Method for producing a MEMS structure and corresponding MEMS structure

Abstract

The invention provides a method for producing a MEMS structure and a corresponding MEMS structure and a MEMS component. The method comprises the following steps: providing a substrate (S), applying a micromechanical functional layer component (FS) having one or more functional layers on the substrate, the functional layer component (FS) having a cavity (K), the cavity being exposed to the outside of the functional layer (FS) through a through-opening (D; D'), the through-opening having a smaller lateral extension than the functional layer component (FS); depositing a sealing layer (O, O') on the outside of the functional layer component (FS) and the through-opening (D; D') by means of an HDP method such that a first region (O) of the sealing layer (O, O') grows on the outside of the functional layer component (FS), and a second region (O') of the sealing layer (O, O') grows columnarly from within the cavity (K) below the through-opening (D; D'); forming a sealing region (VBO) in the through-opening (D; D') from the second region (O') of the sealing layer (O, O').

Description

Technical Field

[0001] The invention relates to a method for producing a MEMS structure and a corresponding MEMS structure. Background Art

[0002] Although any desired micromechanical components (MEMS) can also be used, the invention and the problem underlying the invention are explained with reference to a MEMS absolute pressure sensor device.

[0003] Many MEMS components require a defined gas pressure enclosed in a cavity in order to operate, in particular in a vacuum or at least at a pressure far below 100 Torr. Examples of this include resonant systems such as rotational speed sensor devices, oscillators operating as time references, or MEMS absolute pressure sensor devices.

[0004] Figure 5a )-c) are schematic cross-sectional views for explaining an exemplary production method of a MEMS structure in the form of an absolute pressure sensor device and its mode of operation.

[0005] exist Figure 5a )-c) in the reference numeral S denotes a substrate, such as a silicon wafer substrate. A micromechanical functional layer component FS having one or more functional layers (such as a polysilicon layer, an oxide layer, a nitride layer, a metal layer, etc.) is applied on the substrate S, wherein the functional layer component FS has a cavity K.

[0006] The cavity K is used to span the membrane M for absolute pressure detection, wherein the membrane M has a convex mold-like Electrode ST. A closing layer V is deposited on the outside of the functional layer component FS, which closes the through-openings D, D″ which are located on the side of the membrane and open into the cavity K. The lateral extension of the through-openings D, D″ is much smaller than the lateral extension of the cavity K located therebelow.

[0007] Figure 5a ) shows the state immediately after the deposition of the sealing layer V, wherein a predetermined reference pressure P0 is enclosed in the cavity K.

[0008] Next, refer to Figure 5b ) The sealing layer V is partially removed so that only the sealing regions VS, VS″ remain in the through-openings D, D″ in a plug-like manner.

[0009] like Figure 5c), an external pressure P acting on the membrane leads to a deformation of the membrane in the direction of the substrate S. In this case, a punch-shaped electrode ST is close to the substrate S and the absolute pressure can be detected capacitively by means of a substrate electrode (not shown).

[0010] To manufacture in Figure 5a )-c) There are many different possibilities in micromechanics for the MEMS structure shown in FIG. 1-4. A standard method is, for example, to apply and structure different micromechanical functional layers and sacrificial layers on a substrate S. The sacrificial layer is then removed by an etching process using through openings D, D″.

[0011] Furthermore, it is also possible to provide two or more substrates having recesses and to connect them to one another by means of a bonding method.

[0012] These two basic methods can be combined with each other in any desired way.

[0013] When depositing the sealing layer V, it is important to seal a low pressure P0 in the cavity, which is usually well below 1 bar.

[0014] The through-openings D, D″ are usually also embodied as narrow trenches and have the additional function of electrically separating the electrically conductive layers. By means of oxide, nitride or oxynitride deposition, electrically insulating properties can additionally be achieved.

[0015] LPCVD or PECVD oxide deposition or nitride deposition is particularly suitable for the sealing process.

[0016] For example, an LPCVD method with TEOS can be used. At a temperature of typically 700° C., TEOS is guided at a low pressure of typically 300 mTorr through the MEMS structure to be sealed. A decomposition reaction of the TEOS occurs at the surface, and an oxide layer grows. This allows a relatively high degree of uniformity to be achieved. The uniformity describes the ratio of the growth of the layers on the vertical planes relative to the layers on the horizontal planes during deposition. In principle, there is no preferred direction with this growth method and therefore theoretically a uniformity of 1 is to be expected at very low operating pressures and high flow rates. However, due to the depletion of TEOS in narrow channels or through-openings at operating pressures that still allow reasonable layer growth rates, a completely uniform deposition cannot be achieved, but only a nearly uniform deposition.

[0017] Furthermore, even at lower temperatures of 250° C. to 350° C., oxide layers can be deposited with the aid of plasma-supported PECVD of TEOS or silane. Due to the plasma support and the directional deposition components associated therewith, only low uniformity can be achieved with this method in principle. The higher the plasma power, the higher the deposition rate, but the lower the uniformity. It is therefore important to find a good balance between uniformity and plasma power. The PECVD method is advantageous if oxide layers are to be deposited at low temperatures or if low uniformity is intentionally desired.

[0018] With a very high conformity, it is possible to close narrow inlets with a relatively low layer thickness. In the case of a low conformity, a very high layer thickness is required to close narrow channels or narrow through-openings.

[0019] Figure 6a )-c) are schematic partial cross-sectional views for illustrating an exemplary method for manufacturing a MEMS structure, wherein the deposition of the sealing layer has an ideal uniformity equal to one.

[0020] exist Figure 6a )-c), for the sake of simplicity, only Figure 5a )-c) area A. Figure 6a )-c) show that in the case of a deposition with an ideal uniformity equal to 1, a closing layer V1 with a layer thickness d1 is required, which corresponds exactly to half the width B2 of the through-opening D. The through-opening D is therefore closed over the entire height with a closing region VB.

[0021] A disadvantage here is that the entire layer thickness d1 is also deposited in the cavity K, while the thickness d2 is deposited in some areas. This can result in the mobility of the membrane M being restricted or impeded. The closing layer V1 deposited in the cavity K can also impair the high performance of other functional elements.

[0022] Figure 7a )-c) are schematic partial cross-sectional views for illustrating an exemplary manufacturing method of a MEMS structure, wherein the deposition of the sealing layer has a high uniformity close to unity.

[0023] and Figure 6a )-c)Similarly, in Figure 7a)-c) shows the time course of the closure in the through-opening D in the region A during the deposition of a highly consistent closure layer V2, which is achieved, for example, during LPCVD deposition. A layer thickness d1' which corresponds approximately to the width d2 of the through-opening D is required to close the through-opening D. Due to the depletion of TEOS in the through-opening D, the closure region VB' is located in the oxide of the closure layer V2 above the through-opening D. In the case of this closure method as well, a relatively thick closure layer V2 is deposited in the cavity K, which can have a negative impact on the function of the components in the cavity K.

[0024] Figure 8a )-c) are schematic partial cross-sectional views for illustrating an exemplary manufacturing method of a MEMS structure, wherein the deposition of the sealing layer has a much lower uniformity than one.

[0025] exist Figure 8a )-c) the temporal closing of the narrow channel or through opening D in the region A can be seen, in which the closing layer V3 is deposited with low uniformity, for example PECVD deposition provides this low uniformity.

[0026] In order to close the through opening D with the aid of the closing layer VB", a layer thickness d1" which is much larger than the width d2 of the through opening D is required. Due to the low uniformity of the deposition, this closed area VB" in the oxide of the closing layer V3 is located far above the through opening D. The required thickness d1" of the closing layer V3 is therefore disadvantageous, but it is advantageous that relatively little oxide of the closing layer V3 is deposited in the cavity K, and therefore the functionality of the components in the cavity K is not affected or is only slightly affected.

[0027] Overall, therefore, a relatively large layer thickness of the sealing layer is required in the described method, which is undesirable, since it has a different thermal expansion coefficient than the silicon of the functional layer component FS, which causes bending and stresses in the MEMS. Compared to thermal oxides, LPCVD oxides and especially PECVD oxides have a lower density and a tendency to form cracks at higher temperatures, which leads to the risk of leakage in the sealing area. If the sealing area is located above the through-opening D, the sealing width is relatively small.

[0028] It is often desirable to remove oxide in areas without oxide sealing, for example in order to achieve stress-free areas of the membrane M. However, since the sealed areas are located above the through-openings and the oxide located there cannot be removed, very high topography is produced on the surface, which is disadvantageous for further process steps.

[0029] Finally, in the case of a consistency not equal to 1 at the closed area, a deeper notch is usually formed on the lower layer and a shallower notch is formed on the upper side of the closed area, which results in the closed area having an expected breaking point when tensioned or bent, since excessive pressure would occur here.

[0030] DE 10 2009 045 385 A1 and DE 10 2010 000 895 A1 describe a method for closing a trench of a micromechanical component by means of a lattice structure.

[0031] EP 2 637 007 A1 describes a capacitive MEMS absolute pressure sensor device.

[0032] US 6,261,957 B1 discloses a self-planarizing trench filling method using HD-PCVD. Summary of the invention

[0033] The present invention provides a method according to the invention for producing a MEMS structure and a corresponding MEMS structure according to the invention.

[0034] Preferred embodiments are the subject matter of the respective dependent claims.

[0035] Advantages of the present invention

[0036] The idea underlying the invention is to apply a closing layer with a deposition having very low consistency, so that no material of the closing layer (e.g. oxide) is deposited at the edges. In particular, a HDP layer deposition with a sputtering component is proposed. An “HDP layer” is to be understood here as a high-density plasma layer which can be used as a passivation layer, for example, wherein the HDP layer is formed by a chemical vapor deposition (CVD) method. If no closing material grows on the sides in the through-opening, the through-opening can be closed from the bottom and, if necessary, can also be completely filled.

[0037] On the one hand, the disadvantages of the prior art can thereby be avoided, while on the other hand, an HDP sealing material (for example an HDP oxide) is a very dense sealing material which has only a very low tendency to cracks compared to PECVD sealing materials or LPCVD sealing materials.

[0038] Due to the very high deposition rates in the HDP method, the method according to the invention offers great advantages in terms of cost. The HDP deposition process can be used both at the front end and at the back end, and thus a high degree of process flexibility can be achieved. The closed areas that can be achieved by the method according to the invention are stable and compact. Due to the small surface shapes, it can be easily combined with other process steps.

[0039] According to a preferred embodiment, the substrate below the cavity is exposed, wherein the second region is grown on the exposed substrate. This enables the formation of a large number of stable closed regions.

[0040] According to another preferred embodiment, an auxiliary layer is provided below the through-opening, which is surrounded by the cavity and overlaps the through-opening, wherein the second region grows on the auxiliary layer. This makes it possible to accelerate the formation of a closed region that requires only a smaller volume of the closing layer.

[0041] According to a further preferred embodiment, the auxiliary layer is suspended laterally in the functional layer component in a self-supporting manner and / or the auxiliary layer is suspended laterally in the functional layer component via spring elements. In this way, internal stresses can be compensated.

[0042] According to another preferred embodiment, the through-opening has a first funnel-shaped The first funnel-shaped region and the second channel-shaped region below the first funnel-shaped region can accelerate the formation of the closed region.

[0043] According to another preferred embodiment, the first region of the sealing layer is at least partially removed on the outer side of the functional layer component. This makes it possible to achieve a planar surface shape.

[0044] According to another preferred embodiment, an etch stop layer is applied to the functional layer component on the outside below the sealing layer, wherein the first region of the sealing layer is completely removed. This allows the first region of the sealing layer to be removed effectively without damaging the functional layer component.

[0045] According to another preferred embodiment, the etching stop layer is removed after the first region is removed, and then the second region is etched from above. This results in a planar outer side of the functional layer component. This enables a particularly planar surface shape.

[0046] According to another preferred embodiment, the HDP method has a back-sputtering component and has a uniformity of 0.2 or less. This ensures efficient and rapid formation of the closed region.

[0047] According to a further preferred embodiment, the closing layer comprises an oxide layer and / or a nitride layer and / or an oxynitride layer. Such layers can be deposited particularly well by means of the HDP method. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The features and advantages of the present invention are described below based on the embodiments with reference to the accompanying drawings. The accompanying drawings show:

[0049] Figure 1a )-g) show schematic partial cross-sectional views for explaining a method for manufacturing a MEMS structure according to a first embodiment of the present invention;

[0050] Figure 2a )-g) show schematic partial cross-sectional views for explaining a method for manufacturing a MEMS structure according to a second embodiment of the present invention;

[0051] Figure 3a )-i) shows a schematic partial cross-sectional view for explaining a method for manufacturing a MEMS structure according to a third embodiment of the present invention;

[0052] Figure 4a )-c) show a schematic partial cross-sectional view for explaining a method for manufacturing a MEMS structure according to a fourth embodiment of the present invention;

[0053] Figure 5a )-c) show schematic cross-sectional views for explaining an exemplary production method of a MEMS structure in the form of an absolute pressure sensor device and its mode of operation;

[0054] Figure 6a )-c) show schematic cross-sectional views for illustrating an exemplary manufacturing method of a MEMS structure, wherein the deposition of the sealing layer has an ideal uniformity equal to one;

[0055] Figure 7a )-c) show schematic cross-sectional views for illustrating an exemplary manufacturing method of a MEMS structure, wherein the deposition of the sealing layer has a high uniformity close to unity;

[0056] Figure 8a )-c) show schematic cross-sectional views for illustrating an exemplary production method for a MEMS structure, wherein the deposition of the sealing layer has a much lower uniformity than one. DETAILED DESCRIPTION

[0057] In the figures, identical elements or elements having the same function are denoted by the same reference symbols.

[0058] Figure 1a )-g) are schematic partial cross-sectional views for explaining the manufacturing method for the MEMS structure according to the first embodiment of the present invention.

[0059] according to Figure 1a )-g) providing a substrate S, on which a micromechanical functional layer component FS is applied, which has one or more functional layers. The substrate S is, for example, a silicon wafer substrate, and the functional layer component FS includes one or more functional layers, for example, made of polysilicon, oxide, nitride, metal, etc. The functional layer component FS has a cavity K, which has a smaller lateral extension than the functional layer component FS. Figure 1a ), the through opening is exposed toward the outside of the functional layer component FS.

[0060] The cavity K is spanned by a membrane M for absolute pressure detection, wherein the membrane M has a convex electrode ST on its underside, as in Figure 5a )-c) as already explained. Figure 1a )-g) shows Figure 5a )-c) area A.

[0061] like Figure 1b )-g) are shown in sequence, a closing layer O, O' composed of an oxide is deposited on the outside of the functional layer component FS and above the through-opening D by means of the HDP method. In this case, a first region O of the closing layer O, O' grows on the outside of the functional layer component FS, and a second region O' of the closing layer O, O' grows columnarly from the inside of the cavity K below the through-opening D. During the HDP deposition, a closing region VBO is formed in the through-opening D from the side of the substrate S.

[0062] HDP deposition is a degenerate PECVD method. For deposition, a very low gas pressure is used. At the same time, a high plasma power is used, wherein the plasma potential is controlled so that a reverse sputtering effect is produced on the MEMS structure. By correspondingly selected parameters, it is possible to ionize the deposition gas to a large extent, which is TEOS in this example. Therefore, a high deposition rate can be obtained under very low consistency. The reverse sputtering part in the plasma can reduce the consistency to zero. The growth rate on the horizontal plane is greater than the reverse sputtering rate. On the vertical plane, for example, in the through opening D, the reverse sputtering rate is greater than the growth rate. Balance is adjusted on the inclined surface, wherein a typical leveling area (Abflachungen) with an inclination of about 45° is produced at the edge. A portion of the deposition material sputtered on the leveling area is coated (auftragen) at the bottom of the edge below. This effect helps to fill deep trenches. Funnels are formed as the layer deposition increases, which accelerates the deposition in the trench.

[0063] In a preferred embodiment of HDP deposition, the uniformity is less than 0.2. Plasma powers greater than 2500 W / m2 are preferably used. Process pressures are typically less than 50 mTorr.

[0064] Although an oxide layer is deposited as the closing layer in the above-described embodiment, a nitride layer or an oxynitride layer can also be deposited.

[0065] Figure 2a )-g) are schematic partial cross-sectional views for explaining a method for manufacturing a MEMS structure according to a second embodiment of the present invention.

[0066] Figure 2a )-g) shows Figure 5a )-c) area A.

[0067] like Figure 2a )-g), in a second embodiment, an auxiliary layer HS is provided below the through-opening D and is suspended laterally in a self-supporting manner in the functional layer assembly FS, which auxiliary layer is surrounded by the cavity K and overlaps the through-opening D. This makes it possible to grow the second region O' of the closed layer O, O' on the auxiliary layer HS. Therefore, only a smaller volume portion of the second region O' of the closed layer O, O' is required to create the closed layer VBO. This can be adjusted by the spacing a1 between the auxiliary layer HS and the lower end of the through-opening D. Here, a spacing a1 that is smaller than the other spacing a2 in the cavity K can be selected.

[0068] Therefore, the formation of the closed area VBO is accelerated in the second embodiment compared to the first embodiment.

[0069] The auxiliary layer HS can be integrated into one of the functional layers of the functional layer assembly FS, or the auxiliary layer can already be present in some MEMS processes.

[0070] Figure 3a )-i) is a schematic partial cross-sectional view for explaining a method for manufacturing a MEMS structure according to a third embodiment of the present invention.

[0071] Figure 3a )-i) shows Figure 5a )-c) area A.

[0072] like Figure 3a )-i), in the third embodiment, the auxiliary layer HS is suspended laterally in the functional layer assembly FS by spring elements FE. Such spring elements can absorb the stresses in the closing layers O, O'. Due to the self-supporting limitation in the horizontal direction, some of these stresses in the auxiliary layer HS can be relaxed in the direction of the spring elements FE, thereby ensuring a very robust closing region VBO.

[0073] In a third embodiment, the etch stop layer ES is deposited on the outer side of the functional layer component FS before the HDP deposition and the HDP deposition is performed only thereafter.

[0074] refer to Figure 3g )-i), which makes it possible to remove the unwanted oxide of the first region O of the closing layer O, O' from the unwanted regions on the outside. This can be achieved with the aid of a CMP step, which stops on the etch stop layer ES. Figure 3i ), after which the etch stop layer ES is removed and the oxide of the second region O' is slightly etched back, a particularly planar outer side of the functional layer component FS can be produced, which is particularly suitable for further processing.

[0075] Figure 4a )-c) are schematic partial cross-sectional views for explaining a method for manufacturing a MEMS structure according to a fourth embodiment of the present invention.

[0076] Figure 4a )-c) shows Figure 5a )-c) area A.

[0077] In accordance with Figure 4a )-c) in a fourth embodiment, the through opening D' has a first funnel-shaped region TB, which adjoins the outside of the functional layer assembly FS. The first funnel-shaped region TB is connected to the second channel-shaped region KB. The first funnel-shaped region TB can be produced by a long first isotropic etching step. The first funnel-shaped region TB enables the filling of the oxide to be accelerated by HDP deposition at a very early stage of the layer deposition. The second channel-shaped region KB can be closed near the surface by the closing region VBO.

[0078] Optionally, in Figure 4c ), a covering layer SC (for example a nitride layer) is also deposited above the closing region and structured in such a way that it covers the closing layer VBO and thus additionally seals it.

[0079] Although the invention has been described based on preferred embodiments, it is not limited thereto. In particular, the materials and surface shapes mentioned are merely exemplary and are not limited to the examples described.

[0080] Although in the above embodiment, a closed region for forming a defined gas pressure is formed within the absolute pressure sensor device, the present invention is not limited thereto but can be used for any closed region on any MEMS structure in principle.

Claims

1. A method for manufacturing a MEMS structure, the method comprising the following steps: A substrate (S) is provided, on which a micromechanical functional layer component (FS) is applied, the functional layer component having one or more functional layers, wherein: The functional layer component (FS) has a cavity (K) which is exposed toward the outside of the functional layer (FS) through a through-opening (D; D'), wherein the through-opening has a smaller lateral extension than the functional layer component (FS); Depositing a sealing layer (O, O') on the outer side of the functional layer component (FS) and above the through-opening (D; D') by means of an HDP method in such a way that a first region (O) of the sealing layer (O, O') grows on the outer side of the functional layer component (FS) and a second region (O') of the sealing layer (O, O') grows in a columnar manner starting from the interior of the cavity (K) below the through-opening (D; D'); wherein a closed region (VBO) is formed in the through-opening (D; D') by a second region (O') of the closed layer (O, O'), It is characterized in that an auxiliary layer (HS; HS') is provided below the through opening (D; D'), the auxiliary layer is self-supportingly suspended laterally in the functional layer component (FS) and / or the auxiliary layer is suspended laterally in the functional layer component (FS) via a spring element (FE), and the auxiliary layer is surrounded by the cavity (K) and overlaps with the through opening (D; D'), wherein the second region (O') grows on the auxiliary layer.

2. The method according to claim 1, wherein The through opening (D') has a first funnel-shaped area (TB) and a second channel-shaped area (KB), wherein the first funnel-shaped area is adjacent to the outer side and the second channel-shaped area is below the first funnel-shaped area (TB).

3. The method according to claim 1 or 2, wherein: A first region (O) of the sealing layer (O, O′) is at least partially removed on the outer side of the functional layer component (FS).

4. The method according to claim 3, wherein: An etch stop layer (ES) is applied to the functional layer component (FS) on the outer side below the terminating layer (O, O′), and the first region (O) of the terminating layer (O, O′) is completely removed.

5. The method according to claim 4, wherein: After the first region (O) has been removed, the etch stop layer (ES) is removed and subsequently the second region (O′) is etched from above, so that a planar outer side of the functional layer component (FS) is obtained.

6. The method according to claim 1 or 2, wherein: The HDP process has a reverse sputtering portion and has a uniformity of 0.2 or less.

7. The method according to claim 1 or 2, wherein: The sealing layer (O, O′) comprises an oxide layer and / or a nitride layer and / or an oxynitride layer.

8. A MEMS structure, comprising: A substrate (S) on which a micromechanical functional layer component (FS) is applied, the functional layer component having one or more functional layers, wherein: The functional layer component (FS) has a cavity (K), which extends toward the outside of the functional layer component (FS) through a through-opening (D; D'), wherein the through-opening has a smaller lateral extension than the functional layer component (FS); a sealing layer (O, O') having a second region (O') which is formed cylindrically within the cavity (K) below the through-opening (D; D') and forms a sealing region (VBO) in the through-opening (D; D'), It is characterized in that an auxiliary layer (HS) is provided below the through opening (D; D'), the auxiliary layer (HS) is self-supportingly suspended laterally in the functional layer component (FS) and / or the auxiliary layer (HS) is suspended laterally in the functional layer component (FS) via a spring element (FE), and the auxiliary layer is surrounded by the cavity (K) and overlaps with the through opening (D; D'), wherein the second area (O') is constructed on the auxiliary layer (HS).

9. The MEMS structure according to claim 8, wherein: The through opening (D') has a first funnel-shaped area (TB) and a second channel-shaped area (KB), wherein the first funnel-shaped area is adjacent to the outer side and the second channel-shaped area is below the first funnel-shaped area (TB).

10. The MEMS structure according to claim 8 or 9, wherein: The MEMS structure comprises an absolute pressure sensor device, and the through-opening (D; D') adjoins a membrane (M) for absolute pressure detection, wherein the cavity (K) extends beneath the membrane.

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