JP2016069722A - Thin film manufacturing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing stably a large-area hydroxide thin film by a sputtering method, and to provide the large-area hydroxide thin film.SOLUTION: A sputtering device can provide a method for manufacturing stably a hydroxide thin film, and a large-area hydroxide thin film, by adding a steam supply mechanism and a cooling mechanism for controlling a steam partial pressure to a conventional sputtering device.SELECTED DRAWING: Figure 1

Description

  A thin film production system using water vapor as a reaction gas

  As one of the conventional techniques for producing a compound thin film by a reactive sputtering method, a reactive sputtering method is used in which a metal target as a raw material is sputtered in a reactive gas atmosphere.

For example, a silicon oxide (SiO ₂ ) thin film can be produced by sputtering a silicon (Si) target in an Ar + O ₂ mixed gas, and a silicon nitride (SiN) thin film can be produced by sputtering in an Ar + N ₂ mixed gas. In order to produce a high-quality compound thin film using the reactive sputtering method, it is necessary to stably and precisely control the composition of the reaction gas (partial pressure of Ar, O ₂ , N _2, etc.) in the sputtering chamber. .

  Therefore, in general, a stable reaction gas composition is realized by using a mass flow controller (mass flow meter) that can supply a certain amount of gas even if the temperature and pressure of the use environment fluctuate.

In addition, when preparing a compound thin film by the reactive sputtering method, it is known that the composition of the compound thin film changes rapidly in the vicinity of a certain critical value when the reaction gas partial pressure of O ₂ , N ₂ or the like is gradually increased. It has been.

For example, when the Si target is sputtered in an Ar + O ₂ mixed gas atmosphere, when the O ₂ partial pressure is lower than the critical value, a Si thin film slightly containing oxygen is formed, but when the O ₂ partial pressure exceeds the critical value, Then, an Si oxide (SiO ₂ ) thin film is formed, and even if the O ₂ partial pressure is made higher than the critical value, excess O ₂ molecules do not react with Si atoms, so that a stable SiO ₂ thin film is formed. Since it is formed and the composition does not change greatly, the O ₂ partial pressure may be set to a critical value or more in order to stably produce the compound thin film.

  In the production of a hydroxide thin film by reactive sputtering using water vapor as a reactive gas, for example, a hydroxide thin film such as nickel oxyhydroxide (NiOOH) or cobalt oxyhydroxide (CoOOH) is a basic aqueous electrolyte. When an oxidation-reduction reaction is carried out in the medium, it is colored dark brown in the oxidized state, and transparent or pale yellow in the reduced state.

  This phenomenon is called electrochromism and can be applied as a display or smart window. Conventionally, NiOOH and CoOOH thin films have been fabricated using wet processes using solutions such as electrolytic deposition and sol-gel methods. However, it has been difficult to produce a thin film having a uniform composition and thickness on a large-area substrate.

  Therefore, we have developed a sputter deposition technology that uses water vapor as the reactive gas. Metal atoms sputtered from the metal target react with water molecules supplied as a reaction gas, and a hydroxide thin film is formed. (Non-Patent Document 1)

Journal of the Vacuum Society of Japan, Vol. 515-520 (2010)

However, the hydroxide film, unlike the oxide or nitride thin film, with increasing partial pressure of water vapor in the sputtering gas, water molecules number is increased to be incorporated in the film in the form of hydrates, MO x _· nH A thin film having a composition of ₂ O or M (OH) _n (M is a metal atom) is formed. Here, since the number n of hydrated water molecules may exceed 10, in order to control the composition of the hydroxide thin film, in the sputtering atmosphere, compared to the case of forming an oxide thin film or a nitride thin film. It is necessary to control the water vapor partial pressure more precisely.

  The schematic view of the sputtering apparatus of the present invention shown in FIG. 1 is a gas supply system using a mass flow controller, in which a sputtering target serving as a raw material is installed in a sputtering chamber (vacuum vessel) as in the conventional sputtering apparatus, and An evacuation system combining a turbo molecular pump (TMP) and a rotary pump (RP) is provided. The total gas pressure and gas composition in the sputtering chamber are adjusted by changing the gas supply amount by the mass flow controller and changing the exhaust speed of the vacuum exhaust system by the main valve.

  When performing sputtering film formation, the pressure in the sputtering chamber is controlled to about 0.1 to 10 Pa, and then several hundred volts of direct current, alternating current, or pulse voltage is applied to the sputtering target by a high-voltage power source to generate plasma. When ions generated in the plasma bombard the target and repel the target atoms, the skipped target atoms are deposited on the substrate to form a thin film.

  The sputtering apparatus of the present invention is characterized in that a water vapor supply mechanism and a cooling mechanism for controlling the water vapor partial pressure are added to the conventional sputtering apparatus. First, the water vapor supply mechanism will be described.

  Since water is in a liquid state at room temperature and has a low vapor pressure (about 2.3 kPa), it is difficult to supply a sufficient amount of water vapor. Therefore, for example, a stainless steel water tank is installed in a thermostatic bath, and about 60 Increase water temperature to ℃. Thus, a water vapor pressure of about 30 kPa can be obtained, and this water vapor is introduced into a high-temperature mass flow controller heated to about 80 ° C. through piping and valves that are kept warm so as not to condense.

  By using the mass flow controller, water vapor whose flow rate is stable and precisely controlled can be supplied to the sputtering chamber. A cooling mechanism for controlling the pressure of water vapor in the sputter chamber includes a Peltier element, a DC power source for the Peltier element, and a cooler for cooling the heat radiation side of the Peltier element using a refrigerant. As shown in the enlarged view of b), in order to prevent the deposition of a thin film on the surface of the Peltier element and to improve the temperature uniformity, a plate having good thermal conductivity is adhered to the surface of the Peltier element. For example, there is a cooling plate made of copper.

  As shown in FIG. 1, we installed a cooling unit in the sputtering apparatus, and controlled the water vapor pressure in the sputtering chamber by this temperature. The maximum pressure of water vapor present in the gas phase is determined by the saturated water vapor pressure, and when this value is exceeded, the water vapor condenses to form water or solidifies to ice at low temperatures.

  Therefore, if water vapor is supplied to a sputtering apparatus provided with a sufficiently low temperature cooling unit, the water vapor exceeding the saturated water vapor pressure becomes water or ice, and the water vapor pressure can be controlled to be constant. Further, since the saturated water vapor pressure decreases as the temperature decreases, the water vapor pressure can be controlled by changing the temperature of the cooling unit installed in the sputtering chamber. If the temperature of the substrate used for thin film production is lower than the temperature of the cooling part, water or ice film is generated on the surface of the substrate. Therefore, the temperature of the cooling part should be lower than the temperature of the substrate. is necessary.

  The cooling method of the cooling part is 1) Cooling a low melting point liquid such as ethylene glycol or ethanol and circulating it to the cooling part. 2) Direct cooling with Stirling refrigerator, Gifford McMahon refrigerator, pulse tube refrigerator, etc. 3) There is a method using a Peltier element, but it takes time to cool the liquid, and a mechanical refrigerator is large in size and expensive, so the Peltier element is easy to use.

  A Peltier element is a type of thermoelectric element that utilizes the phenomenon that heat is transferred when a current is passed through a junction between two types of metals and semiconductors. Cooling efficiency is low, but high-precision temperature control is possible depending on the magnitude of the current. Is possible. Moreover, since it is small and has a small volume, it can be easily installed inside the vacuum apparatus.

となる。In the sputtering apparatus of the present invention, the water vapor pressure is kept constant by adsorbing the water vapor supplied to the chamber to the cooling unit. Therefore, when calculating the area of the cooling unit required to stably control the water vapor pressure, assuming ideal gas, 0 ° C., the volume of 1mol of gas at 1 atm 22.4L (= 2.24 × 10 ^{- 2} m ³ ) and Avogadro's number N _A = 6.02 × 10 ²³ , so when the supply amount of water vapor is F _in (sccm) (= F _in × 10 ⁻⁶ m ³ / min), supply is performed for 1 second. The number of water molecules N _in

It becomes.

で与えられることが、麻蒔立男著、薄膜作成の基礎、第４版、日刊工業新聞社、ｐ．２８に記載されている。ここで、Ｐは気体の圧力（Ｐａ）、Ｍは分子量、Ｔは気体の温度（Ｋ）である。冷却板の面積をＳ（ｍ^２）とし、水蒸気の温度を室温（２９３Ｋ）、冷却板に衝突した水分子（水の分子量Ｍ＝１８）は全て吸着されると仮定すると、１秒間に冷却板に吸着する水分子数Ｎ_ａｂは、

となる。On the other hand, the number Z of gas molecules that collide with the wall of the unit area per second is

Is given by Tatsuo Maya, Basics of Thin Film Production, 4th Edition, Nikkan Kogyo Shimbun, p. 28. Here, P is gas pressure (Pa), M is molecular weight, and T is gas temperature (K). Assuming that the area of the cooling plate is S (m ² ), the temperature of the water vapor is room temperature (293 K), and all the water molecules that collide with the cooling plate (molecular weight M = 18 of water) are adsorbed per second. The number of water molecules N _ab adsorbed on

It becomes.

より、冷却板の面積Ｓを計算でき、冷却板への水分子の吸着確率は、１００％より小さいことと、長時間、水蒸気雰囲気中でスパッタリングした場合、吸着板の表面に氷膜が生成し、冷却効率が低下することを考慮すると、冷却板の面積はこれよりも、広くすることが望ましい。Further, when the number of water molecules exhausted out of the sputtering chamber per second by the vacuum exhaust system is N _out , the number of water molecules supplied to the sputtering chamber and the adsorption to the cooling plate and the vacuum exhaust system in a steady state. Because the number of water molecules discharged by
N _in = N _ab + N _out
Become, but if the discharge from the vacuum exhaust system dominant, it takes a very long time until the pressure stabilizes as shown in FIG. 6, in order to stabilize in a short time the water vapor pressure N _ab >> N _out , that is, the number of water molecules adsorbed on the cooling plate needs to be sufficiently larger than the number of water molecules discharged from the vacuum exhaust system.

Thus, the area S of the cooling plate can be calculated, and the probability of water molecule adsorption to the cooling plate is less than 100%. Considering that the cooling efficiency is lowered, it is desirable to make the area of the cooling plate wider than this.

  The sputtering method of the present invention is an application of a technology widely used in the production of thin film materials for liquid crystal displays and semiconductor devices as a typical dry process technology. By using this method, water vapor in a sputtering atmosphere is applied. Since the partial pressure can be controlled more precisely, large-area NiOOH and CoOOH thin films can be produced, and can be used as an electrochromic smart window for windows in office buildings and ordinary homes.

  The electrochromic smart window can electrically control the light transmittance, so it can block the strong sunlight in summer and save energy for cooling, and also increase the transmittance in winter. Therefore, sunlight can be actively taken indoors to save energy for heating.

  In addition, by appropriately controlling the transmittance of light entering from the outside, it is possible to save energy for indoor lighting, and without completely blocking the view like blinds and thick curtains, Since the outside can be seen, the comfort of residents is improved.

It is the schematic of the sputtering device of this invention. This is a change with time in the pressure in the sputtering chamber when the current flowing through the Peltier element is changed while supplying water vapor at a constant flow rate (2 sccm). It is the relationship between the current passed through the Peltier element and the temperature of the cooling plate (A) pressure change when the current passed through the Peltier element is increased or decreased stepwise while supplying water vapor at a constant flow rate (2 sccm), (b) the relationship between the pressure and Peltier current 10 minutes after setting the Peltier current, c) The relationship between the temperature and pressure of the cooling plate. Change in temperature of Peltier element and water vapor pressure over time. (A) When the temperature fluctuation of the Peltier element is small, (b) When the temperature fluctuation of the Peltier element is large. It is a time change of the pressure in a sputtering chamber when supply of argon and water vapor is started at a constant flow rate (5 sccm) and when supply is stopped. This is the relationship between the supply gas flow rate and the pressure in the sputtering chamber. (A) Pressure change when the argon flow rate is increased or decreased stepwise, (b) Pressure after 10 minutes of argon flow setting, (c) Pressure change when the water vapor flow rate is increased or decreased, (d) Water vapor flow rate This is the pressure 10 minutes after setting the flow rate.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

With the sputtering apparatus of the present invention shown in FIG. 1, while supplying water vapor at a constant flow rate of 2 sccm (standard, cubic, centimeter, per, minute) to the sputtering chamber, the current flowing through the Peltier element is changed and the chamber pressure is measured. did. As shown in FIG. 2, when the current passed through the Peltier element is increased or decreased stepwise from 2.5A to 5.0A and from 5.0A to 2.5A, the chamber pressure also changes correspondingly. It can be seen that the pressure stabilizes after about 10 minutes.

  FIG. 3 shows the results of measuring the temperature of the cooling plate (3 cm × 3 cm, 1 mm thick copper plate in close contact with the Peltier element) by changing the current passed through the Peltier element used in the sputtering apparatus of the present invention shown in FIG. Show. In addition, since the cooling liquid (ethylene glycol antifreeze) cooled to 5 ° C. by a cooler installed outside is circulated in the heat radiating part of the Peltier element, the temperature when no current is passed through the Peltier element is about 6 ° C. When the current passed through the Peltier element is increased, the temperature of the cooling plate is also decreased, and it can be confirmed that the temperature is decreased to about −60 ° C. with the current 6A.

  When the current flowing through the Peltier element is increased and decreased stepwise, as shown in FIG. 4 (a), a pressure change close to a step shape is shown, and as shown in FIG. The chamber pressure is almost the same between when the value is increased and when the value is decreased, and the hysteresis as seen in FIG. 7D (Comparative Example 2) is not recognized. FIG. 4 (c) shows the relationship between the temperature of the cooling plate and the water vapor pressure. From this figure, the cooling part is cooled to −35 ° C. or lower, and 0.1% used for normal sputtering film formation. It can be seen that the water vapor pressure can be controlled within a pressure range of about 10 Pa.

  Even if the current passed through the Peltier element is constant, the temperature changes when the temperature of the coolant that cools the Peltier element fluctuates. FIG. 5 shows an example of a change in the water vapor pressure in the chamber due to the temperature fluctuation of the cooling unit. FIG. 5A shows the experimental results when a stable cooler with a temperature fluctuation range of ± 0.1 ° C. is used, and it can be seen that the temperature of the cooling section is stable and there is almost no pressure fluctuation. On the other hand, FIG. 5 (b) shows the experimental results when using a cooler having a relatively large fluctuation range with a temperature fluctuation range of about ± 1 ° C., and the pressure corresponding to the temperature change of the cooling section. You can see that it fluctuates. From this result, in order to keep the water vapor pressure constant, it is necessary to stably control the temperature of the cooling section. To make the pressure fluctuation range within ± 10%, the temperature change of the cooling section is ± 1. It can be seen that it is necessary to keep the temperature below about ℃.

Comparative Example 1

  Changes in pressure in the sputtering chamber when the gas supply amount is changed using the prior art (in the sputtering apparatus of the present invention shown in FIG. 1 without using a cooling device) and a mass flow controller, using a capacitance manometer. The result of the examination is shown in FIG. The exhaust speed of the exhaust system was constant. FIG. 6 shows a change in pressure over time when gas supply is stopped at time 60 minutes after starting supply of gas at a constant flow rate of 5 sccm from time 0 minutes. For both argon and water vapor, it can be confirmed that the pressure in the chamber increases with the start of gas supply and decreases after the supply is stopped. However, in the case of argon, the gas is stabilized at a constant pressure of about 7 Pa after 2-3 minutes from the start of gas supply, whereas in the case of water vapor, the pressure does not stabilize after 60 minutes and gradually increases. You can see that it continues. In addition, even when the gas supply is stopped, the pressure of argon decreases rapidly, and the pressure decreases to 0.1 Pa after 3 minutes, whereas the pressure of water vapor decreases slowly and the supply of water vapor is reduced. 60 minutes after stopping, the pressure finally decreases to 0.1 Pa. Thus, it can be seen that it is difficult to control the water vapor pressure in the sputtering chamber only by changing the supply amount.

Comparative Example 2

  Using the conventional technology (when the cooling device is not used in the sputtering apparatus of the present invention shown in FIG. 1) and the mass flow controller, the gas supply amount is increased step by step to 0, 1, 2, 3, 4, 5 sccm. On the contrary, the chamber pressure when decreased to 5,4,3,2,1,0 sccm was measured.

  As shown in FIG. 7A, when the supply amount of argon gas is increased or decreased, it can be seen that the pressure changes almost stepwise according to this, and the pressure 10 minutes after setting the flow rate is As shown in FIG. 7B, it can be confirmed that the ratio changes in proportion to the supply amount of the argon gas. Further, it can be seen that there is no difference in the chamber pressure between when the flow rate of argon gas is increased and when the flow rate is decreased, and the pressure can be accurately controlled by the flow rate of argon gas supplied to the sputtering chamber. On the other hand, in the case of water vapor, as shown in FIG. 7C, the rate of change of pressure is slow, and it takes a long time to reach a constant pressure. For this reason, as shown in FIG. 7 (d), the chamber pressure 10 minutes after setting the gas flow rate is not proportional to the water vapor flow rate, and the pressure is increased when the flow rate is increased and when the flow rate is decreased. It can be confirmed that different hysteresis is shown.

  When such hysteresis occurs, it becomes very difficult to control the water vapor pressure by the gas flow rate. In the reactive sputtering method, it is known that the composition, crystal structure, electrical / optical properties, etc. of the compound thin film produced vary greatly depending on the composition of the reaction gas. Therefore, when producing a hydroxide thin film by reactive sputtering using a mixed gas of argon and water vapor, the partial pressure of water vapor is not stable, and the chemical composition and electrical / optical properties of the formed thin film vary. Problem arises.

  By using this method, large-area NiOOH and CoOOH thin films can be produced, and electrochromic devices using these hydroxide thin films are dimming glass (smart window etc.), anti-glare mirrors for automobiles It can be used for displays (electronic paper, smart tags, etc.).

DESCRIPTION OF SYMBOLS 1 Sputter chamber 2 Substrate holder 3 Capacitance manometer 4 Peltier element 5 Cooler 6 Main valve 7 Sputter target 8 Constant temperature bath 9 Substrate 10 Water tank 11 High temperature mass flow controller 12 Mass flow controller 13 DC power supply 14 High pressure power supply 15 Turbo molecular pump (TMP)
16 Rotary pump (RP)
17 Plasma 18 Water Vapor Supply Mechanism 19 Cooling Mechanism 20 Chamber Wall 21 Cooler 22 Pipe for Coolant Circulation 23 Cooling Plate 24 Peltier Element 25 Peltier Element Radiation Unit 26 DC Power Supply

Claims (8)

  Thin film manufacturing apparatus having a cooling unit separated from a substrate having a room temperature or less inside a water vapor supply mechanism and a film forming chamber   The sputtering apparatus according to claim 1.   3. The sputtering apparatus according to claim 2, wherein the temperature of the cooling unit is lower than the temperature of the substrate for forming a thin film and not more than −35 ° C.   4. The sputtering apparatus according to claim 1, wherein the cooling unit is cooled by a Peltier element. When the water vapor supply amount at the time of sputtering film formation is Fin (sccm) and the water vapor pressure in the sputtering chamber is P (Pa), the area S of the cooling unit is 1.4 × 10 ⁻⁵ Fin / P (m ² ) or more. The sputtering apparatus according to claim 1, wherein:   A hydroxide thin film, an oxyhydroxide thin film, or a hydrated oxide thin film produced by the thin film manufacturing apparatus or sputtering apparatus according to claim 1.   A method for producing a hydroxide thin film, an oxyhydroxide thin film, or a hydrated oxide thin film, wherein the thin film production apparatus or sputtering apparatus according to claim 1 is used.   An electrochromic smart window using the hydroxide thin film, the oxyhydroxide thin film, or the hydrated oxide thin film according to claim 7.

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