JPH0396231A - Dry etching method - Google Patents

Abstract

PURPOSE:To improve a patterning accuracy without considerably complicating a device control by removing a material-to-be-etched layer not covered with a resist layer by etching while forming a thin sidewall protective film on the side of the material-to-be-etched layer covered with the resist layer, then forming other sidewall protective film and then overetching it. CONSTITUTION:When a material to be treated, formed with a resist layer 18 selectively covered with a material-to-be-etched layer 14 on a base 12 is dry etched, the layer 14 is anisotropically removed by etching until it reaches the base 12 under treating conditions that thin sidewall protective films 16, 16' of the degree capable of preventing the layer 18 from being undercut are formed on the side of the layer 14A covered with the layer 18. Then, a thick sidewall protective film made of laminated layers of the sidewall protective films 16, 16', 20 is formed under treating conditions that the films 16, 16' are covered with the other sidewall protective film 20. Thereafter, a material to be etched remaining partly on the upper surface of the base 12 is removed by etching while protecting the layer 14A covered with the layer 18 by the thick sidewall protective film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to improvements in dry etching methods such as plasma etching and ion etching.

[Summary of the Invention] This invention provides a method for dry etching a layer of a material to be etched on a base body using a resist layer as a mask, by covering a sidewall protective film thin enough to prevent undercutting under the resist layer. After forming the etched material layer on the sides of the etched material layer and removing the etched material layer not covered by the resist layer by anisotropic etching until reaching the base body, another sidewall is formed so as to cover the sidewall protective film. By performing over-etching after forming a protective film, it is possible to pattern faithfully to the resist pattern and improve the cleaning effect. [Prior art] Conventionally, in the manufacture of semiconductor devices such as LSI, Aft
, dry etchers capable of anisotropic etching, such as reactive ion etching (RIE) and microwave plasma etching equipment (bias ECR etching equipment), are widely used when patterning wiring materials such as polysilicon. .A conventional dry etching method using this type of dry etching will be explained with reference to Figs. 4 and 5. First, as shown in Fig. 4, a base layer [12 such as Si02] is coated on the surface of a semiconductor substrate 10 made of Si or the like. After forming the layer 14 of the material to be etched such as polySt, the layer 14 of the material to be etched is
A resist layer 18 is selectively formed on the surface. and,
The product to be processed thus formed is placed in a processing chamber of a dry etcher, and a dry etching process using the resist layer l8 as a mask is performed in the following first and second steps.

In the first step, as shown in FIG. 4, the resist layer is formed under processing conditions such that side wall protection 1lI16, 16° is formed on the side of the etched material layer portion 14A covered with the resist layer l8. The portion of the layer of the material to be etched that is not covered by 18 (corresponding to the broken line) is anisotropically etched away until it reaches the base film 12.

Side wall protective film 16. For example, in the case of ion etching, the formation of 16' can be carried out by adding a film-forming gas such as C or Fn type gas to the etching gas. In addition, the side wall protective film 16. The thickness of 16° is thick enough to not only prevent undercuts that may occur under the resist layer in the first step, but also prevent undercuts that may occur under the resist layer in the second step described later. do. In the first step, unnecessary reaction products often adhere to the upper surface of the base layer 1i12 and inside the dry etcher. Next, in the second step, while stopping the addition of the film-forming gas, the etched material layer portion 1 is removed as shown in FIG.
4A as side wall protective film 18. Undercoat while protecting with 16' [
The material to be etched remaining on a part of the upper surface of the base film 12 is removed by etching (so-called over-etching). In this case, the sidewall protective film 16. 16' may be left thinly. Note that the step on the upper surface of the base film 12 The reason why the material to be etched remains in some parts is that the layer of material to be etched 14 is formed to have a thickness T2 which is thicker than the thickness TI in the flat part in the step part, as shown in FIG. 'tS7 As shown in the figure, 7 during anisotropic etching
The remainder 14a equivalent to 2-TI is generated. [The invention attempts to solve i! According to the above-mentioned prior art, in the first step, a large amount of sidewall protection material is attached to the side of the etched material layer portion 14A in consideration of preventing undercuts during over-etching. As shown, the etched material layer portion 14A
The side portions of the resist pattern 14A have a forward tapered shape, and the bottom dimension W of the resist pattern 14A is larger than the resist pattern dimension Wl, resulting in so-called pattern thickening. Therefore, the fidelity of the etched shape to the resist pattern is impaired (patterning accuracy is reduced). One way to deal with these problems is to alternately introduce a film-forming gas and an etching gas into the processing chamber to protect the sidewalls. A chotting method has been proposed in which anisotropic etching is achieved by repeating a cycle of alternating formation and etching several times. but,
According to this method, the alternating introduction of the two gases is repeated, which complicates equipment control and makes it difficult to stabilize gas pressure, gas flow rate, etc. An object of the present invention is to improve patterning accuracy without complicating device control.

[A Thousand Steps to Solve the Problems] The present invention provides for storing an article to be processed in which a resist layer is formed so as to selectively cover a layer of material to be etched on a base body in a processing chamber of a dry etcher, and etching the resist layer. In a dry etching method in which a dry etching process is performed using a resist layer as a mask, the process in the process chamber is divided into first to third steps, and in the first step, the process is performed to the extent that undercutting under the resist layer can be prevented. Under processing conditions such that a thin sidewall protective film is formed on the sides of the etched material layer covered with the resist layer, the etched material layer that is not covered with the resist layer is heated until it reaches the base body. In the second step, a thick sidewall protective film consisting of a stack of these sidewall protective films is formed under processing conditions such that another sidewall protective film is deposited on the sidewall protective film. In a third step, the material to be etched remaining on a part of the upper surface of the base body is removed by etching while protecting the part of the material to be etched covered by the resist layer with the thick sidewall protective film. It is characterized by this.

[Function] According to the method of the present invention, in the first step, only the minimum amount of sidewall protection material is deposited, so that the sidewall protection material is deposited on the side of the layer of the etched material to be left as shown in FIG. Almost no tapered portions are generated, and an etched shape that is faithful to the resist pattern can be obtained. In addition, since a thick sidewall protective film is formed in the second step, sufficient over-etching can be performed in the third step without damaging the portion of the etched material layer that is to remain. Therefore, unnecessary reactive substances can be etched away not only from the upper surface of the base body but also from the walls of the processing chamber, etc., and the cleaning effect is improved.

[Example] FIGS. 1 to 3 show a dry etching method according to an embodiment of the present invention. In each figure, the same parts as in FIGS. 4 and 5 are given the same reference numerals. It has been done.

First, a base layer [! A resist layer 18 is formed so as to selectively cover the layer 14 of the material to be etched, such as at A.degree. Then, the product to be processed thus formed is placed in a processing chamber of a dry etcher, and dry etching processing using the resist layer l8 as a mask is performed in first to third steps.

In the first step, as shown in FIG. 1, the resist N18 is coated with the resist N18 under conditions such that sidewall protective films 16, 16° are formed on the sides of the etched material layer portion 14A covered with the resist layer 18. The uncovered portion of the material layer to be etched (corresponding to the broken line) is anisotropically etched away until it reaches the base film 12.

In this case, the sidewall protective films 16, 16' are formed as thin as possible to prevent undercuts occurring under the resist layer in the first step. For this purpose, when using either an RIE device or a microwave plasma etching device as a dry etcher, the polymer dissociated from the resist layer 18 during etching must be deposited on the side wall of the etched material layer portion 14A in an amount necessary to prevent undercut. All you have to do is choose conditions that will allow it to adhere. Alternatively, a small amount of film-forming gas may be added to the etching gas.

In the second step, as shown in FIG. 2, the sidewall protective film 18. A thick sidewall protection film is formed by stacking these sidewall protection films under conditions such that the sidewall protection 1ii20 is applied to the sidewall protection film 18'. For this purpose, when using an RIE apparatus, it is possible to adopt a method of (a) lowering the high frequency power and increasing the reaction gas pressure, or (b) a method of adding a film-forming gas, When using a microwave plasma etching device, (c) a method of turning off the high-frequency bias voltage, or (2) a method of adding a film-forming gas (or increasing the flow rate if it is already being added). can be adopted.

In the third step, as shown in FIG.
Over-etching is performed while protecting the upper surface of the base film 12 by etching away unnecessary reaction products on the upper surface of the base film 12, and also removes the material to be etched remaining on a part of the upper surface of the base film 12 (steps, etc.). Remove etch. In this case, the thin sidewall protective film 18. 16' may remain.

Over-etching in the third step can be performed under conditions with low anisotropy (that is, poor film formation properties and near isotropy) because a thick sidewall protective film was formed in the second step. In order to lower the anisotropy, RI
When using either the E device or the microwave plasma etching device, the conditions may be selected such that the high frequency power is set low and the number of neutral radicals serving as etchants is increased.

When over-etching is performed under conditions of low anisotropy, not only the reaction products on the upper surface of the substrate @12 but also the reaction products attached to the walls of the processing chamber can be efficiently etched away. Therefore, the inside of the processing chamber is kept clean, the reproducibility of etching characteristics is improved, and defects due to peeling off of deposits from the inner wall of the processing chamber can be avoided.

[Effects of the Invention] As described above, according to the present invention, since the sidewall protective film is thinly formed during anisotropic etching, fine patterning faithful to the resist pattern is possible, and a thick sidewall protective film can be formed. Since the over-etching is performed after the formation, the cleaning effect is improved. Therefore, a dry etching process with good yield and reproducibility can be realized.

[Brief explanation of drawings]

1 to 3 are cross-sectional views of a substrate showing a dry etching method according to an embodiment of the present invention, FIGS. 4 and 5 are cross-sectional views of a substrate showing a conventional dry etching method, and FIGS. FIG. 7 is a cross-sectional view showing the adhesion and etching of the material to be etched in the stepped portion of the base, and FIG. 8 is a cross-sectional view showing the thickening of the pattern by the conventional method. 10... Semiconductor substrate, 12-... Base film, l4...
Etched material layer, 16. 16', 20... side wall protective film, l8... resist layer.

Claims (1)

[Claims] A workpiece comprising a resist layer formed to selectively cover a layer of material to be etched on a base body is housed in a processing chamber of a dry etcher, and a dry etching process is performed using the resist layer as a mask. In the dry etching method to be carried out, the processing in the processing chamber is divided into first to third steps, and in the first step, a sidewall protective film thin enough to prevent undercutting under the resist layer is formed on the resist layer. The part of the material layer to be etched that is not covered by the resist layer is anisotropically etched away until it reaches the base body under processing conditions such that the part of the material layer to be etched is formed on the side of the part of the material layer covered by the resist layer. In the second step, a thick sidewall protective film is formed by laminating these sidewall protective films under processing conditions such that another sidewall protective film is deposited on the sidewall protective film, and in the third step, . A dry etching method, characterized in that the etched material remaining on a part of the upper surface of the base body is removed by etching while protecting the etched material layer covered by the resist layer with the thick sidewall protection film.