JP2014101564A - Formation method of cobalt film - Google Patents

Abstract

The present invention provides a method for forming a cobalt film that can be formed as a continuous film with a thin film thickness.
In the method for forming a cobalt film according to the present invention, a film-forming object S has a base layer 17 containing metal or silicon on the surface thereof, and the film-forming object is disposed in a processing chamber. Introducing a reducing gas into the substrate and supplying the reducing gas over the entire surface of the underlayer, and with the reducing gas introduced, a metal precursor is further introduced into the processing chamber, and a cobalt metal nucleus is formed on the surface of the underlayer. And forming a cobalt film 19 by growing the metal nuclei.
[Selection] Figure 2

Description

  The present invention relates to a method for forming a cobalt film in which a film formation target has a base layer containing metal or silicon on the surface thereof, and more specifically, a fine groove ( The present invention relates to a film suitable for forming a thin cobalt film on the inner surface of a trench or a hole.

  In recent years, Cu (copper) has attracted attention as a wiring material for semiconductor devices because of its high melting point and excellent migration resistance. A groove is formed in an insulating film on one surface of a semiconductor substrate such as a silicon wafer, and a barrier layer made of tantalum or the like is formed on the inner surface (inner wall surface) of the groove so as to cover the inner surface of the groove covered with the barrier layer. A method is known in which a seed Cu layer (hereinafter referred to as “Cu layer”) is formed by sputtering, and then the Cu layer is flowed by reflow to fill the groove with Cu to obtain a Cu wiring layer ( For example, see Patent Document 1).

  By the way, with the further higher integration of semiconductor devices in recent years, the opening width of the upper surface of the groove has become narrower. In this case, when the Cu layer is formed with a film thickness equivalent to that of the conventional film by sputtering, the upper opening of the groove is closed by the Cu layer (so-called pinch-off). In such a pinch-off state, it was found that when the Cu layer was flowed by reflow as in the conventional example, a cavity remained in the groove.

  Therefore, the present applicant has proposed that the groove portion (that is, the barrier layer surface) is covered with a cobalt film serving as a flow promoting layer prior to the formation of the Cu layer (see Japanese Patent Application No. 2012-233842). According to this, even if the Cu layer is reflowed from the pinch-off state, the fluidity of the Cu layer into the groove is improved, and Cu can be embedded in the groove without any gap.

  As a method for forming the cobalt film, a thermal CVD method excellent in coverage is preferably used. In this case, it is assumed that the surface of the film formation target is covered with a barrier layer, the film formation target is disposed in the processing chamber, and the metal precursor and the reducing gas are simultaneously introduced into the processing chamber to A cobalt film is obtained by forming a metal nucleus of cobalt and growing the metal nucleus.

  Here, if the opening width of the upper surface of the groove is narrow, the line width of the Cu wiring layer formed in this groove is narrowed, so it is necessary to reduce the resistance of the wiring layer. Since cobalt has a higher resistance than Cu, it is effective to reduce the resistance of the wiring layer by forming a thin cobalt film, and from the viewpoint of increasing the fluidity of the Cu layer during reflow. It is also effective to reduce the thickness of the cobalt film. However, it has been found that when the cobalt film is formed by the conventional method, the cobalt film does not become a continuous film when the cobalt film is thin. The inventors of the present invention have conducted extensive research and have found that the above-described conventional example has a cobalt metal nucleus non-uniformly formed on the surface of the barrier layer, so that it does not become a continuous film when the cobalt film is thin. Obtained.

JP 2008-71850 A

  This invention makes it the subject to provide the film-forming method of the cobalt film which can form a cobalt film with a thin film thickness as a continuous film in view of the above point.

  In order to solve the above-described problems, the cobalt film forming method of the present invention has a film formation target having a base layer containing metal or silicon on the surface thereof, and the film formation target is disposed in a processing chamber. Introducing a reducing gas into the processing chamber and supplying the reducing gas over the entire surface of the underlayer; and introducing the reducing gas into the processing chamber while introducing the reducing gas; Forming a cobalt metal nucleus, and growing the metal nucleus to form a cobalt film.

  According to the present invention, the reducing gas is supplied over the entire surface of the underlayer before the cobalt metal nucleus is formed on the surface of the underlayer. At this time, it is sufficient that the entire surface of the underlayer is exposed to the reducing gas, and molecules of the reducing gas may be adsorbed on the surface of the underlayer. By introducing a metal precursor into the processing chamber with the reducing gas introduced, metal nuclei can be formed uniformly and densely over the entire surface of the underlayer. The cobalt film obtained by growing the metal nuclei formed uniformly and densely as described above becomes a continuous film even if the film thickness is thin. According to the experiments by the present inventors, it was confirmed that the cobalt film formed with a film thickness of 0.8 nm is a continuous film.

  In the present invention, the metal-containing underlayer is preferably tantalum, tantalum nitride, tungsten, tungsten nitride, titanium, or titanium nitride, and more preferably tantalum. Further, when the underlayer includes silicon, a cobalt silicide layer can be obtained by forming a cobalt film on the surface of the underlayer and then performing an annealing process at a predetermined temperature. In this case, the underlying layer containing silicon includes a silicon substrate and a polycrystalline silicon gate electrode.

  In the present invention, it is preferable to use ammonia gas and hydrogen gas as the reducing gas.

The schematic diagram explaining the thermal CVD apparatus which enforces the formation method of the cobalt film of embodiment of this invention. (A)-(d) is process drawing explaining the formation method of the cobalt film of embodiment of this invention. The gas introduction time in the formation method of the cobalt film of the embodiment of the present invention is a time chart. The graph which shows the experimental result which confirms the effect of this invention. (A) And (b) is a SEM image which shows an experimental result. (A) And (b) is process drawing explaining the manufacturing method of the semiconductor device which used the cobalt film as a flow promotion layer.

  Referring to FIG. 1, M is a thermal CVD apparatus that performs the method for forming a cobalt film according to the embodiment of the present invention, and the thermal CVD apparatus M includes a vacuum chamber 1 that defines a processing chamber 1a. A stage 2 is provided in the vacuum chamber 1, and the film formation target S is positioned and held by the stage 2 with its film formation surface facing upward. A heater 21 is built in the stage 2 so that the film-forming target S can be heated.

  At the bottom of the vacuum chamber 1, an exhaust pipe EP1 having a pressure control valve APC connected to a dry pump as a vacuum pump VP1 and a turbo molecular pump being a vacuum pump VP3 connected to a dry pump as a vacuum pump VP2 are provided. The exhaust pipe EP2 is connected to the exhaust pipe EP3 that joins between the vacuum pump VP2 and the vacuum pump VP3 of the exhaust pipe EP2. These exhaust pipes EP1 to EP3 are provided with on-off valves V1 to V3, respectively.

  A shower plate 3 is provided on the upper portion of the vacuum chamber 1 so as to face the stage 2, and a reducing gas and a metal precursor can be introduced into the processing chamber 1 a through the shower plate 3. The shower plate 3 is connected to a reducing gas introduction pipe 4 for introducing a reducing gas and a precursor introduction pipe 5 for introducing a metal precursor.

The reducing gas introduction pipe 4 is branched into three gas introduction pipes 41, 42, and 43 that communicate with the H ₂ gas source, the NH ₃ gas source, and the Ar gas source, respectively. Mass flow controllers 41a, 42a, 43a are respectively provided in the gas introduction pipes 41, 42, 43, and on-off valves 41b, 42b, 43b are provided on the upstream side of the mass flow controllers 41a, 42a, 43a, respectively. On the side, on-off valves 41c, 42c, 43c are provided.

  The precursor introduction pipe 5 is connected to a vaporizer 51, and an on-off valve 51a is provided on the upstream side (vacuum chamber 1 side). A bypass pipe 6 is connected between the vaporizer 51 and the on-off valve 51a, and the other end of the bypass pipe 6 is connected to the exhaust pipe EP3. Until the flow rate of the metal precursor is stabilized, a metal precursor is obtained. The body can be exhausted. The vaporizer 51 is connected to gas introduction pipes 53 and 54 communicating with a canister 52 for storing a metal precursor and an Ar gas source for carrier gas, respectively, so that the metal precursor can be vaporized. The gas introduction pipes 53 and 54 are provided with a liquid mass flow controller (LMFC) 53a and a mass flow controller 54a. On the upstream side thereof, on-off valves 53b and 54b are provided, and on the downstream side, on-off valves 53c and 54c. Is provided. The canister 52 is connected to a gas introduction pipe 55 that is connected to a He gas source for carrier gas, with an open / close valve 55 a interposed therebetween, so that the metal precursor can be pumped to the gas introduction pipe 53. The gas introduction pipes 5, 53 through which the metal precursor passes and the liquid mass flow controller 53a are preferably heated to 120 ° C. or higher by a heater (not shown) so that the metal precursor is not adsorbed.

  As a metal precursor, what dissolved cobalt alkylamidinate in dodecane can be used. A known solvent other than dodecane can also be used.

  The thermal CVD apparatus M has a control means C having a microcomputer, a sequencer, etc., and includes a heater 21, vacuum pumps V1 to V3, mass flow controllers 41a, 42a, 43a, 53a, 54a, pressure control valves APC, and open / close It is designed to control the operation of valves.

Hereinafter, with reference to FIG. 2 and FIG. 3, in the method for forming a cobalt film of the present invention, a film formation target S is a semiconductor substrate (hereinafter referred to as “substrate”) 11 such as a silicon wafer, on its surface. A groove (trench) 16 as a recess is formed in an insulating film (for example, an interlayer insulating film made of SiO ₂ ) 15, and a barrier layer 17 made of Ta is formed as a base layer in the groove 16. A case where the cobalt film 18 is formed on the surface of the barrier layer 17 using the thermal CVD apparatus M will be described as an example. Here, the groove 16 is formed such that the upper surface opening width W thereof is, for example, about 10 nm to 50 nm, and the depth D thereof is, for example, about 20 nm to 200 nm. Further, an interlayer insulating film 12 made of, for example, SiO ₂ is formed as a lower layer of the insulating film 15, and a connection hole 13 reaching the substrate 11 is formed in the interlayer insulating film 12, and the connection hole 13 is made of, for example, tungsten. A wiring layer 14 is embedded and formed. In the present invention, the underlying layer may be the barrier layer 17 made of Ti.

  First, the film formation target S is transferred onto the stage 2 of the vacuum chamber 1 by a transfer robot (not shown). When the conveyance is completed, the heater 21 is actuated by the control means, and heating of the film formation target S to a predetermined temperature (180 to 280 ° C., preferably 235 ° C.) is started. In this temperature rising process (time t1 shown in FIG. 3), ammonia gas and hydrogen gas, which are reducing gases, are supplied to the processing chamber 1a, for example, ammonia gas flow rate: 50 to 1000 sccm (preferably 500 sccm), hydrogen gas flow rate: 50 to Each is introduced at 1000 sccm (preferably 100 sccm). Thereby, the reducing gas is supplied over the entire surface of the barrier layer 17, and the entire surface of the barrier layer 17 is exposed to ammonia gas and hydrogen gas. At this time, ammonia gas or hydrogen gas molecules may be adsorbed on the surface of the barrier layer 17.

  Then, when a predetermined time has elapsed from the introduction start time t1 of the reducing gas (at this time, the temperature of the film-forming target S has reached the predetermined temperature), at the time t2, the reducing gas is introduced and further Cobalt alkyl amidinate as a metal precursor is introduced into the processing chamber 1a at a flow rate of 0.2 to 1.0 g / min (preferably 0.5 g / min). The pressure in the processing chamber 1a is preferably controlled, for example, within a range of 30 to 500 Pa (preferably 200 Pa) by the pressure control valve APC. The time (t2-t1) for introducing only the reducing gas can be set in the range of 5 to 30 sec, and preferably 15 sec. The introduced metal precursor is reduced on the surface of the barrier layer 17 to form cobalt metal nuclei (initial nuclei) 18 (see FIG. 2B). At this time, since the entire surface of the barrier layer 17 has been exposed to the reducing gas in advance as described above, the metal nuclei 18 are formed uniformly and densely over the entire surface. When the reducing gas and the metal precursor are continuously introduced, the metal nuclei 18 grow on the entire surface of the barrier layer 17 to form a cobalt film 19 (see FIG. 2C). At this time, the uniformly and densely formed metal nuclei 18 grow respectively, so that even if the film thickness of the cobalt film 19 is small, it becomes a continuous film. The introduction of the metal precursor is stopped at time t3 when a predetermined time (for example, 60 sec) has elapsed from time t2, and then the introduction of the reducing gas is stopped at time t4. The metal precursor and the reducing gas may be introduced and stopped at the same time.

  Here, the present inventors conducted the following invention experiment. In the inventive experiment, a film-forming object S using a tantalum film with a thickness of 5 nm on the surface of a φ300 mm silicon substrate was used. Then, 100 sccm of hydrogen gas was introduced, and after 15 seconds, cobalt alkylamidinate was further introduced at 0.50 g / min to form a cobalt film on the surface of the tantalum film. The film thickness of the cobalt film was changed to 0.6 nm, 0.8 nm, 1.6 nm, and 2.8 nm by changing the introduction time of the cobalt alkyl amidinate, and the sheet resistance value of the obtained cobalt film was measured ( Invention). The thickness of the cobalt film was determined by XRF (fluorescence X-ray analysis). As shown in FIG. 4, in the product according to the invention, when the thickness of the cobalt film is 0.8 nm, the sheet resistance value decreases, and it can be seen that this cobalt film is a continuous film. Moreover, it was confirmed from the SEM image of what formed the cobalt film with the introduction time of cobalt alkyl amidate being 20 sec (FIG. 5 (FIG. 5)). a)).

  As a comparative experiment, the same film formation target S as in the above-described invention experiment was used, and ammonia gas was introduced at 500 sccm, hydrogen gas at 100 sccm, and cobalt alkyl amidate at 0.50 g / min. A cobalt film was formed (comparative product). That is, in the comparative experiment, the reducing gas and the metal precursor were simultaneously introduced from the beginning without introducing only the reducing gas prior to the formation of the metal nucleus. Also in this case, the sheet resistance value was measured by changing the gas introduction time and changing the film thickness of the cobalt film to 0.4 nm, 0.6 nm, 1.2 nm, and 2.2 nm. As shown in FIG. 4, in the case of the comparative product, although the film is a continuous film when the film thickness of the cobalt film is 1.2 nm, the sheet resistance value does not decrease when the film thickness is 0.8 nm, and the film becomes a continuous film. (Ie, it is a discontinuous film). Further, from the SEM image of the cobalt film formed by introducing the reducing gas and the metal precursor for 20 seconds, it was confirmed that the unevenly formed metal nuclei were growing (FIG. 5B). reference).

  As described above, by supplying a reducing gas over the entire surface of the barrier layer 17 before the cobalt metal nucleus 18 is formed on the surface of the barrier layer 17, the entire surface of the barrier layer 17 is Exposure to reducing gas. By further introducing the metal precursor in this state, the metal nuclei 18 can be formed uniformly and densely over the entire surface of the barrier layer 17. Then, by growing the metal nuclei 11 uniformly and densely formed in this way, the cobalt film 19 can be obtained as a continuous film even with a small film thickness.

  A semiconductor device can be manufactured by using the cobalt film 19 thus obtained as a flow promoting layer. That is, a Cu layer 20 is formed on the surface of the cobalt film 19 by sputtering (see FIG. 6A), and the substrate 11 on which the Cu layer 20 has been formed is heated to a temperature of 100 to 400 ° C. (preferably 350 ° C.). Perform reflow. Here, when the upper surface opening width W of the groove portion 16 is narrow, the upper opening of the groove portion 16 may be blocked by the Cu layer 20 as shown in FIG. Acts in such a manner that the wetting angle θ with the Cu fluid generated during the reflow is 90 ° or less (in other words, so as to increase the contact area with the Cu fluid). The conductive material Cu can be buried without being formed (see FIG. 6B). As a result, a highly accurate Cu wiring layer 21 having no local disconnection portion can be obtained, and a semiconductor device having wiring with excellent conductivity can be obtained.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to said thing. In the above embodiment, the case where the cobalt film is formed as the base layer containing metal on the surface of the barrier layer has been described. However, the present invention can also be applied to the case where the cobalt film is formed on the surface of the base layer containing silicon. . For example, a cobalt silicide layer can be formed by forming a cobalt film on the surface of a silicon substrate as a base layer and heat-treating the cobalt film in a rare gas (eg, argon gas) atmosphere. Further, at the same time as forming the cobalt film on the silicon substrate surface, the cobalt film can be formed on the upper surface of the polycrystalline silicon gate electrode formed on the silicon substrate surface via the gate insulating film. In these cases, there is an advantage that the low resistance cobalt silicide layer can be thinly formed (that is, shallow in the thickness direction from the surface of the silicon substrate and the gate electrode) by forming the cobalt film as a thin continuous film.

  During the introduction of the reducing gas, the on-off valve 51a is closed and the on-off valve 61a is opened (at this time, the on-off valve V3 is closed), so that the metal precursor vaporized by the vaporizer 51 passes through the exhaust pipe EP3. It is preferable to evacuate through. If the on-off valve 51a is opened and the on-off valve 61a is closed, the metal precursor can be introduced into the processing chamber 1a at a stable flow rate.

  DESCRIPTION OF SYMBOLS S ... Film-forming object, 1a ... Processing chamber, 17 ... Barrier film (underlayer, tantalum layer), 18 ... Cobalt metal nucleus, 19 ... Cobalt film.

Claims (3)

The film formation target has a base layer containing metal or silicon on its surface, the film formation target is disposed in the processing chamber, and a reducing gas is introduced into the processing chamber to cover the entire surface of the base layer. Supplying a reducing gas;
A step of introducing a metal precursor into the processing chamber in a state where the reducing gas is introduced, forming a cobalt metal nucleus on the surface of the underlayer, and growing the metal nucleus to form a cobalt film. A method for forming a cobalt film.   2. The method of forming a cobalt film according to claim 1, wherein the underlayer is tantalum. The method of forming a cobalt film according to claim 1 or 2, wherein ammonia gas and hydrogen gas are used as the reducing gas.