JP4016739B2 - Micromachine and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a micromachine and a manufacturing method thereof, and more particularly to an optical micromachine using an electrode surface as a light reflecting surface and a manufacturing method thereof.
[0002]
[Prior art]
With the progress of microfabrication technology on a substrate, a so-called micro machine (MEMS: Micro Electro-Mechanical Systems) element (hereinafter referred to as a MEMS element) has been attracting attention.
[0003]
The MEMS element is formed as a fine structure on a substrate such as a silicon substrate or a glass substrate, and electrically connects a driving body that outputs a mechanical driving force and a semiconductor integrated circuit that controls driving of the driving body, Furthermore, the element is mechanically coupled. The basic feature of a MEMS element is that a drive body configured as a mechanical structure is incorporated in a part of the element, and the drive output of the drive body applies Coulomb attractive force between electrodes. In general, it is performed electrically.
[0004]
As an example of the MEMS element, a light modulation element used in a GLV (Grating Light Valve) device will be described as an example, and the structure will be described.
[0005]
FIG. 2 is a perspective view for explaining the structure of a GLV device constituted by MEMS elements as light modulation elements. A GLV device is a device in which a plurality of MEMS elements 11 are densely arranged in parallel with each other on a common substrate 10. The MEMS element 11 constituting the GLV device is referred to as MOEMS (Micro Optical Electro-Mechanical Systems) including a lower electrode 12 on the substrate 10 and an electrostatically driven beam 13 having a light reflecting surface 13a on the upper surface. It is a MEMS element.
[0006]
FIG. 3 is a perspective view illustrating the configuration of the MEMS element 11. As shown in this figure, the MEMS element 11 includes an insulating substrate 10, a lower electrode 12 formed on the substrate 10, and an electrostatically driven beam 13 straddling the lower electrode 12 in a bridge shape. ing. The electrostatic drive beam 13 and the lower electrode 12 are electrically insulated by a gap a between them.
[0007]
The electrostatic drive beam 13 stands on the substrate 10 across the lower electrode 12 in a bridge shape, and has an insulating structure 14 provided as an electrode support member, and an upper electrode 15 provided on the structure 14. It is composed of The structure 14 is provided to support the upper electrode 15 so as to be opposed to the lower electrode 12 by a predetermined distance and to be parallel to the lower electrode 12 so as to secure the gap a. ing. The upper electrode 15 has a surface serving as a light reflecting surface of the electrostatic drive beam 13 and is formed of a metal film, mainly an aluminum (Al) film.
[0008]
The electrostatic drive beam 13 having such a configuration is commonly called a ribbon, but the structure 14 has two ends of a beam portion extending in parallel to the lower electrode 12 as shown in FIG. In addition to the bridge-shaped one that is supported by the column portion of the book, there is also a cantilever type that has only one column portion and supports only one end of the beam portion.
[0009]
In the MEMS element 11 having such a configuration, when a minute voltage is applied between the lower electrode 12 and the upper electrode 15 facing the lower electrode 12, the electrostatic drive beam 13 is applied to the lower electrode 12 due to an electrostatic phenomenon. When approaching and stopping the application of voltage, they are separated to return to the original state. Then, with the approach and separation of the electrostatic drive beam 13 with respect to the lower electrode 12, the intensity of the reflected light is modulated by changing the height between the upper electrodes 15, and functions as a light modulation element. In this case, the mechanical characteristics of the electrostatic drive beam 13 driven by using electrostatic attraction and electrostatic repulsion are substantially determined by the physical properties of the material (for example, SiN) constituting the structure 14, and the upper electrode 15. Is mainly used as a reflection mirror.
[0010]
Next, the manufacturing process of the MEMS element 11 that operates in this manner will be described with reference to the sectional view of FIG. First, as shown in FIG. 4A, the lower electrode 12 is patterned on the substrate 10 made of, for example, silicon. Next, a sacrificial layer 21 to be removed later is patterned in a state of being laminated on the lower electrode 12. Thereafter, a bridge-shaped structure 14 straddling the sacrificial layer 21 is patterned on the substrate 10.
[0011]
Next, as shown in FIG. 4B, a metal film (Al film) 23 is formed so as to cover the structure 14, and the metal film 23 is subjected to pattern etching using the resist pattern 25 as a mask. The upper electrode 15 stacked on the body 14 is formed. As a result, an electrostatically driven beam 13 composed of the structure 14 and the upper electrode 15 is formed.
[0012]
Next, as shown in FIG. 4C, the resist pattern (25) for forming the upper electrode 15 is removed. Here, finally, a wet process using a stripping solution is performed to remove reaction by-products such as a polymer generated by pattern etching when the upper electrode 15 is formed. Thereby, the surface of the upper electrode 15, that is, the light reflecting surface 13a is exposed.
[0013]
Next, as shown in FIG. 4D, the sacrificial layer (21) is selectively removed by a dry etching method using XeF ₂ gas, whereby a gap is formed between the structure 14 and the lower electrode 12. a is provided to complete the MEMS element 11.
[0014]
[Problems to be solved by the invention]
However, the MEMS device manufacturing method as described above has the following problems. That is, in an optical MEMS element having a light reflecting surface, a metal film such as an Al film is used as a material constituting the light reflecting surface. However, for example, as described with reference to FIG. 4C, when the resist pattern (25) on the upper electrode 15 formed by patterning this metal film is removed by wet treatment using a stripping solution, and FIG. As described with reference to 4 (d), when the sacrificial layer (21) is removed by dry etching, the corrosion of the surface of the metal material (Al) constituting the upper electrode 15 proceeds.
[0015]
Usually, a natural oxide film such as aluminum oxide is formed on the surface of the metal film, and this natural oxide film serves as a protective film on the surface of the metal film. However, in order to remove the reaction by-product generated by the etching when patterning the upper electrode, the stripping solution containing fluoride is used for the stripping solution described above. Is not resistant to the XeF ₂ gas used for removing the stripping solution and the sacrificial layer. Therefore, during these treatments, the natural oxide film on the surface of the metal film is removed, the corrosion proceeds in the removed portion, and black spots B are generated on the surface of the upper electrode 15. Specifically, when the upper electrode 15 is made of Al, aluminum hydroxide is generated on the surface of the upper electrode 15 by the above processing, and this becomes a black spot B.
[0016]
This black spot B becomes a factor of deteriorating the light reflection characteristics such that the wavelength dispersion of the light reflectivity in the visible light region becomes large on the light reflection surface 13a constituted by the surface of the upper electrode 15, and the MEMS element has a problem. Causes optical performance degradation. It has been found that such deterioration of the MEMS element also causes deterioration of the dark level of the GVL using the MEMS element, and deteriorates the reliability and yield of the MEMS element and the GVL using the MEMS element.
[0017]
Accordingly, an object of the present invention is to provide an optical MEMS element capable of suppressing corrosion of an electrode surface serving as a light reflecting surface and maintaining a light reflecting effect on the light reflecting surface, and a method for manufacturing the same. To do.
[0018]
[Means for Solving the Problems]
The MEMS element (micromachine) of the present invention for solving such a problem is an optical MEMS element that uses the surface of an electrode patterned on a substrate as a light reflecting surface, and the electrode is made of a metal material. The surface is covered with a nitride film.
[0019]
Further, a lower electrode formed on the substrate, a structure in which a beam portion is extended from the support portion erected on the upper portion of the substrate to the upper portion of the lower electrode via a gap portion, and the structure The upper electrode is provided with an upper electrode, and the upper electrode is made of a metal material, and the surface thereof is covered with a nitride film.
[0020]
In the MEMS element having such a configuration, the surface of the electrode (or upper electrode) made of a metal material is covered with a chemical-resistant nitride film, so that the surface of the electrode (or upper electrode), that is, light The reflective surface is protected. Therefore, alteration such as corrosion of the light reflecting surface can be suppressed, and the light reflecting characteristics on the light reflecting surface can be maintained.
[0021]
The first manufacturing method of the MEMS element of the present invention is a method of manufacturing a micromachine including a step of forming an electrode using the surface as a light reflecting surface by patterning a metal film formed on a substrate. In addition, before the metal film is patterned, a step of nitriding the surface of the metal film is performed.
[0022]
In the first manufacturing method having such a configuration, the metal film is patterned in a state where the surface of the metal film is nitrided. That is, a patterning process is performed on the metal film whose surface is protected by a nitride film having excellent chemical resistance to form an electrode. Therefore, the influence of the patterning process and the post-processing accompanying this is prevented from being exerted on the electrode surface used as the light reflection surface, and an electrode having a light reflection surface with good light reflection characteristics can be obtained.
[0023]
The second manufacturing method of the present invention includes a step of patterning a sacrificial layer so as to be laminated on the lower electrode on the substrate, and an insulating film and a metal film on the substrate in a state of covering the lower electrode and the sacrificial layer. Forming a structure in which the insulating film is patterned in a band extending from the bottom to the top of the sacrificial layer, and forming an upper electrode stacked on the structure by patterning the metal film; Also, a manufacturing method in which a sacrificial layer is removed to form a gap between the lower electrode and the structure, and after the metal film is formed and until the sacrificial layer is removed In addition, a step of nitriding the surface of the metal film or the upper electrode is performed.
[0024]
In such a second manufacturing method, before removing the sacrificial layer, a step of nitriding the surface of the metal film or the upper electrode formed by patterning the metal film is performed. That is, when the surface of the metal film is nitrided, the metal film is patterned with the surface of the metal film nitrided, and the sacrificial layer is removed thereafter. Therefore, it is possible to prevent the effects of the patterning process and the post-processing associated therewith and the removal of the sacrificial layer from being exerted on the electrode surface used as the light reflecting surface, and an electrode having a light reflecting surface with good light reflecting characteristics can be obtained. can get. On the other hand, when the surface of the upper electrode is nitrided, the sacrificial layer is removed while the surface of the upper electrode is nitrided. Therefore, the influence of removing the sacrificial layer is prevented from being exerted on the surface of the electrode used as the light reflecting surface, and an electrode having a light reflecting surface with good light reflecting characteristics can be obtained.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, a method for manufacturing an optical MEMS element (MEOMS) that operates in the same manner as described with reference to FIGS. 2 and 3 in the prior art will be described based on the sectional process diagram of FIG. It should be noted that the same components as those described in the prior art are denoted by the same reference numerals for description.
[0026]
First, as shown in FIG. 1A, a metal film such as a W (tungsten) film is formed on a substrate 10 made of silicon or the like, and the lower electrode 12 is formed by patterning the metal film.
[0027]
Next, an amorphous silicon film or a polysilicon film is formed on the entire surface of the substrate 10 and patterned to form a sacrificial layer 21 on the lower electrode 12. The sacrificial layer 21 is made of a material that can be selectively removed by etching with respect to the substrate 10, the lower electrode 12, the structure formed in the subsequent steps, and the upper electrode. An amorphous silicon film, a polysilicon film, or the like is used.
[0028]
Next, a SiN (silicon nitride) film is formed as an insulating film 22 on the entire surface of the substrate 10 so as to cover the sacrificial layer 21 and the lower electrode 12. Then, the insulating film 22 is patterned in a band shape extending from the lower part to the upper part of the sacrificial layer 21 to form a plurality of structures 14 that stand on the substrate 10 with the lower electrode 12 straddling the bridge. As a result, a bridge-like structure 14 including a support portion 14 a erected on the upper portion of the substrate 10 and a beam portion 14 b provided to face the lower electrode 12 from the support portion 14 a is obtained.
[0029]
Here, the SiN film is selected as the insulating film 22 constituting the structure 14 on the assumption that the physical properties such as strength and elastic constant are appropriate for the mechanical drive of the structure 14. However, an insulating film made of another material may be used instead of the SiN film as long as the structure 14 has appropriate physical properties. In addition, a plurality of structures 14 are formed in the depth direction on the drawing.
[0030]
After that, as shown in FIG. 1B, a metal film 23 is formed on the entire surface of the substrate 10 so as to cover the structure 14, the sacrificial layer 21, and the lower electrode 12. The metal film 23 is, for example, an Al film. Al is preferably used as an optical component material because (1) it is a metal that can be formed relatively easily and (2) the wavelength dispersion of the light reflectance in the visible light region is small. It is a metal.
[0031]
Next, the surface of the metal film 23 is nitrided, and the surface of the metal film 23 is covered with the nitride film 30. At this time, for example, nitriding using nitrogen plasma is performed under the following conditions.
Process gas and flow rate: N _2/100 [sccm]
sccm: standard cubic centimeter / minutes
Processing atmosphere pressure: 40 [Pa]
Source side applied power: 13.56 [MHz]
Substrate temperature: 300 [° C]
Substrate bias: 50 [W] / 800 [KHz]
Processing time: 1 [min. ]
[0032]
In the nitriding process described above, when a natural oxide film is formed on the surface of the metal film 23, the natural oxide film is nitrided to form the nitride film 30. For example, when the metal film 23 is an Al film and aluminum oxide (Al ₂ O ₃ ) is formed as a natural oxide film on the surface, the aluminum oxide is nitrided to form a nitride film 30 made of AlN. .
[0033]
Thereafter, as shown in FIG. 1C, a resist pattern 25 is formed on the metal film 23 on which the nitride film 30 is formed. Next, the metal film 23 covered with the nitride film 30 is etched using the resist pattern 25 as a mask to leave the metal film 23 only on the beam portion 14b facing the lower electrode 12 in the structure 14. Is formed as the upper electrode 15. Etching of the metal film 23 is performed by a dry etching technique or a wet etching technique.
[0034]
Next, as shown in FIG. 1D, the resist pattern (25) remaining on the upper electrode 15 (on the nitride film 30) and reaction by-products (not shown) generated by etching using the resist pattern as a mask. ) Is removed with a release agent. At this time, as the stripping solution, for example, a solution containing hydrofluoric acid, ammonium fluoride, or the like is used. The resist pattern (25) may be removed by plasma ashing. In this case, after the plasma ashing process, the reaction by-product generated by the etching is removed with a solution containing hydrofluoric acid, ammonium fluoride, or the like.
[0035]
After the above, as shown in FIG. 1E, the sacrificial layer (21) made of an amorphous silicon film or a polysilicon film is removed by a dry etching method using XeF ₂ gas. As a result, a gap a is formed between the structure 14 and the lower electrode 12, and the electrostatic drive beam 13 including the structure 14 and the upper electrode 15 is obtained.
[0036]
As described above, the lower electrode 12, the structure 14 in which the beam portion 14 b extends from the support portion 14 a erected on the upper portion of the substrate 10 to the upper portion of the lower electrode 12 through the gap portion a, and the structure 14. The MEMS element 11 ′ having the upper electrode 15 provided on the upper surface of the upper electrode 15 and having the surface of the upper electrode 15 covered with the nitride film 30 is obtained. In the MEMS element 11 ′, the surface of the upper electrode 15 covered with the nitride film 30 becomes the light reflecting surface 3 a of the electrostatic drive beam 13, and operates in the same manner as described with reference to FIGS. 2 and 3. MEMS element (MEOMS).
[0037]
In the above manufacturing method, as described with reference to FIGS. 1C and 1E, the metal film 23 is patterned in a state where the surface of the metal film 23 is covered with the nitride film 30. Thereafter, the sacrificial layer 21 is removed. Therefore, it is possible to prevent the patterning process of the metal film 23 and the post-processing associated therewith and further the removal of the sacrificial layer 21 from being exerted on the surface of the upper electrode 15 used as the light reflecting surface 13a, and the light reflecting characteristics are improved. Thus, it is possible to obtain the upper electrode 15 having the light reflecting surface 13a.
[0038]
Further, the MEMS element 11 ′ thus obtained has a structure in which the surface of the upper electrode 15 made of a metal material is covered with a nitride film 30 having chemical resistance. The reflective surface 13 a is protected by the nitride film 30. Therefore, alteration such as corrosion of the light reflecting surface 13a can be suppressed, and the light reflecting characteristics on the light reflecting surface 13a can be maintained. Further, in the GVL (Grating Light Valve) element formed using the MEMS element 11 ′ thus obtained, deterioration of the dark level can be prevented. As a result, it becomes possible to improve the reliability and yield of the MEMS element and the GVL element using the MEMS element.
[0039]
In the above-described embodiment, as described with reference to FIG. 1B, the surface of the metal film 23 is nitrided. However, in the manufacturing method of the present invention, the surface of the upper electrode 15 is removed after removing the resist pattern 25 on the upper electrode 15 as described with reference to FIG. It is good also as a structure to nitride. The nitriding process is performed in the same manner as described with reference to FIG. In this case, the side wall of the upper electrode 15 is also nitrided, and a nitride film is also formed on this side wall. Therefore, good light reflection characteristics can be ensured also on the side wall of the upper electrode 15.
[0040]
Further, when only the corrosion of the upper electrode 15 surface during the manufacturing process is to be prevented, the step of removing the nitride film 30 may be performed after the step described with reference to FIG. However, when the nitride film 30 is removed, it is essential to perform under conditions that do not corrode the surface of the upper electrode 15.
[0041]
In the above-described embodiment, the case where the present invention is applied to the MEMS element having the configuration in which the upper electrode 15 is provided on the bridge-shaped structure 14 has been described. However, the present invention can be widely applied to a MEMS device using the surface of an electrode made of a metal material as a light reflecting surface and a method for manufacturing the same, and the same effect can be obtained. For example, instead of the structure 14 described in the above embodiment, the present invention can be similarly applied to a MEMS element having a structure of a cantilever type structure that supports only one end of the beam.
[0042]
【The invention's effect】
As described above, according to the MEMS element of the present invention and the manufacturing method thereof, by forming a nitride film on the surface (light reflecting surface) of the electrode made of a metal material, corrosion of the light reflecting surface is prevented, and It is possible to maintain and improve the light reflection effect on the light reflection surface. As a result, it is possible to improve the optical characteristics of the optical MEMS element and the optical element using the same, and to improve the reliability and the yield.
[Brief description of the drawings]
FIG. 1 is a cross-sectional process diagram for explaining an embodiment of the present invention.
FIG. 2 is a perspective view of a GLV device configured using a MEMS element.
FIG. 3 is a perspective view of a MEMS element.
FIG. 4 is a diagram for explaining a conventional method of manufacturing a MEMS element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 11 '... MEMS element (micromachine), 12 ... Lower electrode, 14 ... Structure, 14a ... Supporting part, 14b ... Beam part, 15 ... Upper electrode (electrode), 13a ... Light reflecting surface, 21 ... Sacrificial Layer, 23 ... metal film, 30 ... nitride film, a ... void

Claims (3)

A lower electrode formed on a substrate, a structure in which a beam portion is extended from a support portion standing on the upper portion of the substrate to the upper portion of the lower electrode via a gap, and an upper portion of the structure An optical micromachine using the upper electrode as a light reflecting surface.
The upper electrode is made of a metal material, and the surface thereof is covered with a nitride film formed by nitriding the metal material . In a manufacturing method of a micromachine including a step of forming an electrode using a surface as a light reflection surface on the substrate by patterning a metal film formed on the substrate.
Before patterning the metal film, a step of nitriding the surface of the metal film is performed. Patterning a sacrificial layer to be laminated to the lower electrode on the substrate;
An insulating film and a metal film are formed in this order on the substrate in a state of covering the lower electrode and the sacrificial layer, and a structure is formed by patterning the insulating film in a band shape extending from the lower part to the upper part of the sacrificial layer, Forming an upper electrode laminated on the structure by patterning the metal film;
In the method of manufacturing a micromachine that performs the step of forming a gap between the lower electrode and the structure by removing the sacrificial layer,
The surface is used as a light reflecting surface by performing a step of nitriding the surface of the metal film or the surface of the upper electrode after forming the metal film and before removing the sacrificial layer. A method of manufacturing a micromachine, comprising forming the upper electrode .

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