DE102018209503A1 - Method of making a MEMS pressure sensor - Google Patents

Abstract

The invention relates to a method for producing a MEMS pressure sensor, comprising the steps of providing a cavern enclosed in a carrier layer, providing a first electrode structure with a conductive layer above the enclosed cavern, providing at least one insulating layer above the first electrode layer, providing a sacrificial layer above the first electrode layer and cavern enclosed, providing a second electrode structure with at least one conductive layer above the sacrificial layer, producing at least one access by the second electrode structure to the sacrificial layer and removing the sacrificial layer by means of the at least one access.

Description

Technical area

The invention relates to a method for producing a MEMS pressure sensor.

The invention further relates to a MEMS pressure sensor.

State of the art

It has become known to produce micromechanical pressure sensors or MEMS sensors with piezoresistive measuring principle. The pressure-sensitive membrane is either a silicon or a steel layer. The piezoresistive structures are placed on or in the surface of the membrane. Furthermore, it has become known to manufacture a buried cavity in a silicon wafer by means of an APSM process and thus to realize an absolute pressure sensor in a wafer piece in which the buried cavity serves as the reference pressure under vacuum. However, the piezoresistors are expensive to adjust to correct temperature effects and require comparatively much power during operation.

Disclosure of the invention

• - Bereitstellen einer in einer Trägerschicht eingeschlossenen Kaverne,
• - Bereitstellen einer ersten Elektrodenstruktur mit einer leitenden Schicht oberhalb der eingeschlossenen Kaverne,
• - Bereitstellen zumindest einer Isolierschicht oberhalb der ersten Elektrodenschicht,
• - Bereitstellen einer Opferschicht oberhalb von erster Elektrodenschicht und eingeschlossener Kaverne,
• - Bereitstellen einer zweiten Elektrodenstruktur mit zumindest einer leitenden Schicht oberhalb der Opferschicht,
• - Herstellen von zumindest einem Zugang durch die zweite Elektrodenstruktur zu der Opferschicht und
• - Entfernen der Opferschicht mittels des zumindest einen Zugangs.

In one embodiment, the invention provides a method of making a MEMS pressure sensor comprising the steps

• Providing a cavern enclosed in a carrier layer,
• Providing a first electrode structure with a conductive layer above the enclosed cavern,
• Providing at least one insulating layer above the first electrode layer,
• Providing a sacrificial layer above the first electrode layer and enclosed cavern,
• Providing a second electrode structure with at least one conductive layer above the sacrificial layer,
• - Producing at least one access through the second electrode structure to the sacrificial layer and
• - Remove the sacrificial layer by means of at least one access.

In a further embodiment, the invention provides a MEMS pressure sensor made by a method according to any one of claims 1-11.

One of the advantages achieved with this is that, instead of introducing piezoelectric resistors which are later to be matched with great difficulty, a measuring electrode and, moreover, a self-supporting, mechanically stable counterelectrode are now applied. This eliminates costly adjustment operations. Another advantage of a capacitive sensor is the lower energy consumption compared to piezoresistors.

Further features, advantages and further embodiments of the invention are described below or will become apparent.

According to an advantageous development, the cavern is provided in the carrier layer by producing the cavern in the carrier layer by means of an APSM process. An APSM process enables a robust, structurally small cavern as a reference vacuum, which is also very resistant to overpressure due to a self-limiting stop. The abbreviation "APSM" stands for Advanced Porous Silicon Membrane.

According to a further advantageous development, an insulating layer is applied before and after the provision of the first electrode structure. This allows reliable isolation of the first electrode layer.

According to a further advantageous development, the insulating layer is applied in a thickness between 25 and 150 nm, preferably between 50 and 100 nm, in particular between 60 and 80 nm. The advantage of this is that a relatively thin insulator or insulating layer is applied, which protects the electrode from environmental influences and at the same time does not affect the electrical function of the capacitive measuring principle.

According to a further advantageous development, several accesses to the sacrificial layer in the second electrode structure are produced after the application. The advantage of this is that the removal of the sacrificial layer is facilitated.

According to a further advantageous development, the second electrode structure is produced in multiple layers with at least two separate conductive layers separated by an insulating layer. This allows separate structuring in different planes of the second electrode structure. For example, the first electrode layer, which is in particular thinner than the second electrode structure, can be optimized for the electrical properties such as basic capacitance and linearity, while the second electrode structure can be optimized for the mechanical properties (stability).

According to a further advantageous development, at least one of the conductive layers is additionally formed in the second electrode structure as a carrier layer, in particular wherein the conductive layer formed as a carrier layer by at least a factor 2 , preferably at least the factor 3 having greater thickness. This increases the stability of the second electrode structure without having to arrange further layers.

According to a further advantageous development, the sacrificial layer, in particular made of germanium, is removed by means of a reactive etching process, in particular by means of XeF ₂ . One of the advantages achieved with this is that a high etch rate and, if appropriate, owing to the high strength of the counterelectrode in the form of the second electrode structure, large undercutting widths can be realized.

According to a further advantageous development, the at least one access to the sacrificial layer is produced from above in the edge region of the carrier layer above the cavern. Advantage of this is that a later Vergelen is facilitated. In addition, mechanically strong structures can be obtained, at least in some areas.

According to a further advantageous development, the second electrode structure is produced in one layer from polycrystalline silicon, preferably in a thickness of between 1 .mu.m and 10 .mu.m, in particular between 2 .mu.m and 6 .mu.m. The advantage of this is a simple structuring of the second electrode structure with a low use of material.

According to a further advantageous development, the second electrode structure is structured in grid form with at least two different distances, in particular wherein the wider distance has a size between 5 μm and 10 μm. The advantage of this is that the mechanical stability can be flexibly adapted.

Further important features and advantages of the invention will become apparent from the subclaims, from the drawings, and from associated figure description with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments and embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components or elements.

list of figures

• 1-9 Teile von Schritten eines Verfahrens gemäß einer Ausführungsform der vorliegenden Erfindung;
• 10 Schritte eines Verfahrens gemäß einer Ausführungsform der vorliegenden Erfindung;
• 11 Teile von Schritten eines Verfahrens gemäß einer Ausführungsform der vorliegenden Erfindung; und
• 12 Teile von Schritten eines Verfahrens gemäß einer Ausführungsform der vorliegenden Erfindung;

Show

• 1-9 Parts of steps of a method according to an embodiment of the present invention;
• 10 Steps of a method according to an embodiment of the present invention;
• 11 Parts of steps of a method according to an embodiment of the present invention; and
• 12 Parts of steps of a method according to an embodiment of the present invention;

Embodiments of the invention

The 1 to 9 as well as the 11 and 12 show parts of steps of a method of manufacturing a pressure sensor according to an embodiment of the present invention.

In 1 becomes a cavern 100 in a silicon layer 2 for a pressure sensor 1 provided, in particular by means of an APSM process, wherein above the cavern 100 then part of a membrane 101 is formed.

In 2 will now be on the silicon layer 2 first an insulating layer 3 in particular an oxide, for example in a thickness of 50-100 nm, then a metal electrode 4 , which is structured and then again a thin insulating layer 5 , in particular an oxide applied in a thickness of 50-100nm. As metal electrode 4 For example, tungsten, in particular in a layer thickness of 100 nm, can be used, which enables good conductivity. Here, the metal of the metal electrode 4 the depositions of the following layers such as germanium in the range -370 ° C - 400 ° C, oxide in the range 400 ° C as PECVD, plasmaenhanced chemical vapor deposition, or in the range 800 ° C as LPCVD, low pressure chemical vapor deposition, and / or poly-Si, polycrystalline silicon, in the range 550 ° C - allow 670 ° C. This is for example given to tungsten but also other metals, with tungsten having comparatively high tensile stress. Another metal may be with respect to the strain of the membrane 101 , be advantageous from layers of silicon, an oxide, a metal and turn an oxide. Instead of a metal, it is also possible to use a doped silicon layer, which has the advantage that it can be applied virtually stress-free. The insulating layers 3 . 5 will not structured, substrate contacts and contact to the measuring electrode are advantageously prepared later.

Now, as in 3 shown a germanium sacrificial layer 6 applied and structured. Advantageously, thin layers with thicknesses of 300-500 nm, in order to obtain a high basic capacity and thus sensitivity. In the case of thicker layers, the structuring is advantageously carried out in such a way that the flanks have, in particular, a clearly positive angle in order to be able to apply the subsequent layers. In particular, a positive flank angle of, for example, 70 ° -80 ° is also advantageous for thin layers.

Next, as in 4 shown one or more layers applied to the counter electrode 8th . 10 to the metal electrode 4 form. Here can either be a single layer 10 be made of poly-Si, or it may also be a two-layer structure can be prepared, optionally with intermediate oxide layers as insulating layers, which allows a separate structuring of the electrically active surface and the mechanical support. The latter increases the flexibility in optimizing the individual electrical and mechanical properties.

In order to obtain the greatest possible freedom in optimizing the properties, there is a two-layer structure of the counterelectrode layer 8th . 10 to be preferred in the 4-7 is shown. First, on the germanium sacrificial layer 6 a thin oxide layer 7 applied as an insulating layer, then a conductive layer 8th , For example, a metal layer, in particular, a tungsten layer, preferably in a thickness of 100 nm, and this conductive layer 8th is then structured. This conductive layer 8th will turn with a thin oxide layer 9 covered as an insulating layer.

Next, as in 5 shown the electrical contact openings 50 to the lower measuring electrode 4 or first electrode layer and the carrier layer 2 exposed by the insulating layers 3 . 5 . 7 locally structured, in particular etched. When using thin insulating layers 3 . 5 . 7 with a thickness of the order of 100 nm, the etching can advantageously be carried out in a single step.

As in 6 is then a mechanically stable and self-supporting layer 10 deposited to form a solid counter electrode, for example a poly-Si layer, preferably in a thickness of 2-5 microns, in particular doped with phosphorus or boron. On this layer are metal pads 11 applied for later contacting as in 6 shown. The mechanically stable layer 10 is structured according to the mechanical function with access 51 , as in 7 shown, for example, as a lattice structure or as a closed layer with one or more accesses to the sacrificial layer 6 , At the same time, the electrical accesses to the two electrode layers 4 . 8th and the carrier layer 2 , so far on the conductive layer 10 were interconnected, isolated from each other. Overall, so that the counter electrode through the two conductive layers 8th . 10 educated.

Alternatively to the two-layer preparation of the counterelectrode from the two layers 8th . 10 the electrical and mechanical function of the counter electrode can also be combined in one layer. For this purpose, one skips individual steps of the production of the two-layer counterelectrode, in particular the deposition and structuring of the conductive layer 8th and the insulating layer 9 above this conductive layer 8th , This simplified structure is in the 11 and 12 shown. It still contains a thin oxide insulating layer 7 over the germanium sacrificial layer 6 , the electrical contact openings 50 to the measuring electrode 4 and carrier layer 2 , as in 11 represented, and then applied mechanically stable and cantilevered electrode layer 10 and the metal pads 11 as in 12 shown. The electrode layer 10 now provides the electrical and mechanical function of a counter electrode. The subsequent structuring then takes place analogously to 7 ,

8th shows the preparation of the subsequent sacrificial layer etching of the germanium layer 6 , It becomes all of the accessible structures with a silicon oxide or silicon nitride insulating layer 12 coated. This insulating layer 12 is structured below and then in the field of metal pads 11 and the accesses 52 to the germanium sacrificial layer 6 especially with at least one access 52 per sacrificial layer area is provided, but there are also several accesses 52 per sacrificial layer area possible to complete, rapid removal of the sacrificial layer 6 sure.

Finally, the sacrificial layer etching according to 9 which is per se selective to all metals and oxides / nitrides, and also to poly-Si, which here as the material of the carrier layer 2 , and the membrane 101 is used, can be selectively guided. However, especially in the case of complex, so for example, a multi-layered counter electrode, all poly-Si structures in insulating layers, in particular made of an oxide, included, so that a less good selectivity of 1: 1-1: 5 is possible.

Due to the high etching rate of XeF ₂ , the freedom of many accesses 51 in the second carrier layer 10 , and then over part of these accesses 52 to the sacrificial layer 6 to be able to create, because the counter electrode 8th does not have to be closed and the high strength, ie restoring force of the fixed counter electrode 8th large undercrossings can be realized.

An advantage of the more elaborate, two-layer counterelectrode 8th . 10 with insulating layers 7 . 9 . 12 is that the electrode surface can be made free to avoid parasitic effects or nonlinearities by suitable design of the electrode surfaces. Furthermore, the last insulating layers 9 . 12 also very selective etching access to the germanium sacrificial layer 8th then, for example, at the edge of the membrane 101 , in the middle of the membrane 101 or even off the membrane 101 can be positioned in foothills. This facilitates a later gagging. Furthermore, certain germanium regions in the sacrificial layer can also be used 6 not be opened at all so that they remain as mechanically strong structures. This can be done around the membrane 101 around a kind of non-positive, stable filling structure are generated so that the counter electrode 8th . 10 does not protrude above the chip or protrudes.

Furthermore, the reference membrane, which is pressure-insensitive for a capacitive pressure sensor, can be accommodated on a supported piece of a chip.

10 shows steps of a method according to an embodiment of the present invention.

In 10 a method of manufacturing a MEMS pressure sensor is shown.

Here, a first step S1 providing one in a carrier layer 2 enclosed cavern 100 ,

This is done in a second step S2 providing a first electrode layer 4 with a conductive layer above the enclosed cavern 100 ,

This is done in a third step S3 providing at least one insulating layer 5 above the first electrode layer 4 ,

This is done in a fourth step S4 providing a sacrificial layer 6 above the first electrode layer 4 and enclosed cavern 100 ,

This takes place in a fifth step S5 providing a second electrode layer 10 with a conductive layer above the sacrificial layer 6 ,

This is done in a sixth step S6 a manufacture of at least one access 52 through the second electrode layer 10 to the sacrificial layer 6 ,

This is done in a seventh step S7 a removal of the sacrificial layer 6 by means of at least one access 52 ,

• • Vermeidung später aufwändig abzugleichender Piezo-Widerstände
• • Bereitstellung einer stabilen freitragenden Gegenelektrode
• • Insgesamt niedrigerer Energieverbrauch

In summary, at least one of the embodiments has at least one of the following advantages:

• • Avoidance of later complicated piezo resistors
• • Provision of a stable self-supporting counterelectrode
• • Overall lower energy consumption

Although the present invention has been described in terms of preferred embodiments, it is not limited thereto, but modifiable in a variety of ways.

Claims (12)

A method of making a MEMS pressure sensor (1) comprising the steps Providing (S1) a cavern (100) enclosed in a carrier layer (2), Providing (S2) a first electrode structure (4) with a conductive layer above the enclosed cavern (100), Providing (S3) at least one insulating layer (5) above the first electrode layer (4), Providing (S4) a sacrificial layer (6) above the first electrode layer (4) and enclosed cavern (100), Providing (S5) a second electrode structure (8, 10) with at least one conductive layer (8, 10) above the sacrificial layer (6), - Producing (S6) of at least one access (52) through the second electrode structure (10) to the sacrificial layer (6) and - removing (S7) the sacrificial layer (6) by means of the at least one access (52). Method according to Claim 1 in which provision (S1) of the cavern (100) in the carrier layer (2) takes place by producing the cavern (100) in the carrier layer (2) by means of an APSM process. Method according to one of Claims 1 - 2 , wherein before and after the provision of the first electrode structure (4) an insulating layer (3, 5) is applied. Method according to Claim 3 in which the insulating layer (3, 5) has a thickness between 25-150 nm, preferably between 50-100nm, in particular between 60-80nm is applied. Method according to one of Claims 1 - 4 wherein multiple accesses to the sacrificial layer (6) are made in the second electrode structure (8, 10) after application. Method according to one of Claims 1 - 5 in that the second electrode structure (10) is produced in multiple layers with at least two separate conductive layers (8, 10) separated by an insulating layer (9). Method according to Claim 6 , wherein additionally in the second electrode structure (8, 10) one of the conductive layers (10) is formed as a carrier layer, in particular wherein this has a greater by at least a factor of 2, preferably a factor of 3 greater thickness. Method according to one of Claims 1 - 7 , wherein the sacrificial layer (6), in particular made of germanium, by means of a reactive etching process, in particular by means of XeF _{2 is} removed. Method according to one of Claims 1 - 8th , wherein the at least one access (52) to the sacrificial layer (6) is produced from above in the edge region of the carrier layer (2) above the cavern (100). Method according to one of Claims 1 - 9 wherein the second electrode structure (10) is made of polycrystalline silicon, preferably in a thickness of between 1-10 micrometers, more preferably between 2-6 micrometers. Method according to one of Claims 1 - 10 wherein the second electrode structure (8, 10) is structured in a lattice-like manner with at least two different distances, in particular wherein the wider distance has a size of 5 and 10 μm. MEMS pressure sensor manufactured by a method according to any one of Claims 1 - 11 ,

Images