Device for detaching a wafer from a carrier

Abstract

Device for detaching a wafer (4) from a carrier (2), with which a detachment force acting on the wafer (4) is applied to the wafer (4) by deformation of a contact surface adhering to the wafer (4), wherein first the edge of the wafer (4) is detached, -with adhesives for adhering the wafer (4) to the contact surface, -with deformation means arranged rearwardly of the contacting surface for the defined, controllable deformation of the contacting surface, wherein the deformation means comprise a pressure chamber (8) formed from a pressure trough (9) and a base (7b), wherein the base (7b) of the pressure chamber (8) can be convexly curved by applying excess pressure in the pressure chamber (8).

Description

[0001] The invention relates to a device according to claim 1 for detaching a wafer from a carrier.

[0002] Wafer rethinning is frequently required in the semiconductor industry and can be performed mechanically and / or chemically. For rethinning, the wafers are typically temporarily fixed to a carrier, with various fixing methods available. Examples of carrier materials include foils, glass substrates, or silicon wafers.

[0003] Depending on the carrier materials used and the bonding layer used between the carrier and the wafer, various methods for dissolving or destroying the bonding layer are known, such as the use of UV light, laser beams, temperature exposure or solvents.

[0004] Detachment is increasingly becoming one of the most critical process steps, as thin substrates with thicknesses of just a few µm are prone to breakage or damage during detachment / peeling due to the forces required for the detachment process.

[0005] Furthermore, the thin substrates have little to no dimensional stability and typically curl without support material. Therefore, during handling of the re-thinned wafers, fixation and support of the wafers is practically unavoidable. JP H11 - 245 163 A discloses a substrate attachment / detachment device capable of preventing the formation of stagnant air during a process of bonding a thin semiconductor wafer to its carrier substrate. JP 2004 - 241 568 A discloses a wafer attachment / detachment device without creating an air reservoir by providing an adsorptive holding member provided with a recessed chamber capable of reducing the pressure therein to a vacuum.

[0006] It is therefore the object of the present invention to provide a device and method for detaching a wafer from a carrier as non-destructively as possible, which also enables a wafer to be applied to a carrier as bubble-free as possible.

[0007] This object is achieved with the features of claim 1, wherein a device for detaching a wafer from a carrier is disclosed, with which device a detachment force acting on the wafer is applied to the wafer by deforming a contact surface adhering to the wafer, wherein the edge of the wafer is detached first, - with adhesive means for adhering the wafer to the contact surface, - with deformation means arranged rearwardly of the contact surface for the defined, controllable deformation of the contact surface, wherein the deformation means comprise a pressure chamber formed from a pressure trough and a base, wherein the base of the pressure chamber (8) can be convexly curved by applying excess pressure in the pressure chamber. Advantageous developments of the invention are specified in the subclaims.

[0008] The invention is based on the idea of ​​providing a device for applying the detachment force acting on the thinned wafer in a targeted manner to the wafer by deforming the contacting surface, wherein preferably the edge of the mostly circular wafer is first detachable by the wafer adhering to the contacting side.

[0009] A combination of horizontal pulling force and vertical deflection is preferred, which causes the edge to be lifted off gradually and gently.

[0010] In other words, the detachment force increases from the periphery of the wafer to the center during detachment, with a transverse force component being particularly advantageous. According to the device, the invention relates in a further example to a device for applying and / or detaching a wafer to / from a carrier: - with a deformable membrane that can be aligned parallel to a contact surface of the wafer and has a contact side for at least partially contacting the contact surface, - deformation means arranged rearwardly to the contact side for defined, controllable deformation of the membrane and - with adhesives to adhere the wafer to the membrane.

[0011] Due to the defined, controllable deformation of the membrane, the thinned wafer, in conjunction with the adhesion of the wafer to the membrane, can be detached from the carrier in a targeted manner, preferably from the outside to the inside. In an advantageous embodiment of the invention, the membrane is omnipermeable, in particular through holes penetrating the membrane, Preferably, the number and / or diameter of the holes are predetermined. This measure makes it possible to suction the wafer onto the membrane with a defined adhesion force, given a predetermined number and / or diameter of holes. This also avoids the negative effects of vacuum grooves on the wafer.

[0012] A corresponding effect is achieved by applying a pressure difference to the membrane through the adhesive.

[0013] In a particularly preferred embodiment of the invention, the adhesives comprise: - a suction chamber formed by a suction pan and a membrane covering the suction pan and - a vacuum pump connected to the suction chamber.

[0014] Furthermore, it is advantageous to form the suction trough by a, in particular impermeable, pressure-deformable base and a peripheral wall, since in this way pressure forces can be transmitted from the outside via the deformable base into the suction chamber.

[0015] In an advantageous embodiment of the invention, the deformation means comprise: - the deformable bottom of the suction tray and - at least one, preferably a plurality of, spacers for the defined spacing of the membrane from the floor.

[0016] The aforementioned design enables a particularly effective transmission of the pressure forces to the membrane and, since the base has a similar basic shape to the membrane and also to the wafer, the pressure forces applied across the surface of the deformable base can be optimally transmitted to the membrane.

[0017] In a further advantageous embodiment of the invention, the spacers are edge-free, particularly spherical, which allows for the most uniform force distribution and transmission to the membrane and thus to the wafer. Preferably, the spacers are evenly distributed from the center of the membrane across the surface of the membrane. The spacers can have different geometries, but are preferably identical. Even more preferably, a plurality of small spheres are filled into the suction chamber as spacers.

[0018] Furthermore, the deformation means can advantageously comprise: - a pressure chamber formed by a pressure tank and the floor covering the pressure tank, and - a pressure pump connected to the pressure chamber.

[0019] The pressure chamber can be pressurized to a pressure of up to 10 bar.

[0020] Due to the aforementioned design of the deformation means, not only the adhesive means but also the deformation means can be operated by a vacuum pump, potentially even exploiting synergistic effects of the vacuum device. For example, the vacuum pump could simultaneously serve as the pressure pump.

[0021] It is further advantageously provided that the deformation means comprise at least one limiter configured to limit the deformation of the base toward the pressure chamber, in particular such that the base is flat when the base rests against the limiter. By limiting the deformation of the base, an initial position of the device can advantageously be specified, which position is present when atmospheric pressure / ambient pressure or negative pressure to vacuum is present at least in the pressure chamber.

[0022] By making the area of ​​the contact side smaller than the area of ​​the contact surface in order to prevent any adhesive beads that may be formed when the wafer is removed from the carrier from being transferred to the membrane, contamination of the membrane and in particular its holes is avoided.

[0023] Advantageously, one embodiment of the device according to the invention provides heating means that are integrated into a receiving unit for receiving the carrier and / or arranged below a receiving unit for receiving the carrier. When the heating means are arranged below the receiving unit, the receiving unit can be moved away before the heating means heat up to detach the wafer, thus enabling direct heat application to the carrier and wafer.

[0024] Because the suction chamber is pressurized with negative pressure, especially below 500 mbar, the heat optimally affects the bonding agent between the wafer and the carrier. This allows the heating agents to be even smaller.

[0025] To destroy the bonding force, it is important to bring the bonding agent very precisely and evenly to the temperature necessary to destroy the adhesive properties. This is achieved in particular by reducing and minimizing cooling on the side opposite to the heat input. This creates a very small temperature difference between the temperature of the carrier and the wafer (high uniformity). If this were not the case, the carrier could have a high temperature, especially on the side exposed to the radiation source, and the temperature gradient to the wafer membrane would be very large. Because the wafer is particularly thin and silicon has very good thermal conductivity, the adhesive layer would not reach the temperature necessary to destroy the adhesive properties. It is therefore particularly important for the wafer to have a high insulation value.According to the method, a method for detaching a wafer from a carrier using a device as described above is disclosed, which comprises the following method steps, in particular in the order given:. a) Aligning the deformable membrane with its contact side parallel to the contact surface of the wafer, b) Contacting of membrane and wafer, and c) Deformation and detachment of the membrane by means of the deformation means in the direction of the contact side, whereby the deformation of the membrane is convex.

[0026] When aligning the deformable membrane with its contact side parallel to the contact surface of the wafer, a wedge error may have to be compensated for by methods and devices known in the art. For contacting, it is possible to move the membrane towards the wafer or vice versa or by moving the two components, membrane and wafer, towards each other.

[0027] Instead of a membrane, an adhesive film can also be used.

[0028] By applying a negative pressure to the back of the membrane, the adhesion is achieved by the negative pressure on the back of the membrane, which has the additional effect of ensuring excellent insulation during heating due to the vacuum, thus ensuring uniform heating with low energy loss.

[0029] The deformation of the membrane during detachment of the wafer is advantageously convex, i.e. the detachment force increases as evenly as possible from the edge of the membrane to the center of the membrane.

[0030] Conversely, the method for applying a wafer to a carrier with the device described above can also be carried out by the following process steps, in particular in the following order: a) Contacting of membrane and wafer and adhesion of the wafer to the membrane by the adhesive, b) aligning the deformable membrane and the wafer adhering to it with a carrier, c) convex deformation of the membrane and the wafer by means of the deformation means and application of the wafer to the carrier.

[0031] Due to the convex deformation of the wafer, the application is advantageously carried out from the center of the wafer, so that air inclusions, which are often unavoidable when the wafer is placed flat on the carrier, are largely avoided.

[0032] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings, which show: Fig. 1: a schematic side view of a device according to the invention and Fig. 2: a schematic plan view of the membrane according to the invention.

[0033] In the figures, identical components and components with the same function are marked with the same reference symbols.

[0034] In Fig. 1, a device according to the invention is shown schematically as an embodiment, wherein components such as a housing surrounding the device or positioning and / or adjusting devices, such as a robot arm, are not shown, since these are sufficiently known in the prior art.

[0035] A carrier 2 can be fixed by means of vacuum fixing means 16 on a receiving unit 1 with integrated heating means 14, which in this case are designed as heating coils. A wafer 4, which has been thinned back in a previous process step, is connected to the carrier 2 by means of connecting means 3, for example an adhesive, so that a contact surface 4k of the wafer 4 is exposed on the side of the wafer 4 facing away from the carrier 2.

[0036] An essential component of the device according to the invention is the device consisting of the components arranged above the wafer 4, on the underside of which a membrane 5 is arranged with its contact side 5k opposite the contact surface 4k of the wafer 4.

[0037] Any non-parallelisms resulting from a wedge in the wafer stack are compensated by a so-called wedge error compensation, which is well known in the art.

[0038] The contact side 5k is therefore aligned as parallel as possible to the contact surface 4k and flush with the contact surface 4k. The contact surface 4k and the contact side 5k are usually circular.

[0039] The membrane 5 is fixed in a force-fitting and tightly sealed manner to a circular end face 7s, wherein the membrane 5 has holes 13 distributed over the contact side 5k in order to be able to suck in the wafer 4 via a pressure difference applied to the membrane 5.

[0040] Above the membrane 5, a suction chamber 17 is formed by a peripheral wall 7u and a bottom 7b of a suction trough 7 together with the membrane 5, which can be subjected to negative pressure via a suction line 12 by a vacuum pump (not shown).

[0041] The floor 7b is in its Fig. 1 shown initial position is flat and parallel to the membrane 5, so that the suction chamber 17 has a substantially flat cylindrical shape.

[0042] Spherical spacers 6 are evenly distributed in the suction chamber 17 and their spherical diameter 6d corresponds in the initial state to the distance between the base 7b and the membrane 5.

[0043] Above the suction trough 7, a pressure trough 9 with an end face 9s, a peripheral wall 9u and a bottom 9b is arranged in approximately the same shape, the end face 9s of which lies flat and tightly on the bottom 7b of the suction chamber 7.

[0044] The space enclosed by the pressure pan 9 and the base 7b forms a pressure chamber 8, which can be pressurized via a pressure line 11 and a pump (not shown). The pressure pan 9 is fixed to the suction pan 7, for example, by a force on the base 9b of the pressure pan 9 or by another force-locking connection.

[0045] In the Fig. In the initial state shown in Figure 1, in which atmospheric pressure or ambient pressure prevails in the suction chamber 7 and the pressure chamber 8, the impermeable base 7b is flat and rests against limiters 10 arranged between the base 7b and the base 9b in the pressure chamber 9.

[0046] Below the receiving unit 1, further heating means 15 can be provided in addition to or as an alternative to the heating means 14.

[0047] The area of ​​the contact side 5k is smaller than the area of ​​the contact surface 4k of the wafer 4 in order to avoid contamination of the membrane 5 by connecting means 3 when detaching the wafer 4 from the carrier 2.

[0048] The detachment of the wafer 4 from the carrier 2 with the Fig. The device shown in Figure 1 operates as follows: After the wafer 4 (wafer stack) fixed to the carrier 2 by the connecting means 3 has been thinned back, this wafer stack is positioned by the thinning device onto the receiving unit 1 by a robot arm (not shown) and then fixed to the receiving unit 1 by vacuum fixing means 16. Using the same or another robot arm, the membrane 5 connected to the pressure chamber 9 and the suction chamber 7 is aligned with its contact side 5k parallel to the contact surface 4k and flush with it.

[0049] Subsequently, the membrane 5 is lowered onto the wafer 4 and contacts it in the Fig. 1 shown pressure-free initial position.

[0050] The robot arm can also transfer the wafer stack directly to the membrane 5, without fixing it to the receiving unit 1, so that the receiving unit 1 can be omitted. In this case, only heating means 15 are required. The transverse force when detaching the carrier from the wafer 4 is applied by the gripper 18 ( Fig. 3), which is described below.

[0051] The membrane 5 is adhered to the wafer 4 by the adhesive means, consisting of the membrane 5 with holes 13, the suction chamber 17 and the vacuum pump connected via the suction line 12.

[0052] During or following the adhesion and / or contacting of the membrane 5 with the wafer 4, the stack consisting of wafer 4, connecting means 3 and carrier 2 is heated by the heating means 14 and / or heating means 15, wherein the suction chamber 17 serves as a heat insulator and regulator.

[0053] The process is controlled by a control unit not shown.

[0054] After reaching the temperature required to release the adhesive (connecting means 3), the wafer 4 adhering to the membrane is detached by convex deformation of the membrane 5 using the deformation means, whereby the wafer 4 is automatically detached from the edge 4r of the wafer 4. Preferably, a transverse force is introduced by relative movement of the carrier 2 to the membrane 5.

[0055] The deformation means are formed by the pressure chamber 8 pressurized via the pressure line 11 and the pump (not shown), as well as the impermeable, deformable base 7b, the spacers 6 and the membrane 5.

[0056] The pressure pan 9 and the suction pan 7 can be formed as a single piece. Likewise, the limiters 10 and / or the spacers 6 can be formed from the bottoms 7b and / or 9b.

[0057] By applying overpressure in the pressure chamber 8, the bottom 7b is convexly curved or dynamically deflected due to the more massive construction of the pressure tank 9, whereby the deflection is proportional to the applied overpressure of up to 10 bar and thus programmable or controllable by the control unit.

[0058] Due to the deflection of the base 7b, the spacers 6 are pressed towards the membrane 5, whereby the membrane 5 is also deflected analogously to the base 7b. Due to this effect of a uniform, precise and exactly programmable deflection of the membrane 5 while maintaining the adhesive force on the membrane 5, the wafer 4 can be detached from the carrier 2 from the edge. In addition to the vertical force component via the membrane 5, the wafer 4 can be gripped by a gripper 18 according to Fig.3 in a horizontal direction, whereby the wafer 4 is gently detached from the carrier 2 without damaging chips 19 located on the wafer 4.

[0059] The gripper 18 is designed in the form of a hook, with a projection 20 which has a smaller height H than the thickness D of the wafer 4. The transverse force or horizontal force component can also be transmitted by the receiving unit 1 or a vacuum gripper.

[0060] In order to enable precise maintenance of the temperature in the case of thermal temporary adhesive connections as connecting means 3, one or more temperature sensors are located in the receiving unit 1 and / or in the area of ​​the suction chamber 17, which enable control of the introduced temperature and control the detachment process via control software of the control device (not shown).

[0061] Due to the insulating effect of the suction chamber 17, the stack of wafer 4, connecting means 3 and carrier 2 only needs to be heated from one side.

[0062] The device described above can further be used for a method for applying the wafer 4 to a further carrier 2', for example a sawing foil or a processed wafer, and in order to avoid air inclusions during transfer or contact of the thin wafer 4 with the further carrier 2', application of the wafer 4 in a curved form is particularly advantageous.

[0063] This means that the wafer 4 removed by the above process remains bent on the membrane 5 and is aligned with the other carrier 2'. The convex-shaped wafer 4 is then placed on the carrier 2' in the center and applied to the carrier 2' by reshaping, i.e., lowering the pressure in the pressure chamber 9, whereby air inclusions are largely avoided.

[0064] The risk of air inclusions is particularly high with adhesive films, so that the present method allows wafers to be deposited on adhesive materials without air inclusions. List of reference symbols 1 recording unit 2, 2' beams 3 connecting devices 4 wafers 4k contact area 4r edge 5 Membran 5k contact page 6 spacers 6d sphere diameter 7 Suction tray 7b Floor 7s frontal surface 7u perimeter wall 8 Printing room 9 Pressure tank 9b Floor 9s frontal area 9u perimeter wall 10 limiters 11 Pressure line 12 Suction line 13 holes 14 Heating agents 15 heating agents 16 Vacuum fixatives 17 Suction chamber 18 griefers 19 chips 20 lead H Height D Thickness

Claims

[1] Device for detaching a wafer (4) from a carrier (2), with which a detachment force acting on the wafer (4) is applied to the wafer (4) by deformation of a contact surface adhering to the wafer (4), wherein first the edge of the wafer (4) is detached, -with adhesives for adhering the wafer (4) to the contact surface, -with deformation means arranged rearwardly of the contacting surface for the defined, controllable deformation of the contacting surface, wherein the deformation means comprise a pressure chamber (8) formed from a pressure trough (9) and a base (7b), wherein the base (7b) of the pressure chamber (8) can be convexly curved by applying excess pressure in the pressure chamber (8). [2] Device according to claim 1, characterized by that the detachment force increases during detachment from the circumference of the wafer (4) to the center during detachment, in particular additionally with a transverse force component.

Images