Film formation method and film formation device

Abstract

Provided is technology with which it is possible, when forming a metal film such as a Cu-containing film serving as a seed layer or a Ta-containing film serving as a base layer for the Cu-containing film on the inner surface of a trench serving as a fine recess Sf, to form a metal film with excellent coverage and with continuity on the inner-side surface thereof.　A sputtering gas containing a rare gas is introduced into a vacuum chamber 1 in a vacuum atmosphere, electric power having a negative potential is applied to a target 2, a positive potential is applied to a reflector plate to generate plasma, and then the introduction of the sputtering gas is stopped and the target is sputtered while self-discharge is induced under low pressure. High-frequency bias electric power is inputted from a high-frequency power source 61 via an impedance matching device 62 to a stage 5 on which there is installed an object Sw on which a film is to be formed. An electronic matcher having an electronically controlled variable reactor is used as the impedance matching device, and the high-frequency bias electric power is intermittently inputted to the stage at a prescribed frequency.

Description

Film forming method and film forming apparatus

[0001] The present invention relates to a film formation method and a film formation apparatus, and more particularly to a film formation method and apparatus for forming a metal film with good coverage on the inner surface of each of a plurality of fine recesses formed on the surface of an object to be film-formed by sputtering using SIS (Self Ionized Sputter) technology.

[0002] Semiconductor device manufacturing processes include depositing metal films, such as a Cu film as a seed layer or a Ta film as a base layer for the Cu film, on the inner surfaces (inner side and inner bottom surfaces) of trenches, which serve as micro-recesses. A so-called self-ion sputtering apparatus is used to deposit such metal films. This apparatus includes a vacuum chamber in which a metal target, such as a Cu or Ta target, and a film-forming target are positioned directly opposite each other. The apparatus also includes a magnetic field generating means positioned above the target, with the direction from the target toward the substrate downward, for generating a leakage magnetic field in the space below the target; a gas introducing means for introducing a sputtering gas containing a rare gas into the vacuum chamber; a sputtering power supply that applies power with a negative potential to the target; and a reflector plate positioned to surround the space below the target and apply a positive potential. A stage is also provided within the vacuum chamber on which the film-forming target is placed. High-frequency bias power is continuously applied from a high-frequency power supply via an impedance matching device that matches the impedance of the plasma with that of the high-frequency power supply.

[0003] When forming a metal film using the self-ion sputtering apparatus, a sputtering gas is introduced into a vacuum chamber in a vacuum atmosphere, a negative potential power is applied to the target, and a positive potential is applied to the reflector plate. Plasma is then generated in the space below the target, and the plasma is confined in the space below by a magnetic field generated by a magnetic field generating means. When the introduction of sputtering gas is stopped in this state, self-discharge occurs under low pressure. Ions of the sputtering gas in the plasma collide with the sputtering surface of the target and are sputtered. Cu atoms and ionized Cu ions scattered from the target and appropriately reflected by the reflector plate are attracted with strong linearity toward the target, to which a high-frequency bias potential is applied, and adhere and deposit on the surface of the target, including the inner surfaces of each micro-recess, thereby forming a Cu film.

[0004] Incidentally, some micro-recesses as film-forming targets have high aspect ratios and, moreover, the inner surfaces (sidewalls) of the micro-recesses are not smooth (in other words, have minute irregularities). Furthermore, the metal films formed on the inner surfaces of the micro-recesses are becoming thinner (for example, to thicknesses in the range of 300 Å to 500 Å). In such cases, when a Cu film is formed using the above-mentioned self-ion sputtering apparatus, not only does so-called overhang occur, but the continuity of the Cu film (thin film) formed on the inner surfaces of the micro-recesses may also be impaired (poor side coverage). This impaired continuity of the Cu film poses a problem: it is not possible to successfully embed Cu wiring by plating in a subsequent process.

[0005] Japanese Patent Application Laid-Open No. 2010-209453

[0006] In view of the above, an object of the present invention is to provide a film forming method and a film forming apparatus that can form a metal film with good coverage and continuity on the inner surface of a minute recess.

[0007] In order to solve the above problems, the present invention provides a film formation method for forming a metal film on the inner surface of each of the fine recesses of a film formation target placed in a vacuum chamber, the method comprising the steps of: introducing a sputtering gas containing a rare gas into a vacuum chamber in a vacuum atmosphere; applying power with a negative potential to a metal target to generate plasma; stopping the introduction of the sputtering gas; and sputtering the target while allowing it to self-discharge under low pressure; applying a positive potential to a reflector plate arranged to surround the space between the film formation target and the target; and applying high-frequency bias power from a high-frequency power source to a stage on which the film formation target is placed via an impedance matcher that matches the impedance of the plasma with the impedance of the high-frequency power source, wherein the step of applying the high-frequency bias power uses an electronic matcher having an electronically controlled variable reactor as the impedance matcher, and intermittently applies high-frequency bias power to the stage at a predetermined frequency.

[0008] Here, an electronic matcher as an impedance matching device has the characteristic of being able to match impedance in a relatively short time of a few milliseconds, compared to a matcher that mechanically drives a variable capacitor. It is also known that a high Vdc is generated instantaneously when high-frequency bias power is first applied via an impedance matching device. Focusing on this, the present invention employs a configuration in which an electronic matcher is used as an impedance matching device, and when high-frequency bias power is applied to the stage, the high-frequency bias power is applied intermittently at a predetermined frequency (for example, by turning the power on and off).

[0009] According to this method, not only do metal atoms and ions from the target side adhere to the inner surface of the micro-recess, but the metal film on the inner bottom surface (bottom) of the micro-recess is resputtered due to the high Vdc that is instantaneously generated each time the high frequency bias power is applied, and this resputtered material adheres and deposits on the inner surface of the micro-recess from the opposite direction to that from the target side. As a result, even if the inner surface of the micro-recess is not smooth, a metal film can be formed with a predetermined thickness on the inner surface of the micro-recess with good coverage and continuity. At this time, by changing the applied high frequency bias power, the height position from the inner bottom surface of the micro-recess, where the resputtered material mainly adheres, can be adjusted.

[0010] It has also been confirmed that the occurrence of overhangs can be minimized by intermittently applying high-frequency bias power at a predetermined frequency. This is because, when high-frequency bias power is continuously applied to the stage while a positive potential is applied to the reflector plate, Cu ions are attracted directly to the film-forming target while maintaining a strong linearity. At this time, some Cu ions are attracted to the film-forming target not only in a direction perpendicular to the surface of the film-forming target, but also at an angle relative to the perpendicular direction (i.e., they are incident obliquely on the film-forming target). Furthermore, electric fields tend to concentrate at the corners between the surface of the film-forming target and the micro-depressed recesses. In contrast, the present invention can suppress such electric field concentration by intermittently applying high-frequency bias power. Furthermore, when the high-frequency bias power is turned off, the attraction of Cu ions to the film-forming target momentarily ceases, correcting the trajectory of the Cu ions so that they are incident perpendicular to the surface of the substrate Sw. As a result, it is believed that the occurrence of overhangs can be minimized.

[0011] In the present invention, when a metal film is to be deposited on the inner bottom surfaces of the micro-recesses with good coverage by resputtering the metal film deposited on the inner bottom surfaces of the micro-recesses, it is preferable to initially deposit the metal film preferentially on the inner bottom surfaces of the micro-recesses. Therefore, in the present invention, the step of supplying the high-frequency bias power includes a first step of setting the high-frequency bias power to a first power (e.g., in the range of 10 W to 100 W, preferably 50 W, depending on the aspect ratio of the micro-recesses) at the start of film formation to preferentially deposit the metal film on the inner bottom surfaces of the micro-recesses, and a second step of supplying the high-frequency bias power at a second power (e.g., in the range of 500 W to 900 W, preferably 700 W) greater than the first power.

[0012] This ensures that a metal film can be deposited on the inner surface of the micro-recess with good coverage and continuity to a predetermined thickness. When the aspect ratio of the micro-recess is 3 or greater, the frequency of the intermittent application of the high-frequency bias power is set to a range of 1 kHz to 20 kHz, and the duty ratio of the intermittent application of the high-frequency bias power is set to a range of 50% to 90%. The ratio of the film thickness when the first power is applied to the film thickness when the second power is applied can be set to, for example, 1:3. While it is possible to increase the high-frequency bias power continuously or stepwise when applying the high-frequency bias power, if the overall film deposition time is short (e.g., 10 seconds or less), this may result in a long film deposition time with a relatively low high-frequency bias power, potentially preventing effective enhancement of side coverage. Therefore, if the film deposition time set according to the desired film thickness is short, it is preferable to apply the high-frequency bias power while varying it in two steps.

[0013] In the present invention, when the metal film is a Cu-containing film formed as a seed layer or a Ta-containing film formed as an underlayer for the Cu-containing film, it has been confirmed that a Cu-containing film or a Ta-containing film can be formed with a relatively thin film thickness (for example, a film thickness in the range of 200 Å to 700 Å) on the inner surface of a fine recess with good coverage and film continuity. Note that the term "Cu-containing film" as used herein refers to a film primarily composed of Cu elements, and is composed of 90 at% or more of Cu elements. Furthermore, the term "Ta-containing film" includes not only pure Ta films but also Ta nitride films, oxide films, and oxynitride films.

[0014] In addition, in order to solve the above-mentioned problems, the film formation apparatus of the present invention is for forming a metal film on the inner surface of each of the fine recesses of a film formation target placed in a vacuum chamber, the film formation apparatus comprising: a gas introduction means for introducing a sputtering gas containing a rare gas into a vacuum chamber in a vacuum atmosphere; a sputtering power supply for supplying power with a negative potential to a metal target; a reflector plate arranged to surround the space between the film formation target and the target and to which a positive potential is applied; and a stage on which the film formation target is placed and to which high-frequency bias power is supplied from the high-frequency power supply via an impedance matcher that matches the impedance of the plasma with the impedance on the high-frequency power supply side, wherein after plasma is generated in the space in front of the sputtering surface of the target, the introduction of the sputtering gas is stopped and the target is sputtered while allowing self-discharge under low pressure, the impedance matcher is composed of an electronic matcher having an electronically controlled variable reactor, and the high-frequency power supply is configured to intermittently supply high-frequency bias power at a predetermined frequency.

[0015] 1A and 1B are cross-sectional views each showing a schematic diagram of a film forming apparatus according to an embodiment of the present invention; FIG. 1B is a diagram explaining the application of high-frequency bias power during film formation; FIG. 1C is a diagram explaining how ionized sputtered particles are attracted to a film-forming target; and FIG. 1C is an SEM image of an experimental result showing the effect of the present invention.

[0016] Hereinafter, with reference to the drawings, an embodiment of the film formation method and film formation apparatus of the present invention will be described, taking as an example a semiconductor substrate (hereinafter referred to as "substrate Sw"), such as a silicon wafer, on whose surface an insulating layer is formed, and a plurality of micro-recesses Sf are formed in a predetermined pattern in the insulating layer. The film formation apparatus is a self-ion sputtering apparatus SM, and a metal film, such as a Cu film or a Ta film, is formed with good coverage on the inner surfaces Sf1 and the inner bottom surfaces Sf2 of the micro-recesses Sf. Note that the present invention is suitable for "micro-recesses" having, for example, an opening diameter d1 of 0.65 μm or less and an aspect ratio of 3 or more. Since well-known methods for forming such micro-recesses can be used, detailed description thereof will be omitted. Hereinafter, directional terms will be used based on FIG. 1 , which shows the self-ion sputtering apparatus SM in an installed position.

[0017] Referring to FIG. 1 , the self-ion sputtering apparatus SM of this embodiment includes a vacuum chamber 1 capable of forming a vacuum atmosphere. A cathode unit Uc is provided at the top of the vacuum chamber 1. The cathode unit Uc includes a target 2 made of copper or tantalum with a predetermined purity and a magnet unit 3 disposed above the target 2. The target 2 is attached to a backing plate 21a and detachably attached to the upper opening of the vacuum chamber 1 via an insulator 11a with its sputtering surface 21b facing downward. The magnet unit 3 generates a magnetic field in the space below the sputtering surface 21b, capturing electrons ionized below the sputtering surface 21b during sputtering and efficiently ionizing sputtered particles scattered from the target 2. Since a known magnet unit 3 can be used, a detailed description thereof will be omitted here. The target 2 is connected to the output of a first DC power source E1 serving as a sputtering power source, and a predetermined power (18 kW or more) with a negative potential can be applied to the target 2 during film formation.

[0018] A conductive reflector plate 4 is disposed within the vacuum chamber 1. The reflector plate 4 is a cylindrical member that extends downward and surrounds the target 2, with its lower end extending to a height approximately half the TS distance between the target 2 and the substrate Sw. The output of a second DC power supply E2 is connected to the reflector plate 4, and a positive potential (5 V to 100 V) is applied to the reflector plate 4 during film formation, reflecting ionized sputtered particles and assisting their emission toward the substrate Sw with strong linearity. A stage 5 is disposed at the bottom of the vacuum chamber 1, facing the target 2. Although not specifically shown or described, an electrostatic adsorption mechanism is provided on the upper surface of the stage 5, allowing the substrate Sw to be positioned and adsorbed and held. The stage 5 also incorporates a heating and cooling mechanism, which, for example, when forming a Cu film, can be controlled to a temperature range that does not cause agglomeration. The output from a high frequency bias power supply 61 is connected to the stage 5 via an impedance matcher 62 that matches the impedance with that of the plasma, and during film formation, high frequency bias power is supplied to the stage 5 and ultimately to the substrate Sw, actively attracting mainly metal atomic ions toward the substrate Sw.

[0019] The RF bias power supply 61 is a known power supply capable of outputting 10 kW or less at a frequency of, for example, 13.56 MHz, and further includes a known pulse generating circuit (not shown). As shown in FIG. 2, a switching element (not shown) of the pulse generating circuit is turned on and off to output RF bias power at a predetermined frequency. The impedance matching device 62 is an electronic matcher having electronically controlled variable reactors 62a and 62b, which can match the impedance of the plasma with the impedance of the RF bias power supply 61 in a short time of several milliseconds (see the enlarged portion in FIG. 1). Because a known electronic matcher can be used, detailed description of its control circuit and control method will be omitted here.

[0020] A gas pipe 7 constituting gas introduction means for introducing a sputtering gas, which is a rare gas such as argon, is connected to the side wall of the vacuum chamber 1, and the sputtering gas, the flow rate of which is controlled by a mass flow controller 71 installed in the gas pipe 7, can be introduced into the vacuum atmosphere of the vacuum chamber 1. The self-sputtering apparatus SM has a known control controller Cr equipped with a microcomputer, sequencer, etc., and the control controller Cr controls the operation of various devices such as the first and second DC power supplies E1, E2, the high-frequency bias power supply 61, and the mass flow controller 71. A film formation method will be specifically described below, taking as an example the case of forming a Cu film using the self-ion sputtering apparatus SM.

[0021] After the substrate Sw is positioned and held on the stage 5 in the vacuum chamber 1 to which the target 2 made of copper of a predetermined purity is attached, the inside of the vacuum chamber 1 is evacuated to a predetermined pressure (for example, 10 －５ The vacuum chamber 1 is evacuated to a pressure of 100 Pa. When the pressure inside the vacuum chamber 1 reaches a predetermined value, the mass flow controller 71 is controlled to introduce Ar gas into the vacuum chamber 1 at a predetermined flow rate (e.g., in the range of 10 sccm to 20 sccm). A positive potential (e.g., in the range of 5 V to 100 V) is applied to the reflector plate 4 from the second DC power supply E2, a predetermined negative potential power (e.g., in the range of 18 kW to 24 kW) is applied to the target 2 from the first DC power supply E1, and high-frequency bias power (e.g., in the range of 50 W to 1300 W) is applied to the stage 5 from the high-frequency bias power supply 61 via the impedance matcher 62. Plasma is then generated in the space below the target 2, and the plasma is contained in this space by the leakage magnetic field from the magnet unit 3. In this state, the mass flow controller 71 is controlled to stop the introduction of sputtering gas, causing self-discharge under low pressure. Then, ions of the sputtering gas in the plasma collide with the sputtering surface 21b of the target 2 and are sputtered, and Cu atoms and ionized Cu ions scattered from the target 2 and appropriately reflected by the reflector plate 4 are attracted with strong linearity toward the surface of the substrate Sw, and adhere and deposit on the inner surfaces Sf1, Sf2 of each fine recess Sf, thereby forming a Cu film.

[0022] In this embodiment, when RF bias power is supplied to the stage 5 by the RF bias power supply 61 during Cu film deposition, the RF bias power is supplied intermittently at a predetermined frequency by controlling the on / off of a switching element (not shown) of the pulse generating circuit, and the RF bias power is supplied in two stages, large and small (see FIG. 2 ). That is, at the beginning of Cu film deposition, the RF bias power is set to a first power (e.g., in the range of 10 W to 100 W, preferably 50 W) (step 1). After a predetermined time has elapsed, the RF bias power is changed to a second power (e.g., in the range of 500 W to 900 W, preferably 700 W) greater than the first power, and the RF bias power is continuously supplied (step 2). The supply times of the first power and the second power are set based on the thickness of the Cu film to be deposited, and can be set so that the ratio of the film thickness when the first power is supplied to the film thickness when the second power is supplied is, for example, in the range of 1:3. Furthermore, the frequency when the high-frequency bias power is intermittently applied is set in the range of 1 kHz to 20 kHz, and the duty ratio when the high-frequency bias power is intermittently applied (on time per cycle) is set in the range of 50% to 90%. If the frequency is lower than 1 kHz or the duty ratio is less than 50%, the adhesion effect to the inner surface Sf1 by re-sputtering cannot be effectively exerted, while if the duty ratio is greater than 90%, the in-plane uniformity of the film thickness distribution is impaired. Furthermore, if the frequency is higher than 20 kHz, a problem occurs in that voids (air gaps) are generated in the fine recesses Sf when Cu wiring is embedded by plating in a subsequent process.

[0023] According to this, at the beginning of Cu film formation, material scattered from the target 2 preferentially adheres and deposits on the inner bottom surface Sf2 of each micro-concave Sf, forming a Cu film. Then, when the high-frequency bias power is changed from the first power to the second power, the Cu film on the inner bottom surface Sf2 of the micro-concave Sf is resputtered due to Cu atoms and ionized Cu ions from the target 2, as well as the high Vdc instantaneously generated each time the high-frequency bias power is applied. This resputtered material adheres and deposits on the inner side surface Sf1 of the micro-concave Sf from the opposite direction (below) to that from the target side. This allows a Cu film to be formed to a predetermined thickness with good coverage on the inner side surface Sf1, even if the inner side surface Sf1 of the micro-concave Sf is not smooth. By changing the applied high-frequency bias power, the height position from the inner bottom surface Sf2 of the micro-concave Sf, to which the resputtered material primarily adheres, can be adjusted.

[0024] Furthermore, by forming a Cu film in the manner described above, it is possible to minimize the occurrence of overhangs. This is thought to be due to the fact that, when a positive potential is applied to the reflector plate 4 while a high-frequency bias power is continuously applied to the stage 5 as in the conventional example, Cu ions are attracted directly to the substrate Sw while maintaining a strong tendency to move in a straight line, but some of the Cu ions are attracted not only in a direction perpendicular to the surface (top surface) of the substrate Sw but also in a state tilted relative to the perpendicular direction (i.e., they are obliquely incident on the substrate Sw), as shown in Figure 3(a), and moreover, an electric field is likely to concentrate at the corner between the surface of the substrate Sw and the inner side surface of the micro-depression recess.

[0025] In contrast, in this embodiment, such electric field concentration can be suppressed by intermittently applying high-frequency bias power. Moreover, as shown in FIG. 3B, each time the high-frequency bias power is turned off, the attraction of Cu ions to the substrate Sw is momentarily eliminated, and the trajectory of the Cu ions is corrected so that they are incident perpendicularly to the surface of the substrate Sw, thereby minimizing the occurrence of overhangs. As a result, even if the inner surface Sf1 of the fine recess Sf is not smooth, a Cu film can be formed with good coverage and continuity on the inner surface Sf1 at a relatively thin thickness (e.g., a thickness in the range of 200 Å to 700 Å). It has been confirmed that the above-described film formation method is also effective when the target 2 is made of tantalum of a predetermined purity and a Ta film is formed on the inner surfaces Sf1 and Sf2 of each fine recess Sf. Furthermore, when high-frequency bias power is applied intermittently at a predetermined frequency, if the potential applied to the reflector plate 4 is changed, the film formation rate can be changed accordingly, and it was confirmed that the film thickness distribution within the surface of the substrate Sw can be made approximately constant, regardless of the potential applied to the reflector plate 4.

[0026] To confirm the above effects, a Cu film was deposited using the self-sputtering apparatus SM shown in FIG. 1 . The substrate Sw was a 300 mm diameter Si wafer. A silicon oxide film was then formed over the entire surface of the wafer. Then, fine recesses (70 nm wide, 210 nm deep) were patterned in the silicon oxide film using a known method. Then, TaN and Ta films were deposited to a thickness of 13 nm on the inner surfaces Sf1 and Sf2 of the fine recesses Sf. The target used was a Cu target with a composition ratio of 99.9999%. The deposition conditions were as follows: the distance between the sputtering surface 21b of the target 2 and the substrate Sw was 300 mm; the power input to the target 2 was 16 kW (current 38 A); the voltage input to the reflector plate 4 was 100 V; and the flow rate of the initially introduced argon gas was 10 sccm. The Cu film was deposited for a predetermined time while the temperature of the substrate Sw was maintained below room temperature.

[0027] In Comparative Experiment 1, the RF bias power was set to 700 W and continuously applied from the beginning of film formation. In contrast, in Inventive Experiment 1, the RF bias power was set to 1 kHz and a duty ratio of 50% and applied intermittently. In addition, at the beginning of film formation, the RF bias power was set to 50 W for a predetermined time to form a Cu film, and then the RF bias power was changed to 700 W to form a Cu film. Figures 4(a) and 4(b) are SEM images of the center of the substrate Sw in Inventive Experiment 1 and the Comparative Experiment. According to these images, in Comparative Experiment 1, the surface film thickness of the substrate Sw was 36 nm, the film thickness on the inner bottom surface Sf2 of the micro-concave Sf was 7.1 nm, the average film thickness on the inner side surface Sf1 was 6.2 nm, and the overhang (i.e., the film thickness of the Cu film protruding into the micro-concave Sf at the position where the surface of the substrate Sw intersects with the upper end of the inner side surface Sf1 of the micro-concave Sf) was 19.1 nm (see Figure 4(b)). In contrast, in invention experiment 1, the film thickness on the surface of the substrate Sw was 39.7 nm, the film thickness on the inner bottom surface Sf2 of the fine recess Sf was 12.7 nm, the average film thickness on the inner side surface Sf1 was 7.5 nm, and the overhang was 13.9 nm.Compared to comparison experiment 1, the side coverage was improved, the overhang was suppressed, the asymmetry was small, and it was confirmed that the Cu film was formed continuously on the inner side surface Sf1 (see Figure 4(a)).

[0028] Next, in Inventive Experiment 2, a Cu film was formed under the same film formation conditions as Inventive Experiment 1, with a frequency of 10 kHz and a duty ratio of 10%, 50%, and 90%. SEM images were analyzed. It was confirmed that, when the duty ratio was 10%, the film thickness on the inner bottom surface was thinner at some locations on the substrate compared to Comparative Experiment 1, and the overhang was not significantly reduced. On the other hand, when the duty ratio was 50% or 90%, the film thickness on the inner surface was thicker by 1 nm or more compared to Comparative Experiment 1, and the overhang was reduced by 5 nm or more. Next, in Inventive Experiment 3, a Cu film was formed under the same film formation conditions as Inventive Experiment 1, with a duty ratio of 50%, a frequency of 1 kHz, 10 kHz, and 20 kHz. According to this, it was confirmed that when the frequency is in the range of 1 kHz to 20 kHz, the film thickness of the inner surface is 1 nm or more thicker than that of Comparative Experiment 1, and a Cu film is formed continuously on the inner surface Sf1, and furthermore, the overhang is reduced by 5 nm or more, and asymmetry is also small.

[0029] Next, in Inventive Experiment 4, a comparison was made between a case in which a Cu film was formed by setting the high frequency bias power to 30 W and continuously supplying it from the beginning of film formation (Inventive Experiment 4) and a case in which a Cu film was formed by setting the high frequency bias power to 0 W (Comparative Experiment 2). According to this, the film thickness on the inner surface of the fine recess was almost the same in Inventive Experiment 4 and Comparative Experiment 2, but it was confirmed that the film thickness on the inner surface of the fine recess in Inventive Experiment 4 was 1.3 to 1.6 times greater than that in Comparative Experiment 2, and overhang was also suppressed. From this, it was confirmed that if the high frequency bias power was supplied at a relatively small first power at the beginning of film formation, a metal film could be preferentially formed on the inner bottom surface of the fine recess.

[0030] Although the above embodiments of the present invention have been described with reference to the drawings, various modifications are possible without departing from the scope of the technical concept of the present invention. In the above embodiments, the RF bias power supply 61 is provided with a known pulse generating circuit that turns on and off at a predetermined frequency. However, this is not a limitation as long as it can intermittently supply RF bias power to the stage 5. Furthermore, while an electronic matcher is used as the impedance matcher 62, this is not a limitation as long as it can match the impedance of the plasma with the impedance of the RF bias power supply 61 in a short time of several milliseconds. Furthermore, while the above embodiments have been described with reference to the deposition of metal films such as Cu and Ta films, this is not a limitation. For example, the present invention can be widely applied to depositing Ta nitride films, oxide films, or oxynitride films (Ta-containing films) with good coverage on the inner surfaces of the micro recesses Sf by using tantalum targets 2 with a predetermined purity and introducing reactive gases such as nitrogen gas and oxygen gas during deposition.

[0031] SM...self-sputtering device, Sw...substrate (film formation target), Sf...fine recess, Sf1...inner surface, Sf2...inner bottom surface, 1...vacuum chamber, 2...target, 4...reflector plate, 5...stage, 61...high frequency bias power supply, 62...electronic matcher (impedance matching device), 7...gas pipe (component of gas introduction means).

Claims

1. A method for forming a metal film on the inner surface of each of the fine recesses of a film-forming target placed in a vacuum chamber, the method comprising the steps of: introducing a sputtering gas containing a rare gas into a vacuum chamber in a vacuum atmosphere; applying power with a negative potential to a metallic target to generate plasma; stopping the introduction of the sputtering gas; and sputtering the target while allowing it to self-discharge under low pressure; applying a positive potential to a reflector plate disposed so as to surround the space between the film-forming target and the target; and applying high-frequency bias power from a high-frequency power source to a stage on which the film-forming target is placed, via an impedance matching device that matches the impedance of the plasma with the impedance of the high-frequency power source, wherein the step of applying the high-frequency bias power uses an electronic matcher having an electronically controlled variable reactor as the impedance matching device, and intermittently applies high-frequency bias power to the stage at a predetermined frequency.

2. A film forming method according to claim 1, characterized in that the process of supplying the high frequency bias power includes a first process of setting the high frequency bias power to a first power at the beginning of film formation to preferentially form a metal film on the inner bottom surface of each fine recess, and a second process of changing the high frequency bias power to a second power greater than the first power and supplying the high frequency bias power.

3. A film forming method according to claim 1, wherein the frequency at which the high frequency bias power is intermittently applied is set within the range of 1 kHz to 20 kHz.

4. A film forming method according to claim 1, wherein the duty ratio when the high frequency bias power is intermittently applied is set within the range of 50% to 90%.

5. The film forming method according to any one of claims 2 to 4, wherein the metal film is a Cu-containing film formed as a seed layer or a Ta-containing film formed as an underlayer for the Cu-containing film.

6. A film forming apparatus for forming a metal film on the inner surface of each of the fine recesses of a film-forming target placed in a vacuum chamber, the film forming apparatus comprising: a gas introduction means for introducing sputtering gas containing a rare gas into a vacuum chamber in a vacuum atmosphere; a sputtering power supply for supplying power with a negative potential to a metal target; a reflector plate arranged to surround the space between the film-forming target and the target and to which a positive potential is applied; and a stage on which the film-forming target is placed and to which high-frequency bias power is supplied from the high-frequency power supply via an impedance matcher that matches the impedance of the plasma and the impedance of the high-frequency power supply side, the film forming apparatus stopping the introduction of the sputtering gas after generating plasma in the space in front of the sputtering surface of the target and sputtering the target while allowing it to self-discharge under low pressure, characterized in that the impedance matcher is composed of an electronic matcher having an electronically controlled variable reactor, and the high-frequency power supply is configured to intermittently supply high-frequency bias power at a predetermined frequency.

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