1. Field of the Invention
The present invention relates to a vaporizing and supplying method intended for supplying a semiconductor manufacturing apparatus with a gaseous CVD (chemical vapor deposition) material. More particularly, the present invention pertains to a vaporizing and supplying method which is intended for supplying a semiconductor manufacturing apparatus with a liquid CVD material by controlling the flow rate of a liquid CVD material with an extremely high accuracy and vaporizing the liquid CVD material, and is also intended for enabling the production of a semiconductor thin film with an extremely high accuracy of film thickness.
2. Description of the Related Arts
Along with the development of semiconductor industries in recent years, there has been much progress in enhancement of performance and integration for a semiconductor device. Thus, a variety of organometal compounds in liquid form come to be used as materials for metallic films and insulation films to take the place of gaseous hydrides and halides that have heretofore been employed.
For instance, there are employed in metallic films for a semiconductor device, dimethyl aluminum hydride {(Al(CH3)2H} as CVD materials of aluminum films; hexafluoroacetylacetone copper vinyl trimethylsilane {(CF3CO)2CHCu.CH2CHSi(CH3)3} as CVD materials of copper films; bis(ethylcyclopentadienyl)ruthenium {(Ru(C5H4C2H5)2} as CVD materials of ruthenium films; etc.
With regard to an insulated film for a semiconductor device, there are known SiO2 as a gate insulating film, Si3N4 as a capacitor insulating film and PSG (phosphorus/silicon/glass) and BPSG (boron/phosphorus/silicon/glass) as an interlaminar insulating film. In addition, there are used tetraethoxysilicon {Si(OC2H5)4} as a CVD material for SiO2 film, trimethoxyboron {B(OCH3)3}, trimethoxyphosphorus {P(OCH3)3} and the like as a CVD materials for PSG and BPSG films.
On the other hand, as a method for vaporizing a liquid CVD material and supplying a semiconductor manufacturing apparatus with the resultant gaseous CVD material, there has been used a method in which a carrier gas is introduced in a liquid CVD material so as to vaporize part of the liquid CVD material, and the mixed gas of the carrier gas and the CVD material is subjected to flow rate control with a mass flow controller and is supplied to a semiconductor manufacturing apparatus. However, this method is difficult to stabilize vaporization conditions and produce a feed gas at a definite concentration and a flow rate. Accordingly, there is prevailingly employed at the present time, a method in which a liquid CVD material is subjected to flow rate control with a liquid flow controller, and supplied to a vaporizer, where it is vaporized, and the resultant gaseous CVD material is supplied to a semiconductor manufacturing apparatus.
As a method for subjecting a liquid CVD material to flow rate control, there are available a method in which an inert gas is pressurized into a liquid CVD material vessel, whereby the liquid CVD material is introduced into a liquid mass flow controller, and is subjected to flow rate control; and a method in which the flow rate of a liquid CVD material is controlled with a flow variable micropump. In any of the above-mentioned methods, a CVD material is supplied to a vaporizer after the flow rate thereof is measured in the state of liquid. Among the methods, there is generally carried out a vaporizing and supplying method using a liquid mass flow controller which is relatively easy in maintenance work.
A mass flow controller for general purpose used for the flow rate control of a liquid CVD material is constituted of a flow rate sensor, an electrical circuit, a control valve and the like. The flow rate sensor is of such a constitution that two self-heating type resistors wound on the outside of CVD material piping are incorporated in a bridge circuit, and is in such a state that the resistors are heated by a current flowing at all times. The bridge circuit is constituted so that voltage is generated when the balance of the self-heating type resistors is lost. The voltage of the bridge circuit which is caused by the heat transfer due to the flowing of a CVD material in piping is directly proportional to the mass flow rate of the CVD material, and accordingly the flow rate control of the CVD material with the mass flow controller is carried out, for instance, by measuring the flow rate of the CVD material through measurement of electric output, and thus controlling the flow rate to a prescribed level.
However, in the case of measuring the flow rate of liquid CVD material by means of the liquid mass flow controller, a large error exists between the true and measured values because of much difference in specific heat and volume per unit time each of the CVD material flowing inside the piping as compared with the measurement of the flow rate of a gaseous CVD material with a gas mass flow controller. Hence it has been impossible to produce a semiconductor thin film with a very high accuracy of film thickness. On the other hand, a method in which the flow rate is measured with flow variable micropump involves a large error on account of pulsation flow of the liquid CVD material.
In such circumstances, an object of the present invention is to provide a vaporizing and supplying method for subjecting a liquid CVD material to flow rate control with a liquid flow rate controller, supplying a vaporizer with the material, vaporizing the same, and supplying a semiconductor manufacturing apparatus with the vaporized material, characterized in that the method enables a semiconductor thin film to be manufactured with an extremely high accuracy, while controlling the flow rate of the liquid CVD material with a high accuracy.
Other objects of the present invention will become obvious from the text of this specification hereinafter disclosed.
Under such circumstances, intensive extensive research and development were accumulated by the present inventors in order to solve the above-described problems involved in the prior arts. As a result, the following has been found. Specifically, by installing in parallel, a plurality of liquid flow rate controllers, preferably at least two types of liquid flow rate controllers each having a different controllable range of flow rate and by using in combination so as to enable any of the aforesaid controllers to be used alone, or in plurality at the same time, or switchingly one after another, it is made possible to supply a vaporizer with the liquid CVD material in a wide range of capacity including a small to large capacity with a high accuracy, vaporize the material and supply a semiconductor manufacturing apparatus with the vaporized material. Thus, the present invention has been accomplished by the foregoing findings and information.
That is to say, the present invention is related to a vaporizing and supplying method for subjecting a liquid CVD material to flow rate control with a liquid flow rate controller, supplying a vaporizer with the material, vaporizing the same, and supplying a semiconductor manufacturing apparatus with the vaporized material, which comprises installing in parallel, a plurality of liquid flow rate controllers for the same type of liquid CVD material, and supplying the vaporizer with the material at a variable flow rate thereof by altering the single use of any of the controllers to simultaneous use of a plurality thereof or vice versa, and/or switching any of the controllers one after another.