Integrated circuit comprising multi-layer micromechanical structures with improved mass and reliability by using modified vias and method for forming the same

Abstract

An integrated circuit and the method to produce the integrated circuit comprising: a substrate (10); active devices (11); plurality of metal layers (17), wherein said metal layers are separated by dielectric layers (13) and connected to each other by plurality of vias (19); at least one micromechanical region (15) wherein some of the dielectric layers are removed leaving hollow spaces (23), thereby some of said metal and via layers form a micromechanical device in said micromechanical region, wherein said micromechanical device comprises at least one multi-layer structure (165) that is built of a plurality of metal layers and at least one via layer and said multi-layer structure is characterized by that at least two metal layers of said multi-layer structure are joined by at least one modified via (41).

Claims

1. An integrated circuit comprising: a substrate (10); active devices (11); a plurality of metal layers (17), wherein said metal layers are separated by dielectric layers (13) and connected to each other by a plurality of vias (19); and at least one micromechanical region (15) wherein some of the dielectric layers are removed leaving hollow spaces (23), thereby some of said metal and via layers form a micromechanical device in said micromechanical region, wherein said micromechanical device comprises at least one multi-layer structure (165) that is built of a plurality of metal and at least one via layer, wherein at least two metal layers of said multi-layer structure (165) are joined by at least one modified via (41) comprising a void space (44), wherein said void space is at least partially filled by the metal layer situated on top of said modified via, wherein the void space is situated in the part of the area of the via that is substantially distant from a via opening perimeter (35), and wherein in the at least one modified via (41), an area of the via that is substantially distant from the via opening perimeter (35) specifically occurs at a cross (414) or junction (413) of at least two via bars.

2. The integrated circuit according to claim 1, wherein some of the via bars are arranged in a form of mesh (417, 418).

3. The integrated circuit according to claim 1, wherein the multi-layer structure (165) contains at least one metal layer that is thicker than other metal layers.

4. The integrated circuit according to claim 1, wherein at least one multi-layer structure (165) is arranged as a part of movable mass electrically coupled to an electronic circuit and said electronic circuit is at least partially arranged from the active devices at the same substrate, thereby said electronic circuit converts a position of said mass with respect to the substrate into an electrical signal and/or said electronic circuit changes the position of the mass with respect to the substrate by applying a proper electrical signal.

5. The integrated circuit according to claim 4, wherein the movable mass is a part of an acceleration sensor, gyroscope or their combination.

6. The integrated circuit according to claim 1 wherein some of the active devices are situated under the micromechanical region (15).

7. A method of manufacturing of an integrated circuit comprising a substrate, at least one micromechanical region (15) with at least one multilayer structure (165), the method including: producing active devices (11) on the substrate (10); patterning and depositing metals (17), vias (19) and inter-metal dielectric (IMD) layers (13); removing the sacrificial part of IMD layers within the micromechanical regions, thereby creating hollow spaces (23), wherein in the micromechanical regions, the via deposition process does not fill entirely the parts of at least a modified via (41) said parts being substantially distant from a via opening perimeter (35), thereby producing voids (44) in said vias, so that the subsequent metal deposition at least partially fills the void with the subsequent metal layer, thereby producing vertical extension (45) of said subsequent metal layer towards the void (44) in the modified via (41), and wherein in the at least one modified via (41), the area of the via that is substantially distant from the via opening perimeter (35) specifically occurs at a cross (414) or junction (413) of at least two via bars.

8. The method according to claim 7, wherein the modified vias (41) are produced using chemical vapour deposition process.

9. The method according to claim 7, wherein the vias contain Tungsten or any Tungsten alloy.

10. The method according to claim 7, wherein the dielectric layer is removed from a micromechanical region by means of wet or dry isotropic etching.

11. The method according to claim 7, wherein the dielectric layers contain silicon dioxide.

12. The method according to claim 7, wherein the metal layers contain Aluminum or Copper or Aluminum-Copper alloy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a pre-etching cross-section view of an integrated circuit comprising a multi-layer micromechanical component wherein different metal layers are joined using standard-size vias.

(2) FIG. 2 is a post-etching cross-section view of the integrated circuit from FIG. 1, where the multi-layer micromechanical component suffers decomposition due to insufficient attaching force provided by standard vias.

(3) FIG. 3 is a detailed cross-section view of a standard via.

(4) FIG. 4 is a detailed cross-section view of a modified via.

(5) FIG. 5 is a post-etching cross-section view of the integrated with multi-layer micromechanical structure comprising modified vias.

(6) FIGS. 6a to 6g are top views of vias in different embodiments of the invention.

(7) FIGS. 7a to 7d are exploded views of multi-layer cantilevers comprising different modified via types.

(8) FIGS. 8a, 8b are isometric and exploded views of in-plane/out-of-plane capacitive transducer section comprising multi-layer metal structures joined by via mesh.

DETAILED DESCRIPTION OF EMBODIMENTS

(9) FIG. 5 represents a simplified cross-section of an integrated circuit with a multi-layer micromechanical structure 165 comprising modified vias 41. The modified vias are capable to resist the residual stress of the metal layers, so that the micromechanical structure 165 preserves its integrity. The multi-layer micromechanical structure 165 presented in the figure uses three metal and two via layers, however the invention neither specifies a particular number layers that are stuck nor the thickness of the stacked via and metal layers.

(10) FIGS. 6a-6g reveal a variety of via shapes seen from the top. The CVD process deposits a Tungsten within a radius R from the via perimeter. For the sake of clarity it is assumed that R is equal to half-size of a standard via 19, however in some technologies R can be bigger. Increasing the diameter of a standard via leads to a modified via of a first type 411 with a void 441 located in the centre of the via 411.

(11) Another type of a modified via structure can be obtained by stretching the via with increased diameter along one axis in order to obtain a widen via bar 412 with a void that takes a shape of trench 442.

(12) Yet another embodiment of modified via 413 is obtained by joining two via bars of standard width, generating a void 443 in the via bar junction area. Similarly a crossing 414 of two standard width via bars can generate a void 444 in the centre of the crossing. The angle at which the via bars cross or join each other does not have to be 90 degree as in FIGS. 6d and 6e, although in some IC technologies other angles may be forbidden.

(13) In some cases a void diameter obtained by a via bar crossing or junction may be insufficient to guarantee enough metal deposition depth inside the void. In such case the void size can be increased 445 by locally increasing the via diameter 415 around the point of the via bar crossing or junction.

(14) Crossing 416 of two via bars of extended width is yet another embodiment of the invention. In this case the void 446 in the via takes shape of two crossed trenches having increased diameter in the centre of the crossing.

(15) In order to teach better the invention, in FIGS. 7a-7d exploded views of metal-via-metal cantilevers using different shapes of modified vias are presented.

(16) The first exemplary cantilever presented in FIG. 7a comprises bottom metal layer 171 with a matrix of vias of extended diameter 411 that have voids 441 in the centres of vias 411 that are partially filled with the top metal layer 172 forming pin-shaped vertical metal extensions 451 that are stuck inside the voids 441.

(17) The second exemplary cantilever presented in FIG. 7b comprises bottom metal layer 171 with a via bar of extended width 412 with a trench-shaped void 442, that is partially filled with the top metal layer 172 forming a wedge-shaped vertical metal extension 452 that is stuck inside the void 442.

(18) The third exemplary cantilever presented in FIG. 7c comprises a bottom metal layer 171 with several via crossings of standard diameter 414 wherein voids 444 are formed in the centres of the crossings and are partially filled with the top metal layer 172 forming pin-shaped vertical metal extensions 454 that are stuck inside the void 444.

(19) The fourth exemplary cantilever presented in FIG. 7d comprises a bottom metal layer 171 with the modified via 416 arranged as a bar of extended width crossed with several other via bars of extended width, wherein the via void 446 having a shape of a trench crossed with several other trenches is partially filled by a metal structure of corresponding shape 456 and said metal structure is stuck inside the void 446.

(20) The invention is not limited to the geometries presented in FIGS. 6a-6g and FIGS. 7a-7d. The invention in general view reveals a method to obtain a via void and vertical metal extension of a particular shape stuck inside the via void, by taking advantage of the fact that in a standard Tungsten via CVD process, the material is deposited towards entire height of the via only in the area that is within a technology-specific distance R from the via perimeter, while the via area that is more distant to the via perimeter is not entirely filled and in that area the void, that can be filled by the subsequent metal layer, is created. The via geometries presented in FIGS. 6a-6g and FIGS. 7a-7d form a general guideline to obtain other modified vias of desired and possibly more complex shapes that could result in other embodiments of the invention. Also any combination or arrangement of the via geometries presented in FIGS. 6a-6g and FIGS. 7a-7d would produce yet another embodiment of the invention.

(21) The presented method of obtaining modified via shapes is a convenient method that is compatible with standard IC production process and does not require its modification. However a person skilled in the art may develop a different process to obtain similar shapes of vias and vertical metal extensions using different materials than Tungsten and AlCu alloy. Furthermore one could also deposit a via of extended size with another process that does not generate desired void in the via and then pattern the void using a dedicated etching step obtaining in the end a modified via and multi-layer microstructure with similar characteristics.

(22) Another exemplary application of modified vias can be seen in FIGS. 8a and 8b, where a section of a capacitive transducer that can move in-plane and out-of-plane is depicted. Such a microstructure can be a building block of a multi-axis inertial sensor such as accelerometer, gyroscope or a combination of both.

(23) A multi-layer mass 80 is suspended using springs 86 attached to the anchor 872 which is supported on the substrate (not shown). The mass further comprises plurality rotor fingers 88 that are placed between two stator fingers 89 attached to the substrate by anchors 87. For the sake of clarity only one rotor and only two stator fingers are drawn.

(24) The multi-layer mass can be electrically coupled to an electronic circuit arranged at least partially from the active devices on the same substrate, so that the electronic circuit converts the mass position into an electrical signal or by applying a proper electronic signal the circuit can change the position of the mass. For example, by coupling to an electronic circuit, capacitances C1 and C2 between the stator and rotor fingers can be used to sense the horizontal position of the device or can be used to generate electrostatic force that modifies the horizontal position. Similarly the vertical position can be sensed through the capacitance C3 between the multi-layer suspended 80 mass and the bottom fixed plate 82 placed under the suspended multilayer mass 80 and fixed to the substrate.

(25) The multi-layer mass 80 as well as the fingers 88 and 89 are composed of top metal layer 172, via meshes 417 and 418 and bottom metal layer 171. Furthermore via meshes 417 and 418 may enclose a part of IMD 13. Holes 85 facilitate the IMD removal between the multi-layer mass 80 and bottom fixed plate 82.

(26) The via meshes 417 and 418 provide excellent attachment of the metal 172 deposited over the mesh, by generating voids 443 and 444 on the mesh nodes that are partially filled by the metal 172 deposited over the mesh producing pin-shaped vertical metal extensions 453 and 454 that are stuck inside the voids 443 and 444 respectively. In the presented example two-metal-layer structures with modified vias are used, however the concept can be extended to more metal layers.

(27) Furthermore using the via mesh built of Tungsten or another high-density material is a very convenient way of producing microstructures that have much higher overall density than those made mainly from light metals like aluminium or aluminium-copper alloy used to produce interconnection layers. Therefore multi-layer microstructures comprising via meshes are especially predestined to be employed as proof masses of inertial sensors. The via mesh may also protect some part of the IMD 13 from being removed during the etching, what improves even more the overall device density and attachment forces between the layers.

(28) Yet another advantageous feature of via meshes is that a via layer of such shape contribute to the overall lateral capacitance (like C1 and C2) better than would standard vias do and almost as well as the metal layers it joins, therefore it improves a potential device lateral capacitive sensing and actuating performance.

(29) The presented method of obtaining the modified via shapes as well as its application to develop multi-layer microstructures is especially advantageous in case of IC technologies that provide thick metal layers in within the BEOL stack. The vias used to connect thick metal layers tend to usually have also higher thickness and bigger diameter than vias used to connect normal metal layers. Therefore combining multi-layer structures comprising thick metal layers and thick vias is a very convenient way to build bulky micromechanical devices like accelerometers or gyroscopes, as it provides high mass to area ratio and a high lateral capacitance.

(30) The inventors noticed that multi-layer structures comprising thick metal layers and vias with nominal size are even more likely to suffer disintegration after the IMD etching process, than the structures using standard-thickness metal and via layers. On the other hand applying any of the presented techniques to a via with a bigger nominal diameter, like those used for thick metal layers, generates a shape with a higher void diameter, which is filled better by the metal. Furthermore thick metals are less likely to exhibit severe local metal planarity degeneration 47.

CITATION LIST OF REFERENCES

(31) US 20120280393 A1 DAI, CHING-LIANG, et al. A maskless wet etching silicon dioxide post-CMOS process and its application. Microelectronic engineering. 2006, vol. 83, no. 11, p. 2543-2550. FERNNDEZ, DANIEL, et al. Experiments on the release of CMOS-micromachined metal layers. Journal of Sensors. 2010.