JP4720298B2 - Method for forming conductive compound thin film - Google Patents

Description

The present invention relates to a method of forming the conductive compound thin film, particularly relates to method of forming a precisely controlled conductive compound thin film composition.

  A thin film made of a conductive compound such as a metal oxide or a metal nitride is an indispensable material for realizing an electronic / optical device. These conductive compound thin films are formed by sputtering using a target made of a conductive compound or reactive sputtering using a metal target. For example, when an ITO (tin-doped indium oxide) thin film is formed by sputtering, sputtering is performed in an oxygen-containing atmosphere using an ITO target (Japanese Patent Laid-Open No. 2004-149848).

  In the ITO thin film formed by such sputtering method or reactive sputtering method, doped Sn and oxygen deficiency serve as an n-type carrier generation source and develop conductivity. However, in the case of an ITO thin film having a perfect stoichiometric composition without oxygen vacancies, the generation of carriers due to oxygen vacancies does not occur and the conductivity deteriorates. Therefore, the amount of oxygen in the ITO thin film is made smaller than the stoichiometric composition. It is necessary.

  However, when forming an ITO thin film by the reactive sputtering method, it is difficult to control the amount of oxygen in the film to be slightly less than the stoichiometric composition. If the amount of oxygen in the ITO thin film is large, the film becomes low in conductivity, and conversely, if the amount of oxygen in the ITO thin film is too short, it becomes a metallic film and the transmittance is lowered.

  When forming a conductive compound thin film by reactive sputtering, the emission wavelength and emission intensity of discharge such as oxygen during sputtering are monitored, and the film is formed while performing feedback control based on the monitoring result. To do is generally done. However, there is no conventional example in which this feedback control is applied to the formation of a conductive compound thin film in which oxygen and nitrogen in the film are less than the stoichiometric ratio.

Further, when feedback control is appropriately performed, for example, as shown in FIG. 4, when the measured value of the oxygen flow rate is plotted on the horizontal axis and the measured value of the emission intensity of oxygen is plotted on the vertical axis, the maximum value A and the minimum value are plotted on the oxygen flow rate It is known to draw an S-shaped curve with B. In addition, it is known that when the measured value of the emission intensity of metal instead of oxygen is plotted in the same manner on the vertical axis, an inverted S-shaped curve is obtained (S. Ohno, D. Sato, M. Kon, PKSong, M Yoshikawa, K. Suzuki, P. Frach, Y. Shigesato, Thin Solid Flims 445 (2003) 207-212, “Plasma emission control of reactive sputtering process in mid-frequency mode with dual cathodes to deposit photocatalytic TiO ₂ films”). However, there is no conventional example in which such a phenomenon is applied to the formation of a conductive compound thin film in which oxygen and nitrogen in the film are less than the stoichiometric ratio.
Japanese Patent Application Laid-Open No. 2004-149884 S. Ohno, D. Sato, M. Kon, PKSong, M. Yoshikawa, K. Suzuki, P. Frach, Y. Shigesato, Thin Solid Flims 445 (2003) 207-212, `` Plasma emission control of reactive sputtering process in mid -frequency mode with dual cathodes to deposit photocatalytic TiO2 films "

  As described above, it is difficult to form a metal oxide thin film or metal nitride thin film in which oxygen or nitrogen is slightly less than the stoichiometric ratio and the composition is accurately controlled by the reactive sputtering method.

The present invention aims to oxygen or nitrogen less than the stoichiometric ratio, and the composition provides a method of forming the conductive compound thin film made of the precisely controlled metal oxide or metal nitride .

The method for forming a conductive compound thin film according to claim 1 is a method for forming a conductive compound thin film made of a metal oxide by a reactive sputtering method in which sputtering is performed using a metal target in an atmosphere containing oxygen. In the method of forming a conductive compound thin film by feedback control for monitoring the emission wavelength and emission intensity of the discharge during sputtering and controlling the flow rate of oxygen based on the monitoring result, In this method, feedback control is performed so that oxygen in the conductive compound thin film is less than the stoichiometric ratio. In the transition region, the oxygen flow rate when the oxygen flow rate reaches a maximum value is A, and the emission intensity is X. And the oxygen flow rate when the oxygen flow rate becomes a minimum value is B, and the oxygen flow rate is A−α (A−B) (where α is greater than 0 and less than or equal to 0.5 Value) at which the emission intensity P and Q when (However, when P <X <Q), in which emission intensity and performs the feedback control so that the P or Q or less.

Method of forming the conductive compound film of 請 Motomeko 2, according to claim 1, wherein the metal target is In, Sn, Zn, Cd, Ti, Cu, Sb, Pb, Al, that consists of at least one of Ga It is characterized by.

Method of forming the film forming method of the conductive compound thin film according to claim 3, in claim 1 or 2, wherein the conductive compound film of tin-doped indium oxide, antimony-doped tin oxide, aluminum-doped zinc oxide or gallium doped zinc oxide It is characterized by being .

In the deposition how the conductive compound thin film according to claim 1, in the transition region, by the oxygen of the conductive compound thin film performs feedback control such that less than the stoichiometric ratio, oxygen It is possible to form a conductive compound thin film that is less than the stoichiometric composition ratio and whose composition is accurately controlled.

  In FIG. 4, the present inventors can accurately form a film in which oxygen is less than the stoichiometric composition ratio by performing feedback control so that the oxygen flow rate becomes a value near the maximum value A. I found out that I can do it.

That is, in the method for forming a conductive compound thin film according to claim 1 , in the transition region, the oxygen flow rate when the oxygen flow rate reaches the maximum value is A, the emission intensity is X, and the oxygen flow rate is the minimum value. The oxygen flow rate is B, and the emission intensity when the oxygen flow rate is A−α (A−B) (where α is a predetermined value greater than 0 and less than or equal to 0.5) is P and Q (where P If <X <Q), a film having less oxygen than the stoichiometric composition ratio can be accurately formed by performing the feedback control so that the emission intensity is P or more and Q or less .

As 請 Motomeko 2, the metal target may be used In, Sn, Zn, Cd, Ti, Cu, Sb, Pb, Al, those composed of at least one of Ga.

As described in claim 3 , as the conductive compound thin film, tin-doped indium oxide, antimony-doped tin oxide, aluminum-doped zinc oxide or gallium-doped zinc oxide can be obtained .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram for explaining a method of forming a conductive metal oxide thin film according to an embodiment by a dual cathode magnetron sputtering method, and FIG. 2 is an example of a voltage applied to the target electrode of FIG. It is a figure to do.

  As shown in FIG. 1, a first sputtering unit is composed of a target electrode 20A provided with a first target 21a on a support 20a and a magnet 22a disposed below the target electrode 20A. In addition, a second sputtering unit is configured by a target electrode 20B provided with a second target 21b on a support 20b and a magnet 22b disposed below the target electrode 20B. The first sputtering unit and the second sputtering unit are installed adjacent to each other, and an AC power supply 25 is connected to these sputtering units via a switching unit 24.

  As the metal of the first and second targets 21a and 21b, for example, at least one selected from the group consisting of In, Sn, Zn, Cd, Ti, Cu, Sb, Pb, Al, and Ga is used.

  These target electrodes 20A and 20B are covered with a cover 26. The cover 26 is connected to a pump (not shown) via an exhaust port 28 and is connected to a gas supply source (not shown) via a gas introduction port 27.

  Collimators 30a and 30b are provided in the cover 26, and these collimators 30a and 30b are respectively connected to plasma emission monitors (hereinafter also referred to as PEMs) 31a and 31b through a filter and a photomultiplier tube (not shown). It is connected to the. The collimators 30a and 30b, the filters, the light amplification amplifiers, and the PEMs 31a and 31b constitute first and second monitors.

  The PEM is an apparatus that monitors an electrical signal obtained by condensing plasma emission with a collimator and photoelectrically converting it with a photomultiplier tube (PM). The PEM is set to a certain sensitivity and monitors the emission intensity of the plasma.

  In the present embodiment, a filter capable of passing the wavelength 777 nm of the emission spectrum of oxygen is used as the filter for the targets 21a and 21b.

  When a metal oxide thin film is formed using the above apparatus, first, the substrate 1 is placed above the targets 21a and 21b in the cover 26, and the inside of the cover 26 is evacuated by a pump, and then an argon or the like is used. A mixed gas containing oxygen in the active gas is introduced into the cover 26, and the inside of the cover 26 is brought to a predetermined pressure.

  Next, for example, as shown in FIG. 2, a pulse packet voltage is alternately applied to the target electrodes 20A and 20B to form a glow discharge. As a result, particles are sputtered from the targets 21a and 21b, and these particles adhere to the substrate 1 above the targets 21a and 21b. At this time, the targets 21a and 21b or the sputtered particles are oxidized by oxygen gas.

  The emission wavelength and emission intensity of the oxygen discharge in the vicinity of the targets 21a and 21b become electric signals via the collimators 30a and 30b, the filter, and the optical doubler, and are detected by the PEMs 31a and 31b.

  Based on these electrical signals, feedback control of the emission intensity of oxygen is performed. That is, electric power to be applied to the targets 21a and 21b is applied, and the light emission intensity of oxygen is detected by the PEMs 31a and 31b. Based on the detection result, the flow rate of oxygen introduced into the cover 26 is controlled.

  Next, the relationship between the emission intensity and the oxygen flow rate when the emission intensity of oxygen is increased in the state where the feedback control is appropriately performed will be described with reference to FIG.

  That is, as the light emission intensity of oxygen is increased, the oxygen flow rate increases, and the inside of the cover 26 shifts from the metal mode to the transition region. Thereafter, the oxygen flow rate further increases and reaches a maximum value A. Let X be the value of the light emission intensity at this time. Thereafter, the oxygen flow rate decreases and reaches a minimum value B. The value of the emission intensity at this time is Y. Thereafter, the oxygen flow rate increases, and the inside of the cover 26 shifts from the transition region to the oxide mode. As described above, when the emission intensity of oxygen is increased, a locus of an S-shaped curve having a maximum value and a minimum value in the oxygen flow rate is drawn.

  When the film is formed under the condition where the oxygen flow rate is maximum in the S-curve, the oxygen composition ratio is less than the stoichiometric composition ratio, and a thin film having excellent transparency and conductivity can be obtained. it can. The details of this reason are unknown, but we guess it is because of the following reasons. In the vicinity of the maximum value of the oxygen flow rate, the area of the oxidized state on the target surface increases and the sputtering rate from the target begins to decrease, so that the introduced oxygen starts to be excessive. It is considered that the stoichiometric composition in the film is slightly deficient in oxygen in the vicinity where oxygen begins to be excessive.

  In the present embodiment, the control range of feedback control is first determined as follows. That is, film formation is performed while performing feedback control, and the S-curve graph of FIG. 4 is created. Then, C = A−α (A−B) is calculated from the maximum value A and the maximum value B of the oxygen flow rate (where α is a predetermined value greater than 0 and less than or equal to 0.5), and on the S-shaped curve. The emission intensity values P and Q (where P <X <Q <Y) when the oxygen flow rate value is C are obtained from the graph. A range from P to Q is set as a control range of feedback control.

  Thereafter, film formation is performed while performing feedback control so that the emission intensity is in the range of P to Q.

  Note that the control range of the feedback control may be determined using a substrate for film formation, and film formation may be performed on the substrate as it is. Further, the control range of the feedback control may be determined using a substrate different from that for film formation, and then the film may be formed by replacing with a substrate for film formation.

  The pulse power, the pulse amount, and the pulse width vary depending on the volume of the target, the volume in the cover 26, the required film formation speed, and the like. For example, the pulse power is 1 kW to 20 kW, the pulse amount is 30% to 80%, the pulse The width is about 10 μS to 100 mS. If the pulse power is 50 kW or more, abnormal discharge occurs, and a metal oxide thin film having a precisely controlled composition cannot be stably formed. On the other hand, if the pulse power is 500 W or less, the film formation speed is reduced. Becomes slower. When the pulse amount is 80% or more, continuous discharge occurs, and when it is 10% or less, the discharge becomes unstable.

  The oxygen supply amount is, for example, about 50 to 300 sccm.

  The pressure in the cover 26 during the film formation is preferably controlled within a range of 0.1 Pa to 30 Pa, particularly 0.5 to 5.0 Pa.

  After the metal oxide thin film formed on the substrate 1 reaches a predetermined thickness, the sputtering is terminated, and the substrate 1 on which the metal oxide thin film is laminated is taken out with the inside of the cover 20 at atmospheric pressure. Thereby, sputtering can be performed in a state where oxygen in the conductive compound thin film is slightly deficient, and a film excellent in transparency and conductivity can be formed.

  The above embodiment is an example of the present invention, and the present invention is not limited to the above embodiment.

For example, the emission intensity of oxygen is detected by PEM, but the emission intensity of metal in the target may be detected. In this case, the emission intensity of the metal decreases as it goes from the metal mode to the oxide mode. Therefore, when the relationship between the emission intensity of the metal and the oxygen flow rate is measured, the emission intensity of the metal and the oxygen flow rate are upside down S-shaped curves. Will be drawn. Also in this case, film formation is performed while feedback control is performed on the light emission intensity of the metal so that the light emission intensity is in the vicinity of the maximum oxygen flow rate .

  Hereinafter, although Example 1 and Comparative Examples 1 and 2 are described, the present invention is not limited to Example 1.

<Example 1>
[Determination of feedback control range]
An alloy in which Sn was doped at 10 atm% with respect to In 100 atm% was used as a target (length 500 mm × width 100 mm × thickness 5 mm), and reactive sputtering was performed using a DC power source. As the gas, a mixed gas of Ar and O ₂ was used, and the total pressure was controlled to be 1.0 Pa. The input power to the target was 5.0 kW.

  The emission intensity of oxygen was monitored by PEM, and feedback control for controlling the oxygen flow rate was performed based on the monitoring.

  While performing this feedback control, the emission intensity of oxygen was increased, and the emission intensity and oxygen flow rate were measured. The result is shown in FIG.

  As shown in FIG. 3, the maximum value A of the oxygen flow rate was 110 sccm, and the minimum value B was 68 sccm. When α = 0.4, C = A−α (A−B) was calculated, and the emission intensities P and Q when the oxygen flow rate was C were obtained from the graph. C = 93, P = 2.0, Q = 2.7.

[Film formation]
Next, a substrate for film formation (material: non-alkali glass, size 50 mm × 50 mm × 1.0 mm) is installed above the target, and feedback control is performed so that the emission intensity is 2.0 or more and 2.7 or less. The film formation was performed.

When the obtained thin film was melt | dissolved and the composition analysis was performed using ICP-mass, it was set to In: Sn: O = 100: 10: 168 (atm%). The film formation rate was approximately 30 nm · m / min. The specific resistance of the film was 3.5 × 10 ⁻⁴ Ω / cm.

<Comparative Example 1>
Instead of performing feedback control, the oxygen flow rate is monotonously increased from the metal mode to the oxide mode, and then the oxygen flow rate is monotonously decreased from the oxide mode to the metal mode. Then, the film was formed and the emission intensity of oxygen and the oxygen flow rate were measured. The result is shown in FIG.

  As shown in FIG. 3, the hysteresis curve has different trajectories in the increasing process and decreasing process of the oxygen flow rate.

<Comparative Example 2>
Instead of performing feedback control, film formation was performed in the same manner as in Example 1 except that the oxygen flow rate was controlled to be 100 sccm, and composition analysis was performed. As a result, In: Sn: O = 100: 10: 171 (atm%). The film formation rate was approximately 30 nm · m / min. The specific resistance of the film was 10 ⁵ Ω / cm and was almost insulating.

It is the schematic for demonstrating the dual cathode system magnetron sputtering method. It is a figure explaining an example of the voltage applied to the target electrode of FIG. It is a graph which shows the relationship between the oxygen flow rate and emission intensity when performing reactive sputtering by feedback control, and the relationship between the oxygen flow rate and emission intensity when performing reactive sputtering without feedback control. It is a graph explaining the relationship between the oxygen flow rate and light emission intensity when performing film formation by feedback control.

1 Substrate 20a, 20b Support 20A, 20B Target electrode 21a, 21b Target 22a, 22b Magnet 24 Switching unit 25 AC power supply 26 Cover 27 Gas inlet 28 Exhaust outlet 30a, 30b Collimator 31a, 31b PEM

Claims (3)

A method of forming a conductive compound thin film made of a metal oxide by a reactive sputtering method in which sputtering is performed using a metal target in an atmosphere containing oxygen,
In the method of forming a conductive compound thin film by feedback control for monitoring the emission wavelength and emission intensity of the discharge during sputtering and controlling the flow rate of the oxygen based on the monitoring result,
A method of performing feedback control so that oxygen in the conductive compound thin film is less than the stoichiometric ratio in the transition region ,
In the transition region, the oxygen flow rate when the oxygen flow rate becomes a maximum value is A, the emission intensity is X, the oxygen flow rate when the oxygen flow rate becomes a minimum value is B,
If the emission intensity when the oxygen flow rate is A-α (AB) (where α is a predetermined value greater than 0 and less than or equal to 0.5) is P and Q (where P <X <Q),
The method for forming a conductive compound thin film , wherein the feedback control is performed so that the emission intensity is P or more and Q or less . 2. The method for forming a conductive compound thin film according to claim 1 , wherein the metal target is made of at least one of In, Sn, Zn, Cd, Ti, Cu, Sb, Pb, Al, and Ga. 3. The method for forming a conductive compound thin film according to claim 1 , wherein the conductive compound thin film is tin-doped indium oxide, antimony-doped tin oxide, aluminum-doped zinc oxide, or gallium-doped zinc oxide.

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