JP2014024173A - Method of manufacturing micromechanical structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deformation of a movable structure, which is caused after the movable structure is made operable, in a manufacturing process of the micromechanical structure.SOLUTION: A protective layer 105 used for protection of the surface of an SOI layer 103 is exposed, for example, to an active oxygen such as an oxygen plasma or UV/ozone, and thereby burned to ashes and removed. Also, the surface of the SOI layer 103 is oxidized by ashing processing of the protective layer 105 and a thin surface oxidized layer is formed, so that the surface oxidized layer is removed by the plasma exposure using inert gaseous species such as the argon plasma. Then, the whole of a chip (micromechanical structure) formed by separating a movable structure 134 into an operable state is subjected to heating treatment.

Description

  The present invention relates to a method for manufacturing a micromechanical structure in which a movable structure is formed by patterning a surface silicon layer of an SOI substrate having a surface silicon layer formed on a surface of a base portion via a buried insulating layer. .

  In recent years, micro electro mechanical systems (MEMS) have been developed on the extension of the advancement of semiconductor micromachining technology. Three-dimensional processing technology in MEMS has been developed for information input / output devices such as acceleration sensors, angular velocity sensors, inkjet printer heads, and displays using movable micromirrors, and is expected to be a fundamental technology for elements that build ubiquitous sensing and ubiquitous networks. Has been done.

  A MEMS device manufactured using this technology is a device in which mechanical elements (movable structures) and electric elements that control the mechanical elements are integrated on a silicon substrate in a compact manner. As a driving method of such a MEMS device, there is a “static operation” in which various functions are expressed by mechanically moving a movable part using electrostatic attraction generated between a movable structure and an electric element such as a drive electrode. "Electric drive type" has become mainstream. In such a MEMS device, since it is important to precisely control the gap between the movable structure and the electric element, it is desirable that the movable structure be formed in a flat state.

  In particular, in communication devices and optical devices that use a movable structure as a micromirror, deformation of the movable structure, the micromirror, directly leads to deterioration of optical characteristics such as insertion loss and crosstalk. The flattening control of the micromirror which is a movable structure is an important technique.

Japanese Patent No. 03827977 US Pat. No. 6,369,931

  However, at present, as described below, there is a problem that the movable structure is curved at the stage where the movable structure is separated from the opposing surface.

  For example, there is a technique for manufacturing MEMS (Micro Electro Mechanical Systems) including a mirror using an SOI (Silicon On Insulator) substrate (see Patent Document 1 and Patent Document 2). In this technique, a mirror structure is formed by patterning an SOI layer disposed via a buried insulating layer on a base portion, and an opening is formed in the base portion in a region corresponding to the formed mirror structure. The structure can perform operations such as rotation.

  Specifically, as shown in the cross-sectional view of FIG. 5A, the SOI layer 503 of the SOI substrate including the base portion 501, the embedded insulating layer 502, and the SOI layer 503 is patterned using a photolithography technique and an etching technique. By this patterning, a frame portion 531, a first movable beam 532a, a second movable beam 532b, a mirror structure 534, a first connection portion 533a, and a second connection portion 533b are formed.

  The first movable beam 532a and the second movable beam 532b are fixed at one end to the frame portion 531 and displaceable at the other end, are opposed to each other at the other end side, and are arranged in a row at a predetermined distance. Yes. The mirror structure 534 is arranged in a row with the first movable beam 532a and the second movable beam 532b and is disposed between the first movable beam 532a and the second movable beam 532b. Further, the other end of each of the first movable beam 532a and the second movable beam 532B and the mirror structure 534 are coupled by the pair of first coupling portion 533a and second coupling portion 533b.

  As will be described later, in a state where these portions are separated, the first movable beam 532a and the second movable beam 532b function as cantilever beams, and the other ends on the first connection portion 533a and the second connection portion 533b side. However, it can be displaced in the normal direction of the plane of the SOI layer 503. Further, the mirror structure 534 can be rotated around an axis passing through the pair of first connecting portions 533a and second connecting portions 533b.

  Next, as shown in FIG. 5B, a protective layer 505 made of an organic resin is formed on the surface of the SOI layer 503 on which the above-described portions are formed.

  Next, a photolithography technique and an etching technique are applied to the base portion 501 corresponding to the region including the first movable beam 532a, the second movable beam 532b, the mirror structure 534, the first connecting portion 533a, and the second connecting portion 533b. Is used to form an opening 501 a that reaches the buried insulating layer 502. Next, the embedded insulating layer 502 exposed in the opening 501a is removed by etching to form an opening 502a following the opening 501a. By forming the opening 502a, an opening reaching the back surface of the SOI layer 503 from the back surface side of the SOI substrate is formed.

  Next, dicing is performed to form a chip.

  Next, after forming the chip, the protective layer 505 used for protecting the surface of the SOI layer 503 is removed. In this removal, the protective layer 505 is exposed to active oxygen such as oxygen plasma or UV / ozone to be ashed and removed. In addition, the layer formed by the ashing process using the plasma formed on the surface of each structure body by the SOI layer 503 is removed by performing plasma exposure with an inert gas species such as argon plasma. As a result, the first movable beam 532a, the second movable beam 532b, the mirror structure 534, the first connecting portion 533a, and the second connecting portion 533b are separated from each other and can be operated. Produced.

  However, the movable structure 534 of the micromechanical structure manufactured in the manufacturing process described above is configured by a single silicon layer (SOI layer) and does not have a multilayer structure including two or more types of layers. Nevertheless, as illustrated in FIG. 5D, it has been found that the state is curved (deformed). Although the cause of this is not clear, the protective layer 505 made of an organic material is incinerated, followed by plasma exposure with an inert gas species, so that the movable structure 534 is operatively separated. In the manufacturing process, it is an unavoidable problem.

  The present invention has been made to solve the above-described problems, and suppresses deformation of the movable structure that occurs after the movable structure is made operable in the manufacturing process of the micromechanical structure. With the goal.

  The method for manufacturing a micromechanical structure according to the present invention includes patterning a surface silicon layer of an SOI substrate having a surface silicon layer formed on a surface of a base portion via a buried insulating layer, and moving the movable structure in an element formation region. The first step of forming the substrate, and an opening that penetrates the base portion and the buried insulating layer from the back surface of the base portion in the element forming region, and the buried insulating layer around the opening portion is supported as a support structure and can operate. A second step of forming the micromechanical structure including the movable structure, and a third step of heating the micromechanical structure after forming the micromechanical structure including the movable structure operable. And at least.

  In the method for manufacturing a micromechanical structure, in the third step, the micromechanical structure may be heated in an inert gas or vacuum atmosphere.

In the method for manufacturing a micromechanical structure, the micromechanical structure is heated at a heating time at which the relationship of heating time = 4 × 10 ⁻⁵ × exp (8340.7 / absolute temperature) is satisfied and at a heating temperature indicated by the absolute temperature. It is good to heat.

  In the method for manufacturing a micromechanical structure, in the third step, the micromechanical structure may be heated at a temperature condition of 500 ° C. In the third step, the micromechanical structure may be heated for 2 hours.

  In the method for manufacturing the micromechanical structure, after the first step, the protective layer made of an organic resin that covers at least the element formation region of the surface silicon layer is formed, the opening is formed, and the opening is formed. Then, the protective layer is removed by ashing treatment of the organic material, and the oxide layer on the surface of the movable structure after removing the protective layer is removed by plasma treatment, so that the micro provided with the movable structure that is operable. A mechanical structure may be formed.

  As described above, according to the present invention, it is possible to obtain an excellent effect that the deformation of the movable structure that occurs after the movable structure can be operated in the manufacturing process of the micromechanical structure can be suppressed. .

FIG. 1A is a configuration diagram for explaining a state in each step for explaining a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1B is a configuration diagram for explaining a state in each step for explaining a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1C is a configuration diagram for explaining a state in each step for explaining a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1D is a configuration diagram for explaining a state in each step for explaining a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1E is a configuration diagram for explaining a state in each step for explaining a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1F is a configuration diagram for explaining a state in each step for explaining a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1G is a configuration diagram for explaining a state in each step for explaining a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1H is a configuration diagram for explaining a state in each step for explaining a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 2 is a characteristic diagram showing the relationship between the heating time and the curvature of the movable structure 134. FIG. 3 is an Arrhenius plot in which the vertical axis indicates “a value obtained by taking a natural logarithm of the amount of change in curvature of the movable structure 134 before and after heat treatment” and the horizontal axis indicates “reciprocal of absolute temperature”. FIG. 4 is a characteristic diagram showing the relationship between the saturation time of the curvature relaxation phenomenon and the reciprocal of the absolute temperature at the heat treatment temperature. FIG. 5A is a cross-sectional view for explaining a state in each step for explaining a conventional method for manufacturing a micromechanical structure. FIG. 5B is a cross-sectional view for explaining a state in each step for explaining a conventional method for producing a micromechanical structure. FIG. 5C is a cross-sectional view for explaining a state in each step for explaining a conventional method for manufacturing a micromechanical structure. FIG. 5D is a cross-sectional view for explaining a state in each step for explaining a conventional method for producing a micromechanical structure.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1A to 1H are configuration diagrams for explaining states in respective steps for explaining a method for manufacturing a micromechanical structure according to an embodiment of the present invention. Here, FIG. 1A, FIG. 1B, and FIG. 1D to FIG. FIG. 1C is a plan view, and cross sections taken along line aa ′ are shown in FIGS. 1A, 1B, and 1D to 1H.

  First, as shown in FIG. 1A, for example, an SOI substrate including a base portion 101 made of single crystal silicon, a buried insulating layer 102, and a surface silicon layer (SOI layer) 103 made of single crystal silicon is prepared. For example, the base portion 101 has a thickness of 400 μm, the buried insulating layer 102 has a thickness of 1.0 μm, and the SOI layer 103 has a thickness of 4.7 μm.

  Next, the SOI layer 103 is patterned by a known photolithography technique and etching technique, and as shown in FIGS. 1B and 1C, the frame portion 131, the first movable beam 132a, the second movable beam 132b, and the movable structure 134 are obtained. , A first connecting part 133a and a second connecting part 133b are formed.

  The first movable beam 132a and the second movable beam 132b are fixed at one end to the frame 131 and displaceable at the other end, are opposed to each other on the other end side, and are arranged in a row at a predetermined distance. Yes. The movable structure 134 is arranged in a row with the first movable beam 132a and the second movable beam 132b, and is disposed between the first movable beam 132a and the second movable beam 132b. Further, the other end of each of the first movable beam 132a and the second movable beam 132B and the movable structure 134 are coupled by the pair of first coupling portion 133a and second coupling portion 133b. The movable structure 134 is supported by the first movable beam 132a and the second movable beam 132B via the first coupling portion 133a and the second coupling portion 133b.

  As will be described later, in a state where these structures are separated from the insulating layer 102 and the like, the first movable beam 132a and the second movable beam 132b function as cantilever beams, and the first connecting portion 133a and the second connecting portion. The other end on the 133b side can be displaced in the normal direction of the plane of the SOI layer 503. In addition, the movable structure 134 can be rotated around an axis passing through the pair of first connecting portions 133a and second connecting portions 133b. At this stage, each structure is fixed on the buried insulating layer 102 and is separated by a gap 135 on the plane of the buried insulating layer 102.

  In patterning these structures, the SOI layer 103 may be etched using RIE (Reactive Ion Etching) using a resist pattern formed by a known photolithography technique as a mask. In this etching process, the buried insulating layer 102 can be used as an etching stop layer. Further, these structures are formed in the element formation region.

  Next, as shown in FIG. 1D, a protective layer 105 made of an organic resin is formed on the SOI layer 103. The protective layer 105 may be formed so as to cover at least the element formation region including the above-described structures in the SOI layer 103. The protective layer 105 may be formed, for example, by applying a resist and subjecting it to heat treatment (thermosetting). This heat treatment may be performed under a nitrogen atmosphere at a temperature of 250 ° C. for 30 minutes.

  Next, as illustrated in FIG. 1E, an opening 101 a in which the embedded insulating layer 102 is exposed is formed in the base body 101. The opening 101a is formed corresponding to an element formation region including the first movable beam 532a, the second movable beam 532b, the mirror structure 534, the first coupling portion 533a, and the second coupling portion 533b. For example, the opening 101a may be formed by a known photolithography technique and etching technique. This etching process is performed by dry etching, and the buried insulating layer 102 may be used as an etching stop layer.

  Next, the embedded insulating layer 102 exposed in the opening 101a is removed by etching to form an opening 102a following the opening 101a as shown in FIG. 1F. By forming the opening 102a, an opening reaching the back surface of the SOI layer 103 from the back side surface of the SOI substrate is formed. For example, the buried insulating layer 102 may be etched by wet etching using a hydrofluoric acid buffer (BHF). It has also been confirmed that the buried insulating layer 102 can be etched by dry etching using exposure to hydrogen fluoride gas in the atmosphere.

  Next, dicing is performed to form a chip. For the dicing, known blade dicing using a dicing saw may be used. FIG. 1C illustrates an area of one chip.

  Next, the protective layer 105 used for protecting the surface of the SOI layer 103 is removed by ashing by exposure to active oxygen such as oxygen plasma or UV / ozone. Further, since the surface of the SOI layer 103 is oxidized by the ashing treatment of the protective film 105 and a thin surface oxide layer is formed, the surface oxide layer is removed by plasma exposure with an inert gas species such as argon plasma. By removing these protective layers 105, as shown in FIG. 1G, the movable structure 134, the first connecting portion 133a, and the second connecting portion 133b are separated into an operable state. In this state, the movable structure 134 is deformed (curved).

Next, the entire chip (micromechanical structure) separated from the movable structure 134 and the like in an operable state is subjected to heat treatment, and the deformed movable structure 134 has a desired curvature as shown in FIG. 1H. The movable structure 134 is in a flat state suppressed to less than (<1 m ⁻¹ ). By appropriately performing the heat treatment, the movable structure 134 can be suppressed to less than a desired curvature (<1 m ⁻¹ ).

  Here, the measurement result of the relationship between the heat treatment time (heating time) after the separation described above and the curvature of the movable structure 134 will be described with reference to FIG. FIG. 2 is a characteristic diagram showing the relationship between the heating time and the curvature of the movable structure 134. The temperature of the heat treatment was 500 ° C. In the heating time of 2 hours, the change in curvature is saturated. Therefore, the heat treatment may be performed, for example, in a nitrogen atmosphere at a temperature of 500 ° C. (T = 773 K) for 2 hours.

  The heat treatment for suppressing deformation of the movable structure 134 is preferably performed in an inert atmosphere in order to avoid oxidation of the micromechanical structure, for example, nitrogen, helium, neon, argon, krypton, xenon, or the like. Heat treatment may be performed in an inert gas atmosphere or a mixed gas atmosphere thereof. Needless to say, the heat treatment may be performed in a vacuum.

  In order to quantitatively determine the heat treatment conditions (heat treatment temperature and heat treatment time), the heat treatment time is fixed at 2 hours under a nitrogen atmosphere, and the curvature of the movable structure 134 when the treatment temperature is used as a parameter is determined. The measurement results are shown in FIG. FIG. 3 is an Arrhenius plot in which the vertical axis indicates “a value obtained by taking a natural logarithm of the amount of change in curvature of the movable structure 134 before and after heat treatment” and the horizontal axis indicates “reciprocal of absolute temperature”. Here, the movable structure 134 has a width perpendicular to the arrangement direction of the first movable beam 132a, the second movable beam 132b, etc. of 100 μm to 140 μm, a length in the arrangement direction of 450 μm to 600 μm, and a thickness. The thickness was 4 μm to 10 μm.

A plateau region in which the effect of curvature relaxation becomes constant regardless of temperature at a heat treatment temperature of 500 ° C. or higher (reciprocal of absolute temperature: 1 / T ≦ 0.0129 K ⁻¹ ) appears. This means that at a heat treatment temperature of 500 ° C. or higher, the reaction related to curvature relaxation is completed in a shorter time than 2 hours. Further, since the Arrhenius plot has an inflection point at 500 ° C., it is shown that the curvature relaxation phenomenon is completed in 2 hours at a heat treatment temperature of 500 ° C. In other words, “the saturation time in curvature relaxation at a heat treatment temperature of 500 ° C. is 2 hours”.

  Accordingly, the activation energy of the curvature relaxation phenomenon is the Arrhenius plot of FIG. 3 at 500 ° C. or less (the reciprocal of the absolute temperature: 1 / T ≧ 0.0129 K−1) at which the curvature relaxation does not reach saturation in the heat treatment time of 2 hours. This value is calculated as 0.74 eV.

  Further, from the obtained activation energy, the acceleration coefficient for each temperature is uniquely obtained from the Arrhenius equation, and the relationship between “the saturation time of the curvature relaxation phenomenon and the reciprocal of the absolute temperature at the heat treatment temperature” shown in FIG. 4 is obtained. .

This relationship is approximated by the expression “saturation time of curvature relaxation phenomenon (time; h) = 4 × 10 ⁻⁵ × exp (8340.7 / absolute temperature)”. Further, the saturation time of the curvature relaxation phenomenon is replaced with the heat treatment time, and the heat treatment temperature satisfying the expression “heat treatment time (hour; h) = 4 × 10 ⁻⁵ × exp (8340.7 / absolute temperature)” The heat treatment time is a necessary condition for the heat treatment conditions. Needless to say, the heat treatment condition may be the shaded region in FIG. 4 including the above relational expression.

  With respect to the size of the movable structure 134, the width is set to 100 μm to 140 μm. Regarding the thickness, the curvature before the heat treatment becomes smaller as the thickness becomes larger than the Stony equation, so that the effect of reducing the curvature can be obtained even when the thickness is increased.

  From the viewpoint of shortening the process time, the heat treatment temperature should be as high as possible. On the other hand, first, as the temperature rises, unexpected side reactions can occur other than the curvature relaxation phenomenon. In addition, manufacturers that can manufacture inert ovens that can perform heat treatment at temperatures exceeding 500 ° C. are limited, and there are disadvantages such as the inert oven itself being expensive. If these things are judged comprehensively, it can be said that “heat treatment temperature: 500 ° C., heat treatment temperature time: 2 hours” is an appropriate heat treatment condition.

As described above, according to the present invention, the heat treatment is performed after the protective layer is removed and the movable structure is separated, so that the movable structure can be operated in the manufacturing process of the micromechanical structure. After that, the deformation of the movable structure that occurs is suppressed, and the deformation of the movable structure can be suppressed to less than the desired curvature (<1 m ⁻¹ ).

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, a reflective structure may be formed on the plane of the movable structure.

  DESCRIPTION OF SYMBOLS 101 ... Base | substrate part, 101a ... Opening part, 102 ... Embedded insulating layer, 102a ... Opening part, 103 ... Surface silicon layer (SOI layer), 105 ... Protective layer, 131 ... Frame part, 132a ... 1st movable beam, 132b ... 2nd movable beam, 133a ... 1st connection part, 133b ... 2nd connection part, 134 ... movable structure, 135 ... clearance gap.

Claims (6)

A first step of patterning the surface silicon layer of an SOI substrate having a surface silicon layer formed via a buried insulating layer on the surface of the base portion to form a movable structure in the element formation region;
An opening penetrating the base portion and the buried insulating layer is formed from the back surface of the base portion in the element forming region, and the buried insulating layer around the opening portion is supported as a support structure to be operable. A second step of forming a micromechanical structure comprising the movable structure;
A micromechanical structure manufacturing method comprising: a third step of heating the micromechanical structure after forming the micromechanical structure including the movable structure that is operable. In the manufacturing method of the micro mechanical structure of Claim 1,
In the third step, the micromechanical structure is heated in an inert gas or vacuum atmosphere. In the manufacturing method of the micro mechanical structure of Claim 2,
The micromechanical structure is heated at a heating time that satisfies the relationship of heating time = 4 × 10 ⁻⁵ × exp (8340.7 / absolute temperature) and a heating temperature indicated by the absolute temperature. A method for manufacturing a mechanical structure. In the manufacturing method of the micro mechanical structure of Claim 2,
In the third step, the micromechanical structure is heated at a temperature condition of 500 ° C. In the manufacturing method of the micro mechanical structure of Claim 4,
In the third step, the micromechanical structure is heated for 2 hours. In the manufacturing method of the micro mechanical structure of any one of Claims 1-5,
After the first step, after forming a protective layer made of an organic resin covering at least the element formation region of the surface silicon layer, the opening is formed,
After the opening is formed, the protective layer is removed by an ashing treatment of an organic material, and the oxide layer on the surface of the movable structure after removing the protective layer is removed by a plasma treatment. A method for producing a micromechanical structure, comprising forming a micromechanical structure including the movable structure.

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