JP7684418B2 - Film forming method - Google Patents

Description

The present invention relates to a film forming method, and more specifically, to a method for forming a high melting point metal film on a large-area substrate by a sputtering method.

The manufacturing process of liquid crystal displays includes, for example, a process of depositing a thin film of a high-melting point metal such as molybdenum or tungsten on a substrate. A highly productive magnetron sputtering device is used to deposit the high-melting point metal film. Among them, with the recent increase in the size of liquid crystal displays, a method is generally used in which multiple targets, each of which is rectangular in plan view and made of the same high-melting point metal, are arranged side by side in a vacuum processing chamber, a substrate with an area smaller than the area where the targets are arranged side by side is placed opposite each target, and each target is sputtered by applying power to each target from a sputtering power supply while a leakage magnetic field is applied to the substrate side of each target, and sputtering is performed by attaching and depositing sputtered particles on the surface of the substrate facing each target, thereby depositing a high-melting point metal film.

In the above sputtering device, multiple targets are arranged at a predetermined interval so that sputter particles are not emitted from the areas between the targets. This results in uneven film thickness distribution on the film-forming surface of the substrate, with a wavy pattern (for example, thick and thin film thicknesses are repeated at the same period). For this reason, a device is known, for example in Patent Document 1, in which the targets are moved back and forth together at a constant speed parallel to the substrate during film formation by sputtering the targets. In this device, the direction in which the targets are arranged side by side is set as the direction of movement, and the targets are moved back and forth together relative to the substrate during film formation to change the areas from which sputter particles are not emitted, thereby improving the unevenness of the film thickness distribution. However, this increases the difference in stress of the refractory metal film between the central and peripheral regions of the substrate.

A method for depositing a high melting point metal film that can minimize such stress differences is known, for example, from Patent Document 2. In this method, the targets facing each other at both outer edge portions in the target arrangement direction of the substrate are set as the origin target, the origin target and targets positioned outward from the origin target in the target arrangement direction are set as a first target group, and targets positioned inward from the origin target in the target arrangement direction are set as a second target group, and the power input to each target in the first target group by the sputtering power supply is set as steady power, and power higher than the steady power (twice the steady power) is controlled to be input to each target in the second target group.

In the above-mentioned sputtering apparatus, a cylindrical target formed in a cylindrical shape may be used instead of a target having a rectangular shape in plan view (so-called a rotary cathode). When forming a film by sputtering such a cylindrical target, the area of the sputtered target is small, so that the amount of sputtered particles scattered per unit time is smaller than that of a target having a rectangular shape in plan view. For this reason, in order to increase the film formation rate, it is necessary to increase the power input to the cylindrical target. In such a case, if it is necessary to input twice the power to each target of the second target group compared to that of the first target group as in the above-mentioned conventional example, a high-output sputtering power source for each target of the second target group is required, which not only leads to high costs, but also leads to problems such as melting and cracking of the targets due to insufficient cooling of the targets.

JP 2010-236051 A Patent No. 6588351

In view of the above, the present invention has an objective of providing a film formation method capable of forming a high-melting point metal film with as small a stress difference as possible, and which is particularly suitable when a cylindrical target is used.

In order to solve the above problems, the film formation method of the present invention involves arranging at least three targets, each made of the same high-melting point metal, side by side in a vacuum processing chamber, placing a substrate having an area smaller than the area where the targets are arranged side by side opposite each target, supplying power to each target from a sputtering power supply to perform sputtering, and forming a high-melting point metal film on the surface of the substrate facing each target. The method is characterized in that it includes a first step in which, at the start of formation of a high-melting point metal film on the substrate, power is supplied to each target of the second target group from the sputtering power supply to form a film, and simultaneously with or prior to the cessation of power supply to each target of the second target group, power is supplied to each target of the first target group from the sputtering power supply to form a film.

Here, when each target arranged side by side at intervals on the same plane is a cylindrical target formed in a cylindrical shape and each cylindrical target is sputtered to form a high-melting point metal film, if the same power is input to each cylindrical target and sputtered simultaneously, the high-melting point metal film in the central region of the substrate tends to have a strong tendency toward tensile stress, while the high-melting point metal film in the four corners of the substrate tends to have a strong tendency toward compressive stress, resulting in a large difference in stress between the central region and the peripheral region (Note that the central region of the substrate does not show tensile stress, and even if the value is compressive stress, the tendency toward tensile stress is stronger than in the peripheral region of the substrate, and as a result, it may show a small compressive stress). This is thought to be due to the fact that in the central region of the substrate, in addition to the sputter particles scattered from each target of the second target group facing it, the sputter particles scattered from each target of the first target group located on both sides of it adhere and accumulate at different angles of incidence, resulting in a high-melting point metal film with more defects than the peripheral region of the substrate. Therefore, in the present invention, in the first step, each target of the second target group is sputtered to form a high-melting point metal film in the central region of the substrate (i.e., at the beginning of the film formation, each target of the first target group is not sputtered, but only each target of the second target group is sputtered to form a high-melting point metal film preferentially in the central region of the substrate), thereby forming a dense high-melting point metal film in the central region. Then, in the second step, each target of the first target group is sputtered to form a similarly dense high-melting point metal film in the peripheral region of the substrate.

This makes it possible to form a high-melting-point metal film that has compressive stress over the entire film formation surface of the substrate and has a small stress difference. In this case, it is advantageous to eliminate the need to apply twice as much power to each target of the second target group as to the first target group, as in the conventional example. In the second step, sputter particles scattered from each target of the first target group may adhere and accumulate in the central region of the substrate, but it has been confirmed that if a dense high-melting-point metal film is once formed in the central region in the first step, the stress in the central region does not change significantly. Taking this into consideration, the timing of applying power to each target of the first target group prior to stopping the application of power to each target of the second target group is appropriately set. In this way, in the present invention, by depositing a high-melting point metal film separately in the central region and the peripheral region of the substrate (i.e., with a time difference), it is possible to eliminate the need to input high power only to each target in the second target group, and therefore the same sputtering power source can be used for each target in the first target group and the second target group, and further, it is possible to reduce the likelihood of targets melting or cracking due to insufficient cooling, which is advantageous.

However, when a high melting point metal film is formed separately in the central region and the peripheral region of the substrate, depending on the thickness of the high melting point metal film to be formed on the film formation surface of the substrate and the input power, the sputtering time may be longer than when the same power is simultaneously input to all targets, which may reduce productivity. In the present invention, when the first power is input to each target of the first target group prior to the stop of the power input to each target of the second target group in the second step, a configuration may be adopted that further includes a step of inputting power to each target of the first target group at a second power lower than the first power until the power input to each target of the second target group is stopped. According to this, it is possible to advance the film formation in the peripheral region of the substrate in part to a range that does not hinder the formation of a dense high melting point metal film in the central region of the substrate, thereby shortening the film formation time, which is advantageous. The second power and the timing of inputting the second power are appropriately set within a range in which a dense high melting point metal film can be formed in the central region.

In addition, in the present invention, the target may be a cylindrical target formed in a cylindrical shape, and a configuration may be adopted that further includes a step of rotating each cylindrical target about its axis while power is supplied to each cylindrical target by the sputtering power supply, and rotating a leakage magnetic field acting on the substrate side of each cylindrical target back and forth within a predetermined angle range with respect to a reference line perpendicular to the axis by a magnet unit assembled in each cylindrical target. It has been confirmed that this makes it possible to form a high-melting point metal film with a smaller stress difference between the central region and the peripheral region of the substrate.

1 is a schematic cross-sectional view of a magnetron sputtering apparatus capable of carrying out a film forming method according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a portion of the rotary cathode shown in FIG. 1 . 4 is a timing chart showing the timing of power supply to each target. 13A and 13B are timing charts showing the timing of power supply to each target according to a modified example.

Hereinafter, with reference to the drawings, an embodiment of the film formation method of the present invention will be described using as an example a case where the target is a cylindrical target made of molybdenum and formed into a cylindrical shape, the substrate is a glass substrate of a predetermined thickness having a rectangular outline (hereinafter referred to as "substrate Sw"), and a molybdenum film is formed on one side of the substrate by magnetron sputtering. In the following, terms indicating directions such as up and down are based on FIG. 1, which shows the installation posture of a magnetron sputtering device capable of implementing the film formation method of this embodiment, and the direction in which the targets are arranged side by side, which will be described later, is the X-axis direction, and the up and down direction perpendicular to the X-axis direction is the Z-axis direction.

Referring to FIG. 1, the sputtering apparatus Sm includes a vacuum chamber 1 that defines a vacuum processing chamber 1a. A vacuum pump 2 is connected to the vacuum chamber 1 via an exhaust pipe 21, and the vacuum processing chamber 1a can be evacuated to a predetermined pressure (for example, 1×10 ⁻⁵ Pa). A substrate transport device 3 is provided at the bottom of the vacuum chamber 1. The substrate transport device 3 has a carrier 31 that holds the substrate Sw with the upper surface of the substrate Sw as a film formation surface open, and can transport the carrier 31 and thus the substrate Sw to a film formation position facing each cylindrical target 5 described later by a driving device not shown. Since a known device can be used as the substrate transport device 3, further explanation is omitted. The vacuum chamber 1 is also provided with a gas introduction means 4. The gas introduction means 4 communicates with a gas source not shown through a gas pipe 42 having a mass flow controller 41 interposed therebetween, and can introduce a sputtering gas into the vacuum processing chamber 1a at a predetermined flow rate. The sputtering gas includes not only rare gases such as argon gas for forming a plasma atmosphere, but also reactive gases such as oxygen gas and nitrogen gas used in reactive sputtering. A cathode unit Cu is provided at the upper part of the vacuum chamber 1 so as to face the substrate Sw transported by the substrate transport device 3 to the film formation position shown in FIG.

The cathode unit Cu includes a plurality of cylindrical targets 5 (5a to 5h) having the same structure and a magnet unit 6 assembled therein. Each cylindrical target 5 is made of molybdenum, a high melting point metal, and is formed into a cylindrical shape by a known method. Each cylindrical target 5 is arranged in parallel in the vacuum chamber 1 with its longitudinal direction aligned in a direction perpendicular to the X-axis direction and at a predetermined interval (for example, at equal intervals) from each other in the X-axis direction. In this case, the length of each cylindrical target 5 is set to be longer than the width of the substrate Sw (the length in the direction perpendicular to the X-axis direction), and the number of cylindrical targets 5 arranged in parallel is at least three or more and is appropriately set according to the length of the substrate Sw (the length in the X-axis direction). In this embodiment, one cylindrical target 5a, 5b is provided above both outer edges of the substrate Sw in the X-axis direction, and these cylindrical targets 5a, 5b are used as starting targets. One cylindrical target 5c, 5d is provided outside the starting targets 5a, 5b in the X-axis direction, and four cylindrical targets 5e to 5h are provided inside the starting targets 5a, 5b in the X-axis direction. As a result, at the film formation position, the substrate Sw having an area smaller than the area where the targets 5a to 5h are arranged side by side is arranged concentrically opposite the area. In the following, the starting targets 5a, 5b and the cylindrical targets 5c, 5d outside the X-axis direction are referred to as the first target group 50a, and the other cylindrical targets 5e to 5h are referred to as the second target group 50b.

A driving block 51 and a driven block (not shown) are attached to both longitudinal ends of each cylindrical target 5, respectively, and each cylindrical target 5 can be rotated around its axis at a predetermined number of revolutions. Since the driving block 51, the driven block, and the structure for circulating the coolant inside the cylindrical target 5 can be known, further explanation is omitted. Each cylindrical target 5 is connected to a sputtering power source 7 arranged outside the vacuum chamber 1, and DC power with a negative potential is input to each cylindrical target 5. Note that AC power may be input to each of the paired cylindrical targets 5.

As shown in FIG. 2, the magnet unit 6 applies a leakage magnetic field leaking from the surface of the cylindrical target 5 so that a line passing through a position where the vertical component of the magnetic field becomes zero in the space between the cylindrical target 5 and the substrate Sw extends along the generatrix of the cylindrical target 5 and closes in a racetrack shape, and is provided with a support plate (yoke) 61 made of a magnetic material extending along the longitudinal direction of the cylindrical target 5. The yoke 61 is composed of a plate-shaped member made of a magnetic material that forms a top surface 61a parallel to the substrate Sw and an inclined surface 61b that inclines upward from the top surface 61a. A central magnet 62 is arranged on the top surface 61a of the yoke 61, and peripheral magnets 63 are arranged on both inclined surfaces 61b. Although not specifically shown and described, corner magnets (not shown) are arranged at both ends of the generatrix direction of the top surface 61a of the yoke 61 to surround the ends of the central magnet 62 and bridge between the peripheral magnets 63. The central magnet 62, the peripheral magnets 63, and the corner magnets are made of neodymium magnets having the same magnetization, and may be, for example, rod-shaped magnets having an approximately rectangular cross section that are integrally molded.

A shaft 64 is protruded from one end surface of the yoke 61 on the drive block 51 side along the axis of the cylindrical target 5, and the shaft 64 is connected to the drive shaft of the motor Mt arranged in the drive block 51. The magnet unit 6 can be rotated back and forth at a predetermined speed within an angle range of, for example, ±30 degrees from the reference position, with the position where the top surface 61a of the yoke 61 faces downward in the Z-axis direction being the reference position. The sputtering device Sm has a control unit Pu equipped with a microcomputer, a sequencer, etc., which controls each sputtering power supply 7 as well as the mass flow controller 41, the vacuum pump 2, and the motor Mt. Below, with reference to FIG. 3, the film formation method of this embodiment using the sputtering device Sm will be described.

After the substrate transport device 3 transports the carrier 31 holding the substrate Sw to a film formation position with the top surface of the substrate Sw open, the vacuum processing chamber 1a is evacuated by the vacuum pump 2. When the pressure in the vacuum processing chamber 1a reaches a predetermined pressure (e.g., 1×10 ⁻⁵ Pa), the control unit Pu introduces argon gas at a predetermined flow rate from the gas pipe 42 into the vacuum processing chamber 1a (the pressure in the vacuum processing chamber 1a becomes in the range of 0.2 Pa to 2.0 Pa), and supplies power (e.g., 30 kW to 60 kW) from each sputtering power source 7 to each of the targets 5e to 5h in the second target group 50b with the first power P1. Then, in the space between the substrate Sw and each of the targets 5e to 5h of the second target group 50b, a racetrack-shaped high-density plasma is generated by the leakage magnetic field acting from the magnet unit 6, and while each of the magnet units 6 is rotated back and forth at a predetermined speed within an angular range of, for example, ±30 degrees from a reference position, each of the targets 5e to 5h is sputtered by argon gas ions in the plasma. As a result, the sputtered particles scattered from each of the targets 5e to 5h are preferentially attached and deposited in the central region of the substrate Sw (a region equal to or larger than the region where each of the targets 5e to 5h are arranged side by side), forming a molybdenum film (first step).

In the first step, the targets 5a to 5d of the first target group 50a are not sputtered, in other words, the sputtered particles scattered from the targets 5a to 5d are not obliquely incident on the central region of the substrate Sw, so that the molybdenum film formed in the central region is dense (i.e., has the same film quality as that formed in the peripheral region) and has compressive stress. The time (t1) of the first step is set appropriately depending on, for example, the input power and the film thickness of the molybdenum film to be formed in the central region of the substrate Sw.

Next, at the same time as the end of the first step (stopping the supply of power from each sputtering power supply 7 to each target 5e-5h of the second target group 50b), each sputtering power supply 7 supplies power to each target 5a-5d of the first target group 50a with the first power P1 equivalent to the first step (in this case, the introduction of argon gas is maintained as is). Then, the plasma generated in the space between the substrate Sw and each target 5e-5h of the second target group 50b disappears, and a racetrack-shaped high-density plasma is generated in the space between the substrate Sw and each target 5a-5d of the first target group 50a by the leakage magnetic field acting from the magnet unit 6. Then, while each magnet unit 6 is rotated back and forth at a predetermined speed within an angle range of, for example, ±30 degrees from the reference position, each target 5a to 5d is sputtered by argon gas ions in the plasma, and sputtered particles scattered from each target 5a to 5d are attached and deposited in the peripheral region (region outside the central region) of the substrate Sw to form a molybdenum film (second process). This makes it possible to make the molybdenum film formed in the peripheral region a dense film having compressive stress. The time (t2) of the second process is also appropriately set according to, for example, the input power and the film thickness of the molybdenum film to be formed in the peripheral region of the substrate Sw. Note that, during the second process, sputtered particles scattered from each target 5a to 5d of the first target group 50a may adhere and deposit in the central region of the substrate Sw, but since a dense molybdenum film has been formed in the central region once in the first process, the stress in the central region does not change much. Depending on the thickness of the molybdenum film, the first and second steps may be repeated several times to form the film.

According to the above, by forming a molybdenum film in two steps, a first step in which a film is formed in the central region of the substrate Sw and a second step in which a film is formed in the peripheral region of the substrate Sw, a molybdenum film having compressive stress over the entire film formation surface of the substrate Sw and with a stress difference as small as possible can be formed. In this case, it is not necessary to apply twice the power to each of the targets 5e-5h of the second target group 50b as to each of the targets 5a-5d of the first target group 50a, as in the above conventional example. This allows the same sputtering power source 7 to be used for each of the targets 5a-5h of the first target group 50a and the second target group 50b, and is advantageous in that it is difficult to induce melting or cracking of each of the targets 5e-5h of the second target group 50b due to insufficient cooling.

Next, to confirm the above effects, the following experiment was conducted using the sputtering device Sm. In invention experiment 1, a rectangular glass substrate of 1850 x 1500 mm was used as the substrate Sw, and eight cylindrical targets 5a to 5h with a diameter of 153 mm and an axial length of 2336 mm were arranged in parallel in the X-axis direction at intervals of 235 mm so that the area of the target was larger than the area of the substrate Sw. In addition, as sputtering conditions, the pressure of the vacuum processing chamber 1a when introducing argon gas was 0.2 Pa, the first power P1 was 50 Kw, and t1 and t2 were set so that the target film thickness of the substrate Sw was 230 nm.

Here, as a comparative experiment, the first power P1 (50 kW) was simultaneously applied to all targets 5a to 5h, and a molybdenum film was formed in a single process (time t1 + t2). The stress of the formed molybdenum film was then measured at a total of five points, the center and four corners of the substrate Sw. It was confirmed that the molybdenum film at the center of the substrate Sw had a stronger tendency toward tensile stress, whereas the molybdenum film at the measurement points at the four corners of the substrate Sw had a stronger tendency toward compressive stress, resulting in a stress difference of up to 878 MPa.

In contrast, in invention experiment 1, the stress of the molybdenum film after deposition was measured at five points, the center and four corners of the substrate Sw, and it was confirmed that the molybdenum film after deposition at each measurement point had compressive stress, and the stress difference between the measurement point with the largest compressive stress and the measurement point with the smallest compressive stress was 395 MPa, and it was confirmed that the stress difference between the central region and the outer peripheral region of the substrate Sw could be reduced. In addition, in invention experiment 2, a molybdenum film was deposited under the additional condition that the magnet unit 6 was rotated back and forth within a range of ±30 degrees with respect to the reference line Ls by the motor Mt during sputtering in the first and second steps. It was confirmed that the molybdenum film after deposition at each measurement point had compressive stress, and the stress difference between the measurement point with the largest compressive stress and the measurement point with the smallest compressive stress was 300 MPa, and it was confirmed that the stress difference could be reduced even further compared to the above invention experiment 1.

Although the embodiment of the present invention has been described above, various modifications are possible without departing from the scope of the technical concept of the present invention. In the above embodiment, a molybdenum film is formed using a cylindrical target 5 made of molybdenum (Mo), but the present invention can also be applied to a case where a high-melting point metal film is formed using a cylindrical target made of one type of high-melting point metal selected from tungsten (W) and tantalum (Ta) or an alloy of two or more types of high-melting point metals (e.g., Mo-W). In addition, although the above embodiment has been described using a cylindrical target, the present invention can also be applied to a case where a target that is rectangular in plan view is used.

In the above embodiment, the second step is started simultaneously with the end of the first step, but the present invention is not limited to this. For example, as shown in FIG. 4(a), the second step may be started before the end time t1 of the first step. In this case, the start time t1a of the second step may be set appropriately within a range that does not hinder the formation of a dense molybdenum film in the central region of the substrate Sw as long as it is after the start of the first step. On the other hand, as shown in FIG. 4(b), the start time t1b of the second step may be set even earlier than the above-mentioned time t1a, and a second power P2 smaller than the first power P1 may be input to each target 5a to 5d of the first target group 50a between the start time t1b and the end time t1 of the first step. This is advantageous in that the film formation on the peripheral region of the substrate Sw can be partially advanced, thereby shortening the film formation time. In this case, the start time t1b of the second step may be set, for example, after half the period of the first step has elapsed.

In addition, in the above embodiment, a case has been described in which film formation is performed on the substrate Sw in a horizontal position with its film formation surface facing vertically upward, but the present invention can also be applied to a case in which film formation is performed on the substrate Sw in an upright position with its film formation surface facing horizontally (in this case, each target 5a to 5h is positioned in an upright position with its axial direction aligned with the vertical direction).

1a...vacuum processing chamber, Sw...substrate, 5 (5a to 5h)...cylindrical target, 5a, 5b...starting target, 50a...first target group, 50b...second target group, 6...magnet unit, 7...sputtering power supply.

Claims (3)

A film formation method comprising: arranging at least three targets, each made of the same high-melting point metal, side by side in a vacuum processing chamber; arranging a substrate having an area smaller than an area where the targets are arranged side by side, facing each of the targets; and applying power to each target from a sputtering power source to perform sputtering, thereby forming a high-melting point metal film on a surface of the substrate facing each target,
a first target group including targets positioned outward from the origin target in the target arrangement direction and inward from the origin target in the target arrangement direction, and a second target group including targets positioned inward from the origin target in the target arrangement direction; a first step of supplying power to only the targets in the second target group using a sputtering power supply at the start of deposition of a high-melting point metal film on the substrate to deposit a film; and a second step of supplying power to each target in the first target group using a sputtering power supply simultaneously with or prior to the stopping of the supply of power to each target in the second target group to deposit a film.
The film forming method according to claim 1, further comprising the step of: when, in the second step, power is supplied to each of the targets in the first target group at a first power prior to stopping the supply of power to each of the targets in the second target group, supplying power to each of the targets in the first target group at a second power lower than the first power until the supply of power to each of the targets in the second target group is stopped. The film forming method according to claim 1 or 2, further comprising the steps of: making the targets cylindrical targets formed in a cylindrical shape; rotating each cylindrical target about its axis while supplying power to each cylindrical target from the sputtering power source; and rotating a leakage magnetic field acting on the substrate side of each cylindrical target by a magnet unit assembled inside each cylindrical target back and forth within a predetermined angle range with respect to a reference line perpendicular to the axis.

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