DE4303423C2 - Sensor and method for its production - Google Patents

Description

The present invention relates to a sensor with a Semiconductor carrier body, which has a recess, one Recess at least partially spanning membrane or silicon nitride membrane and a semiconductor region arranged on the membrane or silicon nitride membrane comprehensive sensor structure according to the generic terms of the patent claims 1 and 2. Furthermore, the invention is concerned with Method for producing such sensors according to the Preamble of claims 12 and 13.

A large number of sensors, both mechanical sen sensors as well as thermal sensors have an im essential frame-like semiconductor support body, the one Has recess that completely or at least partially se is covered by a membrane. Is on this membrane arranged at least one sensitive structure that at least partially consists of semiconductor areas.

Such sensors are found in the case of mechanical sensors sor structures typically for pressure sensors, force sensors sensors, accelerometers and flow sensors. in the This basic structure is found in the case of thermal sensors structures in a so-called thermopile, as it is for example se for measuring the intensity of infrared radiation can be used, or with a bolometer.

In principle, the recess lies in such sensors of the semiconductor support body based on the front of the Semiconductor wafers from which the overall structure is formed, below the membrane, typically the recess from a silicon nitride mask on the back Back of the semiconductor wafer through the semiconductor wafer through to the front silicon nitride membrane stretches. The sensitive structure is regularly on the Side of the membrane facing away from the recess. The structures which are realized on this membrane front side, consist of either polysilicon or metal or  these two substances.

In the example, a thermopile are on the front the membrane, paired conductor tracks made of polysili zium and aluminum integrated, for example in Cover the central area of the membrane around which there is de temperature and to measure the intensity the infrared radiation to be measured.

In principle, it would be desirable to inscribe it on the membrane stalline silicon for such sensitive structures To have available which differs from polysilicon has the following advantages:

• - Single-crystal silicon has a high piezoresistive Coefficients, making it outstanding for education resistance measuring strips,
• - Single crystal silicon has one compared to poly silicon higher thermoelectric coefficients,
• - Single-crystal silicon is long-term stable and stable against high temperatures.

Techniques for producing single-crystalline ones already exist Silicon layers on insulators. This as SOI technology however, known method is complex and expensive. Furthermore, with this technology, the single-crystal silicon only Silicon oxide generated, which is not a membrane material is suitable.

U.S. Patent 3,758,830 discloses a sensor of the type mentioned in the preamble of claim 1, the in a thin semiconductor membrane that supports peripherally is, is formed. This has a single-crystalline semiconductor substrate, whose middle section is etched around a frame and the To form membrane. The known sensor also includes a sensor structure which is arranged on the membrane, wherein the sensor structure has a semiconductor region formed in the membrane.  

IEEE Transactions on Electron Devices, Vol. ED-33, 1986, No. 1, pages 72-77 a sensor of the type mentioned in the preamble of claim 2, namely a silicon thermopile. Here is the sensor structure on one of the Side of the membrane facing away from the recess.

DE 40 17 265 A1 discloses a micromechanical sensor, a semiconductor carrier body with a recess and has a membrane spanning this, the one with a mechanical-electrical Signal converter is equipped. The recess is one below the Membrane etched cavity. The detection of the deformation of the membrane is by applying piezoresistive resistors to the membrane certainly.

Based on this state of the art, this is the case the invention is therefore based on the object of a sensor type or method for manufacturing mentioned above set such a sensor to further develop that improved properties of the membrane on the sensor arranged sensor structure can be achieved.

This object is achieved by a sensor according to claim 1 and 2 and by methods of manufacturing a sensor solved according to claims 12 and 13.

The basic concept of the invention is to turn away from arrangement of the Sensor structure on the membrane, d. H. on the of the recess opposite side of the membrane. The invention sees that Sensor structure under the self-supporting membrane, i.e. on the the recess facing the semiconductor carrier body the membrane. Due to this reverse arrangement, it is in the  Contrast to that on which the prior art is based Technology possible, the semiconductor areas of the sensor structure structure made of a single-crystalline semiconductor material, preferably wise to produce from a single-crystal silicon.

Preferred developments of the sensor according to the invention or the manufacturing method according to the invention are specified in the subclaims.

Below are with reference to the accompanying Drawing preferred embodiments of the Invention according to the sensor and the method for producing it Exemplary embodiments explained in more detail. Show it:

Fig. 1 is a cross-sectional view through an example of the embodiment of the sensor according to the invention in the form of a thermopile;

FIG. 2a to 2c sectional views through a semiconductor wafer in the manufacture of a second exporting of the sensor according to the invention approximately example in the form of a Strömungsmeßsensors or pressure sensor;

Fig. 3 is a plan view of the second exemplary embodiment of the sensor; and

Fig. 4 is a cross-sectional view of a third exemplary embodiment of the sensor according to the invention produced by a different method.

The first exemplary embodiment of a sensor according to the principles of the present invention is designed as a thermopile and is designated in its entirety by reference number 1 . The water thermopile sensor 1 comprises a substantially frame-shaped semiconductor support body 2 , which consists of p-silicon in the embodiment shown here. The semiconductor carrier body 2 is spanned on the front side by a membrane 3 made of silicon nitride. The membrane 3 has a first through hole 4 in its central region and a further through hole 5 at the membrane edge region above the semiconductor carrier body 2 .

In the exemplary embodiment shown here in the form of a thermopile 1 , a sensor structure comprising a semiconductor region is formed by two conductor tracks, namely a metal track 6 arranged above the membrane on this and a monocrystalline, doped silicon conductor track 7 arranged on the underside of the membrane 3 on the water . In the embodiment shown here, the metal conductor 6 is made of aluminum and the silicon conductor is made of monocrystalline p⁺-silicon. The metal conductor 6 and the silicon conductor 7 are in contact with one another at the first through hole 4 . The metal conductor track extends from the first through hole 4 via the membrane 3 to a first contact point on the membrane above the semiconductor carrier body 2 , which can be formed by a bond pad 8 . The silicon conductor 7 runs below the membrane 5 from the first through hole 4 to the second through hole 5 , where it is connected to a further contact point 9 , which can be formed, for example, by an aluminum region within the second through hole 5 or another type of metal bond pad .

To manufacture this thermopile 1 according to FIG. 1, a mask is first applied to the front of a silicon wafer, which mask is structured by photolithography. A p⁺-doping is then introduced into the area of the later silicon conductor 7 by implantation or diffusion. After removing the mask, silicon nitride layers are deposited on the front and back of the silicon wafer. Starting from a rear window in the silicon nitride layer, which is defined by photolithography and etching, there is a free etching in KOH up to the etching stop, which is formed by the front silicon nitride membrane 3 on the one hand and the p⁺-doped silicon conductor 7 on the other hand.

With reference to FIGS . 2a to 2c, a manufacturing method and with reference to FIG. 3 a plan view representation of a second embodiment of a sensor is described which can be used as a flow sensor. With the first Ausführungsbei game just described parts are designated by the same reference numerals.

As can be seen from the plan view of FIG. 3, a frame-like semiconductor support body 2 made of silicon is also spanned by a membrane 3 made of silicon nitride, under which three silicon conductor tracks 7 a, 7 b, 7 c run, which pass through respective through holes of the membrane 3 above the frame-like semiconductor carrier body 2 to form bond pads 9 on the membrane surface. The three silicon tracks 7 a, 7 b, 7 c on the back of the membrane 3 facing the recess form a heating resistor 7 b and two temperature measuring resistors 7 a, 7 c, which are in terms of flow before or after the heating resistor 7 b. The three silicon conductor tracks 7 a, 7 b, 7 c lie on the back of the membrane which is not exposed to the flow, while the flow to be measured runs over the front of the membrane in the direction of arrow F.

To manufacture this sensor, an n or p-doped [100] silicon wafer is provided, on which in a first phototechnical step, crosses defined, which are then etched.

In a second phototechnical step, a front mask 10 is defined, whereupon an boron implantation for doping the later silicon conductor tracks 7 a, 7 b, 7 c with a doping of 3 × 10 ¹⁵ / cm ² takes place at an acceleration voltage of 30 keV. Subsequent healing of the doping regions takes place over a period of 60 minutes at 900 ° C.

A silicon nitride layer of 300 nm is now deposited in an LPCVD process (in a chemical low-pressure vapor deposition process). Here, the later front membrane 3 and a rear nitride mask 11 are formed . The rear mask 11 is structured in a third phototechnical step. Now there is a free etching in KOH up to the etching stop, which is formed by the p⁺-silicon conductor tracks 7 a, 7 b, 7 c or the membrane 3 . After defining the through holes in the nitride layer on the front side, contact is made by vapor deposition of aluminum.

In deviation from the manufacturing step described with reference to FIG. 2c, the p⁺-silicon conductor tracks 7 a, 7 b, 7 c can be contacted via a shadow mask from the rear. Contacting by laser deposition is also possible from the rear. The contact on the back, which represents the side of this flow sensor facing away from the flow, is advantageous in many applications.

In the manufacturing process shown in FIG. 2c, which leads to a front-side contacting of the p⁺-silicon conductor track, the sensor is suitable as a piezoresistive working pressure sensor. Here the deformation of the membrane 3 is measured by measuring the resistances of the conductor tracks 7 a, 7 b, 7 c.

Another process is identical to the manufacturing process just described up to and including the step of depositing silicon nitride. A third phototechnical step serves to define the openings for the conductor tracks on the front. Now aluminum is deposited on the front. In a fourth phototechnical step, conductor tracks and bond pads are defined, whereupon an aluminum etching is carried out. The fifth phototechnical step serves to open the back of the rear nitride mask 11 , whereupon the free etching takes place in KOH up to the etching stop on the membrane 3 or the p⁺ conductor tracks.

Such a pressure sensor is suitable for a measuring range of, for example, 5 mbar. The advantages of the so manufactured Pressure sensor versus a sensor with a silicon membrane bran and polysilicon resistors consist in that for a low measuring range of, for example, 5 mbar sili zium membranes are difficult to implement. Single crystal Silicon is better suited for piezoresistive measurement the membrane deformation as polysilicon, which ver compared with the single-crystal silicon lower piezo has resistive coefficients.

The further embodiment shown in cross section in FIG. 4, for example of a sensor according to the invention, is intended to illustrate a different manufacturing process. In this, a doped semiconductor layer is epitaxially grown on the front side of the wafer after the provision of the semiconductor wafer which forms the later semiconductor support body 2 . This is to define the later conductor tracks 7 a, 7 b, 7 c structured photolithographically and etching technically. Then the later membrane 3 is deposited, for example by LPCVD deposition of silicon nitride. After applying and defining the mask on the back, there is a free etching on the back, which can be done in KOH, for example.

Completely irrespective of the type of production method, the rear recess used in the described exemplary embodiments, which extends from the rear of the wafer 2 to the membrane 3 , can be replaced by a front-side etching recess. In this case, the rear nitride layer 11 is preferably left closed and the front nitride layer, which forms the membrane 3 , is provided with openings by means of a suitable photolithography and etching technique, from which a front undercutting of the membrane with KOH takes place until the etching stop , which is formed by the p⁺-silicon conductor tracks.

The sensor according to the invention is suitable for all types thermal sensors, namely for flow sensors, Vacuum sensors, sensors for catalytic gas measurement, Thermal conductivity sensors, infrared radiation sensors, UV radiation sensors, sensors for measuring the change power output, dew point sensors and sensors for detection the mass occupancy.

Pressure sensors, force sensors come as mechanical sensors and acceleration sensors.

In deviation from the silicon technology described can of course also use other semiconductor materials including the compound semiconductors.

In deviation from the described photolithographic Laser processes are also considered, one Allow partial diffusion without a mask.  

The temperature sensor described can deviate in this regard delt that a instead of a resistance measuring strip Diode for temperature measurement or a tempera transistor serving for measurement below the membrane below Inclusion of the monocrystalline semiconductor area pre see is.

Instead of a strip-shaped measuring resistor, the includes monocrystalline semiconductor area, also comes So-called distributed resistance, which is flat over the Extends membrane, and for example in its mid-be is richly contacted.

In the described preferred embodiments de the semiconductor area of the sensor structure with a p⁺-Do tation provided in the subsequent etching step as Etching stop serves. Any other doping jump between the later semiconductor area of the sensor structure and the semiconductor region to be removed by etching can be used in Use of electrochemical etching processes. The doping jump can also be generated by this that the semiconductor region to be removed is doped, during the later semiconductor area of the sensor structure remains undoped.

Claims (19)

1. Sensor comprising a semiconductor support body (2) having a recess at least partially arranged with a recess spanning the membrane (3) and one on the membrane (3), a semiconductor region (7) comprising sensor structure (6, 7), characterized in that the semiconductor region ( 7 ) of the sensor structure ( 6 , 7 ) is arranged on the side of the membrane ( 3 ) facing the recess. 2. Sensor with a semiconductor support body ( 2 ) which has a recess, with a silicon nitride membrane ( 3 ) at least partially spanning the recess and with a semiconductor region ( 7 ) arranged on the silicon nitride membrane ( 3 ) comprehensive sensor structure ( 6 , 7 ), characterized in that the semiconductor region ( 7 ) of the sensor structure ( 6 , 7 ) is arranged on the side of the silicon nitride membrane ( 3 ) facing the recess. 3. Sensor according to claim 1 or 2, characterized in that the sensor structure (6, 7) comprises a monocrystalline silicon doped region (7). 4. Sensor according to any one of claims 1 to 3, characterized in that the sensor structure (6, 7) a p + silicon region comprises (7). 5. Sensor according to one of claims 1 to 4, characterized in that
that the sensor is a thermopile
that the membrane ( 3 ) has a first through hole ( 4 ), and
in that the sensor structure ( 6 , 7 ) comprises a monocrystalline semiconductor conductor track ( 7 ) which is arranged on the side of the membrane ( 3 ) which extends up to the first through hole ( 4 ), and also one on which the recess facing away from the membrane arranged metal conductor track ( 6 ), which also extends to the first through hole ( 4 ) it stretches and here adjoins the monocrystalline semiconductor conductor track ( 7 ). 6. Sensor according to claim 5, characterized in
that the first through hole ( 4 ) is arranged in the central region of the membrane ( 3 ),
that the metal conductor track ( 6 ) extends from the first through hole ( 4 ) over the membrane ( 3 ) to an above the semiconductor support body ( 2 ) on the membrane ( 3 ) lying connection point ( 8 ), and
that the monocrystalline, doped semiconductor conductor track ( 7 ) extends from the first through hole ( 4 ) via the membrane ( 3 ) to a second through hole ( 5 ) of the membrane ( 3 ), which extends above the semiconductor support body ( 2 ) is located, through which ( 5 ) the monocrystalline semiconductor conductor track ( 6 ) is connected to a further connection point ( 9 ). 7. Sensor according to one of claims 1 to 4 or 5, characterized in that
that the sensor is a temperature sensor, and
that the sensor structure comprises at least one monocrystalline semiconductor ( 7 a, 7 b, 7 c) which detects the temperature of the membrane ( 3 ). 8. Sensor according to claim 7, characterized in
that the membrane ( 3 ) has two through holes, both of which are arranged above the semiconductor support body ( 2 ), and
that the semiconductor strip ( 7 a, 7 b, 7 c) extends from one through hole to the other through hole and is connected there to connection points. 9. Sensor according to one of claims 1 to 8, characterized in
that the membrane ( 3 ) consists of silicon nitride, and
that the semiconductor support body ( 2 ) consists of silicon. 10. Sensor according to one of claims 1 to 8, characterized in that the recess is a rear etching recess which extends through the semiconductor support body ( 2 ) from the back of the membrane ( 3 ) facing away to the membrane ( 3 ). 11. Sensor according to one of claims 1 to 9, characterized in that the recess is one of perforations of the membrane ( 3 ) or of perforations of a front etching mask from under the membrane ( 3 ) extending front side etching recess. 12. A method for producing a sensor according to claim 1, characterized by the following method steps:

• - Providing a semiconductor wafer;
• Generating a doping jump between the later semiconductor region of the sensor structure and a semiconductor region to be removed by etching, starting from the front side of the semiconductor wafer;
• - Front application of the later membrane; and
• - Etching a recess below the membrane, which extends up to the membrane and to the semiconductor region of the sensor structure, which is arranged on the side of the membrane facing the recess, to form the semiconductor carrier body.

13. A method for producing a sensor with a semiconductor carrier body which has a recess, with a membrane which at least partially spans the recess and with a sensor structure which is arranged on the membrane and comprises a semiconductor region, characterized by the following method steps:

• - Providing a semiconductor wafer;
• epitaxially growing a semiconductor layer on the front of the wafer;
• - Structuring the semiconductor layer to define the semiconductor region of the sensor structure;
• - Front application of the later membrane; and
• - Etching a recess below the membrane, which extends up to the membrane and to the semiconductor region of the sensor structure, which is arranged on the side of the membrane facing the recess, to form the semiconductor carrier body.

14. The method according to claim 12, characterized in that the method step of doping comprises the following sub-steps

• - Creating a mask layer on the semiconductor layer;
• - photolithographic definition of the mask; and
• - Implantation and / or diffusion of dopants.

15. The method according to claim 13, characterized in that the structuring step comprises the following substeps:

• - Creating a mask layer on the semiconductor layer;
• - photolithographic definition of the mask; and
• - Implantation and / or diffusion of dopants.

16. The method according to claim 13, characterized in
that the epitaxially grown semiconductor layer is a doped semiconductor layer, and
that the structuring step comprises the following substeps:

• - Generating a mask layer on the doped semiconductor layer;
• - photolithographic definition of this mask layer; and
• - Front-side etching away of unmasked parts of the doped semiconductor layer.

17. The method according to any one of claims 12 to 16, characterized featured, that the recess is based on back etching is generated by a back etching mask. 18. The method according to any one of claims 12 to 16, characterized featured, that the recess is based on front-side etching of breakthroughs in the membrane or a front side gen etching mask is generated. 19. The method according to claim 12, characterized in that the step of applying the membrane is carried out before doping the later semiconductor region of the sensor structure, and
that the doping of the semiconductor region is carried out through the membrane.