Method for manufacturing a micro-optic

Abstract

Method for manufacturing a micro-optic comprising the steps of: providing a transparent substrate with a first side and an opposing second side; applying a first photoresist to the first side and a second photoresist to the second side, wherein the first photoresist and the second photoresist are different; and 3D laser writing by means of 2-photon absorption of a first structure into the first photoresist and a second structure into the second photoresist, wherein the first structure and / or the second structure is an optical element, characterized in that the first photoresist and the second photoresist have different transmission.

Description

[0001] The present invention relates to a method for producing a micro-optic and a micro-optic produced by such a method.

[0002] There are two writing modes for 3D-printed micro-optics using 2-photon lithography. In the immersion configuration, an immersion fluid is introduced between the lens and the substrate to establish optical contact. The writing material is applied to the back of the substrate, where the structure is then created. This mode limits the possible structure height by the working distance of the lens. The other writing mode is dip-in lithography, in which the writing medium itself serves as the contact medium and is inserted between the lens and the substrate. In this case, the structure is created on the front of the substrate, and there is no height limitation due to the working distance. However, both writing modes only allow 3D printing on one side of the substrate.If, for example, one wants to print structures on the front and back of the substrate for a multi-lens optical system, this has so far only been possible through two consecutive printing processes, between which the substrate must be removed, developed, and reinstalled after being turned over. Markers are also required to align the structures on the front and back. These markers are produced during the first print and used for alignment during the second print. However, the application of the markers, their reading, and readjustment involve inaccuracies that must be avoided at all costs.

[0003] The existing solutions then require a second printing process on the second substrate side, which makes the manufacturing process more laborious, longer, and more complex due to the removal, reassembly, and development. In addition, the markers for alignment must be manufactured and used for adjustment in the second production step. The alignment of the second side relative to the first is then inaccurate, which can destroy the functionality of the optics due to aberrations.

[0004] The object of the present invention is to provide a method with which micro-optics can be produced in a simplified manner.

[0005] The problem is solved by the method of claim 1 and the micro-optics according to claim 16.

[0006] The method according to the invention for producing a micro-optic comprises the following steps: Providing a transparent substrate having a first side and an opposite second side; Applying a first photoresist to the first side and a second photoresist to the second side; and 3D laser writing by means of 2-photon absorption of a first structure into the first photoresist and a second structure into the second photoresist, wherein the first structure and / or the second structure is an optical element.

[0007] Here, a first photoresist is first applied to the first side of the transparent substrate and a second photoresist is applied to the second side. The order can be reversed here, so that a second photoresist is first applied to the second side and then a first photoresist is applied to the first side. In any case, however, the application of the first photoresist and the second photoresist are two directly consecutive steps. Here and below, “transparent” refers to the property of the respective material due to which light in the near infrared range, the visible spectral range and / or the near UV range can pass through the substrate essentially unhindered. In this context, “essential” means more than 50% of the light passes through the substrate, preferably more than 75% and more preferably more than 90% and particularly preferably more than 95%.The substrate can be transparent across the entire wavelength range from the near infrared through the visible spectral range into the near UV range. Alternatively, the substrate can also be transparent only for certain wavelength ranges and thus be designed as a filter. In particular, however, the substrate is transparent for the wavelength range of 3D laser writing. 3D laser writing is an additive manufacturing process in which structures are created from the photoresist using a 3D printer based on a predetermined or predefined layout or design by locally curing the photoresist. The 3D printer can, for example, be a 3D lithography system, in particular a 3D laser lithography system or a 3D multiphoton laser lithography system, which is based on 2-photon absorption of a UV-curing photoresist and uses this to create three-dimensional complex structures.For this purpose, the liquid photoresist is cured at specific locations which are specified by the 3D design. The remaining liquid resist is then removed to obtain the 3D structure. Thus, 3D laser writing using 2-photon absorption creates a first structure in the first photoresist and a second structure in the second photoresist. In this case, the first structure or the second structure is an optical element. Alternatively, both the first structure and the second structure are optical elements. In this case, a first structure can first be written in the first photoresist and then a second structure in the second photoresist. Alternatively, the sequence is reversed, so that first a second structure is written in the second photoresist and then a first structure in the first photoresist.Alternatively, a first structure or only a part of the first structure is alternately created in the first photoresist and a second structure or only a part of the second structure is created in the second photoresist. In each case, the writing or creation of the first structure in the first photoresist and the writing or creation of the second structure in the second photoresist are two directly consecutive steps. No readjustment of the substrate is required between the creation of the first structure and the creation of the second structure. Further steps such as applying another photoresist or developing the first structure or the second structure are also omitted between the creation of the first structure and the second structure. This automatically aligns the first structure with the second structure with a high degree of accuracy.This simplifies the process for producing the micro-optics, as steps are eliminated. At the same time, the accuracy of the resulting micro-optics is improved due to the improved alignment of the first structure on the first side of the substrate and the second structure on the second side of the substrate.

[0008] Preferably, the optical element is an aperture, a lens, a prism, a diffraction grating, an axicon, a mirror, an array of apertures, an array of lenses, an array of one of the other optical elements, or combinations of the aforementioned elements.

[0009] Preferably, the first structure and the second structure are an optical element, wherein the optical axes of the optical elements on the first side and the second side of the substrate coincide, in particular with an accuracy of 1 µm or less. If, for example, the first structure is a lens and the second structure is an aperture, a transverse alignment of the aperture and the lens on the different sides of the substrate can be achieved with an accuracy of 1 µm or less. In particular, the creation of markers and the subsequent alignment using these markers is eliminated due to the method according to the invention.

[0010] During 3D laser writing, the first photoresist on the first side preferably faces a lens of the 3D printer. In this case, the first photoresist can also serve as an immersion fluid, bonding the lens and the substrate, thereby avoiding refractive index differences, for example, caused by intervening air layers.

[0011] Preferably, the first structure is created first on the first side of the substrate and then the second structure on the second side of the substrate. Alternatively, the second structure is created first on the second side and then the first structure on the first side of the substrate. It has been found that curing the photoresist results in minimal differences in the refractive index in the photoresist, which may lead to an unwanted deflection of the 3D printer's laser beam. To increase accuracy, it is therefore advantageous to first write the second structure on the second side of the substrate through the uncured first photoresist and only then write the first structure.

[0012] Preferably, the first structure and / or the second structure are written layer by layer, in particular starting from the substrate.

[0013] Preferably, the first photoresist is printed on the first side using dip-in lithography. Additionally, the second photoresist is printed on the second side using immersion lithography. These are the two previously separately used modes of 3D lithography, which are combined according to the present invention.

[0014] The substrate preferably has a thickness of 25 µm to 1000 µm. The thickness of the substrate is adapted to the respective application.

[0015] Preferably, the thickness of the first photoresist and / or the thickness of the second photoresist is 100 µm - 3 mm. The thickness of the photoresist also limits the maximum height of the respective structures. A further limitation arises from the maximum travel distance or working distance of the 3D printer lens relative to the substrate.

[0016] Preferably, the first photoresist and the second photoresist are different from each other. Because the two photoresists are separated by the intermediate substrate, the photoresists can be selected independently and specifically adapted to the respective application.

[0017] Preferably, the first photoresist and the second photoresist have different refractive indices. This allows lenses to be produced whose optical properties are specifically adapted to the respective application. At the same time, the refractive index can be used to optimize the writing process for creating the first structure and the second structure. For example, a photoresist with a refractive index equal to or close to the refractive index of the substrate can be selected as the first photoresist.

[0018] Preferably, the first photoresist and / or the second photoresist are transparent substantially over the entire wavelength range of at least visible light or from the near infrared range to the near UV range.

[0019] Preferably, the first photoresist and the second photoresist have different transmittances. Thus, one photoresist can be transparent over substantially the entire wavelength range of visible light, whereas the transmittance of the other photoresist is limited to a specific, smaller range, whereby the other photoresist acts as a color filter. Alternatively, both photoresists can be transparent only in a small wavelength range and act as color filters, whereby the respective wavelength ranges of the first photoresist and the second photoresist can be the same or different.

[0020] Preferably, the second photoresist is an absorptive photoresist, and the second structure can then be a diaphragm or an array of diaphragms. Thus, an absorptive photoresist can be used on the second side of the substrate to prevent stray light and thereby improve the imaging quality of the lenses on the first side of the substrate.

[0021] The second structure is preferably a connecting structure for connecting to an optical device. The connecting structure is aligned with the optical element on the first side. The connecting structure can, for example, be elements which come into contact with corresponding connecting elements of the optical device in order to connect the micro-optics to the optical device and at the same time align them with one another. For example, the optical device can be an optical fiber. The connecting structure can be round and have an opening which corresponds to the diameter of the optical fiber. This round opening is aligned with the optical element on the first side so that optimal coupling takes place between the optical fiber and the optical element on the first side.

[0022] Preferably, the first structure is a lens and the second structure is also a lens, wherein the first lens and the second lens are aligned to form an achromatic doublet, also known as a Fraunhofer doublet. This allows lenses to be created that can reduce achromatic aberration in images. This is particularly possible because the first photoresist and the second photoresist can have different refractive indices.

[0023] Preferably, a reference letter is carried out before the 3D laser writing, whereby the reference letter comprises the following steps: 3D laser writing of the target structure to create a preliminary structure; Detecting local deviations between the generated pre-structure and the target structure; Determining a correction structure from the target structure taking into account the local deviation; and Using the correction structure for subsequent 3D laser writing.

[0024] Thus, the target structure is first created using the specified layout or design as a preliminary structure through additional 3D laser writing. Local deviations between the generated preliminary structure and the target structure are subsequently recorded. These deviations are then taken into account when determining a corrective structure, which is then used for the subsequent 3D laser writing. If the preliminary structure deviates from the desired design, this is taken into account when determining the corrective structure, so that an adapted design is used for the subsequent 3D laser writing. This allows the target structure, which corresponds to the original design or layout, to be created during the subsequent 3D laser writing.For example, if the preliminary structure exhibits a deviation of 1 µm from the desired layout at a certain position, this 1 µm deviation is added or subtracted in the correction structure to achieve an approximation of the desired target structure. The aforementioned steps can be performed iteratively until the original and desired design or layout is generated as accurately as possible.

[0025] Furthermore, the present invention relates to a micro-optic produced by the method described above.

[0026] The invention is explained in more detail below using preferred embodiments with reference to the attached figures.

[0027] They show: Fig. 1 is a flowchart of the method according to the present invention, Fig. 2A and Fig. 2B a detailed view of the steps of the method according to Fig. 1 and Fig. 3A - Fig. 3D different micro-optics manufactured using the process according to Fig. 1.

[0028] In the following, reference is made to the Fig. 1. According to the present invention, a method is provided for producing a micro-optic comprising the steps of: In step S01, providing a transparent substrate having a first side and an opposite second side; In step S02, applying a first photoresist to the first side and a second photoresist to the second side; and In step S03, 3D laser writing by means of 2-photon absorption of a first structure into the first photoresist and of a second structure into the second photoresist, wherein the first structure and / or the second structure is an optical element.

[0029] Thus, according to the present invention, immersion lithography and dip-in lithography are combined in a single process step. Between the 3D laser writing of the first resist on the first side and the 3D laser writing of the second resist on the second side of the substrate, there is no need to change the substrate, turn the substrate over, reapply another photoresist, develop the previously created structure, or perform any further process steps. Rather, a first structure can be created on the first side of the substrate in one step, followed by a second structure on the second side of the substrate, or vice versa.

[0030] In the following, reference is made to the Fig. 2A and Fig. 2B, which schematically illustrate the different steps of 3D laser writing. In step S01, a substrate 10 is first provided, and subsequently, in step S02, a first resist 20 is applied to a first side 11 of the substrate. In the immediately following step, a second photoresist 14 is applied to a second side 13 of the substrate. The steps of applying the material to the first side 11 of the substrate 10 and to the second side 13 of the substrate 10 can be interchanged, but in any case represent directly successive process steps. Subsequently, a 3D laser printer is used to create a structure 16, initially on the second side 13. For this purpose, the 3D laser printer has an objective 12, which is moved layer by layer over the substrate, or the substrate is moved layer by layer over the objective. In this case, the first photoresist 20 serves as an immersion liquid between the objective 12 and the substrate 10, orthe second photoresist 14. Laser light from the 3D printer is focused by the lens 12 into a beam path 18, wherein the second photoresist 14 hardens at the location of the focus due to 2-photon polymerization and, in particular, the second structure 16 is created layer by layer starting from the substrate 10. The following is done according to . Fig. 2B, a first structure 22 is created in the first resist 20 on the first side 11 of the substrate 10. This is again done layer by layer, in particular starting from the substrate. Thus, according to the present invention, a structure can be created simultaneously and in one process step on both the first side 11 of the substrate 10 and the second side 13 of the substrate 10, wherein the structure 16, 22 can in particular be an optical element such as a lens, an aperture, an array of lenses, or an array of apertures. The first structure 22 is aligned transversely to the second structure 16 due to the fact that both structures are produced in one process step and thus no rotation of the substrate has to take place when creating the structure on the other side, and thus manual realignment, for example by means of markers or the like, and the associated inaccuracies, are also eliminated.

[0031] In the following, reference is made to the Fig. 3A-3D, which depict micro-optics produced using the present method.

[0032] Fig. 3A shows a lens 24 which has been formed on the first side 11 of the substrate. The lens 24 can be formed from a transparent photoresist. Furthermore, according to the Fig. 3A, an aperture 26 is created on the second side 13 of the substrate 10. In particular, the aperture 26 can be created from an absorptive photoresist. Lens 24 and aperture 26 are aligned with their optical axes 28, in particular with an accuracy of less than 1 µm.

[0033] Fig. 3B shows a first lens array 32 on the first side 11 of the substrate 10 and a second lens array 30 on the second side 13 of the substrate 10. The optical axes 28 of the individual lenses are aligned with each other with a high degree of accuracy, whereby imaging errors of the micro-optics consisting of the lens arrays 30, 32 can be avoided.

[0034] Fig. 3C shows a lens doublet, with a first lens 36 written on the first side 11 of the substrate 10 and a second lens 34 written on the second side 13. The lenses 34, 36 can each be made from a photoresist with different refractive indices, thus creating an achromatic doublet (also called a Fraunhofer doublet). Alternatively, a thick lens can be used that surrounds the substrate 10. The optical axes 28 of the lenses 34, 36 are aligned with each other with high precision, thereby reducing aberrations of the thick lens or the doublet.

[0035] Fig.3D shows a lens 36 on the first side 11 of the substrate 10. Furthermore, a connecting structure 38 is created on the second side 13 of the substrate 10. By means of the connecting structure 38, for example, an optical fiber 40 or another optical device can be aligned with high precision with the lens 36 on the first side 11 of the substrate, so that the optical axis 28 of the lens 36 coincides with the optical axis of the optical device and in particular of the optical fiber 40.

Claims

[1] Method for producing a micro-optic comprising the steps: Providing a transparent substrate having a first side and an opposite second side; Applying a first photoresist to the first side and a second photoresist to the second side; and 3D laser writing by means of 2-photon absorption of a first structure in the first photoresist and a second structure in the second photoresist, wherein the first structure and / or the second structure is an optical element. [2] Method according to claim 1, characterized by that the optical element is an aperture, a lens, a prism, a diffraction grating, an axicon, a mirror, an array of apertures, an array of lenses, an array of one of the other optical elements, or combinations of the above-mentioned elements. [3] Method according to claim 1 or 2, characterized bythat the first structure and the second structure are an optical element, wherein the optical axes of the optical elements on the first side and the second side of the substrate coincide, in particular with an accuracy of 1 µm or less. [4] Method according to one of claims 1 to 3, characterized by that the first photoresist on the first side faces a lens during 3D laser writing. [5] Method according to claim 4, characterized by that the second structure is created first and then the first structure. [6] Method according to one of claims 1 to 5, characterized by that the second photoresist is printed on the second side using immersion lithography and the first photoresist is printed on the first side using dip-in lithography. [7] Method according to one of claims 1 to 6, characterized by that the substrate has a thickness of 25 µm to 1000 µm. [8] Method according to one of claims 1 to 7, characterized by that the thickness of the first photoresist and / or the thickness of the second photoresist is 100 µm to 3 mm. [9] Method according to one of claims 1 to 8, characterized by that the first photoresist and the second photoresist are different. [10] Method according to claim 9, characterized by that the first photoresist and the second photoresist have a different refractive index. [11] Method according to claim 9, characterized by that the first photoresist and the second photoresist have a different dispersion n(λ). [12] Method according to one of claims 9 or 10, characterized by that the first photoresist and the second photoresist have different transmission. [13] Method according to one of claims 1 to 11, characterized bythat the second photoresist is an absorptive photoresist and the second structure is an aperture or an array of apertures. [14] Method according to one of claims 1 to 11, characterized by that the second structure is a connecting structure for connection to an optical device, wherein the connecting structure is aligned with the optical element on the first side. [15] Method according to one of claims 1 to 11, characterized by that the first structure is a first lens and the second structure is a second lens, wherein the first lens and the second lens are aligned to form a Fraunhofer / achromatic doublet. [16] Method according to one of claims 1 to 14, characterized by that a reference letter is issued before the 3D laser writing, whereby the reference letter includes the following steps: 3D laser writing of the target structure to create a preliminary structure; Detecting local deviations between the generated pre-structure and the target structure; Determining a correction structure from the target structure taking into account the local deviation; and Using the correction structure for subsequent 3D laser writing. [17] Micro-optics manufactured by the method according to one of claims 1 to 15.

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