Device and method for drying disk-shaped substrates

Abstract

Proposed is a device for drying disk-shaped substrates, comprising a body having a horizontal main direction of extent and having a cross-sectional profile transverse to the main direction of extent, the cross-sectional profile tapering upwardly in the vertical direction, wherein: the body has on its top side a plurality of support positions which are suitable for supporting disk-shaped substrates; the plurality of support positions are arranged along the main direction of extent; the plurality of support positions are adjoined by surfaces of the body which slope downward from the support positions; at least a proportion of the downwardly sloping surfaces of the body which adjoin the support positions have an upper portion and a lower portion; and the upper portion is more hydrophilic than the lower portion.

Description

[0001] Device and method for drying disc-shaped substrates

[0002] Technical area

[0003] The present invention relates to an apparatus for drying disc-shaped substrates and a method for drying disc-shaped substrates.

[0004] State of the art

[0005] Wafers of semiconductor material, such as wafers of monocrystalline silicon (silicon wafers), are manufactured in a variety of process steps, including pulling a single-crystal rod from a melt, sawing the crystal into wafers, grinding, edge rounding, polishing, and chemical cleaning of the wafers. Chemical cleaning removes impurities and passivates the wafer surfaces. One form of chemical cleaning is wet cleaning, which requires subsequent drying of the wafers.

[0006] During chemical cleaning, the disc-shaped substrates are immersed for a short time in one or more baths containing a liquid and then removed slowly so that as little liquid residue as possible remains on the substrates. The reason for this is that the liquid residue adhering to the disc-shaped substrates represents a source of contamination and can significantly affect the quality of the surface of the disc-shaped substrate, especially in the edge area. Liquid residues that initially adhere between the disc holder and a substrate can spread to the side surfaces of the substrate and, after drying, leave particles on the substrate. Since the liquid residues can contain semi-volatile compounds such as metal particles, the contaminants remain on the disc surface even after the liquid has evaporated.

[0007] For drying disc-shaped substrates immersed in liquid, a suitable method involves transferring the substrates from the liquid into a gas space containing vapor that does not condense on the substrates and reduces the surface tension of the liquid residues adhering to the substrate. The method and the physical effect utilized are described in EP0385536 A1, as is a device suitable for carrying out such a method.

[0008] Further devices and methods for improving the cleaning quality with respect to remaining particles on the disc-shaped substrate are also described in the documents DE 102014207266 A1, EP 3 840 021 A1, EP 3 840 022 A1, and EP 3 840 023 A1. However, when using these devices and methods, particles still remain that reduce the quality of the disc-shaped substrates. The object of the present invention is to further improve the drying devices and methods described in the prior art and thus reduce the number of particles that remain on the dried substrates.

[0009] Technical problem of the invention and its solution

[0010] The aim of the present invention is therefore to provide a device and a method for drying disc-shaped substrates which make it possible to remove the liquid residues, and thus the particles contained in the liquid which adhere to the disc-shaped substrates, better and more efficiently.

[0011] The object is achieved according to the invention by a device for drying disc-shaped substrates according to the first aspect of the present invention.

[0012] This device comprises a body with a horizontal main extension direction and a cross-sectional profile transverse to the main extension direction, which tapers upwards in the vertical direction, wherein the body has a plurality of support positions on its upper side, which are suitable for supporting disc-shaped substrates arranged at a plurality of support positions along the main extension direction, surfaces of the body adjoining the plurality of support positions which slope downwards from the support positions, at least some of the sloping surfaces of the body adjoining the support positions have an upper section and a lower section, and the upper section is more hydrophilic than the lower section.

[0013] It was surprisingly found that by designing the surfaces adjacent to the support positions and sloping from the support positions with an upper, more hydrophilic section and a lower, more hydrophobic section, liquid residues can be removed more quickly and efficiently and thus the degree of contamination on the surface of a disc-shaped substrate can be further reduced.

[0014] According to the second aspect, the present invention is directed to a method for drying disc-shaped substrates immersed in a liquid. The method comprises the following steps: positioning the disc-shaped substrates immersed in the liquid on the device according to the first aspect of the present invention; and transferring the disc-shaped substrates with the device from the liquid into a gas space containing a vapor that does not condense on the disc-shaped substrates and reduces the surface tension of liquid residues adhering to the disc-shaped substrates.

[0015] In this process, residual liquid between the disc-shaped substrates and the device supporting the discs can drain away via the downwardly inclined surfaces of the body adjacent to the support positions and thus be removed. Thus, there is no need to actively remove the residual liquid between the disc-shaped substrates and the disc holder.

[0016] Because the upper section is designed to be more hydrophilic, aqueous liquid residues or liquid residues containing polar solvents that have accumulated at the lower edge of the disc-shaped substrates can more easily transfer to the adjacent, downward-sloping surfaces of the body at the support positions. Because the lower section of the surfaces is more hydrophobic, the liquid residues can be more easily drained from the surfaces and returned to the liquid bath. This enables efficient removal of liquid residues from the disc-shaped substrates. This can reduce the number of particles remaining on the disc-shaped substrates after drying. In addition, the improved drainage of the liquid residues when removing the substrates from the bath further reduces the net removal of cleaning liquid, which improves the economics of dry cleaning.In addition, the improved drainage of liquid residues can reduce the amount of liquid evaporating from the substrate surface, which leads to an improvement in the atmosphere in the cleanroom.

[0017] Short description of the characters

[0018] Fig. 1 shows a body (1) of an inventive device for drying disc-shaped substrates. The body has a cross-sectional profile (3) transverse to the main direction of extension (2), which tapers upwards in the vertical direction. On its upper side, the body has a zigzag-shaped edge profile (6) that runs along the main direction of extension (2). The individual edges (4) that abut one another in the main direction of extension form deeper creases (5) that serve as support positions for the disc-shaped substrates.

[0019] Fig. 2a shows the cross-sectional profile and Fig. 2b the longitudinal profile of the body (1) shown in Fig. 1.

[0020] Fig. 3 shows the measurement results of the determination of the contact angle a of a water drop on sloping surfaces of the body of the device according to the invention adjacent to the support positions, as a function of the distance s from the support position.

[0021] Detailed description of the invention

[0022] Disc-shaped substrates within the meaning of the present invention are, for example, discs made of semiconductor material, preferably discs made of monocrystalline silicon, which is optionally doped. The disc-shaped substrates preferably have a diameter of 150 to 450 mm, particularly preferably 200 mm or 300 mm, most preferably 300 mm. The inventive device for drying disc-shaped substrates according to the first aspect of the present invention comprises a body with a horizontal main extension direction and a cross-sectional profile transverse to the main extension direction, which tapers upwards in the vertical direction. Preferably, the cross-sectional profile is symmetrical with respect to a vertical axis of symmetry. Preferably, the cross-sectional profile of the body has an acute angle in its upper part.In this case, the apex of the acute angle, as the highest point of the cross-sectional profile, forms the support point for the disc-shaped substrate.

[0023] Preferably, the body tapers vertically upwards to an edge or an edge profile. The edge profile consists of several abutting edges that lie in the same plane, preferably in a plane perpendicular to the cross-sectional profile. At each edge of the edge profile, two surfaces sloping down from the edge abut each other. The points at which two edges of the edge profile abut each other are referred to below as kinks. For example, the edge profile can be a zigzag profile. The edge profile preferably runs along the main extension direction. This means that the edge profile and the main extension direction lie in the same plane, which is preferably arranged perpendicular to the cross-sectional surface.

[0024] The body has a plurality of support positions on its upper side, which are suitable for supporting disc-shaped substrates, wherein the plurality of support positions are arranged along the main extension direction and border on surfaces of the body that slope downwards starting from the support positions. The support positions are preferably formed by one or more edges on the upper side of the body, wherein two sloping surfaces abut one another at each edge. Preferably, the support positions are formed by edges at which surfaces of the body that slope downwards from the edge abut one another. At least some of the sloping surfaces bordering the support positions have an upper section and a lower section, wherein the upper section is more hydrophilic than the lower section.Preferably, all sloping surfaces adjacent to the support positions have an upper section and a lower section, the upper section being more hydrophilic than the lower section. If the body tapers vertically upwards to an edge, for example if the body is designed as a wedge-shaped body, the upward-facing edge serves to support the disc-shaped substrates. In this case, the one upward-facing edge provides several support positions. If the body tapers vertically upwards to an edge profile, the support positions are preferably formed by kinks in the edge profile, particularly preferably by the downward-facing kinks. If the edge profile is a zigzag profile, the kinks preferably serve as a support position for the disc-shaped substrates, from which two edges run upwards.A support position can therefore also be formed by two edges that run along the top side of the body along the main extension direction, are adjacent to each other, and have a different inclination with respect to the horizontal.

[0025] The support position can also be configured as a recess on the upper side of the body, transverse to the main extension direction. The recess can reduce or completely prevent slipping or tilting of the disc-shaped substrate supported at the support position along the main extension direction, especially when the disc-shaped substrates are arranged transversely to the main extension direction. The extent of the individual recesses along the main extension direction exceeds the thickness of the disc-shaped substrates, so that the latter can be inserted into the recesses and supported by them transversely to the main extension direction. The recesses preferably run in the transverse direction, i.e., perpendicular to the main extension direction and perpendicular to the vertical. The recesses can be cuboid-shaped, beveled, V-shaped, or rounded on their underside.

[0026] Adjacent to the support positions are surfaces of the body which slope downwards starting from the support positions. At least some of these surfaces each have an upper section and a lower section, the upper section being more hydrophilic than the lower section. Preferably, each support position, which is preferably formed by one or more edges, is adjoined by at least two downwardly sloping surfaces, each having an upper section and a lower section, the upper section being more hydrophilic than the lower section. Preferably, the at least two downwardly sloping surfaces are arranged on opposite sides starting from the respective support position. A downwardly sloping surface within the meaning of the present invention can, for example, have an inclination of more than 10° and less than 80° with respect to the vertical. A sloping surface within the meaning of the present invention can also be curved or arched.Sloping, in the context of the present invention, means that the part of the surface adjacent to the support position is located higher than a part of the surface farther away from the support position. Thus, liquid residues can be drained away from the substrates supported on the support positions via the sloping surfaces by gravity.

[0027] The upper section preferably borders directly on a support position of the body. Because the upper section is more hydrophilic than the lower section, aqueous liquid residues, for example in the form of drops, can be more easily transferred from the lower edge region of the disc-shaped substrates supported by the body to the body and thus removed from the substrate. Preferably, the surface in the upper section of the downwardly sloping surfaces of the body bordering the support positions is more hydrophilic than the surface of the disc-shaped substrate. In this case, aqueous liquid residues can flow from the substrate to the upper section. Furthermore, in this case, a water bridge that forms when the substrate and body are separated is drawn to the more hydrophilic body, or to the more hydrophilic upper section of the surface bordering the support position, and is thus removed from the substrate.Due to gravity, these residual fluids then flow from the upper to the lower sections of the body's sloping surfaces. Because the surface of the lower section is more hydrophobic, it is less easily wettable, allowing the residual fluids to flow further away and be transferred from the body back into the fluid bath or another collection container.

[0028] Hydrophilicity is a measure of wettability. A more hydrophilic surface therefore has better wettability with respect to water. In the present invention, the contact angle α of a drop of liquid at a specific point on a surface is used as a measure of the hydrophilicity at that point on the surface. Preferably, the contact angle α of a drop of water, particularly preferably a drop of deionized water, is used to determine hydrophilicity. A more hydrophilic surface within the meaning of the present invention is a surface on which a drop of water has a smaller contact angle α compared to another surface. A more hydrophobic surface within the meaning of the present invention is a surface on which a drop of water has a larger contact angle α compared to another surface.Preferably, a more hydrophilic surface within the meaning of the present invention is characterized in that a water droplet, preferably a droplet of deionized water, has a contact angle α of no more than 45°, more preferably a contact angle α of no more than 40°, most preferably no more than 30°. In one embodiment of the present invention, the more hydrophilic, upper section of the surfaces adjacent to the support positions is designed such that a water droplet, preferably a droplet of deionized water, has a contact angle α of no less than 20° and no more than 30°. Accordingly, a more hydrophobic surface within the meaning of the present invention is characterized in that a water droplet, preferably a droplet of deionized water, has a contact angle α of no less than 50°, preferably no less than 60°.

[0029] Preferably, the contact angle α of a drop of liquid on the downwardly sloping surfaces of the body adjacent to the support positions is a monotonic function of the distance s from the support position. Particularly preferably, the contact angle α of a water drop on the downwardly sloping surfaces of the body adjacent to the support positions is a monotonic increasing function of the distance s from the support position. The contact angle α of a water drop on a downwardly sloping surface of the body adjacent to the support positions thus increases with increasing distance s or remains the same.

[0030] The contact angle a can be determined according to the following procedure:

[0031] (i) wetting at least one point of a surface, preferably at least one point of the upper portion and at least one point of the lower portion of a sloping surface of the body, with one drop of a liquid each;

[0032] (ii) taking an image of each drop, preferably a shadow image;

[0033] (iii) determining the contour of the respective drop based on the respective image, preferably the shadow image, using suitable software; and

[0034] (iv) Determining the contact angle between the surface and the respective droplet based on the determined contour of the respective droplet. In step (i), the area of ​​the surface to be examined is wetted with a drop of a liquid; preferably with a drop of water, particularly preferably with a drop of deionized water. In step (ii), an image of the droplet, preferably a shadow image, is taken using a camera. In step (iii), the contour of the droplet is then determined based on the image using suitable software. Contour detection can be performed using a grayscale analysis of the image, and a geometric model describing the droplet contour can then be identified. The identification of the geometric model describing the droplet contour can be achieved, for example, by fitting.The contact angle is determined from the angle between the determined drop contour function and the surface of the examined area, whose projection in the drop image can be referred to as the baseline. Geometric models describing the drop contour can be, for example, circles, conic sections, ellipses, or polynomials.

[0035] The body can be made of metal, ceramic, or plastic. The body is preferably made of a thermoplastic, most preferably a high-temperature-resistant thermoplastic. The high-temperature-resistant thermoplastic can be, for example, a polyaryletherketone, preferably polyetheretherketone (PEEK), which has high chemical resistance, wear resistance, and good sliding properties. The body of the device according to the invention for drying disc-shaped substrates is therefore preferably made of PEEK.

[0036] The hydrophilicity of a surface can be modified by physical methods, such as plasma treatment, or by chemical methods, such as surface reactions, coating or incorporation of a chemical compound.

[0037] The hydrophilicity of a surface of a thermoplastic such as PEEK can be increased by direct gas-phase fluorination. For example, the surface of a PEEK body can be treated with a gas mixture of fluorine and air, where the gas mixture can have a fluorine content of 5 mol%. Surfaces can also be hydrophilized using a laser. For example, surfaces of metallic materials or ceramics can be cleaned with a laser in an air atmosphere, resulting in a more hydrophilic surface. Hydrophilization of a surface can also be achieved using a laser and a silicating liquid, which cleans the surface and additionally functionalizes it. This makes the treated surface even more hydrophilic.Laser silicating can be performed in an immersion bath. Depending on the optics used, the spatial resolution can be varied, with the smallest possible laser spot diameter being less than 100 pm. Using a laser, cleaning and, if necessary, silicating is performed with very high spatial resolution. This makes this process particularly well-suited for producing surfaces with different sections and varying degrees of hydrophilicity.

[0038] According to the second aspect, the present invention is directed to a method for drying disc-shaped substrates immersed in a liquid. The method comprises the following steps: positioning the disc-shaped substrates immersed in the liquid on the device according to the first aspect of the present invention; and transferring the disc-shaped substrates with the device from the liquid into a gas space containing a vapor that does not condense on the disc-shaped substrates and reduces the surface tension of liquid residues adhering to the disc-shaped substrates.

[0039] In this process, residual liquid between the disc-shaped substrates and the disc holder can drain away via the downwardly inclined surfaces of the device body adjacent to the support positions and thus be removed. Thus, there is no need to actively remove the residual liquid between the disc-shaped substrates and the disc holder.

[0040] A vapor that does not condense on the substrates has a vapor pressure that is not saturated at the temperature of the bath and the substrates, whereas a vapor that condenses on the substrates actually has such a saturated vapor pressure. The substrates can be treated in various liquid baths. If the cleaning bath contains water, the vapor of an organic solvent, preferably one or more compounds selected from alcohols, glycols, aldehydes, esters, ketones, or tetrahydrofuran, is preferably used. The process according to the invention can also be applied when the bath contains other polar liquids, for example alcohols. The substrates can then be brought into contact with the vapor of the organic solvent 1,1,1-trifluorotrichloroethane directly from the alcohol.

[0041] Because the upper section is more hydrophilic, aqueous liquid residues or liquid residues containing polar solvents that have accumulated at the lower edge of the disc-shaped substrates can more easily transfer to the adjacent, downward-sloping surfaces of the body at the support positions. Because the lower section of the surfaces is more hydrophobic, the liquid residues can be more easily drained from the surfaces and returned to the liquid bath.

[0042] Description of an embodiment according to the invention and a comparative example

[0043] In the exemplary embodiment, a device according to the invention as shown in Fig. 1 was used to dry 50 wafers of monocrystalline silicon with a diameter of 300 mm and a thickness of 750 pm. The body of the device tapered upwards to form a zigzag-shaped edge profile along the main extension direction (see Fig. 2b). The body was made of PEEK, and the upper section of the surfaces adjacent to the edges of the edge profile was treated with a gas mixture of 5 mol% fluorine and air as a purge gas. The sloping surfaces of the body of the device thus had an upper section and a lower section, with the upper section being more hydrophilic than the lower section. The wafers were transferred from a water-filled basin into a gas space containing isopropanol vapor, standing on their upper edge in the transverse direction to the main extension direction of the device.

[0044] In a comparative example, the same device was used as in the exemplary embodiment, with the exception that the sloping surfaces of the device body were not treated with fluorine. Otherwise, the procedure was exactly the same as in the exemplary embodiment. The dried semiconductor wafers were examined for the presence of particles in the region of the support position on the body. A comparison of the exemplary embodiment with the comparative example showed that the drying carried out with the device according to the invention and according to the method according to the invention in the exemplary embodiment resulted in significantly fewer residues on the dried wafers.

Claims

Patent claims 1. A device for drying disc-shaped substrates, comprising a body (1) with a horizontal main direction of extension (2) and a cross-sectional profile (3) transverse to the main direction of extension (2), which cross-sectional profile tapers upwards in the vertical direction, wherein the body (1) has a plurality of support positions on its upper side which are suitable for supporting disc-shaped substrates which are arranged in a plurality of support positions along the main direction of extension (2), surfaces of the body which slope downwards from the support positions adjoin the plurality of support positions, at least some of the sloping surfaces of the body adjoining the support positions have an upper section and a lower section, and the upper section is more hydrophilic than the lower section.

2. Device for drying disc-shaped substrates according to claim 1, characterized in that the contact angle a of a drop of a liquid on a specific point of a surface is used as a measure of the hydrophilicity of this point of the surface.

3. Device for drying disc-shaped substrates according to claim 1 or 2, characterized in that the contact angle a on the sloping surfaces of the body adjacent to the support positions can be described as a monotonically increasing function of the distance s from the support position.

4. Device for drying disc-shaped substrates according to one of claims 1 to 3, characterized in that the determination of the contact angle a is carried out according to the following method; (i) wetting at least one point of the upper section and at least one point of the lower section with one drop of a liquid each; (ii) taking an image of each drop; (iii) determining the contour of the respective drop from the respective image using suitable software; and (iv) Determining the contact angle between the surface and the respective droplet based on the determined contour of the respective droplet.

5. Device for drying disc-shaped substrates according to one of claims 1 to 4, characterized in that the support positions are designed such that the disc-shaped substrates supported thereon are arranged transversely to the main extension direction.

6. Device for drying disc-shaped substrates according to one of claims 1 to 5, characterized in that the cross-sectional profile has an acute angle at the support positions in its upper part.

7. Device for drying disc-shaped substrates according to one of claims 1 to 6, characterized in that the body tapers vertically upwards to an edge or an edge profile.

8. Device for drying disc-shaped substrates according to one of claims 1 to 7, wherein each support position is characterized by a kink in the edge profile.

9. Device for drying disc-shaped substrates according to one of claims 1 to 8, characterized in that the support positions are designed such that the disc-shaped substrates supported thereon are inclined from the vertical.

10. Device for drying disc-shaped substrates according to one of claims 1 to 9, characterized in that the body is designed such that the disc-shaped substrates rest on the highest point of the respective cross-sectional profile at the support positions.

11. A method for drying disc-shaped substrates immersed in a liquid, comprising positioning the disc-shaped substrates immersed in the liquid on the device according to any one of claims 1 to 10; and transferring the disc-shaped substrates with the device from the liquid into a gas space containing a vapor that does not condense on the disc-shaped substrates and reduces the surface tension of liquid residues adhering to the disc-shaped substrates.

12. A method for drying disc-shaped substrates according to claim 11, comprising removing liquid residues between the disc-shaped substrates and the body of the device via the sloping surfaces of the body of the device adjacent to the support positions.

13. A method for drying disc-shaped substrates according to claim 12, characterized in that there is no need to actively remove the liquid residues between the disc-shaped substrates and the body of the device.

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