Abstract
A method for fabricating semiconductor based sensor devices with sensors which are in communication with the environment surrounding the sensor devices, and such a sensor device is described. The method comprises the steps of providing a semiconductor-based device wafer, fabricating a plurality of sensors on the semiconductor-based device wafer, providing a capping wafer, and attaching the capping wafer on the device wafer with each sensor arranged below a recess of the capping wafer. The capping wafer comprises at least one gas permeable section between each recess and the second side, to provide a gas passage between the recess and the environment surrounding the sensor device. The method further comprises the steps of applying a protective layer on all gas permeable sections of the capping wafer, dividing the device wafer and the attached capping wafer into individual sensor devices, and removing the protective layer from all gas permeable sections.
Claims
1. A method for fabricating semiconductor-based sensor devices comprising sensors which are configured to interact with the environment surrounding the sensor devices, comprising the steps of providing a semiconductor-based device wafer, fabricating a plurality of sensor parts comprising micro- and/or nanostructures on different device areas on a device side of the device wafer, providing a capping wafer comprising a first side and a second side and a plurality of recesses on the first side, attaching the first side of the capping wafer on the device side of the device wafer with each sensor part arranged below a recess such that a cavity is formed between each recess and the device wafer, characterized in that the capping wafer is in contact with the device wafer in contact areas arranged at the periphery of the recesses, wherein the capping wafer comprises at least one gas permeable section between each recess and the second side, to provide a gas passage between the recess and the environment surrounding the sensor device, wherein the method further comprises the steps of applying a protective layer on all gas permeable sections of the capping wafer, dividing the device wafer and the attached capping wafer into individual sensor devices, and removing (108) the protective layer from all gas permeable sections.
2. The method according to claim 1, wherein the capping wafer is made entirely of a gas permeable material.
3. The method according to claim 1, wherein the capping wafer is semiconductor-based and comprises gas permeable sections.
4. The method according to claim 1, wherein the contact areas completely enclose each recess after the step of dividing such that gas exchange is possible only through the gas permeable material of the capping wafer.
5. The method according to claim 4, wherein the step of applying a protective layer on all gas permeable sections comprises applying a protective layer covering the second side of the capping wafer.
6. The method according to claim 5, wherein the gas permeable material consists of a porous material.
7. The method according to claim 6, wherein the porous material has a hydrophobic surface.
8. The method according to claim 7, wherein the sensors comprising micro- and/or nanostructures are photonic gas sensors.
9. A semiconductor-based sensor device with a sensor part which is configured to interact with the environment surrounding the sensor device, comprising a semiconductor-based substrate, a sensor part comprising a micro- and/or nanostructure arranged on a device side of the substrate, a cap comprising a first side and a second side and a recess on the first side, wherein the cap is arranged with its first side on the device side of the substrate with the sensor part arranged below the recess such that a cavity is formed between the recess and the substrate, characterized in that the cap is in contact with the substrate in contact areas arranged at the periphery of the recess, and in that the cap comprises at least one gas permeable section extending from the recess to the second side, to provide a gas passage between the recess and the environment surrounding the sensor device.
10. The sensor device according to claim 9, wherein the cap is made entirely of a gas permeable material.
11. The sensor device according to claim 9, wherein the cap is semiconductor-based and comprises at least one gas permeable section.
12. The sensor device according to claim 9, wherein the contact areas completely encloses each recess such that gas exchange is possible only through the gas permeable material of the cap.
13. The sensor device according to claim 9, wherein the gas permeable material consists of a porous material.
14. The method according to claim 13, wherein the porous material has a hydrophobic surface.
15. The sensor device according to claim 9, wherein the sensor part comprising micro- and/or nanostructures are photonic gas sensor parts.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1-6 illustrates a method for production of a semiconductor based sensor device according to an embodiment.
[0046] FIG. 7 in a perspective view a sensor device according to FIG. 6.
[0047] FIG. 8 is a flow diagram of a method according to the present invention.
DETAILED DESCRIPTION
[0048] In the following detailed description of embodiments, similar features in the different drawings are denoted with the same reference numerals. The drawings are not drawn to scale.
[0049] FIG. 1-6 illustrates the method for production of a semiconductor based sensor device. FIG. 1 shows in cross section a semiconductor based device wafer 1. A plurality of sensors 2 comprising micro- and/or nanostructures have been fabricated on different device areas 3 on the semiconductor-based device wafer 1. The semiconductor may be silicon, silicon nitride, silicon carbide, gallium arsenide or any other semiconductor on which a sensor may be fabricated. In the embodiment of FIG. 1, the sensors are infrared gas sensors. The sensor parts of each sensor 2 comprise a waveguide 4, which is supported on pillars/posts 5 extending from the device wafer 1 to the waveguide 4, such that the waveguide 4 is free hanging between the pillars/posts 5. In the embodiment of FIG. 1, the sensor parts of each sensor 2 also comprises a light source 6 such as a light emitting diode, LED, a laser diode, or a resistive emitter, in one end of the waveguide 4 and a photodetector 7 in the other end of the waveguide 4. The light source 6 is configured to transmit light into the waveguide 4 and the photodetector 7. The wavelength of the light from the light source is chosen to correspond to an absorption peak of the gas to be detected by the sensor. The wavelength is typically in the infrared wavelength band for most gases of interest. The cross sectional dimensions of the waveguide 4 are such that the light in the waveguide 4 forms an evanescent wave, which interacts with the gas surrounding the waveguide. Thus, the attenuation of the light in the waveguide 4 will depend on the concentration of the gas surrounding the waveguide.
[0050] It is possible to have the light source 6 and/or the photodetector outside the sensor device.
[0051] According to alternative embodiments, the sensor is not a gas sensor as shown in FIG. 1. In such alternative embodiments, the micro- and/or nanostructures may constitute pressure or humidity sensors. It is well known to skilled persons how pressure and/or humidity sensors based on micro- and/or nanostructures may be fabricated.
[0052] FIG. 2a shows a semiconductor based capping wafer 8 comprising a first side 9 and a second side 10 and a plurality of recesses 11 on the first side 9. The capping wafer 8 comprises at least one gas permeable section extending between each recess 11 and the second side 10, to provide a gas permeable passage between the recess 11 and the environment surrounding the sensor device 20 (FIG. 7). In the embodiment of FIG. 2a, the capping wafer comprises a semiconductor base layer 13 in which openings 12 have been fabricated. A continuous porous layer 14 is arranged on top of the semiconductor base layer 13. The porous ceramic layer covers the openings and constitutes a gas permeable membrane. The parts of the porous ceramic layer 14 covering the openings 12 constitute gas permeable sections 14 providing a gas passage between the first side 9 and the second side 10. The recesses 11 and the openings may be fabricated using standard etching techniques. The porous ceramic layer may for example be made of alumina ceramics, silicon carbide ceramics, and zirconia oxide ceramics.
[0053] FIG. 2b shows a capping wafer 8 according to an alternative embodiment. In FIG. 2b, the openings 12 are filled with porous material. The porous material in the openings constitute gas permeable sections 14 between the first side and the second side 10, to provide a gas passage between the first side 9 and the second side 10. In FIG. 2c, the entire capping wafer 8 is of a porous material.
[0054] As an alternative to the gas permeable material being a porous material it is possible to use a non-porous polymer, wherein the polymer allows diffusion of gas through it, such as, e.g., polydimethylsiloxane, PDMS, which is well known to have a rather high diffusion coefficient of CO2, and polymethyl methacrylate, PMMA.
[0055] FIGS. 3a, 3b and 3c shows the capping wafers of FIGS. 2a, 2b, and 2c when a protective layer 15 has been applied on the second side 10 of the capping wafer 8. It is possible to apply a number of different protective layers.
[0056] FIGS. 4a, 4b, and 4c shows the device wafer 1 with the capping wafer 8 attached with the first side 9 of the capping wafer 8 on the device wafer 1 with each sensor 2 arranged below a recess 11 such that a cavity is formed between each recess 11 and the device wafer 1. The capping wafer 8 is in contact with the device wafer 1 in contact areas 16 arranged at the periphery of the recesses 11. In the embodiments of FIGS. 4a and 4b the contact areas completely encloses each recess 11, such that gas exchange is possible only through the gas permeable section 14. It would of course be possible to have also other gas permeable areas apart from the gas permeable sections 14, but the embodiments of FIGS. 4a and 4b the fabrication is facilitated. It has been described above that the polymer layer 15 is applied on the capping wafer 8 before the capping wafer 8 is attached to the device wafer 1, but the polymer layer 15 may alternatively be applied after the attachment of the capping wafer 8 on the device wafer 1. The polymer layer 15 may be applied in liquid form. After application of the polymer layer 15 the polymer layer 15 is heat-treated for curing to solidify the liquid polymer. Alternatively, a solid sheet of polymer may be applied by lamination. In case the protective layer is a metal layer it may be applied using any standard technique known to skilled persons, such as, e.g., sputtering.
[0057] In FIGS. 5a, 5b, and 5c it is illustrated how the device wafer 1 and the attached capping wafer 8 according to FIGS. 4a and 4b, respectively, are divided into individual sensor devices 20. The dividing process may be performed using a rotating saw blade 17 while applying cooling water to the saw blade 17. Alternatively, a laser may be used for the dividing. During dividing particles are formed. The polymer layer 15 prevents the particles and/or the water from passing through the porous gas permeable sections 14. After dividing the polymer layer is removed from all gas permeable sections 14. The removal may be performed by for example dissolving the polymer layer or by oxygen plasma treatment. FIG. 6 shows the sensor devices 20 after dividing and after dissolving of the polymer layer 15.
[0058] FIGS. 6a, 6b, and 6c illustrate the sensor devices 20 after dividing the device wafers and the attached capping wafers in FIGS. 5a, 5b, and 5c, respectively. In FIGS. 6a, 6b, and 6c, the polymer layer 15 has been removed. The sensor devices comprise a substrate 1 on which sensors 2 are arranged. The sensors 2 comprise a waveguide 4 which is supported on pillars/posts 5 extending from the substrate 1 to the waveguide 4, such that the waveguide 4 is free hanging between the pillars/posts 5. Each sensor 2 comprises a light source 6 in one end of the waveguide 4 and a photodetector 7 in the other end of the waveguide 4. A cap 8, comprising a gas permeable section 14, covers the substrate and the sensor 2. The light source 6 may be, e.g., a laser a light emitting diode, LED, or a resistive element. FIG. 7 shows a sensor device 20 according to FIGS. 6a, 6b, and 6c in a perspective view.
[0059] FIG. 8 is a flow diagram method for fabricating semiconductor based sensor devices comprising micro- and/or nanostructures, which are in communication with the environment surrounding the sensor devices of the method according to an embodiment of the invention. The flow diagram will be described with reference to FIGS. 1-4 described above. In a first step 101, a semiconductor based device wafer 1 is provided. In a second step 102, a plurality of sensors 2 comprising micro- and/or nanostructures are fabricated on different device areas 3 on the semiconductor based device wafer 1. In a third step 103 a capping wafer 8 comprising a first side 9 and a second side 10 and a plurality of recesses on the first side 9, is provided. In a fourth step 104 the first side of the capping wafer 11 is attached on the device wafer 1 with each sensor 2 arranged below a recess 11 such that a cavity is formed between each recess 11 and the device wafer 1. The capping wafer 8 is in contact with the device wafer 1 in contact areas 16 arranged at the periphery of the recesses 11. The capping wafer comprises at least one gas permeable section 14 between each recess 11 and the second side 10, to provide a gas passage between the recess 11 and the environment surrounding the sensor device 20. In a fifth step 105 a protective layer in the form of a polymer layer 15 is applied on all gas permeable sections 14 of the capping wafer 8. Steps 104 and 105 may be performed in the reverse order. The step of application of a polymer layer may comprise the step of heat treating a liquid polymer to solidify the polymer. In a sixth step 106, the device wafer 1 and the capping wafer 8 are divided into individual sensor devices 20. In a seventh step 107, the protective layer in the form of a polymer layer 15 is dissolved from the sensor devices 20.
[0060] The described embodiments may be amended in many ways without departing from the scope of the invention, which is limited only by the appended claims.
