JPH10177992A - Taper etching method of micro contact hole - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a tapered micro contact hole having a high aspect ratio in the interlayer insulating film of a multilayer interconnection structure. SOLUTION: The etching of a contact hole H is performed by depositing fluorocarbon polymeric films 6 containing fluorine and carbon at a fluorine/ carbon ratio of 1 to 2 on the side walls of the hole H. The etching condition is controlled so that the ratio of the depositing rate RD of the C-F polymeric films 6 on the side walls of the hole H to the etching rate RE in the vertical direction may become 12-17. The gaseous starting material used for the etching is prepared by mixing a gas such as C4 F8 in which carbon atoms are cyclically coupled and one hydrogen substitute of fluorocarbon, such as CHF3 , CH2 F2 , CH3 F, etc., at a mixing ratio of 1:5 to 1:10 and an Ar gas is mixed with the gaseous starting material so that the flow rate of the Ar gas can become 60-85% of the total quantity of the mixed gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for taper-etching a contact hole of an interlayer insulating film of a multilayer wiring structure with good controllability, and more particularly to a method in which the contact hole has a bottom diameter of 0.2 .mu.m and an aspect ratio of 5, for example. The present invention relates to a method suitable for tapered etching of a fine contact hole.

[0002]

2. Description of the Related Art In recent years, as the design rules of electronic devices have become finer and multilayer wiring has progressed, the following problems have arisen when etching fine contact holes in interlayer insulating films. FIG. 8 is an explanatory view showing steps from formation of a contact hole to an interlayer insulating layer to formation of an upper wiring layer. In this step, as shown in FIG. 8A, after forming an interlayer insulating film 2 and a lower wiring layer 3 on a silicon substrate 1, a photoresist 4 for forming a contact hole H is patterned. 8B, a step of forming a contact hole H in the interlayer insulating film 2 by dry etching, and a step of forming the upper wiring layer 5 after removing the photoresist 4 as shown in FIG. 8C. 2 and burying the upper wiring layer 5 in the contact hole H. In such a structure, the horizontal distance a between the lower wiring layer 3 and the upper wiring layer 5 buried in the contact hole H is larger as the breakdown voltage between the upper wiring layer 5 and the lower wiring layer 3 is ensured. desirable.

FIG. 9 is an explanatory view of forming a contact hole when the design rule of a device is reduced, and the interval between the lower wiring layers 3 is reduced. in this case,
When patterning the photoresist 4, the opening hole K
It is necessary to reduce the diameter of the opening hole formed in the photoresist as shown in FIG. 9A, or the opening hole formed in the photoresist as shown in FIG. 9B. If the horizontal position of the first wiring pattern varies, it becomes difficult to secure the distance a, and the lower wiring layer 3 and the upper wiring layer 5 may be short-circuited. Further, when the diameter of the opening hole K of the photoresist 4 is reduced to absorb such variations, the focus margin of patterning is reduced, and as shown in FIG. This causes a problem of disappearing.

FIG. 10 is an explanatory view showing a tapered contact hole forming step when the device design rule is reduced. With the miniaturization of device design rules, in order to form a finer and higher aspect ratio contact hole H while securing the distance a to the lower wiring layer 3, the contact hole H is formed by dry etching.
In the step of forming, as shown in FIG.
In order to form an opening hole K having a diameter b so as to have a sufficient process margin and to secure a distance a to the lower wiring layer 3, the upper diameter of the contact hole H is set to a photoresist as shown in FIG. In addition to maintaining the bottom diameter b of the contact hole 4, a technique for etching the contact hole H in a tapered shape so that the bottom diameter is not smaller than the upper diameter b is required.

Conventional methods of taper etching the interlayer insulating film 2 are roughly classified into the following three methods (1) to (3).
Different methods are known. (1) A method using isotropic etching and anisotropic etching (2) A method of forming a taper in a photoresist in advance and transferring the taper (3) A method of forming a sidewall protective film by low-temperature etching

The above method (1) is disclosed in, for example,
No. 53190, and FIG.
As shown in FIG. 11A, an opening hole K is formed in the photoresist 4 and then, as shown in FIG. In this method, a contact hole H is formed, and then, as shown in FIG. 11C, the photoresist 4 is removed and the upper wiring layer 5 is buried.

The method (2) is described in, for example,
No. 83358, and FIG.
(A) As shown in FIG.
A tapered opening hole K is formed in the photoresist 4 in advance by multiple exposures, and then the taper of the photoresist 4 is insulated by etching under conditions having a low selectivity to the photoresist 4 as shown in FIG. This is a method in which a contact hole H is formed by transferring to the film 2 and then the photoresist 4 is removed and the upper wiring layer 5 is buried as shown in FIG.

The method (3) is described in, for example, Japanese Patent Application Laid-Open No. 5-102107.
As shown in FIG. 3A, an opening hole K is formed in the photoresist 4.
After the formation, a contact hole H is formed by etching while depositing a fluorocarbon polymer film 6 as shown in FIG. 13B, and then the photoresist 4 is removed as shown in FIG. 13C. Then, the upper wiring layer 5 is buried.

[0009]

However, in the method (1), since the opening of the contact hole H is the same as the bottom diameter b of the opening hole K formed in the photoresist 4, the method of (1) is difficult. There is no margin at distance a,
As shown in FIG. 11C, the lower wiring layer 3 and the upper wiring layer 5
There is a problem that a short circuit may occur. Also, the diameter b of the opening hole K formed in the photoresist 4
Can be reduced to, for example, 0.2 μm, there is a margin, but it is difficult to form such an opening hole K.

According to the above method (2), the top diameter of the contact hole H is larger than the bottom diameter of the opening hole K formed in the photoresist 4, so that there is no margin with the lower wiring layer 3 and FIG. As shown in c), there is a problem that the upper wiring layer 5 and the lower wiring layer 3 may be short-circuited.

The above method (3) uses CF ₄ / CHF ₃ / A
Using an r gas system, CF ₄ utilizes reactive ions, and CHF ₃ utilizes radicals that form the basis of a polymer film, and is a method of etching while depositing a fluorocarbon polymer film. The problem that the top diameter of the contact hole H is larger than the bottom diameter of the opening hole K formed in the photoresist 4 as in the case of (2) is solved. However, as shown in FIG. 13B, the deposition of the polymer film 6 also occurs at the bottom of the hole H, so that the hole H having a fine size (for example, a hole bottom diameter of 0.2 μm) and a high aspect ratio (for example, 5) is formed. In order to perform this, the incident amount of the etching species is reduced, and furthermore, the progress of the etching is hindered by the excessive protection effect, or the etching is stopped halfway (generation of the microloading effect), as shown in FIG. There is a problem of causing poor opening.

Therefore, the method (3) is not suitable for etching a fine and high aspect ratio contact hole H, and controls the taper angle of the fine and high aspect ratio contact hole H as compared with the conventional method. In order to perform the etching, it is necessary to solve a trade-off between the deposition of the polymer film on the side wall of the hole H and the occurrence of the microloading effect. That is, when the taper etching method of the conventional example (3) is applied to the contact hole H having a fine and high aspect ratio, a problem is that a polymer film for protecting the side wall is deposited also on the bottom of the hole. Etching is hindered.

The present invention has been made in view of the above-mentioned conventional problems, and provides a taper etching method for a fine contact hole capable of forming a fine, high aspect ratio tapered contact hole in an interlayer insulating film having a multilayer wiring structure. The purpose is to do.

[0014]

In order to obtain a margin of the above-mentioned distance a at a minute interval of the lower wiring layer 3 when etching a device having a fine multilayer wiring structure, there is provided a method of controlling a deposition phenomenon of a polymer film. Is required. In this case, first, qualitatively, it is necessary to deposit a large amount of a polymer film on the side wall to obtain a tapered shape, and the ratio of the deposition rate on the hole side wall to the etching rate in the vertical direction of the hole bottom surface is sufficiently large. There is a need to. In addition, in order to progress the etching even if the diameter is small, it is necessary that the dry etching resistance of the polymer film is weak, and that the polymer film on the bottom surface of the hole having the ion bombardment can be easily removed.

In the present invention, in order to achieve the above object,
In a taper etching method for a fine contact hole in which a fine contact hole of an interlayer insulating film of a multi-layer wiring structure is dry-etched with a taper angle of not less than 75 ° and less than 90 °, a fluorine / carbon ratio of 1 to 2 is provided on a side wall of the hole. And etching while depositing a fluorocarbon polymer film having the following composition. The ratio R _E / R _D of the deposition rate R _D of the polymer film to the side wall of the hole and the etching rate R _{E in the} vertical direction is preferably 12 to 17.

The etching can be carried out by using a narrow gap type dry etching apparatus. A gas having a structure in which carbon is cyclically bonded and a hydrogen-substituted fluorocarbon gas such as CHF ₃ , CH ₂ F ₂ , CH ₃ F are used. Mixing ratio 1: 5
1:10, and the Ar flow rate is 60% of the total gas amount.
A mixed gas of up to 85% can be used.
The fluorocarbon gas may be of one type or a mixture of a plurality of types.

Next, the shape of the contact hole formed by the method of the present invention will be described. When a gas having a carbon ring bond and a large molecular weight such as C ₄ F ₈ is used for parallel plate RIE (reactive ion etching),
In the parallel plate narrow gap type RIE, the decomposition of C ₄ F ₈ is difficult to proceed, and the C ₄ F ₈ is deposited on the substrate with a large molecular weight having a plurality of C—C bonds, so that the deposition rate of the C—F polymer film increases. . In particular the presence of CH _X F _Y gas containing hydrogen (mixing ratio, for example, _{C 4 F 8 / CHF 3 =} 0.1~0.2)
, The deposition rate increases (deposition rate R _D = 200
Å400 ° / min). Further, since the side wall of the hole H is basically free of ion bombardment and the radical polymerization reaction is dominant, the amount of the polymer film deposited increases, and therefore, the side etching can be completely prevented. The diameter gradually decreases with the progress of
A tapered shape can be obtained.

Next, the control of the taper angle by the method of the present invention and the fact that the etching can proceed even with a fine hole will be described. Another effect of using a gas having a cyclic bond of carbon and a high molecular weight such as C ₄ F _{8 in} the etching of parallel plate RIE in the presence of hydrogen-containing CH _X F _Y gas is another effect of the polymer film. Composition is F
It is to become rich. The F / C ratio can be controlled to 1 or 2 in the range of the flow rate ratio of C ₄ F ₈ / CHF ₃ of 0.1 to 0.2 and the flow rate of C ₄ F ₈ of 3 to 6 sccm. The bottom surface of the hole H is subjected to ion bombardment, and the polymer film is removed by spattering, decomposed by oxygen generated by etching the oxide film, or consumed for etching. The rate of decomposition and consumption becomes larger as the F-rich becomes (the dry etching resistance becomes weaker), and even fine holes can be processed without being hindered by the polymer film, and the etching rate R _E in the substrate direction at the bottom of the hole can be reduced. Obtainable.

Further, the etching rate R _E and sidewall deposition rate R _D of the substrate direction of the hole bottom can be controlled by the Ar gas flow rate. In this case, Ar is set to 6 of the total gas flow rate.
It is possible to control the R _E / R _D ratio 12 to 17 by the 0-80%, to control the taper angle of the contact hole less than 75 ° or 90 ° by the control of the R _E / R _D ratio be able to. In addition, such a tapered contact hole reduces heat insulation defects due to the metal oxide material.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a process chart showing one embodiment of a taper etching method for a fine contact hole according to the present invention. According to the present invention, a step of patterning a photoresist 4 for forming a contact hole H after forming an interlayer insulating film 2 and a lower wiring layer 3 on a silicon substrate 1 as shown in FIG. 1B, a step of forming a tapered contact hole H in the interlayer insulating film 2 by dry etching, and a step of forming the upper wiring layer 5 after removing the photoresist 4 as shown in FIG. Forming an upper wiring layer 5 in the contact hole H by forming it on the interlayer insulating film 2.

When the interlayer insulating film 2 is etched to form a tapered contact hole H, a narrow gap type RIE (reactive ion etching) is used to form a fluorine / carbon ratio (F / C ratio) on the side wall of the contact hole H. ) Is 1-2
(CF) polymer film 6 having the following composition:
Is etched while depositing. Further, the deposition rate R of the CF polymer film 6 on the side wall of the contact hole H is shown.
_D and the ratio of the vertical etching rate R _E (R _E / R
Etching is performed so that the ( _D ratio) becomes 12 to 17.

Further, the composition ratio of the CF polymer film 6 (F / C
Ratio) and R _E / R _D ratio are controlled so as to be within the above numerical ranges by using a narrow gap type RIE apparatus.
As a raw material gas for forming the F-based polymer film 6, C ₄ F ₈
Gas having a structure in which carbon is cyclically bonded to CHF ₃ , C
H ₂ F _2, CH ₃ fluorocarbon such as F (C-F) volume mixing ratio of hydrogen substituted product gas (flow ratio) 1: 5:00 to 1:10
And the Ar gas flow rate is 60 to 8 of the total gas amount.
A mixed gas having a concentration of 5% is used.

FIG. 2 is a diagram showing the relationship between the C ₄ F ₈ flow rate, the C ₄ F ₈ / CHF ₃ flow rate ratio, the deposition rate _RD of the polymer film, and the F / C ratio. From FIG. 2, the C ₄ F ₈ flow rate, C ₄ F ₈ / CHF
_{3 It} can be seen that when the flow rate ratio increases, the F / C ratio increases as the deposition rate _RD of the polymer film 6 increases. Also,
FIG. 3 shows the etching rate R _{E in} the vertical direction when the F / C ratio and the diameter of the opening hole formed in the photoresist are 0.4 μm.
FIG. FIG. 3 shows that the etching rate R _E increases as the F / C ratio increases. FIG.
Therefore, when the F / C ratio is in the range of 1-2, the deposition rate _{RD on} the side wall of the polymer film 6 is large, but the fine diameter (φ = 0.4 μm) is obtained.
It can be seen that even etching progresses at a high etching rate R _E without being inhibited etching in the case of m). The analysis was performed by X-ray photoelectron spectroscopy.

FIG. 4 is a diagram showing the relationship between the F / C ratio and the taper angle. FIG. 4 shows that taper etching with a taper angle of 80 ° to 84 ° is possible when the F / C ratio is in the range of 1 to 2.

The control range can be further expanded by controlling the taper angle by the ratio of the Ar gas flow rate to the total gas flow rate. The fact that the taper angle can be controlled by the ratio of the Ar gas flow rate to the total gas flow rate will be described with reference to FIGS.

[0026] Figure 5, when changing the total gas flow rate was fixed Ar gas flow rate 5 sccm, the substrate direction of the etching rate ratio and the hole bottom of the Ar gas flow rate to the total gas flow rate R _E and sidewall deposition rate R _D ratio R
It is a figure which shows the relationship with _E / _RD . When the Ar gas flow rate is in the range of 60 to 80% of the total flow rate, the R _E / R _D ratio becomes 12
~ 17. When the ratio of the Ar gas flow rate is less than 60%, micro-loading effect becomes remarkable decreases the etching rate R _E together with the deposition on the sidewalls becomes excessive. The ratio of the Ar gas flow rate is 80
%, The density of the etching species (ions, radicals) decreases, and the etching rate R _E
And the microloading effect becomes significant.

FIG. 6 is a diagram showing the relationship between the taper angle and the ratio R _E / R _D. The taper angle can be set according to the device structure, but according to the method of the present invention, it can be controlled within the range of 75 ° or more and less than 90 °.

Referring to FIG. 7, based on these basic data, the mechanism by which the taper angle can be controlled according to the present invention and the micro-loading effect is suppressed in fine holes will be described. FIG. 7 shows the FC polymer film 6 deposited thickly.
The reason is that radicals having a carbon cyclic bond, such as C ₄ F _8, as a parent molecule are deposited with a large molecular weight having a plurality of CC bonds, so that the deposited molecular weight per unit time increases. It is.

Since the side wall is basically not subjected to ion bombardment in the film thickness direction, the surface reaction on this side wall is a dominant radical deposition reaction, and protection against etching radicals that etch the oxide film on the side wall. Great effect. Therefore, as the etching progresses, the diameter of the contact hole gradually decreases, and a tapered shape is formed.
On the other hand, at the bottom of the hole, radical deposition itself is isotropic and occurs similarly to the side wall. However, the polymer film 6 is subjected to ion bombardment as shown in FIG.
It is decomposed by oxygen generated by etching SiO ₂ . Further, since the polymer film 6 is an F-rich film, the F radicals generated by the decomposition work as etching species for the oxide film, so that the protection effect on the side wall is small and the etching proceeds.

The taper angle can be controlled by the balance of the protective effect of the polymer film on the side wall and the bottom surface. As shown in FIGS.
Quantitative control can be performed by the r gas flow rate.

Here, a specific example of the etching will be described. For example, the lower wiring layer 3 exists at a height of 0.7 μm from the Si substrate 1 and the interlayer insulating film 2 (TEO
A hole pattern having a lower diameter φ = 0.45 μm is formed on the S-NSG) by the photoresist 4, and a margin of 0.2 μm or more is secured between the lower wiring layers 3 at intervals of 0.7 μm. When performing the taper processing of °, the etching conditions are set as follows.

Pressure: 200 to 400 mTorr High frequency power density: 3.5 to 4.5 w / cm ² CF ₄ : 10 to ₃₀ sccm CHF ₃ : 20 to 50 sccm C ₄ F ₈ : 3 to 10 sccm Ar: 100 to 450 sccm Temperature: lower part Electrode setting 0 ° C

Then, in order to obtain a taper angle of 82 °,
5 and 6, the ratio of the Ar gas flow rate to the total gas flow rate is set to 73%. After etching under these conditions, the cross-sectional shape was observed by SEM. As a result, a tapered contact hole having an upper diameter of φ = 0.5 μm, a lower diameter of φ = 0.2 μm, and a taper angle of 82 ° was obtained. did it.

[0034]

According to the present invention, a tapered fine contact hole having an upper diameter substantially equal to the lower diameter of the mask material with respect to the interlayer insulating film of the multilayer wiring structure and having a margin with the lower wiring layer. Can be formed. Therefore, the diameter can be increased in the patterning of the photoresist mask, and the contact hole of a fine multilayer wiring structure device can be easily formed.

[Brief description of the drawings]

FIG. 1 is a process chart showing an embodiment of a taper etching method for a fine contact hole according to the present invention.

FIG. 2 is a diagram showing a relationship between a C ₄ F ₈ flow rate, a C ₄ F ₈ / CHF ₃ flow rate ratio, a deposition rate _RD of a polymer film, and an F / C ratio.

Figure 3 is a graph showing the relationship between F / C ratio and the vertical etching rate R _E.

FIG. 4 is a diagram showing a relationship between an F / C ratio and a taper angle.

FIG. 5 is a diagram showing the relationship between the ratio of the Ar gas flow rate to the total gas flow rate and the ratio R _E / R _D of the etching rate R _{E in} the substrate direction at the bottom of the hole and the side wall deposition rate R _D.

FIG. 6 is a diagram showing the relationship between the taper angle and the ratio R _E / R _D.

FIG. 7 is an explanatory diagram showing the principle of the present invention.

FIG. 8 is a process chart showing a general contact hole forming method.

FIG. 9 is an explanatory diagram of general contact hole formation when a design rule is reduced.

FIG. 10 is an explanatory view showing a tapered contact hole forming step when the device design rule is reduced.

FIG. 11 is a process chart showing a conventional taper etching method.

FIG. 12 is a process chart showing a conventional taper etching method.

FIG. 13 is a process chart showing a conventional taper etching method.

[Explanation of symbols]

 H: Contact hole K: Opening hole 1: Silicon substrate 2: Interlayer insulating film 3: Lower wiring layer 4: Photoresist 5: Upper wiring layer

Claims (3)

[Claims] 1. A taper etching method for a fine contact hole in which a fine contact hole of an interlayer insulating film of a multilayer wiring structure is etched by dry etching with a taper angle of 75 ° or more and less than 90 °. A taper etching method for a fine contact hole, characterized in that etching is performed while depositing a fluorocarbon polymer film having a composition with a ratio of 1 to 2. 2. The ratio R _E / R between the deposition rate R _D of the polymer film on the side wall of the hole and the etching rate R _{E in the} vertical direction.
2. The method according to claim 1, wherein the etching is performed so that R _D is 12 to 17. 3. The etching is performed using a narrow gap type dry etching apparatus, using a gas having a structure in which carbon is cyclically bonded and a hydrogen-substituted fluorocarbon gas in a volume mixing ratio of 1: 5 to 1:10, 3. The method according to claim 1, wherein a mixed gas having an Ar gas flow rate of 60 to 85% of the total gas amount is used.