Device and method for heating the surface of a substrate

Abstract

The invention relates to a device (100) for heating a surface (201) of a substrate (200), in particular a mirror carrier for semiconductor technology equipment, and a corresponding method. The device (100) comprises a radiation emitter (110) for emitting excitation radiation onto a surface (201) of the substrate (200) for heating the surface (201) and a cooling device for cooling the substrate (200) away from the irradiated surface (201). In this process, the surface (201) to be heated is exposed to excitation radiation, while the substrate (200) is cooled.

Description

[0001] The invention relates to a device for heating the surface of a substrate, in particular a mirror substrate for semiconductor technology equipment, and a corresponding method.

[0002] In the prior art, semiconductor technology equipment refers to equipment used for the production or testing of microstructured devices or the components required for their manufacture. An example of such equipment is a projection exposure system for photolithography.

[0003] Photolithography is used to manufacture microstructured components, such as integrated circuits. The projection exposure system used comprises an illumination system and a projection system. The image of a mask (also called a reticulum) illuminated by the illumination system is projected in a reduced size onto a substrate, such as a silicon wafer, coated with a photosensitive layer and positioned in the image plane of the projection system. This transfers the mask structure onto the photosensitive coating of the substrate.

[0004] Both illumination and projection systems, particularly projection exposure systems designed for EUV applications (i.e., exposure wavelengths from 5 nm to 30 nm), typically employ multiple optical elements, especially mirrors, to achieve the desired image of the mask onto the substrate. Due to the required accuracy, especially in projection systems, it is essential to ensure that the optical elements, particularly the mirror surfaces, are manufactured with high precision. Furthermore, the optical elements must be designed to minimize deformation under temperature changes.

[0005] To achieve this, semiconductor manufacturing techniques are used in the production of the optical elements themselves. In particular, it is known to apply a structured resist to the surface of a substrate, which will later form the mirror surface (possibly after the application of a reflective coating), in order to selectively influence the removal of substrate material in a subsequent etching process: In the areas where resist is applied, it must first be etched away before the substrate is affected, while in other areas without resist, material from the substrate is removed directly. The resist can be, in particular, a photoresist, which, after application, is irradiated with a predetermined wavelength in the desired structure, so that after a possible etching process, the substrate material is removed.The development step of the coating only remains in the areas where it was previously irradiated or not irradiated, depending on the type of coating.

[0006] It is known to subject the resist to a so-called "bake" process after application but before a subsequent etching process, or, in the case of photoresist, before or after development. During this process, the resist is heated to a predetermined temperature so that residual solvents, other moisture, or dissolved gases in the resist evaporate and / or the resist's resistance during subsequent etching is increased. In the case of photoresist, baking can also improve the homogeneity of the exposure result. After development, any remaining solvent residues can be removed by an optional second baking.

[0007] To perform the drying process, it is known to heat the entire substrate, including the coating. This can be done by heating the entire substrate in an oven or by using a heated liquid through fluid channels, which may be provided in the substrate and are typically intended as coolant channels for later use. The maximum permissible temperature is generally determined by the substrate and is usually significantly lower than the temperature desired for the actual drying process. Therefore, such drying is often incomplete or can only be carried out at the risk of damaging the substrate. This risk is particularly high in the area of ​​the fluid channels, where, according to the prior art, not only temperature peaks but also significant temperature gradients regularly occur during heating and subsequent cooling.

[0008] The object of the present invention is to provide a device and a method for heating a surface of a substrate which no longer exhibit the disadvantages known in the prior art, or only to a reduced extent.

[0009] This problem is solved by a device according to claim 1 and a method according to claim 9. Advantageous further developments are the subject of the dependent claims.

[0010] Accordingly, the invention relates to a device for heating a surface of a substrate, in particular a mirror carrier for semiconductor technology equipment, comprising a radiation emitter for emitting excitation radiation onto a surface of the substrate to heat the surface and a cooling device for cooling the substrate away from the irradiated surface.

[0011] Furthermore, the invention relates to a method for heating a surface of a substrate, in particular a mirror substrate for semiconductor technology equipment, wherein the surface to be heated is exposed to excitation radiation, while the rest of the substrate is cooled.

[0012] The device and method according to the invention are characterized in that the actual heating, resulting from the input of excitation radiation (which is used to heat the surface), can be essentially limited to the area of ​​the substrate's surface actually being irradiated, while the substrate can be cooled away from this surface. This allows, for example, a coating on the surface in question to be heated to a temperature sufficiently high for heating, while the underlying substrate experiences no or only minimal heating due to the cooling provided. In any case, the substrate temperature should be kept below its maximum permissible temperature. The type and intensity of the excitation radiation, as well as the degree of cooling, must be selected appropriately for this purpose.

[0013] It is preferred if the wavelength of the excitation radiation emitted by the radiation emitter is selected such that the excitation radiation is predominantly reflected by the substrate itself and predominantly absorbed by a coating applied to the surface of the substrate.

[0014] In this context, "predominantly reflective" means a reflectance greater than 0.5, preferably greater than 0.7, and more preferably greater than 0.85. Similarly, "predominantly absorptive" means an absorptivity greater than 0.5, preferably greater than 0.7, and more preferably greater than 0.85. By appropriately selecting the wavelength, the excitation radiation is largely absorbed by the coating, thus heating it, while the substrate itself absorbs only a small amount of excitation radiation and is therefore hardly heated directly by the excitation radiation.

[0015] The device preferably comprises at least one reflector, which is arranged and designed such that excitation radiation reflected from the surface of the substrate is reflected back onto the surface of the substrate. This prevents excitation radiation originally directed towards the surface of the substrate from being emitted uncontrollably into the environment and thus being lost for the desired heating in the area of ​​the substrate surface.

[0016] For cooling the substrate, the device can include connections for integrating cooling channels running through the substrate into a temperature-controlled coolant circuit. Substrates, such as mirror substrates for semiconductor technology systems, can be provided with cooling channels for their subsequent use, through which a cooling medium can be circulated to temper the substrate to a desired set temperature. If these cooling channels are already present when the substrate is to be processed in the device according to the invention, they can be used for the desired cooling of the substrate. For this purpose, they are connected to a coolant circuit via the provided connections and integrated in such a way that the coolant of the cooling circuit flows through them. A coolant circuit typically includes a heat extraction element from the coolant as well as an element, such as...A pump is required to circulate the coolant through the system. Such elements can be part of the device according to the invention. However, it is equally possible that the device itself is connected to a higher-level coolant circuit, in which case the device only needs to be designed to convey coolant between the higher-level coolant circuit and the cooling channels of the substrate.

[0017] Alternatively or additionally, the device can include at least one fan for applying cooling air to the substrate away from the irradiated surface. A fan can create forced convection around the substrate, which, if the air temperature is sufficient, results in cooling.

[0018] To ensure precise control of the device, for example during a bake-out process, it is preferred that it includes a temperature sensing device for measuring the temperature of the irradiated surface of the substrate or a portion thereof. The temperature measured by the temperature sensing device can be processed by a control unit, also to be provided, to control the radiation emitter and / or the cooling device, taking the temperature measured by the temperature sensing device into account. In this way, the control unit can regulate the radiation emitter and / or the cooling device so that the temperature required for the desired process is reached on the top surface of the substrate, but not exceeded. Furthermore, if the temperature of the substrate is also measured, directly or indirectly, e.g.,By monitoring the temperature of the cooling medium flowing through the substrate, it can simultaneously be ensured that the maximum permissible temperature for the substrate is not exceeded.

[0019] The radiation emitter can be designed to emit radio waves and / or microwaves. "Microwaves" refers to electromagnetic waves with a frequency of approximately 1 GHz to 300 GHz, while "radio waves" refers to electromagnetic waves with a frequency below 1 GHz. Regardless of the frequency, the requirement is that the emitted electromagnetic waves must cause heating, at least in the coating on the irradiated surface of the substrate. A qualified professional can readily determine suitable frequencies within these ranges.

[0020] The temperature sensing device preferably comprises an infrared temperature sensor. Such a sensor offers the advantage that the temperature can be measured without contact, thus avoiding damage to the substrate as well as potential shadowing of the excitation radiation by the temperature sensing device.

[0021] The device is preferably designed on a mirror substrate for semiconductor technology equipment, wherein the coating to be heated on the surface of the substrate is a lacquer layer, in particular a layer of already exposed and preferably not yet developed photoresist. The device according to the invention can also be used to treat non-planar surfaces of a substrate, e.g., to subject them to a bake-out process.

[0022] For an explanation of the method according to the invention and its preferred further developments, reference is made to the preceding statements.

[0023] The invention will now be described by way of example using an advantageous embodiment with reference to the accompanying drawing. It shows: Fig. 1: A schematic representation of an embodiment of a device according to the invention.

[0024] In Fig. Figure 1 shows an embodiment of a device 100 according to the invention. The device 100 serves to heat a surface 201 of a substrate 200 which is partially provided with a coating 210.

[0025] The substrate 200 is a mirror support which, after further processing steps including the application of a reflective coating, is intended for use as a mirror in a semiconductor technology system, namely a projection exposure system. For this reason, the surface 201 of the substrate 200 already has the basic shape of the later mirror surface. In the illustrated embodiment, the surface 201 is curved; however, it can also have any other shape and, in particular, be flat. Cooling channels 202 are also already formed inside the substrate 200, through which coolant is passed during later use to cool the mirror.

[0026] In this example, the coating 210 serves for the subsequent processing of the surface 201 of the substrate 200 using processes known from semiconductor manufacturing, in particular the creation of depressions in the surface 201 of the substrate 200 in the areas not covered by the coating 210 by etching. The coating 210 can be a previously exposed and possibly also developed photoresist.

[0027] The device 100 comprises a radiation emitter 110 with which the surface 201 of the substrate 200 to be heated can be irradiated. The radiation emitter 110 is arranged in the device 100 such that only the desired surface 201 is irradiated when the substrate 200 is properly positioned in the device 100. The wavelength of the radiation emitted by the radiation emitter 110 is selected from the frequency range of radio or microwaves such that the radiation is absorbed as effectively as possible by the coating 210, while being reflected as much as possible by the substrate 200 itself. Consequently, the direct heat input from the radiation into the coating 210 is high, while the direct heat input from the radiation into the substrate 200 remains low.

[0028] To ensure that the reflected radiation is not emitted into the environment but is actually used to heat the surface 201 of the substrate 201 or the coating 210 applied thereto, the device includes reflectors 120. These reflectors redirect radiation originating from the radiation emitter 110, which is reflected from the substrate 200, back onto the surface 201 of the structure 200 so that it can be absorbed there, particularly by the coating 210. Naturally, the reflectors are matched to the wavelength of the radiation emitted by the radiation emitter 110.

[0029] The device 100 further comprises connections 130 to which the cooling channels 202 of the substrate 200 can be connected in such a way that they are integrated into a temperature-controlled coolant circuit 140, i.e., are supplied with coolant during operation of the coolant circuit 140. The coolant circuit 140 includes a pump 141 for conveying the coolant and an element 142 for actively temperature-controlling the coolant.

[0030] The coolant circuit 140 can, as shown, be part of the device 100, but it is also possible that the device 100 itself is connected to a higher-level coolant circuit that is not part of the device 100. In this case, the connections 130 are passageways for coolant from the higher-level coolant circuit into the cooling channels 202 of the substrate 200 and back.

[0031] The device 100 further comprises blowers 150, with which the substrate 200 can be supplied with cooling air on its side facing away from the irradiated surface 201. Cooling via the blowers 150 can be carried out alternatively or additionally to cooling via the coolant circuit 140.

[0032] The device 100 further comprises a temperature sensing device 160. The temperature sensing device 160 is an image-based infrared temperature sensor, essentially an infrared camera, with which two-dimensional thermal images can be acquired. The temperature sensing device 160 is directed at the irradiated surface 201 of the substrate 200 and, due to its image resolution, can acquire the temperature of both the coating 210 and the substrate 200 in the uncoated areas.

[0033] Furthermore, temperature sensors 143 are provided to detect the temperature of the coolant in the coolant circuit 140, namely before the coolant enters the substrate 200 and after it exits.

[0034] The temperature detection device 160 and the temperature sensors 143 are connected to a control unit 170, which can control the radiation emitter 110 and the controllable components of the coolant circuit 140 on the basis of the detected temperatures.

[0035] The device 100, controlled by the control unit 170, allows the already exposed but not yet developed photoresist, intended as a coating 210, to be heated out in order to evaporate solvent residues, other moisture, or gases dissolved in the resist, to increase the resist's resistance for a subsequent etching process, and / or to improve the homogeneity of the preceding exposure process. At the same time, it is ensured that the substrate 200 is not heated above a predetermined maximum temperature to prevent damage to the substrate 200.

[0036] While monitoring the temperatures on the surface 201 of the substrate 200 using the temperature sensing device 160, the surface 201 is exposed to excitation radiation from the radiation emitter 110 such that the temperature in the area of ​​the coating 210 reaches a predetermined temperature. Simultaneously, the temperature of the substrate 200 is monitored directly or indirectly using the temperature sensing device 160 and the temperature sensors 143, ensuring that a predetermined maximum permissible temperature for the substrate 200 is not exceeded.The latter condition takes absolute priority for the protection of the substrate 200: If it is not possible to increase the temperature on the surface 201 of the substrate 200 and especially in the coating 210 to a desired value without the temperature of the substrate 200 itself exceeding the specified maximum value, then the heating of the coating 210 is not possible, at least with the selected process parameters.

[0037] As a rule, the device 100, due to its special design, enables the coating 210 to be heated out. Firstly, by appropriately selecting the wavelength of the radiation from the heat radiation source 110, which is readily absorbed by the coating 210 but more readily reflected by the substrate 200 itself, the heat is primarily transferred directly into the coating 210 and less so into the substrate 200 itself. Any heat nevertheless transferred into the substrate 200 – whether through absorption of excitation radiation by the substrate 200 or through heat transfer from the coating 210 to the substrate 200 – can be immediately dissipated from the substrate 200 by connection to the coolant circuit 140 and / or by the flow of cooling air via the fans 150, generally to a sufficient extent that the specified maximum temperature for the substrate 200 is not exceeded.

[0038] The method according to the invention, in its preferred embodiment, is thus directly explained by the functioning of the device 100, as described in Fig. 1 is shown.

Claims

[1] Device (100) for heating a surface (201) of a substrate (200), in particular a mirror carrier for semiconductor technology equipment, comprising a radiation emitter (110) for emitting excitation radiation onto a surface (201) of the substrate (200) for heating the surface (201) and a cooling device for cooling the substrate (200) away from the irradiated surface (201). [2] Device according to claim 1, characterized by , that the wavelength of the excitation radiation emitted by the radiation emitter (110) is chosen such that the excitation radiation is predominantly reflected by the substrate (200) itself and predominantly absorbed by a coating (210) applied to the surface (201) of the substrate (200). [3] Device according to any one of the preceding claims, characterized by, that the device (100) comprises at least one reflector (120) which is arranged and designed such that excitation radiation reflected from the surface (201) of the substrate (200) is reflected back onto the surface (201) of the substrate (200). [4] Device according to any one of the preceding claims, characterized by , that the cooling device includes connections (130) for integrating cooling channels (202) passing through the substrate (200) into a temperature-controlled coolant circuit (140). [5] Device according to any one of the preceding claims, characterized by , that the cooling device includes at least one blower (150) for applying cooling air to the substrate (200) away from the irradiated surface (201). [6] Device according to any one of the preceding claims, characterized by, that the device (100) comprises a temperature sensing device (160) for sensing the temperature of the irradiated surface (201) of the substrate (200) or a part thereof and a control device (170), wherein the control device (170) is configured to control the radiation emitter (110) and / or the cooling device taking into account the temperature detected by the temperature sensing device (160). [7] Device according to any one of the preceding claims, characterized by , that the radiation emitter (110) is designed to emit radio waves and / or microwaves. [8] Device according to any one of the preceding claims, characterized by , that the temperature sensing device (160) includes an infrared temperature sensor. [9] Method for heating a surface (201) of a substrate (200), in particular a mirror support for semiconductor technology equipment, wherein the surface (201) to be heated is exposed to excitation radiation, while the substrate (200) is cooled. [10] Method according to claim 9, characterized by , that the wavelength of the excitation radiation is chosen such that the excitation radiation is predominantly reflected by the substrate (200) itself and predominantly absorbed by a coating (210) applied to the surface (201) of the substrate (200). [11] Method according to one of claim 9 or 10, characterized by , that excitation radiation reflected from the surface (201) of the substrate (200) is reflected back to the surface (201) of the substrate (200) by means of at least one reflector (120). [12] Method according to any one of claims 9 to 11, characterized by, that the substrate (200) through which cooling channels (202) pass is supplied with a coolant. [13] Method according to any one of claims 9 to 12, characterized by , that the substrate (200) is surrounded by cooling air away from the irradiated surface (201). [14] Method according to any one of claims 9 to 13, characterized by , that the temperature of the irradiated surface (201) of the substrate (200) or of a part is detected, preferably without contact, and taken into account in the control of the excitation radiation and / or the cooling. [15] Method according to any one of claims 9 to 14, characterized by that the excitation radiation includes radio waves and / or microwaves. [16] Method according to any one of claims 9 to 15, characterized by that the method is carried out using a device (100) according to one of claims 1 to 8.

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