JP3887123B2 - Dry etching method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dry etching method for forming a connection metal in a wiring groove or a connection hole formed in an interlayer insulating film on a semiconductor substrate.
[0002]
[Prior art]
Conventionally, in the manufacture of a semiconductor device, a wiring groove is formed in an interlayer insulating film on a semiconductor substrate and a connecting metal is embedded in the wiring groove, and a conductive layer such as a resistance layer or a lower layer wiring on the semiconductor substrate. When a connection metal is embedded in the connection hole of the interlayer insulating film reaching the thickness, the following steps are performed.
[0003]
First, an interlayer insulating film made of a silicon oxide film or the like is formed on a semiconductor substrate. Next, the interlayer insulating film is etched by dry etching or the like using a mask such as a photoresist having a predetermined pattern, thereby forming a wiring groove or a connection hole reaching the conductive layer.
[0004]
After that, by a film forming method such as sputtering, a composite film of a titanium film and a titanium compound film or a titanium compound film is formed in the wiring trench and on the interlayer insulating film, or in the connection hole and on the interlayer insulating film. A barrier metal film is formed. Next, a tungsten film is formed on the barrier metal film by chemical vapor deposition (CVD) or the like, and the inside of the wiring trench or the connection hole is filled with the tungsten film.
[0005]
Next, by leaving the tungsten film and the barrier metal film inside the wiring trench or the connection hole, and removing the tungsten film and the barrier metal film in other portions, the connecting metal composed of the tungsten film and the barrier metal film is removed. Further, it can be embedded in the wiring groove or the connection hole.
[0006]
Here, in the process of removing the tungsten film and the barrier metal film, generally, first, the tungsten film other than the inside of the wiring trench or the connection hole is removed by a chemical dry etching (CDE) method, and then the chemical mechanical A two-stage method is employed in which the barrier metal film on the interlayer insulating film is removed by a polishing (CMP) method. Further, a reactive ion etching (RIE) method may be used instead of the CDE method.
[0007]
[Problems to be solved by the invention]
However, in the CMP method used in the above-described conventional technology, the interlayer insulating film may be scratched called scratch. In addition, when the RIE method is used, charged particles generated in the plasma are accelerated by self-bias and are incident on the etching target film, so that contamination due to ion implantation or damage due to disorder of the crystal occurs in the base of the etching target film. There was a problem.
[0008]
In the conventional technique, the barrier metal film remains after the etching in any case, whether the CDE method or the RIE method is used. Therefore, the process of removing the remaining barrier metal film by the CMP method or the like is performed. Otherwise, the connecting metal embedding process could not be completed.
[0009]
The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a dry etching method capable of completing a connection metal embedding process by dry etching without using a CMP method. And
[0010]
[Means for Solving the Problems]
The present invention provides a dry etching method for forming a connection metal inside a wiring groove or a connection hole formed in an interlayer insulating film on a semiconductor substrate, wherein the upper surface of the interlayer insulating film and the wiring groove or the connection hole are formed. At least a gas containing fluorine atoms and an oxygen gas are provided on the surface of an object having a titanium-based barrier metal film formed on the inner surface and a tungsten-based metal film formed on the titanium-based barrier metal film. A metal film removing step of activating and supplying a process gas containing and selectively removing the tungsten-based metal film in a portion other than the inside of the wiring groove or connection hole with respect to the titanium-based barrier metal film; And a process gas including at least a gas containing fluorine atoms, a gas containing chlorine atoms, and an oxygen gas on the surface of the object to be processed after the metal film removal step. And removing the titanium-based barrier metal film remaining after the metal film removal step by selectively etching the titanium-based barrier metal film remaining in the wiring groove or the connection hole. In the barrier metal film removing step, the temperature of the object to be processed is maintained at 70 to 130 ° C. and the chlorine atoms with respect to the total flow rate of the gas containing fluorine atoms and the oxygen gas are changed. The titanium-based barrier metal film is selectively etched by setting the flow rate ratio of the contained gas to 12% or more .
[0011]
Further, in the above metal film removing step, the temperature of the object to be treated can be held in 5 to 50 ° C. performing selective etching of the tungsten-based metal film.
[0012]
In the metal film removal step and the barrier metal film removal step, the tungsten-based metal film and the titanium-based barrier metal film may be removed by chemical dry etching using a discharge separation type chemical dry etching apparatus. it can.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a dry etching method according to an embodiment of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 is a schematic cross-sectional view of a discharge separation type chemical dry etching apparatus (hereinafter referred to as “CDE apparatus”) used when performing the dry etching method according to the present embodiment. In this CDE apparatus, an object to be processed 3 such as a silicon wafer is etched in an etching chamber 2 in a vacuum vessel 1 under a reduced pressure atmosphere. The etching chamber 2 is provided with a mounting table 4 on which the workpiece 3 is mounted. The mounting table 4 has a temperature adjustment mechanism (not shown) having a heat source such as an electric heater or an induction heating device. The temperature of the workpiece 3 placed thereon can be controlled.
[0015]
One end of the active species transport tube 5 is connected to the top wall of the vacuum vessel 1, and one end of the discharge tube 6 is connected to the other end. The other end of the discharge tube 6 forms a gas introduction port 7, and a process gas (reaction gas) is introduced from the gas introduction port 7. A microwave waveguide 8 is connected to the discharge tube 6, and a microwave guided through the microwave waveguide 8 is applied to the process gas introduced into the discharge tube 6 from the gas inlet 7. Plasma is generated in the discharge tube 6.
[0016]
The process gas is activated by the plasma in the discharge tube 6 to generate active species (radicals). The active species are guided into the etching chamber 2 through the active species transport tube 5, and the surface of the workpiece 3 is processed. The surface of the workpiece 3 is etched by the active species that has reached The process gas and reaction product gas used for etching the workpiece 3 are exhausted to the outside of the etching chamber 2 through the exhaust port 9.
[0017]
FIG. 2 is a partial vertical cross-sectional view showing the workpiece 3 processed by the dry etching method according to the present embodiment. In the description of the present embodiment, a connection hole (also referred to as a via hole or a contact hole) is illustrated, but the structure of the connection metal is the same for the wiring groove, and the dry etching method according to the present embodiment is similarly performed. Can be applied.
[0018]
As shown in FIG. 2, in the object 3 to be processed, an insulating film 102 is formed on a silicon semiconductor substrate 100, and a lower layer wiring 101 is formed through the insulating film 102. A silicon oxide film (SiO ₂ ) 10 that is an interlayer insulating film is formed on the lower layer wiring 101. A connection hole 14 is formed in the silicon oxide film 10, and the lower layer wiring 101 is exposed at the bottom of the connection hole 14. The connection hole 14 is formed by coating the silicon oxide film 10 with a photoresist, patterning it, forming a mask, and dry etching using this mask.
[0019]
A titanium (Ti) film 11 and a titanium nitride (TiN) film 12 are sequentially formed on the upper surface of the silicon oxide film 10 and the inner surface of the connection hole 14 by a sputtering method or a CVD method to form a titanium-based barrier metal film 15. Yes. Further, a tungsten (W) film 13 which is a tungsten-based metal film is formed thereon by using the CVD method. The tungsten film 13 fills the inside of the connection hole 14 and a part other than the connection hole 14. The surface of the titanium nitride film 12 is also covered.
[0020]
FIG. 3 is a characteristic diagram showing the temperature dependence of the etching rate (etching rate) of the tungsten film and the titanium nitride film constituting the connecting metal. The vertical axis represents the etching rate (nm / min) for the tungsten film and the titanium nitride film, and the horizontal axis represents the temperature (1000 / T (= K), C (° C.) = (1000 / K) −273. 16).
[0021]
As can be seen from FIG. 3, the etching rate of the tungsten film increases linearly up to 100 ° C., but since the rate-limiting reaction is performed at 100 ° C. or higher, the etching rate of the tungsten film is constant. On the other hand, the etching rate of the titanium nitride film is substantially the same as the etching rate of the tungsten film in the temperature range of 70 ° C. or higher. Therefore, by setting the temperature of the mounting table 4 to 70 ° C. or less, preferably 50 ° C. or less, the tungsten film can be selectively removed by etching with respect to the titanium nitride film.
[0022]
FIG. 4 is a characteristic diagram showing the chlorine gas flow rate dependency of the etching rate (etch rate) of the tungsten film, titanium nitride film, and titanium film. The vertical axis represents the etching rate (nm / min), and the horizontal axis represents the ratio of the flow rate of chlorine gas (Cl ₂ ) to the combined flow rate of oxygen gas (O ₂ ) and CF ₄ (reaction rate of chlorine gas). Is shown.
[0023]
As can be seen from FIG. 4, the etching rate of the tungsten film rapidly decreases as the chlorine flow ratio increases. On the other hand, for a titanium-based barrier metal such as a titanium nitride film or a titanium film, the etching rate does not change much even if the proportion of chlorine gas increases. In particular, in the region where the chlorine flow ratio is 12% or more, the etching rate difference (selectivity) between the tungsten film and the titanium-based barrier metal film is large, and the selectivity ratio of the titanium-based barrier metal film to the tungsten film is sufficiently large. Can be secured.
[0024]
In the dry etching method according to the present embodiment, the metal film removal step and the barrier metal film removal step are performed on the workpiece 3 shown in FIG. 2 under the following conditions.
[0025]
First, in the metal film removal step, a mixed gas of CF ₄ gas and O ₂ gas is used as a process gas (reactive gas). The total flow rate of the mixed gas is 250 sccm, the microwave power is 700 W, and the pressure is 30 Pa. Under these conditions, the temperature (substrate temperature) of the mounting table 4 on which the workpiece 3 is mounted is controlled to 5 to 50 ° C. Under such conditions, the tungsten film 13 is selectively etched with respect to the titanium nitride film 12 because the etching rate of the titanium nitride film 12 (titanium-based barrier metal) is sufficiently low as can be seen from FIG.
[0026]
In place of CF ₄ gas, C ₂ F ₆ , C ₃ F ₈ , NF ₃ , C ₅ F ₈ or SF ₆ can be used.
[0027]
It is also possible to add Cl ₂ into the process gas.
[0028]
FIG. 5A shows a state after the metal film removal step, that is, a state after the tungsten film 13 is selectively etched and removed. As can be seen from FIG. 5A, the tungsten film 13 is etched back, but the titanium-based barrier metal film 15 remains without being etched.
[0029]
Next, in the barrier metal film removing step, the total flow rate of the mixed gas of CF ₄ gas, O ₂ gas, and Cl ₂ gas is set to 500 sccm, the microwave power is set to 700 W, and the pressure is set to 50 Pa. Is controlled at 70 to 130 ° C., and the ratio of the flow rate of Cl ₂ gas to the total flow rate of CF ₄ gas and O ₂ gas is 12% or more. To do.
[0030]
Under such conditions, the etching rate of the tungsten film 13 decreases as can be seen from FIG. 4, so that the titanium-based barrier metal film 15 composed of the titanium nitride film 12 and the titanium film 11 is selective to the tungsten film 13. Can be etched. At this time, C ₂ F ₆ , C ₃ F ₈ , NF ₃ , C ₅ F ₈ or SF ₆ can be used in place of the CF ₄ gas.
[0031]
FIG. 5B shows a state after the barrier metal film removing step, that is, a state where the titanium-based barrier metal film 15 is selectively etched and removed. As can be seen from FIG. 5B, the titanium-based barrier metal film 15 is etched back, and the flat connection metal made of the tungsten film 13, the titanium nitride film 12, and the titanium film 11 is well embedded in the connection hole 14. It is.
[0032]
In the post-process, the object to be processed 3 thus processed is formed with a wiring on the silicon oxide film 10, and this wiring is connected to the connecting metal in the connection hole 14 so that the wiring and the lower layer wiring 101 are connected. The semiconductor device is formed by electrical connection and further post-processing.
[0033]
FIG. 6 shows a vapor pressure curve of a reaction product generated when the tungsten film is etched. With reference to FIG. 6, the method for selectively etching away the titanium-based barrier metal film 15 in the dry etching method according to the present embodiment will be further described.
[0034]
In the discharge separation type chemical dry etching method used in the present embodiment, the fluorine film obtained by discharging a mixed gas of CF ₄ gas, O ₂ gas and Cl ₂ gas causes the titanium film 11 and the titanium nitride film 12 to be removed. The titanium-based barrier metal film 15 and the tungsten film 13 are removed by etching. When the titanium-based barrier metal film 15 is removed by etching, the temperature (substrate temperature) of the mounting table 4 is set to 70 to 130 ° C. as described above. To do. Further, in order to selectively etch the titanium-based barrier metal film 15, a Cl ₂ gas is added and the flow rate ratio is set to a predetermined value (12%) or more.
[0035]
When Cl ₂ gas is added, as shown in FIG. 6, W + 6Cl → WCl ₆ reaction occurs on the surface of the tungsten film 13, and WCl ₆ has a sufficiently lower vapor pressure than WF _6. The reaction is less likely to occur. That is, by adding Cl ₂ gas, the titanium-based barrier metal film 15 can be selectively removed by etching with respect to the tungsten film 13.
[0036]
As described above, according to the dry etching method according to the present embodiment, the tungsten film 13 is selectively etched by controlling the workpiece 3 at a relatively low temperature, and then the workpiece 3 is controlled at a relatively high temperature. In addition, since the titanium-based barrier metal film 15 is selectively etched by adding a Cl ₂ gas having a flow rate ratio or higher, a flat connection metal is embedded in the wiring groove or the connection hole 14. Can do.
[0037]
【The invention's effect】
As described above, according to the dry etching method of the present invention, after removing the tungsten-based metal film formed on the titanium-based barrier metal film by selectively etching the titanium-based barrier metal film, The remaining titanium-based barrier metal film is selectively removed by etching with respect to the tungsten-based metal film remaining inside the wiring trench or connection hole, so that the titanium-based barrier metal by the conventional CMP method is removed. The removal of the film is unnecessary, and the connecting metal embedding step can be completed by dry etching.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a schematic configuration of a discharge separation type chemical dry etching apparatus used in a dry etching method according to an embodiment of the present invention.
FIG. 2 is a partial longitudinal sectional view of an object to be processed which is processed by a dry etching method according to an embodiment of the present invention.
FIG. 3 is a characteristic diagram showing the temperature dependence of the etching rate of a tungsten film and a titanium nitride film constituting the connecting metal.
FIG. 4 is a characteristic diagram showing the chlorine gas flow rate dependence of the etching rate of a tungsten film, a titanium nitride film, and a titanium film.
FIGS. 5A and 5B are partial vertical sectional views showing an object to be processed which is processed by a dry etching method according to an embodiment of the present invention, in which FIG. 5A shows a state after a metal film removing step, and FIG. The state after a metal film removal process is shown.
FIG. 6 is a graph showing a vapor pressure curve of a reaction product generated when a tungsten film is etched.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Etching chamber 3 To-be-processed object 4 Mounting stand 5 Active species transport tube 6 Discharge tube 7 Gas inlet 8 Microwave waveguide 10 Silicon oxide film (interlayer insulation film)
11 Titanium film 12 Titanium nitride film 13 Tungsten film (tungsten metal film)
14 Connection hole 15 Titanium-based barrier metal film 100 Silicon semiconductor substrate 101 Lower layer wiring 102 Insulating film

Claims (3)

In a dry etching method for forming a connection metal inside a wiring groove or connection hole formed in an interlayer insulating film on a semiconductor substrate,
A titanium-based barrier metal film formed on the upper surface of the interlayer insulating film and the inner surface of the wiring groove or connection hole, and a tungsten-based metal film formed on the titanium-based barrier metal film. A process gas including at least a gas containing fluorine atoms and an oxygen gas is activated and supplied to the surface, and the tungsten-based metal film in a portion other than the inside of the wiring groove or connection hole is used as the titanium-based barrier metal film. In contrast, a metal film removing step of selectively etching and removing,
A process gas containing at least a gas containing fluorine atoms, a gas containing chlorine atoms, and an oxygen gas is activated and supplied to the surface of the workpiece after the metal film removal step, and remains after the metal film removal step. A barrier metal film removing step of selectively etching and removing the titanium-based barrier metal film with respect to the tungsten-based metal film remaining inside the wiring groove or connection hole ,
In the barrier metal film removing step, the ratio of the flow rate of the gas containing chlorine atoms to the total flow rate of the gas containing fluorine atoms and the oxygen gas is maintained while maintaining the temperature of the object to be processed at 70 to 130 ° C. A dry etching method , wherein the titanium-based barrier metal film is selectively etched at 12% or more . Wherein in the metal film removing step, said dry etching method according to claim 1, wherein the TURMERIC row selective etching of the tungsten-based metal film by keeping the temperature at 5 to 50 ° C. of the object. In the metal film removing step and the barrier metal film removing step, the tungsten-based metal film and the titanium-based barrier metal film are removed by chemical dry etching using a discharge-separated chemical dry etching apparatus. The dry etching method according to claim 1 or 2.

Images