JP3008522B2 - Dry etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method applied to the etching of a copper (Cu) -based material layer in the field of manufacturing semiconductor devices and the like, and more particularly to a barrier metal and Cu etching method.
The present invention relates to a method for enabling anisotropic etching of a multilayer film formed by stacking a base material layer.

[0002]

2. Description of the Related Art As semiconductor devices have become more highly integrated and higher in performance as seen in recent VLSIs and ULSIs, the design rules of metal wirings have been reduced to sub-microns and even quarter-microns. I have. Conventionally, metal wiring in a semiconductor device is made of aluminum (A).
l) The mainstream is based on system materials. However, in the case of Al-based metal wiring, if the design rule becomes finer than 0.5 μm, the reliability of the wiring deteriorates due to electromigration and the like, and the aspect ratio becomes as large as 1-2 because the resistance value must be kept low. This makes it difficult to perform a series of subsequent processes such as formation of an insulating film and planarization. From such a background, formation of wiring using a Cu-based metal material has attracted attention. Cu has a high electromigration resistance and a low electrical resistivity of about 1.4 μΩcm, which is only about half that of Al. Therefore, it is possible to reduce the thickness of the metal wiring layer without impairing reliability, and the aspect ratio is reduced.

However, the possibility of etching a Cu-Cu-based material layer is still being explored at the research level, and there are many technical issues to be solved before practical application is aimed at. For example, Cu is unlikely to be etched by a halogen-based gas unlike other wiring materials such as an Al-based material and a high-melting-point metal material. This is because the vapor pressure of the reaction product copper halide at around room temperature is extremely low. For example, CuCl and CuCl ₂ have a melting point of 430 ° C. and 620 ° C., respectively, and rapid volatilization and removal of reaction products cannot be expected unless the substrate to be etched (wafer) is heated to a high temperature to increase the vapor pressure.

[0004] Conventionally, in an etching process for removing Cu in the form of chloride, the temperature of the wafer is about 2 ° C.
It is set at 00 to 400 ° C. For example, the Japanese Journal of Applied Physics (Japanese Journal of Applied Physics)
ed Physics) Vol. 28 No. 6 L1070-L1
In the technique reported on page 072 (1989), reactive ion etching of a Cu thin film is performed by a mixed gas of SiCl ₄ and N ₂ while heating a wafer to around 250 ° C.

Since Cu causes an alloying reaction with silicon (Si) -based materials such as single crystal silicon and polycrystalline silicon, it is used as a multilayer film structure laminated with a barrier metal at the practical level, similarly to the case of Al wiring. It is thought that it is done. The barrier metal is usually formed of a transition metal or a transition metal compound such as a nitride, carbide, oxynitride or boride thereof, as well as a refractory metal silicide, an alloy or the like. Further, the structure is not limited to a single layer, and a plurality of types of films are often combined.

For example, a barrier metal (Ti / TiN-based) having a two-layer structure in which a Ti layer and a TiN layer are sequentially stacked from the substrate side to the metal wiring layer side is a typical example.
Since the Ti layer has a high affinity for oxygen, it has a function of reducing a natural oxide film formed on the surface of the impurity diffusion layer, and is an excellent contact material from the viewpoint of stably achieving a low-resistance ohmic contact. It is. But,
Alone does not have sufficient barrier properties. On the other hand, the TiN layer is thermodynamically stable with respect to Si and has a higher barrier property than the Ti layer. However, in particular, the contact resistance with respect to p-type Si is high. Have difficulty. Therefore, a Ti layer and a TiN layer are sequentially laminated to take advantage of both layers.

In recent years, as a measure for further improving the barrier properties of the TiN layer, a TiON layer in which oxygen is segregated at the grain boundaries of the TiN layer by introducing oxygen during the formation of the TiN layer is also known. Proposed. this is,
This is a method of suppressing the grain boundary diffusion of the metal wiring material by inactivating the grain boundaries that serve as fast diffusion paths.

[0008]

The etching of the Cu-based material layer needs to be performed while heating the wafer as described above.
In the case where the barrier metal is laminated on an N-based barrier metal, if the barrier metal is etched under the same heating condition, a problem occurs that the barrier metal is undercut. Therefore, in order to etch such a multilayer film with high anisotropy, it is necessary to add some improvement to the conventional dry etching method. Therefore, the present invention
An object is to achieve high anisotropy in dry etching of a multilayer film in which a barrier metal and a Cu-based material layer are laminated.

[0009]

SUMMARY OF THE INVENTION A dry etching method according to the present invention is proposed to achieve the above-mentioned object, and is a multilayer film comprising a substrate and a barrier metal and a Cu-based material layer sequentially laminated. A method of etching
The heating temperature of the substrate during the etching of the barrier metal is set lower than the heating temperature of the substrate during the etching of the Cu-based material layer.

[0010]

The present inventor has studied to achieve the above-mentioned object, and as a result, has noticed that the vapor pressure of the reaction product is greatly different in the etching process of the Cu-based material layer and the barrier metal. For example, when a chlorine-based gas is used as an etching gas, the reaction product, TiCl ₄ , has a low boiling point of 136 ° C.
_It is much higher than the boiling point of ₄ . Therefore, if the barrier metal is etched while maintaining the substrate heating temperature required for volatilizing copper chloride, the vapor pressure of TiCl ₄ becomes too large, and the barrier metal etching reaction is excessively promoted, resulting in undercut. is there. Therefore, in the present invention, based on the above-described findings, the heating temperature of the substrate is reduced during the etching of the barrier metal as compared with the etching of the Cu-based material layer. That is, the etching process of the multilayer film is performed in two steps.
The anisotropic processing can be realized by heating the substrate at a temperature corresponding to the vapor pressure of the reaction product that can be generated from each of the material layers, divided into stages.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. First, before starting the description of the etching process, a configuration example of an etching apparatus used in the present invention will be described with reference to FIG.

This etching apparatus comprises a first etching chamber 11 for etching a Cu-based material layer at a relatively high substrate heating temperature and a second etching chamber for etching a barrier metal at a relatively low substrate heating temperature. The etching chamber 21 is connected via a second gate valve 34 so that the substrate to be etched (wafer) 19 is vacuum-transported between the two chambers 11 and 21.

The first etching chamber 11 includes:
It is based on the structure of parallel plate type RIE (reactive ion etching), and applies an RF electric field between the upper electrode 12 and the first wafer mounting electrode 13 which are arranged to face each other.
A predetermined process is performed on the wafer 19 using the plasma generated by the discharge. This ceiling portion of the first etch chamber 11, a gas supply pipe 15 for supplying the gas required for the processing from the arrow in the drawing B ₁ direction is opened. Also, the first etching
The bottom of the chamber 11, an exhaust port 16 for exhausting the gas in the system in FIG arrow A ₁ direction in order to remove the reaction products and particles and the like generated due to processing are opened. The first wafer mounting electrode 13 is provided with a heater 14.
Is built in, and the wafer 19 placed thereon can be heated. Further, the first wafer mounting electrode 13 is provided with a blocking device for blocking a DC component.
An RF power supply 18 is connected via a capacitor 17, and has a cathode coupling type configuration.

On the other hand, the first etching chamber 1
The second etching chamber 21, which is connected to the first through a second gate valve 34, is also based on a parallel plate type RIE (reactive ion etching), and has an upper part inside. The electrode 22 and the second wafer mounting electrode 23 are arranged to face each other. This ceiling portion of the second etching chamber 21, a gas supply pipe 25 for supplying the gas required for the process from FIG arrow B ₂ direction are opened. Further, on the bottom surface of the second etching chamber 21, an exhaust port 26 for exhausting the gas in the system in FIG arrow A ₂ direction is opened. Above the second wafer setting electrode 23 are self-contained cooling water pipe 24, by circulating cooling water C _1, C ₂ direction in FIG from temperature controller (not shown) or the like is placed thereon Wafer 19 can be cooled. The second wafer mounting electrode 23
Is connected to an RF power supply 28 via a blocking capacitor 27 for blocking a DC component, and has a cathode coupling type configuration.

In front of the first etching chamber 11, a load cassette 32 for collectively storing a plurality of wafers 19 and a load chamber 31 provided with a wafer transfer mechanism (not shown) are provided with a first gate valve. 33. Further, the second etching chamber 2
After the first gate valve 3, an unloading cassette 37 for collectively storing a plurality of wafers 19 and an unloading chamber 36 having a wafer transfer mechanism (not shown) are provided.
5 are connected. According to such a device configuration,
The wafer 19 is loaded from the load chamber 31 into the first etching chamber 11 to perform a high-temperature process, and then loaded into the second etching chamber to perform a low-temperature process.
A series of operations of unloading the wafer 19 to the unload chamber 36 can be performed continuously without exposing the wafer 19 to the atmosphere in the middle. In the following embodiments, an example of an actual process using the above etching apparatus will be described.

Embodiment 1 In this embodiment, a Cu layer etching step and a Ti / TiON
In this example, the etching gas used in the step of etching the barrier metal having a two-layer structure is a mixed gas of BCl ₃ / Cl _2, and the heating temperature of the substrate is lowered in the latter step. This process will be described with reference to FIGS.

First, as shown in FIG. 1A, a Ti layer 2 having a thickness of about 300.degree.
Forming a barrier metal 4 by successively laminating 0 ° TiON layers 3 and subsequently forming a Cu layer 5 to a thickness of about 4000 °;
Further, a heat-resistant etching mask 6 was selectively formed. Here, the etching mask 6 is formed by patterning a SiN film formed by a plasma CVD method with a CF ₄ / O ₂ -based mixed gas through a resist mask, but is formed by CVD, SOG coating or the like. Alternatively, a silicon oxide-based mask may be used.

Next, the above substrate is set as a wafer 19 on the first wafer mounting electrode 13 in the first etching chamber 11, and the wafer 1 is
9 was heated to about 300 ° C. In this state, as an example, B
Cu under the conditions of a Cl ₃ flow rate of 20 SCCM, a Cl ₂ flow rate of 30 SCCM, a gas pressure of 6.7 Pa (50 mTorr), and an RF power density of 0.45 W / cm ² (13.56 MHz).
Layer 5 was etched. Under this condition, CuCl _x is generated on the surface of the Cu layer 5, and this is Cl ⁺ , Cl
Etching proceeded in a form sputtered by ions such as ₂ ⁺ , B ⁺ , and BCl _x ⁺ . BCl ₃ added to the etching gas has a reducing property,
It has the function of reducing the natural oxide film formed on the surface of the layer 5 to pure Cu and promptly progressing the etching. As a result, as shown in FIG. 1B, a Cu electrode layer 5a having an anisotropic shape was formed.

Here, the above-mentioned etching needs to be completed when the underlying TiON layer 3 starts to be exposed on at least a part of the wafer 19 surface. The end point determination in this case is performed, for example, according to the method proposed by the present inventor in the specification of Japanese Patent Application No. 2-415023.
The positions of six peaks that can be observed relatively easily in the molecular spectrum of 1 are: 526 nm, 488 nm, 48
Judgment was made when the emission intensity started to decrease at 5 nm, 435 nm, 433 nm, and 402 nm.
Alternatively, the end point can be determined based on the point in time when the peak intensity derived from the emission of titanium chloride starts to increase.
This method is also disclosed in Japanese Patent Application No. Hei.
No. 96, the wavelength range where the peak appears is 410 to 420 nm.

Next, the wafer 19 is transported to the second etching chamber 21 via the second gate valve 34 and set on the second wafer mounting electrode 23, and the temperature of the wafer 19 is adjusted to the cooling water pipe 24. The wafer 19 was cooled to about 40 ° C. by circulating water. Other than the wafer temperature, the above-mentioned Cu layer 5
The etching of the barrier metal 4 was performed under the same conditions as those used in the etching. Under this condition, the TiON layer 3 or T
TiCl _x generated on the surface of the i-layer 2 becomes Cl ⁺ , C
Etching proceeded in the form of being sputtered by ions such as l ₂ ⁺ , B ⁺ , and BCl _x ⁺ . As a result, FIG.
As shown in (c), both layers 2 and 3 become Ti pattern 2a and TiON pattern 3a having good anisotropic shapes, respectively, and barrier metal pattern 4a is formed without causing abnormal shapes such as undercut. Was.

Embodiment 2 In this embodiment, the etching of the Cu layer is performed using NO ₂ gas and the etching of the barrier metal is performed using BCl ₃ / Cl ₂ mixed gas, and the heating temperature of the substrate is reduced in the latter step. It is. The wafer used as the etching sample is the same as that used in Example 1.

First, the wafer 19 shown in FIG. 1A is set on the first wafer mounting electrode 13 in the first etching chamber 11, and the wafer 19 is Heated to about 150 ° C. In this state, as an example, the NO ₂ flow rate is 50 SCCM, and the gas pressure is 6.7 Pa.
(50 mTorr), RF power density 0.45 W / cm
The etching of the Cu layer 5 was performed under the condition of ² (13.56 MHz). The etching of the Cu-based material layer using NO ₂ was previously proposed by the present inventor in Japanese Patent Application No. 2-97245.
Even at 0 ° C. or lower, Cu can be efficiently sublimated and removed in the form of copper nitrate Cu (NO ₃ ) ₂ . In this method, since there is no halogen-based active species, a large selectivity can be obtained with respect to a mask pattern or an interlayer insulating film as a base. In addition, since a wafer is heated at a relatively low temperature, generation of copper oxide is also reduced. There is an advantage that it becomes less. As a result of this etching, a Cu electrode layer 5a having an anisotropic shape was formed as shown in FIG. Since NO ₂ hardly etches the barrier metal 4, TiON
The etching was completed when the surface of the layer 3 was exposed.

Next, the wafer 19 is conveyed to the second etching chamber 21 via the second gate valve 34, set on the second wafer mounting electrode 23, and temperature-controlled to the cooling water pipe 24. The wafer 19 was cooled to about 40 ° C. by circulating water. In this state, as an example, BCl ₃
Flow rate 20 SCCM, Cl ₂ flow rate 30 SCCM, gas pressure 4
Pa (30 mTorr), RF power density 0.45 W /
The barrier metal 4 was etched under the condition of cm ² . As a result, as shown in FIG. 1 (c), the barrier metal pattern 4a was formed without any shape abnormality such as undercut.

Although the present invention has been described based on two embodiments, the present invention is not limited to the above-described embodiments. For example, as an etching gas for etching the Cu layer 5, the BC gas described in the first embodiment is used.
l ₃ / Cl ₂ mixed gas, Cl ₂ / HCl based, Cl
A conventionally known chlorine-based mixed gas such as a ₂ / HCl / BCl ₃ -based gas can be used. In addition, N described in the second embodiment
In addition to O ₂ , nitric oxide gas such as NO, N ₂ O, N ₂ O ₃ ,
An N ₂ / O ₂ -based mixed gas, a nitrogen-based mixed gas obtained by further adding a fluorine-based gas to a nitrogen oxide or an N ₂ / O ₂ -based mixed gas, or the like can be used. Further, a rare gas such as He or Ar may be appropriately added to the chlorine-based gas or the nitrogen-based gas in order to impart a dilution effect, a sputtering effect, a cooling effect, and the like. On the other hand, as an etching gas for etching the barrier metal 4, similarly to the etching of the Cu layer 5, in addition to the BCl ₃ / Cl ₂ -based mixed gas described in each embodiment, a Cl ₂ / HCl-based, Cl ₂ / HCl-based gas is used. / BC
A chlorine-based gas such as l ₃ -based or SiCl ₄ can be used. Further, TiF can be used CF _4, SF _6, fluorine gas NF _3, etc. Also, in this case to produce _x
Since the vapor pressure of is low, if O ₂ is added to the etching gas to remove sublimation of Ti in the form of oxyfluoride (TiF _x O _y ), the etching rate can be greatly improved.

[0025]

As is clear from the above description, according to the present invention, in the etching of a multilayer film in which a barrier metal and a Cu-based material layer are laminated, the wafer heating temperature is lowered during the etching of the barrier metal. In addition, it is possible to perform favorable anisotropic processing without causing a shape abnormality such as undercut in the barrier metal. Therefore, the present invention is extremely effective for manufacturing a semiconductor device that requires high integration and high performance based on a fine design rule.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing one embodiment of a dry etching method according to the present invention in the order of steps, (a) is a state of a wafer before etching, and (b) is a state in which etching of a Cu layer is completed and Cu is etched. (C) shows a state in which the electrode layer is formed, and (c) shows a state in which the etching of the barrier metal is completed.

FIG. 2 is a schematic cross-sectional view showing one configuration example of an etching apparatus used to carry out the dry etching method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Interlayer insulating film 2 ... Ti layer 3 ... TiON layer 4 ... Barrier metal 5 ... Cu layer 5a ... Cu electrode layer 6 ... Etching mask 11 ... First Etching chamber 13 ... First wafer mounting electrode 14 ... Heater 19 ... Wafer 21 ... Second etching chamber 23 ... Second wafer mounting electrode 24 ... Cooling water pipe 34 ... second gate valve

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065

Claims (1)

(57) [Claims] 1. A dry etching method for etching a multilayer film in which a barrier metal and a copper-based material layer are sequentially laminated on a substrate, wherein the heating temperature of the substrate during the etching of the barrier metal is set to A dry etching method, wherein the heating temperature is set lower than the heating temperature of the substrate during etching.