JPH10116819A - Etching of aluminum film or aluminum alloy film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for dry-etching an aluminum film or aluminum alloy film by which size can be easily controlled and notches or side etching are not produced. SOLUTION: An aluminum film and an aluminum alloy film 3 are dry-etched through a photoresist film 4 as a mask. Nitrogen gas or gas containing C atoms is added for 10-20 seconds immediately after start of etching when the deposition components generated from the mask are lean. By this method, abnormal shape produced in early stage of etching can be prevented and residues and separation can also be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for dry etching an aluminum film or an aluminum alloy film containing a small amount of Cu and Si, which is mainly used for wiring of a semiconductor device.

[0002]

2. Description of the Related Art A typical example of a plasma source used in a dry etching method is a parallel plate type RI.
E, magnetron RIE, and more recently, low pressure and high density plasma sources include ECR (Electron Cyclotron Resonance Plasma), ICP (Inductively Coupled Plasma), and Helicon wave plasma. Among them, in the case of the parallel plate type, the pressure is about several tens to hundreds mTorr, and the obtained electron density is of the order of 10 ¹⁰ / cm ³ . In such a pressure region, the mean free path is short, and it is difficult to perform anisotropic etching on a fine pattern.

On the other hand, in a low-pressure / high-density plasma source, plasma can be generated in a low-pressure region of about several mTorr, and 10 ¹² to 10 ¹³ / cm ^3.
A high level of high density plasma can be obtained. In the case of a low-pressure / high-density plasma source, sufficient anisotropy can be ensured by processing at a low pressure, and the etching rate damaged by the low pressure can be compensated by the high-density plasma. For these reasons, it is considered that low-pressure and high-density plasma are indispensable in recent dry etching methods.

In particular, since the etching of the Al film and the Al alloy film proceeds mainly by a chemical reaction, in order to realize anisotropic etching, a side wall protective film for further preventing side etching of the side wall is required. In general, as a component of the sidewall protective film, a deposition component generated from a mask of a photoresist film during etching is used. However, in the early stage of the etching, the amount of the deposition component generated from the mask is not sufficient, so that a shape abnormality occurs. The mechanism that causes this shape abnormality will be described with reference to the cross-sectional views shown in FIGS.

FIG. 4A shows a thermal oxide film 1 on a silicon substrate.
Is formed to a thickness of 500 nm, and thereafter, the TiN film 2A as a barrier metal is 50 nm, and the Al-Cu film 3 is 50 nm.
A mask is formed by applying and patterning a photoresist film 4 on a film having a laminated structure in which a TiN film 2B as an antireflection film is formed to a thickness of 50 nm by a sputtering method. FIG. 4 (b) shows that the etching starts 1
It represents the cross-sectional shape when 0 to 20 seconds have passed.
At the initial stage of etching, the mask 4 is hardly etched, and the deposition components are weak in the chamber.
A problem occurs such that a notch (locally etched state) 6 is formed at the interface with the l-Cu film 3 or side etching occurs at the initial stage of etching of the Al film and the Al alloy film. FIG. 4C shows a cross-sectional shape after the etching is completed. This shows a state in which a notch or side etching generated in the early stage of etching remains as “constriction”, and a deposition component adheres to that portion later to form a deposition film 5A.

As one means for compensating for such a shortage of the deposition component, there is a method of forming a dummy pattern to increase the area occupied by the photoresist film on the wafer (Japanese Patent Laid-Open No. 63-250823). ). Further, as a means for compensating for the shortage of the deposition component without depending on the wafer, there is a method of adding a deposition gas such as a nitrogen gas or a gas containing a C atom.

[0007]

When the Al film and the Al alloy film are etched without supplementing the deposition components, notch or side etching is performed at the beginning of the etching because the deposition components are weak at the beginning of the etching. Occurs.

As one means for compensating for the shortage of the deposition component, there is a method of forming a dummy pattern to increase the area occupied by the photoresist on the wafer. However, even in this method, the deposition component is weak at the beginning of etching. However, there is a possibility that dimensional control becomes difficult due to generation of unnecessary deposition components in the latter half of the etching. Furthermore, in recent years with high integration, it can be said that it is difficult in design to form useless patterns on a wafer.

As a means for compensating for the shortage of the deposition component without depending on the wafer, there is a method of adding a deposition gas. In this method, in a high-density plasma of a level of 10 ¹² / cm ³ , Deposition components excessively adhere to the upper portion of the mask and the side walls of the wiring and react with each other, causing a problem that dimensional control becomes difficult. In addition, there is also a problem that the film cannot be completely peeled off even when the wet treatment is performed.

An object of the present invention is to provide a dry etching method for an aluminum film or an aluminum alloy film, which can be easily dimensionally controlled and does not cause notch or side etching.

[0011]

To dry-etch an Al film or an Al alloy film using a photoresist film mask, 10 to 20 seconds immediately after the start of the etching, preferably 30% of the total etching time after the start of the etching.
The etching is performed by adding a nitrogen gas or a gas containing C atoms to the reaction gas for a period of time less than or equal to.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIGS. 1A to 1C are cross-sectional views illustrating a first embodiment of the present invention.

First, as shown in FIG. 1A, after a thermal oxide film 1 having a thickness of 500 nm is formed on a silicon substrate, a TiN film serving as a barrier metal is formed to a thickness of 50 nm and a C content of several percent or less.
An Al-Cu film 3 containing u is formed to a thickness of 500 nm, and a TiN film 2B having a thickness of 50 nm is sequentially formed as a reaction preventing film by a sputtering method. Next, a photoresist film 4 is formed on the entire surface and then patterned to form a mask.

Next, as shown in FIG. 1 (b), TiN films 2B and A are formed by adding CF ₄ as a deposition gas to a Cl ₂ / BCl ₃ gas as a reaction (etching) gas.
The l-Cu film 3 is etched for 10 to 20 seconds. Even in the initial stage of etching where the deposition component from the photoresist film 4 is small, the deposition film 5 is formed on the side surfaces of the etched TiN film 2B and Al—Cu film 3 because CF ₄ is added. It is possible to suppress abnormalities in the etching shape due to the shortage of the deposition component as in the conventional example shown in FIG.

Next, as shown in FIG. 1C, about 20 seconds after the start of the etching, the addition of CF ₄ is stopped, and Cl ₂ / BC
completely etched Al-Cu film 3 and a TiN film 2A only l ₃ series gas. Total etching time is 50
~ 60 seconds. In this way, by using the method of adding the deposition gas with the minimum necessary, the problems such as generation of etching residue and inability to remove the photoresist film and the deposition film can be solved.

FIG. 2 shows carbon tetrafluoride (CF ₄ ) as an additive gas.
The table below summarizes the effects of the addition amount and the addition time when using on shape control, residue suppression, and releasability. The etching apparatus used here is a helicon wave plasma etching apparatus, and a schematic diagram is shown in FIG.

In this apparatus, an antenna coil 11 is arranged around a bell jar 10 made of quartz, and generates a plasma by applying a high frequency of 13.56 MHz. Further, a magnetic field coil 12 for controlling the plasma distribution is arranged around the antenna coil. The plasma generated inside the bell jar diffuses into the chamber 13 and reaches the wafer 14 arranged below the bell jar 10. The stage 15 on which the wafer is mounted is configured so that a high frequency of 13.56 MHz can be applied to control the ion energy. The etching gas is Cl ₂ / BCl ₃
A process gas obtained by adding CF ₄ gas to a system gas of 100 sccm was used. The conditions during the process were as follows: a pressure of 10 mTorr, a source power of 1500 W, a bias power of 140 W, a magnetic field coil current IN / OUT = 40 A / 40 A (about 100 G near the antenna coil), The stage temperature was 40 ° C. (the wafer was about 40 ° C.).

As shown in FIG. 2, when CF ₄ is used as an additive gas, the effect is exhibited when the additive amount is 10 sccm or more. The addition time is 10 seconds after the start of etching.
It is necessary to add at least c. However, when the addition time is 25 seconds or more, a residue is generated, and the addition amount is 15 sc.
When the conditions satisfy the condition of not less than 20 cm and the addition time of not less than 20 sec, the photoresist film and the deposition film adhered to the side wall cannot be completely removed even if the wet treatment is performed, so that the film cannot be used as a process. After all, CF ₄
When the gas was used as the additive gas, the process was possible only in the range indicated by the black frame in FIG. 2, and the best shape was obtained with a combination of the addition amount of 10 sccm and the addition time of 10 sec. Note that CHF ₃ or the like can be used as the additional gas.

Next, a second embodiment will be described. In the second embodiment, as in the first embodiment shown in FIG. 1, an Al--Cu film 3 and a T
The iN films 2A and 2B are etched by using nitrogen (N ₂ ) as an additive gas.

FIG. 4 summarizes the effects on the shape control, residue control, and peelability when N ₂ is used as the additive gas. The sample, etching apparatus, and processing conditions used here are the same as in the first embodiment, and only the additive gas is changed to N ₂ . FIG.
According to the results, when N ₂ is used as the additive gas, the effect is exhibited at an addition amount of 10 sccm or more as in the case of the CF ₄ gas. The addition time needs to be 15 seconds or more after the start of etching. However, when the addition time is 25 sec or more, a residue is generated, and the addition amount is 15 cccm or more, and the addition time is 20 cc.
In a combination of more than sec (excluding the addition amount of 15 sccm and the addition time of 20 sec), the peelability is poor and cannot be used as a process. As a result, when N ₂ is used as the additive gas, the process can be performed only in the range indicated by the black frame in FIG.
cm and the addition time of 15 sec, the best shape was obtained.

In this embodiment, Al-C
Although a u-alloy film was used, it has been confirmed that the same effect can be obtained in etching an Al film and an alloy film containing Si and Cu in Al.

[0022]

As described above, according to the present invention, the deposition gas containing nitrogen or C atoms in the reaction gas is etched for 10 to 20 seconds (total etching time of 30 seconds).
%), Abnormal shapes such as notch and side etching due to shortage of the deposition component immediately after the start of etching can be prevented.
In addition, the problem that is likely to be generated by adding a deposition gas, that is, the problem of the generation of etching residue and the inability to peel off is also solved. For this reason, Al film or Al film
The alloy film can be accurately etched.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining a first embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the amount and time of addition of CF ₄ and the result in the first embodiment of the present invention.

FIG. 3 is a table showing the relationship between the added amount of N ₂ , the addition time, and the result in the second embodiment of the present invention.

FIG. 4 is a cross-sectional view for explaining a conventional etching method without adding a deposition gas.

FIG. 5 is a schematic diagram of a plasma processing apparatus used in an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal oxide film 2A, 2B TiN film 3 Al-Cu film 4 Photoresist film 5, 5A Deposition film 6 Notch 10 Bell jar 11 Antenna coil 12 Magnetic field generating coil 13 Chamber 14 Wafer 15 Stage

Claims (2)

[Claims] 1. A method of dry etching an aluminum film or an aluminum alloy film using a mask of a photoresist film, wherein a deposition gas is added to a reaction gas for 10 to 20 seconds after the start of etching. Or, a dry etching method of an aluminum alloy film. 2. The method for dry etching an aluminum film or an aluminum alloy film according to claim 1, wherein the deposition gas is a gas containing N ₂ or C atoms.