Method for manufacturing a large number of sensor chips for determining the pressure of a medium

Abstract

The invention relates to a method for manufacturing a plurality of sensor chips (1) for determining the pressure of a medium (2), wherein the method comprises at least the following steps: - Providing a substrate disk (3) and an electrically conductive wafer (4) with a plurality of measuring membranes (5), - Forming a wafer composite (6) from the wafer (4) and the substrate disk (3) by joining the wafer (4) and the substrate disk (3) in a materially bonded manner, - Including a plurality of grooves (7) in the wafer assembly (6), wherein the grooves (7) are introduced from the side of the wafer (4) perpendicular to the wafer assembly (6) between the measuring membranes (5), so that the grooves (7) extend at least to the substrate disk (3) and terminate in it, - After inserting the grooves (7), annealing the wafer composite (6) at a specified temperature and for a specified time period, - After tempering, the sensor chips (1) are separated by deepening the grooves (7) beyond the substrate disk (3).

Description

[0001] The invention relates to a method for manufacturing a plurality of sensor chips for determining the pressure of a medium.

[0002] In pressure measurement technology, absolute pressure, differential pressure, and gauge pressure sensors are known. Absolute pressure sensors determine the prevailing pressure of a process medium absolutely, i.e., relative to a vacuum, while differential pressure sensors determine the difference between two different pressures of the process medium or media. With gauge pressure sensors, the pressure of the process medium to be measured is determined relative to a reference pressure, where the prevailing atmospheric pressure in the vicinity of the gauge serves as the reference pressure.

[0003] Pressure sensors have a pressure-sensitive measuring element, the so-called pressure sensor chip, on whose first and second surfaces pressure is applied. In the case of relative or absolute pressure sensors, the pressure to be measured of the process medium acts on the first surface of the pressure sensor chip, while an absolute or reference pressure acts on the second surface. In the case of differential pressure sensors, a first and a second pressure of the process medium are applied to each of the two surfaces. The measuring element bends depending on the applied pressure, which is the difference between the pressures applied to the two surfaces. This bending is converted into an electrical signal proportional to the measured pressure by sensor structures arranged on the pressure sensor chip, which is then available for further processing or evaluation.A distinction is made between capacitive and piezoresistive pressure sensor chips. Many such pressure sensors are manufactured and distributed by companies within the Endress+Hauser Group.

[0004] Pressure sensors can consist of a sensor chip comprising a structured silicon chip and a counterbody. Before being isolated into sensor chips, the silicon chips are arranged in multiples on a wafer substrate. The silicon chips and the wafer substrate are processed using semiconductor planar technology and microsystems technology. The silicon chip is structured to form a measuring diaphragm, with one surface of the silicon wafer potentially featuring passivation or metallization layers. The counterbody is typically made of glass. Due to the use of different materials and any unevenness on the joined surfaces, mechanical and thermomechanical stresses exist within the sensor chip, which are relieved by targeted temperature control processes. The sensor chips initially reside within a wafer substrate.After the sensor chips are separated, a first pick-and-place process is required to transfer them from the saw film used for separation to a temperature-stable tempered tray. After tempering, a second pick-and-place process is necessary to transfer the sensor chips from the tempered tray to a storage tray. These two pick-and-place processes make the tempering of the sensor chips a complex and time-consuming process.

[0005] It is therefore an object of the present invention to provide a method by which the production of tempered sensor chips is simplified.

[0006] The problem is solved according to the invention by a method according to claim 1.

[0007] According to the invention, the problem is solved by a method for manufacturing a plurality of sensor chips for determining the pressure of a medium, wherein the method comprises at least the following steps: - Providing a substrate disk and an electrically conductive wafer with a variety of measuring membranes, - Forming a wafer composite from the wafer and the substrate disk by bonding the wafer and the substrate disk together, - Introducing a large number of grooves into the wafer composite, wherein the grooves are introduced from the side of the wafer perpendicular to the wafer composite between the measuring membranes, so that the grooves extend at least to the substrate disk and terminate in it, - After the grooves have been cut, the wafer composite is annealed at a predetermined temperature and for a predetermined time period, - After annealing, the sensor chips are separated by deepening the grooves beyond the substrate disk, so that each sensor chip has a stack consisting of a section of the wafer with a measuring membrane and a section of the substrate disk.

[0008] By creating grooves in the wafer assembly, the sensor chips and the wafer assembly are partially separated. Within the wafer itself, the wafer assembly is already separated, while it remains at least partially connected in the substrate disk area. The grooves are created perpendicular to the wafer assembly, i.e., transverse to a longitudinal dimension of the wafer assembly and transverse to a surface of both the wafer and the substrate disk. The grooves are created from the wafer side, for example, by starting on a surface of the wafer facing away from the substrate disk. The grooves can be created in such a way that the measuring membranes within the wafer are separated. The grooves extend into the substrate disk, specifically over a transition zone between the wafer and the substrate disk, which is particularly susceptible to thermomechanical stresses.The depth of the grooves can be chosen so that the wafer composite is still mechanically connected in the area of ​​the substrate disk, in particular in such a way that transporting or rearranging the wafer composite is made possible.

[0009] Since the grooves terminate in the substrate disk, thermomechanical stresses in the interface between the wafer and the substrate disk are relieved by the subsequent tempering step. The wafer can have at least one passivation layer and / or metallization layer, which is preferably located on a surface facing away from the substrate disk. The grooves also advantageously allow for stress relief in the area between the at least one passivation layer and / or the at least one metallization layer and the wafer through tempering. Because the sensor chips are still interconnected in the substrate disk area, the wafer assembly can be tempered as a whole. Therefore, a pick-and-place process for rearranging the many individual sensor chips is unnecessary; instead, the wafer assembly is transferred as a whole, for example, into a tempering oven. This simplifies the tempering of the sensor chips.The process step of tempering the wafer composite can be carried out in a tempering oven. After tempering, the sensor chips are separated by deepening or extending the grooves beyond the substrate wafer. No additional grooves are created; only the existing grooves are deepened, thus separating the substrate wafer. The separated sensor chips can then be transferred to a storage tray.

[0010] The wafer and the substrate disk are bonded together, particularly across their entire surface. This bond can extend over the entire surface of the wafer facing the substrate disk. The substrate disk can be made of an electrically conductive material or an insulator. The wafer can be a silicon wafer. The measuring membranes can be embedded in the wafer, specifically by structuring the wafer, particularly by creating a cavity or removing material. This structuring can result in the wafer having a thinner layer in defined areas compared to other areas. These thinner areas can then be configured as measuring membranes.Sensor structures, such as electrical resistance resistors, can be arranged on the measuring membranes. These structures can be designed to detect a deflection of the measuring membrane and convert it into an electrical signal. The measuring membranes are preferably arranged in a regular pattern.

[0011] In one embodiment, the measuring membranes are arranged in a grid, with a rectangular grid being used as the grid for the measuring membranes. The grooves can then be incorporated according to the grid.

[0012] In one embodiment, the wafer has a first surface facing the substrate disk, and the substrate disk has a first surface facing the wafer, both having the same area and shape. The two first surfaces are, in particular, fully bonded to each other.

[0013] In one embodiment, the substrate disk is bonded to the wafer using a wafer bonding process. Examples include anodic bonding, glass-frit wafer bonding, eutectic wafer bonding, or nanoreactive wafer bonding. Wafer bonding ensures that the wafer and the substrate disk are fully bonded across their facing surfaces.

[0014] In one embodiment, each measuring membrane is surrounded by a border, with the grooves being incorporated into the borders of the measuring membranes. The border can be rectangular.

[0015] In one embodiment, the grooves are created and / or deepened using a wafer saw.

[0016] In one embodiment, the grooves are integrated into the wafer assembly without completely cutting through the substrate disk. The wafer assembly or the sensor chips remain partially connected to each other in the area of ​​the substrate disk.

[0017] In one embodiment, the grooves are incorporated into the wafer composite so that they extend partially into the substrate disk.

[0018] In one embodiment, the grooves are incorporated into the wafer composite in such a way that they extend to the end area of ​​the substrate disk facing away from the wafer.

[0019] In one embodiment, the sensor chips are separated from the wafer assembly using a wafer saw.

[0020] In one embodiment, the wafer composite is connected at least in the end area of ​​the substrate disk facing away from the wafer after the grooves have been introduced.

[0021] In one embodiment, the grooves are deepened from the side of the wafer.

[0022] In one embodiment, a saw film is applied to a surface of the substrate disk facing away from the wafer before the grooves are cut, and this film is removed before the wafer composite is tempered.

[0023] In one embodiment, silicon, glass or ceramic is chosen for the substrate disk material.

[0024] The present invention will be further described with reference to the following figures. Fig. 1-4 will be explained in more detail. They show: Fig. 1: A cross-sectional view of the wafer composite. Fig. 2: A top-down view of the wafer assembly. Fig. 3: a design of the wafer composite with the grooves incorporated therein. Fig. 4: a configuration of the individual sensor chips.

[0025] The present invention describes a method for producing a plurality of sensor chips 1 for determining the pressure of a medium. In a first process step, a substrate disk 3 and an electrically conductive wafer 4 with a plurality of measuring membranes 5 are provided. The substrate disk 3 can be made, for example, of silicon, glass, or ceramic. The measuring membranes 5 can be incorporated into the wafer 4 in the form of a structured pattern. For this purpose, the wafer 4 can have a plurality of recesses on a first surface 4a facing the substrate disk 3, through which the measuring membranes 5 are formed.

[0026] In a next process step, the wafer 4 and the substrate disk 3 are bonded together to form a wafer composite 6, which is exemplified in Fig. Figure 1 shows the wafer 4. The wafer 4 can be arranged relative to the substrate disk 3 such that the measuring membranes 5 are positioned facing away from the substrate disk 3. The wafer 4 can further comprise at least one passivation layer and / or at least one metallization layer 12, which is arranged, in particular, on a second surface 4b of the wafer 4 facing away from the substrate disk. The passivation layer 12 can serve to passivate the second surface 4b of the wafer 4. For example, the at least one passivation layer 12 comprises silicon oxide, silicon nitride, and / or polycrystalline silicon. The at least one metallization layer comprises, for example, aluminum. The metallurgical bonding of wafer 4 and substrate disk 3 can be achieved using a wafer bonding method.In particular, a first surface 4a of the wafer 4 facing the substrate disk 3 and a first surface 3a of the substrate disk 3 facing the wafer 4 have the same area and shape. The first surface 4a of the wafer 4 and the first surface 3a of the substrate disk 3 are, in particular, fully bonded.

[0027] The measuring membranes 5 can be arranged in a grid, in particular a rectangular grid. The measuring membranes 5 can furthermore be surrounded by a border 8, as shown in Fig. Figure 2 is shown as an example. Typically, the wafer 4 and the substrate disk 3 are designed as round or elliptical disks, with the measuring membranes 5 extending over the entire wafer 4. Fig. 2 is, by way of example, only a part of the second surface 4b of the wafer 4, which faces away from the substrate disk 3, is provided with measuring membranes 5, which are arranged over a width B and a length L of the wafer 4.

[0028] In a further process step, a large number of grooves 7 are introduced into the wafer assembly 6. The grooves 7 are introduced from the side of the wafer 4 perpendicular to the wafer assembly 6 between the measuring membranes 5, so that the grooves 7 extend at least to the substrate disk 3 and terminate therein. For example, the grooves 7 can be introduced into the borders 8 of the measuring membranes 5. The grooves 7 can be introduced using a wafer saw 9. Before introducing the grooves 7, the wafer assembly can be coated with a saw film 11, which is applied to the second surface 3b of the substrate disk 3 facing away from the wafer 4. Fig. Figure 3 shows examples of different depths of the grooves 7. The grooves 7 can be, as shown on the left in Fig. As shown in Figure 3, the grooves 7 terminate in the substrate disk 3 shortly after the transition between wafer 4 and substrate disk 3. This is sufficient to relieve the thermomechanical stresses in the region of this transition during a subsequent tempering step. However, the grooves 7 can also be machined deeper into the substrate disk 3. For example, the grooves 7 can be machined into the wafer assembly 6 such that they extend partially into the substrate disk 3, or that they extend to an end region 10 of the substrate disk 3 facing away from wafer 4. In any case, the grooves 7 terminate in the substrate disk 3, i.e., in particular, so that the substrate disk 3 is not completely cut through when the grooves 7 are machined or by the grooves 7.

[0029] After the grooves 7 have been machined into the wafer assembly 6, the wafer assembly 6 is tempered at a predetermined temperature and for a predetermined time in the next process step. For example, the wafer assembly 6 can be tempered at a temperature between 150 and 300°C for 0.5 to 2 days. The tempering of the wafer assembly 6 can be carried out in a tempering oven. Any saw-cut film 11 that may have been applied can be removed from the substrate disk 3 before the tempering step.

[0030] After the annealing of the wafer composite 6 is complete, the sensor chips 1 are separated in a further process step by deepening or extending the grooves 7 beyond the substrate disk 3. Each sensor chip 1 then comprises a stack 13 consisting of a section of the wafer 3 with a measuring membrane 5 and a section of the substrate disk 3. The deepening of the grooves 7 can be carried out using a wafer saw 9 and / or from the side of the wafer 4. For example, the wafer saw 9 can be guided into the already formed grooves 7 and deepen them. The deepening of the grooves 7 can be carried out in such a way that the substrate disk 3 is cut through, in particular completely, especially transversely, i.e., transversely to a surface of the substrate disk.

[0031] Optionally, a bore 14 can be machined into the substrate disk 3, which overlaps with the measuring membrane 5 in the wafer assembly 6 or in the sensor chip 1. The bore 14 can be machined before the wafer assembly 6 is formed. The bore 14 can serve to supply a reference medium 15 with a reference pressure to the measuring membrane 5. The medium 2 with a pressure to be determined can be in contact with the second surface 4b of the wafer 4. The medium and reference medium 15 can also be reversed, if necessary. Reference symbol list 1 sensor chip 2 Medium 3 substrate disc 3a first surface of the substrate disk 3b second surface of the substrate disk 4 wafers 4a first surface of the wafer 4b second surface of the wafer 5 measuring membrane 6 wafer composite 7 grooves 8 Border 9 Wafer saw 10 End area of ​​the substrate disk 11 Saw film 12 Passivation layer / Metallization layer 13 stacks 14 bore 15 Reference medium

Claims

[1] Method for manufacturing a plurality of sensor chips (1) for determining a pressure of a medium (2), wherein the method comprises at least the following steps: - Providing a substrate disk (3) and an electrically conductive wafer (4) with a plurality of measuring membranes (5), - Forming a wafer composite (6) from the wafer (4) and the substrate disk (3) by joining the wafer (4) and the substrate disk (3) in a materially bonded manner, - Including a plurality of grooves (7) in the wafer assembly (6), wherein the grooves (7) are introduced from the side of the wafer (4) perpendicular to the wafer assembly (6) between the measuring membranes (5), so that the grooves (7) extend at least to the substrate disk (3) and terminate in it, - After inserting the grooves (7), annealing the wafer composite (6) at a specified temperature and for a specified time period, - After annealing, the sensor chips (1) are separated by deepening the grooves (7) beyond the substrate disk (3), so that each sensor chip (1) has a stack (13) consisting of a section of the wafer (4) with a measuring membrane (5) and a section of the substrate disk (3). [2] Method according to claim 1, wherein the measuring membranes (5) are arranged in a grid, wherein a rectangular grid is used as the grid of the measuring membranes (5). [3] Method according to any of the preceding claims, wherein the wafer (4) has a first surface (4a) facing the substrate disk (3) and the substrate disk (3) has a first surface (3a) facing the wafer (4) which have the same area and shape. [4] Method according to one of the preceding claims, wherein the substrate disk (3) is connected to the wafer (4) by means of a wafer bonding process. [5] Method according to any of the preceding claims, wherein each measuring membrane (5) is surrounded by a border (8), wherein the grooves (7) are provided in the borders (8) of the measuring membranes (5). [6] Method according to one of the preceding claims, wherein the grooves (7) are made and / or deepened by means of a wafer saw (9). [7] Method according to one of the preceding claims, wherein the grooves (7) are introduced into the wafer composite (6) without completely cutting through the substrate disk (3). [8] Method according to one of the preceding claims, wherein the grooves (7) are introduced into the wafer composite (6) so that they extend partially into the substrate disk (3). [9] Method according to one of the preceding claims, wherein the grooves (7) are introduced into the wafer composite (6) such that they extend to an end region (10) of the substrate disk (3) facing away from the wafer (4). [10] Method according to one of the preceding claims, wherein the wafer composite (6) is connected at least in the end region (10) of the substrate disk (3) facing away from the wafer (4) after the grooves (7) have been introduced. [11] Method according to one of the preceding claims, wherein the deepening of the grooves (7) is carried out from the side of the wafer (4). [12] Method according to one of the preceding claims, wherein a saw film (11) is applied to a second (3b) surface of the substrate disk (3) facing away from the wafer (4) prior to the introduction of the grooves (7), which is removed prior to the tempering of the wafer composite (6). [13] Method according to any of the preceding claims, wherein silicon, glass or ceramic is selected for the material of the substrate disk (3).

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