JP3755539B2 - Method for forming copper film - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for forming a copper film and a method for manufacturing a semiconductor device, and more particularly, to a method for forming a copper film using chemical vapor deposition and a semiconductor device for forming a copper wiring layer on a substrate having a step. It relates to a manufacturing method.
[0002]
[Prior art]
Conventionally, Al films have been frequently used as an easy-to-handle and popular wiring material. However, in the present situation where the wiring layer is miniaturized as the density of the semiconductor device is increased, it is expected that a decrease in reliability such as disconnection due to electromigration will be a problem.
[0003]
Copper wiring has advantages such as resistance to electromigration and low resistance over conventional Al wiring, and is expected to be applied to high-density semiconductor devices. Furthermore, in order to cope with an increase in the aspect ratio of contact holes and the like accompanying the increase in density, a process for forming a copper thin film by a chemical vapor deposition method having a high step coverage has been developed.
[0004]
In copper thin film formation technology by chemical vapor deposition, copper organic complexes that are solid at room temperature, for example, Cu (HFA) ₂ have been used as the source gas for copper. Organic complexes such as Cu (HFA) tmvs are used. HFA represents hexafluoroacetylacetone, and tmvs represents trimethylvinylsilyl.
[0005]
For example, the case where the upper wiring layer connected to the lower wiring layer through the opening of the interlayer insulating film on the lower wiring layer is formed will be described with reference to FIGS.
First, as shown in FIG. 5A, an interlayer insulating film 4 is formed by covering a lower wiring layer 3 on a base insulating film 2 formed on a semiconductor substrate 1, and then patterned to form a lower portion. An opening 5 of the interlayer insulating film 4 is formed on the wiring layer 3.
[0006]
Next, after placing the semiconductor substrate 1 on the substrate holder 8 incorporating the heater, the semiconductor substrate 1 is heated and held at a predetermined temperature.
Next, a copper film 6b is formed to cover the opening 5 by a chemical vapor deposition method using liquid Cu (HFA) tmvs. FIG. 5B shows the state of formation of the copper film 6a during film formation, and FIG. 5C shows the state of the copper film 6b after film formation.
[0007]
Thereafter, the upper wiring layer connected to the lower wiring layer 3 is formed by patterning the copper film 6b.
[0008]
[Problems to be solved by the invention]
However, if the flow rate of the source gas is increased and the deposition temperature is increased in order to increase the deposition rate, the source gas particles hardly reach the bottom of the opening 5 as shown in FIG. The upper part of the opening 5 is formed earlier than the bottom part, and constriction occurs. When the film is further thickened, a void 7 is generated inside the opening 5 as shown in FIG.
[0009]
For this reason, there is a problem that the step coverage of the formed copper films 6a and 6b is reduced, the resistance of the wiring is increased, and in the worst case, the wiring is cut.
The present invention was created in view of the problems of the conventional example, and is a method for forming a copper film and a method for manufacturing a semiconductor device capable of improving a film formation rate and ensuring a high step coverage. Is intended to provide.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, the present invention is a method of forming a copper film as an upper wiring layer electrically connected to a lower wiring layer through a contact window patterned and opened in an insulating film on a lower wiring on a substrate. A hydrogen gas is introduced into the plasma generation chamber to form a hydrogen plasma, and the hydrogen radicals remaining after removing ions from the hydrogen plasma through a grounded mesh electrode are activated by contacting the source gas with the hydrogen radicals, and The contact window is formed by metallic copper generated by heating the substrate so that the source gas causes a reaction based on a surface reaction rate to cause a thermal decomposition reaction of the source gas on the substrate and further reacting with hydrogen radicals. A copper film forming method for forming a copper film so as to extend from the inside to the insulating film, wherein the source gas has a chemical structural formula Cu (HFA) tmvs (HFA is Indicates safluoroacetylacetone (hereinafter the same), tmvs indicates trimethylvinylsilyl), Cu (HFA) COD (COD indicates cyclooctadienyl), Cu (HFA) 2-butyne and Cu (HFA) BTMSE (BTMSE Represents the bistrimethylsilylethylene), and the heating temperature is 180 ° C. or lower when the source gas is represented by the chemical structural formula Cu (HFA) tmvs, When it is represented by the chemical structural formula Cu (HFA) COD, it is 200 ° C. or less, and when it is represented by the chemical structural formula Cu (HFA) 2-butyne, it is 220 ° C. or less. When it is represented by the chemical structural formula Cu (HFA) BTMSE, it is characterized by being 190 ° C. or lower.
[0011]
[Action]
FIG. 3 is a characteristic diagram showing thermal decomposition characteristics of Cu (HFA) tmvs of the organic complex. The vertical axis represents the vapor pressure (mTorr), and the horizontal axis represents the temperature (° C.) applied to the source gas.
According to this, this Cu (HFA) tmvs starts to decompose spontaneously at around 130 ° C. and precipitates copper. In FIG. 3, this is indicated by a point A where the increase rate of the vapor pressure with respect to the temperature is changed. Above this temperature,
2Cu (HFA) tmvs → Cu + Cu (HFA) ₂ + ₂ + tmvs
It is thought that this reaction occurs. This reaction dominates the film forming reaction up to the next inflection point B, which is a temperature close to 300 ° C.
[0012]
According to another investigation, when the source gas is Cu (HFA) tmvs, the reaction due to the surface reaction rate control, in which the film formation rate increases with temperature, is dominant in the region where the substrate temperature is 180 ° C. or lower, and at temperatures higher than that, Supply-controlled reaction becomes dominant. The temperature at which the reaction based on the surface reaction rate is dominant varies depending on the type of the source gas. For example, when the source gas is Cu (HFA) COD, the temperature is 200 ° C. or less, and when the source gas is Cu (HFA) 2-butyne, 220 ° C. The temperature is 190 ° C. or lower for Cu (HFA) BTMSE.
By the way, in order to ensure a high level | step difference coverage, it turned out that it is necessary to form into a film using the reaction by surface reaction rate control. This is because in the case of the reaction based on the surface reaction rate control, if the temperature at the bottom of the opening and the temperature at the top of the opening are uniform, the film is formed at the same speed at the bottom and the top.
[0013]
Therefore, in the chemical vapor deposition method, when the source gas is Cu (HFA) tmvs, it is necessary to form a film in a temperature region of 180 ° C. or lower in order to ensure a high step coverage. In the case of other source gases as well, it is necessary to perform film formation in a temperature region where surface reaction rate control is the main reaction mode in order to ensure a high step coverage.
On the other hand, when the source gas is Cu (HFA) tmvs, the film forming rate is reduced in the temperature range of 180 ° C. or lower.
Therefore, in order to improve practicality, when the source gas is Cu (HFA) tmvs, it is necessary to improve the film formation rate while maintaining a temperature of 180 ° C. or lower. Similarly, in order to improve the practicality of other source gases, it is necessary to improve the film formation rate while maintaining the temperature range in which the surface reaction rate control is the main reaction mode.
[0014]
In the method for forming a copper film of the present invention, the activated particles are activated by contacting a source gas, and the substrate is heated to cause a reaction of the source gas, thereby forming a copper film on the substrate. Yes.
Therefore, since the energy from the activated particles is added to the energy of the heating source gas, even if the substrate is heated at such a low temperature that the reaction based on the surface reaction rate is controlled, the source gas that has reached the substrate is converted into the source gas. Is provided with sufficient energy necessary for promoting decomposition.
[0015]
Thereby, the decomposition of Cu (HFA) ₂ generated in the above reaction formula is promoted, and the separation of copper atoms in the source gas is promoted. It is considered that the following reaction occurs in the source gas having sufficient energy. That is, for example, when hydrogen radicals (H ^* ) are used as activated particles,
2Cu (HFA) tmvs + 2H ^* → 2Cu + 2H- (HFA) + 2tmvs
Thus, the hydrogen radical stabilizes HFA and promotes the separation of copper atoms without generating by-product Cu (HFA) ₂ .
[0016]
Therefore, since one atom of copper is deposited per molecule of the source gas Cu (HFA) tmvs, the deposition rate is greatly increased.
Therefore, by using the above-described copper film forming method in the method for manufacturing a semiconductor device of the present invention in which a copper wiring layer is formed on a substrate having an opening, the step coverage is increased and the film forming speed is improved. It becomes possible.
[0017]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
(1) Description of Method for Forming Copper Film According to First Embodiment FIG. 4 shows a film forming apparatus having a triode type electrode used in the method for forming a copper film according to the first embodiment of the present invention. It is a perspective view.
[0018]
In FIG. 4, reference numeral 11 denotes a film formation chamber that can be decompressed, and an exhaust device (not shown) is connected to exhaust the inside of the film formation chamber 11. A source gas containing an organic complex of metallic copper is introduced into the film forming chamber 11 from a gas inlet (not shown). A substrate holder 12 on which the deposition target substrate 17 is placed is installed in the deposition chamber 11. The substrate holder 12 has a built-in heater, and heats the deposited film formation substrate 17.
[0019]
A plasma generation chamber 13 communicates with the film formation chamber 11 through the ion trap electrode 14. Hydrogen gas or the like is introduced into the plasma generation chamber 13 from a gas inlet (not shown) to be turned into plasma. The ion trap electrode 14 is formed in a mesh shape, and traps ions from the plasma generated in the plasma generation chamber 13 by being grounded. Then, only radicals (activated particles) are allowed to flow into the downstream deposition chamber 11 to activate the source gas introduced into the deposition chamber 11.
[0020]
Reference numerals 15 a and 15 b denote triode-type electrodes formed on the outer periphery of the plasma generation chamber 13 and face each other across the plasma generation chamber 13. A high-frequency power having a frequency of 13.56 MHz is applied by a power source 16 connected between the electrodes 15a and 15b, and the hydrogen gas or the like introduced into the plasma generation chamber 12 is turned into plasma.
Next, a method for forming a copper film using the film forming apparatus will be described.
[0021]
First, for example, after a deposition substrate 17 in which an oxide film and a TiN film are sequentially formed on a silicon substrate is placed on the substrate holder 12, the plasma generation chamber 13 and the deposition chamber 11 are evacuated, When the pressure is reached, hydrogen gas is introduced into the plasma generation chamber 13 at a flow rate of 200 SCCM. In addition, the deposition target substrate 17 in the deposition chamber 11 is heated and maintained at a predetermined temperature.
[0022]
Next, a source gas made of an organic complex containing metallic copper is introduced into the film forming chamber 11, and the total pressure in the film forming chamber 11 is maintained at 200 mTorr. Source gas, for example, chemical structural formula
Cu (HFA) tmvs
(HFA indicates hexafluorochloroacetone and tmvs indicates trimethylvinylsilyl)
Vaporized liquid organic complex of copper represented by
[0023]
Subsequently, a high frequency power of 100 W having a frequency of 13.56 MHz is applied between the electrodes 15a and 15b, and the hydrogen gas in the plasma generation chamber 13 is turned into plasma. The hydrogen plasma flows downstream through the ion trap electrode 14. At this time, ions in the hydrogen plasma are trapped or neutralized, and only hydrogen radicals are introduced into the deposition chamber 11.
[0024]
The source gas in the film formation chamber 11 is activated by the hydrogen radicals and reaches the surface of the film formation substrate 17. At this time, the deposition target substrate 17 is maintained at a predetermined temperature, for example, a temperature at which the source gas is naturally decomposed and a reaction based on the surface reaction rate control occurs. Therefore, the source gas that has reached the surface of the deposition target substrate 17 promotes the decomposition of Cu (HFA) ₂ generated in the intermediate process of the decomposition reaction by the energy added by the hydrogen radicals, and further separates the copper atoms. Then, a reaction due to surface reaction rate control occurs on the surface of the substrate 17 to be formed, and a copper film starts to be generated.
[0025]
In the above film formation reaction, the expected reaction process is shown as follows:
2Cu (HFA) tmvs + 2H ^* → 2Cu + 2H- (HFA) + 2tmvs
become. In this way, the hydrogen radical stabilizes HFA and promotes the separation of copper atoms, so that one atom of copper is deposited per molecule of the source gas Cu (HFA) tmvs. Despite the low temperature, the deposition rate is high.
[0026]
After a predetermined time has passed in this state, a copper film having a predetermined thickness is formed on the deposition target substrate 17.
Next, the investigation result of forming a copper film by the above method will be described. In the investigation, the substrate temperature was changed from 130 ° C to 200 ° C.
FIG. 2 is a characteristic diagram showing the relationship of the film formation rate with respect to various substrate temperatures. For comparison, the results of obtaining the relationship between the film formation rate and the substrate temperature using the conventional method are also shown in FIG. The horizontal axis represents the reciprocal of the temperature T indicated by the linear scale (× 1000 / K), and the vertical axis represents the deposition rate (Å / min) indicated by the logarithmic scale.
[0027]
In the case of the conventional example, the same source gas as described above was used as the source gas composed of an organic complex containing metallic copper, and hydrogen gas having a flow rate of 200 SCCM was added to the source gas. Hydrogen gas is not activated.
According to the results shown in FIG. 2, in the case of the example of the present invention, the film formation rate increased as the temperature T increased, and a film formation rate of about 1500 to 2000 mm / min was obtained at a substrate temperature of 180 ° C. Furthermore, the film formation rate was about three times higher than in the conventional case.
[0028]
Moreover, when the film formation state was observed, the step coverage was also high. This indicates that the reaction by surface reaction rate control is dominant.
On the other hand, in the case of the conventional example, when the substrate temperature is 180 ° C., the film forming rate is about 550 Å / min. In addition, the deposition rate does not increase even if the substrate temperature is increased further. In addition, the substrate-controlled reaction is dominant at a substrate temperature of 180 ° C. or higher, and the step coverage is also lowered.
[0029]
This difference is considered to be due to the strong influence of the activation of the source gas by hydrogen radicals. Accordingly, it was possible to increase the deposition rate by activation with hydrogen radicals while maintaining the reaction based on the surface reaction rate by forming the film at a low substrate temperature.
(2) Description of Method for Manufacturing Semiconductor Device According to Second Embodiment Next, a method for manufacturing a semiconductor device including a method for forming a copper wiring layer using the film forming apparatus will be described. FIGS. 1A to 1C are cross-sectional views illustrating a method of forming an upper copper wiring layer connected to the lower wiring layer 23 through the opening 25 of the interlayer insulating film 24. FIG.
[0030]
First, as shown in FIG. 1A, a base insulating film 22 made of a silicon oxide film is formed on a semiconductor substrate 21 made of silicon by thermal oxidation.
Subsequently, a TiN film is formed on the base insulating film 22 by a CVD method (chemical vapor deposition method), and then patterned to form a lower wiring layer 23.
Next, an interlayer insulating film 24 made of a silicon oxide film having a thickness of about 8000 mm is formed by covering the lower wiring layer 23 by the CVD method. Subsequently, the interlayer insulating film 24 is patterned by using a photolithography technique, and an opening 25 is formed on the lower wiring layer 23.
[0031]
Next, after the deposition target substrate 17 is placed on the substrate holder 12 of the above-described deposition apparatus, the inside of the deposition chamber 11 is decompressed. When the predetermined pressure is reached, the film formation substrate 17 is heated by a built-in heater, and the temperature of the film formation substrate 17 is maintained at 180 ° C.
Next, a copper film 26b having a film thickness of about 5000 mm covering the opening 25 is formed on the interlayer insulating film 24 by the same film forming method and conditions as those shown in the first embodiment.
[0032]
FIG. 1B shows the formation state of the copper film 26a during the film formation. Since the temperature of the substrate 17 to be deposited is 200 ° C. or less, the reaction based on the surface reaction rate is dominant, and the film formation rate is determined by the temperature of the film formation location. For this reason, the influence of the unevenness of the substrate to be deposited 17 is reduced. Accordingly, a copper film 26a having a uniform thickness is formed on the bottom and side walls of the opening 25 and the interlayer insulating film 24 in the vicinity of the opening 25. FIG. 1C shows the formation state of the copper film 26b after film formation. Since the copper film 26a having a uniform film thickness can be formed based on the reaction based on the surface reaction rate control, no voids or the like are generated in the opening 25.
[0033]
Thereafter, the copper film 26 b is patterned to form an upper wiring layer connected to the lower wiring layer 23 through the opening 25.
As described above, according to the method for manufacturing a semiconductor device of the embodiment of the present invention, the film is formed while the temperature of the deposition target substrate 17 is maintained at 180 ° C.
Therefore, since the copper film 26b is formed by the film formation reaction based on the surface reaction rate control, a high step coverage can be obtained in the opening 25.
[0034]
Moreover, it is activated by bringing a source gas into contact with hydrogen radicals. Therefore, energy from activated particles is added to the source gas that has reached the film formation substrate 17 in addition to energy due to temperature. For this reason, even if the deposition target substrate 17 is heated at a low temperature at which a reaction based on the surface reaction rate is controlled, sufficient energy for promoting decomposition is imparted to the source gas.
[0035]
For this reason, decomposition of Cu (HFA) ₂ generated in the intermediate process of the reaction is promoted, and copper atoms in the source gas can be further separated. Therefore, since the source gas Cu (HFA) tmvs deposits one atom of copper per molecule, the film formation rate is greatly increased.
As a result, the step coverage can be increased and the film formation rate can be improved.
[0036]
In the above example, Cu (HFA) tmvs is used as the source gas.
Cu (HFA) COD
(HFA represents hexafluoroacetylacetone and COD represents cyclooctadienyl)
Can be used. In this case, a reaction based on the surface reaction rate is obtained at a substrate temperature of 200 ° C. or lower.
[0037]
Also, chemical structural formula
Cu (HFA) 2-butyne
(HFA indicates hexafluoroacetylacetone)
Can be used. In this case, a reaction based on the surface reaction rate is obtained at a substrate temperature of 220 ° C. or lower.
[0038]
Furthermore, chemical structural formula
Cu (HFA) BTMSE
(HFA indicates hexafluoroacetylacetone, BTMSE indicates bistrimethylsilylethylene)
It is also possible to use what is represented by. In this case, a reaction based on the surface reaction rate is obtained at a substrate temperature of 190 ° C. or lower.
[0039]
Further, although hydrogen radicals are used as the activated particles, particles activated by other methods, for example, protons generated by excitation of a compound containing hydrogen by microwaves may be used.
Furthermore, although it is applied to the formation of the upper wiring layer of the semiconductor device, it can also be used to form a wiring layer of a TFT for driving a liquid crystal or a wiring layer of a printed board. In particular, it is optimal when a wiring layer having a high step coverage is formed on a substrate having steps.
[0040]
【The invention's effect】
As described above, in the method for forming a copper film according to the present invention, the substrate is heated and activated by bringing the activated particles into contact with the activated particles.
Therefore, the source gas that reaches the substrate receives energy from hydrogen radicals in addition to the energy due to temperature. Therefore, even if the substrate is heated at a low temperature that causes a reaction based on the surface reaction rate, the source gas can promote decomposition. Sufficient energy is provided. For this reason, the separation of copper atoms contained in the source gas is promoted, and the amount of copper atoms generated per molecule of the source gas is increased, so that the film formation rate is greatly increased.
[0041]
Thus, by applying the copper film forming method to the semiconductor device manufacturing method of the present invention for forming a copper wiring layer on a substrate having a step such as an opening, the step coverage is increased and the film forming speed is increased. Can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a method for manufacturing a semiconductor device using a copper film forming method according to an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing the relationship of film forming speed with respect to various substrate temperatures according to an embodiment of the present invention.
FIG. 3 is a characteristic diagram showing thermal decomposition characteristics of Cu (HFA) tmvs of an organic complex used in the method for forming a copper film according to the present invention.
FIG. 4 is a perspective view showing a film forming apparatus having a triode type electrode used in a method for forming a copper film according to an embodiment of the present invention.
FIG. 5 is a cross-sectional view showing a method for manufacturing a semiconductor device using a conventional copper film forming method.
[Explanation of symbols]
11 Deposition chamber
12 Substrate holder,
13 Plasma production chamber,
14 ion trap electrode,
15a, 15b electrodes,
16 power supply,
17 deposition substrate,
21 semiconductor substrate,
22 Underlying insulating film,
23 Lower wiring layer,
24 interlayer insulation film,
25 opening,
26a, 26b Copper film.

Claims (1)

A method of forming a copper film as an upper wiring layer that is electrically connected to a lower wiring layer through a contact window that is patterned and opened in an insulating film on a lower wiring on a substrate, and introducing hydrogen gas into the plasma generation chamber Then, the hydrogen gas is activated by bringing the source gas into contact with the hydrogen radicals remaining after removing the ions from the hydrogen plasma through the grounded mesh electrode, and the source gas causes a reaction based on the surface reaction rate control. so that the substrate heated by causing thermal decomposition reaction of the source gas on the substrate, further extending over said insulating film from said contact in the window by metallic copper produced by reacting with hydrogen radicals as A method of forming a copper film on a copper film,
The source gas has the chemical structural formula Cu (HFA) tmvs ( HFA represents hexafluoroacetylacetone (hereinafter the same), tmvs represents trimethylvinylsilyl), Cu (HFA) COD ( COD represents cyclooctadienyl) , Cu (HFA) 2-butyne and Cu (HFA) BTMSE ( BTMSE represents bistrimethylsilylethylene), and the heating temperature is the chemical structural formula Cu (HFA) When represented by tmvs , it is 180 ° C. or lower, and when represented by the chemical structural formula Cu (HFA) COD , it is 200 ° C. or lower, and the chemical structural formula Cu (HFA) 2− A method for forming a copper film, characterized in that when it is represented by butyne , it is 220 ° C. or lower, and when it is represented by the chemical structural formula Cu (HFA) BTMSE , it is 190 ° C. or lower .

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