In a manufacturing process of a semiconductor device, a target object to be processed such as a semiconductor wafer or the like is repeatedly subjected to various kinds of processing such as a film forming, an etching, a heat treatment and a modification treatment. For example, there is known a CVD (Chemical Vapor Deposition) method to form a thin film on a surface of a semiconductor wafer. In the CVD method, a semiconductor wafer is arranged within a processing chamber of a processing apparatus. A processing gas containing a source gas is introduced into the processing chamber to generate a reaction product. A thin film made of the reaction product is deposited on the surface of the semiconductor wafer.
In recent years, there is also known an ALD (Atomic Layer Deposition) method as a film forming method. In the ALD method, a source gas and a reaction gas are alternately supplied into a processing chamber to form thin films one layer after another each of which has a thickness of atomic level or molecular level. The ALD method can provide a film having a good quality and can accurately control the film thickness. For that reason, the ALD method draws attention as a manufacturing method of a semiconductor device which is becoming more scaled down.
In case where a thin film of, e.g., TiN, is formed by the ALD method, the thin film is deposited by repeatedly performing a series of the following steps i) through iv), for example.
i) A source gas, e.g., a TiCl4 gas, is supplied into a processing chamber, thereby causing TiCl4 to adhere onto a wafer surface.
ii) The inside of the processing chamber is purged by a N2 gas to remove the remaining source gas from the processing chamber.
iii) A reaction gas, e.g., an NH3 gas, is supplied into the processing chamber to react with the TiCl4 adhered onto the wafer surface to thereby form a thin layer of TiN film.
iv) The inside of the processing chamber is purged by a N2 gas to remove the remaining gas from the processing chamber.
In the ALD method, as described in the TiN film formation example above, supplies and cutoffs of different kinds of gases including the source gas need to be intermittently and repeatedly performed within a short period of time. In an ALD apparatus, the supply and cutoff of the gas is performed with an electromagnetic valve, which is provided in a gas supply path through which the gas is supplied to the processing chamber, and is opened and closed by a signal transmitted from a control unit based on a gas supply recipe.
In case of the film forming process performed by the ALD method, as compared with the film forming process performed by the CVD method, the time required in opening and closing the valve once becomes shorter and the opening/closing frequency of the valve becomes extremely high. Since the opening and closing speed of the valve is very fast in the ALD apparatus, there is a problem in that a conventional control system has a difficulty in monitoring the process status such as a flow rate of a gas introduced into a processing chamber and a pressure increase within the processing chamber caused by the gas introduction.
In respect of the film forming process performed by the ALD method, Japanese Patent Application Publication No. 2002-329674 (e.g., FIG. 1) (corresponding to U.S. Patent Application Publication No. 2002/0127745A1) discloses a valve control system including a programmable logic controller configured in communications with a system control computer and operatively connected to an electrically-controlled valve. In this valve control system, the valve control refresh time is reduced to 10 milliseconds or less.
Japanese Patent Application Publication No. 2003-286575 (e.g., the claims) (corresponding to U.S. Patent Application Publication No. 2003/0143747A1) describes a method in which a sensor detects characteristic parameters such as a pressure in a gas flow path and a valve vibration, and provides a signal indicative of the characteristic parameters as a function of time in order to measure changes in gas pulses supplied into a processing chamber in an ALD apparatus. A curve shape is generated from the sensor signal, and the changes in the curve shape are monitored.
While JP2002-329674A discloses the ALD apparatus capable of coping with the high-speed opening and closing of the valve, no consideration is given to how to rapidly observe the process status such as a flow rate of a gas introduced into a processing chamber and a pressure increase in the processing chamber caused by the gas introduction. In JP2003-286575A, the process status is monitored based on the change in the characteristic parameters. Since the curve shape obtained by providing the sensor signal indicative of the characteristic parameters is monitored in JP2003-286575A, it may not possible to detect a trouble accurately and, further, it may possibly be time-consuming to detect the trouble.