Abstract:
A method for chemical vapor deposition using a showerhead through which at least one reactive gas and a purge gas are injected over a substrate, wherein the method includes: disposing the showerhead such that the bottom surface of the showerhead is spaced apart from the substrate by a predetermined distance; supplying a reactive gas and an injection support gas into the showerhead, wherein reactive gases of different kinds are respectively delivered into compartments formed at inside of the showerhead; mixing each reactive gas with its corresponding injection support gas in each mixing zone at inside of the showerhead; supplying a purge gas into a separated compartment at inside of the showerhead; and injecting the reactive gas mixed with the injection support gas and the purge gas through a plurality of reactive gas exits and a plurality of purge gas exits formed at the bottom surface of the showerhead, respectively.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a divisional application of U.S. Patent Application No. 12/089,695 filed on Jun. 2, 2008, which is a U.S. national phase application of International Application No. PCT/KR2007/000832, filed Feb. 16, 2007, and claims priority to Korean Patent Application No. 10-2006-0089853, filed Sep. 16, 2006, Korean Patent Application No. 10-2006-0124928, filed Dec. 8, 2006, Korean Patent Application No. 10-2007-0008668, filed Jan. 29, 2007, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an apparatus and a method for chemical vapor deposition (CVD) with a showerhead which supplies a plural kind of reactive gases and a purge gas over a substrate to grow a film on the substrate uniformly in thickness and composition. Here, the present invention is associated with U.S. Pat. No. 7,156,921 (“Method and apparatus for chemical vapor deposition capable of preventing contamination and enhancing film growth rate”, filed on Oct. 9, 2002), the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0003]    In an apparatus for chemical vapor deposition (CVD), a reactive gas is introduced into a vacuum reaction chamber, flows through a showerhead, and reaches a susceptor or a substrate holder on which a substrate is located. The reactive gas causes chemical reaction on the substrate to form a desired film. As a means to provide energy necessary to induce chemical reactions on the substrate, a method of simply heating the substrate or atomically exciting the reactive gas, such as making plasma, is widely used. After the reaction is finished, byproduct gases are removed from the reaction chamber by an exhaust system including a vacuum pump, then, passing through a purifying system, finally, being discharged into the atmosphere. However, since it is very important to prevent undesired particle deposition on a wall of the reaction chamber or the showerhead during a deposition process, it is preferable that the reactive gases do not react with each other in a gaseous state. Unfortunately, if reactive gases whose decomposition temperatures are substantially lower than 200° C. like metal-organic compounds are mixed in the reaction chamber, the mixture may cause homogeneous reactions in the gas phase leading to a generation of contaminant particles, or cause heterogeneous reactions on a solid-state surface such as a showerhead surface or a reaction chamber wall. Particularly, it may happen that the reactive gas is sensitive to a specific material. For example, zirconium tert-butoxide (Zr(OC 4 H 9 ) 4 ) is extremely sensitive to moisture, which is strongly like to form zirconium hydroxide (Zr(OH) x ) of white powder type. The moisture could have been physically adsorbed on the inner side of the reaction chamber, but it may be also generated over the substrates as a byproduct gas. Then, the moisture reacts with Zr(OC 4 H 9 ) 4  on the inner wall of the reaction chamber or the surface of the showerhead, depositing zirconium hydroxides. The unwanted deposits are eventually flaked off into fine particles due to a repeated thermal expansion and contraction and/or a lattice parameter mismatch between the surface materials and the deposits. As a result of this, the film formed on the substrate may be contaminated and the productivity becomes deteriorated due to a shortened preventative maintenance cycle time to remove the unwanted deposits. 
         [0004]    When a highly integrated semiconductor is manufactured, contaminant particles may cause a pattern defect such as a short or disconnection between lines and the size of the contaminant particle influencing yield is in proportion to the line width. Therefore, as the line size becomes smaller, that is, as the density of the integration is increased, the size of particle influencing yield becomes smaller, whereby the number of contaminant particles to be permitted in the reaction chamber is more seriously limited. 
         [0005]      FIG. 1  is a brief sectional view of a showerhead of a prior art, U.S. Pat. No. 6,626,998, wherein a plural number of reactive gases flow through without being mixed and are injected over a substrate so as to prevent reactions between the reactive gases therein. As each reactive gas is supplied to the first ring type individual channels  23  through a plurality of gas supply passages  17 , the gases are diffused in the first individual channels  23 , and then, transmitted to the second ring type individual channels  27  through a plurality of transition passages  25  formed at the bottom of each channel. After being diffused in the second channels  27 , the reactive gases are supplied over a substrate through a plurality of second gas transition passages  31  which are formed at the bottom of the second channels. The reactive gases cause chemical reaction on the substrate (not shown) placed on a susceptor keeping temperature of the substrate higher than that of surroundings to form a desired film on the substrate. 
         [0006]      FIG. 2  is a brief sectional view of a prior art showerhead as described in JP2005-129712. The 1st purge gas injection holes  10   b  surround the reactive gas injection holes  10   a  and the 2nd purge gas injection holes  10  care arranged by proper intervals between the 1st purge gas injection holes  10   b.  In this configuration unwanted film deposition at the bottom of the showerhead would be suppressed by the work of the 1st and 2nd purge gases used. 
       SUMMARY OF THE INVENTION 
       [0007]    However, provided not with adequate means, a reactive gas such as metal-organic compound gas having a low decomposition temperature or sensitive to moisture may cause unwanted deposits at the bottom of the showerhead. In the prior art of  FIG. 1 , the reactive gas injected from the bottom of the showerhead may diffuse backwardly and make a contamination at the bottom of the showerhead. 
         [0008]    In the prior art of  FIG. 2 , the injection velocity of the 1st purge gas and the 2nd purge gas are highly dependent on the ratio of the total sectional areas of the 1st and 2nd purge gas injection holes. In this regards it seems very difficult to positively and optimally control the injection velocities of the 1st and 2nd purge gas. And it is described that “post mixing”, that is, mixing of a reactive gas and a purge gas at the space between the bottom of the showerhead and the substrate, is preferred rather than the “pre mixing”, that is, mixing of a reactive gas and a purge gas at the stage before entering into the reaction chamber. However, in case that an inert gas is used as a purge gas, it is very difficult that the purge gas and the reactive gas cause chemical reactions within the showerhead. In this regards it should be reconsidered that “post mixing” is preferable in a CVD system. Moreover, the prior art in  FIG. 2  does not mention about the case using a plural kind of reactive gases. If a plural kind of reactive gas is mixed previously and supplied into the shower head, there is a strong likelihood that particles are generated within the showerhead. 
         [0009]    The behavior of the film growing on substrates is dominated by the mass transport of the reactive gas containing components of the film. The mass transport of reactive gases from the showerhead to the substrate is done via multiple paths including convection, diffusion, and thermo-phoresis. Among those, the convection is relatively easy to handle. It may be an effective solution to regulate the injection velocity of the reactive gases independently for meeting required composition and uniformity of the film. However, prior arts do not mention about the way to enhance the uniformity of the film growing on the substrate. 
         [0010]    A necessity to form various kinds of films using various kinds of reactive gases by CVD process has been increased. However, if the conventional showerhead device is used further, undesired particles may deposit in the showerhead due to the unexpected properties of the reactive gases used, or a good quality of the film grown on substrates may not be attained, which may limit the wide application of the CVD process. 
         [0011]    In the present invention there is provided an apparatus for chemical vapor deposition (CVD) with a showerhead and a method thereof, wherein each reactive gas is supplied to the substrate independently while passing through the showerhead, wherein a purge gas is injected from the bottom surface of the showerhead and forms a protective curtain, wherein the injection velocity of each kind of reactive gas is positively and externally regulated to make a uniform mixing of the reactive gases over the substrate, and wherein the showerhead is applied to a reactive gas confining means which surrounds the substrate and extended to the bottom of the reaction chamber at its one end. 
         [0012]    A plural kind of reactive gases and injection support gases are supplied into the showerhead in such a way that each reactive gas is mixed with each injection support gas in a mixing zone at inside of the showerhead, and a purge gas is supplied into a compartment formed at inside of the showerhead. Then, the reactive gas mixed with the injection support gas and the purge gas are injected through a large number of reactive gas exits and a large number of purge gas exits formed at the bottom surface of the showerhead, respectively, thereby the injection velocities of each reactive gas and the purge gas are positively regulated. 
         [0013]    The showerhead includes a plurality of reactive gas showerhead modules and a purge gas showerhead module separated each other, the number of the reactive gas showerhead modules is same as the number of kinds of reactive gases, and a large number of reactive gas injection tubes are connected to the bottom of a reactive gas shower head module for injecting a reactive gas mixed with an injection support gas which is a kind of a inert gas. A purge gas showerhead module, having a large number of guide tubes of which ends are hermetically joined at the holes formed at top and bottom plate of the purge gas showerhead module for accepting the reactive gas injection tubes along the inside thereof, is mounted under the reactive gas showerhead modules. A large number of exits are formed at the bottom of the purge gas showerhead module for injecting the purge gas. The guide tubes are also inserted to the reactive gas showerhead modules in such a way that reactive gas injection tubes connected to a reactive gas showerhead module at upper position passes through a reactive gas showerhead modules at lower position along the inside of the guide tube of the lower reactive gas showerhead module. 
         [0014]    A cooling jacket constitutes the lowest part of the showerhead by keeping the temperature of the showerhead at proper levels to suppress both condensation and thermal decomposition of the reactive gas in the showerhead. 
         [0015]    As described above the present invention has a function that each reactive gas passes through a showerhead independently, thereby preventing mixing of the reactive gases at inside of the showerhead. Moreover, the present invention has a function that a purge gas is injected from a bottom surface of the showerhead and forms a protective curtain beneath the bottom of the showerhead, thereby suppressing diffusion of the reactive gas backwardly. Moreover, the present invention has a function that the injection velocity of each reactive gas is positively regulated by controlling the amount of the injection support gas which is mixed to the reactive gas in the showerhead, thereby determining composition of the film growing on substrates easily. Furthermore, the present invention has a function that the temperature of showerhead is maintained at proper levels by mounting a cooling jacket which constitutes the lowest part of the showerhead, thereby unwanted film deposition caused by thermal decomposition of the reactive gases is suppressed at inside and bottom of the showerhead. In addition to this, if the present invention is applied to a CVD system together with a reactive gas confining means, the contamination at inside of the reactive gas confining means is prevented, and the film growth rate is increased by confining the reactive gas in the vicinity of the substrates. 
         [0016]    While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: 
           [0018]      FIG. 1  is a brief sectional view showing a conventional showerhead which guides and injects different kinds of reactive gases to the substrate; 
           [0019]      FIG. 2  is a brief sectional view showing a conventional showerhead capable of preventing unwanted film deposition at the bottom thereof in case that one reactive gas is used; 
           [0020]      FIG. 3  is an perspective view of a showerhead of a first embodiment according to the present invention illustrating that a plurality of reactive gas showerhead modules and a purge gas showerhead module are vertically laid in an order; 
           [0021]      FIG. 4  is a sectional view of a showerhead of a first embodiment wherein the mixing of a reactive gas and an injection support gas occurs in a compartment thereof; 
           [0022]      FIG. 5  is a detailed sectional view of a purge gas showerhead module showing purge gas exits and guide tubes of which end is hermetically joined to the bottom thereof; 
           [0023]      FIG. 6  is a detailed sectional view of a purge gas showerhead module showing a gap between the end of the guide tube and the hole at the bottom thereof; 
           [0024]      FIG. 7  is a sectional view of a showerhead of a second embodiment with an improved structure which promotes mixing of the reactive gas and the injection support gas; 
           [0025]      FIG. 8  is a sectional view of a showerhead of a third embodiment illustrating a plurality of reactive gas showerhead modules and a purge gas showerhead module which are vertically laid in an order, wherein mixing of a reactive gas and an injection support gas occurs at the exit part thereof; 
           [0026]      FIG. 9  is a detailed sectional view of a mixing zone of the third embodiment; 
           [0027]      FIG. 10  is a sub-sectional view of a showerhead having a cooling jacket which is placed under the purge gas showerhead module and keeps the temperature of the showerhead at proper levels; 
           [0028]      FIG. 11  is a schematic view showing magnitudes of injection velocities of a plurality of reactive gases and a purge gas at the bottom of the showerhead; 
           [0029]      FIG. 12  is a bottom view showing an arrangement that rows and columns of the reactive gas injection tubes are crossed in a perpendicular direction and the two adjacent columns are shifted at a distance and staggered; 
           [0030]      FIG. 13  is a bottom view showing an arrangement that locations of reactive gas injection tubes are repeated to multiple circumferential directions; 
           [0031]      FIG. 14  is a brief sectional view showing a first example that the showerhead according to the present invention is applied to a reactive gas confining means; 
           [0032]      FIG. 15  is a brief sectional view showing a second example that the showerhead according to the present invention is applied to another type of a reactive gas confining means. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    The purge gas in the present invention doesn&#39;t either dissolve or generate byproducts by itself. For example, the purge gas includes Ar, N 2 , and He. If no chemical reactions are induced in the showerhead, H 2  or O 2  may be included as a purge gas and may participate in the deposition process on substrates as a source material. The purge gas, having a relatively small molecular weight, diffuses instantly in the reaction chamber and is relatively less influenced by a force circulation caused by the act of vacuum pump. 
         [0034]    Meanwhile, the reactive gas is a source material gas that participates directly in the deposition process on substrates by pyrolysis, combination, and/or etc., for example, a gaseous source material containing components of the film deposited, a mixture of a vaporized source material containing components of the film deposited and a carrier gas for vaporizing, or a purely vaporized source material containing components of the film deposited without the aid of carrier gas. The source material includes, for example, Pb(C 2 H 5 ) 4  for Pb, Zr(OC 4 H 9 ) 4  for Zr, and Ti(OC 3 H 7 ) 4  for Ti, which are all metal-organic compounds in the deposition of PZT (Lead Zirconium-Titanate) films. The carrier gas includes, for example, Ar, N 2 , He, H 2  and etc. The reactive gas causes adsorption and surface reaction on all of the inner structure of the reaction chamber including substrates, reaction chamber inner wall, and the showerhead. The injection support gas is a kind of an inert gas, such as Ar, N 2 , or H 2 . If no chemical reactions are induced in the showerhead, H 2  or O 2  may be included as an injection support gas too. 
         [0035]      FIGS. 3 to 6  show a first embodiment of the present invention. As shown in  FIG. 3  two reactive gas showerhead modules and one purge gas showerhead module are vertically laid in an order. If more than two kinds of reactive gases are used, the number of the reactive gas showerhead modules may be 3, 4, or larger. 
         [0036]    As shown in  FIG. 4 , a reactive gas and an injection support gas are respectively introduced into a diffusion room  171  and a mixing room  172  of the upper reactive gas showerhead module  110  along a reactive gas inlet  123  and an injection support gas inlet  125 , respectively. The diffusion room  171  consists of a top plate  161 , an upper wall  163 , and an upper diaphragm  135 , wherein the reactive gas delivered along the reactive gas inlet  123  is diffused. Then, the reactive gas is delivered into the mixing room  172  through a large number of holes  137  of the upper diaphragm  135 . The mixing room  172  consists of the said upper diaphragm  135 , a middle wall  165 , and a lower diaphragm  145 , wherein the injection support gas delivered along the injection support gas inlet  125  is mixed with the reactive gas delivered from the said diffusion room  171  via holes  137  at the upper diaphragm  135 . The mixture of the reactive gas and the injection support gas is delivered into a distribution room  173  through a large number of holes  147  perforated at the lower diaphragm  145 . The distribution room  173  consists of the said lower diaphragm  145 , a lower wall  167 , and a bottom  169 , wherein the mixture of the reactive gas and the injection support gas delivered from the said mixing room  172  is equally distributed to a large number of reactive gas injection tubes  151  joined hermetically to holes of the bottom  169  thereof. In  FIG. 4  it is preferable that the holes  137  of the upper diaphragm  135  and holes  147  of the lower diaphragm  145  are small enough to induce a uniform mixing in the mixing room  172 , for example, 0.3 to 0.6 mm in diameter. The reactive gas injection tube  151  would be extended a rather long distance, about 60 to 120 mm. In this regards, the inner diameter of the reactive gas injection tube  151  is recommended to be at least 1.5 mm. 
         [0037]    Then, the reactive gas injection tube  151  passes through the lower reactive gas showerhead module  210  along a guide tube  281  of which ends are hermetically joined to holes formed at top  261  and bottom plate  269  of the lower reactive gas showerhead module  210 . On the other hand, a purge gas is introduced into a purge gas showerhead module  410  through a purge gas inlet  423  thereof, sufficiently diffused at inside of the purge gas showerhead module  410  after flowing through a large number of holes  437  formed at the intermediate plate  435 , and then, injected from the purge gas exits  446  which are located at the bottom  469  of the purge gas showerhead module  410 . It is preferable that the size of the purge gas exit  446  is small enough to induce uniform distribution of the purge gas within the purge gas showerhead module, where the recommended size is 0.3 to 0.6 mm in inner diameter. It may be necessary that the purge gas exit  446  is extended towards the substrate within a predetermined distance (“d 1 ” in  FIG. 5 ), for example, 3 mm. Finally, the reactive gas injection tubes  151  and  251  which are respectively extended from the reactive gas showerhead modules  110  and  210  pass through the purge gas showerhead module  410  along guide tubes  481 , wherein the ends of the guide tube  481  are hermetically joined to the holes formed at top  461  and bottom plate  469  of the purge gas showerhead module  410  as shown in  FIG. 5 . If there exists a gap between the guide tube  481  and the hole  450  of the bottom  469  of the purge gas showerhead module  410 , “g 1 ” in  FIG. 6 , an enhancement would be expected in the prevention of unwanted particle deposits at the tip of the reactive gas injection tubes  151  or  251 . In this case, however, the structure becomes complicated and it is not easy to determine the injection velocity of the purge gas via the purge gas exits and the injection velocity of the purge gas via the gaps independently. Meanwhile, the inertia of the reactive gas injected from the end tip of the reactive gas injection tube would play more role in the prevention of the contamination at the tips rather than the effect of the purge gas injected from the gap. In this regards even if the gap does not exist and purge gas does not flow through the gap, it is expected that the contamination at the tip is not severe. However, the purge gas injected from the purge gas exit still plays an important role in making a protective curtain beneath the showerhead. 
         [0038]      FIG. 7  shows a second embodiment of the present invention, wherein a mixing of the reactive gas and the injection support gas is promoted within the reactive gas showerhead module. A reactive gas and an injection support gas are respectively introduced into a reactive gas diffusion room  861  and an injection support gas diffusion room  862  of the reactive gas showerhead module  110  along a reactive gas inlet  123  and an injection support gas inlet  125 , respectively. The reactive gas passes through the injection support gas diffusion room  862  along a large number of reactive gas diffusion channels  865 . It is required that one end of the reactive gas diffusion channel  865  is hermetically joined to the bottom  835  of the reactive gas diffusion room  862  so as to suppress the backward diffusion of the injection support gas to the reactive gas diffusion room  861 . Laser welding technology would be used adequately in joining process. And it is recommended that there is no gap between the other end of the reactive gas diffusion channel  865  and the hole formed at bottom  845  of the injection support gas diffusion room  862  to suppress passage of the injection support gas along the gap. It is preferable that the number and the size of the reactive gas diffusion channels are between 0.2 to 0.4 per unit square cm and 0.8 to 1.6 mm in inner diameter, respectively. Instead, a large number of tiny holes  847 , of about 0.3 to 0.6 mm in diameter, are formed at the bottom  845  of the injection support gas diffusion room  862  to assure a uniform injection of the injection support gas to the distribution room  863 . Then, the reactive gas and the injection support gas are mixed in the distribution room  863  and distributed equally to the reactive gas injection tube  151 . 
         [0039]      FIG. 8  shows a third embodiment of the present invention. The main difference of the third embodiment to the first or second embodiment is a location of a mixing zone in the showerhead. A reactive gas is entered into a reactive gas diffusion room  711  via a port  713  and equally distributed to a large number of inner reactive gas injection tubes  751  joined at the bottom  719  thereof. An injection support gas is entered into an injection support gas diffusion room  712  via a port  723  and is equally distributed to a large number of outer reactive gas injection tubes  752  joined at the bottom  729  thereof. As shown in  FIG. 8 , the inner reactive gas injection tube  751 , surrounded by the outer reactive gas injection tube  752 , is extended toward the substrate and passes through the purge gas showerhead module  780  along a guide tube  781 . The inner reactive gas injection tube  751  is shorter than the outer reactive gas injection tube  752  by 5 to 10 mm at its end. The reactive gas diffusion room  711  and the injection support gas diffusion room  712  are hermetically tightened by an O-ring  754  and bolts  799 . An inner reactive gas injection tube and an outer reactive gas channel constitutes a reactive gas injection tube as a pair, and the mixing of the reactive gas and the injection support gas occurs at a mixing zone  777  formed between the ends of the inner and outer reactive gas injection tubes as shown in  FIG. 9 . 
         [0040]    As shown in  FIG. 10 , a cooling jacket  510  is mounted under the purge gas showerhead module in the present invention. The cooling jacket  510  is composed of an upper plate  561 , a wall  563 , and a lower plate  569 , wherein a plurality of guide tubes  582  for reactive gas injection tubes  151 ,  251  and a plurality of guide tubes  581  for the purge gas are hermetically joined to the upper plate  561  and the lower plate  569  at their ends. The purge gas injected from the purge gas showerhead module flows through the guide tube  581  and the annular gap (“g4”) between the guide tube  582  and the reactive gas injection tube  151 , then finally injected to the substrate(not shown). Therefore, as mentioned earlier in the description related with  FIG. 6 , the contamination is effectively prevented at the tip of the reactive gas injection tube  151  and  251  as well as at the bottom of the lower plate  569 . The cooling jacket  510  has a function to keep temperature of the showerhead at proper levels, for example, at temperature of 150-200° C. A coolant supplied into the cooling jacket  510  via a coolant supply port  523  flows through the inner space of the cooling jacket  510 , goes out of the cooling jacket  510  via an exit port  525 , then finally goes out of the reaction chamber (not shown). The coolant may be a compressed air, water, or etc. However, it cannot be emphasized too much that there should be no leakage of the coolant to the reaction chamber. A thermocouple (not shown) may be mounted at any proper place of the surface of the showerhead to measure and control showerhead temperature. The detailed description will be omitted here, since the technology belongs to a general method. The effect of cooling the showerhead in the present invention is apparent in the prevention of unwanted film deposition in the showerhead and on the bottom surface of the purge gas showerhead module caused by thermal decomposition at unnecessarily high temperature. 
         [0041]    As shown in  FIG. 11 , in the present invention the mixture of the reactive gas and the injection support gas is injected from the end of the reactive gas injection tube  151  and  251  toward the substrate (not shown). It is preferable that the end tip of the reactive gas injection tube  151  and  251  has a shape of converging nozzle so as to easily assemble showerhead modules each other to enhance prevention of unwanted particle deposition at the bottom of the showerhead by increasing the injection velocity of the reactive gas. The inner diameter of the nozzle at the end, denoted by d 3  in  FIG. 11 , would be between 0.8 to 2 mm. If the end of the reactive gas injection tube  151  and  251  is extended from the bottom  479  of the showerhead  410  toward the substrate, the effect of the preventing unwanted particle deposition at the bottom of the showerhead would be increased, but the temperature at the end tip of the reactive gas injection tube  151  and  251  would rise much. In this regards the protrusion is recommended within 10 mm. 
         [0042]    In case that a plurality of reactive gases is used, the injection velocity of each reactive gas can be positively regulated by the amount of injection support gas without influencing the delivering rate of the reactive gas. As shown in  FIG. 11 , the injection velocity of the reactive gas A, V A , may be higher than that of reactive gas B, V B . Therefore, the composition of films growing on substrates which is highly dependent on mass transport of each reactive gas can be more effectively determined. In addition to this, the flow rate of the purge gas via the purge gas exit  446  can be positively regulated too. 
         [0043]    A kind of reactive gas does not mix with another kind of reactive gas until they are injected from the showerhead, then, every kind of reactive gases and the purge gas injected are mixed together at the space between the bottom surface  479  of the showerhead  410  and the substrate. It is preferred that the bottom surface  479  of the showerhead  410  is spaced apart to the substrate by 20 mm to 60 mm so as to achieve best compromise between the uniformity and the growth rate of films growing on substrates. 
         [0044]    The number density of reactive gas injection tubes is directly related to the uniformity of the films on substrates. For one kind of reactive gas, the appropriate number density is about 0.2-0.4 per unit square cm. And the effective size of the bottom of the showerhead, that is the area where the reactive gas injection tubes are formed, would be large enough to cover the substrate. For the case of the substrate of 150 mm in diameter, the effective bottom size of the showerhead is about 200 mm in diameter, and the total number of the reactive gas injection tubes of one kind lies between  60  and  120 . With regards to the arrangement of the reactive gas injection tubes, if the arrangement could assure a uniform spreading of the reactive gas, it would have any specific pattern or even randomness. Considering that three reactive gases are used, which are denoted as “A”, “B”, and “C”, respectively,  FIG. 12  is a bottom view showing an arrangement that rows and columns of the reactive gas injection tubes are crossed in a perpendicular direction and the two adjacent columns are shifted at a distance and staggered.  FIG. 13  is a bottom view showing an arrangement that locations of reactive gas injection tubes are repeated to multiple circumferential directions. 
       Example 1 
       [0045]      FIG. 14  shows a first example that the showerhead  100  of the present invention is applied to a reactive gas confining means  900 . Here, the reactive gas confining means  900  is spaced apart from the inner wall  7  and the ceiling of the reaction chamber  1  at a distance, surrounds the substrate  9  with a dome-like roof, touches the bottom  961  of the reaction chamber along its end, has a large number of fine holes formed thereon and an opening part formed at the central portion of the roof thereof on which the rim of the showerhead  100  is placed along the opening so that the bottom surface of the showerhead  100  and the substrate are in parallel to and facing each other. Details about the reactive gas confining means are incorporated in U.S. Pat. No. 7,156,921 by reference. 
         [0046]    As shown in  FIG. 14 , two reactive gases, two injection support gases, and a first purge gas are delivered into the showerhead  100  through a reactive gas supply tubes  954 A and  954 B, injection support gas supply tubes  955 A and  955 B, and a first purge gas supply tube  956 , respectively. A coolant enters into the showerhead  100  through a coolant supply tube  961  and goes out of the reaction chamber  1  through coolant return tube  962 . And a second purge gas is delivered into a space  970  between the reaction chamber wall  7  and the reactive gas confining means  900  via the second purge gas supply port  957 . Then, the reactive gas confining means  900  works to prevent unwanted particle deposition on the inner side thereof by the protective curtain effect of the second purge gas delivered from outside to inside of the reactive gas confining means  900 . In addition to this, the contamination at the bottom of the showerhead is prevented by the function of the showerhead in the present invention described earlier. Moreover, the growth rate of films grown on substrates is much enhanced by the effect of the second purge gas which confines the reactive gas in the vicinity of the substrate. 
       Example 2 
       [0047]      FIG. 15  shows a case that the showerhead  100  of the present invention is applied to a reactive gas confining means  900  of another type. Here, the reactive gas confining means  900  has a ceiling with a flat rim. The ceiling with a rim can be easily mounted on a device such as a protruded spot  966  in the reaction chamber  1 . And a gap between the ceiling and the vertical wall of the reactive gas confining means could be easily formed to permit in and out of the substrate  9 . As the gap  967  is opened by lowering the vertical wall  912  of the reactive gas confining means using a kind of lever (not shown) attached to the bellows  968  which is hermetically joined to the stage  935 , in and out of the substrate  9  would be performed by inserting a robot arm (not shown) from a transfer chamber (not shown) to the reaction chamber  1  through a gate valve  930  and the gap  967  followed by raising and lowering of the stage  935 . 
         [0048]    While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention. 
         [0049]    According to the present invention, regardless of the condition whether the material is complicated to handle or the process is restrictive in CVD, thick films can be deposited without concern about the contamination of the reaction chamber including reaction chamber inner wall and showerhead. Therefore, the present invention can be effectively used as a solution in the process where unwanted films are grown on surfaces of internal parts of the reaction chamber caused by chemical reactions of reactive gases. Since the present invention comprises very simple and compatible structures, the detailed parts of the present invention can be easily adopted. For a new applicability, as the present invention is advantageous in growing PZT films as thick as 2-8 μm for inkjet head, the performance of the inkjet can be greatly enhanced and the inkjet technology can be more widely used in the deposition of electronic materials like LCD color filters. Moreover, the present invention has a wide industrial applicability including the miniaturization and high efficiency of electronic parts such as multi-layer ceramic chip condensers (MLCC).