JP2009266869A - Fabrication process of silicon structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fabrication process of a silicon structure which forms a multilevel structure of a hole or a trench having a high aspect ratio easily with a high process tolerance. <P>SOLUTION: A fabrication process of a silicon structure includes a step of forming an initial recess 4a, i.e., a part of a recess 4, in a base 1 consisting of silicon, a step of forming a protective film 5a on the inner side surface 42a of the initial recess 4a, a step of anisotropically etching the base 1 in the initial recess 4a and the adjacent circumferential region 4R of the initial recess 4a in the direction of depth D1, D2 while leaving the protective film 5a on the inner side surface 42a, and a step of forming the whole recess 4 by removing the protective film 5a thus left and forming a level difference 41g on the inside of the recess 4 in the direction of depth 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. In the conventional technique, it is extremely difficult to adjust the balance between the etching process (1) and the polymer 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 polymer deposited in the step (2) vary depending on the location (position in the depth direction), and an optimum amount of thin film is deposited at a deep position in the depth direction of the recess. It is extremely difficult to do.

Further, the inventors have found that the following problems occur when forming the step of such a recess.
When the film thickness of the polymer 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 step (1), when the thin film is deposited in the process (2), the polymer is uniformly in the vicinity of the corner of the deepest part of the recess. 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 problems, an initial recess forming step of forming an initial recess that is a part of the recess in a base material made of silicon, and a protective film forming step of forming a protective film on the inner surface of the initial recess, An etching step of anisotropically etching the base material in the circumferential region adjacent to the initial recess and the initial recess while the protective film on the inner surface remains, and removing the protective film And forming a step in the depth direction inside the recess, and a protective film removing step.

By manufacturing in this way, first, an initial concave portion that is the shape of the deepest portion of the concave portion is formed on the base material. Next, the bottom surface of the initial concave portion is dug down, and the base material in the surrounding region is dug down to form a new bottom surface of the concave portion on the surface side of the base material. Thereby, the multistage recessed part which has the level | step difference of a depth direction between the bottom faces from which depth differs can be formed.
At this time, in the present invention, a protective film is formed on the inner surface of the initial recess, and the inner surface of the initial recess is protected in the etching process. Thereby, it can prevent that a level | step difference becomes a taper shape in an etching process, or a base material remains in the shape of a protrusion at a level | step difference.
Therefore, according to the method for manufacturing a silicon structure of the present invention, it is possible to easily form a multi-step concave portion having a high aspect ratio with high processing accuracy.

The method for manufacturing a silicon structure according to the present invention is characterized in that the protective film forming step forms the protective film made of silicon oxide by oxidizing the inner surface of the initial recess.
Further, the protective film forming step is performed by thermal oxidation by heating.

By manufacturing in this way, the inner surface of the initial recess formed in the previous process is oxidized and processed into a protective film, and the inner surface of the initial recess is protected in the etching process. For this reason, not only can the parameter adjustment in the manufacturing process of the recesses be facilitated, but also the protective film can be formed more uniformly than the thin film formed by conventional polymer deposition. Thereby, it can prevent that a level | step difference becomes a taper shape in an etching process, or a base material remains in the shape of a protrusion at a level | step difference.
Further, in the protective film removing step, the protective film can be selectively removed using the difference in material between silicon oxide and silicon.
Further, by forming the protective film by thermal oxidation, it is possible to easily adjust the thickness of the protective film and form a protective film having a uniform thickness on the inner surface of the recess.

  In the method for manufacturing a silicon structure according to the present invention, the protective film forming step includes removing the oxide film formed on the bottom surface after oxidizing the bottom surface and the inner side surface of the initial recess. .

  By manufacturing in this way, it becomes possible to oxidize the inner surface of the initial recessed part formed at the previous process collectively. Therefore, the protective film can be easily formed as compared with the case where the protective film is formed by partially oxidizing only the inner surface of the initial recess.

  The method for producing a silicon structure according to the present invention is characterized in that the removal of the oxide film on the bottom surface is performed by anisotropic dry etching.

  By manufacturing in this way, the protective film formed on the side surface of the initial recess can remain, and the oxide film formed on the bottom surface of the initial recess can be selectively removed.

  The method for producing a silicon structure according to the present invention is characterized in that the protective film forming step and the etching step are performed n times to form n steps in the concave portion.

  By manufacturing in this way, it is possible to form a multistage recess having n steps in the recess.

  The method for manufacturing a silicon structure according to the present invention is characterized in that the method further includes a recess oxidation step for oxidizing the inner surface of the initial recess before the protective film removal step.

By manufacturing in this way, even when the inner side surface and bottom surface of the initial recess are in a rough state by the protective film removing step, the rough portion is oxidized and the roughened portion in the protective film removing step The part can be removed.
Therefore, the entire inner surface of the recess can be smoothed, and a recess having a step inside can be formed with high processing accuracy.

In the method for producing a silicon structure according to the present invention, the etching step is performed by dry etching.
The method for producing a silicon structure according to the present invention is characterized in that the protective film removing step is performed by wet etching.

By manufacturing in this way, the substrate can be selectively etched in the depth direction by dry etching.
Further, the protective film can be selectively removed by wet etching.

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

By manufacturing in this way, the base material on the bottom surface of the circumferential region and the initial recess can be etched in a state where the region other than the circumferential region and the bottom surface of the initial recess 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. In addition, by using a hard mask made of silicon oxide, when the protective film is formed of silicon oxide, the hard mask can be removed together with the protective film 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.
In addition, the step of partially removing the hard mask is performed together with the protective film forming 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 protective film forming step, the manufacturing process can be simplified and the productivity can be improved. In particular, when the inner surface and the bottom surface of the recess are collectively oxidized in the protective film forming step and the oxide film is formed on the bottom surface, the removal of the oxide film and the partial removal of the hard mask are collectively performed. Can be done. Thereby, the number of processes can be reduced and 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.
1 (a) to 1 (h) and FIGS. 2 (a) to 2 (e) are cross-sectional views showing a manufacturing process of the silicon structure of the present embodiment.

(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. 1 (c), the photoresist 3 is exposed and developed and patterned to correspond to a formation region 4A (recess formation region) of a multi-step recess 4 (see FIG. 2 (e)) described later. An opening 31 is formed in the region to be processed.

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 the difference between the depths D1 and D2 between the bottom surface 41b (see FIG. 2 (e)) of the first stage of the base material 1 of the recess 4 described later and the bottom surface 42b of the deepest part. The film thickness is reduced to the corresponding film thickness T1. As an etchant (etching gas) for dry etching, for example, a CF-based gas can be used.
Thereby, the formation area 4A of the recess 4 is defined. Here, the film thickness T1 is adjusted in consideration of the film thickness to be thinned by a 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. 1 (f), the photoresist 3 is patterned to correspond to the planar shape of the bottom surface 42 b of the deepest part of the multi-step concave portion 4 (see FIG. 2 (e)), thereby opening the openings 32. Form.
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. Thereby, the area | region formed in film thickness T1 is prescribed | regulated as the surrounding area | region 4R adjacent to the initial recessed part 4a (refer Fig.2 (a)) formed in the below-mentioned initial recessed part formation process.

Next, as shown in FIG. 1H, the photoresist 3 is removed.
Thus, the hard mask 2 having the opening 22 corresponding to the shape of the deepest portion of the recess 4 is formed in the formation region 4A of the recess 4 on the surface 1a of the substrate 1. Further, the multistage hard mask 2 having a film thickness T1 corresponding to the difference between the opening 22 corresponding to the planar shape of the bottom surface 42b at the deepest part of the recess 4 and the depths D1 and D2 of the bottom surface 41b and the bottom surface 42b is provided. It is formed. Further, the hard mask 2 defines the formation region 4A of the recess 4 and the circulation region 4R.

(Initial recess formation process)
Next, as shown in FIG. 2A, the base material 1 is etched through the opening 22 of the hard mask 2 to form an initial concave portion 4 a that is a part of the concave portion 4 in the base material 1. Here, for example, the initial recess 4a is formed by anisotropic dry etching by an etching step using fluorine gas such as SF6 and oxygen and a polymer deposition step using C4F8 gas. At this time, depending on the dry etching conditions, the hard mask 2 may also be etched and the film thicknesses T and T1 may be slightly reduced.
Here, the film thickness T1 of the hard mask 2 takes into account the relationship with the film thickness t of the oxide film 5b (see FIG. 2B) formed on the bottom surface 42b of the initial recess 4a in the protective film forming process described later. Thus, for example, adjustment is made so that the difference from the film thickness t does not become too large.

(Protective film formation process)
Next, as shown in FIG. 2B, the protective film 5a and the oxide film 5b are formed by oxidizing the inner surface including the inner side surface 42a and the bottom surface 42b of the initial recess 4a. The oxidation of the inner surface of the initial recess 4a can be performed by, for example, thermal oxidation in which the inner surface of the initial recess 4a is heated to be oxidized. The film thickness t of the protective film 5a and the oxide film 5b can be controlled by adjusting the temperature in the thermal oxidation, the heating time, and the like.

Next, as shown in FIG. 2C, the oxide film 5b formed on the bottom surface 42b of the initial recess 4a is removed. At this time, the hard mask 2 on the surface 1a of the substrate 1 is also etched at a time, thereby reducing the film thicknesses T and T1 of the hard mask 2 and removing the thin film portion thinned to the film thickness T1. Such removal of the oxide film 5b on the bottom surface 42b and removal of the thin film portion of the hard mask 2 can be performed by, for example, anisotropic dry etching.
As described above, the inner surface (the inner side surface 42a and the bottom surface 42b) of the initial recess 4a is oxidized (processed), and the protective film 5a is formed on the inner side surface 42a. Further, the bottom surface 42b of the initial recess 4a and the surface 1a of the base material 1 in the formation region 4A of the recess 4 are exposed from the oxide film 5b and the hard mask 2, respectively.

(Etching process)
Next, as shown in FIG. 2D, the exposed bottom surface 42b of the initial recess 4a and the surrounding region 4R adjacent to the initial recess 4a are left in a state in which the protective film 5a formed in the above process is left. The surface 1a of the substrate 1 is etched by the anisotropic dry etching described above. And the new bottom face 41b from which the depth D1 from the surface 1a differs from the depth D2 of the bottom face 42b is formed. Here, the substrate 1 is etched by anisotropic dry etching through the hard mask 2.
Note that the above-described etching is performed so that the position of the bottom surface 41b in the depth D1 direction substantially coincides with the end of the protective film 5a (the end on the deepest side of the initial recess 4a).

(Protective film removal process)
Next, as shown in FIG. 2E, the protective film 5a left in the above-described process and the hard mask 2 on the surface 1a of the substrate 1 are removed in a lump. Thereby, the overall shape of the recess 4 is formed, and a step 41g in the depths D1 and D2 direction is formed between the bottom surfaces 41b and 42b having different depths inside the recess 4. Here, the protective film 5a and the hard mask 2 are removed by wet etching using an etchant.
Through the above steps, the multi-step recess 4 having a step 41g between the bottom surfaces 41b and 42b having different depths D1 and D2 from the surface 1a of the base 1 is formed in the formation region 4A of the recess 4 of the base 1. Is done.

Next, the operation of this embodiment will be described.
In the manufacturing method of the present embodiment, an initial concave portion 4a that is a part of the concave portion 4 is formed on the substrate 1 as shown in FIG. 2A, and the bottom surface of the initial concave portion 4a as shown in FIG. 42b is dug down, and the base material 1 in the surrounding region 4R adjacent to the initial concave portion 4a is dug down to a new bottom surface 41b at a depth D1 (surface side of the base material) shallower than the depth D2 of the bottom surface 42b. Is formed.

  At this time, as shown in FIG. 2C, the protective film 5a made of silicon oxide is formed by oxidizing the inner side surface 42a of the initial recess 4a. Therefore, the film thickness t of the protective film 5a can be formed more uniformly than the film thickness of the conventional polymer. Further, the protective film 5a can prevent the inner side surface 42a from being etched in the lateral direction (direction perpendicular to the depths D1 and D2 directions).

  Further, when the bottom surface 42b is dug down, the range in the depth D2 direction in which the polymer on the inner surface 42a is deposited becomes narrow. Therefore, it is easier to adjust parameters in the polymer deposition step of anisotropic dry etching than in the past.

Here, FIGS. 4A to 4B and FIGS. 5A to 5C are cross-sectional views for explaining the problems of the conventional manufacturing method. 4A is a schematic cross-sectional view of a recess 40 formed by a conventional manufacturing method, and FIG. 4B is an enlarged view of a portion B in FIG. 4A.
As shown in FIG. 4A and FIG. 4B, in the conventional manufacturing method, unevenness is formed in the vicinity of the step G on the inner surface 402a of the recess 40, and due to the influence of the protrusion 402c on the inner surface 402a, The polymer deposition on the inner surface 402a may be inhibited. 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, The range in the depth direction in which the polymer is deposited at the deepest portion is increased. 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 a result, when the film 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, etching proceeds in the lateral direction (direction perpendicular to the depth direction), and FIG. The corner C of the step G of the recess 40 is etched as shown in FIG. And 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 film thickness of the inner surface 402a of the concave portion 40 is too thick, the shadowed portion of the convex portion 402c is an anisotropic dry etching etching step as shown in FIG. May remain. In such a case, as shown in FIG. 5B, the base material 10 remains in a protruding shape at the step G of the recess 40.

  Further, as shown in FIG. 5C, when the bottom surface 402b of the deepest portion of the recess 40 is roughened by etching, the corner Cb (bottom surface 402b) of the deepest portion of the recess 40 is deposited in the thin film deposition step. In the vicinity of the boundary between the inner surface 402a and the inner surface 402a, the polymer is not uniformly deposited, and the inner surface 402a at the deepest portion of the recess 40 is also roughened by etching.

Here, FIG. 3 is a cross-sectional view schematically showing the manufacturing process of the present embodiment, where (a) shows an initial recess forming process, (b) shows a protective film forming process, and (c) shows an etching process. Show.
In the present embodiment, as shown in FIG. 3 (a), the initial recess 4a is formed in the substrate 1 in the initial recess forming step, and as shown in FIG. 3 (b), the inner surface (inner surface) of the initial recess 4a. 42a and bottom surface 42b) are oxidized (processed) to form a protective film 5a made of silicon oxide.

Therefore, the film thickness t of the protective film 5a can be formed more uniformly than the film thickness of the conventional polymer. Further, as shown in FIG. 3C, the bottom surface 42b of the initial recess 4a and the surface 1a of the substrate 1 in the surrounding region 4R are deep with the protective film 5a remaining on the inner surface 42a of the initial recess 4a. By etching in the directions D1 and D2, the deep portion and the shallow portion of the recess 4 can be separated and etched. Furthermore, the protective film 5a can prevent the inner side surface 42a from being etched in the lateral direction (direction perpendicular to the depths D1 and D2).
Thereby, as shown in FIG.2 (e), it can prevent that the inner surface 42a of the deep part of the recessed part 4 becomes taper shape. Further, as shown in FIG. 2E, by removing the protective film 5a remaining in the protruding shape in the protective film removing step, it is possible to prevent the base material 1 from remaining in the protruding shape on the step 41g.

Therefore, according to the method for manufacturing the silicon structure of the present embodiment, the multi-step concave portion 4 having a high aspect ratio can be easily formed with high processing accuracy.
Also, the inner surface (inner side surface 42a, bottom surface 42b) of the initial recess 4a is collectively oxidized, so that only the inner surface 42a of the initial recess 4a is partially oxidized to form the protective film 5a. Thus, the formation of the protective film 5a can be facilitated.

Further, by oxidizing (processing) the inner side surface 42a of the initial recess 4a to form the protective film 5a made of silicon oxide, in the protective film removing step, utilizing the difference in material between silicon oxide and silicon, The protective film 5a can be selectively removed.
Further, by forming the protective film 5a by thermal oxidation, it is easy to adjust the film thickness t of the protective film 5a, and the protective film 5a having a uniform film thickness t can be formed on the inner side surface 42a of the recess 4. .

  Further, after oxidizing the inner side face 42a and the bottom face 42b of the initial recess 4a to form the protective film 5a and the oxide film 5b, the oxide film 5b is etched by anisotropic dry etching. As a result, the protective film 5a formed on the inner side surface 42a of the initial recess 4a can remain, and the oxide film 5b formed on the bottom surface 42b of the initial recess 4a can be selectively removed.

Further, in the protective film forming process, the manufacturing process is simplified and the number of processes is reduced by removing the portion of the thickness T1 of the hard mask 2 together with the oxide film 5b formed on the bottom surface 42b of the initial recess 4a. And 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.

  In addition, by performing the etching process through the hard mask 2 made of silicon oxide, when the base material 1 is etched by anisotropic dry etching, the concave portion 4 is selected depending on the selection ratio between the hard mask 2 and the base material 1. Can be etched stepwise. Therefore, it becomes possible to form the recessed part 4 in multistage shape.

  Further, by using the hard mask 2 made of silicon oxide, when the protective film 5a is formed of silicon oxide, it is possible to remove the hard mask 2 in a lump in the protective film removing step. . At this time, by performing the protective film removing step by wet etching, the protective film 5a and the hard mask 2 can be selectively removed collectively without substantially affecting the base material 1.

As described above, according to the silicon structure manufacturing method of the present embodiment, the high aspect ratio concave portion 4 having the step 41g on the inner side 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 differs from the silicon structure manufacturing method described in the first embodiment in that two or more n steps 41g, 42g, ..., 4ng 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 method for manufacturing a silicon structure according to the present embodiment, the opening corresponding to the planar shape of the bottom surface of the initial recess 4a is formed in the hard mask 2 in the hard mask forming step described in the first embodiment, and the depth is different. It is formed in a multistage shape according to the depth of each bottom surface.
That is, as shown in FIGS. 1A to 1D, the formation region 4 </ b> A of the concave portion 4 of the hard mask 2 is divided into the depth D <b> 1 of the bottom surface 41 b formed at the shallowest position and the deepest portion of the concave portion 4. The thickness is reduced to a film thickness T1 (first stage) corresponding to the difference from the depth Dx of the bottom surface 4xb. Next, after re-forming the photoresist 3 as shown in FIG. 1 (e), as shown in FIG. 1 (f), according to the planar shape of the bottom surface 42b formed at a position one step deeper than the bottom surface 41b. The photoresist 3 is opened. 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 depths D2 and Dx of the bottom surface 42b and the bottom surface 4xb of the deepest portion of the recess 4 ( (Not shown).

  By repeating this, a region corresponding to the planar shape of the bottom surface 4nb formed at a position shallower by one step than the bottom surface 4xb of the deepest portion of the recess 4 corresponds to the difference between the depths Dx and Dn of the bottom surfaces 4xb and 4nb. The film thickness is reduced to a film thickness Tn (nth stage) (not shown). Thereby, the film thickness T1, T2,..., Tn of the formation region 4A of the recess 4 of the hard mask 2 is changed to the depths D1, D2,..., Dn, Dx between the bottom surfaces 41b, 42b,. The film is formed in an n-stage multi-stage film thickness corresponding to the difference between the two.

Then, as shown in FIG. 1 (f), a photoresist 3 covering the hard mask 2 formed in a multi-stage shape is opened corresponding to the planar shape of the bottom surface 4xb formed at the beginning of the initial recess 4a. 3x is formed (not shown).
Next, as shown in FIG. 1G, an opening 2x corresponding to the planar shape of the bottom surface 4xb of the initial recess 4a that is formed first by opening the hard mask 2 is formed (not shown), and FIG. The photoresist 3 is removed as shown in FIG.
As a result, the formation region 4A of the recess 4 has the opening 2x corresponding to the planar shape of the bottom surface 4xb of the deepest part of the recess 4, and the bottom surfaces 41b, 42b, ..., 4nb, 4xb of the multistage recess 4 are formed. A hard mask 2 having n stages of multi-layered film thicknesses T1, T2,..., Tn corresponding to the difference between the depths D1, D2,.

(Initial recess formation process)
Next, as shown in FIG. 2A, the substrate 1 is formed in the same manner as in the first embodiment through the openings 2x of the hard mask 2 having n-stage multi-layered film thicknesses T1, T2,. Is etched to form an initial concave portion 4a corresponding to the shape of the deepest portion of the concave portion 4 in the substrate 1, and a bottom surface 4xb is formed (not shown).

(Protective film formation process)
Next, as shown in FIG. 2B, the protective film 5a is formed by oxidizing the inner surface including the inner surface 4xa and the bottom surface 4xb of the initial recess 4a as in the first embodiment.
Next, as shown in FIG. 2C, the oxide film 5b formed on the bottom surface 4xb of the initial recess 4a is removed as in the first embodiment, and the film thicknesses T1, T2,. And the portion formed at the film thickness Tn corresponding to the difference between the depths Dx and Dn between the bottom surface 4xb of the initial recess 4a and the bottom surface 4nb shallower by one step is removed.

(Etching process)
Next, as shown in FIG. 2D, the exposed bottom surface 4xb of the initial recess 4a and the bottom surface 4nb that is one step shallower than that are exposed with the protective film 5a remaining as in the first embodiment. Etching is performed on the base material 1 in the surrounding region 4R.
In the present embodiment, the protective film forming step and the etching step are repeated twice or more and n times in this order, so that the bottom surfaces 41b, 42b,. To form.

(Recess oxidation process)
Further, in this embodiment, after the bottom surfaces 41b, 42b,..., 4nb, 4xb of the initial recess 4a are formed in an n-stage multi-stage shape, before the protective film removal step described in the first embodiment, the initial recess 4a Oxidizes the inner surface.
That is, as shown in FIG. 2D, after the bottom surfaces 41b, 42b,..., 4nb, 4xb of the initial recess 4a are formed in a multi-stage shape having different depths D1, D2,. 4xa and bottom surfaces 41b, 42b,..., 4nb, 4xb (inner surface) of the recess 4a are oxidized to oxidize the entire inner surface of the initial recess 4a in the same manner as the protective film 5a and the oxide film 5b. A film is formed (not shown).

(Protective film removal process)
Then, as shown in FIG. 2E, as in the first embodiment, the protective film 5a left in the above-described process and the hard mask 2 on the surface 1a of the substrate 1 are removed together. At this time, the oxide film on the inner surface of the initial recess 4a formed by the above-described recess oxidation step is also removed, and the entire shape of the recess 4 is formed.
Through the above steps, bottom surfaces 41b, 42b,..., 4nb, 4xb having different depths D1, D2,..., Dn, Dx from the surface 1a of the substrate 1 are formed in the formation region 4A of the recess 4 of the substrate 1. .., 4nb, and 4xb, n-stage multi-stage recesses 4 having steps 41g, 42g,..., 4ng are formed between the bottom surfaces 41b, 42b,.

Next, the operation of this embodiment will be described.
In the present embodiment, in addition to the effects of the first embodiment described above, the protective film forming step and the etching step are performed n times as described above, so that the inside of the recess 4 can be formed in an n-stage multistage shape. it can.
Further, even if the inner surface 41a, 42a,..., 4na, 4xa and the bottom surface 41b, 42b,..., 4nb, 4xb of the initial recess 4a are roughened by the process up to the etching process, the recess is oxidized. By oxidizing the rough portion in the process and removing the rough portion in the protective film removing step, the inner surface of the recess 4 can be smoothed.

Further, when the bottom surface 41b, 42b,..., 4nb, 4xb having different depths D1, D2,..., Dn, Dx is formed by oxidizing the inner surface of the initial recess 4a by the recess oxidation step, the protective film 5a is formed. , And the depths D1, D2,..., Dn of the respective bottom surfaces 41b, 42b,..., 4nb are slightly deviated from each other by oxidizing and removing steps or protrusions caused by the deviation, The inner surface of the recess 4 can be flattened.
Therefore, the entire inner surface of the recess 4 can be smoothed, and the multistage recess 4 can be formed with high accuracy.

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.
For example, the hard mask may be formed of silicon nitride instead of silicon oxide. The protective film may also be formed of silicon nitride by nitriding the inner surface of the recess.

  Further, in the above-described embodiment, the multistage recess is formed by etching the base material using a multistage hard mask, but the hardmask is not limited to the multistage. For example, after forming the bottom surface of the deepest portion of the recess using a hard mask having a uniform film thickness and forming a protective film on the inner surface of the recess, the opening is adjusted to the shape of the bottom surface one step shallower than the bottom surface of the deepest portion You may etch the bottom face of a recessed part and the base material of the formation area of a recessed part through the mask which has a part.

Also, in the protective film forming step, when the protective film is formed on the inner surface of the recess and the bottom protective film is removed by dry etching or the like, the hard mask in the recess forming region remains on the surface of the base material In that case, the portion may be removed by wet etching or the like.
Moreover, the recessed part oxidation process demonstrated in 2nd embodiment can be performed also in 1st embodiment.
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)-(e) is sectional drawing explaining the manufacturing process of the silicon | silicone structure which concerns on 1st embodiment of this invention. (A)-(c) is sectional drawing explaining the manufacturing process of the silicon | silicone structure which concerns on 1st embodiment of this invention. (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

DESCRIPTION OF SYMBOLS 1 Base material, 4 recessed part, 4a initial recessed part, 4A formation area (recessed part formation area), 4E circulation area | region, 41a, 42a, 4na, 4xa Inner side surface (inner surface), 41b, 42b, 4nb, 4xb Bottom surface (inner surface) 41g, 42g, 4ng, step, 5a protective film, 5b oxide film

Claims (13)

An initial recess forming step for forming an initial recess that is a part of the recess in a base material made of silicon;
A protective film forming step of forming a protective film on the inner surface of the initial recess;
An etching step of anisotropically etching the base material in the circumferential region adjacent to the initial concave portion and the initial concave portion with the protective film on the inner surface remaining, and
Removing the remaining protective film to form the whole of the recess, and a protective film removing step of forming a 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 protective film forming step forms the protective film made of silicon oxide by oxidizing the inner surface of the initial recess.   3. The method of manufacturing a silicon structure according to claim 2, wherein the protective film forming step is performed by thermal oxidation by heating.   4. The silicon structure according to claim 2, wherein, in the protective film forming step, after oxidizing the bottom surface and the inner side surface of the initial recess, the oxide film formed on the bottom surface is removed. 5. Production method.   5. The method of manufacturing a silicon structure according to claim 4, wherein the oxide film on the bottom surface is removed by anisotropic dry etching.   6. The silicon structure according to claim 1, wherein the protective film formation step and the etching step are performed n times to form n steps in the inside of the recess. Body manufacturing method.   The method for manufacturing a silicon structure according to any one of claims 2 to 6, further comprising a recess oxidation step that oxidizes an inner surface of the initial recess before the protective film removal step.   The method for manufacturing a silicon structure according to claim 1, wherein the etching step is performed by dry etching.   The method for manufacturing a silicon structure according to claim 1, wherein the protective film 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.   The method of manufacturing a silicon structure according to claim 10, wherein the hard mask is made of silicon oxide.   12. The method of manufacturing a silicon structure according to claim 10, wherein the circumferential region is defined by partially removing the hard mask.   13. The method of manufacturing a silicon structure according to claim 12, wherein the step of partially removing the hard mask is performed together with the protective film forming step.

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