JP2003264229A - Method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a semiconductor device which can form a contact hole at a high aspect ratio while securing the etching selection ratio of an insulating film to a resist. <P>SOLUTION: This manufacturing method for a semiconductor device has; a process of investigating an etching speed at the time of performing dry etching for a silicon oxide based insulating film using etching gas including at least two kinds of fluorocarbon (CF) based gases under a plurality of conditions different in mixture ratios of CF gas and equal in ion energy; a process of obtaining a optimum mixture ratio where the C/F ratio in etching gas becomes maximum within a range where the etching speed does not become a negative value; and a process of forming a resist on the insulating film and performing dry etching with specified ion energy for the insulating film, using the etching gas including CF-based gas at the optimum mixture ratio. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device having a contact hole having a high aspect ratio.

[0002]

2. Description of the Related Art In recent years, in the development of ULSI devices, specifications have been studied in consideration of realization of high speed and low power consumption. In particular, in a multilayer wiring structure of a logic device, a copper wiring and a low dielectric constant film have come to be used in order to realize low resistance of the wiring and low dielectric constant of the interlayer insulating film.

Along with this, the demand for conventional miniaturization has become more and more strict in the field of process development. In order to cope with the miniaturization of devices, development of photolithography using light of shorter wavelength, which uses an ArF laser, an F ₂ laser, or the like as a light source, is also underway.

In these lithography methods, the influence of absorption of light by the resist is reduced, so that it is generally unavoidable to make the resist thin. When etching is performed using a thinned resist as a mask, if the etching selection ratio of the base to the resist cannot be sufficiently secured, the resist disappears before the etching is completed, and a pattern cannot be formed.

Therefore, in photolithography using light of a shorter wavelength, a process capable of processing the underlayer with respect to the resist with a high selection ratio is particularly important. When processing a contact hole having a high aspect ratio in an interlayer insulating film, an etching gas containing a fluorocarbon gas (CF gas) such as C ₄ F ₈ or C ₅ F ₈ is generally used in many cases. In an etching gas containing a fluorocarbon-based gas, the ratio of the total amount of carbon and the total amount of fluorine (C
When the / F ratio) is relatively high, the etching selection ratio of the interlayer insulating film to the resist can be increased.

In actual dry etching, etching and deposition occur in competition with each other, and the etching rate or deposition rate changes depending on the C / F ratio. In general, the higher the C / F ratio of the fluorocarbon radical, that is, the richer the C is, the more likely the deposition is to occur.

[0007]

If the C / F ratio of the etching gas is increased for the purpose of increasing the etching selectivity of the interlayer insulating film with respect to the resist, excessive deposition will occur.
As a result, particularly in a fine contact hole having a high aspect ratio, the hole is filled with the deposit and the etching does not proceed (etch stop).

As described above, the etching selectivity and the hole workability (removability) have a trade-off relationship. As described above, as the device generation advances, the demands on the etching selectivity become more stringent, and a process capable of satisfying both the etching selectivity and the hole workability is desired.

The present invention has been made in view of the above problems, and therefore, the present invention is directed to the manufacture of a semiconductor device capable of forming a contact hole having a high aspect ratio while ensuring an etching selection ratio of an insulating film to a resist. The purpose is to provide a method.

[0010]

In order to achieve the above object, a method of manufacturing a semiconductor device according to the present invention uses an etching gas containing at least two fluorocarbon type gases and an insulating film mainly made of silicon oxide. A step of examining the etching rate when performing dry etching on a plurality of conditions in which the mixing ratio of the fluorocarbon-based gas is different and the energies of the ions incident on the insulating film are equal,
A step of obtaining an optimum mixing ratio that maximizes the ratio of the amount of carbon to the amount of fluorine in the etching gas within a range in which the etching rate does not have a negative value, and a step of forming a resist in a predetermined pattern on the insulating film. And a step of performing dry etching by using the etching gas containing the fluorocarbon-based gas in the optimum mixing ratio and using the resist as a mask to cause ions to enter the insulating film with the energy. .

Preferably, the insulating film is a laminated film composed of a plurality of layers having different compositions, and has a step of obtaining the optimum mixing ratio in each layer, and etching the fluorocarbon-based gas at the optimum mixing ratio. In the step of dry etching the insulating film using gas, the mixing ratio of the fluorocarbon-based gas in each layer is set to the optimum mixing ratio.

[0012] Alternatively, in order to achieve the above object, the semiconductor device manufacturing method according to the present invention is a first method for dry etching a silicon oxide film using an etching gas containing at least two fluorocarbon-based gases. In a plurality of conditions in which the mixing ratio of the fluorocarbon-based gas is different and the energies of the ions incident on the silicon oxide film are equal, and in a range in which the first etching rate does not have a negative value. A step of obtaining a first optimum mixing ratio that maximizes the ratio of the amount of carbon to the amount of fluorine in the etching gas; and F using an etching gas containing at least two fluorocarbon-based gases,
A second etching rate when performing dry etching on the SG film under a plurality of conditions in which the mixing ratio of the fluorocarbon-based gas is different and the ions are incident on the FSG film with the energy; A second optimum mixing ratio that is a mixing ratio that maximizes the ratio of the amount of carbon to the amount of fluorine in the etching gas and is larger than the first optimum mixing ratio within a range in which the etching rate of N is not a negative value. And the silicon oxide film and the F
A step of forming a laminated film containing an SG film, a step of forming a resist on the laminated film in a predetermined pattern; and a step of forming the resist using the etching gas containing the fluorocarbon-based gas in the second optimum mixing ratio. Using as a mask a step of performing dry etching by making ions enter the FSG film with the energy, and using an etching gas containing the fluorocarbon-based gas in the first optimum mixing ratio,
Dry etching is performed by making ions enter the silicon oxide film with the energy using the resist as a mask.

As a result, when performing dry etching on the insulating film mainly made of a silicon oxide film, the etching selection ratio of the insulating film to the resist can be secured, and excessive deposition of reaction products can be suppressed. Therefore, when the contact hole is formed in the insulating film by dry etching, the etch stop due to the deposit does not occur in the contact hole, and the contact hole having a high aspect ratio can be formed.

In the present invention, when etching a silicon oxide film containing fluorine, the ratio of the amount of carbon to the amount of fluorine in the etching gas is higher than that in the case of etching a silicon oxide film containing no fluorine. To increase. According to the present invention, the mixing ratio of the fluorocarbon-based gas can be optimized according to the composition of the layer to be etched, and the contact hole with a high aspect ratio can be formed.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a method for manufacturing a semiconductor device of the present invention will be described below with reference to the drawings. (Embodiment 1) This embodiment shows an example in which a contact hole is formed by dry etching an interlayer insulating film made of a single-layer silicon oxide film using a resist as a mask.

When dry etching is performed on the interlayer insulating film to process the contact hole, an active species flux made of an etching gas as a raw material is incident on the processed surface. C in the activated species flux becomes a volatile product mainly by the following first and second reactions, and is removed from the processed surface. If the removal of C does not proceed sufficiently on the processed surface, excessive deposition occurs, and the etching reaction stops (etch stop) especially in the contact hole having a high aspect ratio.

First, C in the activated species flux is removed
Is a thermal reaction between C and oxygen (O) or nitrogen (N). As the first reaction, for example, the following formula (1)
The reaction represented by C + O → CO ・ ・ ・ (1)

The first reaction is a reaction that proceeds without ion assist. Therefore, the energy of ion irradiation does not affect the reaction, but the reaction rate changes depending on the concentration of O or N. Here, the O radicals or N radicals that react with C include not only those generated from the etching gas but also those generated from the film to be processed by etching.

The second reaction is a reaction between C and F under the donation of energy by ion irradiation. The second reaction is
For example, a reaction represented by the following formula (2) can be mentioned. C + F + [ion energy] → CF ₂ (2) The second reaction is an ion assist reaction, and the reaction rate changes depending on the ion energy and the C / F ratio in the activated species flux.

When the C / F ratio of the etching gas is increased for the purpose of increasing the etching selectivity of the interlayer insulating film with respect to the resist, excessive C is deposited on the processed surface and deposition occurs.
This makes it difficult for the fluorine radicals in the active species flux to react with the silicon oxide film, causing an etch stop in the contact hole.

In this embodiment, in the etching gas
CF gas of_Four F₈ And C _Five F₈ To use. This
By optimizing the mixing ratio of these CF-based gases,
Ensure the etching selectivity of the interlayer insulation film to the
However, the workability of the holes can be improved.

When the ion energy is constant, the reaction rate of the second reaction changes depending only on the C / F ratio. That is, even if the O ₂ flow rate in the etching gas is changed, the C / F ratio at which the etch stop occurs does not change. On the other hand, the reaction rate of the first reaction does not change depending on the ion energy. Therefore, the etching rate was examined by changing the C / F ratio with a specific ion energy, and based on this, the C
The optimum mixing ratio of F-based gas is obtained. Here, when the etching rate has a negative value, it indicates the deposition rate.

An example of optimizing the C / F ratio in the case of forming a contact hole in a silicon oxide film with an ion energy of 1450 V using a parallel plate type reactive ion etching (RIE) device will be described below. explain. The desorption products (volatile products) that are most often generated when etching the silicon oxide film are CF.
_{Is 2} . The generated desorption products include products having a composition slightly richer in C than CF _2. However, the desorption products generally contain C: F.
= About 1: 2.

Therefore, the etching gas is C: F =
When C is richer than 1: 2, for example, the flow rate of the etching gas is C ₄ F ₈ / C ₅ F ₈ / Ar = 8/16/4
In the case of 00 (sccm), in the first reaction, O radicals or the like may be insufficient with respect to excess C, and deposition may occur.

FIG. 1 shows that the ion energy is 1450 V,
The etching rate (or deposition rate) was examined when the sum of the C ₄ F ₈ flow rate and the C ₅ F ₈ flow rate was 22 sccm and the carrier gas (Ar) flow rate was 400 sccm, respectively, and the C ₄ F ₈ flow rate was changed. These are the experimental results.

As shown in FIG. 1, the C ₄ F ₈ flow rate is 9 sc
At more than cm, no deposit growth was observed.
For example, C ₄ F ₈ / C ₅ F ₈ / Ar = 18/4/400
In the case of (sccm), the etching rate is about 250 nm / min. As the flow rate of C ₄ F ₈ increases, that is, C
The lower the / F ratio, the higher the etching rate. From the above, when the ion energy is constant at 1450V,
C ₄ F ₈ / C ₅ F ₈ = 9/13 or more C / F
It is considered that if the ratio is low, etch stop can be suppressed.

On the other hand, in order to increase the etching selection ratio of the silicon oxide film to the resist, it is necessary to increase the C / F ratio. As shown in FIG. 1, C ₄ F ₈ / C ₅ F ₈ =
When the C / F ratio is higher than 9/13, the deposition becomes excessive and an etch stop occurs. Therefore, in order to maximize the etching selection ratio of the silicon oxide film to the resist within the range where etch stop does not occur, C ₄ F ₈ /
It can be seen that C ₅ F ₈ = 9/13 should be set.

FIG. 2 is a cross-sectional view showing a step of forming a contact hole according to the method of manufacturing a semiconductor device of this embodiment. As shown in FIG. 2A, a copper wiring 2 is formed by being embedded in a first interlayer insulating film made of, for example, a silicon oxide film 1. A silicon nitride film 3 is formed on the silicon oxide film 1 including the copper wiring 2.

A second interlayer insulating film made of the silicon oxide film 4 is formed thereon with a thickness of 2 μm. The silicon nitride film 3 is used as an etching stopper layer when the silicon oxide film 4 is etched. A resist 5 is formed on the silicon oxide film 4 in a pattern of contact holes by a lithography process.

Next, as shown in FIG. 2B, the silicon oxide film 4 is dry-etched by RIE using the resist 5 as a mask to form a contact hole 6.
Here, from the experimental result shown in FIG. 1, the flow rate ratio in the etching gas is set to C ₄ F ₈ / C ₅ F ₈ = 9/13.

Specifically, the flow rate of the etching gas is set to C ₄
F ₈ / C ₅ F ₈ / Ar / O ₂ = 4.5 / 6.5 / 600
/ 10 (sccm). Other etching conditions are ion energy of 1450 V and pressure of 4 Pa (≈30 m
Torr), high-frequency output top 2000W, bottom 1
It is set to 500W.

When the aspect ratio of the contact hole becomes high, the bottom of the hole becomes thin, and O generated from the substrate side relatively decreases. When the amount of active species changes in this way and C becomes excessive, etch stop occurs. According to this embodiment, the C / F ratio in the etching gas is set within a range in which excessive C deposition does not occur.

As a result, even when a contact hole having a high aspect ratio is formed, etching stop in the contact hole is prevented. Further, since the etching selection ratio of the silicon oxide film 4 with respect to the resist 5 can be sufficiently secured, it is possible to prevent the resist 5 from disappearing during the etching, and perform the etching of the thickness of the silicon oxide film 4 with high accuracy. Is possible.

(Embodiment 2) This embodiment shows an example in which a contact hole is formed in a layered interlayer insulating film having a FSG film on a silicon oxide film by dry etching using a resist as a mask.

Since the FSG film contains fluorine in the silicon oxide film, fluorine is desorbed from the film when subjected to ion bombardment by RIE. As a result, fluorine radicals are generated, and these fluorine radicals also function as an etchant. Therefore, the removal of excess C proceeds by the second reaction described in the first embodiment.

In the case of etching the FSG film, compared with the case of etching the silicon oxide film, the deposits are less likely to grow even if a relatively C-rich etching gas is used. Therefore, in order to increase the etching selection ratio of the interlayer insulating film with respect to the resist, it is desirable to make the C / F ratio of the etching gas higher than that of the silicon oxide film.

FIG. 3 shows the ion energy as in FIG.
1450V, C_Four F₈ Flow rate and C_Five F ₈ Sum of flow rate is 22s
ccm, carrier gas (Ar) flow rate is 400 sccm
Keep each constant, C_Four F₈ The error when changing the flow rate
It is the result of the experiment that investigated the etching rate (or deposition rate).
It 3a shows the case of a silicon oxide film, which is the same as FIG.
Is one. FIG. 3b shows the case of the FSG film.

As shown in FIG. 3, the C ₄ F ₈ flow rates are the same,
That is, if the composition of the etching gas is the same, FSG
The film (b) has a higher etching rate than the silicon oxide film (a). This is partly because the fluorine radicals generated from the FSG film act as an etchant as described above.

The condition that the etching rate is 0 is
The FSG film shifts to a higher C / F ratio side (lower C ₄ F ₈ flow rate side). Under the experimental conditions of FIG. 3, the etching rate of the FSG film becomes 0 when C ₄ F ₈ / C ₅ F ₈ = 5/17. At higher C / F ratios, deposits grow.

Therefore, the ion energy is 1450 V
In order to maximize the etching selection ratio of the silicon oxide film to the resist within the range where the etch stop does not occur when the contact hole is formed in the FSG film by C ₄
It suffices to set F ₈ / C ₅ F ₈ = 5/17.

FIG. 4 is a cross-sectional view showing a step of forming a contact hole according to the method of manufacturing a semiconductor device of this embodiment. As shown in FIG. 4A, a copper wiring 2 is formed by being embedded in a first interlayer insulating film made of, for example, a silicon oxide film 1. A silicon carbide film (SiC film) 11 is formed on the silicon oxide film 1 including the copper wiring 2.

A silicon oxide film 4 is formed on the silicon carbide film 11, and the silicon oxide film 4 constitutes a second interlayer insulating film. The silicon carbide film 11 is used as an etching stopper layer when the silicon oxide film 4 is etched. F on the silicon oxide film 4
The SG film 12 is formed, and the FSG film 12 constitutes the second interlayer insulating film together with the silicon oxide film 4. FSG
A resist 5 is formed on the film 12 in a pattern of contact holes by a lithography process.

Next, as shown in FIG. 4B, the FSG film 12 is dry-etched by RIE using the resist 5 as a mask to form a part 6a of the contact hole. Here, from the experimental results shown in FIG. 3, in the etching of the FSG film 12, the flow rate ratio in the etching gas was changed to C ₄ F ₈ /
C ₅ F ₈ = 5/17.

Specifically, the flow rate of the etching gas is set to C ₄
F ₈ / C ₅ F ₈ / Ar / O ₂ = 3/8/600/10
(Sccm). Other etching conditions are that the ion energy is 1450 V, the pressure is 4 Pa, and the high frequency output is top 2000 W and bottom 1500 W.

Next, as shown in FIG. 4C, the silicon oxide film 4 is dry-etched by RIE using the resist 5 and the FSG film 12 as a mask. As a result, the contact hole 6 is formed. When etching the silicon oxide film 4, the flow rate ratio in the etching gas is set to C ₄ F 2.
₈ / C ₅ F ₈ = 9/13. Specifically, the flow rate of the etching gas is set to C ₄ F ₈ / C ₅ F ₈ / Ar / O ₂ = 4.
It is set to 5 / 6.5 / 600/10 (sccm). Ion energy, pressure, and high frequency output are the same as in the case of etching the FSG film 12.

According to this embodiment, even when a contact hole is formed in the interlayer insulating film having such a laminated structure,
The etching selection ratios of the FSG film 12 and the silicon oxide film 4 with respect to the resist 5 can be maximized. Therefore, it is possible to prevent the resist 5 from disappearing during the etching, and it is possible to perform the etching by the thickness of the interlayer insulating film with high accuracy. Further, since the C / F ratio in the etching gas is set within the range where excessive C deposition does not occur, it is possible to prevent the etching stop in the contact hole 6.

The embodiment of the semiconductor device manufacturing method of the present invention is not limited to the above description. For example, even when the ion energy is changed, the CF rate depends on the C / F ratio dependency of the etching rate as in FIG. 1 or 3.
The mixing ratio of the system gases can be optimized.

In the above embodiment, the case where two kinds of CF-based gas are mixed is shown, but it is also possible to mix three or more kinds of CF-based gas so that an optimum C / F ratio can be obtained. Is. In the above embodiment, the parallel plate type RIE apparatus is used as an example. However, the present invention can be applied to a case where dry etching is performed using, for example, a plasma etching apparatus. In addition, within the scope of the present invention,
Various changes are possible.

[0049]

According to the method of manufacturing a semiconductor device of the present invention, a contact hole having a high aspect ratio can be formed while ensuring an etching selection ratio of an insulating film to a resist.

[Brief description of drawings]

FIG. 1 shows a C / F ratio dependency of an etching rate according to a first embodiment of a method for manufacturing a semiconductor device of the present invention.

FIG. 2A and FIG. 2B are the first embodiment of the present invention.
FIG. 6 is a cross-sectional view showing the manufacturing process of the method for manufacturing the semiconductor device according to the first embodiment.

FIG. 3 shows a C / F ratio dependency of an etching rate according to a second embodiment of the method for manufacturing a semiconductor device of the present invention.

FIGS. 4A to 4C are cross-sectional views showing manufacturing steps of a method for manufacturing a semiconductor device according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... Silicon oxide film, 2 ... Copper wiring, 3 ... Silicon nitride film, 4 ... Silicon oxide film, 5 ... Resist, 6, 6a ... Contact hole, 11 ... Silicon carbide film, 12 ...
FSG membrane.

Claims (3)

[Claims] 1. An etching rate when dry etching is performed on an insulating film mainly made of silicon oxide by using an etching gas containing at least two kinds of fluorocarbon-based gas, and a mixing ratio of the fluorocarbon-based gas is different, and The step of investigating under a plurality of conditions in which the energy of the ions incident on the insulating film is the same, and the optimum mixing ratio that maximizes the ratio of the amount of carbon to the amount of fluorine in the etching gas within a range in which the etching rate does not have a negative value. And a step of forming a resist in a predetermined pattern on the insulating film, using an etching gas containing the fluorocarbon-based gas in the optimum mixing ratio, using the resist as a mask, the energy in the insulating film And a step of performing dry etching by injecting ions into the semiconductor device. 2. The insulating film is a laminated film composed of a plurality of layers having different compositions, and has a step of obtaining the optimum mixing ratio in each layer, wherein an etching gas containing the fluorocarbon-based gas in the optimum mixing ratio is included. 2. The method of manufacturing a semiconductor device according to claim 1, wherein, in the step of dry etching the insulating film, the mixing ratio of the fluorocarbon-based gas in each layer is set to an optimum mixing ratio. 3. A first etching rate when dry etching a silicon oxide film by using an etching gas containing at least two kinds of fluorocarbon-based gas, and when the mixing ratio of the fluorocarbon-based gas is different and In a plurality of conditions in which the energy of the ions incident on the oxide film is equal, and in a range in which the first etching rate does not have a negative value,
A step of obtaining a first optimum mixing ratio that maximizes the ratio of the amount of carbon to the amount of fluorine in the etching gas, and an etching gas containing at least two fluorocarbon type gases are used to form a FSG (fluorine silicate glass) film. A step of examining the second etching rate when performing dry etching under a plurality of conditions in which the mixing ratio of the fluorocarbon-based gas is different and the ions are incident on the FSG film with the energy, and the second etching rate Within the range where is not negative,
Obtaining a second optimum mixing ratio which is a mixing ratio that maximizes the ratio of the amount of carbon to the amount of fluorine in the etching gas and is larger than the first optimum mixing ratio; and the silicon oxide film and the FSG. A step of forming a laminated film including a film, a step of forming a resist on the laminated film in a predetermined pattern, and a step of forming the resist using an etching gas containing the fluorocarbon-based gas in the second optimum mixing ratio. As a mask, a step of performing dry etching by injecting ions into the FSG film with the energy, and using the etching gas containing the fluorocarbon-based gas in the first optimum mixing ratio and using the resist as a mask, the silicon Dry etching by making ions enter the oxide film with the above-mentioned energy.