JP2006255855A - Manufacturing method for electromechanical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing technology for manufacturing an electromechanical element haivng a narrow gap structure at low cost. <P>SOLUTION: This manufacturing method for an electromechanical element includes: a sacrifice layer forming process of forming a sacrifice layer 12 on a substrate 11; a first conductive layer forming process of forming first conductive layers 13, 14 and 15 on the sacrifice layer; a spacer layer forming process of forming spacer layers 16 on surfaces of the first conductive layers; a second conductive layer forming process of forming second conductive layers 17, 18 coming into contact with the spacer layer on the sacrifice layer; and a release process of removing part of the sacrifice layer and the spacer layer to separate at least part 13, 14 of the first conductive layers or the second conductive layers from the substrate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method for manufacturing an electromechanical element, and more particularly to a manufacturing technique suitable for manufacturing a minute electromechanical element configured as a MEMS structure.

In general, an electromechanical system created by microfabrication technology using semiconductor manufacturing technology
It is called MS (Micro Electro Mechanical System) or NEMS (Nano Electro Mechanical System), and it is widely used for physical sensors, biochemical sensors, electronic devices in RF field such as varactor diodes and resonators. Used in the field.

One of the most typical structures of MEMS is a type of lateral direction that has a fixed electrode and a mechanically movable part separated from the stationary electrode, and measures the movement of the mechanically movable part by changing the capacitance between them. It is known as an operating capacitive element. In order to increase the sensitivity of the conversion function in this element, or to reduce the driving voltage, it is extremely important to reduce the capacitance gap (the gap between the fixed electrode and the mechanically movable part). For this reason, several methods for forming a narrow gap structure of about 100 nm by using a nanolithographic process have been proposed.

Another method for manufacturing the narrow gap structure is to form a spacer layer with an insulating material on the side surface of the mechanically movable part formed on the sacrificial layer, and then to form a seed layer on a part other than the mechanically movable part. After the formation, there is a method of forming a metal electrode on the seed layer, and finally removing the spacer layer together with the sacrificial layer. This method can also produce a narrow gap structure of 100 nm or less ( For example, see the following non-patent document 1).

A sacrificial layer having an opening is formed on the substrate, and a conductive layer constituting a mechanically movable portion is formed on the sacrificial layer, thereby simultaneously forming a support portion aligned with the opening of the sacrificial layer and patterning. Then, a method of forming a mechanically movable portion supported by the support portion by removing the sacrificial layer is known (for example, see Non-Patent Document 2 below).
Double Tea Sue, JR Clark and CTI Neuen “Submicron Capacitance Gap Process of Multi-layer Metal Electrode Transverse Electromechanical Resonator” Technical Digest IEEE International Micro Electromechanical Systems Conference Interlaken Switzerland 2001 January 21-25, pages 349-352 (W.-T. Hsu, JR Clark, and CT-C. Nguyen, "A sub-micron capacitive gap process for multiple-metal-electrode lateral micromechanical resonators," Technical Digest , IEEE Int. Micro Electro Mechanical Systems Conf., Interlaken, Switzerland, Jan. 21-25, 2001, pp. 349-352.) Jay Wang, Zet Len and CTC Neuen "Self-Aligned 1.14GHz Vibration Radial Mode Disc Resonator" Technical Paper Digest The 12th Solid State Sensors and Actuators International Conference (Transducers 03) Boston Massachusetts, June 8-12, 2003, pages 947-950 (J. Wang, Z. Ren, and CT-C. Nguyen, "Self-aligned 1.14-GHz vibrating radial-mode disk resonators," Dig. of Tech. Papers, the 12th Int. Conf. on Solid-State Sensors & Actuators (Transducers'03), Boston, Massachussets, June 8-12, 2003, pp. 947-950.)

However, the above-described method using the nanolithography process has a problem that it is difficult to reduce the manufacturing cost because the cost of the nanolithography process is high and batch processing is difficult.

On the other hand, the method using the spacer layer does not use a nanolithography process, but has a number of manufacturing steps and a complicated process flow, so that it is difficult to reduce the manufacturing cost similarly to the above. is there. In addition, this method uses special processing steps such as formation and patterning of a seed layer and a deposition process of a metal layer on the seed layer, so that it can be adapted to a normal semiconductor manufacturing process (for example, a CMOS process). Cannot
There is also a problem that it is difficult to realize monolithic integration of the MEMS structure and the integrated circuit.

Therefore, the present invention solves the above-described problems, and an object thereof is to provide a manufacturing technique that can manufacture an electromechanical element having a narrow gap structure at a low cost.

In view of such circumstances, the method of manufacturing an electromechanical element of the present invention includes a sacrificial layer forming step in which a sacrificial layer is formed on a substrate, and a first conductive layer forming in which a first conductive layer is formed on the sacrificial layer. A step of forming a spacer layer on the surface of the first conductive layer, a second conductive layer forming step of forming a second conductive layer on the sacrificial layer in contact with the spacer layer, A release step in which a part of the sacrificial layer and the spacer layer are removed and at least a part of the first conductive layer or the second conductive layer is separated from the substrate.

According to the present invention, the first conductive layer, the spacer layer, and the second conductive layer are sequentially formed on the sacrificial layer,
After that, a device structure with a narrow gap can be formed simply by removing a part of the sacrificial layer and the spacer layer, so that a high-performance electromechanical device can be manufactured at low cost. In particular, since it is not necessary to provide a special process other than the process used in the semiconductor manufacturing process such as a CMOS process, it is possible to manufacture with a general-purpose facility, so that it is not necessary to newly install a manufacturing facility. Also, the integration of the electromechanical element and the semiconductor integrated circuit is easy by using the semiconductor manufacturing process.

In the present invention, the first conductive layer is patterned between the first conductive layer forming step and the spacer layer forming step, so that the movable electrode portion, the support beam portion, and the fixed portion are formed. It is preferable to have one patterning step.

In the present invention, it is preferable that in the second conductive layer forming step, the second conductive layer is formed so as to be in contact with the spacer layer on a side surface of the movable electrode portion.

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 1 to 4 are schematic schematic cross-sectional views for explaining each step of the method for manufacturing an electromechanical element of this embodiment (
It is a) and a typical schematic perspective view (b).

In the present embodiment, as shown in FIG. 1, a substrate 11 composed of a semiconductor substrate such as a single crystal silicon substrate is facilitated. This substrate 11 is usually about 10 to 1000 μm thick. Next, a sacrificial layer 12 is formed on the substrate 11 (sacrificial layer forming step). The sacrificial layer 12 is usually made of silicon oxide (SiO ₂ ). In this case, the sacrificial layer 12 may be grown by a thermal oxidation method, or may be formed by a CVD method or the like. The thickness of the sacrificial layer 12 is usually about 0.1 to 100 μm.

Next, a first first conductive layer is formed on the sacrificial layer 12 (first conductive layer forming step). The thickness of the first conductor layer is usually about 0.001 to 100 μm. Thereafter, the first conductor layer is subjected to patterning processing by a normal photolithography process or the like, and the movable electrode portion 13 is then processed.
Then, the support beam portion 14 and the fixed portion 15 are formed (first patterning step). The first conductor layer is preferably a polycrystalline silicon layer, and can be easily formed by forming a film by CVD or sputtering. In the case of the illustrated example, the movable electrode portion 13 is formed in a disk shape, and the two support beam portions 14 are connected to both outer peripheral sides of the movable electrode portion 13. Further, these support beam portions 14 are all connected to the fixed portion 15 at the end opposite to the end connected to the movable electrode 13.

As the above-mentioned polycrystalline silicon layer, a layer doped for providing conductivity is used. In particular, a high impurity concentration is preferable in order to obtain good ohmic properties. When single crystal silicon is used, the movable electrode portion 13, the support beam portion 14, and the fixed portion 1 are patterned by patterning using an SOI (Semiconductor On Insulator) substrate.
5 is formed. Even in this case, the single crystal silicon layer on the surface has a high impurity concentration.

The movable electrode portion 13, the support beam portion 14, and the fixed portion 15 can be patterned by any suitable patterning method, for example, an ultraviolet exposure method, an electron beam exposure method, a NIL (nanoimprint lithography) method, or the like. The various lithographic processes used can be used. In particular, the side surface of the outer peripheral portion of the movable electrode portion 13 needs to be formed as vertically as possible in order to improve the lateral mechanical characteristics. For this purpose, it is preferable to use an anisotropic dry etching technique. This anisotropic dry etching is particularly suitable for polycrystalline silicon and plane orientation (100).
This is effective for single crystal silicon. Further, in the case of single crystal silicon having a plane orientation (110), chemical wet etching using an aqueous solution of KOH (potassium hydroxide) or TMAH (tetramethylammonium) as an etchant can be used.

Next, as shown in FIG. 2, a dielectric spacer layer 16 is formed on the surfaces of the movable electrode portion 13, the support beam portion 14, and the fixed portion 15 (spacer layer forming step). The spacer layer 16 is usually formed of silicon oxide, but is not limited thereto, and may be formed of a material that can be selectively removed leaving the movable electrode portion 13. However, if the spacer layer 16 is made of the same material as the sacrificial layer 12 or a material that can be removed at the same time, the spacer layer 16 and the sacrificial layer 12 can be removed at the same time in a sacrificial layer removing step described later.

Here, when the spacer layer 16 is formed of silicon oxide, it can be formed by a general process such as a thermal oxidation method or a CVD method. An important point in the formation of the spacer layer 16 is that the movable electrode portion 13 has a good step coverage (step coverage). However, this step coverage does not mean that the difference in film thickness between the flat portion and the step portion is small, but can be formed with a uniform thickness on the side surface of the movable electrode portion 13 that is the step portion, and Says that the reproducibility of thickness is high. The thickness of the spacer layer 16 is not particularly limited, but it is preferable that the thickness is less than 1 μm in order to effectively exhibit the advantages of the present embodiment.
It is desirable that it is 0 nm or less.

The spacer layer 16 may be left not only on the movable electrode portion 13 but also on the support beam portion 14 and the fixed portion 15, or may be left on the sacrificial layer 12.

Next, a second conductive layer of the second layer is formed on the structure (second conductive layer forming step). This second conductor layer can also be formed of doped polycrystalline silicon, like the first conductor layer of the first layer. It is also possible to use metals such as Al and Au. However,
The material of the second conductor layer needs to be a material (a material having selectivity) that is not removed in the step of removing the sacrificial layer 12 and the spacer layer 16. The thickness of this conductor layer is usually 0.001
It is about ~ 100 μm.

The second conductor layer is preferably formed directly on the sacrificial layer 12 or the spacer layer 16. As a result, the number of steps can be reduced, and the semiconductor device can be easily manufactured by a normal semiconductor manufacturing process.

Further, the second conductor layer is patterned by a normal photolithography method or the like to form the fixed electrodes 17 and 18 shown in FIG. 3 (second patterning step). These fixed electrodes 17
, 18 are formed in a pattern that leaves a portion in contact with the spacer layer 16 formed on the side surface of the movable electrode portion 13.

Finally, a part of the sacrificial layer 12 and the spacer layer 16 are removed, thereby separating the movable electrode portion 13 and the support beam portion 14 from the surface of the substrate 11 as shown in FIG. 4 (release process). Here, the sacrificial layer 12 may be removed as long as the movable electrode portion 13 and the support beam portion 14 can be separated from the surface of the substrate 11. For example, in the case of the illustrated example, the fixed portion 15 and the fixed electrodes 17 and 18 are used as a patterning mask, and wet etching is performed with an etching solution based on hydrofluoric acid, thereby supporting the movable electrode portion 13 and the support. The state where the sacrificial layer 12 below the beam portion 14 is removed is shown. In this case, the portion of the sacrificial layer 12 disposed below the fixed portion 15 and the fixed electrodes 17 and 18 remains.

A dielectric mask layer (resist) is formed by forming a patterning mask (resist) having an opening necessary for removing a necessary portion of the sacrificial layer 12 and the spacer layer 16, and performing wet etching through the opening. 16 and at least a portion of the sacrificial layer 12 formed below the movable electrode portion 13 and the support beam portion 14 may be removed. In this method, the portion of the sacrificial layer 12 below the movable electrode portion 13 and the support beam portion 14 is surely removed, and at the same time, the portion of the sacrificial layer 12 below the fixed portion 15 and the fixed electrodes 17 and 18 is surely secured. It can be left.

Then, it is washed with pure or the like and dried. At this time, in order to prevent the problem that the movable electrode portion 13 and the support beam portion 14 adhere to the substrate 11, gas etching may be used in place of the wet etching, or the attachment may be performed. In order to prevent this, a surface coating such as a resin film may be applied to the surface of the substrate 11.

An important aspect of the manufacturing method of the present embodiment is that the gap between the movable electrode portion 13 and the fixed electrodes 17 and 18 is formed by the spacer layer 16. Here, when the spacer layer 16 is formed of silicon oxide, the gap can be controlled very accurately by a film forming process such as a general thermal oxidation method or a CVD method. Therefore, a narrow gap of 100 nm or less is formed. It can be easily realized.

In addition, the manufacturing method of the electromechanical element of this invention is not limited only to the above-mentioned illustration example, Of course, various changes can be added within the range which does not deviate from the summary of this invention.

For example, in the above embodiment, the movable electrode portion 13 is formed by the first conductive layer formed first, and the movable electrode portion 13 is separated from the substrate 11. In the final release step of the above embodiment, The first conductive layer is used as a fixed electrode, leaving the sacrificial layer 12 below the portion of the first conductive layer formed on the substrate, and the second conductive layer is movable by removing the sacrificial layer 12 below the portion of the second second conductive layer. It does not matter as an electrode.

Moreover, in the said embodiment, although the structure which supports the outer peripheral part of the movable electrode part 13 as a mechanical movable part by the some support beam part 14 is provided, this invention is not limited to this, A support beam The part 14 and the fixed part 15 may not be formed, and a structure in which a support column is formed at the center of the movable electrode part 13 may be used. In this case, the sacrificial layer 12 below the movable electrode portion 13.
By controlling the etching time of the sacrificial layer 1 under the center of the movable electrode portion 13
It is also possible to leave a part of 2 and to use a part of the remaining sacrificial layer 12 as the support pillar.

Furthermore, in the above-described embodiment, the method of forming the lateral gap has been described. However, even when the longitudinal gap is formed, the present embodiment can be easily applied by using a spacer layer formed on a plane. In this case, a vertical electromechanical element in which the movable electrode and the fixed electrode are opposed in the vertical direction can be formed.

The schematic longitudinal cross-sectional view (a) and schematic perspective view (b) which show typically the 1st state of the manufacturing method of embodiment. The schematic longitudinal cross-sectional view (a) and schematic perspective view (b) which show typically the 2nd state of the manufacturing method of embodiment. The schematic longitudinal cross-sectional view (a) and schematic perspective view (b) which show typically the 3rd state of the manufacturing method of embodiment. The schematic longitudinal cross-sectional view (a) and schematic perspective view (b) which show typically the 4th state of the manufacturing method of embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Board | substrate, 12 ... Sacrificial layer, 13 ... Movable electrode part, 14 ... Supporting beam part, 15 ... Fixed part, 16
... Spacer layer, 17, 18 ... Fixed electrode

Claims (3)

A sacrificial layer forming step in which a sacrificial layer is formed on the substrate;
A first conductive layer forming step in which a first conductive layer is formed on the sacrificial layer;
A spacer layer forming step in which a spacer layer is formed on the surface of the first conductive layer;
A second conductive layer forming step in which a second conductive layer in contact with the spacer layer is formed on the sacrificial layer;
A release step in which a part of the sacrificial layer and the spacer layer are removed and at least a part of the first conductive layer or the second conductive layer is separated from the substrate;
A method for producing an electromechanical element, comprising: A first patterning step in which the movable electrode portion, the support beam portion, and the fixed portion are formed by patterning the first conductive layer between the first conductive layer forming step and the spacer layer forming step. The method of manufacturing an electromechanical element according to claim 1, comprising: 3. The method of manufacturing an electromechanical element according to claim 2, wherein in the second conductive layer forming step, the second conductive layer is formed so as to be in contact with the spacer layer on a side surface of the movable electrode portion. .

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