JP2009078315A - Sealing structure and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sealing structure which can be manufactured in a relatively inexpensive and stable manner to be miniaturized with a protecting film for sealing. <P>SOLUTION: The sealing structure comprises a structure 10 formed on a substrate 1, a dummy member 20 arranged on the substrate 1 for the structure 10, the protecting film 7 provided on the structure 10 and the dummy member 20 for sealing the structure 10 and the dummy member 20, and a hollow space 6 provided between the structure 10 and the protecting film 7. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sealing structure having a structure in which a hollow space is formed around a structure (for example, an electromechanical element) and the structure and the space are sealed with a protective film, and a method for manufacturing the same.

In recent years, with the progress of miniaturization manufacturing technology on substrates, electromechanical elements, so-called MEMS elements (micro electro mechanical systems: Micro Electro Mechanical Systems), and small devices incorporating the MEMS elements have attracted attention. Has been.
The MEMS element is an element obtained by electrically and mechanically coupling a vibrator that is a movable structure and a semiconductor integrated circuit that controls driving of the vibrator. A vibrator is incorporated in a part of the element, and the vibrator is electrically driven by applying a Coulomb attractive force between the electrodes.

  Among such MEMS elements, those formed using a semiconductor process, in particular, have a small area occupied by the device, can realize a high Q value (an amount representing the sharpness of resonance of the vibration system), and other semiconductor devices. For example, utilization as a high-frequency element for wireless communication has been proposed.

In the MEMS element, it is necessary to secure a space around the movable part of the vibrator so that the vibrator can operate.
The space around the movable portion is usually secured by so-called sacrificial layer etching.
That is, a material called a sacrificial layer is formed by filling the periphery of the MEMS element, and the sacrificial layer is removed by etching in a later process.

The MEMS element manufactured in this way is exposed to the atmosphere as it is.
When the MEMS element is exposed to the atmosphere, it is directly affected by the use environment, including adhesion of moisture and dust in the atmosphere, and it is expected that the reliability of the MEMS element will be hindered. For this reason, it is limited to some device applications that directly sense the state of the usage environment, such as a pressure sensor.
Moreover, since the mounting process at the time of device fabrication is exposed to a severer environment than at the time of use, the yield is remarkably reduced. In addition, in some devices utilizing mechanical resonance, operation under reduced pressure may be desirable due to their characteristics.

  For this reason, the MEMS element needs to be finally sealed in some form.

Conventionally, a relatively expensive hermetic package or the like has been used to protect the MEMS element. However, in recent years, a structure for sealing the MEMS element at a wafer level has been studied for cost reduction. Yes.
In particular, in so-called surface MEMS manufactured using a semiconductor thin film process, it is expected that the added value will be improved by making it into a single chip with other peripheral circuits and systems. Therefore, process consistency with elements other than the embedded MEMS is considered. Attempts have also been made to divert standard CMOS processes to this wafer level sealing structure (see, for example, Patent Document 1).

  When sealing a structure such as a MEMS element during a wafer process, usually a step of forming a sacrificial layer on the structure and a protective film for sealing the structure on the sacrificial layer are formed. A film forming step and a step of removing a sacrificial layer inside the protective film to form a hollow structure are taken.

JP 2006-263902 A

  Since the sacrificial layer reflects the shape of the underlying structure, the shape of the internal structure is similarly reflected in the protective film on the sacrificial layer.

For example, as shown in a cross-sectional view in FIG. 8, a space 56 above the MEMS element structure 60 in which the signal line 53 and the vibrator of the cantilever beam 54 are arranged via the space 55 is provided. Let us consider a case where the protective film 57 is formed. In the figure, 51 is a substrate, 52 and 58 are insulating layers, and 59 is a sealing material for sealing holes for etching the sacrificial layer.
A certain amount of space is provided between two adjacent structures 60 for reasons such as securing the characteristics of the MEMS element. And it has a big level | step difference with the structure 60 and the part between them. For this reason, also in the protective film 57, the shape of the level | step difference is reflected and it is bent in the part enclosed with the broken line.

  As described above, when the level difference of the internal structure 60 is large, the shape of the level difference is reflected also in the protective film 57, such as a part of the base of the level difference of the protective film 57, such as a part surrounded by a broken line in FIG. Stress tends to concentrate. For this reason, it has caused the occurrence of cracks in the protective film 57 and a decrease in hermeticity.

On the other hand, in Patent Document 1, a MEMS element and a sealing structure for protection thereof are formed using a wiring process of a semiconductor device having a normal CMOS structure, and a part of an interlayer insulating film between the wirings is formed. A manufacturing method used as a sacrificial layer has been proposed.
In addition, it is described that an interlayer insulating film serving as a sacrificial layer is planarized using a CMP (chemical mechanical polishing) method or the like as necessary.
If the interlayer insulating layer is planarized in this way, the above-described problem of the step of the protective film can be avoided.

However, if such a planarization process is performed in the production of a general MEMS device that does not require multilayer wiring, the manufacturing cost increases.
This is because the planarization process is usually performed by an apparatus different from the film formation process, and thus cannot be performed as a series of processes, and the number of processes increases.

Further, in general, when the planarization process is performed by a CMP method or the like, the uniformity within the wafer surface is inferior to the film formation process or the like, and the dependency on the pattern of the underlying structure is large.
For this reason, when it is desired to precisely control the thickness of the sacrificial layer on the MEMS element, such as a configuration in which the detection electrode is disposed on the upper side of the structure of the MEMS element, the planarization process is not suitable.

  In addition to the configuration using the MEMS element, it is necessary to provide the structure with a hollow structure, and the above-described problem occurs even in a configuration in which the hollow structure is sealed with a protective film.

  In order to solve the above-described problems, the present invention provides a sealing structure that can be stably manufactured at a relatively low cost and can be downsized by sealing with a protective film, and a method for manufacturing the same. Is.

  In the sealing structure of the present invention, a structure is formed on a substrate, a dummy member for the structure is disposed on the substrate, and a protective film that seals the structure and the dummy member on the structure and the dummy member And a hollow space is provided between the structure and the protective film.

  The method for manufacturing a sealing structure of the present invention includes a step of forming a structure and a dummy member on a substrate, a step of forming a sacrificial layer covering at least the structure, and a structure on the sacrificial layer. And forming a protective film for sealing the dummy member, forming an opening reaching the sacrificial layer in the protective film, etching the sacrificial layer through the opening of the protective film, and removing the sacrificial layer And a step of forming a hollow space on the structure and a step of sealing the opening of the protective film with a sealing material.

  According to the configuration of the sealing structure of the present invention described above, the dummy member for the structure is arranged on the substrate, and the protective film for sealing the structure and the dummy member is provided. As a result, the level difference due to the structure can be relaxed by the dummy member, and the level difference of the protective film can be relaxed, so that it is possible to prevent the occurrence of cracks, a decrease in airtightness, and the like in the protective film.

  According to the manufacturing method of the sealing structure of the present invention described above, the structure and the dummy member are respectively formed, the sacrificial layer is formed so as to cover at least the structure, and the structure and the dummy member are sealed on the sacrificial layer. The protective film which stops is formed. Since the dummy member is formed, the step between the sacrificial layer and the protective film due to the structure is relaxed. Thereby, in the protective film, it is possible to prevent the occurrence of cracks and the decrease in airtightness.

  According to the above-described present invention, since it is possible to prevent the generation of cracks and the decrease in airtightness in the protective film, high reliability can be realized in the sealing structure.

As an embodiment of the present invention, FIG. 1 shows a schematic configuration diagram (cross-sectional view) of a sealing structure.
A structure 10 of a MEMS element is formed on an insulating layer 2 on the surface of a substrate 1 such as a silicon substrate.
The structure 10 includes a signal line 3 also serving as an electrode, and a cantilever beam 4 having a support portion 4A at one end (left side in the figure).
In the illustrated cross section, two structures 10 are arranged.

As in the conventional configuration shown in FIG. 8, a protective film (cavity film) 7 is provided on the structure 10 through a hollow space 6.
The space 6 is formed by sequentially removing the sacrificial layer and the protective film 7 and then removing the sacrificial layer by etching.
The protective film 7 has a hole for removing the sacrificial layer by etching, and the hole is filled with a sealing material 9. The space 6 is sealed by the protective film 7 and the sealing material 9.

The insulating layer 2 on the substrate 1 becomes a base stopper layer when removing the interlayer film and the sacrificial layer. An insulating layer that also functions as these functions may be formed, or a stacked film of an interlayer film (for example, a silicon oxide film) and a base stopper film (for example, a silicon nitride film) may be used.
The signal line 3 and the beam 4 can be formed of, for example, polycrystalline silicon. Polycrystalline silicon may be doped with impurities such as phosphorus as necessary.
For the protective film (cavity film) 7, for example, polycrystalline silicon can be used.

In the present embodiment, in particular, the dummy members 20 are arranged around the structures 10, that is, between the adjacent structures 10 and outside the structures 10.
A protective film 7 is provided on the structure 10 and the dummy member 20 via the space 6.
Thus, by arranging the dummy member 20 between the structures 10, the step due to the structure 10 can be relaxed by the dummy member 20, and the upper protective film 7 can be planarized.

The dummy member 20 includes a lower first layer 11 and a second layer 12 having a T-shaped cross section thereon.
The first layer 11 of the dummy member 20 is made of the same material as the signal line 3 of the structure 10 and has the same thickness.
The second layer 12 of the dummy member 20 is made of the same material as the beam 4 of the structure 10 and has the same thickness.

In the dummy members 20 at the left and right ends, the protective film 7 and the sealing material 9 are placed on the second layer 12. The protective film 7 is formed thicker in the lower part than the other part in the part on the dummy member 20, and the protective film 7 is the second layer of the dummy member 20 through this part (support part 7 A of the protective film 7). 12 is supported.
Furthermore, the outer sides of the left and right dummy members 20 are sealed with an insulating layer 8.

In the mask for processing the structure 10, a dummy member 20 having the same height is formed around the structure 10 of the MEMS element without adding a process by adding a pattern for forming the dummy member 20. Can be formed.
At this time, the distance between the structure 10 of the MEMS element and the dummy member 20 is set to be equal to or smaller than the upper sacrificial layer, or the width embedded in the upper sacrificial layer and the protective film 7. As a result, the protective film 7 to be formed is flattened, so that stress concentration on the step or the like as shown in FIG. 8 does not occur.

For example, the interval between the structure 10 and the dummy member 20 is set to 0.5 μm, and the thickness of the upper sacrificial layer, that is, the thickness of the space 6 is set to 0.4 μm.
Needless to say, the present invention is not limited to this combination.

More preferably, the distance between the structure 10 and the dummy member 20 is set to be twice or less the thickness of the space 6.
If the distance between the structure 10 and the dummy member 20 exceeds twice the thickness of the space 6, the surface of the sacrificial layer on the distance is dented when the sacrificial layer for forming the space 6 is formed. Therefore, it is necessary to thicken the protective film formed on the sacrificial layer to some extent.

Further, the interval between the structure 10 and the dummy member 20 is set to an appropriate size corresponding to the size of the structure 10 and the distance between the structures 10 necessary for securing the characteristics required for the structure 10. Selected.
The size of the structure 10 of the MEMS element varies, and is mainly several μm to several tens of μm, but may be less than 1 μm or around 1 mm.

The dummy member 20 may be formed independently of the structure 10, or a part of the structure 10 may be deformed to be a dummy member if there is no problem in device characteristics.
In the cross section shown in FIG. 1, the dummy member 20 is formed independently of the structure 10. For example, in the cross section (not shown), each part of the structure 10 and the dummy member 20 (for example, the signal line 3 and the first member The layers 11 and the like may be connected to each other.

The sealing structure shown in FIG. 1 can be manufactured as follows, for example.
First, an insulating layer 2 is formed on the substrate 1 as a base stopper layer when removing the interlayer film and the sacrificial layer.
Next, a conductor film 21 is formed on the insulating layer 2. Thereafter, the conductor film 21 is patterned to form the signal line 3 and the first layer 11 of the dummy member 20 as shown in FIG. 2A.
Thereafter, as shown in FIG. 2B, the lower sacrificial layer 22 is formed over the entire surface so as to cover the signal line 3 and the first layer 11.

  As described above, the insulating layer 2 may be a laminated film in which an interlayer film and a base stopper layer are formed with insulating films of different materials. In this case, the respective insulating films are sequentially formed.

Next, as shown in FIG. 3C, an opening for forming the support 4A of the beam 4 is provided in the lower sacrificial layer 22, and an opening for opening the first layer 11 is provided in the lower sacrificial layer 22 at the same time. .
Subsequently, these openings in the lower sacrificial layer 22 are filled, and a conductor film 23 is formed on the entire surface. Thereafter, the conductor film 23 is patterned to form the beam 4 of the structure 10 and the second layer 12 of the dummy member 20, respectively. Thereby, many structures 10 and dummy members 20 of cantilever beam 4 can be formed on the same plane, respectively.

Next, as shown in FIG. 4E, an upper sacrificial layer is formed. In FIG. 4E and thereafter, the upper sacrificial layer and the lower sacrificial layer 22 shown in FIG.
Next, as shown in FIG. 4F, openings that reach the second layer 12 of the left and right dummy members 20 are formed in the sacrificial layer 24. This opening is for forming the support portion 7 </ b> A of the protective film 7.

Subsequently, as shown in FIG. 5G, a protective film (cavity film) 7 is formed.
At this time, since the dummy member 20 is disposed around the structure 10 through a gap embedded in the sacrificial layer 24, the surface after the sacrificial layer 24 is formed is generated by the conventional structure. Thus, the protective film 7 on the structure 10 and the protective film 7 on the dummy member 20 are formed in a continuous flat plate shape.
Further, the support portion 7A of the protective film 7 is formed on the second layer 12 of the left and right dummy members 20.

Thereafter, as shown in FIG. 5H, an opening 25 leading to the sacrificial layer 24 is provided in a part of the protective film 7.
Next, an etching agent is injected through the opening 25 of the protective film 7 to etch the sacrificial layer 24. As a result, as shown in FIG. 6I, the place where the sacrificial layer 24 is located becomes a space, and between the signal line 3 and the beam 4 and between the structure 10 and the dummy member 20 and the protective film 7, the space 5, 6 is possible.
Thereafter, as shown in FIG. 6J, the opening 25 of the protective film 7 is filled, a sealing material 9 is formed, and the sealing material 9 is patterned.
In this way, the apparatus shown in FIG. 1 can be manufactured.

According to the above-described embodiment, by providing the dummy member 20 between the adjacent structures 10, the protective film (cavity film) 7 on the space 6 is flattened, and the protective film on the structure 10 is obtained. 7 and the protective film 7 on the dummy member 20 are formed in a continuous flat plate shape, and the protective film 7 does not have a step that causes stress concentration. Therefore, in the protective film 7, it is possible to prevent the occurrence of cracks, the decrease in airtightness, and the like.
Therefore, high reliability can be realized in the sealing structure miniaturized by the protective film 7.

  Further, according to the present embodiment, the signal line 3 of the structure 10 and the first layer 11 of the dummy member 20, the beam 4 of the structure 10 and the second layer 12 of the dummy member 20 are made of the same material. It is formed with layers. Thereby, since it can form simultaneously in the same process, it is not necessary to add a mask or a process.

  Furthermore, since the protective film 7 is planarized by the dummy member 20, no additional process is required, fine control is possible, and variations within the wafer are also required, compared to the case where the sacrificial layer is planarized by CMP or the like. It has the advantage that it does not easily occur.

Even if the gap between the structure 10 and the dummy member 20 is not filled with the sacrificial layer 24 alone, for example, if the filling is completed when the protective film 7 is formed thereon, the surface of the protective film 7 above the gap. Since the step is eliminated, the same effect can be obtained. The gap between the structural body and the dummy member may be filled by sequentially forming the sacrificial layer 24 and the protective film 7.
In this case, a structure in which the protective film 7 partially enters (projects) into the space between the structure 10 and the dummy member 20 is obtained.

In this case, preferably, the distance between the structure 10 and the dummy member 20 is set to not more than twice the sum of the thickness of the space 6 and the thickness of the protective film 7.
If the distance between the structure 10 and the dummy member 20 exceeds twice the sum of the thickness of the space 6 and the thickness of the protective film 7, the protective film 7 on the distance is not flat and bends downward. Compared with the flat protective film 7, stress is easily generated.

  In addition, although the above-described embodiment uses a cantilever beam structure, a structure similar to this, such as a double-supported beam structure or a structure in which a beam is supported at an intermediate portion, can be similarly considered. Needless to say.

  In the above-described embodiment, the structure 10 and the dummy member 20 are formed at the same height by the layer formed by patterning the common layer at the same time. A configuration with a slight difference is also possible. Even in such a case, the effect of flattening the protective film can be obtained by reducing the level difference of the protective film as compared with the configuration without the dummy member.

  In addition, the position where the dummy member is provided between the adjacent structures may be the longitudinal direction of the structure, the direction orthogonal to the longitudinal direction of the structure, or both of the structures having a generally elongated shape. Absent. What is necessary is just to select the position of a dummy member suitably according to the arrangement layout of structures, such as the space | interval of each structure.

Moreover, you may make it support a protective film with arbitrary dummy members.
In FIG. 1, the protective film 7 is supported by the left and right dummy members 20.
On the other hand, as shown in a cross-sectional view in FIG. 7, a support portion 7 </ b> A that supports the protective film 7 may be formed on the dummy member 20 in the middle.
Furthermore, you may make it support a protective film directly with the dummy member in the middle. And it is good also as a structure without a hollow space between the dummy member and protective film which support a protective film.

  In the above-described embodiment, the structure 10 and the dummy member 20 are formed of the same material. However, in the present invention, the structure and the dummy member are not limited to the same material.

The structure is not limited to a structure of an electromechanical element such as a MEMS element. In the present invention, the structure includes other structures as long as the structure requires a hollow structure.
For example, the present invention can be applied to a filter using an element (piezoelectric thin film resonator or the like) having a piezoelectric body other than the MEMS element.

In the above-described embodiment, the case where there are a plurality of structures 10 has been described. However, the present invention can also be applied to the case where there is one structure. When there is one structure body, a dummy member may be provided in the vicinity of the structure body.
For example, the structure of the MEMS element may have a complicated planar layout for realizing its function. In this case, even if there is only one structure, a large step is formed on the protective film. Therefore, it is effective to apply the present invention to provide a dummy member.

  The present invention is not limited to the above-described embodiment, and various other configurations can be taken without departing from the gist of the present invention.

It is a schematic block diagram (sectional drawing) of the sealing structure of one embodiment of this invention. A and B are process diagrams showing a manufacturing method of the sealing structure of FIG. C, D It is process drawing which shows the manufacturing method of the sealing structure of FIG. E, F It is process drawing which shows the manufacturing method of the sealing structure of FIG. G and H are process diagrams showing a manufacturing method of the sealing structure of FIG. I, J It is process drawing which shows the manufacturing method of the sealing structure of FIG. It is a schematic block diagram (sectional drawing) of the structure which deform | transformed the sealing structure of FIG. It is a schematic sectional drawing of the structure which sealed the structure of the MEMS element with the protective film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate, 2 Insulating layer, 3 Signal line, 4 Beam, 5, 6 Space, 7 Protective film (cavity film), 8 Insulating layer, 9 Sealing material, 10 Structure, 20 Dummy member, 21, 23 Conductor film, 22 lower sacrificial layer, 24 sacrificial layer, 25 opening

Claims (10)

A structure is formed on the substrate,
A dummy member for the structure is disposed on the substrate,
A protective film for sealing the structure and the dummy member is provided on the structure and the dummy member,
A hollow structure is provided between the structure and the protective film.   The sealing structure according to claim 1, wherein the protective film on the structure and the protective film on the dummy member are formed in a continuous flat plate shape.   The sealing structure according to claim 1, wherein the dummy member is formed independently of the structure.   The sealing structure according to claim 1, wherein the dummy member and the structure are partially connected.   The sealing structure according to claim 1, wherein the dummy member and the structure are formed by patterning a common layer.   The sealing structure according to claim 1, wherein a gap between the structure and the dummy member is not more than twice the thickness of the hollow space between the structure and the protective film. .   The gap between the structure and the dummy member is not more than twice the sum of the thickness of the hollow space between the structure and the protective film and the thickness of the protective film. The sealing structure according to claim 1.   The sealing structure according to claim 1, wherein the structure is an electromechanical element. Forming a structure and a dummy member on the substrate, and
Forming a sacrificial layer covering at least the structure;
Forming a protective film for sealing the structure and the dummy member on the sacrificial layer;
Forming an opening reaching the sacrificial layer in the protective film;
Etching the sacrificial layer through the opening of the protective film, removing the sacrificial layer, and forming a hollow space on the structure;
Sealing the opening of the protective film with a sealing material. A method for manufacturing a sealing structure, comprising:   The sealing structure according to claim 9, wherein the structure and the dummy member are simultaneously formed by patterning a common layer in the step of forming the structure and the dummy member, respectively. Manufacturing method.

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