DE102010003488A1 - Method for manufacturing integrated micro-electromechanical system component of flux sensor, involves achieving mechanical mobility of structural elements by removal of layer portions of layer stack of substrate rear side - Google Patents

Abstract

The method involves manufacturing a multi-level interconnect layer stack (MLS) on a front side of a silicon substrate (1) with a monolithic integrated microelectronic circuit (3). A recess is formed in the substrate, which reaches a substrate rear side up to the substrate front side facing the interconnect layer stack. Mechanical mobility of membranes (7) is achieved by removal of dielectric sheets (D1-D4) of the interconnect layer stack of the substrate rear side by the recess, where the sheets suppress the mechanical mobility. An independent claim is also included for an integrated micro-electromechanical system (MEMS) component including a substrate.

Description

The invention relates to an integrated MEMS component comprising a substrate which contains a monolithically integrated microelectronic circuit, a multilevel interconnect layer stack on the substrate, and a MEMS layer structure with micromechanical structural elements which is formed in the multilevel interconnect layer stack, wherein the micromechanical structural elements of the MEMS layer structure are mechanically movable. The invention further relates to a method for producing an integrated micromechanical system (MEMS) component.

From the publication WO 2009/003958 A1 It is known to integrate the production of micromechanical structural elements in a CMOS manufacturing process (CMOS: Complementary Metal Oxide Semiconductor). The integration takes place there in the course of a so-called back-end-of-line (BEOL) process, ie in the production of a multi-level interconnect layer stack. For its production, separate metal layers are structured by insulating layers, which serve for the electrical connection of previously produced microelectronic components. Such microelectronic components may, for example, be transistors of a circuit integrated on the surface of a substrate. Simultaneously with this BEOL process also micromechanical structural elements are produced. In this way, micromechanical structural elements such as actuators and sensors can be connected directly and without additional process complexity with microelectronic circuits as so-called MEMS. MEMS devices produced in this way prove to be advantageous, especially at high frequencies in the GHz range. MEMS devices according to this design have a variety of applications such. B. as a switch for high-frequency signals, or sensors.

A disadvantage of the known construction principles is that the MEMS layer structure, which is very sensitive to mechanical influences and contains the micromechanical structural elements, must be protected from the actual capping of the component. This is done according to the prior art by applying a special cap on the device. This special cap requires that the conventional methods of capping microelectronic circuits, including their electrical contacting, have to be greatly modified.

For example, in the EP 1 101 730 proposed to first coat the micromechanical structures applied to the wafer with a sacrificial material, then apply a capping material and then remove the sacrificial material so that the mechanical structure is in a protected cavity.

In one of the US 6,969,635 In known processes, two structured wafers are bonded together in order to achieve effective protection of the mechanical structures, and then divided into individual chips.

The font DE 600 16 701 describes a solution for a vacuum-tight capping using three wafers. In the manufacture of MEMS devices, solutions are also known in which not only the upper side but also the underside of a wafer is patterned. For example, this describes US 7,318,349 Such a solution for the production of an acceleration sensor to expose the reference mass. However, there are no comments on the capping of the now yes on both sides, ie on the substrate front and the back of the substrate to be protected mechanical structure made.

• – Herstellen eines Mehrebenen-Leitbahnschichtstapels auf einer Substratvorderseite eines Substrats, das eine monolithisch integrierte mikroelektronische Schaltung enthält;
• – Anlegen einer MEMS-Schichtstruktur mit mikromechanischen Strukturelementen im Zuge des Herstellens des Mehrebenen-Leitbahnschichtstapels, wobei die mikromechanischen Strukturelemente der MEMS-Schichtstruktur unmittelbar berührend in sie umgebende Schichtabschnitte des Mehrebenen-Leitbahnschichtstapels eingebettet werden, die eine mechanische Beweglichkeit der mikromechanischen Strukturelemente zunächst unterdrücken;
• – Herstellen einer Ausnehmung im Substrat, die von einer dem Mehrebenen-Leitbahnschichtstapel abgewandten Substratrückseite bis zur dem Mehrebenen-Leitbahnschichtstapel zugewandten Substratvorderseite reicht;
• – Herstellen der mechanischen Beweglichkeit der mikromechanischen Strukturelemente mittels Entfernen der die mechanische Beweglichkeit unterdrückenden Schichtabschnitte des Mehrebenen-Leitbahnschichtstapels von der Substratrückseite her durch die Ausnehmung hindurch.

A method according to the invention for producing an integrated microelectromechanical system (MEMS) component comprises:

• Forming a multi-level interconnect layer stack on a substrate front side of a substrate including a monolithically integrated microelectronic circuit;
• - Creating a MEMS layer structure with micromechanical structure elements in the course of producing the multilevel interconnect layer stack, wherein the micromechanical structure elements of the MEMS layer structure are embedded directly touching in surrounding layer portions of the multilevel interconnect layer stack, which initially suppress a mechanical mobility of the micromechanical structure elements;
• - Producing a recess in the substrate, which extends from a the multi-level interconnect layer facing away from the substrate back to the multi-level interconnect layer stack facing substrate front side;
• - Producing the mechanical mobility of the micromechanical structure elements by removing the mechanical mobility suppressing layer portions of the multi-level interconnect layer stack from the substrate back through her through the recess.

In contrast to the prior art, the micromechanical structural elements of the MEMS layer structure embedded in the multilevel interconnect layer stack are completely worked out from the rear side of the substrate, and thus receive their intended mechanical mobility through access by that side of the substrate that faces away from the multilevel interconnect layer stack. This procedure, which is unusual for the structuring of a multilevel interconnect layer stack, makes it possible to perform the capping of the integrated circuit of the MEMS component with a protective layer on the front side of the substrate in accordance with conventional methods, without having to consider the mechanical sensitivity of the MEMS layer structure , This facilitates the further processing of the MEMS device and in particular makes it possible to use known fabrication methods and capping techniques for the integrated electronic circuits of a MEMS device structure with a MEMS layer structure integrated in the multi-level interconnect layer stack.

Furthermore, the method offers the advantage that the MEMS layer structure is not produced - as usual in the prior art - at the end of the process control over a silicon substrate. As a result, the attenuation of RF signals z. For example, in a MEMS layer structure designed as an RF switch, which is advantageous for the high-frequency characteristics of the RF switch.

Hereinafter, embodiments of the method according to the invention will be described. The additional features of the embodiments may be combined with each other to form further embodiments, unless they are disclosed as excluding each other.

While the electronic circuits of the MEMS can be provided with electrical connections and capped by known methods, in one embodiment the capping of the mechanical structures on the back side of the silicon substrate takes place in an additional method step.

In one exemplary embodiment, after the mechanical mobility of the micromechanical structural elements has been established, the recess is covered by the substrate back side. In typical embodiments, since the silicon substrate is planar on the rear side, unlike the relief-like surface of the protective layer of the integrated circuits on the front side of the substrate, the capping can advantageously be effected by a simple planar cover plate with a simple connection technology. For example, after the mechanical mobility of the micromechanical structural elements has been established, the substrate rear side can be connected to a planar cover plate by gluing, bonding or welding. The cover plate may be made of silicon, glass, metal or plastic, for example.

To cap the micromechanical structure elements, the silicon substrate can alternatively be connected to a further carrier substrate. The further carrier substrate may likewise be a silicon substrate. In an alternative embodiment of the invention, the further carrier substrate is a printed circuit board which carries a plurality of MEMS and other electronic components and connects them to one another electrically.

The recess to be covered by the cover plate may be previously filled with an inert gas.

In a preferred embodiment, the cover has an opening which is designed to allow a pressure equalization between a fluidically fillable interior of the MEMS component surrounding the MEMS layer structure and an outer space surrounding the MEMS component as a whole.

The protective layer is preferably deposited on an upper side of the multilevel interconnect layer stack before the recess is made, either above the metal level produced last, ie after the production of at least one intermediate layer, or immediately subsequent to the last metal layer produced.

The fabrication of the recess typically comprises an anisotropic etching process. It has proven useful to use a vertical dry etching process, in particular a deep etching process (eg DRIE, abbreviation for deep reactive ion etching, deep reactive ion etching), for example according to the Bosch process (cf. WO 99/10922 ). But other etching methods are conceivable, such as a wet-chemical method. In the case of a silicon substrate, the recess can be etched with KOH, for example.

The subsequent removal of the mechanical mobility suppressing layer sections of the multilevel interconnect layer stack is preferably carried out by etching. Here, a wet-chemical etching process is preferred.

The protective layer is preferably made of a material that damages the multi-level interconnect layer stack from an upper surface of the MEMS device during fabrication of the recess and during removal, from the viewpoint of such process guidance in fabricating the recess and exposing the MEMS layer structure prevents the mechanical mobility suppressing layer portions of the multi-level interconnect layer stack. For example, silicon oxide or silicon nitride is suitable.

The production of the mechanical mobility of the micromechanical structural elements may comprise, for example, an exposure of a mechanically deformable membrane. To expose such a membrane, preferably openings are made in the membrane and the membrane is then exposed by overetching. The membrane is formed mechanically viable in a further development of this example.

However, the method according to the invention can also be used in many other applications. Other applications of MEMS layer structures which can be integrated into the interconnect layer stack with the method according to the invention form further microelectromechanical sensors such as pressure sensors, acceleration sensors, rotation rate sensors or electrostatic actuators.

• – ein Substrat, das eine monolithisch integrierte mikroelektronische Schaltung enthält,
• – einen Mehrebenen-Leitbahnschichtstapel auf dem Substrat,
• – eine MEMS-Schichtstruktur mit mikromechanischen Strukturelementen, die im Mehrebenen-Leitbahnschichtstapel ausgebildet ist, wobei die mikromechanischen Strukturelemente der MEMS-Schichtstruktur mechanisch beweglich sind;
• – eine Ausnehmung im Substrat, die von einer dem Mehrebenen-Leitbahnschichtstapel abgewandten Substratrückseite bis zur dem Mehrebenen-Leitbahnschichtstapel zugewandten Substratvorderseite und darüber hinaus bis zur MEMS-Schichtstruktur reicht.

Another aspect of the invention is an integrated MEMS device comprising:

• A substrate containing a monolithically integrated microelectronic circuit,
• A multilevel interconnect layer stack on the substrate,
• A MEMS layer structure with micromechanical structure elements which is formed in the multilevel interconnect layer stack, wherein the micromechanical structure elements of the MEMS layer structure are mechanically movable;
• A recess in the substrate, which extends from a substrate back side facing away from the multilevel interconnect layer stack to the substrate front side facing the multilevel interconnect layer stack and, furthermore, to the MEMS layer structure.

The integrated MEMS component according to the invention shares the above-described advantages of the method according to the invention. In addition to the suitability of this structure for the use of known process technology for their production, particular emphasis should be given to the improved high-frequency properties of the MEMS device according to the invention in many embodiments.

Hereinafter, embodiments of the MEMS device according to the invention will be described. The additional features of the embodiments may be combined with each other to form further embodiments, unless they are disclosed as excluding each other.

The recess is, as has been explained in more detail above in connection with the method aspect of the invention, preferably covered by the substrate back, in particular in the form of a cover plate or a carrier substrate which is connected to the substrate back to the substrate. The covered recess may be filled with an inert gas. In preferred embodiments, the cover of the recess has an opening which is designed to allow a pressure equalization between a fluidically fillable interior of the MEMS component surrounding the MEMS layer structure and an outer space surrounding the MEMS component as a whole.

The additional features of further embodiments of the device according to the invention emerge directly from the above description of embodiments of the method according to the invention.

Further embodiments of the invention are described in the dependent claims.

Hereinafter, further embodiments will be explained with reference to the figures. Show it:

1 An embodiment of a method for producing a MEMS device in the context of a CMOS fabrication in a MEMS first manufacturing state

2 the embodiment of 1 in a subsequent MEMS second manufacturing state

3 the embodiment of 1 in a subsequent MEMS third manufacturing state

4 the embodiment of 1 in a subsequent fourth MEMS manufacturing state

The 1 to 4 show an embodiment of a method for producing a MEMS device B in the context of a CMOS fabrication. Process steps that are required for the production of microelectronic circuits in the context of (front-end-of-line, FEOL) CMOS fabrication are not shown here for the sake of simplicity, because they are known as such.

CMOS process technology, like its related MOS technologies (eg, NMOS, PMOS, BiMOS, BiCMOS), is of great economic importance in the semiconductor industry. Therefore, an integrability of the method according to the invention in such a process of great advantage. However, the method according to the invention can be carried out within the framework of these as well as other processes of semiconductor technology, since it only starts when the interconnect layer stack is produced.

In 1 the state of manufacture of the MEMS device B is shown after during a CMOS FEOL process on the surface of the silicon substrate one or more microelectronic circuits 3 and in the first process steps of the back-end-of-line (BEOL) process, a multilevel interconnect layer stack MLS has been applied. This contains structured, mutually insulated metallization levels, here labeled M1 to M5, and intervening dielectric layers D1 to D4. The number of five metallization levels shown here is purely examplary. It is essential to the invention that there are sufficient levels to accommodate a MEMS layer structure, labeled MEM in the figures, in the multi-level interconnect layer stack.

Certain structures of metallization levels M1 to M5 serve together with vias 4 as conductor tracks 5 for the electrical connection of the microelectronic circuits 3 , Other structures of the metallization levels M1 to M5 are used as prepared functional elements of a mechanical system and thus serve as a MEMS layer structure MEM. In the present case is a membrane 7 embedded in the layer structure, which later by electrical control the electronic circuit 3 against an electrode 9 mechanically deformable exposed.

The stack of structured metallization levels M1 to M5 is at this stage of the process 1 already through a protective layer 2 covered. Since drive elements for mechanical systems can have an increased voltage or current requirement compared to microelectronic circuits, strip conductors are in the sense of an exemplary embodiment 8th the metallization M5 amplified, that has been carried out with an increased thickness.

In contrast to the prior art, the MEMS layer structure MEM, which can also be referred to as a micromechanical structure, is produced according to the invention from a back side R of the silicon substrate, ie from that side of the substrate which faces away from the metallization planes M1 to M5. As in 2 is shown, first by etching (also referred to as cavity) recess 10 in the substrate 1 brought in. For example, a deep silicon etching process can be used for this, for example using the known Bosch process. The etching process is carried out on an insulating layer 6 stopped, which is designed for example as a silicon nitride layer.

The exposure of the functional elements of the mechanical system, ie the MEMS layer structure MEM, is then carried out by wet-chemical etching. The state after the exposure is in 3 shown.

Removes all dielectric layers D1 to D4, which are usually formed as insulating oxide layers. The preferred orthogonal to the surface of the silicon substrate 1 acting etching is stopped by metallic layers of metallization levels M1 to M5.

For an undercut of the as a membrane 7 provided MEMS layer structure MEM in the metallization M3 openings can be created in the membrane (not shown here). This makes sense already when structuring the membrane 7 considered in the context of the production of the multi-level interconnect layer stack MLS.

As a result of the wet etching, the in 3 shown structures of the mechanical functional elements exposed, so the membrane 7 and the electrode 9 , As part of the wet etching step, the silicon nitride layer initially becomes 6 removed in the region of the recess to allow access to the structures mentioned.

The protection of sensitive micromechanical structures in the cavity 10 takes place through a cover plate, for example by a glass plate 11 , as in 4 is shown. The fastening of the glass plate 11 on the substrate rear side R, for example, by bonding or gluing, so by an additional process step after the MEMS device B has completed the CMOS manufacturing process.

Also conceivable are other types of rear capping, not shown here, such as an elastic film, which may be made of metal, for example. The cavity 10 can be filled with a protective gas, a liquid or just with air. In a further embodiment, the cavity 10 evacuated. In another embodiment, the cover with an opening 12 for pressure equalization between the cavity 10 and the environment provided. The opening 12 but can also be omitted.

According to an exemplary embodiment of an RF switch, the reinforced conductor tracks form 8th and the electrode 9 an electrostatic drive for the membrane 7 , Will a voltage between the tracks 8th and the membrane 7 applied, the membrane moves 7 in the direction of the electrode 9 , reducing the capacitance between the electrode 9 and the membrane 7 is changed or even a contact is made.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2009/003958 A1 [0002]
• EP 1101730 [0004]
• US 6969635 [0005]
• DE 60016701 [0006]
• US 7318349 [0006]
• WO 99/10922 [0017]

Claims (14)

A method of manufacturing an integrated microelectromechanical system (MEMS) device, comprising: - forming a multi-level interconnect layer stack (MLS) on a substrate front side (V) of a substrate ( 1 ), which is a monolithically integrated microelectronic circuit ( 3 ), - applying a MEMS layer structure (MEM) with micromechanical structure elements ( 7 . 9 ) in the course of producing the multilevel interconnect layer stack (MLS), wherein the micromechanical structural elements ( 7 . 9 ) of the MEMS layer structure (MEM) are embedded directly touching in layer sections (D2, D3) of the multi-level interconnect layer stack (MLS), the mechanical mobility of the micromechanical structure elements ( 7 . 9 ) first suppress; - making a recess ( 10 ) in the substrate ( 1 extending from a substrate back side (R) facing away from the multilevel interconnect layer stack to the substrate front side (V) facing the multilevel interconnect layer stack; Producing the mechanical mobility of the micromechanical structural elements ( 7 ) by removing the mechanical mobility suppressing layer portions (D2, D3) of the multi-level interconnect layer stack (MLS) from the substrate rear side (R) forth through the recess. Method according to Claim 1, in which after the mechanical mobility of the micromechanical structural elements ( 7 ) the recess ( 10 ) is covered by the substrate rear side (R). Method according to Claim 1 or 2, in which the substrate rear side (R) after the mechanical mobility of the micromechanical structural elements ( 7 ) with a cover plate or a carrier substrate ( 11 ) is connected. Method according to one of the preceding claims, in which prior to the manufacture of the recess ( 10 ) a protective layer ( 2 ) is deposited on the multilevel interconnect layer stack (MLS). Method according to one of the preceding claims, in which the production of the recess ( 10 ) comprises performing a deep etching process according to the Bosch method. The method of any one of the preceding claims, wherein removing the mechanical mobility suppressing layer portions (D2, D3) of the multi-level interconnect layer stack (MLS) comprises wet chemical etching. Method according to Claim 4, in which the protective layer ( 2 ) is fabricated from a material which comprises etching the multilevel interconnect layer stack (MLS) from an upper side (O) of the MEMS device during fabrication of the recess (FIG. 10 ) and during the removal of the mechanical mobility suppressing layer sections (D2, D3) of the multilevel interconnect layer stack (MLS). Method according to one of the preceding claims, in which the production of the mechanical mobility of the micromechanical structural elements is an exposure of a mechanically deformable membrane ( 7 ), wherein to expose the membrane openings are produced in the membrane and the membrane is then exposed by etching over. Integrated MEMS device (B) comprising: - a substrate ( 1 ), which is a monolithically integrated microelectronic circuit ( 3 ), a multilevel interconnect layer stack (MLS) on a substrate front side (V) of a substrate ( 1 ), - a MEMS layer structure (MEM) with micromechanical structural elements ( 7 . 9 ) formed in the multi-level interconnect layer stack, wherein the micromechanical structure elements of the MEMS layer structure are mechanically movable; A recess ( 10 ) in the substrate, which extends from a substrate rear side (R) facing away from the multilevel interconnect layer stack to the substrate front side (V) facing the multilevel interconnect layer stack and, moreover, to the MEMS layer structure (MEM). Integrated MEMS device according to Claim 9, in which the recess ( 10 ) from the substrate rear side (R) with a cover ( 11 ) is covered. The integrated MEMS device according to claim 10, wherein the cover is in the form of a cover plate or a carrier substrate ( 11 ) at the substrate rear side with the substrate ( 1 ) connected is. Integrated MEMS device according to claim 10 or 11, in which the MEMS layer structure (MEM) comprises a mechanically deformable membrane ( 7 ) having openings. Integrated MEMS device according to one of Claims 10 to 12, with an opening in the cover ( 11 ), which is designed to allow a pressure equalization between an inner space surrounding the MEMS layer structure of the MEMS component and an outer space surrounding the MEMS component as a whole. Flow sensor comprising an integrated MEMS device according to one of claims 9 to 13.

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