JP2973439B2 - Substrate etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

INDUSTRIAL APPLICATIONS Overview of the Invention Prior Art Problems to be Solved by the Invention Means for Solving the Problems Operation Example Example-1 Example-2 Example-3 Effect of the Invention FIELD OF THE INVENTION The present invention relates to a method for etching a substrate. The etching method of the present invention can be suitably used to form a wall-shaped or column-shaped portion having a small thickness by etching a substrate. For example, in the field of electronic materials, formation of a fine element such as a quantum well thin line element, Alternatively, it can be used for forming a fine portion having the above-described shape on a semiconductor substrate, or can be used for forming a small mechanical element having the above-described shape in the field of machinery.

[Summary of the Invention]

In the invention according to the present application, a layer serving as a mask is formed on a vertical side wall of a mask forming layer, and at least a part of the layer serving as a mask is left as a mask when etching a substrate. Even if it is fine, it is intended to prevent problems such as falling down or being removed, so that a side wall is formed and a layer serving as a mask is sandwiched between the side wall and a mask forming layer. Thus, the above problem has been solved.

[Conventional technology]

2. Description of the Related Art Conventionally, various techniques have been used in the field of semiconductor device manufacturing and other microfabrication fields (for example, JP-A-59-110168). Among such techniques, it is known that a substrate can be finely processed by forming a layer serving as a mask on a side surface of a mask forming layer and performing etching using the mask.

For example, in the field of semiconductor processing technology, if an oxide film on a side surface formed when a polysilicon layer is oxidized is used as a mask, fine processing of 1000 mm or less is possible. Such a prior art will be described below with reference to FIG.

In the prior art, as shown in FIG. 3 (a), an etching-resistant film (such as a SiO ₂ film) 2 on a substrate 1 such as a silicon substrate.
The polysilicon layer 3 having the side wall 31 formed thereon is oxidized by means such as thermal oxidation to form an oxide film 8 serving as a mask, which is an SiO ₂ film. Next, anisotropic etching such as RIE removes the oxide film 8 only on the upper surface of the polysilicon layer 3 by etching, leaving a mask 81 on the side wall of the polysilicon layer 3.
Thus, the structure shown in FIG. 3B is obtained. Next, the polysilicon layer 3 is removed by means such as RIE, leaving a mask 81 as shown in FIG. 3 (c). Thereby, the width of the oxide film 8 (the direction parallel to the base, the same thickness as that of FIG.
That is, a fine mask having a width in the horizontal direction in the drawing)) can be formed.

[Problems to be solved by the invention]

In the above-described conventional technique, the formed mask 81 made of SiO ₂ has a small width, and thus may be shaved during etching and fall. In particular, while the polysilicon layer 3 is being etched by RIE or the like, the right side in the figure denoted by reference numeral 81a in FIG. 3B is in contact with the polyethylene layer 3, so that the mask 81 does not have to worry about falling to the right side in the figure. . On the other hand, the left side surface in the figure (indicated by 81b in FIG. 1B) is exposed, and may fall to the left side or be etched from the left side.

The etching resistant layer 2 is indispensable to protect the substrate 1 from etching when etching the upper surface of the oxide film 8 and when etching the polysilicon layer 3. It must be removed prior to use and etching. At this time, the etching resistant film 2 is formed from SiO _{2 as in the} conventional example shown in FIG.
If 81 is also formed of SiO _{2, the} mask 81 will be etched during the etching for removing the etching resistant film 2. That is, as shown schematically in FIG. 1 (d), the portion indicated by reference numeral 82 in the figure is etched.

As described above, the technique of forming a mask using the side wall of the layer for forming a mask is effective for fine processing because a fine mask having a small width can be formed. In extreme cases, the mask may be etched and disappear in extreme cases.

The present invention solves such a problem and forms a mask on the side wall portion of the mask forming layer, thereby preventing the mask from falling down or being etched even when performing an etching process. It is another object of the present invention to provide an etching method capable of achieving a desired etching.

[Means for solving the problem]

The invention of claim 1 of the present application includes a step of forming an etching-resistant film on a substrate, and a side wall perpendicular to the etching-resistant film.
It is not always necessary to be strictly perpendicular to the surface of the base, and the case where the portion formed on the side wall is almost perpendicular to the extent that it can serve as a mask is also included. The same applies to the invention of claim 2)
Selectively forming a mask-forming layer having: a step of forming a layer serving as a mask at a desired thickness on the surface of the mask-forming layer; and forming a sidewall-forming layer over the entire surface; A step of forming a sidewall by etching back the sidewall forming layer and leaving only the side wall portion of the mask forming layer to leave the layer; and a step of forming the sidewall on the upper surface of the mask forming layer among the mask layers Removing the portion to leave only the portion of the layer serving as the mask located on the side wall portion of the mask forming layer; removing the mask forming layer and the sidewall; removing the etching resistant film on the substrate And a step of performing anisotropic etching of the substrate using the remaining portion of the layer serving as a mask as a mask.

According to a second aspect of the present invention, in the first aspect of the present invention, in the step of forming a layer serving as a mask to a desired thickness on the surface of the mask forming layer, a material having an etching rate smaller than the etching resistant film is used. To form a layer to be the mask.

(Operation)

The invention of claim 1 of the present application is directed to a mask formed by forming a layer on the entire surface of a mask forming layer having a vertical side wall and having a desired thickness on the surface of the mask and further etching back the layer. Forming sidewalls only on the sidewalls of the formation layer,
In this state, the upper surface of the mask forming layer among the layers serving as the mask is etched, and the mask forming layer and the sidewalls are further removed. Each of the above-described etchings is performed while being sandwiched between the sidewall and the mask forming layer. Therefore, it is possible to reliably prevent the mask from falling or being etched during the etching.
This is because a layer serving as a mask exists between the side wall and the mask forming layer and is sandwiched.

〔Example〕

Hereinafter, embodiments will be described with reference to the drawings. Naturally, each invention of the present application is not limited to the embodiments described below.

Embodiment 1 This embodiment embodies the invention of claim 1 of the present application, and applies the invention to the fine processing technology of a semiconductor device.

 Please refer to FIGS. 1 (a) to 1 (i).

The substrate 1 to be processed in the present embodiment is a silicon substrate.

In this embodiment, first, an oxide film (SiO ₂ film) is formed on a silicon substrate as a base 1, and this is used as an etching resistant film 2. The structure after this step is shown in FIG. The oxide film can be formed by thermal oxidation or CVD. The etching resistant film is not limited to the oxide film, and may be a silicon nitride (SiN) film which can be a nitride film (which can be formed by CVD or heating under a nitrogen atmosphere), or any other film that can serve as a protective film against etching. It is.

Next, a first polysilicon layer having vertical side walls is selectively formed on the etching resistant film 2 (here, an oxide film), and the polysilicon layer is used as a mask forming layer 3. More specifically, a polysilicon layer is formed on the etching resistant mask 1 to obtain the structure shown in FIG. 1B, and this is patterned by using a photoresist (indicated by PR in FIG. 1) 4 (FIG. 1). With the structure shown in FIG. 1C, the mask forming layer 3 having side walls (indicated by reference numeral 31 in FIG. 1C) is selectively obtained. In this embodiment, the polysilicon forming the mask forming layer 3 is doped with impurities as necessary. Thereby, the etching rate can be controlled.

Next, on the surface of the mask forming layer 3 having the side wall 31,
The layer 5 serving as a mask is formed. In this example, since the mask forming layer 3 is made of polysilicon, the surface is oxidized to form an SiO ₂ film having a desired thickness, and the layer 5 serving as a mask is formed. Surface oxidation can be achieved, for example, by thermal oxidation. In addition to surface oxidation, under conditions that a film is formed on the entire surface of the mask forming layer 3
A layer may be formed of a material to be used as a mask when etching the substrate 1 by performing CVD or the like. The layer serving as a mask is formed over the upper surface and the side wall of the mask forming layer 3, as shown in FIG. 1 (d).

Next, the side wall forming layer 6 is formed on the entire surface.
In this example, a second polysilicon layer is formed on the entire surface to form a first polysilicon layer.
A side wall forming layer 6 as shown in FIG. The sidewall forming layer 6 is formed with a thickness suitable for forming a sidewall by etch back. This polysilicon layer is also doped as necessary. As a result, the etching rate can be controlled, and in particular, the etching rate with the mask forming layer 3 made of polysilicon in this example can be matched.

Next, the second polysilicon layer serving as the sidewall forming layer 6 is etched back to leave the second polysilicon layer only on the side wall of the mask forming layer 3. As a result, the structure shown in FIG. 1 (f) in which the sidewall 61 made of polysilicon is formed on the side wall of the mask forming layer 3 is obtained.

Next, of the mask forming layer 3 (here, SiO ₂ film) formed on the surface of the mask forming layer 3, the mask forming layer 3 is formed.
Of the upper surface of the SiO ₂ film is removed, and leaving only a portion positioned on the side wall of the mask-forming layer 3 of the layer 5. At this time, the upper surface of the polysilicon layer which is the mask forming layer 3 is exposed. The mask layer existing on the side wall is also slightly etched. Thus, the structure shown in FIG. 1 (g) is obtained. In FIG. 1 (g), Si on the mask forming layer 3
In accordance with the etching of the O ₂ film, the etching resistant film on the substrate 1 is also a SiO ₂ film in this example. Therefore, this is also etched substantially equal to the SiO ₂ film thickness on the mask forming layer 3 and is slightly thinner. Become. However, when the mask forming layer 3 is polysilicon and the SiO ₂ film thereon is a thermal oxide film of polysilicon, the etching rate is generally different from that of SiO ₂ on the substrate 1 which is a silicon substrate. Therefore, the etching resistant film 2
Can be reduced to a small extent.

Next, the mask forming layer 3 made of the first polysilicon layer and the sidewall 61 made of the second polysilicon layer are used.
Is removed. Here, both may be removed by etching at the same time. In this example, since both the members 3 and 61 are made of polysilicon, simultaneous removal is convenient. At this time, the layer 5 serving as a mask
Of these, the remaining film 51 (which becomes a mask when the base 1 is etched) is sandwiched between the side wall 61 and the mask forming layer 3, so that it falls down or is etched from the side. Is prevented. The structure after this step is as shown in FIG. The sidewalls 61 and the mask forming layer 3 may be separately etched, for example, when both materials are different. In this case, the order of etching may be any order, but in order to prevent the remaining film 51 from falling down, it is preferable to remove both of them at the same time.

Next, a step of removing the etching-resistant film 2 (an oxide film in this example) on the substrate, which is the base 1, and the anisotropy of the base 1, using the remaining film 51, which is a vertical SiO ₂ film, as a mask. Perform etching. The removal of the etching resistant film 2 and the anisotropic etching of the substrate 1 may be performed continuously or in two steps (FIG. 1 (i)).

Although the present example goes through the above-described steps, the present example was specifically implemented as follows.

That is, the formation of the etching resistant film 2 (FIG. 1 (a)) on the substrate 1, which is the base, is performed by oxidizing the silicon substrate to form an oxide film having a thickness of, for example, 500.degree. And

In addition, in order to provide the mask forming layer 3, polysilicon is deposited by CVD at a thickness of, for example, 3000 ° (first example).
Figure (b).

In order to pattern the first polysilicon layer, which is the mask forming layer 3, the polysilicon was RIE using the photoresist 4 as a mask (FIG. 1 (c)).

Further, the layer 5 serving as a mask was formed by removing the resist and oxidizing polysilicon (first example).
Figure (d).

The sidewall forming layer 6 is made of, for example, polysilicon.
It was formed by CVD at a thickness of 3000 mm (FIG. 1 (e)).

The side wall 61 was formed by etching the entire surface of the layer 6 by RIE (FIG. 1 (f)).

Layer 5 (SiO 2) serving as a mask on the upper surface of mask forming layer 3
₂ ) was etched by RIE. At this time, SiO ₂ on the mask forming layer 3 and a part of the upper portion of the SiO ₂ sandwiched between the sidewall 61 and the mask forming layer 3 were etched.

The polysilicon which is the side wall 61 and the mask forming layer 3 was etched by RIE. Thereby, SiO ₂
(FIG. 1 (h)).

Then, firstly, by SiO ₂ RIE, to remove the SiO ₂ which is etching-resistant mask 2 on the substrate 1, the SiO ₂ mask 51 remaining, the silicon substrate is a substrate 1 to RIE processing,
The desired processing shape 11 was obtained.

FIG. 1 (j) shows the processed shape 11 actually obtained in this manner. In this embodiment, the width l is about 480 °,
The processed shape 11 having a fine and very good etching shape as shown in the figure was obtained.

The width of the mask 51 is determined when the layer 5 serving as a mask is formed as shown in FIG. 1D. In this embodiment, the layer 5 is obtained by oxidizing the mask forming layer 3 made of polysilicon.
It is determined by the means and degree of the oxidation. That is, the oxidation method (using dry O ₂ or using O ₂ containing water vapor,
Etc.), the oxidation temperature, the oxidation time, and the parameters such as the doping concentration of the polysilicon forming the mask forming layer 3 as shown in FIG.
Set so as to obtain a desired thickness. Thus, the width of the mask 51 can be controlled with high accuracy and high reproducibility.

In this embodiment, it is preferable to use an apparatus having high anisotropy and a high selectivity ratio to SiO ₂ for RIE of polysilicon used in each step.

Reference Example This example is provided as a reference example.

In this embodiment, the base 1 is embodied as a silicon substrate, the etching resistant film 2 is embodied as an LP-SiN film (that is, a silicon nitride film formed by low pressure CVD), and the mask forming layer 3 is embodied as polysilicon.

The steps of this embodiment are shown in FIGS. 2 (A) to 2 (G), and FIGS. 2 (A) to 2 (C) are the same as those of the embodiment 1, except that the substrate 1 LP- as etching resistant film 2
An SiN film is formed (FIG. 2A).

Next, a first polysilicon layer is selectively formed on the etching resistant film 2, and the polysilicon layer is used as a mask forming layer 3 (FIGS. 2B and 2C).

Since the above steps can be performed in the same manner as in Example 1, detailed description is omitted.

In the photoresist patterning step of FIG.
A mask forming layer 3 having a side wall 31 is provided. Thereafter, an etching resistant film 2 (FIG. 2A) is formed on the surface of the mask forming layer 3 which is a polysilicon layer, that is, on the upper surface and the side wall.
A protective film 7 having a smaller etching rate is formed. In this example, an SiO ₂ film, which is an oxide film, was formed as the protective film 7. SiO ₂ has a smaller etching rate than LP-SiN, because selectivity to the LP-SiN can take, even when etching etching resistant film (LP-SiN film) 2 of the process after, made of this SiO ₂ The amount of etching of the mask 71 can be reduced.

That is, as shown in FIG. 2 (D), after forming a protective film 7 on the surface of the mask forming layer 3, the protective film 7 on the upper surface of the mask forming layer 3 made of polysilicon is removed. The protective film 7 is left only on the side wall of the layer 3. This state is the second
It is shown in FIG. The remaining portion of the protective film is indicated by reference numeral 71.

Next, the mask forming layer 3 is removed by etching.
As a result, the structure shown in FIG. 2 (F) is obtained.

Next, using the remaining protective film 71 as a mask, the etching resistant film 2 and the base 1 are etched. Here, the protective film and the etching resistant mask have different etching rates. In the present embodiment, the remaining protective film 71 is made of SiO ₂ and the etching resistant film 2 is made of LP-SiN. Also in the etching removal of the etching resistant film 2, the etching amount of the mask 71 having a smaller etching rate can be reduced.

The etching of the etching resistant film 2 and the etching of the base 1 using the protective film 71 of the remaining side wall as a mask can be continuously performed.

As an etching gas, for example, a mixed gas of CF ₄ and O ₂ may be used.

Also in this embodiment, a good etching shape as shown in FIG. 1 (j) can be obtained.

In the above example, SiO ₂ was used as the protective film 7. However, any other material having an etching rate lower than the etching resistant film 2 can be used. For example, when a metal (Al, Ti, etc.) is used for the LP-SiN etching resistant film 2, a high metal / etching resistant selection ratio of, for example, RIE can be obtained when the etching resistant film 2 is peeled off.

As described above, in this embodiment, the material serving as the mask is made different from the material of the etching-resistant film for protecting the substrate to be etched, and the mask is not etched even by RIE or the like for removing the etching-resistant film. This makes it difficult to prevent the conventional mask from disappearing by etching or losing the function as a mask.

Embodiment 2 This embodiment embodies the invention of claim 2 of the present application, and applies the present invention to the fine processing technology of a semiconductor device, as in Embodiment 1.

That is, in this embodiment, the process is the same as that shown in FIG. 1, and LP-SiN is used as the etching resistant film 2, but the etching rate of the etching resistant film 2 and the etching rate are set as the material of the layer 5 serving as a mask. A different material, SiO ₂ (a metal may be used) was used. Thereby, the effect that the mask 51 is protected by the sidewall 61 and the effect that the mask 51 is not etched even when the etching resistant film 2 is removed due to the different etching rate are obtained.
Both are demonstrated.

According to this embodiment, a good etching shape as shown in FIG.

In Embodiments 1-2, the inventions of the present application were applied to microfabrication of a semiconductor device. However, the present invention is not limited to this. For example, the formation of a quantum well thin wire element or a silicon micromachine (a silicon actuator such as a silicon motor). About these
NIKKEI ELECTRONICS can be used to produce the August 21, 1989 issue (Nikkei McGraw-Hill).

〔The invention's effect〕

As described above, in the etching method of the present invention, even when a mask is formed on the side wall portion of the mask forming layer and the etching process is performed by this, the mask is prevented from falling down and being etched, so that the desired method is ensured. This has the effect that etching can be achieved.

[Brief description of the drawings]

1 (a) to 1 (j) show Example 1 of the present invention, and FIGS. 1 (a) to 1 (i) show workpieces in cross section in the order of steps. () Is a perspective view showing the shape after etching. 2 (A) to 2 (G) show reference examples in the order of steps. 3 (a) to 3 (d) are diagrams showing a conventional technique. DESCRIPTION OF SYMBOLS 1 ... Base (substrate), 2 ... Etching-resistant film, 3 ... Mask forming layer, 4 ... Photoresist, 5 ... Layer to be a mask, 51 ... Remaining film (mask), 6 ... ... Sidewall forming layer, 61... Sidewall, 7... Protective film, 71... Remaining protective film (mask).

Claims (2)

(57) [Claims] 1. A step of forming an etching resistant film on a substrate, a step of selectively forming a mask forming layer having a vertical side wall on the etching resistant film, and a mask on a surface of the mask forming layer. Forming a layer having a desired thickness, forming a sidewall-forming layer over the entire surface, etching back the sidewall-forming layer, and leaving the layer only on the side wall of the mask-forming layer. Forming a sidewall, and removing a portion of the layer serving as a mask located on the upper surface of the layer for forming a mask, and leaving only a portion located on a side wall portion of the layer for forming a mask among the layers serving as a mask Removing the mask-forming layer and the sidewalls; removing the etching-resistant film on the substrate; and using the remaining portion of the masking layer as a mask as an anisotropic edge of the substrate. Etching process of the substrate, characterized in that a step of performing a ring. 2. The step of forming a layer serving as a mask with a desired thickness on the surface of the mask forming layer, wherein the layer serving as a mask is formed of a material having an etching rate smaller than that of the etching resistant film. 2. The method for etching a substrate according to claim 1, wherein