WO2008113707A1

WO2008113707A1 - Pressure sensor chip

Info

Publication number: WO2008113707A1
Application number: PCT/EP2008/052825
Authority: WO
Inventors: Dieter Stolze; Anh Tuan Tham
Original assignee: Endress+Hauser Gmbh+Co.Kg
Priority date: 2007-03-22
Filing date: 2008-03-10
Publication date: 2008-09-25
Also published as: DE102007014468A1

Abstract

The invention relates to a pressure sensor chip having as many applications as possible and being used for measuring differential pressure, said chip being usable at high temperatures, comprising a substrate (1) made of silicon, an oxide layer (3) disposed on the substrate (1), a silicon layer (5) disposed on the oxide layer (3), an insulating layer (7) disposed on the silicon layer (5), and a recess (9) provided in the substrate (1), said recess exposing a region of the adjacent composite comprising the oxide layer (3), silicon layer (5), and insulating later (7) to form a differential pressure measurement membrane (11), the deflection of said membrane, which is dependent upon the differential pressure acting thereon, being detected by at least one piezoresistive element (13) disposed on the side of the insulating layer (7) of the differential pressure measurement membrane (11) facing away from the recess (9).

Description

description

Pressure sensor chip

The invention relates to a pressure sensor chip for measuring a differential pressure.

Differential pressure sensors are used to detect a pressure difference between a first and a second pressure acting on the sensor and are used for example in industrial metrology pressure gauges. There they are used for example for level measurement or flow measurement. In the case of level measurement, for example, the difference between a first pressure acting down in a container and a second pressure prevailing above the contents is measured. The difference is proportional to a level-dependent hydrostatic pressure in the tank and thus to the level. In the flow measurement, for example, a flow resistance is used in a line and determined by means of a Differenzdruckmessaufnehmers a difference of a prevailing before the first resistance and a pressure prevailing behind the resistance second pressure. This differential pressure is a measure of the flow through the pipe.

There are a variety of industrial applications in which extreme demands are placed on the differential pressure sensors. You should e.g. to be capable of very small differential pressures, e.g. Differential pressures of less than 30 mbar, at high temperatures, esp. To measure at temperatures of more than 125 ° C with high accuracy and long-term stability.

Frequently, it is important to measure these small differential pressures at high system pressures, esp. At system pressures of more than 100 bar. System pressure here refers to the outlet pressure to which the pressure difference is superimposed. For example, the system pressure is the lower of the two pressures whose difference is to be measured.

Semiconductor chips, eg silicon chips with doped piezoresistive elements, are used as pressure-sensitive elements in pressure measurement technology. such Differential pressure sensor chips comprise a differential pressure measuring diaphragm, one side of which is subjected to a first pressure during measuring operation and the second side to a second pressure. The applied pressures cause a resulting deflection of the differential pressure measuring diaphragm, which corresponds to the differential pressure to be measured. Pressure sensor chips are usually very sensitive and are therefore not directly exposed to a medium whose pressure is to be recorded. Instead, with a liquid filled diaphragm seals are connected upstream.

A force acting on the measuring diaphragm differential pressure causes a differential pressure dependent deflection of the differential pressure measuring diaphragm, which detects by means of the piezoresistive elements, and converted into an electrical signal that is then a further processing and / or evaluation available.

Semiconductor sensors are now regularly silicon-based, e.g. manufactured using silicon-on-insulator (SOI) technology. Among other things, BESOI wafers (bonded and etched silicon on insulator) are used as starting material. BESOI wafers are manufactured using silicon direct bonding. For this purpose, for example, two oxidized silicon wafers are aligned against each other and bonded under pressure and high temperature. This results in a three-layered wafer, in which there is an oxide layer between two silicon layers. The buried oxide layer known as BOX (buried oxide layer) has a thickness of a few nm to a few μm. This composite is thinned and polished from one side. The thinned polished side subsequently forms the active layer. The active layer may be a few microns thick and is known in the English speaking art e.g. referred to as device wafer or as silicone overlayer (SOL). The thickness of the active layer can already be produced very accurately and uniformly and with high reproducibility using today's production methods.

A major advantage of using BESOI wafers for the manufacture of pressure sensors is that the buried Oxide layer (BOX) forms a reliable etch stop. This is used primarily for the production of movable electrodes of capacitive pressure sensors.

However, methods are also known in which BESOI wafers are used for the production of piezoresistive pressure sensors.

Such a method is described in the Journal of

Micromechanical Engineering, Volume 10, pages 204-208, published article: 'Optimized technology for the fabrication of piezoresistive pressure sensors', described by A. Merlos, J. Santander, M.D. Alvares and F. Campabadal. There it was shown that with BESOI wafers it is possible to produce sensor chips which have a precisely defined membrane thickness which is constant over the entire area of the membrane. Esp. Piezoresistive sensors with very thin membranes with the smallest thickness tolerances of less than 1 μm can be produced. For this purpose, a recess is etched into the silicon layer opposite the active layer, via which the membrane is exposed. The buried oxide layer serves as etch stop. The remaining after the etching outer edge of the silicon layer bounds the recess on the outside and forms a support for the exposed through the recess membrane. After this etching process, the area of the oxide layer serving as an etching stop is removed by a further etching process.

In conventional pressure sensor chips, the piezoresistive elements are for example a positive doping elements, which are applied to a silicon layer having a negative doping. As a result, there is a pn junction between the p-doped piezoresistive elements and the silicon layer, which results in that the temperature range in which these pressure sensor chips can be used is limited. Typically, above temperatures of about 125 ° C sufficient electrical insulation between the piezoresistive elements and the substrate on which they are arranged is no longer guaranteed.

It is an object of the invention as versatile as possible Specify piezoresistive pressure sensor chip for measuring differential pressures, which can be used at high temperatures. Another

The object of the invention is a process for the preparation of this

Specify pressure sensor chips. For this purpose, the invention consists in a pressure sensor chip for measuring a differential pressure with [0014] a carrier made of silicon, an oxide layer arranged on the carrier, a silicon layer arranged on the oxide layer, [0017] ] - an insulating layer arranged on the silicon layer, and - a recess provided in the support which exposes a region of the oxide pressure layer, silicon layer and insulating layer which adjoins [0019] a differential pressure measuring membrane, - whose deflection, which is dependent on a differential pressure acting on it, is detected by at least one piezoresistive element, in that on the side of the insulating layer of the differential pressure measuring diaphragm facing away from the recess is arranged. [0025] According to a first development of the invention, the

Pressure sensor chip additionally designed as a system pressure sensor

Area on where

[0026] on the support of silicon the oxide layer is arranged, [0027] on the oxide layer the silicon layer is arranged, [0028] on the silicon layer the insulating layer is arranged, and [0029] in the oxide layer one of the Differential pressure measuring membrane spaced recess is provided, which on its [0031] side facing away from the carrier of a one

System pressure measuring diaphragm

[0032] The forming region of the composite of silicon layer and insulating layer [0033] is completed, and its dependent on a system pressure acting thereon

deflection

Is detected by at least one piezoresistive element that on the [0036] side facing away from the recess side of the insulating layer of [0037] System pressure measuring membrane is arranged.

According to one embodiment of the first development extends through the oxide layer, the silicon layer and the insulating layer, a section through which the differential pressure measuring membrane is mechanically decoupled from the system pressure measuring diaphragm.

According to a further development of the first development, the system pressure measuring diaphragm has a cylindrical opening arranged in its center, which is closed by a plug which extends through the opening and the recess in the oxide layer to the carrier and a spacer between the carrier and the system pressure measuring diaphragm forms.

According to a preferred embodiment, an electronics is arranged on the side facing away from the carrier top of the pressure sensor chip, to which the arranged on the insulating layer piezoresistive elements are connected.

According to a development of the latter development, the piezoresistive elements for measuring the differential pressure and / or the piezoresistive elements for measuring the system pressure are each connected together to form a resistance bridge, and the electronics is used to a temperature that is exposed to the pressure sensor chip based derive an internal resistance of at least one resistance bridge and to provide compensation for temperature-dependent measurement error.

Furthermore, the invention consists in a method for producing a pressure sensor chip according to the invention, in which

A first and a second silicon layer and a

Interposed oxide layer BESOI wafer

Is used

[0046] the first silicon layer forms a support of silicon,

In the second silicon layer by implantation of ions and

Subsequent annealing an insulating layer is generated, which is a

Is covered overlying silicon film,

[0050] Piezoresisitive arranged from the silicon film on the insulating layer Elements are generated

- In the carrier a recess is etched, the one

Differential pressure measuring membrane forming region of the adjacent thereto

Composite of oxide layer, silicon layer and insulating layer exposed,

[0055] - their dependent on a differential pressure acting on it

Deflection detected by at least one of the piezoresistive element

Is that on the side remote from the recess side of the

insulating

[0058] The differential pressure measuring diaphragm is arranged. The invention further comprises a first development of the method according to [0060] - in a region of the distance from the differential pressure measuring diaphragm

[0063] Pressure sensor chip is formed a cylindrical opening which penetrates the insulating layer and the silicon layer, - through the opening a recess spaced from the differential pressure measuring membrane [0064] is etched into the oxide layer, which is referred to [0065] FIG ] whose side facing away from the carrier is closed by a region of the composite of silicon layer and insulating layer which forms a system pressure measuring membrane, the temperature of which depends on a system pressure acting on it

deflection

Is detected by at least one piezoresistive element, that on the side facing away from the recess side of the insulating layer of the system pressure measuring membrane is arranged, and - the opening is closed under vacuum.

According to a development of the silicon film piezoresisitive elements are generated by the silicon film is doped by implantation of ions, and a structuring of the doped silicon film is made in which only serving as piezoresistive elements regions of the doped silicon film remain on the insulating layer. [0074] According to a development of the first development of the method the cylindrical opening is sealed under vacuum by deposition of at least one material, wherein a plug is built from the material, which extends through the opening and the recess in the oxide layer to the carrier and forms a spacer between the carrier and the system pressure measuring membrane.

[0075] According to a further development, at least one

Deposition process carried out, in which at least one layer 33 of an insulating material on the side facing away from the carrier 1 surface of the pressure sensor chip with the piezoresisitive elements 13, 19 thereon is deposited, which is a primary passivation of the top of the pressure sensor chip and the thereon Piezoresistive elements causes.

The pressure sensor according to the invention has the advantage that it can be used at high temperatures of up to 250 ° C. One reason for this is that the piezoresistive elements are electrically insulated by the insulating layer from the substrate on which they are located. The insulation layer provides reliable insulation even at high temperatures of up to 250 ° C.

A further advantage is that the oxide layer arranged on the carrier serves as a reliable etch stop in the production of the recess through which the differential pressure measuring membrane is exposed. As a result, in particular thin differential pressure measuring membranes can be produced with a very homogeneous thickness over the entire surface of the membrane. This means that even very small differential pressures, esp. Differential pressures of less than 30 mbar can be detected with the pressure sensor chip of the invention high accuracy and reproducibility.

The invention and its advantages will now be explained in more detail with reference to the figures of the drawing, in which two embodiments are shown. Identical elements are provided in the figures with the same reference numerals.

Fig. 1 shows a section through a differential pressure sensor

[0080] having a pressure sensor chip; Fig. 2 shows a section through a differential pressure sensor and a

System pressure sensor comprising pressure sensor chip; FIG. 3 is a view of the pressure sensor chip of FIG. 2; FIG. Fig. 4 shows a section through a BESOI wafer with a thinned [0085] silicon layer; Fig. 5 shows an implantation of an insulating layer, which is a thin

Silicon film is covered;

Fig. 6 shows a doping of the silicon film of Fig. 5 with boron; FIG. 7 shows a surface of the pressure sensor chip structured to produce the piezoresistive elements; FIG. Fig. 8 shows a recess in the carrier through which the

Differential pressure measuring membrane is exposed; Fig. 9 shows one for generating the system pressure measuring membrane in the

chip

[0092] introduced opening;

Fig. 10 shows a recess etched through the aperture in the oxide layer, through which the system pressure sensing membrane is exposed;

Fig. 11 shows a stopper closing the opening and a layer of insulator applied on the pressure sensor chip; and FIG. 12 shows a metallization applied to the pressure sensor chip, which causes electrical connection of the piezoresistive elements and forms contact pads for contacting the elements interconnected [0101]. Fig. 1 shows a pressure sensor chip according to the invention. Of the

Pressure sensor chip is a differential pressure sensor that can be used in particular for measuring low differential pressures, in particular of differential pressures of less than 30 mbar, at high temperatures, in particular at temperatures of up to 250 ° C. FIG. 2 shows a section through a further development of the

Pressure sensor chips of Fig. 1. Fig. 3 shows a view of the top of the

Pressure sensor chips of Fig. 2. This is a multifunctional pressure sensor chip, especially for measuring low differential pressures, in particular of differential pressures of less than 30 mbar, at high system pressures, in particular at system pressures of more than 100 bar, at high temperatures, in particular at temperatures of up to 250 ° C is usable. For this purpose, the pressure sensor chip comprises a region I designed as a differential pressure sensor and a region II designed as a system pressure sensor.

The area I designed as a differential pressure sensor is identical to the differential pressure sensor shown in FIG. In the following, therefore, only the pressure sensor chip shown in FIGS. 2 and 3 will be described in detail. The description contained therein of the area I designed as a differential pressure sensor apply in identical form to the pressure sensor chip shown in FIG. 1 and is therefore not listed twice. The same applies in analogous form for the associated manufacturing process described below.

Since the pressure sensor chip shown in Figs. 2 and 3 both a

Differential pressure sensor and a system pressure sensor, it is very versatile. The integration of these two sensors in a single pressure sensor chip has the advantage that it is very compact and allows a compensation of system pressure dependent measurement errors of the differential pressure sensor. As a result, the measurement accuracy that can be achieved with the differential pressure sensor, which can greatly depend on the system pressure, especially when measuring low differential pressures at high system pressures, can be significantly increased.

The pressure sensor chip has a carrier 1 made of silicon, on which an oxide layer 3 is arranged. The carrier 1 is preferably a monocrystalline substrate with negative doping. Alternatively, however, it is also possible to use a monocrystalline substrate without doping or with positive doping. The oxide layer 3 is made of silicon dioxide (SiO ₂ ). On the oxide layer 3 is another silicon layer 5, which preferably also has a negative doping. Alternatively, a monocrystalline substrate without doping or with positive doping can also be used here. On the Silicon layer 5, an insulating layer 7 is arranged, which preferably also consists of silicon dioxide (SiO ₂ ).

In the carrier 1 is formed in the as a differential pressure sensor

Region I of the pressure sensor chip, a recess 9 is provided which exposes a differential pressure measuring diaphragm 11 forming region of the adjacent thereto composite of oxide layer 3, silicon layer 5 and insulating layer 7. In measuring operation, the differential pressure measuring diaphragm 11 is exposed to a differential pressure, which causes a differential pressure-dependent deflection of the differential pressure measuring diaphragm 11. For this purpose, a first pressure p1 of the side facing away from the carrier 1 side of the differential pressure measuring diaphragm 11 is supplied. A second pressure p 2 is supplied through the recess 9 of the side facing the carrier 1 of the differential pressure measuring diaphragm 11. The differential pressure to be measured corresponds to the difference between the first and the second pressure p1, p2. The force acting on the differential pressure measuring diaphragm 11 differential pressure dependent deflection of the differential pressure measuring diaphragm 11 is detected by at least one piezoresistive element 13 that is arranged on the side facing away from the recess 9 side of the insulating layer 7 of the differential pressure measuring diaphragm 11.

The insulating layer 7 causes an electrical insulation of the piezoresistive elements 13 with respect to the underlying silicon layer 5. This makes it possible to use the pressure sensor chip at high temperatures, esp. At temperatures up to 250 ° C.

Preferably, a plurality of piezoresistive elements 13 are provided for this purpose, which are interconnected to form a Wheatstone bridge. FIG. 3 shows four piezoresistive elements 13, which are shown here only schematically, and which are combined by a connection, not shown in the figures, to form a Wheatstone bridge. Wheatstone bridges have a temperature-dependent internal resistance, which can be determined via corresponding taps on the differential pressure measuring diaphragm 11, in a simple manner. This temperature-dependent internal resistance is then available Determining the temperature that is exposed to the pressure sensor chip is available. Based on the temperature compensation of temperature-dependent measurement errors of the differential pressure sensor can then be made. Likewise, based on the temperature compensation of temperature-dependent measurement errors of the system pressure sensor can be made.

[0110] The system pressure sensor is located in the second area II of the

Pressure sensor chips. To form the system pressure sensor, in the second region II of the pressure sensor chip in the oxide layer 3, a recess 15 is provided which is spaced from the differential pressure measuring diaphragm 11 and which faces away from the carrier 1 from a region of the composite of silicon layer 5 and forming a system pressure measuring diaphragm 17 Insulating layer 7 is completed. The system pressure p _sys to be measured is supplied to the side facing away from the carrier 1 side of the system pressure measuring diaphragm 17, and causes a system pressure p _sys dependent deflection thereof. For detecting this deflection, at least one piezoresistive element 19 is likewise provided, that is arranged on the side of the insulating layer 7 of the system pressure measuring membrane 17 facing away from the recess 15.

Again, the insulating layer 7 causes an electrical insulation of the piezoresistive elements 19 with respect to the underlying silicon layer 5, which makes it possible to use the pressure sensor chip at high temperatures, esp. At temperatures up to 250 ° C.

Preferably, a plurality of piezoresistive elements 19 are also provided here, which are interconnected to form a Wheatstone bridge. FIG. 3 shows four piezoresistive elements 19, which are shown here only schematically, and which are connected together by a connection, not shown in the figures, to form a Wheatstone bridge. Again, the temperature dependent internal resistance of the Wheatstone bridge can be detected and used to determine the temperature to which the pressure sensor chip is exposed. As a rule, it is sufficient to determine the temperature on the basis of one of the two pressure sensors integrated on the pressure sensor chip and for all desired compensations of temperature-dependent measuring errors.

Preferably, in the pressure sensor chip a through the oxide layer 3, the silicon layer 5 and the insulating layer 7 extending section 21 is provided, through which the differential pressure measuring diaphragm 11 is mechanically decoupled from the system pressure measuring diaphragm 17. In the illustrated embodiment, the section 21 is a longitudinal section, which separates the two regions I, Il of the pressure sensor chip from each other and leads into the carrier 1 into it.

The system pressure measuring diaphragm 17 has a cylindrical opening disposed in the center thereof, which is closed by a plug 23 made of an insulator. The plug 23 extends through the opening and the recess 15 in the oxide layer 3 through to the carrier 1 and forms a spacer between the carrier 1 and the system pressure measuring diaphragm 17. Through this plug 23, the system pressure measuring diaphragm 17 is a rigid annular membrane, which is also at low Membrane thickness is able to take very high system pressures, for example system pressures of more than 100 bar. This offers the advantage that the thicknesses of the differential pressure measuring diaphragm 11 and the system pressure measuring diaphragm 17 can be identical even up to the thickness of the oxide layer 5, if the differential pressure measuring diaphragm 11 is designed for low differential pressures, especially for differential pressures of less than 30 mbar, and System pressure measuring diaphragm 17 for the detection of high system pressures, esp. Of system pressures of up to 100 bar, is designed. For this purpose, for example, in the case of a membrane thickness for differential pressure and system pressure measuring diaphragm in the order of magnitude of 10 μm, a differential pressure measuring diaphragm 11 with a size of 4 mm × 4 mm can be combined with a system pressure measuring diaphragm 17 with a diameter of 0.5 mm.

Preferably, an electronics 25 is arranged on the side facing away from the carrier 1 top of the pressure sensor chip, to which the piezoresistive elements 13 for measuring the differential pressure and the piezoresistive elements 19 for measuring the system pressure are connected. In the simplest case, this electronics 25 is a simple amplifier circuit that processes the measurement signals for further processing and / or evaluation and provides them via a corresponding output. But it can also contain other signal processing and / or evaluation circuits. Examples include a circuit which is the temperature of the chip is exposed, based on the internal resistance of the Wheatstone bridge, and circuits for compensating temperature-dependent measurement errors of the two sensors and circuits for compensating a system pressure dependent measurement error of the differential pressure sensor.

The invention further comprises a method for producing a pressure sensor chip according to the invention. This is explained in detail below with reference to the pressure sensor chip shown in FIGS. 2 and 3 for measuring the differential pressure and the system pressure. Since the pressure sensor chip of FIG. 1 is part of this embodiment, this description also contains the description of the corresponding manufacturing method for the pressure sensor chip according to the invention shown in FIG. 1, which exclusively comprises the differential pressure sensor. The production of this pressure sensor chip is therefore not listed again separately.

The pressure sensor chip of the present invention is a silicon based semiconductor chip fabricated using silicon-on-insulator (SOI) technology. The starting material is a commercially available BESOI wafer (bonded and etched silicon on insulator). BESOI wafers are made from two oxidized silicon wafers, which are aligned and bonded under pressure and high temperature. This results in a three-layer wafer shown in FIG. 4, which has a first and a second silicon layer. Both layers have, for example, a negative doping and are designated in FIG. 4 with n-Si1 and n-Si2. The negative doping can be achieved for example by phosphorus. Alternatively, the two layers but also a positive doping or even have no doping.

Between the first and the second silicon layer n-Si1, n-Si2 is the oxide layer 3. The known under the name BOX (buried oxide layer) buried oxide layer 3 has a thickness of a few nm to a few microns and consists for example made of silicon dioxide SiO ₂ .

This composite is thinned and polished from one side. The thinned polished side, here the second layer n-Si2, is described in the English-speaking art e.g. referred to as silicone overlayer (SOL) and may have a thickness of a few nm to a few microns. The thickness of this layer can already be produced very accurately and uniformly and with high reproducibility using today's production methods.

The first silicon layer n-Si1 forms the carrier 1 of the pressure sensor chip.

Subsequently, in the thinned polished second silicon layer n-Si 2, by implanting ions and then annealing, the insulating layer 7 and an overlying thin monocrystalline silicon film 27 covering the insulating layer 7 are formed. The implantation of the ions is shown in FIG. 5 by arrows. For this purpose, for example, oxygen or nitrogen ions with a high dose, esp. A dose of 10 16 to 10 ¹⁸ ions / cm ² , in the n-doped monocrystalline silicon {100} - orientation of the second silicon layer n-Si2 implanted. The implantation energy is preferably between 100 keV and 1000 keV. Subsequently, the structure is tempered at a temperature of 1150 ° C to 1400 ° C. Implantation and subsequent annealing can be repeated several times. This results in the formation of an insulating layer 7 of silicon dioxide or silicon nitride arranged on the silicon layer 5, which is covered by the thin silicon film 27. Oxygen implantation is known by the name Separation by implantation of oxygen (SIMOX). The SIMOX technology makes it possible to produce the thin silicon film 27 with a thickness which can be precisely set and reproduced to within 5 nm. The thickness of the silicon film 27 is preferably less than 500 nm.

In a next step, the thin silicon film 27 becomes the piezoresistive elements 13, 19 generates. This is preferably done by doping the silicon film 27 in a first operation by implantation of ions. In the described embodiment with a negatively doped silicon layer 5, a positive doping is carried out in the silicon film 27 located on the insulating layer 7. This can be done, for example, as shown in Fig. 6 symbolically by arrows, by the implantation of boron. This results in the thin silicon film 27, a homogeneous layer 29 with uniform positive doping.

Alternatively, if a positively doped silicon layer was used, a homogeneous layer with uniform negative doping is generated when the piezoresistive elements are produced from the thin silicon film 27. For an undoped silicon layer, both a positive and a negative doping of the layer can be used. Investigations have shown, however, that pressure sensors with positively doped piezoresistive elements on negatively doped substrates have a lower linearity error, and are therefore to be preferred.

After the doping, a structuring of the homogeneous layer 29 is carried out, in which only the areas of the layer 29 serving as piezoresistive elements 13, 19 remain on the insulating layer 7. The remaining areas of the layer 29 are removed during structuring. The structuring takes place for example by means of dry etching. For this purpose, for example, a plasma etching, as it is known for example under the name Reactive Ion Etching (RIE). The remaining on the insulating layer 7 piezoresistive elements 13, 19 are shown in Fig. 7. The temperature coefficients of the resistances of these piezoresistive elements 13, 19 and the temperature coefficients of the piezoresistive constants of the piezoresistive elements 13, 19 are decisively determined by the dose used for the last implantation, here the boron. Preferably, the dimensions of the piezoresistive elements 13, 19 are selected as a function of these parameters. As a result, a desired resistance of the piezoresistive element 13, 19 can be targeted be set. The insulating layer 7, which is arranged between the p-doped piezoresistive elements 13, 19 and the n-doped silicon layer 5, effects a very effective insulation of the piezoresistive elements 13, 19 that is effective even at high temperatures. Because of this insulation, it is possible to use the invention Pressure sensor chip at very high temperatures, especially at temperatures of up to 250 ° C and more to use. Investigations have shown that the insulation even withstands temperatures of up to 400 ° C.

In a next operation illustrated in FIG. 8, the

Differential pressure measuring diaphragm 11 produced. For this purpose, the recess 9 is etched into the carrier 1. For this purpose, for example, an anisotropic wet-chemical etching method, in particular using a KOH etching solution, can be used. The buried oxide layer 3 of the BESOI wafer serves as a reliable etch stop. This offers the advantage that the differential pressure measuring membranes 11 can be produced reliably and reproducibly with a predetermined thickness, and the thickness of the differential pressure membranes 11 has only the smallest tolerances, esp. Thickness deviations of less than one μm, over their total area. Thinner differential pressure measuring membranes 11 provide a higher sensitivity for the same size. Due to the achievable precision in the production of the membrane thickness, it is thus possible to produce the differential pressure measuring membrane 11 thinner and also smaller, with a certain required sensitivity, and thereby to achieve a cost saving.

As a result of the etching process, the region of the adjacent composite of oxide layer 3, silicon layer 5 and insulating layer 7 that forms the differential pressure measuring diaphragm 11 is uncovered. In measuring operation, a deflection of the differential pressure measuring membrane 11 which is dependent on a differential pressure acting thereon is detected by at least one of the piezoresistive element 13 as described above in connection with the pressure sensor chip according to the invention with reference to FIG. 2, that on the side facing away from the recess 9 Side of the differential pressure measuring diaphragm 11 is arranged. The same is true, of course also for the pressure sensor chip shown in Fig. 1.

Subsequently, the system pressure sensor is generated in the second area II.

Among other things, process steps are carried out as described in similar form in US-A 5,510,276. US-A 5 510 276 relates to a piezoresistive pressure sensor chip and related manufacturing method. Starting material there is a silicon substrate with negative doping, in the top side by an implantation of oxygen ions and subsequent annealing an oxide layer is introduced, which is covered by a silicon film. On the silicon film is epitaxially deposited another silicon layer with negative doping. Subsequently, the piezoresistive elements are produced by forming in the regions of the further silicon layer, which subsequently form the piezoresistive elements, a positive doping limited to these regions, e.g. by boron, is introduced. This results in a pn junction between the piezoresistive elements and the further silicon layer. Subsequently, an opening is created which leads through the further silicon layer and the silicon film to the oxide layer. Through this opening, a recess is etched into the oxide layer, which is closed on its side facing away from the substrate from an absolute pressure measuring diaphragm forming region of the composite of the silicon layer and the further silicon layer. Subsequently, the opening is sealed under vacuum by deposition of a material, wherein a plug is built from the material, which extends through the opening and the recess in the oxide layer to the substrate and forms a spacer between the substrate and the absolute pressure measuring diaphragm. It is described to construct the plug of successively deposited layers of silicon dioxide (SiO 2) and silicon nitride (Si 3 N 4).

In the case of the pressure sensor chip according to the invention described here, a cylindrical opening 28 is created in a region II of the pressure sensor chip which is at a distance from the differential pressure measuring diaphragm 11 and penetrates the insulating layer 7 and the silicon layer 5. This is shown in FIG. 9. The opening 28 is centered between the for measuring the System pressure p _sys provided piezoresistive elements 19 arranged. For example, classical photolithography methods which are preferably used in conjunction with a plasma etching or an ion etching, for example a reactive ion etching (RIE), are suitable for the production of the opening 28. In this case, the buried oxide layer 3 of the BESOI wafer, just as in the generation of the differential pressure measuring membrane 11 exposing recess 9, serves as an etch stop.

In a next operation, a recess 29 spaced from the differential pressure measuring diaphragm 11 is etched into the oxide layer 3 through the opening 28. In this case, the oxide layer 3 forms a sacrificial layer in this area, which is preferably removed by means of a selective etching solution, for example based on hydrofluoric acid (HF). This lateral etching is perfectly reproducible and has a speed of the order of 1 μm / min at room temperature. The recess 29 is on its side facing away from the carrier 1 side of a system pressure measuring membrane 17 forming region of the composite of silicon layer 5 and insulating layer 7 completed. In measuring operation, a deflection which is dependent on a system pressure p _sys acting on the system pressure measuring diaphragm 17 is detected by the piezoresistive element 19, which are arranged on the side of the insulating layer 7 of the system pressure measuring diaphragm 17 facing away from the recess 29.

Finally, the recess 29 is evacuated and the opening 28 is closed under vacuum. Preferably, the opening 28 is closed by a deposition of a material, wherein from the material, a plug 31 is constructed, which extends through the opening 28 and the recess 29 in the oxide layer 5 through to the carrier 1. The plug 31 hermetically seals the opening 28 and forms a spacer between the carrier 1 and the system pressure measuring diaphragm 17. The plug 31 turns the system pressure measuring diaphragm 11 into a rigid annular diaphragm. This makes it possible even with relatively thin system pressure measuring membranes 11 to detect high static pressures of up to 100 bar.

The material is preferably an insulating material, such as. B.

Silicon dioxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ) or silicon oxynitride (SION). Preferably, the plug 31 is made up of layers of silicon dioxide (SiO ₂ ) and silicon nitride (Si ₃ N ₄ ) deposited on one another. The deposition of the material or the material layers is preferably carried out by chemical vapor deposition under vacuum (LPCVD) or by plasma enhanced chemical vapor deposition (PECVD). In this case, for example, classic photolithographic methods can be used to limit the deposition to the region of the opening 28.

Preferably, at least one deposition process is carried out in which at least one layer 33 of an insulating material is deposited on the surface of the pressure sensor chip facing away from the carrier 1 with the piezoresisitive elements 13, 19 thereon. In this case, a small area 34 is preferably recessed in the immediate vicinity of each piezoresistive element 13, 19, in which subsequently an electrical contacting of the piezoresistive elements 13, 19 can take place. The regions 34 may be e.g. be covered by corresponding photolithographic processes by means of appropriately shaped masks during the deposition, which are then subsequently removed again. In principle, it would also be possible to provide the entire chip with the layer, and to subsequently remove these in the areas 34. However, this may be difficult depending on the material and may result in damage to the surface of the chip in the affected areas 34.

The large-area deposition of the layer 33 on the chip surface has the advantage that it causes a primary passivation of the chip surface and esp. The piezoresistive elements 13, 19. The passivation forms a protection of the piezoresistive elements 13, 19 from moisture and at the same time prevents a charge transport on the surface of the Pressure sensor chips. Preferably, silicon nitride (Si ₃ N ₄ ) or silicon oxynitride (SION) is used to form the layer 33. These materials offer the advantage of providing additional shielding from electromagnetic radiation. The layer 33 preferably has a thickness of more than 50 nm. Ideally, the thickness of the layer 33 is between 80 nm and 100 nm.

Subsequently, a metallization 35 is applied to the pressure sensor chip, by which an electrical interconnection of the piezoresistive elements 13, 19 is effected and contact pads for contacting the interconnected elements 13, 19 are generated. The contacting takes place in the previously recessed in the deposition of the layer 33 areas 34. This is shown in Fig. 12. Preferably, for the metallization 35, a contacting material system suitable for use at high temperatures, such as e.g. TiWN / Au used.

In a final operation, the saw cut 21 already described above is then introduced into the pressure sensor chip, by means of which the differential pressure measuring diaphragm 11 is mechanically decoupled from the system pressure measuring diaphragm 17.

Table 1

[0137]

Claims

claims

1. 1. Pressure sensor chip for measuring a differential pressure with

a support (1) made of silicon,

- One on the support (1) arranged oxide layer (3),

a silicon layer (5) arranged on the oxide layer (3),

- One on the silicon layer (5) arranged insulating layer (7), and

- One in the carrier (1) provided recess (9) which exposes a differential pressure measuring membrane (11) forming region of the adjoining composite of oxide layer (3), silicon layer (5) and insulating layer (7),

- Which is determined by a differential pressure acting thereon deflection by at least one piezoresistive element (13) that on the side facing away from the recess (9) side of the insulating layer (7) of the differential pressure measuring diaphragm (11) is arranged.

2. 2. Pressure sensor chip according to claim 1, which additionally comprises a trained as a system pressure sensor area (II), in which

- On the support (1) made of silicon, the oxide layer (3) is arranged,

on the oxide layer (3) the silicon layer (5) is arranged,

- On the silicon layer (5), the insulating layer (7) is arranged, and

- In the oxide layer (3) from the differential pressure measuring diaphragm (11) spaced recess (29) is provided on the side facing away from the carrier (1) side of a system pressure measuring membrane (17) forming region of the composite of silicon layer (5) and insulating layer (7) is completed,

- Which is determined by a system pressure acting thereon deflection by at least one piezoresistive element (19) that on the side facing away from the recess (29) side of the insulating layer (7) of the system pressure measuring diaphragm (17) is arranged.

3. Pressure sensor chip according to claim 2, in which through the oxide layer (3), the silicon layer (5) and the insulating layer (7) extends a section (21) through which the differential pressure measuring diaphragm (11) mechanically from the system pressure measuring membrane ( 17) is decoupled,

4. 4. Pressure sensor chip according to claim 2, wherein - The system pressure measuring diaphragm (17) has a cylindrical opening (28) arranged in its center, and

- This opening (28) is closed by a plug (31),

- which extends through the opening (28) and the recess (29) in the oxide layer (3) through to the carrier (1) and forms a spacer between the carrier (1) and the system pressure measuring diaphragm (17).

5. 5. Pressure sensor chip according to claim 1 or 2, wherein on the side facing away from the carrier (1) top of the pressure sensor chip, an electronics (25) is arranged, to which on the insulating layer (7) arranged piezoresistive elements (13 , 19) are connected.

6. 6. pressure sensor chip according to claim 5, wherein the piezoresistive elements (13) for measuring the differential pressure and / or the piezoresistive elements (19) for measuring the system pressure are each connected together to form a resistance bridge, and the electronics (25) thereto is used to derive a temperature, which is exposed to the pressure sensor chip, based on an internal resistance of at least one resistance bridge and to provide compensation for temperature-dependent measurement errors.

7. 7. A method of manufacturing a pressure sensor chip for measuring a differential pressure, wherein

a BESOI wafer having a first and a second silicon layer (n-Si1, n-Si2) and an oxide layer (3) arranged therebetween is used,

the first silicon layer (n-Si1) forms a carrier (1) made of silicon,

in the second silicon layer (n-Si 2), an insulating layer (7) is produced by implantation of ions and subsequent tempering, which is covered by an overlying silicon film (27),

- From the silicon film (27) piezoresistive elements (13, 19) are generated,

- In the carrier (1) a recess (9) is etched exposing a differential pressure measuring membrane (11) forming region of the adjoining composite of oxide layer (3), silicon layer (5) and insulating layer (7),

- whose deflection dependent on a differential pressure acting thereon by at least one of the piezoresistive element (13) is detected, that on the side facing away from the recess (9) side of the insulating layer (7) of the differential pressure measuring diaphragm (11) is arranged.

8. 8. A method of manufacturing a pressure sensor chip according to claim 7, wherein

in a region (II) of the pressure sensor chip which is at a distance from the differential pressure measuring diaphragm, a cylindrical opening (28) is produced which penetrates through the insulating layer (7) and the silicon layer (5),

- Through the opening (28) through one of the differential pressure measuring diaphragm (11) spaced recess (29) is etched into the oxide layer (3) on its side facing away from the carrier (1) side of a system pressure measuring membrane (17) forming region of the composite silicon layer (5) and insulating layer (7) is completed,

- Which is determined by a system pressure acting on it acting deflection by at least one piezoresistive element (19) that on the side facing away from the recess (29) side of the insulating layer (7) of the system pressure measuring diaphragm (17) is arranged, and

- The opening (28) is closed under vacuum.

9. A method for producing a pressure sensor chip according to claim 7 or 8, wherein from the silicon film (27) piezoresistive elements (13, 19) are generated by

- The silicon film (27) is doped by implantation of ions, and

- A structuring of the doped silicon film (29) is made, in which only serve as the piezoresistive elements (13, 19) areas of the doped silicon film (29) remain on the insulating layer (7).

10. The method for manufacturing a pressure sensor chip according to claim 8, wherein the cylindrical opening (28) is sealed under vacuum by deposition of at least one material, wherein from the material, a plug (31) is constructed, which through the opening (28) and the recess (29) in the oxide layer (3) passes through to the carrier (1) and forms a spacer between the carrier (1) and the system pressure measuring diaphragm (17).

11. The method according to claim 10, wherein at least one deposition process is carried out in which at least one layer (33) is deposited from an insulating material on the surface of the pressure sensor chip facing away from the carrier (1) with the piezoresistive elements (13, 19) thereon, which has a primary passivation of the upper side of the pressure sensor chip and of the piezoresistive elements (13, 13) thereon. 19) causes.