JP6734711B2 - Deposition method - Google Patents

Description

The present invention relates to a film forming method, and more particularly, to a method of forming an aluminum oxide film on the surface of an object to be formed by reactive sputtering.

The aluminum oxide film may be conventionally used as a protective film (passivation film) or an insulating film for elements such as thin film transistors in display devices and semiconductor devices. A sputtering method is generally known for forming such an aluminum oxide film (see, for example, Patent Documents 1 and 2), and among them, a so-called reactive sputtering method is generally used. In this case, a target made of aluminum is used, and the target and the film-forming target are placed in a vacuum chamber and evacuated, and when a predetermined pressure is reached, a rare gas for discharge and a reaction gas such as oxygen gas are discharged. Are introduced, and the target is sputtered by applying a predetermined electric power having a negative potential to the target. As a result, a reaction product of aluminum atoms scattered from the target and oxygen adheres to and deposits on the film formation target, and an aluminum oxide film is formed on the surface thereof.

The aluminum oxide film formed as described above usually has a stress in the compressing direction, but when the compressive stress becomes large, there arises a problem that the warp of the substrate becomes large. Therefore, development of forming an aluminum oxide film having a stress within a predetermined value by a reactive sputtering method is an urgent task. Therefore, the inventors of the present application have conducted intensive studies and have found out the following.

That is, when a predetermined power is applied to an aluminum target to form an aluminum oxide film by reactive sputtering, oxygen in the vacuum chamber reacts with aluminum atoms and adheres to the film formation target. When the amount of oxygen gas introduced into the chamber is increased relatively to increase the oxygen partial pressure in the vacuum chamber, the amount of oxygen adhering to the target surface increases, and eventually the target surface is oxidized. It has been found that the stress of the aluminum oxide film can be reduced as much as possible by sputtering the target in such a state and forming the aluminum oxide film by reactive sputtering. However, if the oxygen partial pressure remains high, for example, the film quality of the aluminum oxide film may change, and the time for forming a film with a predetermined film thickness becomes long (that is, the film forming rate is slow). ..

JP, 2003-3259, A JP, 2010-114413, A

The present invention is based on the above findings, and its object is to provide a film forming method capable of efficiently forming an aluminum oxide film having a stress within a predetermined value.

In order to solve the above problems, the present invention arranges an object to be film-formed and a target made of aluminum in a vacuum chamber, introduces a rare gas and an oxygen-containing gas into the vacuum chamber in a vacuum atmosphere, and targets the target. In the film forming method of forming an aluminum oxide film whose stress is within a predetermined value on the surface of the film formation target by applying a predetermined power to the target and sputtering the target, only a rare gas is introduced into the vacuum chamber, The discharge voltage when a predetermined electric power is applied to the target to discharge it in the vacuum chamber is a first voltage, the partial pressure of oxygen in the vacuum chamber in which the first voltage is maintained is a reference partial pressure, and the partial pressure of oxygen is The first introduction amount is the introduction amount of the oxygen-containing gas when the discharge voltage drops to the second voltage lower than the first voltage and higher than the reference partial pressure, and is larger than the first introduction amount at the beginning of film formation by sputtering of the target. introducing oxygen-containing gas in the second introduction amount, the discharge voltage is lowered from a first voltage to a second voltage, a first step of sputtering a target in a state of the discharge voltage and the second voltage, the discharge voltage first A second step of introducing a oxygen-containing gas with a third introduction amount smaller than the first introduction amount while maintaining the voltage at 2 and sputtering the target until the aluminum film reaches a predetermined film thickness. To do. In this case, it is preferable that the third introduction amount be a constant value in the second step.

According to the present invention, at the beginning of film formation by sputtering of the target, the oxygen-containing gas is introduced at a second introduction amount to increase the oxygen partial pressure in the vacuum chamber, so that the target surface is in an oxidized state (first Process). Then, when the target surface is oxidized, the introduction amount of the oxygen-containing gas is reduced to the third introduction amount, the oxygen partial pressure in the vacuum chamber is reduced, and the discharge voltage is maintained at the second voltage. The sputtering of the target is continued, and when the film thickness reaches a predetermined value, the film formation is finished (second step). As a result, the film formation rate is improved as compared with the case where the target is sputtered with the second amount introduced, and an aluminum oxide film having a stress within a predetermined value can be efficiently formed on the object to be formed. Moreover, the problem that the film quality of the aluminum oxide film changes does not occur. The second introduction amount of the oxygen-containing gas and the time for introducing the oxygen-containing gas at the second introduction amount are sputtering conditions such as the partial pressure of the rare gas or the oxygen-containing gas in the vacuum chamber during film formation and the input power. Accordingly, the discharge voltage is maintained at the second voltage (that is, the target surface is oxidized) during the film formation time required to form the aluminum oxide film with a predetermined film thickness. Is set as appropriate.

The schematic cross section of the sputtering device to which the film forming method of the present invention can be applied. The graph explaining the relationship between the amount of oxygen introduced and the discharge voltage.

Hereinafter, with reference to the drawings, the present invention will be described with reference to the case where a target is made of aluminum and a film formation target is a rectangular glass substrate (hereinafter, referred to as a substrate S), and an aluminum oxide film is formed by reactive sputtering. A method of forming a film will be described.

Referring to FIG. 1, SM is a magnetron-type sputtering apparatus capable of carrying out the film forming method of the present invention. The sputtering apparatus SM includes a vacuum chamber 1 that defines a film forming chamber 11. In the following, terms indicating directions such as “up” and “down” are based on the attitude of the sputtering apparatus SM shown in FIG. An exhaust port 12 is opened on a side wall of the vacuum chamber 1, and an exhaust pipe 13 from a vacuum exhaust unit P including a rotary pump, a dry pump, a turbo molecular pump, etc. is connected to the exhaust port 12, and the film forming chamber is formed. The inside of 11 is evacuated and can be maintained at a predetermined pressure (for example, 1×10 ⁻⁵ Pa).

In the lower part of the vacuum chamber 1, there are provided two cathode units Cu composed of aluminum targets (purity 99.999%, for example) 2 ₁ and 2 ₂ and magnet units 3 ₁ and 3 ₂ . .. Each of the targets 2 ₁ and 2 ₂ is formed in the same substantially rectangular parallelepiped shape, and a copper backing plate 22 that cools the targets 2 ₁ and 2 ₂ during film formation by sputtering is formed on the lower surface thereof. They are bonded to each other via a bonding material (not shown) such as indium. Each target 2 _1, 2 ₂ are placed through an insulator 23 of the vacuum seal also serves to lower inner surface of the vacuum chamber 1 in a state joined to a backing plate 22. In this case, the targets 2 ₁ and 2 ₂ are arranged at a predetermined interval in the left-right direction of the film forming chamber 11, and the upper surfaces of the unused targets 2 ₁ and 2 ₂ are parallel to the substrate S described later. It is located in the same plane. Each target ₂ 1, _{2 2,} AC power supply output Pk from Ps are respectively connected, the AC power source each target ₂ 1 by Ps, _{2 2} between the predetermined frequency (e.g., 1 kHz to 100 kHz) AC power is turned on It has become so.

The magnet units 3 ₁ and 3 ₂ arranged below the respective backing plates 22 (outside the vacuum chamber 1) have the same form, and the magnet units 3 ₁ and 3 ₂ are parallel to the backing plate 22. And a support plate 31 (yoke) formed of a flat plate made of a magnetic material. On the support plate 31, a central magnet 32 which is arranged on the center line of the support plate 31 and a periphery which is annularly arranged along the outer periphery of the upper surface of the support plate 31 so as to surround the periphery of the central magnet 32. The magnet 33 and the magnets 33 are provided by changing the polarities on the targets 2 ₁ and 2 ₂ side. In this case, for example, the volume of the central magnet 32 when converted to the same magnetization is converted to the volume of the peripheral magnets 33 surrounding the same magnetized volume (peripheral magnet: central magnet: peripheral magnet=1:2: 1 (see FIG. 1)). As a result, balanced leaky magnetic fields (not shown) are formed above the targets 2 ₁ and 2 ₂ , respectively. The central magnet 32 and the peripheral magnet 33 are known ones such as neodymium magnets, and these central magnet and the peripheral magnet may be integrated or may be constituted by arranging a plurality of rows of magnet pieces of a predetermined volume. .. In addition, for example, in order to improve the utilization efficiency of the targets 2 ₁ and 2 ₂ , a driving unit (not shown) is connected to the magnet units 3 ₁ and 3 ₂ , and at least one of the vertical direction and the horizontal direction is formed during film formation by sputtering. You may make it reciprocate with a predetermined stroke in the direction.

Further, gas supply ports 41a and 41b are opened on the side wall of the vacuum chamber 1, and gas pipes 42a and 42b are connected to the gas supply ports 41a and 41b, respectively. The gas pipes 42a and 42b are connected to a gas source of a noble gas such as argon (not shown) and a gas source of an oxygen-containing reaction gas such as oxygen gas or ozone (not shown) through the mass flow controllers 43a and 43b to form a film. The rare gas and the reaction gas whose flow rates are controlled can be introduced into the chamber 11.

When the targets 2 ₁ and 2 ₂ are sputtered by the sputtering apparatus SM to form an aluminum oxide film on the surface of the substrate S by reactive sputtering, the targets 2 ₁ and 2 arranged in parallel by a vacuum transfer robot (not shown). _The substrate S is set at a predetermined position above the film forming chamber 11 facing ₂ and the film forming chamber 11 is evacuated to a predetermined pressure. When the film forming chamber 11 reaches a predetermined pressure, the mass flow controllers 43a and 43b are controlled to introduce the rare gas and the reactive gas, and AC power is supplied between the targets 2 ₁ and 2 ₂ by the AC power supply Ps. As a result, high-density plasma is generated in a racetrack shape above each of the targets 2 ₁ and 2 ₂ . Then, the targets 2 ₁ and 2 ₂ are sputtered by the ions of the rare gas in the plasma. Accordingly, the target 2 _1, 2 ₂ reaction product of aluminum atoms and oxygen scattered from adhesion to the surface of the substrate S, the aluminum oxide film is formed deposited to.

When the aluminum oxide film is formed as described above, oxygen in the vacuum chamber 1 reacts with aluminum atoms and adheres to the substrate S, but the amount of oxygen gas introduced into the vacuum chamber 1 is relatively large. Then, when the oxygen partial pressure in the vacuum chamber 1 is increased, the amount of oxygen attached to the surfaces of the targets 2 ₁ and 2 ₂ increases, and the surfaces of the targets 2 ₁ and 2 ₂ are eventually oxidized. Here, referring to FIG. 2, looking at the relationship between the introduction amount of oxygen gas and the discharge voltage (V) between the targets 2 ₁ and 2 ₂ when the reaction gas is oxygen gas, the mass flow controller 43a is When only rare gas is introduced under control and a predetermined AC power is applied between the targets 2 ₁ and 2 ₂ by the AC power supply Ps, the discharge voltage between the targets 2 ₁ and 2 ₂ becomes the voltage V1. Next, when the oxygen gas is introduced by controlling the mass flow controller 43b, the discharge voltage of the targets 2 ₁ and 2 ₂ is maintained at the voltage V1 (that is, in the vacuum chamber 1) up to a predetermined introduction amount Fs. Oxygen is mainly consumed by the reaction with aluminum atoms, and the surfaces of the targets 2 ₁ and 2 ₂ are hardly oxidized). The partial pressure of oxygen in the vacuum chamber 1 in which the first voltage V1 is maintained as described above is used as a reference partial pressure.

Next, as shown by the solid line in FIG. 2, when the introduction amount Fs is exceeded, the oxygen partial pressure in the vacuum chamber 1 becomes higher than the reference partial pressure, and the discharge voltage of the targets 2 ₁ and 2 ₂ begins to drop. , When the introduction amount F1 is reached, the voltage drops to a relatively low voltage V2, and thereafter, discharge is performed in this state (that is, oxygen in the vacuum chamber 1 oxidizes the surfaces of the targets 2 ₁ and 2 _2). Become). On the other hand, as shown by the broken line in FIG. 2, when the introduction amount of oxygen is reduced, the discharge voltage of the targets 2 ₁ and 2 ₂ is maintained at a relatively low voltage V2 even if the introduction amount F1 is exceeded. However, when the amount of introduced Fe is reduced to a predetermined amount Fe, the discharge voltage of the targets 2 ₁ and 2 ₂ rises and eventually becomes the initial predetermined voltage V1.

Therefore, in the present embodiment, when a film having a predetermined thickness is formed on the substrate S by reactive sputtering, the amount of the oxygen gas introduced and the discharge voltage (V) between the targets 2 ₁ and 2 ₂ are From the relationship, it was decided to form the film separately in the first step and the second step. That is, the target 2 _1, 2 initially deposited by _two sputtering, a reactant gas is introduced into the second introduction amount F2 larger than the first introduction amount F1 controls the mass flow controller 43 b, discharge voltage first from a first voltage V1 The voltage drops to 2 V2, and the targets 2 ₁ and 2 ₂ are sputtered for a predetermined time while keeping the second voltage V2 (first step). In this case, the surfaces of the targets 2 ₁ and 2 ₂ are in an oxidized state. Next, the reaction gas is introduced at a third introduction amount F3 between the first introduction amount F1 and a predetermined introduction amount Fe, and the targets 2 ₁ , 2 ₂ are maintained with the discharge voltage maintained at the second voltage V2. Is sputtered, and an aluminum oxide film is formed on the substrate S in a time period until it reaches a predetermined film thickness (second step).

According to the above, the film formation rate is improved as compared with the case where the target is sputtered with the second introduced amount, and an aluminum oxide film having a stress within a predetermined value can be efficiently formed on the substrate S. Moreover, the problem that the film quality of the aluminum oxide film changes does not occur. The second introduction amount F2 of the reaction gas and the time for introducing the reaction gas with the second introduction amount F2 (that is, the sputtering time in the first step) are the rare gas and oxygen in the vacuum chamber 1 at the time of film formation. A state in which the discharge voltage is maintained at the second voltage V2 during the film formation time required to form an aluminum oxide film with a predetermined film thickness according to the sputtering conditions such as the partial pressure of the contained gas and the input power. It is appropriately set so that Note that, for example, when an aluminum oxide film having a relatively large film thickness is formed on one substrate S, the first step and the second step can be repeated a plurality of times to form the film. Further, when the introduction amount of oxygen gas is reduced from the second introduction amount F2 to the third introduction amount F3, the oxidized state of the target surface is maintained during the second step depending on the film formation time and the like. You may make it reduce continuously or in steps at a predetermined speed.

In order to confirm the above effects, an experiment for forming an aluminum oxide film on the surface of the substrate S was conducted using the sputtering apparatus SM shown in FIG. First, as a comparative experiment, the distance between each target 2 ₁ and 2 ₂ and the substrate S is 180 mm, the input power (AC power) between the targets 2 ₁ and 2 ₂ by the AC power supply Ps is 10 kW, and the film formation time is The mass flow controllers 43a and 43b are controlled so that the pressure in the film forming chamber 11 is set to 1250 seconds and the pressure in the film forming chamber 11 that is evacuated is maintained at 0.5 Pa. Oxygen gas was introduced at a flow ratio of 6:4. When the film thickness and the stress of the aluminum oxide film formed on the surface of the substrate S were measured in the center of the substrate S, the film thickness was 50 nm and the stress was about -1400 MPa (compressive stress). The film thickness was measured using an ellipsometer, and the stress was measured using a thin film stress measuring device.

Next, as an experiment showing the effect of the present invention, based on the film forming conditions of the above comparative experiment, in the first step, the introduction amount of oxygen gas was changed without changing the total introduction amount of argon gas and oxygen gas. Is increased to 40%, the film formation time is set to 60 seconds, and subsequently, in the second step, the introduction amount of oxygen gas is reduced to 20% without changing the total introduction amount of argon gas and oxygen gas. Then, the aluminum oxide film was formed by setting the film formation time to 980 seconds. In this case, the discharge voltage between the targets 2 ₁ and 2 ₂ was about 400 V at the beginning of the first step, but then the discharge voltage between the targets 2 ₁ and 2 ₂ dropped to about 200 V, and the second step was performed. The discharge voltage was maintained until the end. According to this, it was confirmed that the thickness of the aluminum oxide film was 50 nm, and the stress of the aluminum oxide film could be reduced to about −400 MPa (compressive stress).

Although the embodiment of the film forming method of the present invention has been described above, the present invention is not limited to the above. In the above-described embodiment, an example is described in which two targets 2 ₁ and 2 ₂ are arranged in parallel and AC power is supplied to the pair of targets 2 ₁ and 2 ₂ by the AC power supply Ps, but the present invention is not limited to this. For example, the present invention can be applied to the case where one target is used, DC power having a negative potential is applied by a DC power source, and film formation is performed by reactive sputtering. In this case, the amount of oxygen-containing gas introduced may be controlled by the discharge voltage between the target and ground.

Further, in the above-described embodiment, the case where the rare gas and the oxygen gas are introduced from the gas supply ports 41a and 41b provided on the side wall of the vacuum chamber 1 has been described as an example, but the present invention is not limited to this. Although not particularly shown and described, for example, a gas pipe is penetrated through the bottom wall of the vacuum chamber 1, and a rare gas, oxygen gas, or water vapor is jetted from the tip of the gas pipe located around the targets 2 ₁ and 2 _2. You may do it. Further, in the above embodiment, the case where the film formation target is a glass substrate has been described as an example, but the film formation target may be a sheet-shaped resin base material, for example. In this case, the present invention can also be applied to one in which a resin base material is moved at a constant speed between a drive roller and a winding roller to form a film on one surface of the base material by reactive sputtering.

SM... Sputtering device, 1... Vacuum chamber, 2 ₁ , 2 ₂ ... Target, 42a... Gas pipe (for rare gas), 43a... Mass flow controller (for rare gas), 42b... Gas pipe (for reactive gas), 43b... Mass flow controller (for reaction gas), S... Substrate (deposition object), V1, V2... Discharge voltage, F1, F2, F3, Fs, Fe... Introduced amount of reaction gas (oxygen gas).

Claims (2)

Placing an object to be deposited and a target made of aluminum in a vacuum chamber, introducing a rare gas and an oxygen-containing gas into the vacuum chamber in a vacuum atmosphere, and applying predetermined power to the target to sputter the target. In the film forming method for forming an aluminum oxide film whose stress is within a predetermined value on the surface of the object to be formed,
The discharge voltage when only a rare gas is introduced into the vacuum chamber and a predetermined electric power is applied to the target to cause the discharge in the vacuum chamber is a first voltage, and the discharge voltage when the first voltage is maintained is the oxygen content in the vacuum chamber. As the first introduction amount, the introduction amount of the oxygen-containing gas when the discharge voltage drops to a second voltage lower than the first voltage due to the pressure being a reference partial pressure and the oxygen partial pressure being higher than the reference partial pressure,
At the beginning of film formation by sputtering the target, the oxygen-containing gas is introduced at a second introduction amount higher than the first introduction amount, the discharge voltage drops from the first voltage to the second voltage, and the discharge voltage is at the second voltage. A first step of sputtering a target,
A second step in which a target is sputtered until the aluminum film reaches a predetermined thickness by introducing an oxygen-containing gas with a third introduction amount smaller than the first introduction amount while maintaining the discharge voltage at the second voltage. A film forming method comprising: The film forming method according to claim 1, wherein the third introduction amount is set to a constant value in the second step.

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