JP2004128483A - The vertical boring method for silicon substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vertical boring process for a silicon substrate where the cost is low, a bore of even dimension can be bored on a silicone substrate of big diameter and boring of big aspect ratio can be performed. <P>SOLUTION: The method is the vertical boring method for the silicon substrate. In the vertical boring processing to the silicon substrate by using anisotropic etching with an alkali solution, the silicon substrate whose crystal plane orientation is [211] is used, the opening of a hole is of square or rectangle, the crystal plane orientation of a side wall at the hole comprises [111] and [110]. In addition, before the anisotropic etching is performed, boring is partially performed on the opening at the hole in advance to remove the silicon from a boring section. A bore of even dimension can be bored in the silicon substrate of big dimension at a low cost and boring of big aspect ratio can be obtained. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for drilling a vertical hole in a silicon substrate.
[0002]
[Prior art]
Silicon substrate is not only a material for semiconductors and optical communication, but also has excellent workability, strength, and physical properties.Therefore, microfabrication is performed on the silicon substrate, and micromachines such as pressure sensors, acceleration sensors, etc., nozzles of inkjet printers, It is used in various fields such as an X-ray exposure mask, an electron beam projection exposure mask, and a DMD (Digital Micromirror Device) member. The silicon substrate is manufactured by cutting a single crystal silicon ingot into a predetermined crystal plane orientation, and performing processes such as grinding and polishing. In order to manufacture products in the various fields mentioned above, processing technologies such as micro-processing technology and film-forming technology are used for silicon crystals. Among various processing technologies, the technology for drilling a vertical hole in a silicon substrate is basically used. It is important as a common technology.
[0003]
2. Description of the Related Art Conventionally, as a method for drilling holes in a silicon substrate, the following techniques are known. One of the methods is a method in which a mask layer made of a photoresist, a silicon oxide film, or the like at the time of silicon etching is formed on a silicon substrate, and then vertical holes are formed by plasma dry etching. As another method, after forming a mask layer made of a photoresist, a silicon oxide film, or the like on a substrate having a crystal plane orientation of {100} or {110} on the surface of a silicon substrate, the etching rate is reduced to the plane orientation. There is a method in which a hole is formed by wet etching using an alkaline etching solution that depends on the etching. Further, there is a method in which dry etching and wet etching are combined. Patent Document 1 and Patent Document 2 are exemplified as examples using the above method.
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. Hei 9-11479 [Patent Document 2]
JP-A-10-10706 [0005]
However, the above prior art has the following problems. In the method using plasma dry etching, it takes time and cost to drill holes in the entire processing surface of the silicon layer having a thickness of several 100 μm by dry etching alone, and the etching rate depends on the aperture ratio of the drilled portion. Since the speed and its distribution in the plane of the substrate change, there is a problem that it is difficult to form a hole having a uniform size in a large-diameter silicon substrate. Further, there is a problem that the flatness and the verticality of the hole-formed side wall are low. In the method of using an alkaline etchant on a silicon substrate having a crystal plane orientation of {100} or {110}, although the side wall is high in flatness, the opening is widened at the same time as etching is performed in the depth direction of the hole. Etching also progresses in the horizontal direction, and the deeper the hole, the narrower the tip of the hole becomes, so it is necessary to increase the opening in advance, making it impossible to process a hole with a large aspect ratio (ratio of depth to opening) There was a problem that is. Therefore, there has been a demand for a fine processing technology for vertically drilling silicon.
[0006]
[Problems to be solved by the invention]
Therefore, the present invention has been made to solve such a problem. It is an object of the present invention to provide a vertical hole drilling method for a silicon substrate capable of drilling holes of uniform dimensions in a large-diameter silicon substrate at a low cost and capable of drilling holes having a large aspect ratio. It is.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, a vertical hole drilling method for a silicon substrate according to the first aspect of the present invention provides a method for vertical hole drilling in a silicon substrate using anisotropic etching with an alkaline solution, wherein the crystal plane orientation is ｛. The present invention is characterized in that a silicon substrate of 211% is used, the opening of the hole is square or rectangular, and the crystal plane orientation of the side wall of the hole is {111} and {110}.
[0008]
In the method of forming a vertical hole in a silicon substrate according to the second aspect of the present invention, a part of an opening is pre-drilled before anisotropic etching with an alkaline solution, and silicon in the pre-drilled part is removed. It is characterized in that
[0009]
According to a third aspect of the present invention, there is provided the vertical hole drilling method for a silicon substrate, wherein the pattern to be drilled before the anisotropic etching with the alkaline solution has a square or rectangular shape on the {211} plane. , A triangle, an L-shape, or a combination thereof, and one side of the pattern to be pre-drilled is at least part of each of two sides where the crystal plane orientation of the side wall of the opening is {111}. Are common.
[0010]
According to a fourth aspect of the present invention, there is provided a method of forming a vertical hole in a silicon substrate, wherein a dry etching process or a laser beam process is used for forming a hole before anisotropic etching with an alkaline solution. It is a feature.
[0011]
According to the method for forming a vertical hole in a silicon substrate according to the fifth aspect of the present invention, the laser light is irradiated in an alkaline solution used for the anisotropic etching, in order to perform the hole processing in advance before the anisotropic etching with the alkaline solution. Is vertically irradiated on the opening.
[0012]
According to a method of forming a vertical hole in a silicon substrate according to the invention of claim 6, at least a part of the opening is vertically irradiated with laser light in advance before the anisotropic etching with an alkaline solution. Is characterized in that the crystal structure is altered.
[0013]
According to a seventh aspect of the present invention, there is provided the vertical hole drilling method for a silicon substrate, wherein the alkaline solution used for the anisotropic etching is a mixture of isopropyl alcohol and an alkaline aqueous solution.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the present invention, a silicon substrate having a crystal plane orientation of {211} is used, and a mask pattern having a square or rectangular opening in which side walls of holes are {111} and {110} is formed. Processing in which a square or rectangular vertical hole composed of {111} and {110} is formed on four sides of the side wall by performing etching with an alkaline solution under the condition that the etching rate of the {111} and {110} planes is low. Is the way. Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 is a schematic plan view illustrating vertical hole drilling in a silicon substrate according to the present invention. A mask pattern 2 having a square or rectangular opening with side walls of {111} and {110} is formed on a silicon substrate 1 having a surface crystal orientation of {211}. In FIG. 1, a rectangular portion 3 is provided in advance as a portion to be drilled in contact with two opposing sides of the {111} face of the mask pattern 2, and the two rectangular portions are drilled in advance by a method such as dry etching. Part of the silicon layer is etched away.
[0016]
Next, after the silicon of the rectangular portion 3 is removed, the silicon layer between the two rectangular portions 3 is wet-etched using an alkaline solution composed of a mixture of isopropyl alcohol (IPA) and an aqueous alkaline solution. IPA has an effect of reducing the etching rate of the {110} plane, and the present inventors have found that an alkaline aqueous solution containing 30% of IPA can easily control the etching and is suitable for wet etching of the {211} plane. It is a thing.
[0017]
FIG. 2 is a cross-sectional view illustrating a state in which a silicon substrate having a surface crystal plane orientation of {211} shows a plane orientation that appears obliquely on the bottom surface when wet etching is performed using an alkaline solution. The plane orientation {111} appears at an angle of 19 ° with respect to the {211} plane, and the plane orientation {110} appears at an angle of 55 °. On two sides of the opening in the <110> direction, the wet etching with the alkaline solution stops on the {111} plane. On two sides of the opening in the <111> direction, {110} planes appear perpendicular to the substrate. Therefore, as shown in FIG. 1, the silicon layer portion where the side wall of the opening is in contact with the two sides of the {111} plane is removed in advance by means such as dry etching, or at least a part of the silicon layer is removed. If so, wet etching proceeds from that portion, the silicon layer is removed, and a vertical hole corresponding to the mask pattern 2 is formed.
[0018]
Therefore, any one of a square, a rectangle, a triangle, an L-shape, or a combination thereof can be used as the shape of the pattern of the portion to be drilled in advance. For example, even when the mask pattern opening 2 is used, it is also possible to use the pattern-formed holes 4 and 5 as shown in FIG. 3 (a) or 3 (b). As for the dimensions of the portion to be drilled in advance, if the value of the smallest side of the pattern shape is 10 or less in aspect ratio with respect to the thickness of the silicon layer, vertical drilling can be sufficiently performed.
[0019]
Plasma dry etching, laser beam machining, machining, and electric discharge machining are used as a method for previously machining at least a part of the side where the side wall of the hole is the {111} plane. Plasma dry etching, laser beam machining, or electric discharge machining is more preferable in that the micromachining is excellent and the micromachining is excellent.
[0020]
Another method of pre-drilling is to vertically irradiate laser light during wet etching to accelerate the etching, thereby forming {111} and {110} planes obliquely on the bottom surface. It is also possible to prevent the etching in the direction from being stopped and to perform vertical hole processing with a large aspect ratio. As the laser light, for example, a pulse energy of 0.1 to 0.4 J at a power density of 0.5 to ² MW / cm ² using a Nd: YAG laser can be exemplified.
[0021]
Before the anisotropic etching with an alkaline solution, at least a part of the opening is irradiated with laser light vertically in advance to destroy and alter the silicon single crystal structure of the irradiated part, thereby providing irradiation. It is also possible to make the part soluble in the etching solution. The part to be irradiated with the laser light in advance may be at least partly common to the side where the crystal plane orientation of the opening is {111}, but it is preferable that the entire part of the opening is irradiated. Is also good. As the laser light, a pulse energy of 0.1 to 0.4 J can be exemplified at a power density of 0.5 to ² MW / cm ² using an Nd: YAG laser as described above.
[0022]
In the present invention, the processing of a vertical hole in a silicon substrate means providing a square or rectangular vertical through hole in a silicon layer portion, but is not necessarily limited to this. And vertical holes stopped at a depth in the middle of the silicon layer.
[0023]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 4 and FIG. 5 subsequent to FIG. 4 are schematic partial cross-sectional views showing a method for forming a vertical hole in a silicon substrate according to the present invention. FIG. 6 and FIG. 7 subsequent thereto are schematic plan views of FIGS. 4 and 5.
[0024]
As shown in FIGS. 4 (a) and 6 (a), a silicon layer 7 having a diameter of 150 mm, a crystal plane orientation of {211} and a thickness of 625 μm, a silicon oxide film 8 having a thickness of 1 μm, and An SOI (Silicon On Insulator) substrate 6 made of a 20 μm silicon layer 9 was prepared.
[0025]
The surface of the SOI substrate 6 is immersed in a mixed aqueous solution of sulfuric acid and hydrogen peroxide (mixing 97% sulfuric acid and 30% hydrogen peroxide at a volume ratio of 4: 1) for 10 minutes, and rinsed with ultrapure water for 10 minutes. Immersion in 1% aqueous hydrofluoric acid for 1 minute, rinsing with ultrapure water for 10 minutes, mixed aqueous solution of hydrochloric acid and hydrogen peroxide heated to 80 ° C (volume of 35% hydrochloric acid, 30% hydrogen peroxide and ultrapure water (Mixing at a ratio of 1: 1: 6) for 10 minutes, rinsing with ultrapure water for 10 minutes, immersion in 1% hydrofluoric acid aqueous solution for 1 minute, and rinsing with ultrapure water for 10 minutes, thereby contaminating the silicon surface. The substances (metals, organic substances, fine particles) and the natural oxide film were removed.
[0026]
Next, using an LPCVD apparatus, dichlorosilane (SiH ₂ Cl ₂ ) ammonia (NH ₃ ) is used as a source gas under the conditions of 75 sccm and 150 sccm, respectively, at a pressure of 100 Pa and a temperature of 800 ° C., with a thickness of 0.1 mm on both surfaces of the SOI substrate 6. A silicon nitride film (Si ₃ N ₄ ) of 2 μm was formed.
[0027]
Next, using an LPCVD apparatus, as shown in FIGS. 4B and 6B, tetraethoxysilane (TEOS) and oxygen are respectively used as source gases under the conditions of 75 sccm and 10 sccm, a pressure of 40 Pa, and a temperature of 650 ° C. Then, a silicon oxide film (SiO ₂ ) 11 having a thickness of 0.2 μm was formed on the silicon nitride film 10 on both sides of the SOI substrate.
[0028]
Next, a photoresist film having a thickness of 1 μm was formed on the silicon oxide film 11 on one surface side of the silicon layer 7 to be a processed surface of the substrate. Specifically, a positive photoresist (AZ-5206E manufactured by Clariant) was spin-coated on the substrate, and then prebaked at 120 ° C. for 90 seconds using a hot plate.
[0029]
Next, alignment is performed on the basis of the orientation flat of the silicon substrate so that the direction of the side of the opening coincides with the <111> and <110> directions of the silicon substrate. As shown in FIG. 4 (c) and FIG. 6 (c), a large number of opening resist patterns 12 (opening 1 mm × 1 mm) for vertical hole processing were formed on the substrate. The development was performed with a predetermined developing solution (NMD-3, manufactured by Tokyo Ohka Kogyo Co., Ltd.), and post-baked at 120 ° C. for 90 seconds using a hot plate.
[0030]
Next, the silicon oxide film 11 where the opening of the resist pattern 12 is exposed is removed by etching by dipping in buffered hydrofluoric acid (LAL1000 manufactured by Stella Chemifa) for 2.5 minutes. As shown in FIG. 6D, the silicon nitride film 10 was exposed.
[0031]
Next, the photoresist was removed by ultrasonic cleaning with acetone for 10 minutes, isopropyl alcohol for 10 minutes, and ultrapure water for 10 minutes.
[0032]
Next, as shown in FIGS. 4E and 6E, the silicon nitride film at the opening of the silicon oxide film was etched and removed as shown in FIGS. The temperature of the heated phosphoric acid aqueous solution, which is an etching solution, was controlled at a constant value of 154 ° C., and was constantly kept in a boiling state. A small amount of ultrapure water was added dropwise to maintain the phosphoric acid concentration at a constant value of 85%. After forming an opening in the silicon nitride film, it was washed with water and dried.
[0033]
Next, before the silicon layer is subjected to anisotropic etching, a hole is partially formed in the opening in advance, and in order to remove silicon in the hole-formed portion, a positive photoresist (AZ-L manufactured by Clariant Co., Ltd.) is again formed. 5206E), and a resist pattern was formed by photolithography. In this embodiment, as shown in FIGS. 5 (f) and 7 (f), a rectangular (1 mm × 70 μm) resist pattern is formed in which a side wall of the opening is in contact with two sides forming {111} planes. 15 was formed.
[0034]
Next, the silicon layer 7 exposed from the photoresist was dry-etched using an ICP plasma dry etching apparatus. Specifically, a plasma is generated by applying 500 W of 13.56 MHz high frequency to the ICP coil of the chamber in which the pressure is adjusted to 3.5 Pa, and 100 sccm of sulfur hexafluoride (SF ₆ ) is used as a process gas. By switching and supplying 100 sccm of cyclobutane (C ₄ F ₈ ) every 10 seconds to perform etching, a vertical hole is formed in the silicon layer 7, and as shown in FIGS. 5 (g) and 7 (g), A portion 16 was pre-drilled to a depth of 625 μm reaching the silicon oxide film 8 of the SOI substrate.
[0035]
Next, using an ICP plasma etching apparatus, as shown in FIGS. 5H and 7H, the photoresist on the surface was removed. The pressure and applied frequency were the same as those described above, and 100 sccm of oxygen was supplied as a process gas.
[0036]
Next, the silicon between the pre-drilled portions 16 of the opening is etched with an alkaline solution to form a substrate 20 having a vertical hole 18 as shown in FIGS. Was formed. Etching was performed at 60 ° C. using an aqueous solution of potassium hydroxide (20% by weight) to which 30% by weight of IPA was added as an etching solution. The etching of the silicon layer was performed to a depth of 625 μm reaching the silicon oxide film 8 of the SOI substrate.
[0037]
The cross section of the SOI substrate processed in this manner was measured with a scanning electron microscope. As a result, it was confirmed that a hole of approximately 1 mm × 1 mm and a depth of 625 μm was formed vertically as designed.
[0038]
【The invention's effect】
As described above, according to the present invention, a hole with a uniform size can be formed in a large-diameter silicon substrate at a low cost, and a hole with a large aspect ratio can be obtained. Therefore, the present invention can be applied to various products having fine vertical holes in silicon, such as micromachines and masks for electron beam projection exposure.
[Brief description of the drawings]
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view illustrating vertical drilling of a silicon substrate according to the present invention. FIG. 2 is a cross-sectional view illustrating a state showing a plane orientation appearing at the time of etching. FIG. FIG. 4 is a schematic cross-sectional view showing a method for forming a vertical hole in a silicon substrate according to the present invention. FIG. 5 is a view showing a method for forming a vertical hole in a silicon substrate according to the present invention following FIG. FIG. 6 is a schematic plan view of FIG. 4; FIG. 7 is a schematic plan view of FIG. 5;
DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Mask pattern openings 3, 4, 5 Pre-drilled portion 6 SOI substrate 7, 9 Silicon layer 8 Silicon oxide film 10 Silicon nitride film 11 Silicon oxide film 12 Opening resist pattern 13 Opening provided Silicon oxide film 14 Silicon nitride film 15 with openings 15 Pre-drilled resist pattern 16 Pre-drilled portions 17 and 19 Etched silicon layer 18 Vertical holes 20 Vertically drilled SOI substrate

Claims (7)

In the vertical drilling of a silicon substrate using anisotropic etching with an alkaline solution, a silicon substrate having a crystal plane orientation of {211} is used, and the opening of the hole is square or rectangular, and the crystal plane of the side wall of the hole is used. A vertical hole drilling method for a silicon substrate, wherein the orientation comprises {111} and {110}. 2. The silicon substrate according to claim 1, wherein a part of the opening is pre-drilled before the anisotropic etching with the alkaline solution, and silicon in the pre-drilled part is removed. Vertical hole drilling method. The shape of the pattern to be drilled before the anisotropic etching with the alkaline solution is any one of a square, a rectangle, a triangle, an L-shape or a combination thereof on the {211} plane. 3. The method according to claim 2, wherein one side of the pattern to be drilled has at least a part in common with each of two sides where the crystal plane orientation of the side wall of the opening is {111}. Vertical hole drilling method for silicon substrate. 4. The silicon substrate according to claim 2, wherein a hole is formed in advance before the anisotropic etching with the alkaline solution by dry etching, laser beam machining, or electric discharge machining. Vertical hole drilling method. 3. The method according to claim 2, wherein the hole is preliminarily drilled before the anisotropic etching with the alkaline solution, and the opening is vertically irradiated with laser light in the alkaline solution used for the anisotropic etching. 4. The method for processing a vertical hole in a silicon substrate according to item 3. 2. The method according to claim 1, wherein, prior to the anisotropic etching with the alkaline solution, at least a part of the opening is irradiated with laser light vertically in advance to change the crystal structure of silicon in the irradiated part. 4. A method for processing a vertical hole in a silicon substrate according to the above. 7. The method according to claim 1, wherein the alkaline solution used for the anisotropic etching is a mixture of isopropyl alcohol and an alkaline aqueous solution.

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