Patent Publication Number: US-2009229971-A1

Title: Thin-Film Deposition System

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a thin-film deposition system such as sputtering system. 
     2. Description of the Related Art 
     Deposition of a thin film onto a substrate is widely carried out in manufacturing semiconductor devices and other electronic parts. For example, a conductor film or insulator film is deposited on a substrate for forming a fine circuit thereon in manufacturing a semiconductor device such as memory or processor, an electronic element such as piezoelectric element or sensor head, or a display device such as liquid crystal display or plasma display. 
     In a thin-film deposition system depositing such a thin film onto a substrate, the substrate is often heated prior to or during the deposition. For example, prior to deposition a substrate is heated for degassing, i.e., release of adsorbed gasses, so that the gasses can not be released thermally from the substrate during the deposition. Heating of a substrate is also carried out during deposition in the case the deposition rate is enhanced when the substrate is at a hot temperature. 
     As a method of heating a substrate, a heat body with which the substrate is contacted is employed, utilizing heat transmission by the contact conduction. This method often employs a mechanical clamp clamping the substrate to the heat body for enhancing the contact thereof. As well, the method often employs boosting-gas introduction into the interface of the substrate and the heat body for enhancing the heat transmission therebetween. This is in consideration of that minute spaces formed on the interface are at a vacuum pressure. Moreover, the method often employs an electrostatic chuck (ESC) chucking the substrate onto the heat body by the electrostatic force for enhancing the contact thereof. 
     In the manufacture of semiconductor devices and electronic parts, levels of circuit integration and circuit fineness have been advancing much. In addition, lamination of thinned substrates and light exposure of the both surfaces of a substrate has been carried out widely. In a light-exposure steps, the focus accuracy improvement by reducing scars on the back side of a substrate is demanded more seriously than ever, as well as reduction of the number of particles on the right side of the substrate. In manufacturing a piezoelectric element or relay element, the process accuracy is demanded for the back side of a substrate as well as the right side. 
     SUMMARY OF THE INVENTION 
     This invention is to meet the above-described demands, and presents a thin-film deposition apparatus comprising a vacuum chamber and a partition separating the inside of the vacuum chamber into two areas. A substrate is capable of passing through an inside opening provided in the partition. The inside opening is closed by a valve. A thin film is deposited onto the substrate in the first area by a deposition unit. The substrate is heated by a heater in the second area prior to the deposition. The substrate is held by a holder while heated by the heater. The substrate is in point contact with the holder. A boosting-gas is introduced into the second area during the heating, thereby increasing pressure in the second area up to a viscous flow range. A pumping line evacuates the first area at a vacuum pressure all the time. The pumping line also evacuates the introduced boosting-gas from the second area to make the second area at a vacuum pressure when the valve is opened to make the second area communicate with the first area. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic front cross-sectional view of a thin-film deposition system as a preferred embodiment of the invention. 
         FIG. 2  is a schematic plane view of the heat body  31  shown in  FIG. 1 . 
         FIG. 3  is a schematic front cross-sectional view showing operation of the system in  FIG. 1 . 
         FIG. 4  is a schematic plane view of a thin-film deposition system of another preferred embodiment. 
         FIG. 5  is a schematic cross-sectional view on the X-X in  FIG. 4   
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of this invention will be described as follows. The system shown in  FIG. 1  comprises a vacuum chamber equipped with a couple of pumping lines  13 , 14 , and a deposition unit  2  for a thin-film deposition onto a substrate  9  in the vacuum chamber  1 . The system further comprises a heater  3  heating the substrate  9  prior to the deposition, and a holder holding the substrate  9  while heated by the heater  3 . The substrate  9  is in the point contact with the holder. 
     A partition  10  is provided, separating the inside of the vacuum chamber  1  into to two areas, which are the upper area  101  and the lower area  102 . The partition  10  comprises an opening through which the substrate  9  is capable of passing, and a valve  15 , hereinafter “partition valve”, closing the opening. The opening is hereinafter called “inside opening”. 
     A reflector  151  is provided on the undersurface of the partition  10 . The reflector  151  may be a reflecting plate fixed to the partition  10  or a reflecting film deposited on the partition  10 . The reflector  151  reflects radiant rays emitted from the heated substrate  9 , returning them to the substrate  9 . As a result, efficiency of the heating is enhanced. 
     The deposition unit  2  is installed in the upper wall of the vacuum chamber  1  so that a thin-film can be deposited onto the substrate placed in the upper area  101 . The structure and components of the deposition unit  2  is appropriately designed according to contents of the deposition, e.g., method, kind of the film, and the like. This embodiment employs the deposition unit  2  that carries out sputtering. 
     Concretely, the deposition unit  2  comprises a target  21  exposed to the upper area  101 , a magnet assembly  22  provided behind the target  21 , and a sputtering power source  23  to apply voltage for the sputtering to the target  21 . The target  21  is made of the same material as the thin film to be deposited. For example, in the case an aluminum film for wiring is deposited, the target  21  is made of aluminum or aluminum alloy. The magnet assembly  22  is to enable the magnetron sputtering. The magnet assembly  22  includes a center magnet  221  and a peripheral magnet  222  surrounding the center magnet  221 . A rotation mechanism to rotate the magnet assembly  22  relatively against the target  21  may be provided so that the erosion on the target  21  can be made uniform. 
     The system comprises a deposition-gas introduction line  4  introducing a gas for the deposition into the upper area  101 . The deposition-gas introduction line  4  comprises a pipe  41  communicating with the upper area  101  in the vacuum chamber  1 , and a valve  42  and a gas-flow controller (not shown) both provided on the pipe  41 . Because of the deposition by the sputtering, a gas for the sputtering discharge such as argon or nitrogen is used as the deposition gas. In the case the system carries out chemical vapor deposition (CVD), a means for introducing a reactive gas is provided as the deposition unit  2 . 
     The system comprises a deposition shield  5  lengthened downward from the upper wall of the vacuum chamber  1 . The upper end of the deposition shield  5  surrounds the target  15 . The deposition shield  5  is to prevent sputter-particles, which means particles released from the target  21  during the sputtering, from unnecessarily adhering to interior surfaces of the vacuum chamber  1 . The deposition shield  5  is essentially composed of a cylindrical portion  51  with a diameter a little wider than the target  21 , and an end portion  52  that is a ring-shaped-plate and fixed to the bottom end of the cylindrical portion  51 . The cylindrical portion  51  and the end porting  52  both are coaxial to the target  21 . The substrate  9  is circular. The inner diameter of the end portion  52  is a little larger than the diameter of the substrate  9 . 
     The heater  3  is installed within a heat body  31 . The heat body  31  is commonly used for the holder. The heat body  31  is disposed in the lower area  102  on standby. The heat body  31  is a stage on which the substrate  9  is placed to be heated. The heater  3  is the resistance heating type. The heat body  31  comprises protrusions  32  on the upper surface. The placed substrate  9  is in contact only with the protrusions  32 . 
     As shown in  FIG. 2 , the heat body  31  in this embodiment is circular in the plane view, and four protrusions  32  are provided. Each protrusion is located along the edge of the heat body  31  with equal distances, i.e., at every 90 degree. The substrate  9  is held only by the placement onto the heat body  31 . That is, this embodiment comprises neither means for electro-statically chucking the substrate  9  nor means for mechanically clamping the substrate  9 . 
     Four through holes are provided with equal distances in the heat body  31 . As shown in  FIG. 2 , a transfer pin  6  is provided in each through hole. Each transfer pin  6  is fixed uprightly on the bottom of the vacuum chamber  1 . There may be the case that only three transfer pins  6  are respectively provided in three through holes provided at every 120 degree. 
     As shown in  FIG. 1 , the system of this embodiment comprises a locator  33  locating the substrate  9  with an adjusted distance from the heating body  32 . In this embodiment, the locator  33  adjusts the distance by shifting the heat body  31 . The locator  33  is provided outside the vacuum chamber  1 . The heat body  31  is supported by a column  34 . An opening through which the column is inserted is provided in the bottom of the vacuum chamber  1 . The bottom end of the column  34  is located beneath the vacuum chamber  1 , and a bracket  35  is fixed thereto. 
     The locator  33  comprises a driven screw  331  fixed to the bracket  35 , a driving screw  332  engaging the driven screw  331 , and a motor  333  rotating the driving screw  332 . The driven screw  331  and the driving screw  332  compose a so called precision screw mechanism. The driving screw  332  is vertically lengthened and hung from the bottom of the vacuum chamber  1  by a fixing member  334 . The driving screw  332  is capable of rotation around the vertical axis and not capable of elevation. The motor  333 , specifically a servo motor, rotates the driving screw  332 , thereby shifting up and down the bracket  35 , the column  34  and the heat body  31  together. A bellows  36  is provided, surrounding the column  34 . The top end of the bellows  36  is air-tightly fixed to the bottom of the vacuum chamber  1 , surrounding the opening through which the column  34  is inserted. The bottom end of the bellows  36  is air-tightly fixed to the bracket  35 . The bellows  36  prevents leakage of vacuum through the opening through which the column  34  is inserted. The system comprises a carrier carrying the heated substrate  9  to a position in the upper area  101 , at which the substrate  9  has to be located during the thin-film deposition, hereinafter “deposition position”. The described locater  33  is commonly as the carrier The locater  33  carries the substrate  9  to the deposition position through the inside opening. 
     The system further comprises a boosting-gas introduction line  7  introducing a gas into the lower area  102  so that pressure can be increased to be in a viscous flow range. The boosting-gas introduction line  7  comprises a pipe  71  communicating with the lower area  102  in the vacuum chamber  1 , and a valve  72  and a gas-flow controller (not shown) both provided on the pipe  71 . The boosting gas is introduced for enhancing efficiency of the heating. Therefore, such a gas as helium, argon or nitrogen having high coefficient of thermal conductivity is used as the boosting gas. 
     An opening  11  for transferring the substrate  9 , hereinafter “transfer opening”, is provided in the side wall of the vacuum chamber  1 . The transfer opening  11  is closed by a valve  12 , hereinafter “transfer valve”. The transfer opening  11  and the transfer valve  12  are located as high as the lower area  102 . 
     The vacuum chamber  1  is equipped with a couple of pumping lines  13 , 14 . The first pumping line  13  is to evacuate the upper area  101  solely. The second pumping line  14  is to evacuate the lower area  102  solely. 
     As shown in  FIG. 1 , the vacuum chamber  1  has the cross-sectional configuration that the upper area  101  is wider than the lower area  102 , jutting to the side. The first pumping line  13  evacuates the upper area  101  through an evacuation hole  131  provided at the jutting portion of the vacuum chamber  1 . The first pumping line  13  comprises a main valve  142  adjacent to the evacuation hole  131 , a vacuum pump  143  evacuating the upper area  101  through the main valve  142 , and a pumping speed controller (not shown). 
     Operation of the system of this embodiment is described as follows, referring to  FIG. 3 . Though the system can be a cluster-tool type, the following description is on the assumption that it is a stand-alone type. 
     The upper area  101  is evacuated to be at a required vacuum pressure by the first pumping line  13  in advance. The lower area  102  is made at atmospheric pressure by the boosting-gas introduction line  7  or a ventilation-gas introduction line (not shown). The heat body  31  is located at a standby position in the lower area  102 . 
     In this state, the transfer valve  12  is opened. Then, the substrate  9  is transferred into the lower area  102  through the transfer opening  11 . As shown in FIGS.  3 ( 1 ), the substrate  9  is plated on the transfer pins  6 . This transfer operation is typically carried out by such an automatic mechanism as robot. Still, manual handling by an operator is not excluded in this invention. 
     After the transfer valve  12  is closed, the second pumping line  14  evacuates the lower area  102  to a required vacuum pressure. Next, the boosting-gas introduction line  7  is operated to increase pressure in the lower area  102  to the viscous flow range. Then, as shown in FIGS.  3 ( 2 ), the locator  33  shifts the heat body  31  up to a required upper position. In this elevation, the substrate  9  is passed from the transfer pins  6  to the heat body  31 , being placed thereon. The substrate  9  is in contact with the protrusions  32  only. 
     The heat body  31  is in a state of hot temperature because the heater  3  is operated in advance. Therefore, the placed substrate  9  is heated by the heat body  31 . In this heating, the conductive heat transmission is minor because the contact area of the substrate  9  onto the heat body  31  is small, and the heat transmission via the gas molecules in the space, which includes convection, is major. In addition, the substrate  9  is heated by radiant rays from the heat body  31   
     After the substrate  9  is heated up to a required temperature, the boosting-gas introduction line  7  stops the operation, and the second pumping line  14  evacuates the lower area  102  again down to a required vacuum pressure. Then, the partition valve  15  is opened, and the locator  33  shifts the heat body  31  up further. When the substrate  9  reaches the deposition position, the locator  33  stops shifting. As shown in FIGS.  3 ( 3 ), the deposition position is where the substrate  9  is inside the end portion  52 . 
     After the substrate  9  is located at the deposition position, the deposition-gas introduction line  4  is operated to introduce the deposition gas at a required flow rate confirming by a vacuum gauge (not shown) that the vacuum chamber  1  is kept at a required vacuum pressure, the sputtering power source  23  is operated to apply the voltage to the target  21 , thereby igniting the sputter discharge. As a result, sputter-particles released from the target  21 , which are normally in a state of atom, reach the substrate  9 , depositing a thin film. In this sputtering, because the heater  3  keeps the operation, the substrate  9  is continuously heated by the heater  3 . Still, the heating efficiency might decrease compared to the one during the heating, when pressure in the upper area  101  under the introduction of the deposition gas is lower than under the introduction of the boosting gas. 
     After the deposition is carried out for a required thickness of the film, the sputtering power source  23  is stopped, and the vacuum chamber  1  is evacuated again at a required vacuum pressure by the first and second pumping lines  13 , 14 . Afterward, the locator  33  shifts the heat body  31  down to the initial standby position. In this shift down, the substrate  9  is passed to the transfer pins  6  and placed thereon. 
     After the partition valve  15  is closed, the lower area  102  is ventilated to be at atmospheric pressure by the boosting-gas introduction line  7  or the ventilation gas introduction line (not shown). Then, the transfer valve  12  is opened, and the substrate  9  is transferred to the outside through the transfer opening  11 . 
     During heating the substrate  9 , the locator  33  locates the substrate  9  with an appropriately-adjusted distance from the surface of the heat body  31 . The above-described operation is the example where the distance is adjusted to zero, that is, the substrate  9  is contacted onto the heat body  31 . The locator  33  may dispose the heat body  31  at a lower position, making the substrate  9  placed on the transfer pins  6 . In this state, the substrate  9  is floated, i.e., apart from the heat body  31 . The distance is adjusted by the shift-down length of the heat body  31 , thereby adjusting the total efficiency of the heating. 
     In the above-described system, the heating can be highly efficient even through the point contact of the substrate  9  onto the heat body  31 , because pressure in the lower area  102  is made in the viscous flow range by the boosting gas introduction. The point that the substrate  9  is held only through the point contact brings the advantage of reducing the probability of the scar generation on the back surface of the substrate  9 . During the heating, the substrate  9  and the heat body  31  thermally expand. The back surface of the substrate  9  is slightly rubbed with the heat body  31 . If the contact area of the substrate  9  onto the heat body  31  is larger, the probability of the scar generation is higher. As in this embodiment, contrarily, if the substrate  9  is held only through the point contact, the probability of the scar generation is very low. 
     Because the point contact is for inhibiting the scar generation, “how much small the contact area is”, satisfying the term “point contact”, corresponds to “as far as the scar generation is sufficiently inhibited”. Specifically, the contact area of one point, i.e., one protrusion, is preferably in the range of 0.15 mm 2  to 100 mm 2 , more preferably 0.2 mm 2  to 7 mm 2 . If the contact area is larger than 100 mm 2 , the scar generation is not inhibited sufficiently. If the contact area of one point is smaller than 0.15 mm 2 , the substrate  9  is in a state of being placed on a sharp protrusion like the tip of a needle. Therefore, the scar generation would be rather promoted. The protrusion with the contact area of 0.15 mm 2  to 100 mm 2  does not bring these problems, and the contact area of 0.2 mm 2  to 7 mm 2  is completely free from these problems. 
     The protrusions  32  shown in  FIG. 2  are hemisphere shaped. This is one example for the point contact. Still, any protrusions having square contact areas or ellipse cross sections may be employed. The heat dissipation is a little in the structure that the substrate  9  is held through the point contact. This also contributes to enhancing the heating efficiency. 
     As described, the substrate  9  is held, only being placed on the protrusions  32 . That is, the substrate  9  is neither electro-statically chucked nor mechanically clamped onto the heat body  32 , but just placed thereon. This point also contributes to reduction of the scar generation on the back side of the substrate  9 . The electro-static chuck and the mechanical clamp are effective to enhancing the conductive heat transmission. However, scars are easily generated because the substrate  9  is strongly pressed onto the heat body  31 . This embodiment accomplishes the high heating efficiency neither by electro-statically chucking nor by mechanically clamping, but by increasing pressure of the atmosphere, that is, by enhancing the heat transmission via the gas molecules. Therefore, the scar generation on the back surface of the substrate  9  is inhibited furthermore. As understood from the above description, “the substrate is held through only the placement on the protrusions” means that it is pressed to the protrusions only by its own weight without any electrostatic chucking force and without any mechanical clamping force. Strictly, the frictional force acts at the interface between the substrate  9  and the protrusions  32 , and the gas molecules in the space press the substrate  9 . “The substrate is held through only the placement on the protrusions” does not exclude the actions of these forces. 
     The heat body  31  has the technical meaning of enlarging the contact area with the introduced boosting gas. In the case where the heater  3  itself has a large surface area, the heat body  31  is dispensable. The substrate  9  needs to hold a position in the vacuum chamber  1  during the heating. In this embodiment, the heat body  31  is commonly used as the holder for making the substrate  9  hold the position. Therefore, the structure in the vacuum chamber  1  is simplified, and the number of the components is reduced, cutting down the system cost thereby. 
     As described, the inside of the vacuum chamber  1  is separated into two areas  101 , 102  by the partition  15 , and the deposition is carried out in the upper area  101  separated from the lower area  102  where pressure is in the viscous flow range. This point brings the advantage of preventing the boosting gas from affecting the property of the thin-film deposition. Without the partition  10 , that is, in a structure the lower area  102  communicates with the upper area  101 , the boosting-gas introduced in the lower area  102  diffuses to the upper area  101 , resulting in that such contamination as incorporation of the gas molecules into the deposited film would take place. This embodiment with the partition  10  is free from this problem. As described, the locator  33  locates the substrate  9  with the adjusted distance from the surface of the heat body  31 . This adjustment enables fine control of the heating, enhancing accuracy of the heating. 
     The shift of the heat body  31  against the standing transfer pins  6  is for transferring the substrate  9  between the heat body  31  and the transfer pins  6 . The locator  33  shifting the heat body  31  is commonly used as the means for transferring. This point also brings the advantages of simplifying the chamber structure and reducing the system cost by cutting down the number of the components. For transferring the substrate  9  between the heat body  31  and the transfer pins  6 , the locator  33  may shift all of the transfer pins  6  together, making the heat body  31  standing. 
     The advantages of simplifying the chamber structure and reducing the system cost by cutting down the number of the components are further brought by the structure that the locator  33  is capable of shifting the substrate  9  to the upper area  101  and placing it at the deposition position. If not the locator  33  is as such, additionally the carrier is required for carrying the heated substrate  9  to the deposition position. 
     The system may be designed so as to cool the substrate  9  in the lower area  102  after the deposition. For example, the flow of a coolant gas is made in the lower area  102  when the processed substrate  9  is passed from the heat body  31  to the transfer pins  6 . The coolant gas cooled at a required cold temperature flows along the substrate  9 , thereby cooling it. 
     Next, the thin-film deposition system as the other embodiment of the invention, which is shown in  FIG. 4  and  FIG. 5 , will be described as follows. The system shown in  FIG. 4  and  FIG. 5  is one of the cluster tool type. Concretely, as shown in  FIG. 4 , a transfer chamber  81  is provided center, and process chambers  82  to  86  and a load-lock chambers  80  are connected air-tightly on the periphery of the transfer chamber  81 . A transfer valve  800  is provided at each boundary of each chamber  80 ,  82  to  86 . A thin-film deposition process is carried out in the process chamber  82 . The structure of the process chamber  82  may be the same as of the vacuum chamber  1  in the described embodiment. Therefore, detailed description is omitted. 
     A transfer robot  811  is provided in the transfer chamber  81 . The transfer robot  811  comprises a multi-joint type arm. The substrate  9  is held at the tip of the arm while transferred. The transfer robot  811  is preferably the one optimized for usage in vacuum environment, for example, without releasing dusts. Structures in the process chambers  83  to  86  are optimized according to the processes carried out therein. In the case a multilayer film is deposited, for example, the chambers  83  to  86  may be designed so as to carry out thin film depositions therein as well. One of the chambers  83  to  86  may be for cooling the substrate  9  after the deposition(s). As shown in  FIG. 4 , cassettes  88  in which unprocessed or processed substrates  9  are stored are provided at the atmospheric outside. Auto loaders  87  are provided for transferring the substrates  9  between the cassettes  87  and the load-lock chambers  80 . 
     In this system, any of the substrates  9  is transferred by any of the auto loaders  88  from any of the cassettes  87  to any of the load-lock chambers  80 . After the load-lock chamber  80  is evacuated at the same vacuum pressure as in the transfer chamber  81 , the transfer valve  800  is opened, and the substrate  9  is transferred from the load-lock chamber  80  to the process chamber  82  by the transfer robot  811 . 
     In this, the lower area in the process chamber  82  is evacuated at the same vacuum pressure as in the transfer chamber  81  by the second pumping line in advance. After the transfer valve  800  is closed, the pre-heating and the deposition onto the substrate  9  are carried out through the same operation as described. After the process in the process chamber  82  is finished, the substrate  9  is transferred out thereof. In this, the lower area is evacuated again at the same vacuum pressure as in the transfer chamber  81  by the second pumping line, not ventilating to atmospheric pressure. Afterward, the substrate  9  is transferred to the process chambers  83  to  86  in order, and the required processes are carried out in the process chamber  83  to  86  in order. After all the processes are finished, the substrate  9  is transferred to any of the load-lock chambers  80 . Then, the substrate  9  is returned to any of the cassettes  87  and stored therein by any of the auto loaders  88 . 
     In this embodiment, the lower area of the process chamber  82  is at a vacuum pressure even when the substrate  9  is transferred in and out. Therefore, the heat body disposed in the lower area of the process chamber  82  is under a vacuum pressure all the time, being not exposed to the atmosphere. In other words, the load-lock chamber  80  isolates the second area from the outside atmosphere. If the heat body in the state of a hot temperature is exposed to the atmosphere, the surface would be oxidized by oxygen or moisture in the atmosphere. The oxidized surface could be the source of contaminants, releasing oxide contaminants. The system of this embodiment is free from this problem because the heat body is under the vacuum pressure all the time. The phrase “all the time” in this description means “all the time while the system is regularly operated”. When operation of the system is suspended for maintenance, for example, the lower area is ventilated to be at atmospheric pressure, not at a vacuum pressure. In this situation, the heat body may be exposed to the atmosphere, because it is not at a hot temperature but at room temperature. 
     As a system comprising a load-lock chamber, i.e., other than the stand-alone type, an inline type is practical as well as the described cluster-tool type. The system of the invention can be modified to the inline type. An inline type system has a structure where a multiplicity of chambers are provided serially in a line. In any type other than the stand-alone type, though the load-lock chamber  80  is required between the process chamber  82  and the outside atmosphere, the process chamber  82  may communicate directly with the load-lock chamber  80  without another chamber such as the transfer chamber  81 . In other words, the load-lock chamber  80  may communicate either directly or indirectly with the process chamber  82 , as far as the vacuum environment is continuously maintained. 
     In the above-described embodiment, the first area was at the upper side, and the second area  102  was at the lower side. This may be inverted. Otherwise, the first and the second areas may be disposed side by side. This structure is practical in the case where the substrate posing upright is transferred into the chamber. Though the vacuum chamber  1  in the described embodiment was equipped with the couple of the pumping lines  13 , 14 , only one pumping line may be provided and commonly used. In this case, the first and the second areas are evacuated at optimum timing by the open-close operations of valves provided on evacuation pipes. One vacuum pump may be commonly used as a roughing pump in the other pumping line.