DE102019201236B4 - Method for producing a MEMS structure and corresponding MEMS structure - Google Patents

Abstract

A method for producing a MEMS structure with the following steps: Providing a substrate (S) with a micromechanical functional layer arrangement (FS) applied thereon with one or more functional layers, the functional layer arrangement (FS) having a cavity (K) which is opened via a through opening ( D; D '), which has a smaller lateral extent than the functional layer arrangement (FS), is exposed towards an outside of the functional layer arrangement (FS); anddeposition of a sealing layer (O, O ') over the outside of the functional layer arrangement (FS) and 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 ') is on the Outside of the functional layer arrangement (FS) grows and a second area (O ') of the sealing layer (O, O') grows in columnar form from within the cavern (K) below the through opening (D; D '); the second area (O ') the sealing layer (O, O') forms a sealing area (VBO) in the through opening (D; D '), characterized in that an auxiliary layer (HS; HS') is provided below the through opening (D; D ') which • is cantilevered laterally in the functional layer arrangement (FS) and / or is suspended laterally via a spring element (FE) in the functional layer arrangement (FS), and • is surrounded by the cavity (K) and with the through opening (D; D ') overlaps, with the second area (O ') on the Auxiliary layer (HS) grows up

Description

The invention relates to a method for producing a MEMS structure and a corresponding MEMS structure.

State of the art

Although any micromechanical components (MEMS) can also be used, the present invention and the problems on which it is based are explained using MEMS absolute pressure sensor devices.

For their operation, many MEMS components require a defined atmosphere enclosed in a cavern, in particular a vacuum or at least a pressure of well below 100 Torr. Systems that oscillate in resonance, such as rotation rate sensor devices, oscillators that work as a time reference, or MEMS absolute pressure sensor devices, can be cited as an example of this.

5a) -c ) are schematic cross-sectional representations to explain an exemplary production method for a MEMS structure in the form of an absolute pressure sensor device and its mode of operation.

In 5a) -c ) reference symbol S denotes a substrate, for example a silicon wafer substrate. A micromechanical functional layer arrangement is on the substrate S FS with one or more functional layers, such as polysilicon layers, oxide layers, nitride layers, metal layers, etc., applied, the functional layer arrangement FS a cavern K having.

The cavern K is spanned by a membrane M for measuring the absolute pressure, the membrane M having a stamp-shaped electrode ST on its underside. Over the outside of the functional layer arrangement FS A sealing layer V is deposited, which closes through openings D, D ″ which are located to the side of the membrane and into the cavity K flow out. The lateral extension of the through openings D, D ″ is significantly smaller than the lateral extension of the cavern below K .

5a) shows the state immediately after deposition of the sealing layer V, with in the cavern K a predetermined reference pressure P0 is included.

This is followed by reference to 5b) the closure layer V is partially removed, so that only closure areas VS, VS ″ remain in the shape of a plug in the through openings D, D ″.

As in 5c ), an external pressure P on the membrane causes a deformation of the membrane in the direction of the substrate S. The stamp-shaped electrode ST approaches the substrate S, and the absolute pressure can be capacitively detected by means of a substrate electrode (not shown).

To produce the in 5a) -c ) there are many different possibilities in micromechanics. A standard method consists, for example, in applying and structuring various micromechanical functional layers and sacrificial layers on the substrate S. The sacrificial layers are then removed by an etching process with the aid of the through openings D, D ″.

However, two or more substrates with depressions can also be provided and connected to one another by means of a bonding process.

These two basic methods can be combined with one another in any way.

When depositing the sealing layer V, it is important that there is a low pressure in the cavity P0 of typically well below 1 bar is included.

Often the through openings D, D ″ are also designed as narrow trenches, and they have the additional function of electrically separating an electrically conductive layer. With oxide or nitride or oxide nitride deposits, the electrically insulating property can also be made possible.

In particular, LPCVD or PECVD oxide deposits or nitride deposits are suitable for the sealing process.

For example, an LPCVD process with TEOS can be used. At temperatures of typically 700 ° C, TEOS is passed over the MEMS structure to be sealed with a low pressure of typically 300 millitorr. A decomposition reaction of the TEOS occurs on the surface and an oxide layer is grown. This enables deposits with a relatively high degree of conformity to be achieved. The conformity describes the growth ratio of a layer of vertical surfaces to horizontal surfaces during the deposition. In principle, there is no preferred direction with this growth process, and one would theoretically expect a conformity of 1 with a very low working pressure and high flow. Since, however, in narrow trenches or through openings at working pressures that still allow reasonable layer growth rates, the TEOS comes into the narrow trenches or through-openings, a completely conformal deposition cannot be achieved, but only almost conformal depositions.

Furthermore, PECVD from TEOS or silane can be deposited with an oxide layer even at lower temperatures of 250 ° C to 350 ° C with plasma assistance. Due to the plasma support and a directed deposition component associated with it, in principle only low conformities can be achieved with this method. The higher the plasma power, the higher the separation rate, but the lower the conformity. So it's important to find a good balance between compliance and plasma performance. The PECVD processes are beneficial if an oxide layer is to be deposited at a low temperature or if lower conformities are deliberately desired.

With a very high level of conformity, it can be achieved that a narrow access is closed with a relatively small layer thickness. In the case of poor conformity, a very high layer thickness is required to close a narrow trench or a narrow access opening.

6a) -c ) are schematic partial cross-sectional representations to explain the exemplary production method for a MEMS structure, with the deposition of the sealing layer having an idealized conformity of one.

In 6a) -c ) is only the range for the sake of simplicity A. of 5a) -5c ) shown. 6a) -c ) illustrate that with a deposition with an ideal conformity of 1, a layer thickness d1 of the sealing layer V1 that are exactly half the width B2 the passage opening D corresponds, is required. The through opening D can thus be closed over the full height with the closure area VB.

The disadvantage here is that also in the cavern K the full layer thickness d1 and in some areas the thickness d2 is deposited. It can thus happen that the mobility of the membrane M is restricted or inhibited. Other functional elements can also be used in the cavern K deposited sealing layer V1 their functionality are impaired.

7a) -c ) are schematic partial cross-sectional representations to explain the exemplary production method for a MEMS structure, the deposition of the sealing layer having a high conformity of almost one.

In 7a) -7c ) is analogous to 6a) -c ) the temporal course of the closure of the passage opening D in the area A. when the sealing layer is deposited V2 high conformity, which is realized, for example, in an LPCVD deposition. A layer thickness d1 'is required which corresponds approximately to the width d2 of the through opening D in order to close the through opening D. Due to the depletion of the TEOS in the through opening D, the closure region VB 'lies in the oxide of the closure layer V2 above the through opening D. Also with this closure method, in the cavern K a relatively thick sealing layer V2 deposited, which may have the function of components in the cavern K can affect negatively.

8a) -c ) are schematic partial cross-sectional representations to explain the exemplary production method for a MEMS structure, with the deposition of the sealing layer having a low conformity of significantly less than one.

In 8a) -c ) is the temporal closure of a narrow trench or a passage opening D in the area A. with a deposition of the sealing layer V3 to be seen with low conformity, which, for example, provides a PECVD deposition.

A layer thickness d1 ″ is required that is significantly greater than the width d2 of the through opening D in order to close the through opening D with the closure area VB ″. Due to the low conformity of the deposition, this closure area VB ″ lies in the oxide of the closure layer V3 far above the through opening D. The required thickness d1 ″ of the sealing layer is thus disadvantageous V3 , beneficial but that in the cavern K relatively little oxide of the sealing layer V3 is deposited and thus the function of components in the cavern K is not or only slightly influenced.

Overall, therefore, relatively large layer thicknesses of the sealing layer are required in the described methods, which, however, is undesirable because they form the functional layer arrangement in comparison with silicon FS Deviating thermal expansion coefficients cause bending and tension in the MEMS structure. The LPCVD oxide and especially the PECVD oxide have a lower density than thermal oxide and have a tendency to form cracks at higher temperatures, which creates the risk of the sealing area becoming leaky. If the closure area is above the through opening D, the closure width is relatively small.

It is often also desirable to remove the oxide in the areas without an oxide seal in order to achieve a stress-free area of the membrane M, for example. However, because the closure area lies above the through opening and the oxide lying there cannot be removed, a very high topography is created on the surface, which is disadvantageous for further process steps.

Finally, with conformities not equal to 1, a deep notch on the underside and a somewhat shallower notch on the top of the closure area typically forms on the closure area, which means that the closure area has predetermined breaking points when it is pulled or bent, since an excessive stress is created here.

The DE 10 2009 045 385 A1 and the DE 10 2010 000 895 A1 describe methods for closing a trench of a micromechanical component with the aid of a lattice structure.

The EP 2 637 007 A1 describes a capacitive MEMS absolute pressure sensor device.

The US 6 261 957 B1 discloses a self-planarizing trench filling process using HD-PCVD.

From scripture US 2014/0 175 571 A1 a method for producing a MEMS structure is known in which openings in a membrane are closed by creating a closure. In this case, part of the sealing material penetrates through the openings into the cavern located under the membrane. The penetrating closure material forms a cone on the substrate forming the bottom of the cavity, which extends to the opening and forms the closure.

Another way to close an opening in a MEMS structure is from the DE 10 2016 217 001 A1 known.

Disclosure of the invention

The invention provides a method of manufacturing a MEMS structure according to claim 1 and a corresponding MEMS structure according to claim 8.

Preferred developments are the subject of the respective subclaims.

Advantages of the invention

The idea on which the present invention is based is to apply the closure layer with a deposit that has very little conformity, so that no material of the closure layer, for example oxide, is deposited on the edge. In particular, an HDP layer deposition with a sputtering component is proposed. An HDP layer is understood to mean a high-density plasma layer which can be used, for example, as a passivation layer, the HDP layer being formed by a chemical vapor deposition (CVD) process. If no sealing material grows laterally in the through opening, it is possible to close the through opening from the underside and, if necessary, to fill it completely.

On the one hand, this avoids the disadvantages of the prior art described above, and on the other hand, an HDP sealing material, for example HDP oxide, is a very dense sealing material which, in contrast to a PECVD or LPCVD sealing material, has only a very low tendency to crack.

The method according to the invention offers great advantages in terms of costs due to the very high separation rates in the HDP process. The HDP separation process is available both in the front end and in the back end and thus allows a great deal of process flexibility. The closure area that can be achieved by the method according to the invention is stable and tight. A combination with further process steps is easily possible due to the low topography.

In the embodiment according to the invention, an auxiliary layer is provided below the passage opening, which is surrounded by the cavity and overlaps with the passage opening, and wherein the second region grows on the auxiliary layer. This enables the accelerated formation of a sealing area which requires less volume of the sealing layer.

Furthermore, in the embodiment according to the invention, the auxiliary layer is suspended laterally in the functional layer arrangement in a self-supporting manner and / or laterally suspended in the functional layer arrangement via a spring element. In this way internal tensions can be compensated.

According to a further preferred development, the through opening has a first funnel-shaped area which adjoins the outside, and a second channel-shaped area below the first funnel-shaped area. In this way, the formation of the occlusion area can be accelerated.

According to a further preferred development, the first area of the closure layer is on the outside of the functional layer arrangement at least partially removed. A planar topography can be achieved in this way.

According to a further preferred development, an etch stop layer is applied to the functional layer arrangement on the outside below the closure layer, the first region of the closure layer being completely removed. In this way, the first area of the closure layer can be effectively removed without damaging the functional layer arrangement.

According to a further preferred development, the etch stop layer is removed after the first area has been removed and the second area is then overetched so that a planar outside of the functional layer arrangement is obtained. This creates a particularly planar topography.

According to a further preferred development, the HDP method has a back-sputtering component and a conformity of 0.2 or less. This ensures an effective, rapid formation of the closure area.

According to a further preferred development, the sealing layer has an oxide layer and / or a nitride layer and / or an oxide nitride layer. Such layers can be deposited particularly well by means of the HDP process.

Figure list

Further features and advantages of the present invention are explained below on the basis of embodiments with reference to the figures.

• 1a)-g) schematische ausschnittsweise Querschnittsdarstellungen zur Erläuterung eines Herstellungsverfahrens für eine MEMS-Struktur gemäß einer ersten Ausführungsform der vorliegenden Erfindung;
• 2a)-g) schematische ausschnittsweise Querschnittsdarstellungen zur Erläuterung eines Herstellungsverfahrens für eine MEMS-Struktur gemäß einer zweiten Ausführungsform der vorliegenden Erfindung;
• 3a)-i) schematische ausschnittsweise Querschnittsdarstellungen zur Erläuterung eines Herstellungsverfahrens für eine MEMS-Struktur gemäß einer dritten Ausführungsform der vorliegenden Erfindung;
• 4a)-c) schematische ausschnittsweise Querschnittsdarstellungen zur Erläuterung eines Herstellungsverfahrens für eine MEMS-Struktur gemäß einer vierten Ausführungsform der vorliegenden Erfindung;
• 5a)-c) schematische Querschnittsdarstellungen zur Erläuterung eines beispielhaften Herstellungsverfahrens für eine MEMS-Struktur in Form einer Absolutdrucksensorvorrichtung und deren Funktionsweise;
• 6a)-c) schematische ausschnittsweise Querschnittsdarstellungen zur Erläuterung des beispielhaften Herstellungsverfahrens für eine MEMS-Struktur, wobei die Abscheidung der Verschlussschicht eine idealisierte Konformität von Eins aufweist;
• 7a)-c) schematische ausschnittsweise Querschnittsdarstellungen zur Erläuterung des beispielhaften Herstellungsverfahrens für eine MEMS-Struktur, wobei die Abscheidung der Verschlussschicht eine hohe Konformität von nahezu Eins aufweist; und
• 8a)-c) schematische ausschnittsweise Querschnittsdarstellungen zur Erläuterung des beispielhaften Herstellungsverfahrens für eine MEMS-Struktur, wobei die Abscheidung der Verschlussschicht eine niedrige Konformität von wesentlich weniger als Eins aufweist.

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• 1a) -g ) schematic partial cross-sectional representations to explain a manufacturing method for a MEMS structure according to a first embodiment of the present invention;
• 2a) -g ) schematic partial cross-sectional representations to explain a manufacturing method for a MEMS structure according to a second embodiment of the present invention;
• 3a) -i ) schematic partial cross-sectional representations to explain a manufacturing method for a MEMS structure according to a third embodiment of the present invention;
• 4a) -c ) schematic partial cross-sectional representations to explain a manufacturing method for a MEMS structure according to a fourth embodiment of the present invention;
• 5a) -c ) Schematic cross-sectional representations to explain an exemplary production method for a MEMS structure in the form of an absolute pressure sensor device and its mode of operation;
• 6a) -c ) schematic partial cross-sectional representations to explain the exemplary production method for a MEMS structure, the deposition of the sealing layer having an idealized conformity of one;
• 7a) -c ) schematic partial cross-sectional representations to explain the exemplary production method for a MEMS structure, the deposition of the sealing layer having a high conformity of almost one; and
• 8a) -c ) Schematic partial cross-sectional representations to explain the exemplary production method for a MEMS structure, the deposition of the closure layer having a low conformity of significantly less than one.

Embodiments of the invention

In the figures, identical reference symbols denote identical or functionally identical elements.

1a) -g ) are schematic partial cross-sectional representations to explain a manufacturing method for a MEMS structure according to a first embodiment of the present invention.

According to 1a) -g ) becomes a substrate S. with a micromechanical functional layer arrangement applied to it FS , which has one or more functional layers, provided. The substrate S. is for example a silicon wafer substrate, and the functional layer arrangement FS comprises, for example, one or more functional layers made of polysilicon, oxide, nitride, metals, etc. The functional layer arrangement FS has a cavern K on, which has a through opening D, which has a smaller lateral extent than the functional layer arrangement FS having. The passage opening is according to 1a) to an outside of the functional layer arrangement FS exposed.

The cavern K is spanned by a membrane M for measuring the absolute pressure, the membrane M having a stamp-shaped electrode ST on its underside, as already described in relation to FIG 5a) -c ) explained. 1a) -g ) show the area A. of 5a) -c ).

As in 1b) -g ) shown sequentially, a sealing layer is deposited O , O' made of oxide over the outside of the functional layer arrangement FS and the through opening D by means of an HDP method. A first area is growing O the sealing layer O , O' on the outside of the functional layer arrangement FS on, and a second area O' the sealing layer O , O' grows columnar within the cavern K below the through opening D. In the course of the HDP deposition, an occlusion area forms VBO in the through hole D from the substrate S side.

HDP deposition is a degenerate PECVD process. A very low gas pressure is used for the separation. At the same time, a high plasma power is used, the plasma potential being controlled in such a way that a back-sputtering effect occurs on the MEMS structure. Correspondingly selected parameters ensure that the deposition gas, in the present example TEOS, is largely ionized. In this way, a high separation rate can be achieved with very little conformity. The back-sputtering proportion in the plasma reduces conformity to zero. On the horizontal surfaces, the growth rate is greater than the back sputter rate. On vertical surfaces, for example in the through opening D, the back sputtering rate is greater than the growth rate. An equilibrium is established on inclined surfaces, with typical flattened areas at the edges with an incline of around 45 °. Part of the separation material that is sputtered off at the flat is reapplied at the bottom of the edges. This effect helps to ensure that deeper trenches can also be filled. With increasing layer deposition, a funnel forms, which accelerates the deposition in the trench.

In a preferred embodiment of the HDP deposition, the conformity is less than 0.2. A plasma power of more than 2500 watt / m ² is preferably used. The process pressure is typically below 50 millitorr.

Although an oxide layer was deposited as a sealing layer in the above-described embodiments, it is also possible to deposit a nitride layer or an oxide-nitride layer

2a) -g ) are schematic partial cross-sectional representations to explain a manufacturing method for a MEMS structure according to a second embodiment of the present invention.

2a) -g ) show the area A. of 5a) -c ).

As in 2a) -g ), in the second embodiment, below the through opening D, there is a self-supporting laterally in the functional layer arrangement FS suspended auxiliary layer HS provided by the cavern K is surrounded and overlaps with the through hole D. This makes it possible to achieve the second area O' the sealing layer O , O' on the auxiliary layer HS grows up. Thus it is necessary to create the closure area VBO a smaller volume fraction of the second area O' the sealing layer O , O' required. This can be determined by the distance a1 between the auxiliary layer HS and the lower end of the through hole D. The distance a1 can be selected to be smaller than other distances a2 within the cavern K .

In the second embodiment, the formation of the closure area is VBO thus accelerated compared to the first embodiment.

The auxiliary layer HS can in one of the functional layers of the functional layer arrangement FS integrated or is already present in some MEMS processes.

3a) -i ) are schematic partial cross-sectional representations to explain a manufacturing method for a MEMS structure according to a third embodiment of the present invention.

3a) -i ) show the area A. of 5a) -c ).

As in 3a) -i ) is the auxiliary layer HS in the third embodiment via a spring element FE laterally in the functional layer arrangement FS hung up. Such a spring element enables stresses in the closure layer to be absorbed O , O' . Due to the self-supporting limitation in the horizontal direction, some of these stresses can be in the auxiliary layer HS relax in the direction of the spring element FE, creating a very robust closure area VBO can be guaranteed.

In the third embodiment, an etch stop layer is used before the HDP deposition IT on the outside of the functional layer arrangement FS deposited and only then carried out the HDP deposition.

This enables with reference to 3g) -i ), the unneeded oxide of the first area O the sealing layer O , O' to be removed from areas of the outside where it is not needed. This can be achieved by means of a CMP step on the etch stop layer IT stops. Becomes the etch stop layer IT , as in 1i ), then removed and the oxide of the second area O' A particularly planar outer side of the functional layer arrangement can be etched back slightly FS create that is particularly suitable for further processing.

4a) -c ) are schematic partial cross-sectional representations to explain a manufacturing method for a MEMS structure according to a fourth embodiment of the present invention.

4a) -c ) show the area A. of 5a) -c ).

In the fourth embodiment according to 4a) -c ) the through opening D 'has a first funnel-shaped area TB on, on the outside of the functional layer arrangement FS adjoins. At the first funnel-shaped area TB a second channel-shaped area closes KB at. The first funnel-shaped area TB can be produced by a long first isotropic etching step. Through the first funnel-shaped area TB What is achieved is that the filling with oxide is accelerated by the HDP deposition in a very early phase of the layer deposition. The second channel-shaped area KB can be close to the surface through the closure area VBO close.

Optionally, above the closure area following the in 4c ) a cover layer SC, for example a nitride layer, is deposited and structured in such a way that it forms the closure area VBO covered and thus additionally sealed.

Although the present invention has been described on the basis of preferred exemplary embodiments, it is not restricted thereto. In particular, the materials and topologies mentioned are only exemplary and are not restricted to the examples explained.

Although in the above embodiments a closure area for forming a defined atmosphere within an absolute pressure sensor device was formed, the present invention is not restricted to this, but can be used in principle for any closure areas on any MEMS structures.

Claims (10)

A method for producing a MEMS structure with the following steps: Providing a substrate (S) with a micromechanical functional layer arrangement (FS) applied thereon with one or more functional layers, the functional layer arrangement (FS) having a cavity (K) which is opened via a through opening ( D; D '), which has a smaller lateral extent than the functional layer arrangement (FS), is exposed towards an outside of the functional layer arrangement (FS); and depositing a sealing layer (O, O ') over the outside of the functional layer arrangement (FS) and 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 ') the outside of the functional layer arrangement (FS) grows and a second region (O ') of the sealing layer (O, O') grows in columnar form from within the cavern (K) below the through opening (D; D '); the second area (O ') of the sealing layer (O, O') forming a sealing area (VBO) in the through opening (D; D '), characterized in that an auxiliary layer (D; D') is below the through opening (D; D '). HS; HS ') is provided, which • is suspended laterally in the functional layer arrangement (FS) in a self-supporting manner and / or is suspended laterally in the functional layer arrangement (FS) via a spring element (FE), and • is surrounded by the cavity (K) and overlaps with the through opening (D; D '), the second region (O') growing on the auxiliary layer (HS) Procedure according to Claim 1 , wherein the through opening (D ') has a first funnel-shaped area (TB) which adjoins the outside, and a second channel-shaped area (KB) below the first funnel-shaped area (TB). Method according to one of the preceding claims, wherein the first region (O) of the sealing layer (O, O ') on the outside of the functional layer arrangement (FS) is at least partially removed. Procedure according to Claim 3 , an etch stop layer (ES) being applied to the functional layer arrangement (FS) on the outside below the sealing layer (O, O ') and the first area (O) of the sealing layer (O, O') being completely removed. Procedure according to Claim 3 wherein the etch stop layer (ES) is removed after removing the first area (O) and then the second area (O ') is overetched, so that a planar outer side of the functional layer arrangement (FS) is obtained. Method according to one of the preceding claims, wherein the HDP method has a back-sputtering component and has a conformity of 0.2 or less. Method according to one of the preceding claims, wherein the sealing layer (O, O ') has an oxide layer and / or a nitride layer and / or an oxide-nitride layer. MEMS structure comprising: a substrate (S) with a micromechanical functional layer arrangement (FS) applied thereon with one or more functional layers, the functional layer arrangement (FS) having a cavity (K) which extends over a through opening (D; D '), which has a smaller lateral extent than the functional layer arrangement (FS), extends towards an outside of the functional layer arrangement (FS); and a closure layer (O, O ') which has an area (O') which is formed in a columnar manner within the cavity (K) below the through opening (D; D ') and a closure area (VBO) in the through opening (D; D '), characterized in that underneath the through opening (D; D') an auxiliary layer (HS) is provided which is • suspended laterally in the functional layer arrangement (FS) in a self-supporting manner and / or laterally in the via a spring element (FE) Functional layer arrangement (FS) is suspended, and • is surrounded by the cavity (K) and overlaps with the through opening (D; D '), the area (O') being formed on the auxiliary layer (HS). MEMS structure according to Claim 8 wherein the through opening (D ') has a first funnel-shaped area (TB) which adjoins the outside, and a second channel-shaped area (KB) below the first funnel-shaped area (TB). MEMS structure according to one of the Claims 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 and wherein the cavity (K) extends under the membrane.

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