Film forming method

Abstract

Provided is a method for forming a silicon film capable of adjusting film stress while maintaining optical characteristics. A target (3) made of a silicon material and a film formation object (Sw) are arranged in a vacuum chamber (1). Sputtering gas is introduced into a vacuum chamber of a vacuum atmosphere, power is applied to a target, and a silicon film (Sf) is formed on the surface of a film formation object by a sputtering method. In this case, the formation of the silicon film is performed in a first step in which a first silicon film (Sf1) having a columnar structure is formed, and a second step in which a second silicon film (Sf2) having a higher film density than the first silicon film is formed in a columnar structure.

Description

Technical Field

[0001] The present invention relates to a film forming method, and more particularly, to a film forming method of a silicon film that can be used for a hard mask or the like. Background Art

[0002] In the manufacturing process of semiconductor devices, there is a process of forming a hard mask to limit the etching range when dry etching is performed on an insulating film (e.g., a silicon oxide film) formed on the surface of a substrate composed of a silicon wafer, and a silicon film is sometimes used as the hard mask at this time (e.g., see Patent Document 1). In such a silicon film, a film density that exhibits strong etching resistance is required, and in order to prevent deformation of the etching shape during dry etching, a film stress within a predetermined range is required.

[0003] On the other hand, when patterning the resist layer applied on the silicon film by using an exposure device, it is sometimes necessary to align with the wiring pattern that has been formed as a substrate. Such alignment is usually performed by using laser detection to form an alignment mark formed at a specified position on the substrate. Moreover, with the miniaturization of wiring patterns in recent years, in order to enable high-precision alignment, a laser with a small spot diameter is used. Therefore, the above-mentioned silicon film is also required to have the following optical properties, that is, the refractive index (n value) and extinction coefficient (k value) of the specified film thickness are respectively within the specified range of optical properties.

[0004] Here, when forming the above-mentioned silicon film, for example, considering productivity, it is possible to consider using a sputtering device. In this case, a rare gas is introduced into a vacuum chamber of a vacuum atmosphere in which a target made of silicon material and a film-forming object are arranged opposite to each other, and a DC power or an AC power having a negative potential is applied to the target, and the target is sputtered, thereby forming a silicon film with a predetermined film thickness. At this time, it is generally known that by adjusting the sputtering conditions such as the partial pressure of the sputtering gas during film formation, the power applied to the target, or the bias power (bias power) to the substrate, the film stress or the optical characteristics can be adjusted to the predetermined range, respectively, but, for example, the film stress cannot be adjusted while maintaining the optical characteristics.

[0005] Prior art literature

[0006] Patent Literature

[0007] [Patent Document 1] Japanese Patent No. 6952866 Summary of the invention

[0008] Technical problem to be solved by the invention

[0009] In view of the above situation, the present invention aims to provide a method for forming a silicon film capable of adjusting film stress while maintaining optical properties.

[0010] Solutions to technical problems

[0011] After repeated and in-depth research, the inventor of the present application finally understood the following situation. That is, when a (single) silicon film is formed with a predetermined film thickness by sputtering a target made of silicon, even if the sputtering conditions such as the partial pressure of the sputtering gas during film formation, the power applied to the target, or the bias power applied to the substrate are adjusted to maintain the film stress within the predetermined range, the desired optical properties (specifically, the refractive index and the extinction coefficient) cannot be maintained. Here, for example, in order to perform the above-mentioned alignment, the refractive index (n value) as an optical property is required to be a value in the range of 4 to 5 and the extinction coefficient (k value) is required to be a value in the range of 0.3 to 0.6, it is known that if the silicon film is set to be a film grown in a columnar structure and the film density at this time is adjusted by changing the sputtering conditions, the desired optical properties can be easily obtained. Therefore, without considering the film stress, the sputtering conditions that maintain the optical properties within the predetermined range are first found, and the silicon film formed under the sputtering conditions at this time is the main silicon film. Then, it was found that, under sputtering conditions in which the film density of the base layer of the main silicon film has a density difference, specifically, if it is set to be a film grown in a columnar structure and the film density at this time is set to a density lower than that of the main silicon film, then the film stress can be adjusted while maintaining the optical properties according to the density difference of the film.

[0012] In order to solve the above-mentioned technical problems, the present invention is characterized in that a film forming method is provided, which comprises the steps of arranging a target made of silicon material and a film forming object in a vacuum chamber, introducing a sputtering gas into the vacuum chamber with a vacuum atmosphere, applying electric power to the target, and forming a silicon film on the surface of the film forming object by sputtering, wherein the film forming of the silicon film is implemented by dividing into a first step of forming a first silicon film having a columnar structure and a second step of forming a second silicon film having a columnar structure and a film density higher than that of the first silicon film.

[0013] By using the above method, it was confirmed that the film stress can be adjusted according to the difference in film density between the first silicon film and the second silicon film while maintaining the optical characteristics. In addition, during the film formation process, a silicon film is also formed on components such as an anti-adhesion plate that are present in the vacuum chamber, but at this time, a second silicon film with a high film density is formed on the surface portion. Therefore, when the silicon film is repeatedly formed, it is peeled off from the surface portion of the above-mentioned component, and the number of particles floating in the vacuum chamber will decrease, thereby minimizing the number of particles attached to the film-forming object after film formation. In addition, it was confirmed that while the film can be formed with a good film thickness distribution within the substrate surface, there is almost no difference in film thickness distribution between the film-forming objects when the film is repeatedly formed on multiple film-forming objects.

[0014] In the present invention, the partial pressure of the sputtering gas in the vacuum chamber in the first step is taken as the reference partial pressure, and the partial pressure of the sputtering gas in the second step is set lower than the reference partial pressure. Therefore, if the partial pressure of the sputtering gas in the first step and the second step is changed, the film density of the first silicon film and the second silicon film can be changed. In this case, it is advantageous to be able to continuously form the first silicon film and the second silicon film with a density difference in a single vacuum chamber. At this time, the partial pressure ratio of the second step to the first step can be set in the range of 0.1 to 0.7. If the partial pressure ratio is less than 0.1, it becomes a high-density film, and the refractive index (n value) and the extinction coefficient (k value) become too high. On the other hand, if it is greater than 0.7, on the contrary, it becomes a low-density film, and the refractive index (n value) and the extinction coefficient (k value) become too low.

[0015] Furthermore, in the present invention, the film thickness ratio of the first silicon film to the silicon film may be set within a range of 0.3 to 0.8. This advantageously allows film stress to be easily adjusted without changing the optical properties of the predetermined film thickness.

[0016] During the formation of the silicon film on the surface of the film-forming object by sputtering, when a bias power is applied to the film-forming object, the bias power in the first step and the second step can be set within the range of 20W to 100W. In this way, the film density of each of the first silicon film and the second silicon film can be adjusted, and the film stress can be adjusted within a larger range. In addition, if the bias power is lower than 20W, the controllability (followability) of the power supply is poor, and there is a risk that the film forming conditions become unstable. On the other hand, if it is higher than 100W, it becomes a high-density thin film, and the refractive index (n value) and extinction coefficient (k value) become too high. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a schematic diagram showing the structure of a sputtering device as a silicon film forming device according to the present embodiment.

[0018] Figure 2 (a) and (b) are diagrams illustrating the silicon film forming process.

[0019] Figure 3 This is a SEM image of a silicon film formed under specified conditions.

[0020] Figure 4 This is a graph showing experimental results when a silicon film is formed using the film forming method of this embodiment.

[0021] Figure 5 This is a graph showing experimental results when a silicon film is formed using the film forming method of this embodiment. DETAILED DESCRIPTION

[0022] Hereinafter, with reference to the accompanying drawings, the following case is used as an example to explain the implementation method of the silicon film forming method of the present invention, that is, a product having a silicon oxide film of a predetermined film thickness formed on one surface of a silicon wafer (hereinafter referred to as "substrate Sw") is used as a film forming object, and a target is made of silicon material of a predetermined purity, and argon gas is used as a sputtering gas to form a silicon film on the surface of the substrate Sw by sputtering. Figure 1 As a benchmark.

[0023] Reference Figure 1 SM represents a magnetron sputtering device capable of implementing the film forming method of this embodiment. The sputtering device SM includes a grounded vacuum chamber 1. A vacuum pump 12 is connected to the vacuum chamber 1 via an exhaust pipe 11, and can exhaust the vacuum chamber 1 to a specified pressure (vacuum degree). An air pipe 13 is connected to the side wall of the vacuum chamber 1, and a mass flow controller 14 is interposed on the air pipe 13 to connect to a gas source of argon gas (not shown). In addition, argon gas whose flow rate is controlled by the mass flow controller 14 can be introduced into the vacuum chamber 1.

[0024] A stand 2 is provided in the vacuum chamber 1. The stand 2 comprises: a base 21 with a spacer insulator 21a disposed on the inner side of the bottom surface of the vacuum chamber 1; and a chuck plate 22, for example, made of aluminum nitride or boron nitride, provided on the base 21. An electrode 22a for an electrostatic chuck is assembled on the chuck plate 22, and by energizing the electrode 22a from a chuck power supply outside the figure, the substrate Sw placed with the film-forming surface facing upward can be electrostatically adsorbed (held). At this time, the substrate Sw is in an electrically floating state. Although not specifically illustrated, a heating and cooling mechanism for the substrate Sw is provided on the chuck plate 22, and the substrate Sw can also be adjusted to a specified temperature during the film-forming process.

[0025] Furthermore, a cathode unit Uc is provided in the vacuum chamber 1. The cathode unit Uc includes: a target 3; and a magnet unit 4 arranged above the target 3 so that a leakage magnetic field acts on the space between the target 3 and the substrate Sw. A back plate 31 is joined to the side of the target 3 opposite to the sputtering surface 3a. When the peripheral edge of the back plate 31 is mounted on the upper wall of the vacuum chamber 1 by the insulating member 32, the target 3 and the substrate Sw are arranged concentrically opposite to each other in the vacuum chamber 1 with a vacuum atmosphere. The output from the sputtering power source Ps is connected to the target 3, and a DC power having a negative potential can be applied in a pulsed manner, for example. In the vacuum chamber 1, there is also provided an anti-adhesion plate 5 made of stainless steel or aluminum material surrounding the space between the substrate Sw and the target 3 to prevent sputtered particles from adhering to the inner wall of the vacuum chamber 1. The anti-adhesion plate 5 is composed of an upper anti-adhesion plate 51 suspended on the upper wall of the vacuum chamber 1 and a lower anti-adhesion plate 52 freely movable in the upper and lower directions by a lifting mechanism Du having a cylinder or a motor.

[0026] In the vacuum chamber 1, a cylindrical block 6 having a truncated cone-shaped profile and located around the stage 2 is provided. The block 6 is made of a metal material such as aluminum or copper, and is provided via an insulator 61 provided on the inner side of the bottom surface of the vacuum chamber 1. In the setting state of the block 6, the top of the block 6 is located in the same plane or lower than the upper surface (film forming surface) of the substrate Sw held by the stage 2, and at least a part of its outer cylindrical surface directly faces the plasma atmosphere formed in the vacuum chamber 1. In addition, the shape of the block 6 is not limited to this, and it is not necessary to completely surround the stage 2. For example, it can be constructed as a plurality of plates with arc-shaped profiles arranged on the same circumference. The block 6 is also connected to an output 71 from a DC power supply 7, and when forming a film, a positive potential is appropriately applied by the DC power supply 7 to act as an anode. In addition, the stage 2 is connected to an output 81 from an AC power supply 8, and when forming a film, a bias power within a specified range can be applied to the substrate Sw. Hereinafter, a film forming method according to the present embodiment will be described in which a silicon film having a predetermined film thickness is formed on a substrate Sw using the sputtering apparatus SM described above.

[0027] The substrate Sw is placed on the stage 2 with its film-forming surface facing upward, and after being electrostatically adsorbed, the vacuum chamber 1 is evacuated. When the vacuum chamber 1 reaches a predetermined pressure, argon gas is introduced at a predetermined flow rate through the control of the mass flow controller 14 in the vacuum chamber 1, which always maintains a constant effective exhaust speed, and a DC power with a negative potential is applied to the target 3 in a pulsed manner through the sputtering power supply Ps. At this time, the flow rate of argon gas is set in the range of 100 sccm to 1000 sccm (the partial pressure of argon gas in the vacuum chamber 1 is 0.3 Pa to 8.0 Pa), and the applied power is set in the range of 1.0 kW to 5.0 kW. When the flow rate of argon gas is less than 100 sccm, a high-density thin film is obtained, and the refractive index (n value) and extinction coefficient (k value) become too high. On the other hand, when it is greater than 1000 sccm, the sputtering rate becomes too slow and the productivity deteriorates. Furthermore, if the applied power is lower than 1.0 kW, the sputtering rate becomes too slow and productivity deteriorates. On the other hand, if it exceeds 5.0 kW, a high-density thin film is obtained, and the refractive index (n value) and extinction coefficient (k value) become too high.

[0028] During the film formation process by sputtering the target 3, a positive potential (for example, in the range of 0V to 100V, preferably 30V) may be applied to the bulk 6 by the DC power supply 7, and a bias power (in the range of 20W to 100W) may be applied to the substrate Sw by the AC power supply 8. If the bias power is lower than 20W, the controllability (followability) of the power supply is poor, and there is a risk that the film formation conditions become unstable. On the other hand, if it is higher than 100W, a high-density thin film is formed, and the refractive index (n value) and extinction coefficient (k value) become too high. Thus, a plasma atmosphere is formed in the space between the substrate Sw and the target 3, and the target 3 is sputtered by the argon ions in the plasma, and the sputtered particles fly from the target 3 according to the prescribed cosine law, such as Figure 2 As shown in (a), a silicon film with a relatively low film density of a columnar structure (hereinafter referred to as "the first silicon film Sf1") is formed (the first step). At this time, the film thickness of the first silicon film Sf1 is determined based on the film thickness of the silicon film Sf to be formed, and the sputtering time when the first silicon film Sf1 is formed is set according to the sputtering rate corresponding to the film thickness and the power applied to the target 3.

[0029] Next, when the pre-set sputtering time is reached, the mass flow controller 14 is controlled while the power applied to the target 3 is maintained to change the flow rate of the argon gas. The flow rate of the argon gas at this time is set in the range of 20sccm to 80sccm (the partial pressure of the argon gas in the vacuum chamber 1 is 0.08Pa to 0.2Pa). In other words, the partial pressure ratio between the second step and the first step is set in the range of 0.1 to 0.7. At this time, when the partial pressure ratio is less than 0.1, it becomes a high-density film, and the refractive index (n value) and the extinction coefficient (k value) become too high. On the other hand, if it is greater than 0.7, on the contrary, it becomes a low-density film, and the refractive index (n value) and the extinction coefficient (k value) become too low. Therefore, if Figure 2 As shown in (b), a dense silicon film (hereinafter referred to as "second silicon film Sf2") having a higher film density than the first silicon film Sf1 is formed in a columnar structure (layered) (second process). The sputtering time is set to achieve the film thickness of the silicon film Sf. In addition, it was confirmed that if the film thickness ratio of the first silicon film Sf1 to the silicon film Sf is set in the range of 0.3 to 0.8, the film stress can be changed without changing the optical properties of the prescribed film thickness. At this time, it was confirmed that if the film thickness ratio of the first silicon film Sf1 to the silicon film Sf is set in the range of 0.3 to 0.7, the optical properties of the prescribed film thickness can be more preferably set.

[0030] By adopting the above embodiment, it was confirmed that the film stress can be adjusted according to the difference in film density between the first silicon film Sf1 and the second silicon film Sf2 grown in a columnar structure while maintaining the optical characteristics. In addition, during the film formation process of the silicon film Sf, a silicon film is also formed on the inner surface of the anti-adhesion plate 5, but at this time, the second silicon film Sf2 with a high film density is formed on the surface portion. Therefore, when the silicon film Sf is repeatedly formed, the number of particles floating in the vacuum chamber 1 by peeling off from the surface portion of the anti-adhesion plate 5 will decrease, thereby minimizing the number of particles attached to the surface of the substrate Sw after film formation. In addition, it can be confirmed that while the film is formed with a good film thickness distribution within the surface of the substrate Sw, there is almost no difference in film thickness distribution between the substrates Sw when the film is repeatedly formed on a plurality of substrates Sw.

[0031] In order to confirm the above effect, the following experiment was conducted using the above sputtering device SM. In this experiment, a product having a silicon oxide film formed on one side surface of a silicon wafer with a film thickness of 100 nm was used as a substrate Sw, and a silicon film was formed on the surface of the silicon oxide film with a film thickness of 50 nm. First, as a preliminary experiment, the target 3 was pulsed with power appropriately set to a frequency of 150 kHz and in the range of 1 kW to 10 kW, and the flow rate of argon gas was appropriately set in the range of 20 sccm to 1000 sccm (at this time, the argon partial pressure in the vacuum chamber 1 was in the range of 0.08 to 8 Pa), and silicon films were formed on multiple substrates Sw with a film thickness of 25 nm. At this time, sputtering conditions were confirmed in which the refractive index (n value) was in the range of 4 to 5 and the extinction coefficient (k value) was in the range of 0.3 to 0.6. Although not particularly illustrated, SEM images of the formed silicon film confirmed that the silicon film having a refractive index and an extinction coefficient within the above ranges grew in a columnar structure and that the film density varied depending on the flow rate of argon gas.

[0032] Next, the power applied to the target 3 in a pulsed state is set to a frequency of 150kHz and 4kW, and the flow rate of argon gas is appropriately changed within the range of 30sccm to 300sccm. For multiple substrates Sw, a first silicon film Sf1 as a base layer is formed with a film thickness of 25nm, and then a second silicon film Sf2 is formed on the surface of the first silicon film Sf1 with a film thickness of 25nm. The sputtering conditions when forming the second silicon film Sf2 are set to the sputtering conditions confirmed from the above-mentioned prior experiment, and the power applied to the target 3 is set to a frequency of 150kHz and 4kW, and the flow rate of argon gas is set to 70sccm (hereinafter referred to as "sputtering condition 1"). Thus, it was confirmed that when the flow rate of argon gas is less than 100sccm, the film stress becomes smaller, and the film stress (MPa) changes according to the flow rate of argon gas. At this time, the refractive index and the extinction coefficient are also maintained within the above range.

[0033] here, Figure 3The sputtering conditions for forming the first silicon film Sf1 are set to the conditions that the power applied to the target 3 in a pulsed state is set to a frequency of 150kHz and 4kW, and the flow rate of argon gas is 240sccm (hereinafter referred to as "sputtering condition 2"), and the SEM image when the first silicon film Sf1 and the second silicon film Sf2 are continuously formed with a film thickness of 25nm by sputtering conditions 1 and 2 respectively. It can be seen that the first silicon film Sf1 and the second silicon film Sf2 each grow in a columnar structure, and the film density of the first silicon film Sf1 at this time is lower than that of the second silicon film Sf2. In addition, it was confirmed that the same tendency also exists when the power applied to the target 3 is changed on the basis of keeping the flow rate of argon gas constant.

[0034] Next, an experiment was conducted in which the sputtering time when forming the first silicon film Sf1 and the second silicon film Sf2 under sputtering conditions 1 and 2 was changed to change the ratio of the film thickness of the first silicon film Sf1 to the film thickness (50 nm) of the entire silicon film Sf. Figure 4 As shown in (a) and (b), it can be confirmed that when the film thickness ratio is in the range of 10% to 80%, the refractive index (n value) is in the range of 4 to 5, and the extinction coefficient (k value) is in the range of 0.3 to 0.6, that is, the prescribed optical properties are maintained. Figure 4 As shown in (c), it was confirmed that if the film thickness ratio is changed, the film stress can be changed. In particular, when the film thickness ratio is in the range of 30% to 80%, a small film stress in the range of ±200 MPa can be formed. Next, when the first silicon film Sf1 and the second silicon film Sf2 are continuously formed with a film thickness of 25 nm using sputtering conditions 1 and 2, a bias power is applied to the substrate Sw from the AC power supply 8, and the bias power is changed in the range of 40W to 100W. It can be seen that, as Figure 5 As shown, the film stress changes according to the bias power while maintaining the predetermined optical characteristics.

[0035] The above is a description of the embodiment of the present invention, but various modifications are possible without departing from the scope of the technical concept of the present invention. In the above embodiment, a silicon film is used as an example, but the present invention can also be applied to a laminated film (for example, a film with silicon as a main component and containing nitrogen or oxygen, etc.) that can adjust the film stress while maintaining optical properties by having a columnar structure and a density difference. In addition, in the above embodiment, the first step and the second step are continuously performed in the same vacuum chamber 1. As an example, it is not limited to this, and can also be performed in different vacuum chambers.

[0036] Description of Reference Numerals

[0037] SM. Sputtering device, Sw. Substrate (film formation object), Sf. Silicon film, Sf1. First silicon film, Sf2. Second silicon film, 1. Vacuum chamber, 14. Mass flow controller (device for adjusting the partial pressure of sputtering gas), 3. Target made of silicon, Ps. Sputtering power supply.

Claims

1. A film forming method, which comprises placing a target made of silicon and a film forming object in a vacuum chamber, introducing a sputtering gas into the vacuum chamber with a vacuum atmosphere, applying power to the target, and forming a silicon film on the surface of the film forming object by sputtering, wherein the method is characterized in that: The formation of the silicon film is performed by dividing into a first step of forming a first silicon film having a columnar structure and a second step of forming a second silicon film having a columnar structure and a higher film density than the first silicon film.

2. The film forming method according to claim 1, characterized in that: The partial pressure of the sputtering gas in the vacuum chamber in the first step is taken as a reference partial pressure, and the partial pressure of the sputtering gas in the second step is made lower than the reference partial pressure.

3. The film forming method according to claim 1, characterized in that: A film thickness ratio of the first silicon film to the silicon film is set in a range of 0.3 to 0.

8.

4. The film forming method according to any one of claims 1 to 3, characterized in that: During the process of forming the silicon film on the surface of the film formation object by sputtering, a bias power is applied to the film formation object, wherein: The bias power in the first step and the second step is set within a range of 20W to 100W.

Images