Method for singulating a wafer, and suitable device

Abstract

The invention relates to a method for singulating a wafer (100) having a first surface (100a) and a second surface (100b) opposite the first surface (100a), the method comprising the following steps: bringing the wafer (100) into contact with a protective device (120) having one or a plurality of carrying structures (122), such that the first surface (100a) of the wafer (100) is in contact with the plurality of carrying structures (122), singulating the wafer (100) that is in contact with the protective device (120) into a plurality of chips (180a, 180b), and removing (440) the chips (180a, 180b) from the wafer (100) that is in contact with the protective device (120). The invention furthermore relates to a protective device (120) having one or a plurality of carrying structures (122) for temporarily carrying a wafer (100), the protective device being configured to be used in a method according to the invention.

Description

[0001] Description

[0002] title

[0003] Method for separating a wafer and suitable device

[0004] Technical area

[0005] The present invention relates to the field of manufacturing semiconductor chips from wafers, in particular for microelectromechanical devices, and concerns a method for singulating a wafer and a protective device for temporarily supporting a wafer for use in such a method.

[0006] State of the art

[0007] Devices with microelectromechanical systems (MEMS), such as micromirror arrays or micromirror actuators, are now used in a wide variety of devices, including smartphones, projectors, head-up displays, barcode readers, mask exposure units in semiconductor manufacturing, and microscopes. Corresponding micromirror arrays are known, for example, from DE 10 2013 208 446 A1, EP 0 877 272 A1, and WO 2010 / 049076 A2. During the manufacture of individual wafer-based microelectromechanical systems, continuous protection of the microelectromechanical structures of these systems must be ensured to prevent unintentional damage.Particularly critical steps include soldering or sintering processes, and especially the separation of wafers into individual chips (dies), as these can easily lead to damage and / or contamination of the microelectromechanical structures. For this reason, the sensitive structures are typically temporarily protected by suitable protective structures, which, however, significantly reduce the fill factor of the final product, i.e., the manufactured chips.

[0008] Disclosure of the invention According to the invention, a method for singulating a wafer and a protective device for temporarily supporting a wafer for use in a method according to the invention are proposed.

[0009] According to a first aspect of the invention, a method is proposed for singulating a semiconductor wafer (also referred to as wafer for short within the scope of this invention), in particular a silicon wafer, having a first and a second surface, wherein the second surface is opposite the first surface. The first and second surfaces are therefore the two different base areas of the wafer. Here, the method comprises bringing the wafer into contact with a protective device, for example positioning the wafer on the protective device, wherein the protective device has one or more support structures. The wafer is brought into contact with the protective device such that the first surface of the wafer is in contact with the one or more support structures. The protective device can, for example, serve to temporarily support the wafer or be temporarily positioned on it.The wafer is typically placed on the protective device or the protective device is positioned on the wafer.

[0010] During or after contacting, the wafer can be bonded to the protective device, for example by sintering or eutectic bonding, to prevent unwanted movement, such as displacement, of the wafer and protective device relative to each other. This facilitates handling of the wafer and protective device and enables the protective device to be moved and / or rotated together with the wafer. Alternatively, such bonding can be omitted and, if necessary, a fixing device can be used to temporarily fix the contact between the protective device and the wafer. Omitting bonding allows the protective device to be reused for additional wafers, possibly after cleaning.

[0011] After the wafer has been brought into contact with the protective device, and after any further steps for processing the wafer have been carried out, such as etching so-called sacrificial regions in semiconductor layers of the wafer (sacrificial layer etching), for example to expose structures for a MEMS (microelectromechanical system), and / or wafer bonding, for example eutectic bonding, of a second wafer to the wafer, the wafer is singulated (in the case of wafer bonding together with singulation of the bonded second wafer, i.e. of the entire coupled wafer) into a plurality of semiconductor chips (also referred to as chips for short in the context of this invention).Sacrificial layer etching can be performed using, for example, chlorine trifluoride (ClF3), chlorine fluoride (ClF), chlorine pentafluoride (ClF5), bromine trifluoride (BrFs), bromine pentafluoride (BrFs), iodine pentafluoride (IF5), iodoheptfluoride (IF7), sulfur tetrafluoride (SF4), xenon difluoride (XeFs), or similar substances. The chips are then removed from the wafer while it is still in contact with the protective device. The dicing and removal steps can coincide, meaning they can occur simultaneously. The wafer can thus be dicing before the chips are removed from the wafer, but can also be performed simultaneously with the removal of the chips.

[0012] The protective device serves to protect parts of the wafer during critical steps such as bonding, for example wafer bonding (such as eutectic bonding) of another wafer to the wafer or bonding of further chips to the wafer, in particular by means of soldering and / or sintering and / or eutectic bonding, wafer testing and / or dicing while temporarily supported by the protective device. The wafer is preferably brought into contact with the protective device, for example, positioned such that structures of the wafer to be protected do not come into contact with the one or more support structures of the protective device. Furthermore, the wafer is preferably brought into contact with the protective device in such a way that the structures to be protected are optimally protected by the protective device for the subsequent processing steps.

[0013] After contacting the wafer with the protective device and before dicing the wafer, a gap structure with multiple gaps is preferably formed in the wafer, enclosing individual chips and perforating (penetrating) the wafer locally (not forming closed shapes such as rectangles). The subsequent dicing takes place at least partially along these multiple gaps. The dicing can be carried out, for example, by breaking and / or cutting using a laser (laser cutting) and / or etching process. A chip to be removed from the wafer is partially separated from the rest of the wafer (remainder of the wafer) by this formation of the gap structure. Typically, the gap structure is formed such that webs (insulated connections) connect the individual chips to the rest of the wafer. This ensures that the chip can later be easily removed from the wafer, for example when removing the chip from the protective device.In such a case, chip removal is performed in parallel with the singulation process, for example, by simply breaking the ridges, thus breaking the chip out of the wafer. Using a suitable laser cutting process, it is also possible to vaporize the ridges. This has the advantage that the ridges are completely removed without creating uncontrolled fragments.

[0014] Alternatively or additionally, a trench structure enclosing the individual chips can also be formed with one or more trenches on the first and / or second surface of the wafer. The trench structure thins the wafer in a targeted manner, i.e., provides it with one or more trenches. The wafer is then singulated at least partially along the one or more trenches. A trench structure with one or more trenches on a surface of a wafer means, in the context of this invention, a structure consisting of one or more trenches in a wafer such that the trench(es) are open towards the surface. The trench(es) of a trench structure typically enclose chips to be removed from the remaining wafer during singulation. In the case of a trench structure, the advantage is also that singulation, for example by breaking the chip out of the remaining wafer, is simplified.A trench structure enclosing the individual chips can also comprise unconnected trenches, for example, consisting of a plurality of trenches enclosing individual chips that do not need to be interconnected. The entirety of these trenches is referred to as a trench structure in the context of this invention.

[0015] Alternatively or additionally, a gap structure enclosing individual chips can be formed with one or more gaps in the wafer. Here, the singulation can be carried out at least partially by forming the gap structure. If all chips on a wafer are enclosed by the gap structure, the wafer is completely singulated by it. Separate singulation is not necessary. As in the case of a trench structure, a gap structure can also consist of recesses that are not connected to one another; for example, a gap-shaped recess enclosing individual chips can be guided around this chip. The entirety of these gaps is referred to in the context of this invention as a gap structure. A locally perforating gap structure is accordingly a gap structure in which the gaps do not form closed shapes.Separating the wafer by forming a gap structure in the wafer is particularly advantageous because it completely prevents the release of particles that could lead to contamination of sensitive structures on the wafer.

[0016] For the purposes of this invention, a gap structure is understood to mean one or more recesses in the wafer that completely penetrate the wafer in the vertical direction. In contrast, a trench structure refers to one or more cutouts that do not extend across the full thickness of a wafer. Dicing a wafer along a locally perforating gap structure means dicing such that multiple recesses in the gap structure are used to separate a chip from the rest of the wafer, which occurs by destroying, for example breaking, any remaining connections (for example in the form of webs) between the chip and the rest of the wafer. Gaps in gap structures and trenches in trench structures can differ from simple gaps and trenches running vertically through the wafer, i.e. rectangular cutouts and recesses; for example, the use of undercuts is conceivable.In particular, the gaps and the trenches can be designed in such a way that at least locally holding structures are formed which continue to fix the individual chips in the wafer after the wafer has been singulated, i.e. which restrict the movement of the individual chips after the singulation, for example in order to prevent the individual chips from accidentally falling out of the wafer when the wafer is moved.

[0017] In a particular embodiment of the method according to the invention, the gaps and / or trenches, and thus also the gap structure and / or the locally perforating gap structure and / or the trench structure, are formed by means of an etching process. Deep reactive ion etching (DRIE), for example, can be used as the etching process. Furthermore, the gap structures and / or trench structure can be formed before the wafer is brought into contact with the protective device. Preferably, the gap structures and / or trench structure are formed after the wafer is brought into contact with the protective device and also preferably after any bonding of the wafer to the protective device, in order to utilize the protective function of the protective device already for this method step.Such an etching process is preferably combined with an etching process for etching structures of the chips, for example a sacrificial layer etching, so that in one method step both the gap structure and / or the locally perforating gap structure and / or the trench structure are formed and a sacrificial layer etching is carried out.

[0018] Finally, the separation can be performed using an etching process, a laser cutting process, and / or a breaking process. Reactive ion etching (DRIE) and xenon difluoride (XeFs) are also possible etching processes.

[0019] The method according to the invention can be used particularly advantageously in the production of microelectromechanical systems. This is particularly the case when the wafer has open structures for microelectromechanical systems (MEMS structures). In such a case, the wafer is brought into contact with the protective device and preferably bonded such that the one or more support structures do not touch the open MEMS structures. If the open MEMS structures are open to the first surface of the wafer, further steps in the processing of the wafer can now be performed on the opposite second surface of the wafer, for example soldering, sintering, wafer bonding, bonding of additional chips, wafer testing, and / or finally dicing the wafer, without endangering the first surface protected by the protective device.The method can be used particularly advantageously if the open MEMS structures also include MEMS structures for a micromirror array, since such structures are particularly sensitive.

[0020] In a particularly preferred embodiment of the method according to the invention, the wafer has holding structures and / or, after contacting the wafer with the protective device and prior to dicing, holding structures are formed in the wafer, wherein the holding structures are designed to restrict possible movement of the chips after dicing in at least one direction. For example, the holding structures can prevent the individual chips from falling out and / or dropping from the wafer after dicing and instead hold the individual chips in the remaining wafer and thus the protective device. A holding structure can be formed, for example, by suitable recesses and / or cutouts with undercuts in the wafer.A holding structure is advantageously arranged at an edge of a chip to be separated by singulation and ensures that the chip is interlocked with the remaining wafer after singulation, preventing free movement of the chip in a direction perpendicular to the first surface of the wafer. This can prevent, for example, the chips from falling if the wafer is arranged horizontally (i.e., perpendicular to the direction of gravity) on the protective device. It is also conceivable for holding structures to be implemented using gap structures, which are suitable for preventing unintentional movement of the chips of the wafer in both directions perpendicular to the first surface of the wafer after singulation.

[0021] Holding structures are particularly advantageous when the wafer is rotated and / or moved together with the protective device. After dicing and before removing the chips, it can be advantageous to rotate the wafer together with the protective device by an angle of 170° to 190°, preferably 180°, about an axis parallel to the first surface of the wafer in order to remove the chips. The holding structures are designed so that the chips remain in the wafer during rotation. For rotation, the protective device is detachably or non-detachably connected to the wafer, for example by means of a bond and / or a fixing device for temporarily fixing the wafer. Gap structures designed for dicing the wafer can be particularly advantageously combined with such rotation if they comprise suitable holding structures.For this purpose, gap structures can, for example, have a groove running parallel to the first surface of the wafer on one side of a gap in the gap structure at suitable locations and a projection on the opposite side of the gap at the same locations, for example in the form of a rail or a projection, such that this rail or projection is received by the groove, with a spatial distance remaining between the two elements. The combination of groove and projection therefore creates a loose connection between an individual chip and the rest of the wafer. In this case, the groove can be implemented in the chip, and the projection accordingly belongs to the rest of the wafer. However, an opposite arrangement (groove in the rest of the wafer, projection belonging to the chip) is also conceivable.The remaining wafer can be designed with one or more suitable recesses so that the projection or rail can be moved away from the chip. This allows this loose connection to be severed. Using such a mechanism, chips can be held in the wafer after singulation and then selectively released, allowing them to be removed from the wafer.

[0022] Rotating the wafer by 170° to 190° can be particularly advantageous if the protective device is arranged above the wafer before rotating, in particular in the case where the wafer and protective device are brought into contact by applying the protective device to the wafer from above. The terms "above" and "from above" refer in the context of this invention to the direction of gravity: An object is located "above" another object if it is arranged opposite to the direction of gravity with respect to the other object. Accordingly, "from above" means that something occurs in the direction of gravity, "upwards" means opposite to the direction of gravity. The terms "below", "from below" and "downwards" are to be understood as equivalent. In the case described, the support structures of the protective device support the wafer after rotation, and the rotation occurs around an axis perpendicular to the direction of gravity.The chips can be removed from the wafer after rotation. Such a procedure is particularly preferred if it is advantageous for certain process steps to orient the first surface of the wafer protected by the protective device upwards, and / or if the protective device is located above the wafer. For example, for etching purposes, an etching gas may be supplied via openings in a region of an outer wall of the protective device. In this case, it is typically advantageous to distribute such openings as homogeneously and over as large an area as possible. If regions of the outer wall are to act as a base for placing the protective device on a shelf, there is a risk that existing openings in these regions will be blocked and no gas supply will be possible. Possible positions for openings for the gas supply are therefore limited.Such a limitation can be circumvented, for example, by orienting the protective device with the wafer so that the protective device is arranged above the wafer for carrying out the etching process. There is no risk of blocking openings for supplying an etching gas; the positions of such openings can be freely selected. However, since removal of the chips after singulation must take place in a direction that is not blocked by the protective device, removal typically requires rotating the wafer. After carrying out the etching process, the wafer is therefore rotated together with the protective device, preferably by 180° about an axis parallel to the first surface (i.e., about an axis perpendicular to the direction of gravity) and placed on a support surface for removal of the chips.

[0023] Any number of steps within the manufacturing process are conceivable before the wafer is singulated. For example, to prepare the wafer for further steps in the manufacturing process after it has been brought into contact with the protective device, a sintering paste and / or solder can be applied to the second surface of the wafer. Wafer bonding, for example, using eutectic bonding, of a second wafer can also be performed. Testing the functionality of the wafer (wafer testing) and / or parts of the wafer can also be performed before singulation while the wafer is in contact with the protective device.

[0024] According to a second aspect of the invention, a protective device with one or more support structures for temporarily supporting a wafer on the protective device and / or for temporarily supporting the protective device on the wafer is proposed, wherein the protective device is configured to be used in a method according to the invention. Typically, a wafer to be protected is placed with a first surface to be protected facing downwards on the one or more support structures of such a protective device, wherein the first surface of the wafer is arranged oriented perpendicular to the direction of gravity. A protective device can also be designed such that it can be placed on the wafer, i.e. is typically applied to the wafer from above, wherein the first surface of the wafer to be protected is oriented upwards. In this case, the support structures support the protective device on the wafer.

[0025] A protective device according to the invention can, for example, consist essentially of silicon provided with a passivation layer that protects against an etching gas used. The use of silicon has the advantage that, when the temperature changes, the protective device expands and contracts to the same extent as a wafer in contact with it, which is also made of silicon. Consequently, there are no displacements or undesirable mechanical stresses between the wafer and the protective device. The passivation layer can, for example, consist of silicon dioxide and / or silicon nitride. Alternatively, a protective device according to the invention can also consist of other materials or material compositions, for example a metal and / or a metal alloy, for example a steel, and / or a ceramic.

[0026] Preferably, the protective device is at least partially shielded from the surroundings of the protective device by one or more outer walls in order to prevent undesirable substances such as foreign particles from reaching the first surface of the wafer to be protected and in particular structures to be protected located there.

[0027] For example, the protective device can have one or more side walls and a base. An outer wall of the protective device can have one or more openings for gas supply. The one or more outer walls preferably enclose an interior space with a wafer placed on the protective device. The one or more outer walls of the protective device are preferably designed to be gas-tight or have only low permeability, except for optional openings for gas supply. The same preferably also applies to connections between an outer wall of the protective device and the wafer and to connections between two outer walls of the protective device. One or more openings for gas supply can be positioned, for example, in an outer wall opposite a wafer (rear outer wall) and / or a lateral outer wall (side wall) and are preferably designed to supply an etching gas to the interior space.By supplying a gas and / or placing such a protective device in a suitable gas atmosphere, the gas pressure in the interior of the protective device can be changed. The protective device preferably has a plurality of openings for the gas supply, which are designed as holes dimensioned such that unwanted particles (foreign particles) originating from outside the protective device and above a certain particle size cannot enter the interior of the protective device at all or with a sufficiently high probability. The holes therefore have a filtering function. The holes can, for example, be dimensioned such that, for example, via an appropriately selected diameter, they do not allow foreign particles with a particle size of 5 pm, 2 pm, 1 pm, 0.5 pm, 0.2 pm or 0.1 pm to pass through at all or only with a tolerable probability.The holes can thus be used to supply etching gas to the interior of the protective device in order to perform an etching process on the wafer placed on the protective device without contaminating the first surface of the wafer with foreign particles originating from the outside. Preferably, the rear outer wall of the protective device, i.e., its rear side, is designed to be flat, allowing particularly easy handling and can be used as a base on which the protective device can be placed together with the wafer, for example, for a wafer test and / or for removing the chips after singulation.

[0028] The one or more support structures of the protective device can, for example, take the form of continuous or discontinuous walls, arches, grids, struts, and / or supports, which are preferably arranged in a grid. Such support structures can preferably run at least partially parallel and / or along gaps and / or trenches of a gap and / or trench structure formed or to be formed for singulating the wafer in the wafer to be supported and thereby enclose the structures to be protected corresponding to the chips and, for example, in the case of continuous walls, offer these structures additional protection. When bringing a wafer into contact with a protective device according to the invention, for example when positioning the wafer on the protective device, the wafer is preferably arranged such that the support structures do not touch particularly sensitive areas of the wafer.To achieve this and / or simplify automatically performed process steps, a protective device can be designed so that a wafer can only be brought into contact with the protective device in a defined orientation. For this purpose, a notch or a flat of the wafer can be utilized in conjunction with a corresponding shape of the protective device.

[0029] In a particularly preferred embodiment of the protective device according to the invention, the protective device comprises a fixing device for fixing the wafer during temporary support of the wafer. The purpose of such a fixing device is therefore to prevent unwanted movement of the wafer. For this purpose, the fixing device preferably has one or more fixing elements for preventing unwanted lateral displacement of the wafer. Such a fixing element can, for example, consist of a frame enclosing the wafer. Such a frame can also be designed to seal the protective device laterally from the outside in order to further protect the first surface of the wafer. In such a case, the frame therefore simultaneously functions as an outer wall.Another preferred possibility to prevent unwanted movements of the wafer, which can be used alternatively or in addition to a fixing device, is to bond the wafer to the protective device.

[0030] Advantages of the invention

[0031] The invention discloses a method and a device for protecting particularly sensitive structures of the corresponding wafers from damage and / or contamination, for example, by foreign particles, during a semiconductor chip manufacturing process. In particular, possibilities are disclosed for protecting the chips even during wafer singulation. In this case, a protective device according to the invention relies on regions outside the chips, whereby the fill factor on the individual chips is not negatively affected. A protective device according to the invention can therefore protect structures on the wafer without necessarily requiring the creation of additional structures on the wafer for such a protective device.

[0032] A protective device according to the invention can be optimized for wafer separation by means of etching, breaking, and / or using a laser. This makes it possible to improve the fill factor of the individual chips and the wafer itself, since wide sawing lines on the wafer do not need to be provided for sawing, and the aforementioned processes are more precise than sawing. In particular, when using an etching process and / or laser cutting, unwanted particle contamination is avoided.

[0033] Although a wafer must preferably be brought into contact with a protective device according to the invention in such a way that the one or more support structures of the protective device are only in contact with the wafer outside the areas to be protected, since corresponding areas typically also have to be kept available for singulation and stabilization of the wafer, the fill factor of the wafer is not impaired as a result.

[0034] Brief description of the drawings Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0035] They show:

[0036] Figure 1A is a schematic representation of a section of an exemplary protective device according to the invention with a first wafer;

[0037] Figure 1B is a schematic representation of a section of an exemplary protective device according to the invention with a second wafer;

[0038] Figure 1C is a schematic representation of a section of the exemplary protective device according to the invention from Figure 1B with the second wafer of Figure 1B after singulation;

[0039] Figure 2 shows a schematic representation of a wafer in a protective device according to the invention in a plan view and a perspective view;

[0040] Figures 3A, 3B, 3C show three schematic representations of a section of another exemplary protective device according to the invention with a third wafer at different times; and

[0041] Figure 4 shows in schematic form as a flow chart a method according to the invention for singulating a wafer using a protective device according to the invention.

[0042] Embodiments of the invention

[0043] In the following description of the embodiments of the invention, identical or similar elements are designated by the same reference numerals, whereby a repeated description of these elements is omitted in individual cases. The figures only schematically illustrate the subject matter of the invention.

[0044] Figure 1A shows a schematic representation of a section of an exemplary wafer 100 with a first surface 100a and a second surface 100b (upper partial figure), which is located on an exemplary protective device 120 according to the invention (only shown in the lower partial figure). The lower partial figure shows the protective device 120 in a surface view and also purely schematically. The lower partial figure represents plane A, indicated by a dashed line in the upper partial figure. The upper partial figure shows a section of the wafer 100 with a view of its first surface 100a with two open MEMS structures 130, wherein two chips 180a, 180b of MEMS systems, which are to be produced by singulating the wafer 100 and which have these MEMS structures 130, are shown. The protective device 120 protects the MEMS structures 130.

[0045] The left-hand chip 180a to be produced is surrounded by a gap structure that locally perforates the wafer, with gaps 140a penetrating the wafer 100 in the vertical direction, and with webs 110 being formed as a connection between the chip 180a to be produced and the remaining part 105 of the wafer 100. To keep the webs 110 as thin as possible and thus simplify a purely mechanical separation of the wafer 100, for example by breaking, recesses 150 can be provided in the wafer 100, as can be seen in the lower part of the figure, which thin the webs 110 compared to the chip 180a and the remaining wafer 105.

[0046] As also shown in the lower part of the figure, the wafer 100 is located on support structures 122 of a protective device 120. The support structures 122 can, for example, be wall-shaped elements that support the wafer 100 from below, parallel to the gaps 140a of the gap structure. The wafer 100 is placed on the support structures 122 such that the first surface 100a with the MEMS structures 130 faces downwards and, at the same time, the support structures 122 only come into contact with insensitive areas of the wafer 100. The MEMS structures 130 can thus be protected, for example by means of support structures 122 designed as continuous walls and / or an outer wall (not shown) surrounding the protective device 120, from foreign particles that may arise during further processing steps performed on or starting from the first surface 100b of the wafer.

[0047] The webs 110 hold the chip 180a shown on the left in its position, so that further work can be performed on the wafer 100, such as printing with solder and / or sintering pastes, bonding, for example, with another wafer, a wafer test, and finally also dicing. To dicing the wafer 100, the webs 110 can, for example, be mechanically broken and / or cut by means of a laser, preferably directly upon removal of the chip 180a from the protective device 120. Any webs 110 remaining on the chips 180 after such dicing or remnants of the webs 110 can, if desired, be completely removed in a further step after dicing, for example mechanically and / or by means of a laser and / or an etching process.

[0048] In the case of the second, right-hand chip 180b in Figure 1A, a further possibility is shown for simplifying subsequent singulation of the wafer 100: In this case, a trench structure with a trench 140b was formed in the wafer 100 on the second surface 100b, although a trench structure on the first surface 100a is also conceivable. In the case of a trench structure on the first surface 100a, it is also conceivable that this is formed together with a sacrificial layer etching (removal of so-called sacrificial regions using an etching process) for processing the wafer 100, for example, to expose the MEMS structures 130. For such a variant, openings through which etching gas can be supplied can be provided in an outer wall of the protective device 120.For the sake of clarity, the trench 140b is also shown in the upper part of this variant, even though it is not visible when looking at the first surface 100a.

[0049] In contrast to the left variant (chip 180a), the right chip 180b does not specifically form ridges 110. Instead, the wafer 100 is thinned continuously by forming the trench 140b around the chip 180b. Subsequent singulation can then be performed along this prepared trench 140b, for example, by etching and / or laser cutting and / or, if the remaining wafer 100 is sufficiently thin in the region of the trench 140b, by breaking.

[0050] Figure 1B shows, in a similar representation to Figure 1A, a second wafer 101 (upper and lower partial figures), also with a first surface 101a and a second surface 101b, with another lateral representation of a section of the exemplary inventive protection device 120 from Figure 1A with respect to a plane A. Like wafer 100, wafer 101 has open MEMS structures 131 on the first surface 101a, which are provided for chips 181. Regions 141 are marked in Figure 1B, which are provided for a subsequent etching process for singulating wafer 101 (etching structures). As can be seen in the lower partial figure, these etching structures 141 only partially penetrate the wafer. These etching structures 141 are also shown in the upper part of the figure for the sake of better illustration, although these etching structures 141 are not visible when looking at the first surface 100a, as can be seen from the lower part of the figure.

[0051] Furthermore, recesses 151 are formed in the wafer 101, which may have been created, for example, by previous etching processes and represent trenches that enclose the individual chips 181. The sum of these trenches 151 therefore represents a trench structure enclosing the individual chips 181 within the meaning of the invention. In contrast to the chip 181 in Figure 1A, a trench structure was formed on the first surface 100a here. The recesses 151 have an L-shape, which is realized by corresponding undercuts 160 in the wafer 101. These undercuts 160 serve as holding structures. If the wafer is singulated by etching in the region of the etching structures 141 along the trench structure formed by the recesses 151 (or another method for removing the wafer material in these regions is used for singulation), the chips 181 are separated from one another and from the remaining wafer 106.The individual chips 181 first fall vertically downward, illustrated in Figure 1B by arrows 190 (when the shown protective device 120 and the wafer 101 are oriented perpendicular to the direction of gravity), but are then decelerated by the support structures as shown in Figure 1C. Unlike what is shown in Figures 1B and 1C, such support structures can also be implemented only locally, i.e., they do not have to be present at every point in a trench or gap.

[0052] Figure 1C shows the wafer 101 and the inventive protective device 120 from Figure 1B after the wafer 101 has been singulated by removing the etched structures 141, which have now been replaced by cavities 142. Corresponding to the etched structures 141 in Figure 1B, the cavities 142, which are not actually visible when looking at the surface 100a of the wafer 100, are shown here for clarity.

[0053] As shown, the projections 185 on the chips 181, realized by the recesses 151 in the wafer 101, ensure that the downward movement 190 of the individual chips 181 is stopped, since these projections 185 catch on remaining parts 106a of the remaining wafer 106. This prevents the chips 181 from striking a base, for example, the protective device 120, with the open MEMS structures 131 after singulation, which could lead to damage to the open MEMS structures 131. However, after singulation, the chips 181 can be removed from the protective device 120 upwards (i.e., opposite to the direction of gravity and thus the direction of the arrows 190) (arrows 195), for example by means of a suitable removal device 192, which can be vacuum-based.After the individual chips have been separated and removed from the protective device, the projections 185 can be completely removed in a further step, for example mechanically and / or by means of a laser cutting and / or an etching process.

[0054] The procedures from Figure 1A can also be combined with the procedure from Figures 1B and 1C in order to prevent the individual chips 180a, 180b from accidentally falling out and / or falling down after separation if the chips 180a, 180b are not removed from the protective device 120 directly with the separation.

[0055] Figure 2 shows a schematic representation of another wafer 200 in another exemplary protective device 220 according to the invention in a plan view (partial figure A) and a perspective view (partial figure B). The wafer 200 has MEMS structures 230 (only shown in part A) located on twelve chips 280 to be manufactured. These MEMS structures 230 are located in part A on the surface of the wafer 200 facing away from a viewer of Figure 2, which is why the squares representing the corresponding MEMS structures 230 are provided with dashed edges. The same applies to the support structures 222 of the protective device 220, which are also shown as dashed lines and symbolize continuous walls below the wafer 200.It is advantageous for a protective device 220 to have a wall 221 laterally enclosing the protective device 220 in order to protect the downward-facing surface of the wafer 220 from damage and contamination. The protective device 220 further comprises a fixing element 224 consisting of a frame 226 enclosing the wafer 220. This frame prevents the wafer 220 from being accidentally displaced laterally. The fixing element 224 is advantageously further shaped such that a notch or flat 228 (not shown in partial figure B) of the wafer 220 is used to achieve a desired orientation when positioning the wafer 220 on the protective device 220 (bringing the wafer 220 into contact with the protective device 220). For this purpose, the frame 226 can, for example, be provided with a corresponding bulge 228 (not shown in partial figure B).

[0056] Figures 3A, 3B, and 3C show three schematic representations of a section of another exemplary protective device according to the invention with a third wafer after various steps of a method according to the invention. All three figures are in the form of a side view. In this embodiment of the invention, a gap structure is used for singulation.

[0057] Figure 3A shows an exemplary protective device 320 according to the invention with support structures 322, which is in contact with a wafer 300 having two surfaces 300a and 300b. The wafer 300 is located on a support 310. Two chips 380a, 380b to be manufactured are shown as examples, which have open MEMS structures 330. These open MEMS structures 330 are directed upwards. The protective device 320 was positioned on the wafer 300 such that the first surface 300a of the wafer is in contact with the support structures 322, wherein the support structures 322 do not touch the open MEMS structures 330. To prevent unwanted displacement of the wafer and the protective device relative to each other and to enable later rotation of the protective device with the wafer, the protective device was bonded to the wafer.

[0058] The wafer 300 has etching structures 340 to the left and right of a chip 380a, 380b to be produced, which delimit the chips 380a, 380b. These etching structures 340 serve to form a gap structure through which the wafer 330 is singulated. At the same time, an etching process is intended to form holding structures 360, wherein these future holding structures 360 comprise laterally placed grooves 386 in the chips 380a, 380b and correspondingly arranged projections in adjacent wafer sections 390 of the remaining wafer 305. The holding structures 360 are locally limited, i.e., they do not run along the entire etching structures 340. Figures 3A, 3B, and 3C each show a sectional plane that runs precisely through the holding structures 360.Recesses 323 are located in the areas below the wafer sections 390 with the projections 385 to enable mobility of the wafer sections 390 with the projections 385 after an etching process for etching the etched structures 340. The support structures 322 are thus exposed in the area of ​​the wafer sections 390. To enable mobility of the projections 385 and the associated wafer sections 390, further etched structures 342 are located in the area of ​​these wafer sections 390. The wafer sections 390 of the wafer 300, which are located between the etched structures 340 and 342, are movable after the etching process has been performed and can, for example, be designed as spring elements.

[0059] Furthermore, holes 328 are located in a rear outer wall 326 of the protective device 320, which serve to supply an etching gas. For this purpose, the protective device 320, together with the wafer 300, is placed in an environment filled with the etching gas. The etching gas penetrates through the holes 328 into the interior 325 of the protective device 328, and the etching structures 340 and the further etching structures 342 are etched. The etching gas can reach the further etching structures 342 via the recesses 323. At the same time, the etching gas guided into the interior 325 can be used, for example, to perform a sacrificial layer etching and thereby expose the ME MS structures 330. For the sake of clarity, only twelve holes 328 are shown in each of Figures 3A, 3B, and 3C, although this number is purely exemplary and can also be significantly higher. Also, the holes 328 in the figures are not drawn to scale.The holes 328 typically have a diameter selected so that unwanted foreign particles of a certain size from the environment cannot enter the interior space 325.

[0060] Figure 3B shows the exemplary inventive protection device 320 from Figure 3A with the corresponding wafer 300 after an etching process was carried out by supplying an etching gas through the holes 328. The etching structures 340 were removed by the etching gas and a gap structure with gaps 350 was thereby formed in the wafer 300, whereby the wafer 300 was singulated. The MEMS structures 330 of the chips 380a, 380b were also exposed by the etching gas, identified in Figure 3B by a different graphic representation of the regions of the MEMS structures 330 compared to Figure 3A. Furthermore, the protection device with the wafer was rotated 180° about a rotation axis 315, which runs parallel to the first surface 300a of the wafer 300, and after the rotation, was placed again on the support 310, which now blocks the holes 328. Accordingly, supplying the etching gas through holes 328 is no longer possible. The turning took place after the etching process.Holding structures 360, which have projections 385 formed by the etching process and interlocking grooves 386, hold the chips 380a, 380b in the wafer 300 after singulation by means of these projections 385 and grooves 386. The chips 380a, 380b cannot move freely upward or downward. As a result, the wafer can be rotated with the protective device without risking the chips 380a, 380b from falling out.

[0061] A removal device 392, which may be vacuum-based, for example, has been placed above the left chip 380a, temporarily securing the chip 380a. To remove this chip 380a, the wafer sections 390, which have the projections 385, are moved out of the grooves 386 of the chip 380a (arrows 396). Such movements in the directions 396 are made possible by the fact that recesses 370 in the wafer 300 have been etched free in the direction of movement 396 corresponding to the further etching structures 342 by the etching process. The now movable wafer sections 390 with the projections 385 can be configured, for example, as spring elements and can be moved away from the chip 380a using a suitable tool (not shown). Here, the chip 380a is continuously held by the removal device to prevent the chip 380a from falling down.

[0062] Figure 3C shows the situation after moving the wafer sections 390 with the projections 385 in the directions 396, with the projections 385 now located completely outside the grooves 386. The chip 380a can now be moved upwards and downwards independently of the remaining wafer 305, but is still fixed by the removal device 392 and can now be removed upwards from the wafer 300 (arrow 395). An identical procedure as shown in Figures 3B and 3C is also possible for the other chips of the wafer 300, such as the chip 380b.

[0063] Figure 4 finally shows in schematic form as a flow chart a method according to the invention for singulating a wafer 100, 101, 200 using a protection device 120, 220 according to the invention, wherein the wafer 100, 101, 200 has a first surface 100a, 101a and a second surface 100b, 101b, wherein structures to be protected, for example ME MS structures 130, 131, 230, are located on the first surface 100a, 101a of the wafer 100, 101, 200.

[0064] The wafer 100, 101, 200 is brought into contact with a protective device 120, 220 according to the invention (step 410), for example, positioned thereon, such that the first surface 100a, 101a of the wafer 100, 101, 200 is in contact with support structures 122, 222 of the protective device 120, 220. A typical protective device 120, 220 according to the invention holds the wafer 100, 101, 200 counter to the direction of gravity, the wafer 100, 101, 200 rests on the support structures 122, 222, and the first surface 100a, 101a of the wafer 100, 101, 200 faces downward (in the direction of gravity). The protective device 120, 220 protects the surface with the structures to be protected, i.e. the first surface 100a, 101a, of the wafer 100, 101, 200, against contamination by foreign particles and other damage.

[0065] The wafer 100, 101, 200 can now be processed as desired. In particular, after positioning the wafer 100, 101, 200 on the protective device 120, 220, the wafer 100, 101, 200 can be provided with a gap structure, a locally perforating gap structure 140a, and / or a trench structure 140b (step 415), for example, by means of etching processes. Such a gap structure and / or locally perforating gap structure and / or trench structure 140a, 140b can later be used to separate the wafer 100, 101, 200 into individual chips 180a, 180b, 181, 280. Alternatively or additionally, such structures may also be formed before bringing 410 the wafer into contact with the protective device 120, 220 (step 405).

[0066] After bringing the wafer into contact 410 with the protective device, further processing steps 420 can also be performed, for example, soldering and / or sintering processes can be performed and / or the corresponding solders and / or sintering pastes can be applied, for example, printed. In particular, wafer bonding with another wafer can be performed to produce a coupled wafer. A wafer test of the wafer 100, 101, 200 and / or the future chips 180a, 180b, 181, 280 can also be performed. Finally, a dicing 430 of the wafer 100, 101, 200 takes place. In the case of a wafer 100, 101, 200 that has been prepared accordingly by gap and / or trench structures 140a, 140b, the dicing 430 is preferably performed by mechanical breaking and / or laser cutting. In this case, for example, in the case of a separation 430 by means of breaking, a removal 440 can take place parallel to the separation 430.For example, the chips 180a, 180b, 181, 280 are broken out of the wafer 100, 101, 200 for this purpose. If the chips 180a, 180b, 181, 280 remain in the protective device 120, 220 after the singulation 430, advantageously held by corresponding holding structures, the chips 180a, 180b, 181, 280 can also be tested for their correct functionality in the protective device 120, 220 before their removal 440. The invention is not limited to the exemplary embodiments described here and the aspects highlighted therein. Rather, a multitude of modifications are possible within the scope specified by the claims, which are within the scope of one skilled in the art.

Claims

Claims 1. Method for singulating a wafer (100, 101, 200, 300) having a first surface (100a, 101a, 300a) and a second surface (100b, 101b, 300b) opposite the first surface (100a, 101a, 300a), comprising the following steps: a. Bringing (410) the wafer (100, 101, 200, 300) into contact with a protective device (120, 220, 320) having one or more support structures (122, 222, 322) such that the first surface (100a, 101a, 300a) of the wafer (100, 101, 200, 300) is in contact with the one or more support structures (122, 222, 322); b. Singulating (430) the wafer (100, 101, 200, 300) in contact with the protective device (120, 220, 320) into a plurality of chips (180a, 180b, 181, 280, 380a, 380b); and c. removing (440) the chips (180a, 180b, 181, 280, 380a, 380b) from the wafer (100, 101, 200, 300) in contact with the protective device (120, 222, 322).

2. The method according to claim 1, wherein after bringing the wafer (100, 101, 200, 300) into contact (410) with the protective device (120, 220, 320) and before or with the singulation (430) of the wafer (100, 101, 200, 300) • forming (405, 415) a gap structure enclosing individual chips (380a, 380b) with one or more gaps (350) in the wafer (300) and dicing (430) is carried out at least partially by forming the gap structure; and / or • a gap structure enclosing individual chips (180a) and locally perforating the wafer (100) is formed (405, 415) in the wafer (100) with a plurality of gaps (140a), and the singulation (430) is carried out at least partially along said plurality of gaps (140a); and / or • forming (405, 415) a trench structure enclosing individual chips (180b, 181) with one or more trenches (140b, 151) on the first surface (100a) and / or the second surface (100b) of the wafer (100, 101) and singulating (430) takes place at least partially along one of the plurality of trenches (140b, 151). The method according to claim 2, wherein the formation (405, 415) of the gaps (140a, 350) and / or the trenches (140b, 151) takes place by means of an etching process. The method according to claim 3, wherein the etching process additionally serves to etch structures of the chips (180a, 180b, 181, 280, 380), for example, a sacrificial layer etching. The method according to one of the preceding claims, wherein the singulation (430) is carried out using an etching process, a laser cutting process, and / or a breaking process. Method according to one of the preceding claims, wherein the wafer (100, 101, 200, 300) has open ME MS structures (130, 131, 230, 330) for microelectromechanical systems.The method of claim 6, wherein the open MEMS structures are open toward the first surface (100a, 101a, 300a) of the wafer (100, 101, 200, 300), and the wafer (100, 101, 200, 300) is brought into contact with the protection device (120, 220, 320) such that the one or more support structures (122, 222, 322) do not touch the open MEMS structures (130, 131, 230, 330). The method of claim 6 or 7, wherein the open MEMS structures (130, 131, 230, 330) comprise MEMS structures for a micromirror array. Method according to one of the preceding claims, wherein the wafer (101, 300) has holding structures (160, 360) and / or after bringing into contact (410) with the protective device and before singulating the wafer (101, 300), holding structures (160, 360) are formed in the wafer (101, 300), wherein the holding structures (160, 360) are designed to restrict possible movements of the chips (181, 380) after singulation in at least one direction.The method of claim 9, wherein the wafer (300) is connected to the protective device (320) and after singulation and before removal of the. Chips (380) are rotated together with the protective device (320) by an angle of 170° to 190° about an axis (315) parallel to the first surface (300a) of the wafer (300), and the holding structures (360) are shaped such that the chips (380) remain in the wafer (360) during the rotation and the wafer (300) is connected to the protective device (320). Method according to claim 10, wherein the protective device (320) is arranged above the wafer (300) before the rotation. Method according to one of the preceding claims, wherein the singulation (430) of the wafer (100) takes place with the removal (440) of the chips (180a) from the protective device (120).A protection device (120, 220, 320) having one or more support structures (122, 222, 322) for temporarily supporting a wafer (100, 101, 200, 300) on the protection device (120, 220, 320) and / or for temporarily supporting the protection device (120, 220, 320) on the wafer (100, 101, 200, 300), wherein the protection device (120, 200, 320) is configured to be used in a method according to any one of claims 1 to 12. The protective device (220) according to claim 13, characterized in that the protective device (220) comprises a fixing device (224) for temporarily fixing the wafer (200), wherein the fixing device (224) preferably has one or more fixing elements (226) for preventing unwanted lateral displacement of the wafer (200). The protective device (320) according to claim 13 or 14, wherein the protective device (320) has an outer wall (326) with an opening (328) for gas supply.

Images