Abstract:
A high quality metallic deposit can be produced inside the micro-cavities formed on a surface of a substrate by the present invention. The method involves immersing the substrate in a liquid held in a processing chamber, evacuating the processing chamber so as to remove residual bubbles from the micro-cavities and to degas the liquid within the micro-cavities, and subjecting the liquid to boiling in at least those regions adjacent to the substrate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to next generation technology for fabricating electrical interconnects in integrated circuit devices, and relates in particular to a method and apparatus for filling micro-cavities formed on a surface of a substrate with metal plating. 
     2. Description of the Related Art 
     Aluminum is a typical material used for fabricating conductor circuit patterns in integrated semiconductor devices. An aluminum conductor line pattern is fabricated by first sputtering an aluminum film on a semiconductor wafer (wafer), followed by forming circuit patterns on the aluminum film by means of photolithography, and etching off unwanted regions to complete the conductor line pattern. As the devices become more highly integrated, there have been increasing demands for a finer conductor line pattern. Referring to FIGS. 27A-27C, to meet such demands for micro-fabrication, the width of grooves  303  and contact hole  301  for producing conductor line  311  and plug  313  must be made smaller, typically in a range of 0.13 to 0.18 μm. When the width of the conductor line becomes so narrow, aluminum begins to show problems due to its inferior properties. 
     To other types of metals than aluminum, the above-described conventional method of circuit fabrication is sometimes difficult to apply, and therefore, a damascene process has been performed by fabricating stud holes and wiring cavities on a circuit board first, and then filling the cavities with a suitable metal by using processes such as chemical vapor deposition (CVD), sputtering or plating, and finishing the circuit board by chemical mechanical polishing (CMP) to complete conductor line fabrication. 
     Plating has been used widely for forming metallic films and has many advantages. FIG. 28 shows a setup for conventional plating. A plating chamber  1  contains a plating solution  9  in which are immersed a cathode  3 , having a substrate W, and an opposing anode  4 , and the plating solution  9  is stirred with a stirrer  11  during plating. 
     Compared to other processes, the plating cost is relatively low, high purity products can be produced, and processes can be done at a relatively low temperature to avoid degrading thermal effects. However, it is difficult to use plating to fill micro-cavities C such as grooves  303  and contact holes  301  without leaving some internal voids. When a substrate W having micro-cavities C is immersed in plating solution  9 , it is not unusual to have residual air remaining inside the cavities C, and it is not possible to infiltrate the cavities C completely with the plating solution  9 . This is considered to be due to the effects of wettability of the substrate W and the surface tension force of plating solution  9 , and, especially for such shapes as the contact hole  301 , which is deeper than it is wide (for example, an aspect ratio, depth/width, of about 5), air tends to remain in the cavity much more frequently. Similarly, it becomes much more difficult to displace spent liquid of plating solution  9  with fresh plating solution containing active metallic ions. This difficulty increases as the width of the cavities C becomes narrower. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method and an apparatus for plating to enable a high quality metallic deposit to be produced inside the micro-cavities formed on a surface of a substrate, such as a semiconductor wafer, by completely infiltrating the micro-cavities with a plating solution and refreshing the plating solution in the micro-cavities during plating. 
     The present invention is to establish such an object by a method for producing a metal deposit inside micro-cavities fabricated on a substrate comprising: immersing the substrate in a liquid held in a processing chamber; evacuating the processing chamber so as to remove residual bubbles from the micro-cavities and to degas the liquid within the micro-cavities; and subjecting the liquid to boiling in at least those regions adjacent to the substrate. 
     Accordingly, after removing the gas dissolved in the liquid or residual bubbles from the micro-cavities utilizing a phenomenon of nucleate boiling, the plating solution is infiltrated into the cavities so that metal can be plated inside of the cavities to efficiently produce a high quality deposit which is free of internal defects. This process is basically applicable to both electro- and electroless-plating processes. 
     The liquid may comprise a plating solution so that plating can be readily performed. In another option, a preferred liquid other than a plating solutions which is more easily introducible to the micro-cavities is usable. Such liquid may include water, alcohol or another suitable liquid. In this case, replacing or diluting the liquid with a plating solution may be necessary prior to plating. 
     The processing chamber may be a plating chamber so that the plating process can be done without transferring the substrate. In another option, the processing chamber may be made as a pre-plating processing chamber only for the pre-plating process. 
     In the boiling step, interior chamber pressure may be reduced to a value less than a saturated vapor pressure of the liquid. This will lower the boiling point of the liquid so that there is no need to raise the temperature of the liquid to a high temperature, thus resulting in an energy efficient and productive plating process. In the boiling step, the substrate may be heated from a back surface of the substrate. This will promote selective heating of those regions close to the cavities so that expelling of bubbles from the cavities and boiling in the cavities are enhanced. In the boiling step, interior chamber pressure may be reduced and at the same time, the substrate may be heated from the back surface. 
     Between a degassing step and a boiling step, interior chamber pressure may be raised to a high pressure. Also, boiling and pressurizing may be repeatedly carried out. These steps will enable the solution to reliably infiltrate the cavities, and to replace the solution inside the cavities periodically with fresh solution, thereby realizing defect-free plating. 
     It is also permissible to perform a boiling step while plating. Boiling may be carried out intermittently or continuously. This will enable to carry out plating while exchanging old plating solution inside the cavities with fresh plating solution to efficiently carry out the process of depositing metal in the cavities. 
     In another aspect of the invention, an apparatus for producing a metal deposit inside micro-cavities fabricated on a substrate comprises a sealable processing chamber; an evacuating device for reducing interior chamber pressure; and a gas inlet device for pressurizing the chamber interior. The evacuating device is capable of selectively reducing interior chamber pressure to at least two pressure values, one being less than a saturated vapor pressure of the liquid, and the other being an intermediate value between the saturated vapor pressure and atmospheric pressure. 
     In this apparatus, liquid such as plating solution in the chamber, air, dissolved gas or gas bubbles in the plating solution, and bubbles attaching to the substrate can be made to undergo volume change or changes in their liquid state, so that liquid may be infiltrated into the cavities and/or the old solution may be refreshed with new solution. This will permit to form a metal deposit within the cavities efficiently by plating, without creating internal defects in the deposited metal. A heating device to heat the plating solution may be provided to facilitate the liquid filtration or to raise plating efficiency. 
     The evacuating device may have an exhaust pipe to connect a vacuum pump for reducing interior chamber pressure, and the exhaust pipe may be provided with a shutoff valve and a control valve for adjusting flow resistance. This will permit the system to be switched between two vacuum levels: a pressure intermediate between one atmosphere and the saturated vapor pressure; and a saturated vapor pressure or lower. Such a switching operation will enhance degassing of dissolved gas in the liquid by reduced pressure and expelling bubbles from the cavities by volume expansion on the one hand, and vapor release due to nucleate boiling in the cavities prompted by a high vacuum. 
     The evacuating device may have a vacuum pump to reduce interior chamber pressure and two parallel exhaust pipings having different flow resistance to connect the vacuum pump to the plating chamber. 
     The apparatus may be provided with a heating device for heating the substrate through a back surface of the substrate. 
     The apparatus may be provided with a vibrator means for stirring the plating solution in the plating chamber. These are all effective means for promoting liquid boiling in the cavities. 
     In another aspect of the invention, a method for fabricating wiring on a substrate comprises: immersing the substrate in a liquid in a processing chamber; evacuating the processing chamber so as to remove residual bubbles from the micro-cavities and to degas the liquid within the micro-cavities; subjecting the liquid to boiling in at least those regions adjacent to the substrate; plating the substrate so as to produce a metal deposit inside the micro-cavities; and removing unwanted portions of metal deposit formed in the micro-cavities by polishing using chemical and mechanical polishing methods. 
     The liquid may be a plating solution so that plating can be readily performed, or, a preferred liquid other than a plating solution easily introducible to the micro-cavities. In this case, a step for replacing or diluting the liquid with a plating solution is necessary between the boiling and plating steps. 
     In another aspect of the invention, an apparatus for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: a sealable processing chamber; a vacuum device for reducing interior chamber pressure; a substrate holder for holding the substrate in such a way that a back surface side of the substrate is liquid-tight in the processing chamber; and a heater provided internally in the substrate holder for heating the substrate. 
     In another aspect of the invention, a method for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: placing the substrate in a sealable processing chamber; evacuating the interior of the chamber; immersing the substrate in a liquid; and pressurizing the liquid surrounding the substrate. 
     Accordingly, after exhausting the non-condensable gases such as air from the surface of the substrate, a liquid is introduced into the chamber at normal temperature and pressure, and when the substrate is immersed in the liquid, the surface of the substrate touches the liquid. Although the cavities may contain bubbles formed by a vapor of the liquid because of surface tension effects, the application of pressure will destroy the bubbles and replace the cavities with infiltrated liquid. 
     The method may include a step of providing a pressure variation to the liquid surrounding the substrate. This will further enhance infiltration of liquid into the cavities. Such liquid may include water, alcohol or a plating solution or a mixture thereof. Selection is made by considering wettability of the substrate by the liquid and compatibility with the plating process to follow. 
     In the immersing step, a surface active agent may be used to improve wettability of the substrate. This will enhance wettability and facilitate infiltration of liquid into the cavities. Such agents may be added to the liquid beforehand, but the agent itself may be introduced first into the chamber to improve the wettability of the cavity surface, and then the liquid may be infiltrated into the cavities. 
     In another aspect of the invention, an apparatus for producing a metal deposit inside micro-cavities fabricated on a substrate comprises a sealable processing chamber; a vacuum exhaust passage for evacuating the processing chamber; a liquid inlet passage for supplying a liquid to the processing chamber; a gas inlet passage for pressurizing the liquid in the processing chamber; and a gas discharge passage for discharging gas from the processing chamber. 
     Substrates may be processed in a group or one at a time. A liquid draining passage is useful to facilitate the processing steps. The apparatus may be shared for both pre-plating treatment and plating processes. A plurality of liquid inlet passages may be provided to enable introducing different types of liquids or surfactants continuously or concurrently. 
     The apparatus may be provided with a pressure varying device to produce pressure changes in the processing chamber. The pressure varying device may be a shutoff valve or a switching valve provided on at least one of the gas inlet passage or the degassing passage. 
     The pressure varying device may be an ultrasonic vibrator device. 
     In another aspect of the invention, a method for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: placing the substrate in a sealable processing chamber; charging the processing chamber with a condensable gas; and cooling the substrate to a temperature lower than a dew point of the condensable gas to form droplets thereof within the micro-cavities. 
     This will allow droplets to form on the surface of the cavities and attach to the inside of the cavities. Therefore, by immersing the substrate in this condition, the plating solution replaces the droplets and infiltrates the cavities by affiliating with the droplets of the condensable gas. 
     The method may include a step of vibrating the substrate. Cooling the substrate to below the dew point of the condensable gas does not always produce droplets. This is because the condensable gas may be in a supercooled state and remain in the gaseous state. The degree of supercooling temperature is not a constant value, and it can sometimes reach a very high value. Therefore, by vibrating the substrate, the supercooled condition of the gas inside the cavities is disturbed, thereby releasing the gas from the supercooled state and reliably forming droplets inside the cavities. 
     In the charging step, the charging pressure of the condensable gas may be varied. This will permit replacing the residual bubbles in the cavities with condensable gas and reliabiltity forming droplets by cooling. The environment may be evacuated first and then filled with a condensable gas so as to facilitate replacement of the residual gas in the cavities with condensable gas and to reliably form droplets by cooling. 
     The method may include a step of immersing the substrate in a liquid. In this case, the liquid may be degassed by subjecting the liquid to boiling or evacuating so as to avoid a formation of bubbles from the dissolved air in the liquid. The liquid for immersing the substrate is preferably a liquid having a smaller surface tension than water so as to reliably infiltrate the cavities with the liquid. The liquid may be a plating solution, then the pre-treatment process may be continued into a plating process. 
     In another aspect of the invention, an apparatus for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: a sealable processing chamber; a gas inlet device for introducing a condensable gas into the processing chamber; a substrate cooling device for cooling the substrate; and a liquid supply device for supplying a liquid into the processing chamber. 
     This apparatus enables forming droplets on the inside surfaces of the cavities and condensing continuously. Further, a vacuum device may be provided to evacuate the processing chamber. Using this apparatus, residual gas in the cavities may be replaced with a condensable gas, and by cooling, droplets can be reliably formed in the cavities. Further, a gas inlet device may be provided to pressurize the processing chamber, thereby enabling reliable infiltration of the cavities with the liquid. 
     A method for producing a metal deposit inside micro-cavities fabricated on a substrate, comprises heating the substrate while exposing the micro-cavities to a liquid so as to expand and expel residual bubbles from the micro-cavities to thereby infiltrate the micro-cavities with the liquid. 
     In this case, a heating step may be accompanied by a cyclic pressure variation in a range above atmospheric pressure such that pressurizing and returning to atmospheric pressure are repeated. 
     The liquid may be first pressurized during the heating step and then is returned to atmospheric pressure to thereby facilitate expelling of the residual bubbles from the micro-cavities. The liquid may be a plating solution. 
     In another aspect of the invention, a method for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: disposing the substrate in a pressure vessel so that both surfaces of the substrate are under an identical pressure; evacuating the pressure vessel so as to expel residual bubbles from the micro-cavities; and introducing a liquid in the pressure vessel and applying a pressure so as to infiltrate the liquid into the micro-cavities. 
     In another aspect of the invention, a method for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: disposing the substrate in a pressure vessel so that both surfaces of the substrate are under an identical pressure; charging the pressure vessel with a gas having a solubility in a liquid; introducing the liquid into the pressure vessel; and pressurizing the liquid so as to forcibly dissolve residual bubbles of the gas in the micro-cavities into the liquid to thereby infiltrate the liquid into the micro-cavities. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a plating apparatus of the present invention; 
     FIG. 2 is a conceptual illustration of an air-removal mechanism for residual air from micro-cavities by pressure reduction; 
     FIG. 3 is a conceptual illustration of a growth process of a bubble due to nucleate boiling; 
     FIG. 4 is a conceptual illustration of an air-removal mechanism by reduced pressure boiling; 
     FIG. 5 is a water vapor pressure curve of saturated vapor; 
     FIG. 6 is a conceptual illustration of plating solution replacement mechanism in the cavities by pressure reduction; 
     FIG. 7 is a second embodiment of the plating apparatus of the present invention; 
     FIG. 8 is a third embodiment of the plating apparatus of the present invention; 
     FIG. 9 is a fourth embodiment of the plating apparatus of the present invention; 
     FIG. 10 is a cross sectional view of a substrate heating device shown in FIG. 9; 
     FIG. 11 is a fifth embodiment of the plating apparatus of the present invention; 
     FIG. 12 is a sixth embodiment of the plating apparatus of the present invention; 
     FIG. 13 is a schematic drawing of a pre-plating treatment apparatus of the present invention; 
     FIG. 14 is a schematic illustration of a liquid infiltration process into micro-cavities; 
     FIG. 15 is a schematic illustration of another embodiment of the pre-plating treatment apparatus; 
     FIG. 16 is a schematic illustration of another embodiment of the pre-plating treatment apparatus; 
     FIG. 17 is a schematic illustration of another embodiment of the pre-plating treatment apparatus; 
     FIG. 18 is a schematic illustration of another embodiment of the pre-plating treatment apparatus; 
     FIG. 19 is a schematic illustration of another embodiment of the pre-plating treatment apparatus; 
     FIG. 20 is a schematic illustration of another embodiment of the pre-plating treatment apparatus; 
     FIG. 21 is a schematic illustration of another embodiment of the pre-plating treatment apparatus; 
     FIG. 22 is an overall schematic view of an embodiment of a plating apparatus for a semiconductor wafer; 
     FIG. 23 is a flowchart for plating process steps for a process in FIG. 22; 
     FIG. 24 is an overall schematic view of another embodiment of the plating apparatus for a semiconductor wafer; 
     FIG. 25 is a flowchart for steps for the plating apparatus shown in FIG. 24; 
     FIG. 26 is another flowchart for the plating apparatus shown in FIG. 24; 
     FIG. 27 is an illustration of bubbles remaining in a micro-cavity on a substrate immersed in liquid; 
     FIG. 28 is a schematic diagram of a conventional plating apparatus; and 
     FIG. 29 is an illustration of air bubbles remaining in cavities. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a schematic drawing of an electroplating apparatus of the present invention. A plating chamber  1  is an air-tightly closable vessel having a cathode  3  with a substrate W and an anode  4  which are both connected to an electrical power source  5 . Plating chamber  1  is provided with a temperature sensor  6  for detecting the temperature of the plating solution  9 , and a chamber liquid heater  10 , which is controlled by a temperature controller (not shown) according to output data from the temperature sensor  6  to maintain the plating solution  9  at a specific constant temperature. 
     Plating chamber  1  is connected by an exhaust pipe  25  having a shutoff valve  23  and a flow control valve  22  to a vacuum pump  21 , thereby enabling selectively maintaining the pressure inside the chamber  1  at a vacuum less than the saturated vapor pressure of the plating solution or a pressure intermediate between atmospheric pressure and the saturated vapor pressure. Plating chamber  1  is also connected to a gas supply source (not shown) through a gas inlet pipe  26  so as to keep the interior chamber pressure at or above the atmospheric pressure. Interior pressure inside the chamber  1  is controlled by a pressure gage  7  and a pressure switch  8 , and switching of pressure is performed by shutoff valves  23 ,  24  in exhaust pipe  25  and gas inlet pipe  26 , respectively. 
     The process of plating a substrate W having micro-cavities (shortened to cavities hereinafter) using the plating apparatus will be explained. The substrate W is disposed inside the chamber  1  and immersed in the plating solution  9 , then the vacuum pump  21  is operated to exhaust air from inside the chamber  1  through the exhaust pipe  25 . Residual air  48  in the cavity C shown in FIG. 2A increases its volume due to pressure reduction in the surrounding, and as shown in FIG. 2B, a part is removed from the cavity C. After this step, the pressure is returned to atmospheric pressure, and the residual air inside the cavity C reduces its volume, and as shown in FIG. 2C, the plating solution  9  flows into a portion of the cavity C. 
     Chamber  1  is again reduced in pressure, and the solubility of air in the plating solution  9  is reduced, and fine-air-bubbles are formed in the solution  9 . Also, with reduction in the interior chamber pressure, the volume of air bubbles adhering to the solid surface of components immersed in the plating solution  9  is also increased, and with a proportional increase in the buoyancy, the bubbles are floated off of the solid surfaces and removed from the plating solution  9 . 
     Next, the pressure in the chamber  1  in the condition shown in FIG. 4A is again reduced to a pressure less than the saturated vapor pressure of the plating solution  9 , the liquid begins to boil or vaporize from the surface as well as from its interior, as illustrated in FIGS. 4A to  4 B. In general, bubbles remaining inside the cavity C, as shown in FIG. 3, act as nuclei for boiling, and generate a process of repeated bubble growth and bubble rising. The cavities C formed on the substrate W can act as boiling nuclei, and the bubbles  44 ,  45 ,  46  generated by nucleate boiling mix with residual air in the cavity C to form a large bubble  49  which is removed from the cavity C. After this step, when the interior pressure is returned to atmospheric pressure, plating solution  9  infiltrates into the cavity C as shown in FIG.  4 C. In this condition, power is turned on to the electrodes to carry out plating. 
     It should be noted that, as shown in FIG. 5, the boiling point of water is dependent on the pressure. Also, the boiling point of plating solution  9  is higher than that of water because of solutes in the plating solution. To boil such a liquid, it is necessary to heat the water to a temperature higher than 100° C., but by reducing the interior pressure of the chamber  1 , the liquid can be boiled at a lower temperature. For example, if the pressure is reduced to about 2700 to 27,000 Pa (20 to 200 Torr), the temperature of the substrate W may need to be only 30˜70° C. so that heating energy can be reduced and processing time shortened. 
     In the above process, pre-plating treatment is infiltration of the plating solution  9  into the cavities C, but it is also possible to replace the plating solution  9  in the cavity C during the plating process by reducing the interior pressure to less than the saturated vapor pressure of the plating solution  9 . When the interior pressure is reduced during the plating process, solution boiling is induced by the cavity C acting as boiling nuclei to thereby stir up the surrounding plating solution  9 . After this, the interior pressure is returned to atmospheric pressure, or pressurized once before returning to atmospheric pressure, and then fresh plating solution  9  flows into the cavity C. It is preferable to carry out this boiling step and pressurizing step repeatedly during the plating process. 
     FIG. 7 shows a second embodiment of the plating apparatus. In this case, the substrate W is attached to the bottom surface of a support jig  13  disposed in the upper section of the plating chamber  1 . Plating solution  9  is stirred and circulated within the chamber  1  by the stirrer  11 . The liquid heater  10  immersed in the plating solution  9  heats the solution, and the temperature sensor  6  monitors the solution temperature and adjusts the heater power through a controller (not shown) to maintain the plating solution  9  at a constant specific temperature. 
     Plating chamber  1  is connected through a set of parallel pipes auxiliary-exhaust pipe  29  and main exhaust pipe  30  to a vacuum pump  21 . The main exhaust pipe  30  is provided with a shutoff valve  32  and the auxiliary-exhaust pipe  29  is provided with a shutoff valve  31  and a variable resistance valve  33 . This arrangement allows a quick pressure reduction from atmospheric pressure by pumping with all the valves  31 ˜ 33  open, and after reaching a certain degree of vacuum, the shutoff valve on the main exhaust pipe is closed, and the interior pressure is adjusted within a narrow range by operating the variable resistance valve  33 . Therefore, the interior pressure of the plating chamber  1  can be switched to a vacuum of less than the saturated vapor pressure or an intermediate pressure between the saturated vapor pressure and the atmospheric pressure. The operation of this embodiment apparatus is the same as the first embodiment apparatus, and explanation will be omitted. 
     FIG. 8 is a schematic illustration of a third plating apparatus. The differences between this embodiment apparatus and the first apparatus are that there are an ultrasonic vibrator device  17  disposed to oppose the substrate holding stage in the chamber  1  and a stirrer  11  in a certain location of the chamber  1 . This apparatus is also able to remove residual air bubbles from the cavities C through the steps described in the previous embodiment, but this apparatus is able to operate the ultrasonic vibrator device  17  at a certain amplitude and frequency in each step as needed to facilitate removal of bubbles from the cavities C and/or nucleate boiling. 
     FIG. 9 shows a fourth embodiment of the plating apparatus of the present invention. This apparatus is provided with a heating section for heating the back surface of the substrate W as shown in FIG.  10 . Specifically, the substrate W is supported on a substrate holding stage  12  comprised by a circular bottom plate  12   a  of a diameter larger than the substrate W and a lateral wall section  12   b  surrounding the bottom plate  12   a.  A sealed liquid space is formed below the substrate W by seals  18 ,  19 , and a heater  14  for heating the substrate W is provided in the space. The substrate heater  14  is encased in a heat-resistant electrical insulating rubber, and is connected to an external power source (not shown) through the substrate stage  12 . The substrate heater  14  is thus able to provide heat to the substrate W without coming into contact with the plating solution  9 . It is also possible to assign the substrate stage  12  to act as the cathode  3 . 
     The operation of the apparatus having the above structure will be explained next. The substrate W is disposed inside the chamber  1  and is immersed in the plating solution  9 , then the interior space is evacuated through the exhaust pipe  25  by operating the vacuum pump  21 . Residual air  48  in the cavity C shown in FIG. 2A increases its volume because of reduced pressure, and as shown in FIG. 2B, a portion of the air is removed from the cavity C. After this step, when the interior pressure is returned to atmospheric pressure, the volume of residual air is compressed and, as shown in FIG. 2C, plating solution  9  enters into the cavity C. 
     In this condition, the substrate W is heated from the back by the substrate heater  14 , which heats the inside space of the cavity C from the underside. In this case, solubility of air that can be dissolved in plating solution  9  inside the cavity C is lowered, and the volume of residual air  48  is expanded. When the temperature of the plating solution inside the cavity C reaches a certain value, the volume of the bubbles adhering to the solid surfaces in the plating solution  9  is also increased, and the buoyancy, increased in proportion to the volume increase, assists the bubbles to depart from the solid surfaces and be removed from the plating solution  9 . 
     When the temperature of plating solution  9  exceeds the boiling point of the plating solution  9  under the existing interior pressure, air  48  in the state shown in FIG. 4A begins to boil or vaporize from the surface as well as from the interior of the liquid  9 , as illustrated in FIG.  4 B. In this case, bubbles  43  remaining inside the cavity C, as shown in FIG. 3, act as nuclei for boiling, and generate a process of repeated growth and rising illustrated by bubbles  44 ,  45 ,  46 . Bubbles  44 ,  45 ,  46  generated by nucleate boiling mix with residual air in the cavity C to form a large bubble  49 , which is removed from the cavity C. After this step, when the interior pressure is returned to atmospheric pressure, plating solution  9  infiltrates the cavity C as shown in FIG.  4 C. In this condition, power is turned on to the electrodes to carry out plating. 
     In the above process, pre-plating treatment is infiltration of the plating solution  9  into the cavities C, but it is also possible to replace the plating solution  9  in the cavity C during the plating process, by heating the substrate W during the plating process. When the substrate W is heated during the plating process so that the temperature of the plating solution  9  locally becomes higher than the boiling point at that pressure, nucleate boiling is generated in the cavity C acting as boiling nuclei to stir up the surrounding plating solution  9 . After this, the interior pressure and is returned to atmospheric pressure, then fresh plating solution  9  flows into the cavity C. 
     FIG. 11 shows a schematic diagram of the plating apparatus in a fifth embodiment. In this apparatus, the substrate W is attached vertically to the bottom surface of a support jig  13  disposed in the upper section of the chamber  1 . Opposite to the substrate W, a fan  16  directs the plating solution  9  towards the surface of substrate W. Similar to the apparatus shown in FIG. 7, plating chamber  1  is provided with auxiliary-exhaust pipe  29  and main exhaust pipe  30  so as to enable quick switching of the interior pressure between a reduced pressure below the saturated vapor pressure of the plating solution  9  and a reduced pressure intermediate between the saturated vapor pressure and atmospheric pressure. Basic operation of the apparatus is the same as that in previous apparatus, and the explanations are omitted. 
     Also, as shown in FIG. 12 for the sixth embodiment, other than heating to boil the liquid in the space of the cavity C, liquid entry into the cavity C or liquid replacement in the cavity C can be enhanced by using the ultrasonic vibration device  17  or by vibrating the substrate W itself. 
     The following embodiments relate to pre-plating treatment apparatuses to provide a pre-plating treatment to substrate W by using the apparatus shown in FIG. 28, for example. The apparatus shown in FIG. 13 is comprised by an air-tightly closable vessel type processing chamber  53 , a vacuum pipe  54 , liquid inlet pipe  55 , gas inlet pipe  56  and gas exhaust pipe  57  each connected to the chamber  53 . Processing chamber  53  is provided with a pressure gage  7 , a pressure switch  8  and a safety valve  36 , and a substrate stage  12  for placing the substrate W. 
     Vacuum pipe  54  is provided with a shutoff valve  23  and a vacuum pump  21 , and is capable of reducing the interior pressure of the chamber  53  to a suitable low pressure. A liquid supply source (not shown) is connected, through the liquid inlet pipe  55  having a shutoff valve  34  and a flowmeter  40 , to a nozzle  55 a facing the substrate stage  12  in the processing chamber  53  to introduce a desired volume of liquid in the processing chamber  53 . Gas inlet pipe  56  has a regulator  51  and a shutoff valve  24 , and gas exhaust pipe  57  is open to atmosphere by way of a shutoff valve  31 . Further, a liquid discharge pipe  58  with a shutoff valve  35  is provided at the bottommost section of the processing chamber  53 . Gas inlet pipe  56  and liquid discharge pipe  58  are operated together to facilitate discharge and blow of the liquid. 
     The process of pre-plating treatment using the apparatus will be explained next. The substrate W is provided with micro cavities C on the surface, similar to those shown in FIG. 29, of a size of 0.2 μm width and 0.8 μm depth, for example. As shown in FIG. 14A, the substrate W is placed on the substrate support and the sealed chamber  53  is evacuated by opening the shutoff valve  23  and operating the vacuum pump  21  to exhaust non-condensable gases, such as air, through the vacuum pipe  54  to attain a reduced pressure of about 0.01 Torr. 
     Next, as shown in FIG. 14B, a suitable liquid medium such as plating solution, high purity water or alcohol is introduced into the chamber  53 , through the liquid inlet pipe  55  and the nozzle  55   a,  at normal pressure and temperature. The liquid at first exists as a vapor  50  in the space of the sealed chamber  53 . When more liquid is supplied so that the pressure inside the chamber  53  reached the saturated vapor pressure, the liquid begins to collect as liquid in the chamber  53 , and when the substrate W is immersed in the liquid, its surface comes into contact with the liquid. 
     In this state, bubbles remain on the inside surfaces of the cavity C on the substrate W, because of surface tension and other effects. Therefore, as shown in FIG. 14D, by opening the shutoff valve  24  of the gas inlet pipe  56 , a gas  28  is introduced into the sealed chamber  53  to pressurize the liquid, or a vibration device is operated to thereby collapse the bubbles and let the liquid infiltrate the cavity C. In the example shown in FIG. 13, vibration is generated by repeating opening and closing of the shutoff valve  31  of gas inlet pipe  57  in short cycles by a driver device (not-shown) while applying gas pressure from the gas inlet pipe  56 . 
     To facilitate infiltration of a liquid into the cavity C, the liquid in this case may preferably be a substance of small surface tension with respect to the substrate W, or some surface active agent may be added to the liquid. 
     After providing such a pre-plating treatment, the substrate W is removed from the processing chamber  53  so as not to dry the substrate W before it is transferred to the plating chamber  1  (refer to FIG.  28 ), and is then immersed in the plating solution  9  to perform electroplating or electroless plating. Because of the pre-plating treatment, the cavity C is already infiltrated with the liquid, and the plating solution  9  can merge into the liquid inside the cavity C to promote plating on the inside surfaces. 
     In the apparatus shown in FIG. 13, substrates W are processed one at a time, but a plurality of substrates W may be processed simultaneously. This is accomplished by using a cassette to contain a plurality of substrates W so as to permit handling of a plurality of processed substrates or substrates to be processed at a time to thereby improve the productivity. If the cassette can hold liquid, substrates W can be prevented from drying by retaining them in the immersed state. Processing chamber  53  and the plating apparatus may be made as one chamber so that pre-plating and plating processes can be carried out continually. 
     FIG. 15 shows another embodiment of the pre-plating treatment apparatus. This apparatus is similar to the one shown in FIG. 13, but differs in the aspect of the method of applying vibration. In this case, gas inlet pipe  56  and gas discharge pipe  57  are branched through a rotary valve  59 . By the rotational action of the rotary valve  59 , the processing chamber  53  is alternately connected to either the gas inlet pipe  56  or the gas discharge pipe  57  thereby to generate a large pressure variation. 
     FIG. 16 shows still another embodiment of the pre-plating treatment apparatus. This apparatus is roughly similar to the previous apparatus, but differs in the method of varying the pressure. In this case, an ultrasonic vibrator  60  is disposed in the processing chamber  53  so that, after the ultrasonic vibrator  60  and the substrate W are immersed in the liquid  52 , the vibrator  60  is activated to apply vibration by ay of plating solution  9  to the substrate W. 
     FIG. 17 shows still another embodiment of the pre-plating treatment apparatus. This apparatus is roughly similar to the previous apparatus also, but differs in the aspect of the liquid admitting system having a plurality of liquid inlet pipes  55 A,  55 B,  55 C. Thus, it is possible to supply a plurality of liquids to the processing chamber  53  sequentially or at the same time. Therefore, depending on the type of substrate and treatment conditions, substances having different properties, such as different boiling points or additive agents such as a surface activator can be supplied to the chamber  53  at a given quantity or in a given sequence. 
     FIG. 18 is a still another embodiment of the pre-plating treatment apparatus. This apparatus is comprised primarily by an air-tightly closable vessel-like processing chamber  53  and a vacuum pipe  54 , a condensable gas inlet pipe  94 , a liquid inlet pipe  56 , a gas discharge pipe  57 , and a liquid discharge pipe  58  each connected to the chamber  53 . A pressure gage  7 , a pressure switch  8 , and a safety valve  36  are attached to the processing chamber  53 . A substrate stage  12  for placing the substrate W is disposed inside the chamber  53 , and the substrate stage  12  is provided with an ultrasonic vibrator  60 . A cooling medium header  70 , provided on the back side of the substrate stage  12 , is connected to a cooling medium chiller device  69  via cooling medium delivery pipes  67 ,  68 . The cooling medium header  70  is filled with a cooling medium supplied from the medium chiller device  69 , and controls the temperature of the substrate W through the substrate stage  12 . 
     Vacuum pipe  54  is connected to a vacuum pump through a shutoff valve  23  to reduce the chamber pressure to a desired low pressure. Condensable gas inlet pipe  94  admits a gas condensable at a certain pressure and a temperature into the chamber  53  through a shutoff valve  95 . Liquid inlet valve  55  is connected to a nozzle  55   a  facing the substrate stage  12  inside the chamber  53  through a shutoff valve  34  and a flowmeter  40  for introducing a certain desired quantity of liquid inside the chamber  53 . The liquid inlet pipe has two branches for admitting two types of liquid sequentially or at the same time. Gas inlet pipe  56  is connected to a gas source through a regulator  51  and a shutoff valve  24 , and gas discharge pipe  57  is connected externally through a shutoff valve  31 . Liquid discharge pipe  58  is connected to a storage tank (not shown) through a shutoff valve  35 . 
     A method of using the apparatus of the construction presented above, to provide a pre-plating process, will be explained next. First, the substrate W is placed on the substrate stage  12 , and the pressure inside the chamber  53  is reduced to an appropriately low level required by the processing parameters. Ethyl alcohol is then introduced into the chamber  53  through the gas inlet pipe  94 , so that the interior pressure will be 5500 Pa (41 Torr). When the interior temperature is 20° C., this alcohol is in a vapor state inside the chamber  53 . Therefore, alcohol vapor fills the chamber space including the cavities C formed on the substrate W. 
     Next, cooling medium at 5° C. is supplied to the cooling medium header  70  from the chiller  69  to cool the substrate W through the substrate stage  12 . As the substrate W is cooled, ethyl alcohol inside the cavity C is cooled and condensation of alcohol takes place. When the vapor is cooled gradually as in this case, the vapor can be in a supercooled state so that often the vapor does not condense (liquefy) even when the temperature reaches below the condensing temperature. Therefore, in this embodiment, the substrate W is vibrated with the ultrasonic vibrator  60  to force the alcohol vapor in the cavities C to be released from the super-cooled state to commence condensation. Ethyl alcohol vapor inside the cavity C begins to condense as the result of application of cooling and ultrasonic vibration, and attaches to the inside surface of the cavity C in the form of droplets or film. Thus, ethyl alcohol liquid is infiltrated inside the cavity C. 
     After applying this pre-plating treatment, plating solution and other liquid are introduced through the liquid inlet pipe  55  to immerse the substrate W, then, these liquids flow into the cavity C by the effect of surface tension forces between the liquid ethyl alcohol already existing inside the cavities C and the new liquids. To assure complete infiltration of those liquids into the cavities C, substrate W may be vibrated with the ultrasonic vibrator  60  or the pressure may be varied using the gas inlet pipe  56  and gas discharge pipe  57 . 
     It should be noted that the condensable gas should have small surface tension with respect to the material of substrate W and high affinity with the plating solution to assure complete liquid infiltration into the cavities C. Condensable gases of such nature includes water, propyl alcohol, acetone and ammonia. 
     After providing such a pre-plating treatment, the substrate W is taken out of the chamber  53 , and is transferred while still wet to plating chamber  1  shown in FIG. 28 to immerse in the plating solution to carry out plating. Because of the pre-plating treatment, the cavities C are filled reliably with the plating solution to produce a metal deposit of high quality inside the cavities C. 
     In the apparatus shown in FIG. 18, substrates W are handled one at a time, but a plurality of substrates W may be treated by having a cassette to hold many substrates. Supply and transfer of substrates can be facilitated by using such a cassette, and by filling the cassette with a liquid, drying of the substrates W can be prevented. 
     FIG. 19 shows another pre-plating treatment apparatus. This apparatus is similar to the one shown in FIG. 18 but differs in one respect of using a Peltier cooling element  66  for cooling the substrate W. The advantage is that coolant chiller device  69  and cooling medium delivery pipes  67 ,  68  are not required. 
     FIG. 20 shows an apparatus which combines the pre-plating apparatus using the Peltier cooling element  66  with the plating apparatus shown in FIG.  28 . In addition to the pre-plating apparatus shown in FIG. 19, this apparatus is provided with a pump  74  for supplying a plating solution to the chamber  53  through a supply pipe  75 , and a drain pipe  77  to drain off spent solution into a storage tank  76  through a valve  32  disposed at the bottom section of the chamber  53 . The combined apparatus is also provided with an anode  4  and a cathode  3  and an electrical power source  5 . 
     In using this apparatus, the plating solution is first drained through the drain pipe  77  to prepare the apparatus for pre-plating treatment in accordance with the method described above. When the cavities C are filled with some treatment liquid, the pre-plating treatment is stopped, and after breaking the vacuum as required, plating solution is supplied through the supply pipe  75  to perform plating. This combination apparatus is advantageous because there is no need to transfer the substrates such that plating process can be carried out following the pre-plating treatment without interruption, thereby saving a considerable number of operational steps. 
     FIG. 21 shows such an apparatus for providing continuous pre-plating and plating operations. The apparatus is comprised by a pre-treatment chamber  97 , a load-and-lock chamber  96  to enable to load and unload the substrates W without breaking the atmosphere in the pre-treatment chamber  97 , a plating chamber  98 , and a substrate supply chamber  100  to supply the substrates W. Load-and-lock chamber  96  is connected to other chambers by way of a gate  100 . The load-and-lock chamber  96  is connected to an exhaust path for evacuation, and is also provided with a substrate transport system such as a robotic hand. In this example, two plating chambers  98  are provided for one pre-treatment chamber  97 , in view of the length of time required for pre-treatment process. 
     In the present apparatus, substrates are transferred between the load-and-lock chamber  96  and pre-treatment chamber  97 , with the load-and-lock chamber  97  in an evacuated state by closing the gate  99  between the plating chamber  98  and the substrate supply chamber  100 . This arrangement permits substrate W to be loaded and unloaded without breaking the vacuum in the pre-treatment chamber  97  so that processing in the pre-treatment chamber  97  can be carried out without loss of time. The load-and-lock chamber may be provided with more than five entrances and also, a cleaning chamber may be provided as needed. 
     In the following, another embodiment of the plating apparatus will be explained with reference to the drawings. FIG. 22 shows an overall schematic view of the apparatus for filling the cavities W with metal plating. 
     The apparatus is comprised by a substrate fixation plate  110  for fixing the substrate W in place by suction on one surface of the substrate W, a cap section  120  for covering the opposite surface of the substrate W, piping  130  attached to the cap section  120 , a liquid switching device  140 , a pressurization control valve  150 , a liquid temperature switching device  160  provided within the piping  130 , and a substrate heating device  170  disposed near the substrate fixation plate  110 . The structure of these components will be explained below. 
     Substrate fixation plate  110  is a pressure resistant quartz plate to withstand pressures in excess of 10 kgf/cm 2 , and has a shallow depression section  111  on one surface for receiving the substrate W at a fixed position, and holes  112  are provided to open within the depression section  111  for vacuum chucking of the substrate W. 
     Cap section  120  is also resistant to pressures in excess of 10 kgf/cm 2  and has a depressed part opposite to the substrate W to form a liquid holding space  121  so that it may be used for electroplating operation by placing an anode  123  on the bottom surface of the liquid holding space  121 . For electroless plating, anode  123  is not required. Liquid supply piping  130  is connected to inlet and outlet ports  125 ,  127  formed in the cap section  120  to provide the liquid holding space  121  with liquids such as plating solution or cleaning solution. A packing  129  is provided around the periphery of the cap section  120  to seal the liquid holding space  121  by having the cap section  120  pressing down on the substrate W. 
     Liquid switching device  140  splits the pipe  130  into two branches provided with a respective switching valve  141  and  143 . For example, by opening the valve  141  and closing the valve  143 , the plating solution flows into the liquid holding space  121  through the valve  141 , and when the valve  141  is closed but the valve  143  is opened, a cleaning solution such as pure water for cleaning out the plating solution is supplied into the liquid holding space  121  through the pipe  130 . When the cleaning solution is being supplied to cap section  120 , valve  187  is opened so that the spent cleaning solution can be drained to the drain trough  189 . 
     Liquid temperature switching device  160  is provided with a low temperature chamber  63  and a high temperature chamber  161  for storing the plating solution, and each tank is connected to the cap section  120  at the discharge end through pipe  130  and respective valves  181 ,  183 . The pipe  130  is introduced to each of the chamber  161 ,  163  by way of a respective pump  165 ,  166  and one-way valve  167 ,  168 . The down stream side of the one way valves  167 ,  168  is merged into one pipe  130  and is connected to a pressurization control valve  150 . High temperature chamber  161  uses a heater  162  to keep the plating solution at a temperature in a range of 25˜40° C. for electroplating or in a range of 50˜90° C. for electroless plating, for example. Low temperature chamber  163  is for keeping the plating solution at room temperature, for example. The pipe  130  on the discharge port side of the cap section  120  is provided with a valve  185 . 
     Substrate heating device  170  may be a lamp heater, and is used to warm the substrate W from its back side through the transparent substrate fixation plate  110  made of quartz. 
     FIG. 23 is a flowchart showing operational procedures for the plating apparatus described above. Operational steps will be explained with reference to FIGS. 22 and 23. First, the back surface of the substrate w not having the cavities C is placed in the depression section  111  to face the fixation plate  110 , and is aspirated through the holes  112  to be vacuum chucked in the depression section  111 . The cap section  120  is placed to cover the opposite fabricated surface of the substrate W and pressed against the packing  129  by means of a clamp device (not shown) (step  1 ). The fabricated surface of the substrate W is thus exposed to the sealed liquid holding space  121 . In this condition, the valves  141 ,  143 ,  181 ,  183 ,  185  and  187  are all closed. 
     Next, the substrate W is heated from its back surface by means of the substrate heating device  170  to warm the substrate W to about 110° C. for example. 
     Next, heating is stopped (step  3 ), and the valves  141 ,  185 ,  183  are opened and the pump  166  is operated, so as to fill the liquid holding space  121  with the plating solution from the low temperature chamber  163  and, thereafter, circulate the low-temperature solution (step  4 ). The flow rate of the circulating liquid should be such as to replace residual air within the cap section  120  with the plating solution effectively, but not so large to cause flow resistance and foaming. The reason for choosing low temperature (room temperature) for the electroplating solution is to increase solubility of air in the solution (solubility of gas increases in general with low temperature and high pressure of a system). In the case of electroless plating, the substrate W is kept at a temperature insufficient for plating in this step. When the substrate W is heated by the heating device  170  in step  6  (to be described later), and if there is a danger of electroless plating of the substrate W, the plating solution is kept free of any catalyst in this stage. 
     The fabricated surface of the substrate W comes into contact with the plating solution by the steps taken so far, but some of the cavities C will still contain some residual air. The plating solution is at atmospheric pressure in this stage. 
     Next, pump  166  is operated while closing the valve  185  so that the plating solution inside the liquid holding space  121  will be pressurized to about 20 kgf/cm 2  by the pressurization control valve  150  (step  5 ). Pressurization causes the residual air inside the cavities C to be compressed to facilitate dissolution into the plating solution, thereby reducing the residual air. 
     While leaving the apparatus in this condition, the substrate W is heated by the heating device  170  to about 100° C. to expand the residual air inside the cavities C (step  6 ). Some of the residual air will be expelled outside of the cavities C at this stage. 
     In this embodiment, the lamp heater is used for the substrate heater device  170  so that only the back surface of the substrate W will be heated rapidly through the transparent quartz plate  110 , while the surface can be quickly cooled by turning off the lamp. Therefore, the present method is more advantageous, compared with heating the substrate W with the fixation plate  110  itself, because the heating/cooling needs of the substrate w can be met very quickly. Thus, this method is not only compatible with other treatments such as pressure changes, but avoids any danger of extending the heating to the solution inside the space  121 , which may cause undesirable plating. 
     Next, valve  185  is opened to quickly reduce the pressure inside the space  121  (step  7 ) from a pressure at 10 kgf/cm 2  to normal pressure, for example. This treatment causes the residual air, trapped in the cavities C at high temperature and pressure, to be rapidly expanded and expelled out and be replaced with the plating solution flowing in and filling the cavities C. 
     The above steps  2 ˜ 7  represent a plating solution infiltration process, but if one such treatment is not sufficient to fill in the cavities C with the plating solution, the process can be repeated by returning to step  3 . 
     Next, the operation moves from the solution infiltration stage to the plating stage. First, the substrate heating device  170  is turned off (step  8 ), and the pump  166  is stopped and valve  183  is closed. The other pump  165  is operated and valve  181  is opened, thereby circulating the high temperature plating solution inside the liquid holding space  121  (step  9 ). The pressure inside the liquid holding space  121  is kept at about atmospheric pressure. The flow rate of circulating liquid is controlled to provide a plating solution flow of a uniform speed over the substrate W and not to affect the flow resistance. The solution temperature is controlled by the heater  162 . 
     If the plating process is electroless plating, the fabricated surface of substrate W is plated with copper at this stage. If the process is electrolytic plating, an electric field is applied between the substrate W and the anode  123  to carry out plating of the substrate W. 
     Electroplating solution may be an aqueous solution containing CuSO 4 .5H 2 O and sulfuric acid, additives and chloride ions, while electroless plating solution may be, for example, an aqueous solution containing CuSO 4 .5H 2 O and ethylenediaminetetraacetic acid tetrasodium salt (EDTA.4Na), tetramethylammonium hydroxide (TMAH) and formalin. 
     After plating for a given period (step  10 ), pump  165  is stopped and valves  141 ,  181  are closed and valves  143  and  187  are opened to supply pure water to the space  121  to replace plating solution to clean the surface of the substrate W (step  11 ). Next, leaning solution is discharged from the space  121  and the substrate W is removed (step  12 ). 
     The substrate W thus plated according to the various embodied methods presented above is illustrated in FIG. 27B, which shows that the cavities C on the substrate surface (wiring grooves  303  and contact holes  301  in FIG. 27) are plated. Plated substrate W is further processed by chemical mechanical polishing (CMP) to leave plated metal inside the cavity C, and remove all other plated deposit on the surface, to thereby produce wiring  311  and plugs  313  shown in FIG.  27 C. In the illustration,  302  designates a SiO 2  insulation film,  306  a barrier layer and  321  a conductive layer. 
     The embodiments have been explained in detail above, but the present invention may be embodied in various modified form as explained below. 
     a) In the embodiments, residual air is first placed under heat and pressure, and by rapidly reducing the pressure, residual air is rapidly expelled out of the cavities, but in some cases, only heating may be employed without pressurization so that expansion due to heating may be sufficient to expel residual air out of the cavities. Conversely, the treatment process may be comprised by cyclic application of pressure/normal pressure steps without involving any heating step to drive off residual air from the cavities. 
     b) In the above embodiment, copper plating was used to plate a semiconductor wafer, but other metal plating may also be used. 
     c) In the above embodiments, a plating process is applied to semiconductor wafer as the substrate material, but it is obvious that a plating solution or other types of liquid may be infiltrated into similar cavities formed on other types of substrate materials. 
     d) In the above embodiments, all of one surface of the substrate W was made to contact a liquid substance, however, the present invention is applicable so long as the fine cavity portion formed on a substrate material is exposed to the liquid. It is permissible to expose both surfaces of a substrate W to the liquid substance. 
     e) In the above embodiments, a lamp heater was used as a substrate heating device, but other types of heating device or structures can be applied for the same purpose, and the location of the heating device is not limited to the back side of a substrate W. 
     FIG. 24 is a schematic overall view of a plating apparatus for a semiconductor wafer. The apparatus is comprised by a pressure vessel  210  containing a substrate W with the outer periphery fixed in place, a gas filling device  240 , a vacuum device  250 , an exhaust device and a liquid pressuring device  260 . Each of these components will be explained below. 
     The pressure vessel  210  is comprised by two roughly circular cover plates  211 ,  221 . These cover plates  211 ,  221  respectively have a spherical protrusion in the center region and outer annular peripheral sections  215 ,  225 . These cover plates  211 ,  221  form the pressure vessel  210  by joining them so that the outer annular peripheral sections  215 ,  225  are intimately mated to each other. 
     In the center of the cover plate  211  is a port  214  for connecting the gas filling device  240 , and in the center of the cover plate  221  is a port  224  for connecting the vacuum device  250 , both of which are described later in detail. There are also two ports  231 ,  233  provided in certain locations of the cover plate  211  for connecting liquid pressuring device  260 . 
     Clamping sections  211   a,    225   a  are provided in the inner edges of both of the peripheral sections  215 ,  225  for clamping a substrate W therebetween when the cover plates  211 ,  221  are joined together, thereby forming two sealed spaces  211   a,    221   a.  The peripheral sections  215 ,  225  are provided with a plurality of transfer routes  216 ,  223  for communicating between the two spaces  11   a,    21   a.  In a certain location of the peripheral section  225 , a port  226  communicated to the transfer routes  216 ,  223  is provided for connecting a pipe  291  for an air release valve  290 . A packing  235  is provided for sealing between the outer peripheral sections  215 ,  225 . 
     Gas filling device  240  comprises a gas supply source  241  such as gas cylinder, and piping  243  having a valve  245  and connected to the pressure vessel  210  through the port  214  of the cover plate  211 . Gas, in this case, is a type that can readily dissolve in the plating solution. 
     Vacuum device  250  also comprises a vacuum pump  251  connected to the port  224  of the cover plate  221  through piping  253  and a valve  255 . 
     Liquid pressuring device  260  is comprised by: a plating solution tank  261 ; piping  271  connecting the plating solution tank  261  to pressure vessel  210  at the port  231  through a pump  263 , a valve  265 , a regulator  267  a valve  269 ; and piping  275  connecting the plating solution tank  261  to the upstream side of the valve  269  of the piping  271  through a valve  273 ; and piping  281  connecting the plating solution tank  261  and a port  233  of the pressure vessel  210  through a valve  277  and a pump  279 . 
     Electroplating solution in the plating solution tank  261  may be an aqueous solution containing CuSO 4 .5H 2 O and sulfuric acid, additives and chloride ions, while electroless plating solution may be, for example, an aqueous solution containing CuSO 4 .5H 2 O and ethylenediaminetetraacetic acid tetrasodium salt (EDTA.4Na), tetramethylammonium hydroxide (TMAH) and formalin. 
     FIGS. 25,  26  are flowcharts for processes using the plating apparatus described above. Each process given in these flowcharts may be carried out separately but they can also be used continually. 
     First, the steps in FIG. 25 will be explained. A substrate W with cavities C is placed in one of the cover plates  211 ,  221 . By joining the cover plates  211 ,  221  together, the peripheral portion is clamped by the clamping sections  15   a,    25   a  of the peripheral sections  215 ,  225 , and two sealed spaces  211   a,    221   a  are formed on both sides of the substrates. The piping  243 ,  253 ,  271 ,  281 ,  291  are connected to respective ports of the pressure vessel  10  (step  1 ). Initially, the valves  245 ,  255 ,  265 ,  269 ,  273 ,  277 ,  290  are closed. 
     Next, the pressure vessel  210  is evacuated by opening the valve  255  and operating the pump  251  (step  2 ). This step removes residual air from the cavities C. 
     Next, a gas is introduced into the pressure vessel  210  while closing the valve  255  and opening valve  245  (step  3 ). In this step, the cavities C which are evacuated can be readily filled with the gas. If the cavities C are of sufficient size that can be filled without evacuating, this step may be omitted. 
     Next, the plating solution is introduced into the pressure vessel  210  while closing the valve  245 , opening the two valves  265 ,  269  and operating the pump  263  concurrently (step  4 ). In this case, air in the vessel  210  is removed by opening the valve  290 . This step wets the surface of the substrate W with the plating solution, but some residual gas may be left in the cavities C because of the surface tension of the gas. 
     After filling the interior of the pressure vessel  210  with the plating solution, valve  290  is closed, and the pump  263  is continued to be operated to pressurize the liquid in the vessel  210  to a high pressure (step  5 ). Pressurization is continued to reach a value set by the pressure regulator  267  (in this embodiment, about 30 kgf/cm 2 ). 
     The pressurization is maintained for a predetermined time (step  6 ). In this step, residual gas in the cavities C is readily dissolved in the plating solution, because of two reasons: first is that the gas is a type that can dissolve in the plating solution and the second is that the system is compressed to a high pressure. Thus, the cavities C are filled with plating solution. 
     If the process is an electroless plating, the surface of the substrate W is plated with copper by holding the plating solution at a certain temperature. If the process is an electroplating process, an electric field is applied between the substrate Wand an anode to carry out plating (step  7 ). In either case, because the cavities C are filled with the plating solution, copper plating deposit can reliably be formed inside the cavities C. 
     After closing the valves  265 ,  269 , pump  263  is stopped, valve  277  is opened and pump  279  is operated to discharge the plating solution (step  8 ), the substrate W can be taken out of the pressure vessel  210  (step  9 ). 
     Operating steps for another operation method for the plating apparatus is shown in FIG. 26 which will be explained next. Similar to the steps shown in FIG. 25, after placing the substrate W in the pressure vessel  210  (step  1 ), valve  255  is opened and pump  251  is operated to evacuate the vessel  210  (step  2 ). In this step, residual air in the cavities C is removed. 
     Next, by closing the valve  255  and opening the two valves  269 ,  273 , the plating solution is introduced into the pressure vessel  210  (step  3 ). In this step, the surface of the substrate W is wetted with the plating solution and the cavities C are filled with the plating solution because the vessel is evacuated. 
     Next, valve  273  is closed, the valve  265  is opened and the pump  263  is operated to pressurize the plating solution in the vessel  210  to a high pressure (step  4 ). Pressurization is continued to reach a value controlled by the pressure regulator  267  (in this embodiment, about 30 kgf/cm 2 ). 
     In this case, although the plating solution infiltrates the cavities C because the system is evacuated, if the evacuation is not complete, residual gas may remain in the cavities C. In such a case, by holding the pressure on the plating solution, residual air is highly compressed and dissolved in the plating solution so that the cavities C can be filled with the plating solution. 
     Here, using either an electroless or electroplating process, copper is plated on the surface of the substrate W (step  5 ). Because the cavities C are filled with the plating solution, copper is reliably plated inside the cavities C. 
     Next, by closing the valves,  265 ,  269  and stopping the pump  263 , and opening the valve  277  and operating the pump  279 , the plating solution is discharged from the vessel  210  (step  6 ) and the substrate W is taken out of the vessel  210  (step  7 ). 
     As explained above, although the steps shown in FIGS. 25,  26  may be carried out separately, they may be carried out continually as one series of processing operations. That is, after carrying out the steps  1 ˜ 5  shown in FIG. 25, the plating solution is removed without performing any plating (skip step  6  and do step  7 ), next, perform steps  2  to  7  shown in FIG.  26 . 
     By following such a sequence of steps, the cavities filled with the plating solution by the operations carried out to step  5  in FIG. 25 will retain the liquid in the cavities even when exposed to a vacuum environment because air bubbles are not contained in the cavities. On the other hand, if filling is inadequate that there are some bubbles remaining in the cavities C, such bubbles are removed when the substrate W is subjected to evacuation in step  2  in FIG.  26 . The overall result is that the cavities C can be filled with the plating solution in the steps to follow, and all the cavities C can thus be filled with the plating solution, thus reliably forming a plating deposit inside the cavities C. 
     It should be noted that although various embodiments are based on performing pre-plating treatment and plating processes in separate vessels or in the same vessel, such a choice may be made individually in any combination unless there are fundamental reasons for choosing one case over the other.