JPH03142829A - Etching of substrate - Google Patents

Abstract

PURPOSE:To surely execute an etching operation in such a way that a mask does not fall or is not etched by a method wherein a layer is formed additionally on the whole surface of a layer which has been formed on the surface of a layer for mask formation use having a vertical sidewall and which is used as a mask, it is etched back to form a sidewall, the surface of the layer for mask formation is etched and the layer for mask formation use and the sidewall are removed. CONSTITUTION:An oxide film is formed on a silicon substrate to form an etching- resistant film 2; a polysilicon layer having a vertical sidewall is formed selectively on it; a layer 3, for mask formation use, having a sidewall 31 is obtained. The surface of the layer is oxidized to form a layer 5 to be used as a mask; a polysilicon layer is formed on the whole surface. A layer 6 for sidewall formation is obtained. The layer is etched back; it is left only on a sidewall part; a sidewall 61 is formed. Then, an SiO2 film on the surface out of the layer 5 is removed; only a part situated at the sidewall part is left; the layer 3 for mask formation use and the sidewall 61 are removed simultaneously. Since a film 51 which is left is sandwiched from both sides, it is possible to prevent that the film falls or is etched from the side. Then, the etching- resistant film 2 is removed; a substrate 1 is etched anisotropically by using the film 51 as a mask.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

Industrial Application Field Overview of the Invention Conventional Technology Problems to be Solved by the Invention Means for Solving Problems Examples of Actions Example-1 Example-2 Example-3 Effects of the Invention [Industrial Applications] Field] The present invention relates to a method for etching a substrate. The etching method of the present invention can be suitably used for etching a substrate to form a wall-like or columnar portion with a small thickness. For example, in the field of electronic materials. It can be used to form minute elements such as quantum well thin wire devices, or to form minute parts with the above shape on semiconductor substrates, or in the mechanical field, to form minute mechanical elements with the above shape. It can be used for forming etc.

[Summary of the invention]

Each of the inventions of the present application forms a layer serving as a mask on the vertical sidewalls of a mask forming layer, and when etching a substrate using this as a mask while leaving at least a part of the layer serving as a mask, the mask is extremely This is to prevent problems such as falling or being removed even in minute cases.
The invention of claim 1 of the present application is characterized by forming a sidewall and sandwiching a layer to serve as a mask between the sidewall and the mask forming layer. The above problem is solved by forming a protective film of a material with a lower etching rate than the etching-resistant film above and etching the substrate using at least a portion of this protective film as a mask.

[Conventional technology]

Conventionally, various techniques have been used in the field of semiconductor device manufacturing and other microfabrication fields (for example, Japanese Patent Application Laid-Open No. 110168/1983). It is known that a substrate can be microfabricated by forming a mask layer on the side surface and performing etching using this mask.

For example, in the field of semiconductor processing technology, if a side oxide film formed when a polysilicon layer is oxidized is used as a mask, microfabrication of 100 Å or less is possible. Such a conventional technique will be explained below using FIG. 3.

In the prior art, as shown in FIG. 3(a), a polysilicon layer 3 is formed on an etching-resistant film (StO, film, etc.) 2 on a base 1 such as a silicon substrate so as to have side walls 31. is oxidized by means such as thermal oxidation to form an oxide film 8 which is a Si0g film and serves as a mask.

Next, for the anisotropy of RIB etc., the oxide film 8 is removed only on the upper surface of the polyethylene layer 3 by etching, leaving the mask 81 on the side wall of the polysilicon layer 3.
The structure shown in FIG. 3(b) is obtained by removing the polysilicon layer 3 by means such as zero-order RIB, and using a mask 8 as shown in FIG. 3(c).
As a result, a fine mask having the same thickness and width as the originally formed oxide film 8 (the width in the direction parallel to the substrate, that is, the width in the left-right direction in the figure) can be formed.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technique, since the formed Sing mask 81 has a narrow width, it is scraped during etching.
There is a possibility that you will fall down. In particular, polysilicon layer 3 is R
1! During etching with E, etc., the right side in the figure indicated by reference numeral 81a in FIG. The left side (81 in Figure 1(b))
b) is exposed and may fall to the left or be etched from the left.

The etching-resistant layer 2 is essential to protect the substrate 1 from etching when etching the upper surface of the oxide film 8 and when etching the polysilicon layer 3. must be removed prior to etching. At this time, if the etching-resistant film 2 is formed of SiO□ and the mask 81 is also formed of Sing as in the conventional example shown in the figure, the S mask 81 will also be etched during the etching to remove the etching-resistant film 112. As schematically shown in Figure (d), a portion 82 in the figure is etched.

As mentioned above, the technique of forming a mask using the side wall part of the mask forming layer can form a fine mask with a small width, so it is effective for fine processing, but as mentioned above, the mask may fall over. In extreme cases, the mask may be etched and disappear.

The present invention solves these problems, and even when etching is performed by forming a mask on the side wall of the mask forming layer, it prevents the mask from falling or being etched, and ensures reliable etching. The object of the present invention is to provide an etching method that can achieve desired etching.

[Means for solving problems]

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 that is perpendicular to the etching-resistant film (here, vertical does not necessarily have to be strictly perpendicular to the surface of the substrate). (The same applies to the invention of claim 2, including cases in which the portion formed on the side wall is close to perpendicular to the extent that it can be used as a mask); A step of forming a layer to serve as a mask on the surface of the mask layer to a desired thickness, a step of forming a sidewall forming layer on the entire surface, and a step of etching back the sidewall forming layer to remove the sidewall portion of the mask forming layer. A step of forming a sidewall by leaving only a core layer on the surface of the layer, and a step of forming a sidewall of the layer that will become a mask by removing a portion of the layer that will become a mask located on the upper surface of the layer for mask formation. A step of removing the mask forming layer and the sidewall, a step of removing the etching-resistant film on the substrate, and a step of leaving only the portion located in the mask layer as a mask. The method is characterized by comprising a step of performing anisotropic etching of the substrate.

The invention according to claim 2 of the present application comprises: a step of forming an etching-resistant film on a substrate; a step of selectively forming a mask-forming layer having vertical sidewalls on the etching-resistant film; forming a protective film having a lower etching rate than the etching-resistant film on the surface of the layer to a desired thickness; and removing a portion of the protective film located on the upper surface of the mask forming layer to form a side wall portion of the mask forming layer. a step of removing the mask-forming layer; and a step of performing anisotropic etching of the etching-resistant film and the substrate using the remaining portion of the protective film as a mask. This is a characteristic feature.

[For production]

The invention of claim 1 of the present application further forms a layer over the entire surface of the mask layer formed to a desired thickness on the surface of the mask forming layer having vertical sidewalls and etch back the layer. A sidewall is formed only on the sidewall portion of the mask forming layer, and in this state, the upper surface of the mask forming layer among the layers to be a mask is etched, and then the mask forming layer and the sidewall are removed. The above-mentioned etching is performed on the layer serving as a mask located on the sidewall portion of the mask-forming layer while being sandwiched between the sidewall and the mask-forming layer. Therefore, the mask is reliably prevented from falling over or being etched during etching. This is because a layer serving as a mask exists between the sidewall and the mask-forming layer, and the layer is sandwiched between the sidewall and the mask-forming layer.

According to the second aspect of the present invention, a protective film is formed on the surface of the mask forming layer having vertical sidewalls to a desired thickness using a material with a low etching rate, such as an etching-resistant layer, and Since the portion of the mask-forming layer located on the side wall portion is used as a mask, even when the etching-resistant layer is removed by etching, the etching rate is different, so that removal by this etching is reliably prevented.

〔Example〕

Examples will be described below with reference to the drawings.

As a matter of course, each invention of the present application is not limited to the examples described below.

Example 1 This example embodies the invention of claim 1 of the present application, and applies the invention to microfabrication technology for semiconductor devices.

Refer to FIGS. 1(a) to (i).

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

In this embodiment, an oxide film (Si0g film) is first formed on a silicon substrate, which is a base 1, and this is used as an etching-resistant film 2. The structure after this step is shown in Figure 1(a).
The oxide film can be formed by thermal oxidation or CDV.

The etching-resistant film is not limited to an oxide film, but may also be a nitride film, silicon nitride (SiN) II (which can be formed by CDV or heating in 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 sidewalls is selectively formed on the etching-resistant film 2 (here, an oxide film), and this polysilicon layer is used as a mask forming layer 3. Specifically, a polysilicon layer is formed on the etching-resistant mask 1 to form the structure shown in FIG. 1(b), and this is coated with photoresist (
4 (indicated by PR in the figure) to form the structure shown in FIG. In this embodiment, the polysilicon constituting the mask forming layer 3 is doped with impurities as necessary. This allows the etching rate to be controlled.

Next, on the surface of the mask forming layer 3 having the side wall 31,
A layer 5 to serve as a mask is formed. In this example, since the mask forming layer 3 is made of polysilicon, this is surface oxidized to form a desired thickness of 5108M. For example, in addition to zero surface oxidation that can be achieved through thermal oxidation, CVO etc. are performed under conditions such that a film is formed on the entire surface of the mask forming layer 3, and a layer is formed using the material that will become a mask when etching the substrate 1. You may do so.

The layer serving as a mask is formed to cover the top surface and sidewalls of the mask forming layer 3, as shown in FIG. 1(d).

Next, in this example where the sidewall forming layer 6 is formed over the entire surface, a second polysilicon layer is formed over the entire surface to obtain the sidewall forming layer 6 as shown in FIG. 1(e). The sidewall forming layer 6 is formed to have a thickness suitable for forming a sidewall by etchback. This polysilicon layer is also doped if necessary, so that the etching rate can be controlled, and in particular, the etching rate can be made to match that of the mask forming layer 3, which is made of polysilicon in this example.

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

Next, the Si0g film on the upper surface of the mask forming layer 3 is removed from the layer 5 (Si0g film in this case) that is formed on the surface of the mask forming layer 3 to form a mask. Only the portions located on the sidewalls of the mask forming layer 3 are left, and at this time the upper surface of the polysilicon layer, which is the mask forming layer 3, is exposed. The mask layer present on the sidewalls is also slightly etched. This results in the structure shown in FIG. 1(g). In FIG. 1(g), the mask forming layer 3
As the upper 5iot film was etched, the substrate 1
The upper etching-resistant film is also a Sin film in this example, so
This layer is also etched to a remarkable extent and becomes slightly thinner than the Si0g film on the mask forming layer 3. However, mask forming layer 3
is polysilicon, and the Stow film thereon is a thermally oxidized film of polysilicon, since this generally has a different etching rate from the Sing on the base 1, which is a silicon substrate, the etching-resistant film 2 is The degree to which this occurs can be reduced.

Next, a mask forming layer 3 made of a first polysilicon layer is formed.
and a side wall 61 made of a second polysilicon layer.
remove. In this example, since both 3 and 61 are made of polysilicon, simultaneous removal is convenient. At this time, the remaining film 51 of the layer 5 serving as a mask (this serves as a mask when etching the substrate 1) is sandwiched between the sidewall 61 and the mask forming layer 3, so it falls down. This prevents the surface from being etched or etched from the sides. The structure after this step is as shown in FIG. 1(h). The sidewall 61 and the mask forming layer 3 may be etched separately if they are made of different materials. In this case, the order of etching may be in any order, but the remaining film 51 may collapse, etc. In order to prevent this, it is preferable to remove both at the same time.

Next, there is a step of removing the etching-resistant film 2 (an oxide film in this example) on the substrate 1, and an anisotropic etching of the substrate 1 using the layered film 51, which is a vertical 5iOt film, as a mask. The removal of the etching-resistant film 2 and the anisotropic etching of the substrate 1 may be performed continuously or in two steps ('! t tl (i-n)).

This example goes through each of the above steps, but in this example, in particular,
The specific implementation was as follows.

That is, an etching-resistant film 2 (Fig. 1 (
A)) was formed by oxidizing a silicon substrate E, forming an oxide film with a thickness of, for example, 500 mm, and using this as the etching-resistant film 2.

Further, in order to provide the mask forming layer 3, polysilicon was CVDed to a thickness of, for example, 3000 nm (
Figure 1(b)).

To pattern the first polysilicon layer, which is the mask forming layer 3, the polysilicon was subjected to RIH using the photoresist 4 as a mask (see Fig. 1(c).
)).

Furthermore, the formation of the layer 5 serving as a mask involves removing the resist,
It was formed by oxidizing polysilicon (Fig. 1 (
d)).

The sidewall forming layer 6 is made of polysilicon, for example, 3
It was formed by CVD L with a thickness of 0.000 mm (Fig. 1(e)).
.

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

Layer 5 (SiO□
The film was etched by RIE. At this time, SiO1 on the mask forming layer 3 and the portion sandwiched between the side wall 61 and the mask forming layer 3! The upper part was slightly etched.

The sidewalls 61 and the polysilicon forming the mask forming layer 3 were etched by RIB. This results in 5
An IoT mask 51 was formed (FIG. 1(h)).

Next, first, SiO□, which is the etching-resistant mask 2, on the substrate 1 is removed by Sing's RIIE, and the silicon substrate, which is the substrate 1, is subjected to RIB processing using the remaining SiO2 mask 51 to form a desired processed shape 11. Obtained.

The processed shape 11 actually obtained in this way is shown in Figure 1 (
In this embodiment shown in j), the width l is approximately 480 people,
As shown in the figure, a finely etched pattern 11 having an extremely good etching shape was obtained.

The width of the mask 51 is determined at the time of forming the layer 5 which becomes the mask shown in FIG.
It depends on the means and degree of oxidation. In other words, the oxidation method (dry (using h or 0□ containing water vapor, etc.), oxidation temperature, oxidation time, and the polysilicon that constitutes the mask forming layer 3 in FIG. 1(b) is necessary. The width of the mask 51 is determined by parameters such as the doping concentration and the like, so it is set so as to obtain the desired thickness.Thereby, the width of the mask 51 can be controlled with high accuracy and good reproducibility.

Note that in this embodiment, it is preferable to use a device with high anisotropy and a high selectivity to Sing for the polysilicon RIB used in each step.

Example 2 This example embodies the invention of claim 2 of the present application, and similarly to Example 1, the invention is applied to microfabrication technology for semiconductor devices.

In this embodiment as well, the base 1 is a silicon substrate, the etching-resistant mask 2 is a SiO□ film, and the mask forming layer 3 is polysilicon.

The steps of this example are shown in FIGS. 2(A) to 2(G).
Figures (A) to (C) are the same as in Example-1. That is, an oxide film (Sift film) is formed as the etching-resistant film 2 on the substrate 1 (FIG. 2(A)).

Next, a first polysilicon layer is selectively formed on the etching-resistant film 2, and this polysilicon layer is used as a mask forming layer 3 (FIGS. 2B and 2C) - as described above. Since the steps can be the same as those in Example-1, detailed explanation will be omitted.

In the photoresist patterning step of FIG. 2(C), the mask forming layer 3 having the sidewalls 31 is provided, but after that, the surface of the mask forming layer 3 which is a polysilicon layer, that is, the top surface and sidewalls, is etched with anti-etching. Membrane 2 (Figure 2 (A))
A protective film 7 with a smaller etching rate is formed. In this example, the protective film 7 is formed of LP-SiN, that is, silicon nitride formed by low pressure CvD. LP
Since -3iN has a selectivity with respect to Sin, the amount of etching of the mask 71 made of LP-3iN can be reduced when etching the etching-resistant film (SiO2 film) 2 in a later step.

That is, after forming the protective film 7 on the surface of the mask forming layer 3 as shown in FIG. This state in which the protective film 7 is left only on the side walls of the protective layer 3 is shown in FIG.

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

Next, using the remaining protective film 71 as a mask, the etching resistor y42 and the substrate l are etched.

Here, the protective film and the etching-resistant mask have different etching rates, and in this embodiment, the mask 71, which is the remaining protective film, is made of LP-SiN, and the etching-resistant film 2 is made of SiO□. Also, when removing the etching-resistant film 2 by etching, the amount of etching for the mask 71 having a lower etching rate can be made smaller.

Etching of the etching-resistant film 2 and etching of the substrate 1 using the remaining side wall portion of the protective film 71 as a mask can be performed continuously.

As the etching gas, for example, a mixed gas of CF4 and 0□ may be used.

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

In the above example, LP-5iN was used as the protective film 7, but any other material having an etching rate lower than that of the etching-resistant film 2 can be used. For example, if a metal (A1, Ti, etc.) is used for the etching-resistant film 2 of SiO□, a high metal/etching-resistant film selectivity can be obtained during peeling of the etching-resistant film 2, for example, by RIE.

As described above, in this embodiment, the material that serves as the mask and the material of the etching-resistant film that protects the substrate to be etched are made different to prevent the mask from being etched even by RIB or the like that removes the etching-resistant film. This makes it possible to prevent a conventional mask from disappearing due to etching or losing its function as a mask.

Example-3 In this example, a technique that combines the above-mentioned Example-1 and Example-2 was implemented. That is, the process is the same as that shown in FIG. 1, and S+0□ is used as the etching-resistant film 2, but LP-3iN, which has an etching rate different from that of the etching-resistant film 2, is used as the material for the layer 5 that becomes a mask.
(metal may also be used). This provides both 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 rates.

In this example, as in Examples 1 and 2, a good etched shape as shown in FIG. 1(j) can be obtained.

In Examples 1 to 3 above, the inventions of the present application were applied to microfabrication of semiconductor devices, but the present invention is not limited to this, and is not limited to the formation of quantum well thin wire elements, silicon micro-machines (silicon actuators such as silicon motors, silicon actuators such as silicon motors, These can be used in the production of NIKKHI I!LtICTRONIC 3, August 21, 1989 issue (Nikkei McGrow Cell).

(Effects of the Invention) As described above, the etching method of the present invention prevents the mask from falling or being etched even when etching is performed by forming a mask on the side wall of the mask forming layer. This has the effect of reliably achieving the desired etching.

[Brief explanation of the drawing]

1 (a) to (j) show Example-1 of the present invention, (a) to (i) in the same figure are cross-sectional views of the workpiece in the order of steps, and (j) ) is a perspective view showing the shape after etching. FIGS. 2(A) to 2(G) show Example 2 of the present invention in the order of steps. Figure 3(a)-(
d) is a diagram showing the prior art. 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). Skilled sumo wrestler = 4 Dally Toko・11) Etchitsuta "way λte 9 l Figure 51 Hiko J East M (? Suge) (v'; ay Lee-1's etching" way λfu 82.1, conventional attack 3rd Figure 2. Etching method of the name of the invention 3゜Relationship with the case of the person making the amendment

Claims (1)

[Claims] 1. A step of forming an etching-resistant film on a substrate; a step of selectively forming a mask-forming layer having vertical sidewalls on the etching-resistant film; A step of forming a layer to serve as a mask on the surface to a desired thickness, a step of forming a layer for forming a sidewall over the entire surface, and a step of etching back the layer for forming a sidewall so that only the sidewalls of the layer for mask formation are covered. A step of forming a sidewall by leaving a layer, and removing a portion of the layer that will become a mask located on the upper surface of the mask forming layer and a portion of the layer that will become a mask that is located on the side wall of the mask forming layer. a step of removing the mask forming layer and the sidewalls, a step of removing the etching-resistant film on the substrate, and an anisotropy of the substrate using the remaining portion of the mask layer as a mask. 1. A method for etching a substrate, the method comprising the step of performing chemical etching. 2. Forming an etching-resistant film on the substrate; selectively forming a mask-forming layer having vertical sidewalls on the etching-resistant film; and forming the etching-resistant film on the surface of the mask-forming layer. A step of forming a protective film with a lower etching rate to a desired thickness, and a step of removing the portion of the protective film located on the upper surface of the mask forming layer, leaving only the portion located on the side wall of the mask forming layer. A method for etching a substrate, comprising: removing the mask-forming layer; and performing anisotropic etching of the etching-resistant film and the substrate using the remaining portion of the protective film as a mask.