Film formation method

Abstract

Provided is a film forming method by which a metal film having a high melting point can be formed in a state where a stress difference is as small as possible and which is suitable in the case of using a cylindrical target.　A film forming method according to the present invention, which forms a metal film having a high melting point on an opposite surface to each target 5 of a substrate Sw disposed in a vacuum treatment room 1a, comprises: a first step for taking, as a first target group 50a, starting point targets 5a, 5b at which both outer edge parts of the substrate face each other and targets 5c, 5d that are positioned outward in a target aligned direction from the starting point targets, for taking, as a second target group 50b, targets 5e–5h that are positioned inward in the target aligned direction from the starting point targets, and for supplying power to each of the targets of the second target group by means of a sputter power supply 7 and forming a film when the metal film having a high melting point starts to be formed on the substrate; and a second step for supplying power to each of the targets of the first target group by means of the sputter power supply and forming a film simultaneously with or prior to the stopping of supplying power to each target of the second target group.

Description

Technical Field

[0001] The present invention relates to a film forming method, and more particularly to a method for forming a high melting point metal film on a large area substrate by a sputtering method.

Background Art

[0002] In the manufacturing process of a liquid crystal display, for example, there is a step of forming a thin film of a high melting point metal such as molybdenum or tungsten on a substrate. For forming a high melting point metal film, a magnetron sputtering apparatus with high productivity is used. Among them, with the recent increase in the size of liquid crystal displays, a plurality of planar rectangular targets each made of the same high melting point metal are arranged in parallel in a vacuum processing chamber, and a substrate having an area smaller than the area where the targets are arranged in parallel is disposed opposite to each target, and each target is energized by a sputtering power source in a state where a leakage magnetic field is applied to the substrate side of each target, and sputtering is performed. Generally, a method is used in which a high melting point metal film is formed by attaching and depositing sputtered particles on the surface of the substrate facing each target.

[0003] In the above sputtering apparatus, by arranging a plurality of targets in parallel at a predetermined interval, sputtered particles are not emitted from the region between the targets. For this reason, the film thickness distribution on the film forming surface of the substrate becomes non-uniform so as to fluctuate (for example, the thick and thin portions of the film thickness repeat at the same period). For this reason, during film formation by sputtering of the target, for example, Patent Document 1 discloses a method in which each target is reciprocated integrally and at a constant speed parallel to the substrate. In this method, the parallel arrangement direction of the targets is set as the moving direction, and during film formation, each target is integrally reciprocated relative to the substrate in parallel to change the region where sputtered particles are not emitted, thereby improving the non-uniformity of the film thickness distribution. However, with this method, the difference in stress of the high melting point metal film between the central region and the peripheral region of the substrate becomes large.

[0004] A method for forming a high melting point metal film capable of minimizing such stress differences is known, for example, from Patent Document 2. In this method, both outer edge portions of the substrate in the direction parallel to the targets are each used as a starting target for a pair of opposing targets. The starting target and the targets located outward in the direction parallel to the targets from the starting target are defined as the first target group, and the targets located inward in the direction parallel to the targets from the starting target are defined as the second target group. The power input to each target in the first target group by the sputtering power supply is set as the steady power, and the power input to each target in the second target group is controlled to be a power higher than the steady power (twice the steady power).

[0005] By the way, in the above-described type of sputtering apparatus, instead of a rectangular target in plan view, a cylindrical target formed in a cylindrical shape may be used (so-called rotary cathode). When forming a film by sputtering such a cylindrical target, due to the small area of the target to be sputtered, the amount of sputtered particles scattered per unit time is less than that of a rectangular target in plan view. Therefore, in order to increase the film formation rate, the input power to the cylindrical target has to be increased. In such a case, if, as in the above conventional example, twice the power as that for the first target group has to be input to each target in the second target group, not only is a high-output sputtering power supply required for each target in the second target group, leading to high costs, but also problems such as melting and cracking of the target due to insufficient cooling of the target are likely to occur.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In view of the above points, an object of the present invention is to provide a film forming method capable of forming a high melting point metal film in a state where the stress difference is as small as possible, and particularly suitable for the case of using a cylindrical target.

Means for Solving the Problems

[0008] In order to solve the above problems, at least three targets each made of the same high melting point metal are arranged in parallel in a vacuum processing chamber, a substrate having an area smaller than the area of the region where the targets are arranged in parallel is disposed opposite to each target, and power is applied to each target by a sputtering power supply to perform sputtering, and a high melting point metal film is formed on the surface of the substrate facing each target. In the film forming method of the present invention, both outer edge portions of the substrate in the target parallel arrangement direction are each set as a starting target with respect to the target facing them, the starting target and the targets located outward in the target parallel arrangement direction from the starting target are defined as the first target group, and the targets located inward in the target parallel arrangement direction from the starting target are defined as the second target group. When starting to form a high melting point metal film on the substrate, it includes a first step of applying power to each target of the second target group by a sputtering power supply to form a film, and a second step of applying power to each target of the first target group by a sputtering power supply to form a film simultaneously with or prior to the stop of power supply to each target of the second target group.

[0009] Here, each target arranged at intervals in the same plane is formed into a cylindrical target, and when a high melting point metal film is formed by sputtering each cylindrical target, if the same power is applied to each cylindrical target and sputtering is performed simultaneously, the high melting point metal film in the central region of the substrate tends to have a strong tensile stress, while the high melting point metal film at the four corners of the substrate tends to have a strong compressive stress. As a result, it has been found that the stress difference between the central region and the peripheral region increases. (Note that in the central region of the substrate, even if it does not show tensile stress and has a compressive stress value, it has a stronger tendency of tensile stress than the peripheral region of the substrate and may show a small compressive stress as a result.) This is because in the central region of the substrate, in addition to the sputtered particles scattered from each target of the second target group facing this, the sputtered particles scattered from each target of the first target group located on both sides thereof adhere and deposit at different incident angles, resulting in a high melting point metal film with more defects compared to the peripheral region of the substrate. Therefore, in the present invention, as a 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 (that is, at the beginning of film formation, without sputtering each target of the first target group, only each target of the second target group is sputtered to preferentially form a high melting point metal film in the central region of the substrate), thereby forming a dense high melting point metal film in the central region. Then, as a 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.

[0010] According to this, it is possible to form a high melting point metal film having compressive stress over the entire film forming surface of the substrate and having a stress difference as small as possible. In this case, unlike the conventional example, it is not necessary to apply twice the power to each target of the second target group as compared with that of the first target group, which is advantageous. In the second step, although sputter particles scattered from each target of the first target group may adhere and deposit in the central region of the substrate, 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 so much. Considering this, the timing of applying power to each target of the first target group is appropriately set prior to the stop of applying power to each target of the second target group. Thus, in the present invention, by forming a high melting point metal film separately in the central region and the peripheral region of the substrate (that is, with a time difference), it is not necessary to apply high power only to each target of the second target group. Therefore, the same sputter power supply can be used for each target of the first target group and the second target group, and moreover, it is possible to hardly induce melting or cracking of the target due to insufficient cooling, which is advantageous.

[0011] By the way, when forming a high melting point metal film separately in the central region and the peripheral region of the substrate, depending on the film thickness of the high melting point metal film to be formed on the film forming surface of the substrate and the input power, the sputtering time may be longer than that in the case of applying the same power to all targets at the same time, which may reduce the productivity. In the present invention, in the second step, when applying power to each target of the first target group with a first power prior to the stop of applying power to each target of the second target group, until the power application to each target of the second target group is stopped, a configuration may be adopted that further includes a step of applying power to each target of the first target group with a second power lower than the first power. According to this, it is possible to shorten the film forming time by advancing a part of the film forming to the peripheral region of the substrate without inhibiting the formation of a dense high melting point metal film in the central region of the substrate, which is advantageous. The second power and the timing of applying the second power are appropriately set within a range where a dense high melting point metal film can be formed in the central region.

[0012] In the present invention, the target is formed as a cylindrical target, and while power is supplied to each cylindrical target by the sputtering power supply, each cylindrical target is rotated about its axis, and a leakage magnetic field acting on the substrate side of each cylindrical target by a magnet unit assembled in each cylindrical target is reciprocally rotated within a predetermined angular range with respect to a reference line perpendicular to the axis. A configuration including this step can be adopted. According to this, it has been confirmed that a high melting point metal film with a smaller stress difference between the central region and the peripheral region of the substrate can be formed.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0014] Hereinafter, with reference to the drawings, an embodiment of the film forming method of the present invention will be described by taking as an example the case where the target is a cylindrical target made of molybdenum, the substrate is a glass substrate (hereinafter referred to as "substrate Sw") having a rectangular contour and a predetermined thickness, and a molybdenum film is formed on one surface of the substrate by the magnetron sputtering method. In the following, terms indicating directions such as up and down are based on FIG. 1 showing the installation posture of the magnetron type sputtering apparatus capable of implementing the film forming method of the present embodiment, and the juxtaposition direction of the targets described later is the X-axis direction, and the up and down direction perpendicular to the X-axis direction is the Z-axis direction.

[0015] Referring to FIG. 1, a sputtering apparatus Sm includes a vacuum chamber 1 that partitions 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 transfer device 3 is provided below the vacuum chamber 1. The substrate transfer 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 the carrier 31 and thus the substrate Sw can be transferred to a film formation position facing each of the cylindrical targets 5 described later by a drive device (not shown). Since a known substrate transfer device 3 can be used, further description thereof is omitted. A gas introduction means 4 is also provided in the vacuum chamber 1. The gas introduction means 4 communicates with a gas source (not shown) through a gas pipe 42 provided with a mass flow controller 41, and a sputtering gas can be introduced into the vacuum processing chamber 1a at a predetermined flow rate. The sputtering gas includes not only a noble gas such as argon gas for forming a plasma atmosphere but also a reactive gas such as oxygen gas or nitrogen gas used in reactive sputtering. And a cathode unit Cu is provided above the inside of the vacuum chamber 1 so as to face the substrate Sw that has been transferred to the film formation position shown in FIG. 1 by the substrate transfer device 3.

[0016] The cathode unit Cu includes a plurality of cylindrical targets 5 (5a to 5h) having the same structure and magnet units 6 respectively assembled therein. Each cylindrical target 5 is made of molybdenum as a high melting point metal and is formed into a cylindrical shape by a known method. Then, each cylindrical target 5 is arranged in parallel in the vacuum chamber 1 in a posture where its longitudinal direction coincides with the direction orthogonal 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 orthogonal to the X-axis direction), and the number of the cylindrical targets 5 arranged in parallel is at least 3 or more and is appropriately set according to the length of the substrate Sw (the length in the X-axis direction). In the present embodiment, one cylindrical target 5a and 5b are provided above both outer edge portions in the X-axis direction of the substrate Sw. Taking these cylindrical targets 5a and 5b as starting targets, one cylindrical target 5c and 5d are respectively provided outside the starting targets 5a and 5b in the X-axis direction, and four cylindrical targets 5e to 5h are respectively provided inside the starting targets 5a and 5b in the X-axis direction. Thereby, at the film formation position, the substrate Sw having an area smaller than the area where the targets 5a to 5h are arranged in parallel is concentrically opposed to the area. Hereinafter, the starting targets 5a and 5b and the cylindrical targets 5c and 5d outside the X-axis direction are defined as the first target group 50a, and the other cylindrical targets 5e to 5h are defined as the second target group 50b.

[0017] At both longitudinal ends of each cylindrical target 5, a drive block 51 and a driven block (not shown) are respectively attached, and each cylindrical target 5 can be rotationally driven at a predetermined number of rotations around its axis. Since known structures such as a structure for circulating a refrigerant in the drive block 51, the driven block, and the cylindrical target 5 can be used, further description thereof is omitted. Each cylindrical target 5 is respectively connected to a sputtering power source 7 disposed outside the vacuum chamber 1, and DC power having a negative potential is applied to each cylindrical target 5. Note that AC power may be applied to the paired cylindrical targets 5 respectively.

[0018] As shown in Fig. 2, the magnet unit 6 acts on the 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. The magnet unit 6 includes 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-like member made of a magnetic material that forms a top surface 61a parallel to the substrate Sw and inclined surfaces 61b that incline upward from the top surface 61a, respectively. A central magnet 62 is disposed on the top surface 61a of the yoke 61, and peripheral magnets 63 are respectively disposed on both inclined surfaces 61b. Although not particularly shown and described, corner magnets (not shown) are disposed at both ends in the generatrix direction of the top surface 61a of the yoke 61 so as to bridge between the peripheral magnets 63 while surrounding the ends of the central magnet 62. As the central magnet 62, the peripheral magnets 63, and the corner magnets, neodymium magnets with the same magnetization are used. For example, a bar-shaped one with a substantially square cross-section formed integrally can be used.

[0019] On one end surface of the yoke 61 on the side of the drive block 51, a shaft body 64 projects along the axis of the cylindrical target 5, and the shaft body 64 is connected to the drive shaft of a motor Mt disposed in the drive block 51. Then, with the position where the top surface 61a of the yoke 61 faces downward in the Z-axis direction as a reference position, the magnet unit 6 can be reciprocally rotated at a predetermined speed within an angular range of, for example, ±30 degrees from the reference position. The sputtering apparatus Sm has a control unit Pu including a microcomputer, a sequencer, etc. In addition to controlling each sputtering power supply 7, the mass flow controller 41, the vacuum pump 2, and the motor Mt are comprehensively controlled. Hereinafter, with reference to Fig. 3, the film forming method of the present embodiment using the sputtering apparatus Sm will be described.

[0020] After the carrier 31 holding the substrate Sw with the upper surface of the substrate Sw opened by the substrate transfer device 3 is transferred to the film forming position, 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 (for example, 1×10 -5When reaching Pa), the control unit Pu introduces argon gas from the gas pipe 42 into the vacuum processing chamber 1a at a predetermined flow rate (the pressure in the vacuum processing chamber 1a ranges from 0.2 Pa to 2.0 Pa), and applies power to each target 5e - 5h of the second target group 50b from each sputtering power supply 7 with the first power P1 respectively (for example, 30 kW to 60 kW). Then, in the space between the substrate Sw and each target 5e - 5h of the second target group 50b, high - density race - track - shaped plasmas are respectively generated by the leakage magnetic field acting from the magnet unit 6. While reciprocally rotating each magnet unit 6 at a predetermined speed within an angular range of, for example, ±30 degrees from the reference position, each target 5e - 5h is sputtered by the ions of argon gas in the plasma. As a result, the sputtered particles scattered from each target 5e - 5h preferentially adhere and deposit on the central region of the substrate Sw (an area equal to or larger than the area where each target 5e - 5h is arranged side by side), and a molybdenum film is formed (the first step).

[0021] In the first step, each target 5a - 5d of the first target group 50a is not sputtered. In other words, by preventing the sputtered particles scattered from these targets 5a - 5d from obliquely incident on the central region of the substrate Sw, the molybdenum film formed in the central region can be made dense (that is, having the same film quality as that formed in the peripheral region), and a film with compressive stress can be obtained. The time (t1) of the first step is appropriately set according to, for example, the input power and the film thickness of the molybdenum film to be formed in the central region of the substrate Sw.

[0022] Next, simultaneously with the end of the first step (stopping the power supply from each sputtering power supply 7 to each target 5e to 5h of the second target group 50b), power is supplied to each target 5a to 5d of the first target group 50a from each sputtering power supply 7 with the first power P1 equivalent to that in the first step (in this case, the introduction of argon gas is maintained as it is). Then, the plasma generated in the space between the substrate Sw and each target 5e to 5h of the second target group 50b disappears, and in the space between the substrate Sw and each target 5a to 5d of the first target group 50a, racetrack-shaped high-density plasmas are generated respectively by the leakage magnetic field acting from the magnet unit 6. Then, while reciprocally rotating each magnet unit 6 at a predetermined speed within an angular range of, for example, ±30 degrees from the reference position, each target 5a to 5d is sputtered by the ions of argon gas in the plasma, and the sputtered particles scattered from each target 5a to 5d adhere and deposit on the peripheral region (the region outside the central region) of the substrate Sw to form a molybdenum film (second step). Thereby, the molybdenum film formed in the peripheral region can be made into a dense film with compressive stress. The time (t2) of the second step 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. During the second step, sputtered particles scattered from each target 5a to 5d of the first target group 50a may adhere and deposit on the central region of the substrate Sw. However, since a dense molybdenum film has been once formed in the central region in the first step, the stress in the central region does not change significantly. Also, depending on the film thickness of the molybdenum film, the first step and the second step can be sequentially repeated a plurality of times to form a film.

[0023] According to the above, by forming the molybdenum film in two steps, namely the first step of forming the film in the central region of the substrate Sw and the second step of forming the film in the peripheral region of the substrate Sw, it is possible to form a molybdenum film having compressive stress over the entire film-forming surface of the substrate Sw and with the stress difference being as small as possible. In this case, it is not necessary to apply twice the power to each of the targets 5a to 5d of the first target group 50a with respect to each of the targets 5e to 5h of the second target group 50b as in the above conventional example. As a result, the same sputtering power supplies 7 can be used for each of the targets 5a to 5h of the first target group 50a and the second target group 50b, and moreover, it is difficult to induce melting or cracking of each of the targets 5e to 5h of the second target group 50b due to insufficient cooling, which is advantageous.

[0024] Next, in order to confirm the above effects, the following experiment was conducted using the sputtering apparatus Sm. In Invention Experiment 1, a rectangular glass substrate of 1850×1500 mm was used as the substrate Sw, and eight cylindrical targets 5a to 5h with a diameter of Φ153 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 parallel target arrangement area was larger than the area of the substrate Sw. Further, as the sputtering conditions, the pressure in the vacuum processing chamber 1a at the time of introducing argon gas was set to 0.2 Pa, the first power P1 was set to 50 Kw, and t1 and t2 were set so that the target film thickness of the substrate Sw became 230 nm.

[0025] Here, as a comparative experiment, power was applied to all the targets 5a to 5h simultaneously at the first power P1 (50 kW), and a molybdenum film was formed in a single step (the time of t1 + t2). Then, when the stress of the molybdenum film after film formation was measured at a total of five points, namely the central part and the four corners of the substrate Sw, it was confirmed that the molybdenum film after film formation in the central part of the substrate Sw had a strong tendency of tensile stress, while the molybdenum film after film formation at the measurement points at the four corners of the substrate Sw had a strong tendency of compressive stress, and as a result, a stress difference of up to 878 MPa occurred.

[0026] In contrast, in Invention Experiment 1, similarly, when the stress of the molybdenum film after film formation was measured at a total of five points, i.e., the central part and the four corners of the substrate Sw, all the molybdenum films after film formation 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. It was confirmed that the stress difference could be reduced between the central region and the outer peripheral region of the substrate Sw. Further, as Invention Experiment 2, during sputtering in the first step and the second step, a condition was added in which the magnet unit 6 was reciprocally rotated within a range of ±30 degrees with respect to the reference line Ls by the motor Mt to form a molybdenum film. As a result, all the molybdenum films after film formation 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. It was confirmed that the stress difference could be further reduced as compared with Invention Experiment 1 above.

[0027] As described above, the embodiments of the present invention have been explained. However, various modifications are possible without departing from the scope of the technical idea of the present invention. In the above embodiment, the case of forming a molybdenum film using the cylindrical target 5 made of molybdenum (Mo) has been described as an example. However, the present invention can also be applied to the case of forming a high melting point metal film using a target made of one kind of high melting point metal selected from tungsten (W) and tantalum (Ta) or a cylindrical target made of an alloy of two or more high melting point metals (for example, Mo-W). Further, in the above embodiment, the case of using a cylindrical target has been described as an example, but the present invention can also be applied to the case of using a target having a rectangular shape in plan view.

[0028] In the above-described embodiment, the case where the second step is started simultaneously with the end of the first step has been described as an example, but the present invention is not limited thereto. 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 after the start of the first step, and can be appropriately set within a range that does not inhibit the formation of a dense molybdenum film in the central region of the substrate Sw. On the other hand, as shown in FIG. 4(b), the start time t1b of the second step may be made earlier than the time t1a, and a second power P2 smaller than the first power P1 may be applied to each of the targets 5a to 5d of the first target group 50a from the start time t1b to the end time t1 of the first step. According to this, by advancing a part of the film formation on the peripheral region of the substrate Sw, the film formation time can be shortened, which is advantageous. In this case, the start time t1b of the second step can be, for example, after half of the period of the first step has elapsed.

[0029] In the above-described embodiment, the case where the film formation is performed with the substrate Sw in a horizontal posture with its film formation surface facing upward in the vertical direction has been described as an example, but the present invention can also be applied to the case where the film formation is performed with the substrate Sw in an upright posture with its film formation surface facing in the horizontal direction (in this case, each of the targets 5a to 5h is arranged in an upright posture with its axial direction aligned with the vertical direction).

Explanation of Reference Numerals

[0030] 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

1. In a film forming method, at least three targets each made of the same high melting point metal are arranged in parallel in a vacuum processing chamber, a substrate having an area smaller than the area of the region where the targets are arranged in parallel is disposed opposite to each target, power is supplied to each target by a sputtering power supply to perform sputtering, and a high melting point metal film is formed on the surface of the substrate facing each target, both outer edge portions of the substrate in the target parallel arrangement direction are each set as a starting target for the target facing them, the starting target and the targets located outward in the target parallel arrangement direction from the starting target are defined as a first target group, and the targets located inward in the target parallel arrangement direction from the starting target are defined as a second target group. At the start of film formation of the high melting point metal film on the substrate, a first step of supplying power only to each target of the second target group by a sputtering power supply to form a film, and a second step of supplying power to each target of the first target group by a sputtering power supply to form a film simultaneously with or prior to the stop of power supply to each target of the second target group. The film forming method is characterized by including these steps.

2. In the second step, when power is supplied to each target of the first target group with a first power prior to the stop of power supply to each target of the second target group, until the power supply to each target of the second target group is stopped, the method further includes a step of supplying power to each target of the first target group with a second power lower than the first power. The film forming method according to Claim 1 is characterized by this.

3. The target is a cylindrical target formed in a cylindrical shape. While power is supplied to each cylindrical target by the sputtering power supply, each cylindrical target is rotated around its axis, and a leakage magnetic field acting on the substrate side of each cylindrical target by a magnet unit assembled in each cylindrical target is reciprocally rotated within a predetermined angular range with respect to a reference line orthogonal to the axis. The film forming method according to Claim 1 or Claim 2 is characterized by including this step.

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