JP2000150482A - Dry etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wiring pattern excellent in form stability by applying a high-frequency in two steps to a laminated body of Al and Ti group material formed on a base material to suppress plasma damages. SOLUTION: At an etching device 20, an etching gas is guided into a reactive chamber 21 as shown by an allow A, and the etching gas is made into a plasma by the microwave introduced through a waveguide. With the high frequency applied in two steps by a high-frequency power source 27, a semiconductor wafer 28 on an application electrode 25 is etched. The high-frequency power source 27 uses such high-frequency power source with high frequency as excellent in form controllability and such high-frequency power source with low frequency suppressing electron shading effect. By applying high-frequency in two steps, a required amount of remaining resist is obtained. So, only by changing applies frequency, plasma damage is suppressed for a wiring pattern excellent in form stability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a dry etching method. More specifically, the present invention relates to a plasma etching method using an etching gas containing a chlorine gas in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, a wiring pattern of an aluminum (Al) -based material is formed on a wafer by etching. In order to form such a wiring pattern, a plasma etching apparatus using an ECR (Electron Cycrotron Resonance) discharge is used.

FIG. 5 is an explanatory view of a process of forming an Al-based wiring pattern by a conventional dry etching method. As shown in FIG. 1A, an interlayer film 11 is formed on a silicon substrate or a base (not shown) such as a lower wiring formed thereon by, for example, a CVD method. This interlayer film 11 is made of, for example, S
It is formed of an insulating oxide film such as iO ₂ or a silicate glass material such as BPSG or PSG. A titanium (Ti) film 12 and a titanium nitride (Ti)
An N) film 13 is formed by, for example, a sputtering method, and an Al film 14 made of aluminum (Al) or an alloy thereof is formed thereon by, for example, a sputtering method, and an Al wiring layer 15 is formed by a laminate of these. The Ti and TiN are used for reducing the resistance of the wiring and improving the adhesion to the interlayer film. After that, in order to form a wiring pattern, a resist mask 16 is formed by patterning, for example, by a lithography method.

[0004] Through this resist mask 16, (B)
As shown in FIG. 7, the wiring layer 15 is etched to form a wiring pattern 17. In this case, overetching is performed after the Al wiring layer 15 is etched. Such etching can be performed, for example, by using chlorine gas as an etching gas.
This is performed by plasma etching using a R discharge and applying a high frequency from a high frequency power supply. In this case, the frequency of the high-frequency power source is, for example, 2 MHz, and a high frequency of a constant frequency is applied to the wafer.

[0005]

However, the Ti film 12, TiN film 13 and Al film 14, which are metal films, are not
When dry etching is performed by plasma etching using CR discharge, if the frequency of the high-frequency power supply is higher than an appropriate value according to the patterning conditions, plasma damage occurs due to an electron shading effect or a microloading effect, and the Al wiring layer and the contact hole are damaged. The gate may be destroyed through the gate. Further, the electron shading effect and the microloading effect become more remarkable as the wiring space becomes smaller, and may cause abnormalities in the shape of the Al wiring such as side etching, which lowers the reliability of the semiconductor device. Also,
The occurrence of such plasma damage
In anticipation of this, it becomes necessary to consider the mitigation of the wiring space on the design rule, and as a result, the method of manufacturing the semiconductor device is restricted.

FIGS. 6A and 6B are explanatory diagrams of such an electronic shading effect and a microloading effect. The electron shading effect occurs due to the difference in the motion state between electrons and ions. Electrons collide with the insulator pattern side wall, while ions are almost vertically incident, so that the side wall charges up negatively. This negative charge forms an electric field that acts as a barrier for the electrons.
Therefore, electrons having only a small velocity component in the vertical direction are decelerated by this electric field, are further bounced off, and cannot enter the pattern. Therefore, only the ions are incident, and the circuit having the dense pattern is damaged.

[0007] The microloading effect occurs due to the dependence of the etching rate on the density. Even if etching is completed in a wide pattern during etching, there is a state in which aluminum material still remains in a narrow pattern portion. Until the aluminum material having the narrow pattern is etched, a damage current flows into the oxide film to cause damage to the circuit.

To cope with such a point, it is conceivable to lower the frequency of the high-frequency power supply. However, when the frequency of the high-frequency power supply is reduced, as shown in FIG. 7, the etching rate of the resist increases, and it becomes impossible to secure the remaining resist amount after the etching. The reason for this is that the lower the frequency is, the higher the ion energy is, and the lower the selectivity between Al and the resist is.

The present invention has been made in view of the above points, and does not significantly change the conventional semiconductor manufacturing process and reduces plasma damage when plasma-etching a laminate of Ti-based and Al-based materials. Another object of the present invention is to provide a dry etching method capable of forming an Al wiring pattern while maintaining a stable remaining amount of resist.

[0010]

In order to achieve the above object, according to the present invention, an etching gas containing chlorine gas is used to apply a high frequency power supply to a laminate of Al-based and Ti-based materials formed on a base. A dry etching method for applying a high frequency to perform plasma etching, wherein a high frequency is applied to the laminate in two steps.

According to this configuration, by etching while changing the frequency of the high-frequency power supply in two stages, a high-frequency power supply with excellent frequency control and a high frequency control according to the etching state, and suppressing the electronic shading effect. A high-frequency power source having a low frequency can be used, and by simply changing the applied frequency using a conventional device, plasma damage can be suppressed and an Al wiring pattern having excellent shape stability can be obtained.

In a preferred configuration example, the two steps include:
The method is characterized by a step of etching the laminate and a step of over-etching the base.

According to this structure, when etching the Al wiring portion, a high frequency having a high frequency excellent in shape controllability by increasing the plasma discharge stability and the selectivity of Al / resist is applied, and the electron shading effect is obtained. At the time of over-etching in which plasma damage occurs, a high frequency having a low frequency is applied.

A further preferred configuration is characterized in that plasma etching is performed using ECR discharge.

According to this configuration, by changing the frequency of the high frequency power supply in two steps using the ECR type plasma etching apparatus, damage can be prevented and high precision pattern formation can be achieved.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of a process for forming an Al-based wiring pattern by a dry etching method according to the present invention. As shown in FIG. 1A, an interlayer film 1 is formed on a silicon substrate or a base (not shown) such as a lower wiring formed thereon by, for example, a CVD method. This interlayer film 1
Is an insulating oxide film such as SiO ₂ or BPSG or P
It is formed of a silicate glass material such as SG. A titanium (Ti) film 2 and a titanium nitride (TiN) film 3 are formed on the interlayer film 1 by, for example, a sputtering method, and an Al film 4 made of aluminum (Al) or an alloy thereof is further formed thereon by, for example, a sputtering method. Then, an Al wiring layer 5 is formed from these laminates. The Ti and TiN are used for reducing the resistance of the wiring and improving the adhesion to the interlayer film. Thereafter, in order to form a wiring pattern, a resist mask 6 is formed by patterning, for example, by a lithography method.

As shown in FIG. 1B, the wiring layer 5 is etched through the resist mask 6 to form a wiring pattern 7.
To form In this case, overetching is performed after the Al wiring layer 5 is etched. Such etching is performed by plasma etching using, for example, an ECR discharge with chlorine gas as an etching gas and applying a high frequency from a high frequency power supply. In the case of the present embodiment, etching of the Al wiring layer 5 is performed by applying a high frequency of 2 MHz, and over-etching is performed by applying a high frequency of 400 KHz or 800 KHz and applying a two-step frequency.

FIG. 2 is a block diagram of an ECR type plasma etching apparatus for performing the dry etching method according to the present invention. The etching apparatus 20 includes a reaction chamber 21
And a waveguide 22 for supplying a microwave from a microwave power supply 23 to the reaction chamber 21 and a solenoid coil 24 for applying a magnetic field. Application electrode 2 in reaction chamber 21
5 and a ground electrode 26 are provided. A high frequency power supply 27 is connected to the application electrode 25. On this application electrode 25,
The semiconductor wafer 28 on which the laminate to be etched shown in FIG. 1 is formed is mounted.

In the etching apparatus 20 having such a structure, an etching gas is introduced into the reaction chamber 21 as shown by an arrow A, and the etching gas is turned into plasma by the microwave guided by the waveguide 22, As described above with reference to FIG. 1, the semiconductor wafer 28 on the application electrode 25 is etched while applying a high frequency in two steps.

[0020]

EXAMPLE A more specific example of the present invention will be described below. In order to evaluate the frequency dependence of the high frequency power supply of the plasma damage at the time of processing the Al wiring by Qbd measurement, a sample 30 for a semiconductor device evaluation test as shown in FIG. 3 was manufactured. 3A is a plan view, and FIG. 3B is a cross-sectional view.

This sample 30 has a large number of comb-shaped terminals 3
1 is obtained by patterning an Al wiring 32 connecting one end of the wiring 1 by etching. The Al wiring 32 is connected to an underlying electrode and the like via a contact hole 34. The width a of the Al wiring 32 is 2 μm, and the interval b between the terminals 31 is 1
μm, the width c between all the terminals 31 was 750 μm, and the number of the terminals 31 was 250.

The flow of manufacturing the sample 30 will be described. First, a LOCOS film 36 for forming an element isolation region is formed on a Si substrate 35 to have a thickness of 400 nm by diffusion. Next, a gate oxide film 37 having a thickness of 9 nm is formed by diffusion. Next, a polysilicon layer having a thickness of 400 nm is formed by CVD. The polysilicon layer is dry-etched to form an electrode 38.

Next, BPSG (Boron-doped Phospho Si
An interlayer film 39 made of a glass (licate glass) is formed by CVD. Next, a contact hole 34 is formed in the interlayer film 39 by dry etching. Next, the Al wiring 32
Is formed together with the terminals 31 by sputtering. This Al
The wiring 32 and the terminal 31 are made of Ti (30 nm) / TiN
(70 nm) / Al-Si (700 nm). The stress current for Qbd evaluation of this sample 30 is 100 mA / cm ² .

The sample 30 was set in the ECR type plasma etching apparatus shown in FIG. 2 and was etched under the conditions shown in Tables 1 and 2.

[0025]

TABLE 1 (1) Al wiring processing etching conditions Reaction chamber pressure: 8 mTorr applied RF power: 50 W etching _{gas: BCl 3 / 90sccm + Cl 2} / 60sccm RF power supply frequency: 2MHz (2) over-etching condition Reaction chamber pressure: 8 mTorr applied RF power: 50 W etching _{gas: BCl 3 / 90sccm + Cl 2} / 60sccm RF power frequency: 800 KHz

[0026]

TABLE 2 (1) Al wiring processing etching conditions Reaction chamber pressure: 8 mTorr applied RF power: 50 W etching _{gas: BCl 3 / 90sccm + Cl 2} / 60sccm RF power supply frequency: 2MHz (2) over-etching condition Reaction chamber pressure: 8 mTorr applied RF power: 50 W etching _{gas: BCl 3 / 90sccm + Cl 2} / 60sccm RF power frequency: 400 KHz result, Qbd characteristic becomes very good results, plasma damage could not be confirmed. FIG. 4 is a graph of the state of occurrence of the etching failure. The horizontal axis represents time, and the vertical axis represents the cumulative failure rate. The Qbd characteristic is evaluated based on such a graph.

As a comparative example, the frequency of the high frequency power
Same 2M for both wiring processing and over-etching
A high frequency was applied at Hz, and the sample was etched under the same conditions as those in Tables 1 and 2 above.
As a result, it was found that the Qbd characteristics were very poor and there was plasma damage.

Further, the samples were etched under the conditions shown in Tables 3 to 7 below. In this case, the dependence of the etching rate of the resist on the frequency of the high-frequency power supply and the remaining amount of the resist on the shoulder after the Al wiring was etched were evaluated. This resist remaining amount evaluation sample is shown in FIG.
The thickness of the Ti film 2 is 30 nm,
The thickness of the iN film 3 is 70 nm, and the thickness of the Al film 4 is 600 n.
m, the thickness of the resist mask 6 was 0.8 μm.
The etching of the Al wiring layer 5 was performed in two steps: a step until the Ti was etched, and an over-etching step. The over-etch step is Al
The test was performed for 50% of the wiring film thickness. The etching conditions are as shown in Tables 3 to 7 below, and the remaining amount of the resist was observed by SEM (scanning electron microscope) after the etching treatment.

[0029]

TABLE 3 Reaction chamber pressure: 8 mTorr applied RF power: 50 W etching _{gas: BCl 3 / 90sccm + Cl 2} / 60sccm RF power frequency: 2MHz

[0030]

TABLE 4 Reaction chamber pressure: 8 mTorr applied RF power: 50 W etching _{gas: BCl 3 / 90sccm + Cl 2} / 60sccm RF power frequency: 800 KHz

[0031]

TABLE 5 Reaction chamber pressure: 8 mTorr applied RF power: 50 W etching _{gas: BCl 3 / 90sccm + Cl 2} / 60sccm RF power frequency: 400 KHz

[0032]

[Table 6] Reaction chamber pressure: 8 mTorr applied RF power: 50 W etching _{gas: BCl 3 / 90sccm + Cl 2} / 60sccm Al wiring etching step RF power frequency: 2 MH
z Over-etching step high frequency power supply frequency: 800
KHz

[0033]

TABLE 7 Reaction chamber pressure: 8 mTorr applied RF power: 50 W etching _{gas: BCl 3 / 90sccm + Cl 2} / 60sccm Al wiring etching step RF power frequency: 2 MH
z Over-etching step high frequency power supply frequency: 400
As a result, as shown in FIG. 8, as compared with the case where the frequency of the high-frequency power supply is performed at a single frequency of 2 MHz, as shown in FIG.
When etching is performed at a single frequency of 800 KHz or 400 KHz, a remaining amount specification value of 300 nm or more (arrow A in the figure) as an index of a required remaining amount of resist cannot be secured. However, the etching is performed in two steps by changing the frequency. As a result, a film thickness with a remaining amount specification of 300 nm could be obtained.

[0034]

As described above, according to the present invention, in a plasma etching method using a chlorine-based etching gas, etching is performed by changing the frequency of a high-frequency power supply in two stages. A high frequency power supply having a high selection ratio and a high frequency having excellent shape controllability and a high frequency power supply having a low frequency for suppressing plasma damage due to the electron shading effect can be used in two steps at two frequencies. By simply changing the applied frequency, it is possible to suppress the plasma damage and obtain a wiring pattern having excellent shape stability.

[Brief description of the drawings]

FIG. 1 is a process explanatory view of an etching method according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a dry etching apparatus for performing the method of the present invention.

FIG. 3 is a configuration diagram of a Qbd evaluation sample.

FIG. 4 is a graph of Qbd evaluation.

FIG. 5 is a process explanatory view of a conventional dry etching method.

FIG. 6 is an explanatory diagram of an electronic shading effect and a microloading effect.

FIG. 7 is a graph showing a relationship between a frequency of a high-frequency power supply and an etching rate.

FIG. 8 is a graph showing the relationship between the frequency of a high-frequency power supply and the remaining amount of resist.

[Explanation of symbols]

1: Si substrate, 2: Ti film, 3: TiN film, 4: Al
Film, 5: Al wiring layer, 6: resist mask, 7: wiring pattern.

Claims (3)

[Claims] 1. A dry etching method for performing plasma etching by applying a high frequency from a high frequency power supply to a laminated body of Al-based and Ti-based materials formed on an underground using an etching gas containing chlorine gas. A dry etching method, wherein a high frequency is applied to the body in two steps. 2. The dry etching method according to claim 1, wherein the two steps are a step of etching the laminate and a step of over-etching a base. 3. The dry etching method according to claim 1, wherein plasma etching is performed using an ECR discharge.