SL series, up to 112 μm for Hitachi HM-40112, and up to 240 μm for DuPont WBR series) and must be stacked, but there are exceptions (e.g., up to 1000 μm for MicroChem SU-8), where larger structural steps can be achieved with only a single photoresist layer 31. Since various dry film resists (e.g., the Hitachi HM series with 56 μm, 75 μm, and 112 μm) are produced only with defined layer thicknesses, in some cases it may be necessary to achieve the desired layer thickness by laminating multiple thin resist layers 31, 32. In this case, as in every other case, the exposure dose must be adapted to the corresponding layer thickness and layer configuration to obtain optimal results after development of the photoresist structure 6.

[0098] Figure 9 son Figure 2 This type of photoresist structure 6 is shown, which is preferably configured to produce a metal structure 71 or metal molded body 72 with a large gradient or protrusion (overhang) with a covering surface (not shown) when the structural step of the lower photoresist layer 31 structural forming region 36 has a large height and the upper photoresist layer 32 structural forming region 36 has a large overhang.

[0099] The metal structure 71 can be used to mechanically stabilize the conductive traces on the flexible substrate 1. By appropriately selecting the height, width, and overhang of the structure 6, the mechanical stability under repeated loading can be improved, while simultaneously reducing the amount of material required for coating / deposition (electroplation) of the metal structure 71. This extends the lifespan of the metal bath used for depositing the metal layer. Furthermore, by changing the aspect ratio of the metal structure 71, the mechanical and electrical properties can be selectively adapted to specific requirements.

[0100] Metal molded bodies 72 are primarily used as micromechanical components or parts that can be mass-produced using the techniques available here.

[0101] In terms of size, it is similar to that of children. Figure 1 and 2 In similar circumstances, Figure 9 son Figure 3 A specific layer structure is shown, specifically oriented to have a high width-to-support width ratio. In this way, the formation of the metal structure 71 is improved, particularly in terms of mechanical stability and adhesion to the flexible substrate 1.

[0102] Using this invention, microstructures can be produced cost-effectively and in high yields from photoresist or metal with reproducible precision and a limited number of process steps in one or several cycles. Therefore, large-scale production using conventional techniques in the semiconductor and printed circuit board industries (but where the height dimensions of the resulting structures are significantly larger than those in conventional circuit and wafer fabrication cycles) is possible for relatively fine edge-stepped bodies, while maintaining reproducible edge quality and precision. By combining photoresist layers 31 to 34, comprising several different photoresists with varying curing sensitivities, layer stacks that can be partially machined in consecutive exposure cycles at different exposure wavelengths and / or exposure doses can be assembled, but photoresist structures 6 can be formed in each case of a combined development process. In this way, particularly high process economy can be achieved in the production of 3D microstructures in the single- to triple-digit micrometer range.

[0103] When the method according to the invention is applied to steppers in the semiconductor industry, the width of the resulting resist structure can be further increased to approximately 150 nm, and the structure height can potentially reach the millimeter range. This is because conventional mercury vapor lamps used in the semiconductor industry are equipped with filters for the wavelengths (365 nm, 405 nm, 436 nm) utilized here. Alternatively, various laser sources (solid-state lasers or laser diodes) with wavelengths of 355 nm, 375 nm, or 405 nm can also be used. This method can also be applied to resists in the deep UV range, which are exposed using wavelengths of 248 nm (KrF* laser) and 193 nm (ArF* laser).

Claims

1. A method for producing three-dimensional structures using photoresist, the method comprising the following steps: - Provide a metal-clad substrate (1) to improve surface adhesion or adaptability to subsequent metal deposition and separation of the structure (6; 71) from the substrate (1); - Coating (3) the copper-clad substrate (1) with a first photoresist at least once to create at least one structural step of a defined height, and coating (3) the first photoresist with a second photoresist at least once to create at least one additional structural step of a defined height, wherein the first photoresist and the second photoresist have different photosensitivity and transmission characteristics for patterning. - In at least one structurally forming region (35) of the first photoresist, the first photoresist is exposed (4) with exposure radiation (41) having a first wavelength range and a first radiation dose; - In at least one structurally forming region (36) of the second photoresist, at least the second photoresist is exposed with exposure radiation (42) having a second wavelength range and a second radiation dose, wherein at least the structurally forming regions (35) of the first photoresist and the second photoresist are exposed. 36) They overlap at least partially with each other; - At least one multilayer photoresist structure (6) is developed (5) from the overlapping structurally forming regions (35; 36; 37) of at least the first photoresist and the second photoresist by developing the non-structurally forming exposure regions of at least the coatings (31; 32; 33; 34) of the first photoresist and the second photoresist.

2. The method according to claim 1, wherein the coating (3) of the first photoresist with the second photoresist is performed before exposing the first photoresist (4) and exposing the second photoresist (4).

3. The method according to claim 1, wherein the coating (3) of the first photoresist with the second photoresist is performed only after the first photoresist is exposed (4), and the exposure (4) of the second photoresist is performed after the coating (3) with the second photoresist.

4. The method according to claim 2 or 3, wherein the coating (3) of the second photoresist with the third photoresist is performed only after the second photoresist has been exposed (4), and the coating (3) of the fourth photoresist or any other photoresist occurs after the third photoresist or any other previously applied photoresist has been exposed (4).

5. The method according to any one of claims 1 to 3, wherein at least the first photoresist or the second photoresist or other photoresists having more than one photoresist layer (31; 32; 33; 34) are stacked and applied to each other to create a structural step of a desired defined height of the photoresist structure (6).

6. The method according to any one of claims 1 to 3, wherein the first photoresist and the second photoresist are selected in each case to have different sensitivities, such that the first photoresist and the second photoresist can be cured by different exposure radiation (41; 42) that the other corresponding photoresist does not react to.

7. The method of claim 6, wherein the first photoresist is sensitive to longer wavelength exposure radiation (41) with a higher exposure dose relative to the effective wavelength and exposure dose of the second photoresist and is insensitive to shorter wavelength exposure radiation (42) with a lower exposure dose that reacts with the second photoresist, and the second photoresist is transparent and insensitive to the longer wavelength exposure radiation (42) and the higher exposure dose of the first photoresist and is sensitive to shorter wavelength exposure radiation (42) relative to the effective wavelength and exposure dose of the first photoresist.

8. The method of claim 6, wherein the different sensitivities of the first photoresist and the second photoresist differ by more than 20 nm in the wavelength range between 375 nm and 436 nm, and differ by between 10 mJ / cm² in terms of applicable dosage. 2 With 2200mJ / cm 2 The range between them.

9. The method of claim 8, wherein the different sensitivities of the first photoresist and the second photoresist differ by more than 30 nm in the wavelength range between 375 nm and 436 nm, and differ by more than 4 times in terms of applicable dosage.

10. The method of claim 6, wherein the third photoresist or another photoresist is selected to have a sensitivity such that, in a wavelength range between 248 nm and 436 nm, the sensitivity differs from the wavelengths of the first and second photoresists by more than 20 nm, and in terms of the applicable dose, it differs from the applied exposure dose of the first and second photoresists by more than 10 mJ / cm². 2 With 2200mJ / cm 2 Within the range between.

11. The method of claim 10, wherein the third photoresist or another photoresist is selected to have a sensitivity such that, in a wavelength range between 248 nm and 436 nm, the sensitivity differs from the wavelengths of the first and second photoresists by more than 30 nm in terms of wavelength, and differs from the applied exposure dose of the first and second photoresists by more than four times in terms of applicable dose.

12. The method according to any one of claims 1 to 3, wherein during the development (5) of at least the first photoresist and the second photoresist, a three-dimensional photoresist structure (6) of the overlapping structurally forming regions (35, 36, ...) of at least the first photoresist and the second photoresist is retained on the substrate (1) and a photoresist gap (61) is formed between adjacent photoresist structures (6), the photoresist gap being capable of serving as a cavity for filling with a moldable material.

13. The method of claim 12, wherein a metal or metal alloy is deposited into the photoresist gaps (61) between the photoresist structures (6).

14. The method of claim 13, wherein at least one metal or an alloy thereof from the group consisting of copper, nickel, titanium, chromium, aluminum, palladium, tin, silver and gold is used as the filling material for the cavity.

15. The method according to any one of claims 1 to 3, wherein the photoresist structure (6) is generated in the form of an elongated or closed stack of layers in order to mold different molded bodies.

16. The method of claim 12, wherein after metal deposition (7) in the gap (61) created between the photoresist structure (6) by developing at least the first photoresist and the second photoresist, resist removal (8) of the photoresist structure (6) is performed by resist developer (81), wherein the metal molded body (72) remains on the metal layer of the metal-clad substrate (1).

17. The method according to claim 16, wherein a metal back etching (9) method of the metal layer (2) on the substrate (1) is performed by a metal etchant (91) in at least the intermediate space between the metal structures (71) formed by the metal deposition (7).

18. The method according to claim 17, wherein the metal back etching (9) method is continued with an etchant (92) suitable for the metal layer (2) of the metallized substrate (1) until the metal layer (2) of the substrate (1) is completely ablated, such that the metal structure (71) is diced into a metal molded body (72).

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