JP2009262258A - Manufacturing method of silicon structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of silicon structure wherein a recess having a bump therein with a high aspect ratio is formed easily and with high processing accuracy. <P>SOLUTION: The manufacturing method includes: an initial recess forming step for forming an initial recess 42 into a substrate 1 comprising silicon; an etching step for forming an initial recess 41 of the depth d1 different from the depth of the initial recess 42, into an orbiting area 4E1, by applying anisotropic etching in the direction of the depths d1, d2 to both the initial recess 42 and the substrate of the orbiting area 4E1 adjacent to the initial recess 42, with the substrate 1 for the internal face 42a of the initial recess 42 remaining as a bulkhead 1w, and also by drilling down the initial recess 42 in the direction of the depth d2; a recess oxidizing step for forming an oxidized part Ox by oxidizing the bulkhead 1W and the multiple internal faces 41a, 41b, 42a, 42b of the initial recesses 41, 42 of the different depths d1, d2; and an oxidized part removing step for removing the oxidized part Ox to form a whole shape of a recess 4 and also to form a bump G1 on the internal side of the recess 4 in the direction of depths D1, D2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a silicon structure.

Conventionally, a device (Micro Electro Mechanical System: MEMS) having a new function by fusing micro mechanical parts and electronic parts is known. In MEMS, products for the market such as automobile parts (airbag sensors, etc.), inkjet heads, image projection devices, etc. are mass-produced mainly by forming minute mechanical structures on silicon (Si) wafers. . In MEMS, there is a demand for further miniaturization and higher performance of these devices.
For example, a mechanical detection unit of an acceleration sensor or an angular velocity sensor is mainly composed of a comb-like beam structure formed on a substrate. To reduce the size and performance of these sensors, increase the width of the groove formed by etching the Si substrate and the aspect ratio (depth / groove width, depth / hole diameter) between the hole diameter and depth. There is a need to.

As a method for forming a hole or groove having a high aspect ratio by etching on a Si substrate, a method of switching a material gas supplied to a chamber for each etching process is disclosed (for example, see Patent Document 1). Patent Document 1 discloses a dry etching technique in which two steps of (1) plasma etching with high anisotropy and (2) polymer-based thin film deposition are alternately performed.
US Pat. No. 5,501,893

However, in the conventional technique, when forming a multi-stage groove (trench) having a high aspect ratio, a multi-stage hole (hole), or a multi-stage structure in which a trench and a hole are combined, the following is performed. There are challenges. With the conventional technique, it is extremely difficult to adjust the balance between the etching process (1) and the thin film deposition process (2). Therefore, the adjustment range (process margin) of various parameters in the manufacturing process becomes very narrow, and optimization of the manufacturing process becomes extremely difficult.
For example, when forming recesses such as holes and trenches by etching on a Si base material, the depth from the surface of the base material is formed when a bottom surface having a different depth is formed to form a step inside the recess. If they are different, the amount of reaching radicals and ions will be different. Therefore, the etching rate in the step (1) and the amount of the polymer-based thin film deposited in the step (2) vary depending on the location (position in the depth direction), and the optimum amount for the deep position in the depth direction of the recess. It is extremely difficult to deposit a thin film.

Further, the inventors have found that the following problems occur when forming the step of such a recess.
When the film thickness of the thin film deposited on the inner surface of the recess in the step (2) is too thin, the side wall of the portion is formed in a tapered shape in the step (1). On the other hand, when the thickness of the thin film deposited in the step (2) is too thick, the base material remains in a protruding shape at the step of the recess. In addition, when the bottom surface of the deepest part of the recess becomes rough in the process (1), the thin film is uniformly formed in the vicinity of the corner of the deepest part of the recess when the thin film is deposited in the process (2). It is not deposited, and the inner surface of the recess is also roughened in the step (1).
Therefore, with the conventional method, it is difficult to form a step with high processing accuracy in a high aspect ratio recess.

  Therefore, the present invention provides a method for manufacturing a silicon structure, which can easily form a high aspect ratio recess having a step inside with high processing accuracy.

  In order to solve the above-described problems, a method for manufacturing a silicon structure according to the present invention includes an initial recess forming step of forming an initial recess that is a part of a recess in a substrate made of silicon, and an inner surface of the initial recess. With the base material remaining as a partition, the base material in the depth direction is anisotropically etched in the depth direction and the initial recess portion is dug down in the depth direction. And an etching step of forming initial recesses having different depths separated by the initial recesses and the partition walls in the circumferential region, and oxidizing the inner surfaces of the plurality of initial recesses having different depths and the partition walls. A recessed portion oxidizing step for forming an oxidized portion; and an oxidized portion removing step for removing the oxidized portion to form the entire shape of the recessed portion and forming the step in the depth direction inside the recessed portion. Characterized by

By manufacturing in this way, the bottom surfaces of the plurality of initial recesses having different depths are separately etched by the partition walls and etched. And the inner surface of an initial recessed part and a partition are oxidized and removed, and the whole shape of a recessed part is formed. Thereby, while the inner surface of a recessed part is smoothed, the partition which isolates initial recessed parts is removed, and a level | step difference is formed inside a recessed part.
Therefore, according to the silicon structure manufacturing method of the present invention, a high aspect ratio recess having a step inside can be easily formed with high processing accuracy.

In the method for manufacturing a silicon structure according to the present invention, the recess oxidation step completely oxidizes the partition wall.
The concave portion oxidation step is performed by thermal oxidation by heating.

By manufacturing in this way, a partition can be more reliably and easily removed in an oxidation part removal process.
In addition, the thickness of the oxidized portion on the inner surface of the initial recess can be made uniform. Further, the thickness of the oxidized portion can be controlled by adjusting the heating temperature, the heating time, and the like.

  Further, in the method for manufacturing a silicon structure according to the present invention, the initial recess is formed on the inner side of the recess than the inner surface of the recess by a thickness that allows the base material to be removed as the oxidized portion. And

  By manufacturing in this way, the base material on the inner surface of the initial recess is oxidized to the boundary of the recess forming region where the final recess is formed to become an oxidized portion. The oxidized portion is removed in the oxidized portion removing step. Therefore, the inner surface of the recess can be processed with high processing accuracy.

  The method for producing a silicon structure according to the present invention is characterized in that the etching step is performed n times to form n steps in the recess.

  By manufacturing in this way, a plurality of steps can be formed inside the recess.

In the method for producing a silicon structure according to the present invention, the etching step is performed by dry etching.
The oxidized portion removing step is performed by wet etching.

By manufacturing in this way, the substrate can be selectively etched in the depth direction.
In addition, the oxidized portion can be selectively removed.

The silicon structure manufacturing method of the present invention is characterized in that the circumferential region is defined by a hard mask.
The hard mask is made of silicon oxide.

By manufacturing in this way, it is possible to etch the base material in the initial concave portion and the peripheral region in a state where the region other than the initial concave portion and the peripheral region is protected by the hard mask.
In addition, by using a hard mask made of silicon oxide, when etching the base material by anisotropic dry etching, the recesses are etched stepwise using the selection ratio between the hard mask and the base material. Can do. Therefore, it becomes possible to form a recessed part in multiple steps.
Further, by using a hard mask made of silicon oxide, the hard mask can be removed together with the oxidized portion removing step.

Further, the silicon structure manufacturing method of the present invention is characterized in that the circumferential region is defined by partially removing the hard mask.
The step of partially removing the hard mask may be performed together with the initial recess forming step or the etching step.

By manufacturing in this way, the circulation area can be defined by the portion from which the hard mask has been removed.
Further, by partially removing the hard mask together with the initial recess forming step or the etching step, the manufacturing process can be simplified and the productivity can be improved.

<First embodiment>
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the following drawings, the scale is appropriately changed for each layer and each member so that each layer and each member can be recognized on the drawing.
In the present embodiment, a silicon structure used in a field such as MEMS (Micro Electro Mechanical System) is manufactured by forming multi-stage recesses (holes, trenches, etc.) having steps inside on a substrate made of silicon. A method will be described. Here, in order to manufacture a silicon structure having a recess having a step inside by etching the substrate, first, a hard mask corresponding to the shape of the recess is formed on the surface of the substrate.
FIG. 1A to FIG. 1H are cross-sectional views showing a manufacturing process of the silicon structure according to this embodiment. FIG. 2A to FIG. 2D are a cross-sectional view showing a manufacturing process of the silicon structure according to the present embodiment and a plan view in the vicinity of the recess forming region.

(Hard mask formation process)
As shown in FIG. 1 (a), on the surface 1a of the substrate 1 made of silicon, for example, a hard mask 2 made of silicon oxide such as SiO _2. The hard mask 2 can be formed, for example, by thermally oxidizing the surface 1a of the substrate 1 or by forming a film on the surface 1a of the substrate 1 by a vacuum deposition method, a sputtering method, a CVD method, or the like. .

Next, as shown in FIG. 1B, a photoresist 3 is formed on the surface 2 a of the hard mask 2.
Next, as shown in FIG. 1C, the photoresist 3 is exposed and developed and patterned, and a first etching region (circular region) 4E1 of an etching region 4E (see FIG. 2B) of the recess 4 described later. The opening part 31 corresponding to is formed. At this time, the outer boundary of the recess 4 in the first etching region 4E1 coincides with the outer boundary of the recess 4 in the etching region 4E. The first etching region 4E1 corresponds to the planar shape of the bottom surface 41b of the initial recess 41 (see FIG. 2B) described later.

Further, the outer boundary of the recess 4 in the first etching region 4E1 is the recess 4 by a thickness To1 at which the base material 1 is removed as the oxidized portion Ox rather than the recess forming region 4A where the recess 4 is finally formed. Set inside.
In addition, the inner boundary of the recess 4 in the first etching region 4E1 extends from the boundary of the second etching region 4E2 described later to the outside of the recess 4 by the thickness Tw of the partition 1w (see FIG. 2B) described later. Set.
The inner boundary of the recess 4 in the first etching region 4E1 and the outer boundary of the recess 4 in the second etching region 4E2 are located at the center of the partition wall 1w in the thickness Tw direction, which will be described later, in the final recess described later. 4 is set so as to match the position of the step G1 (see FIG. 3B).

  Next, as shown in FIG. 1D, the hard mask 2 exposed in the opening 31 is etched by dry etching. Then, the film thickness T of the hard mask 2 is set to a film thickness T1 corresponding to the difference between the etching depths d1 and d2 of the bottom surface 41b (see FIG. 2 (b)) of the initial recess 41 described later and the bottom surface 42b of the initial recess 42. Thin film. As an etchant (etching gas) for dry etching, for example, a CF-based gas can be used.

Note that the etching depth d1 is the thickness of the bottom surface 41b of the final recess 4 by a thickness that allows the base material 1 of the bottom surface 41b to be removed as the oxidized portion Ox (see FIG. 2C) in the oxidation portion removal step described later. It is set shallower (smaller) than the depth D1 (see FIG. 2D).
Accordingly, the first etching region 4E1 of the etching region 4E of the recess 4 is defined to be smaller (inside the recess 4) than the recess 4 by the thickness To1 at which the base material 1 is removed as the oxidized portion Ox. Is done. Here, the film thickness T1 is adjusted in consideration of the film thickness to be thinned in the initial recess forming process described later.

Next, as shown in FIG. 1E, a photoresist 3 is formed again so as to cover the hard mask 2 that has been thinned.
Next, as shown in FIG. 1F, the photoresist 3 is patterned to form an opening 32 corresponding to a second etching region 4E2 of an etching region 4E described later. The second etching region 4E2 corresponds to the planar shape of the bottom surface 42b of the initial recess 42 (see FIG. 2A) described later.

  Here, the outer boundary of the recess 4 in the second etching region 4E2 is the first etching region 4E1 corresponding to the thickness Tw of the base material 1 remaining as a partition wall 1w (see FIG. 2B) in an etching process described later. It is set inside the recess 4 rather than the boundary inside the recess 4. Further, the center position in the thickness Tw direction of the partition wall 1w described later is set so as to match the position of the step G1 of the recess 4 described later (see FIG. 3B).

In addition, the thickness Tw of the partition wall 1w is set to about twice or less the thickness To1 at which the base material 1 is processed as the oxidized portion Ox in the concave portion oxidation step described later.
Here, in the present embodiment, the thickness Tw of the partition wall 1w is, for example, about 1 μm. In this case, the thickness To1 at which the base material 1 is processed as the oxidized portion Ox can be about 0.5 μm or more. The thickness To1 is preferably about 0.62 μm or more. In the present embodiment, the thickness To1 is about 0.8 μm.

  Next, as shown in FIG. 1G, the hard mask 2 exposed in the opening 32 is etched to form the opening 22. The hard mask 2 can be etched by, for example, the dry etching described above.

Next, as shown in FIG. 1H, the photoresist 3 is removed.
As a result, the opening 22 corresponding to the planar shape of the bottom surface 42b of the initial recess 42 is formed in the second etching region 4E2 of the hard mask 2 on the surface 1a of the substrate 1. Further, the hard mask 2 is thinned so that the film thickness T1 in the first etching region 4E1 corresponding to the planar shape of the bottom surface 41b of the initial recess 41 corresponds to the difference between the etching depths d1 and d2 of the bottom surface 41b and the bottom surface 42b. It is formed in a multistage shape. Then, the hard mask 2 defines an etching region 4E of the substrate 1 composed of the first etching region 4E1 and the second etching region 4E2. Further, a first etching region (circular region) 4E1 adjacent to the initial recess 42 is defined.

(Initial recess formation process)
Next, as shown in FIG. 2A, the base material 1 in the second etching region 4 </ b> E <b> 2 is etched through the opening 22 of the hard mask 2, so that the base material 1 is a part of the concave portion 4. A recess 42 is formed. Here, for example, the initial recess 42 is formed by anisotropic dry etching in which an etching step using fluorine-based gas such as SF6 and oxygen and a polymer deposition step using C4F8 gas are alternately performed. At this time, the hard mask 2 is also etched to reduce the thickness T and T1, and the portion corresponding to the first etching region 4E1 is removed.

(Etching process)
Next, as shown in FIG. 2B, the bottom surface 42b of the initial recess 42 exposed in the second etching region 4E2 and the surface 1a of the substrate 1 in the first etching region (circular region) 4E1 are anisotropic. Etching is performed by dry etching. At this time, the bottom surface 42b and the base material 1 of the surface 1a are left between the first etching region 4E1 and the initial recess 42 of the second etching region 4E2 with the base material 1 of the inner side surface 42a remaining as the partition wall 1w. Etch.

Here, the dry etching in the etching process is performed in the same manner as the anisotropic dry etching in the initial recess forming process. At this time, the etching depths d1 and d2 are adjusted by changing the processing time (the number of repetition steps of polymer deposition and etching).
Thereby, the initial recessed part 42 is dug down in the depth d2 direction. At the same time, an initial recess 41 having a new bottom surface 41b having an etching depth d1 from the surface 1a different from the etching depth d2 of the bottom surface 42b of the initial recess 42 is formed in the first etching region 4E1. At this time, the initial concave portion 41 and the initial concave portion 42 are formed in a state of being separated by the remaining base material 1 as the partition wall 1w.

Note that the etching depth d2 is the depth D2 (see FIG. 2D) of the bottom surface 42b of the final recess 4 and the bottom surface 42b in the oxidized portion removing process described later, which is the oxidized portion Ox (see FIG. 2C). ) Is set in consideration of the thickness to be removed.
That is, in the above-described hard mask forming step, the film thickness T1 of the hard mask 2 in the first etching region 4E1 shown in FIG. 1D is set in consideration of the following matters, for example. One is to set the film thickness T1 in consideration of the difference between the etching depths d1 and d2 between the deepest bottom surface 42b and the bottom surface 41b one step shallower than that. Further, the film thickness T1 is set in consideration of the difference in etching rate between the hard mask 2 and the substrate 1.

(Recess oxidation process)
Next, as shown in FIG. 2 (c), the base 1 on the inner surface of the initial recesses 41, 42 including the bottom surfaces 41b, 42b of the initial recesses 41, 42 and the inner side surfaces 41a, 42a is oxidized to give a predetermined The oxidized portion Ox having a thickness To is processed.
The oxidation of the inner surfaces of the initial recesses 41 and 42 can be performed, for example, by thermal oxidation in which the inner surfaces of the initial recesses 41 and 42 are heated to high temperatures. The thickness To of the oxidized portion Ox can be controlled by adjusting the temperature, the heating time, etc. in the thermal oxidation. In this embodiment, thermal oxidation is performed at a high temperature of, for example, 1000 ° C. or higher.
The oxidation of the inner surfaces of the initial recesses 41 and 42 is performed until the partition wall 1w is completely oxidized in the thickness Tw direction until the partition wall 1w becomes a part of all the oxidized portions Ox. By completely oxidizing the partition wall 1w, the thickness Tw of the partition wall 1w increases more than before oxidation.

(Oxidation removal process)
Next, as shown in FIG. 2D, the inner surfaces of the initial recesses 41 and 42 oxidized in the above-described steps, the oxidized portion Ox including the partition wall 1w, and the hard mask 2 on the surface 1a of the substrate 1 are shown. Remove all at once. Here, the oxidized portion Ox and the hard mask 2 are removed by wet etching using an etchant.
Through the above steps, the multi-stage having the step G1 in the depth D1, D2 direction between the bottom surfaces 41b, 42b having different depths D1, D2 from the surface 1a of the base 1 in the recess forming region 4A of the base 1 A recess 4 in the structure is formed.

Next, the operation of this embodiment will be described.
In the manufacturing method of this embodiment, the initial recessed part 42 is formed in the base material 1 as shown to Fig.2 (a). Then, as shown in FIG. 2B, the bottom surface 42b of the initial recess 42 in the second etching region 4E2 is dug down, and the base material 1 in the first etching region 4E1 is dug down. And the initial recessed part 41 which has the new bottom face 41b in the etching depth d1 (surface 1a side of the base material 1 side) shallower than the etching depth d2 of the bottom face 42b of the initial recessed part 42 is formed.

  At this time, the plurality of bottom surfaces 41b and 42b having different etching depths d1 and d2 of the initial recesses 41 and 42 are respectively separated by the partition walls 1w and etched in an isolated state. Then, the inner surfaces of the initial concave portions 41 and 42 and the partition wall 1w are oxidized to become an oxidized portion Ox, and the oxidized portion Ox is removed. Thereby, while the inner surface of the recessed part 4 is smoothed, the partition 1w which isolates the initial recessed parts 41 and 42 adjacent to the surface 1a direction of the base material 1 is removed. And the whole shape of the recessed part 4 is formed, and the level | step difference G1 of depth D1, D2 direction is formed inside the recessed part 4. FIG.

  Here, FIG. 3A and FIG. 3B are cross-sectional views for explaining the operation of the present embodiment. For comparison with the present embodiment, FIGS. 4, 5A to 6B, and 6A to 6C are cross-sectional views for explaining a conventional method for manufacturing a silicon structure. Show. In FIG. 3B, the planar shape of the recess 4 is shown as a rectangular shape in order to show that the operation of the present embodiment does not depend on the planar shape of the recess 4.

In the conventional manufacturing method, as shown in FIG. 4, when the recess 10 having the bottom surfaces 401b and 402b having different depths is formed by etching the substrate 10, the boundary between regions having different depths (A in FIG. 4). Part) exists.
When irregularities are formed on the inner side surface 402a of the recess 40 as shown in FIG. 5A and FIG. 5B at the boundary between such regions having different depths, there are the following problems. For example, polymer deposition on the inner surface 402a may be hindered by the influence of the convex portion 402c of the inner surface 402a. In such a case, a thin film may not be formed on the inner surface 402a in the vicinity of the step G of the recess 40, or the thickness of the thin film in that portion may be reduced.

  Further, in the conventional manufacturing method, after forming the shape of the deepest portion of the concave portion 40, when the bottom surface 402b of the deepest portion of the concave portion 40 and the concave portion formation region 40A of the base material 10 are collectively etched, There is a problem like this. For example, the etching conditions are different between the bottom surface 402b at the deepest portion and the bottom surface 401b at a shallower position. For this reason, the adjustment width (process margin) of various parameters in the process of depositing the polymer is very narrow, and it is very difficult to make the film thickness uniform.

  As described above, when the thickness of the thin film deposited in the vicinity of the step G on the inner surface 402a of the recess 40 is too thin, the etching proceeds in the lateral direction (direction perpendicular to the depth direction), and the step of the recess 40 G corner C is etched. And as shown to Fig.6 (a), the inner surface 402a of the deepest part of the recessed part 40 will be formed in a taper shape.

  On the other hand, when the thickness of the thin film on the inner surface 402a of the recess 40 is too thick, the shadowed portion of the projection 402c is an anisotropic dry etching etching step as shown in FIG. May remain. In such a case, as shown in FIG. 6B, the base material 10 remains in a protruding shape at the step G of the recess 40.

  In addition, as shown in FIG. 6C, when the bottom surface 402b of the deepest portion of the recess 40 is roughened by etching, there are the following problems. For example, in the step of depositing the thin film, the polymer is not uniformly deposited in the vicinity of the deepest corner Cb (the boundary between the bottom surface 402b and the inner surface 402a) of the recess 40, and the inner surface 402a of the deepest portion of the recess 40 is also etched. It will be in a rough state.

  On the other hand, in the present embodiment, as shown in FIG. 2B, the plurality of bottom surfaces 41b and 42b having different etching depths d1 and d2 of the initial recesses 41 and 42 are separated and separated by the partition walls 1w, respectively. Etched with. Therefore, in the etching process, there is no boundary between regions having different depths as in the conventional case. Therefore, the bottom surfaces 41b and 42b having different etching depths d1 and d2 can be independently etched.

This makes it possible to set process conditions corresponding to the etching depths d1 and d2, and to increase the process margin in the process of depositing the polymer.
Therefore, in this embodiment, it becomes possible to deposit a polymer with a more uniform film thickness than the conventional manufacturing method, and the aspect ratio of the recessed part 4 can be improved. In addition, since the process margin is expanded, manufacturing can be facilitated and productivity can be improved.

  In the present embodiment, the bottom surfaces 41b and 42b having different etching depths d1 and d2 can be independently etched with a high aspect ratio, so that the inner side surface 42a of the deepest portion of the recess 4 as in the prior art. Can be prevented from being formed into a tapered shape.

In the present embodiment, as described above, the base portion 1 on the inner surfaces (the inner side surfaces 41a and 42a and the bottom surfaces 41b and 42b) of the initial recesses 41 and 42 is oxidized to form the oxidized portion Ox.
At this time, as shown in FIG. 3 (a), the etching region 4E is recessed by a thickness To1 processed from the recessed portion forming region 4A where the recessed portion 4 is finally formed into the oxidized portion Ox of the base material 1. It is set to be smaller than 4 (inner side of the recess 4 than the inner surface of the recess 4).

Therefore, the base material 1 on the inner surface of the initial concave portions 41 and 42 formed by etching the base material 1 in the etching region 4E is oxidized to the boundary of the concave portion forming region 4A where the final concave portion 4 is formed. Oxidized portion Ox. Then, the oxidized portion Ox is removed in the oxidized portion removing step. Therefore, the recess 4 can be processed with higher processing accuracy than before.
Further, by removing the oxidized portion Ox, the unevenness of the inner surface of the recess 4 can be smoothed, and it is possible to prevent the inner surface of the recess 4 from becoming rough as in the prior art.

Further, as shown in FIG. 3B, after the bottom surfaces 41b and 42b are independently etched, the partition walls 1w existing at the boundaries of the regions having different depths D1 and D2 are oxidized to form a part of the oxidized portion Ox. It has been removed. Therefore, the base material 1 does not remain in a protruding shape at the step G1 of the recess 4 as in the prior art.
Further, since the first etching region 4E1 and the second etching region 4E2 are set by the hard mask so that the center of the partition wall 1w in the thickness Tw direction is aligned with the step G1 of the recess 4, the position of the step G1 is set with high accuracy. It can be formed by positioning.

Further, by forming the oxidized portion Ox by thermal oxidation, the heating temperature, the heating time, and the like can be adjusted to control the thickness To of the oxidized portion Ox. Therefore, the thickness To of the oxidized portion Ox can be easily adjusted, and the oxidized portion Ox having a uniform thickness To can be formed on the inner surface of the recess 4. In addition, the thickness To of the oxidation part Ox becomes thicker than the thickness To1 of the base material 1 before oxidation.
Further, by performing the thermal oxidation at a temperature of, for example, 1000 ° C. or more, the plane orientation dependency when the base material 1 is oxidized to form the oxidized portion Ox can be minimized. Accordingly, the thickness To of the oxidized portion Ox formed on the bottom surfaces 41b and 42b of the initial concave portions 41 and 42 and the thickness To of the oxidized portion Ox formed on the inner side surfaces 41a and 42a of the initial concave portions 41 and 42 are obtained. Can be even.

  Further, the partition wall 1w is oxidized from both directions (inner side and outer side of the recess 4) in the recess oxidation step. Therefore, by setting the thickness Tw of the partition wall 1w to about twice or less the thickness To1 where the base material 1 is processed as the oxidized portion Ox, the oxidized portion Ox having the thickness To is formed on the inner surface of the recess 4. When this is done, the partition wall 1w can be completely oxidized.

In the present embodiment, the thickness Tw of the partition wall 1w shown in FIG. 2B is about 1 μm, and the thickness To1 of the base material 1 removed as the oxidized portion Ox is about 0.8 μm. When the base material 1 having a thickness To1 of 0.8 μm is oxidized and processed into the oxidized portion Ox, the thickness To of the oxidized portion Ox shown in FIG. 2C is about 1.78 μm.
Thus, the thickness To1 of the base material 1 removed as the oxidized portion Ox is more preferably about 0.62 μm or more (0.62 times or more the thickness Tw of the partition wall 1w), whereby the thickness of the oxidized portion Ox. The thickness To can be about 1.38 μm.
Therefore, complete oxidation of the partition wall 1w can be performed more reliably. Thus, by completely oxidizing the partition wall 1w in the recess oxidation step, the partition wall 1w can be more reliably and easily removed in the oxidation portion removal step.

Further, by oxidizing (processing) the inner surfaces of the initial concave portions 41 and 42 and the partition wall 1w to form an oxidized portion Ox made of silicon oxide, the difference in material between silicon oxide and silicon can be reduced in the oxidized portion removing step. By utilizing this, the oxidized portion Ox can be selectively removed.
In addition, by defining the etching region 4E with the hard mask 2 in the etching process, the substrate 1 in the etching region 4E can be etched in a state where the region other than the etching region 4E is protected by the hard mask.

Further, by using the hard mask 2, the etching region 4E can be defined by the portion where the hard mask 2 is removed.
Further, by using the hard mask 2 made of silicon oxide, the hard mask 2 can be removed together with the removal of the oxidized portion Ox in the oxidized portion removing step. At this time, by performing the oxidized portion removing step by wet etching, the oxidized portion Ox and the hard mask 2 can be selectively removed collectively without substantially affecting the substrate 1.

Moreover, when etching the base material 1 by anisotropic dry etching, the recessed part 4 can be etched in steps using the selection ratio of the hard mask 2 and the base material 1. FIG. Therefore, it becomes possible to form the recessed part 4 in multistage shape.
Further, by partially removing the hard mask 2 together with the initial recess forming process, the manufacturing process can be simplified and the productivity can be improved.

  Moreover, the base material 1 can be selectively etched in the depth direction by etching the base material 1 by anisotropic dry etching.

As described above, according to the silicon structure manufacturing method of the present embodiment, the high aspect ratio concave portion 4 having the step G1 on the inside can be easily formed with high processing accuracy.
Therefore, silicon can be stably processed with high processing accuracy even in a complicated structure such as a multi-stage trench having a plurality of steps inside, a multi-stage hole, or a combination of a trench and a hole.

  In addition, since the shape of the concave portion 4 can be prevented from collapsing or becoming an unstable shape, silicon with good reproducibility can be processed. Furthermore, since process variations (variations in parameters and the like affecting production) in the etching process can be minimized, a large process margin (variation width of parameters in the production process) can be ensured. In addition, since silicon can be processed stably with high processing accuracy, the MEMS can be reduced in size, performance, and reliability.

<Second embodiment>
Next, a second embodiment of the present invention will be described with reference to FIGS. This embodiment is different from the silicon structure manufacturing method described in the first embodiment in that two or more n steps G1, G2,..., Gn are formed inside the recess 4. . Since the other points are the same as in the first embodiment, the same parts are denoted by the same reference numerals and description thereof is omitted.

(Hard mask formation process)
In the silicon structure manufacturing method of this embodiment, in the hard mask formation step described in the first embodiment, the hard mask 2 is formed in multiple stages according to the difference in depth between the bottom surfaces having different depths. Then, an opening corresponding to the planar shape of the bottom surface of the deepest portion of the recess 4 is formed in the hard mask 2.

  First, as in the first embodiment shown in FIGS. 1A to 1D, the hard mask 2 in the first etching region (circular region) 4E1 corresponding to the planar shape of the bottom surface 41b of the initial recess 41 is thinned. Turn into. At this time, the hard mask 2 is thinned to a film thickness T1 (first stage) corresponding to the difference between the etching depths d1 and dn + 1 between the bottom surface 41b formed at the shallowest position and the bottom surface 4n + 1b at the deepest part. .

  Next, as shown in FIG. 1E, a photoresist 3 is formed again. Thereafter, as shown in FIG. 1 (f), the opening 32 of the photoresist 3 is formed in the second etching region (circular region) 4E2 corresponding to the planar shape of the bottom surface 42b formed at a position one step deeper than the bottom surface 41b. To do. Then, the hard mask 2 exposed in the opening 32 is thinned to a film thickness T2 (second stage) corresponding to the difference between the etching depths d2 and dn + 1 between the bottom surface 42b and the deepest bottom surface 4n + 1b (illustrated). Abbreviation).

  By repeating this, the thickness of the hard mask 2 corresponding to the planar shape of the bottom surface 4nb formed at a position shallower by one step than the bottom surface 4n + 1b of the deepest portion of the recess 4 is reduced to a thin film. . Then, the hard mask 2 is subjected to film thicknesses T3 (third stage),..., Tn (n-th stage) corresponding to the differences in etching depths d3,..., Dn, dn + 1 between the bottom surfaces 43b,. ) In multiple stages (not shown).

Thereby, the film thicknesses T1, T2,..., Tn of the etching region 4E of the hard mask 2 are different in the etching depths d1, d2,..., Dn, dn + 1 between the bottom surfaces 41b, 42b,. N-stage multi-layered film thickness corresponding to
At this time, an interval corresponding to the thickness Tw of the partition wall 1w is provided between the etching regions from the first etching region 4E1 to the nth etching region 4En as in the first embodiment.

Then, the photoresist 3 covering the hard mask 2 formed in a multi-stage shape is subjected to the (n + 1) th etching corresponding to the planar shape of the bottom surface 4n + 1b of the deepest portion of the recess 4 as in the first embodiment shown in FIG. An opening is formed corresponding to the region 4En + 1 to form an opening 3n + 1 (not shown).
Next, as in the first embodiment shown in FIG. 1G, the hard mask 2 is opened to form an opening 2n + 1 corresponding to the planar shape of the bottom surface 4n + 1b of the initial recess 42 (not shown). As shown in h), the photoresist 3 is removed.

  Thereby, the hard mask 2 is formed in the etching region 4 </ b> E of the recess 4. The hard mask 2 formed by the above steps has an opening 2n + 1 corresponding to the planar shape of the bottom surface 4n + 1b of the initial recess 42. Further, the n-stage multi-stage film thicknesses T1, T2, corresponding to the differences in the etching depths d1, d2,..., Dn between the bottom surfaces 41b, 42b,. ..., Tn (not shown).

(Initial recess formation process)
Next, the substrate 1 is etched in the same manner as in the first embodiment shown in FIG. 2A through the opening 2n + 1 of the hard mask 2 having n stages of multi-layered thicknesses T1, T2,. . And the initial stage recessed part 4n + 1 is formed in the base material 1, and the bottom face 4n + 1b is formed (illustration omitted). At this time, the thicknesses T1 to Tn of the first etching region 4E1 to the nth etching region 4En of the hard mask 2 are thinned, and the thinnest portion of the film thickness Tn is removed.

(Etching process)
Next, as in the first embodiment shown in FIG. 2B, with the partition wall 1w remaining, the exposed bottom surface 4n + 1b of the initial recess 4n + 1 and the bottom surface 4nb that is one step shallower than the bottom surface 4nb. The base material 1 exposed in the n-etching region 4En is etched. As a result, an initial recess 4n having a bottom surface 4nb having a depth dn different from the depth dn + 1 of the bottom surface 4n + 1b of the initial recess 4n + 1 is formed. At this time, the adjacent initial recesses 4n and 4n + 1 are separated by the partition 1w and etched independently.

In addition, the film thicknesses T1, T2,..., Tn-1 of the hard mask 2 are thinned together with the formation of the bottom surface 4nb of the initial recess 4n, and the thinnest part of the film thickness Tn-1 is removed to remove the nth. The surface 1a of the substrate 1 is exposed in the -1 etching region 4En-1.
In this embodiment, this etching process is repeated n times or more twice, and initial recesses 41, 42,... Having bottom surfaces 41b, 42b,..., 4n, 4n + 1b having different depths d1, d2,. , 4n, 4n + 1.

(Recess oxidation process)
Next, as in the first embodiment shown in FIG. 2C, the inner surfaces of the initial recesses 41, 42,..., 4n, 4n + 1 including the plurality of partition walls 1w are oxidized.
That is, each of the partition walls 1w having a thickness Tw remaining between the initial recesses 41, 42,..., 4n, 4n + 1 formed by the above-described steps and the inner surfaces of the initial recesses 41, 42,. The base material 1 having a thickness To1 is oxidized to form an oxidized portion Ox.

(Oxidation removal process)
Then, as in the first embodiment shown in FIG. 2D, the oxidized portion Ox and the hard mask 2 on the surface 1a of the substrate 1 are removed together to form the entire shape of the recess 4.
Through the above steps, bottom surfaces 41b, 42b,..., 4nb, 4n + 1b having different depths D1, D2,..., Dn, Dn + 1 from the surface 1a of the substrate 1 are formed in the recess forming region 4A of the substrate 1. . Then, n-stage multi-stage recesses 4 having depths G1, G2,..., Gn in the direction of Dn, Dn + 1 are formed between the bottom surfaces 41b, 42b,. The

As described above, according to the method for manufacturing a silicon structure of the present embodiment, by performing the etching process n times, a high aspect ratio having n multi-steps G1 to Gn inside the recess 4 is obtained. The concave portion 4 can be easily formed with high processing accuracy as in the first embodiment.
Further, the process of partially removing the hard mask 2 is performed together with the etching process as well as the initial recess forming process, thereby simplifying the manufacturing process and improving the productivity.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
In the above-described embodiment, the multistage recess is formed by etching the substrate using a multistage hard mask, but the hardmask is not limited to the multistage. For example, first, the bottom surface of the deepest portion of the recess is formed using a hard mask having a uniform film thickness, and a protective film is formed on the inner surface of the recess. And you may etch the base material of the bottom face of a recessed part, and the formation area of a recessed part through the mask which has an opening match | combined with the shape of the bottom face one step shallower than the bottom face of the deepest part.

Further, when the hard mask is partially removed, if the hard mask remains on the surface of the substrate, the portion may be removed by wet etching or the like.
Further, in the above-described embodiment, the case where the step inside the recess is formed in a step shape has been described, but the step inside the recess may be an uneven shape in which shallow portions and deep portions are alternately formed. .

(A)-(h) is sectional drawing explaining the hard mask formation process which concerns on 1st embodiment of this invention. (A)-(d) is sectional drawing explaining the manufacturing process of the silicon | silicone structure which concerns on 1st embodiment of this invention, and the top view of the vicinity of a recessed part formation area. (A) And (b) is sectional drawing explaining the manufacturing process of the silicon | silicone structure which concerns on 1st embodiment of this invention, and the top view of the vicinity of a recessed part formation area. It is sectional drawing explaining the manufacturing process of the conventional silicon structure. (A) is sectional drawing explaining the manufacturing process of the conventional silicon structure, (b) is an enlarged view of the B section of (a). (A)-(c) is sectional drawing explaining the problem in the manufacturing process of the conventional silicon structure.

Explanation of symbols

1 base material, 1w partition, 2 hard mask, 4 recess, 41, 42 initial recess, 4E1 first etching region (circumferential region), d1, d2 etching depth (depth), G1 step, 41a, 42a inner surface ( Inner surface), 41b, 42b Bottom surface (inner surface), Ox oxidation part, To1 thickness

Claims (11)

An initial recess forming step for forming an initial recess that is a part of the recess in a base material made of silicon;
In the state where the base material on the inner surface of the initial recess is left as a partition wall, the initial recess and the base in the circumferential region adjacent to the initial recess are anisotropically etched in the depth direction, and the initial recess Digging in the depth direction, and forming an initial recess having a different depth separated by the initial recess and the partition in the circumferential region,
A recess oxidation step of oxidizing the inner surface of the plurality of initial recesses and the partition walls having different depths to form an oxidized portion;
Removing the oxidized portion to form the entire shape of the recess, and forming the step in the depth direction inside the recess;
A method for producing a silicon structure, comprising:   2. The method of manufacturing a silicon structure according to claim 1, wherein the recess oxidation step completely oxidizes the partition wall.   3. The silicon according to claim 1, wherein the initial recess is formed on the inner side of the recess than the inner surface of the recess by a thickness that allows the base material to be removed as the oxidized portion. Manufacturing method of structure.   4. The method for manufacturing a silicon structure according to claim 1, wherein the recess oxidation step is performed by thermal oxidation by heating.   5. The method of manufacturing a silicon structure according to claim 1, wherein the etching step is performed n times to form n steps in the concave portion. ,
The method for manufacturing a silicon structure according to claim 1, wherein the etching step is performed by anisotropic dry etching.   The method for manufacturing a silicon structure according to claim 1, wherein the oxidized portion removing step is performed by wet etching.   The method for manufacturing a silicon structure according to claim 1, wherein the circumferential region is defined by a hard mask.   9. The method of manufacturing a silicon structure according to claim 8, wherein the hard mask is made of silicon oxide.   10. The method for manufacturing a silicon structure according to claim 8, wherein the circumferential region is defined by partially removing the hard mask.   The method for manufacturing a silicon structure according to claim 10, wherein the step of partially removing the hard mask is performed together with the initial recess formation step or the etching step.

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