Patent Publication Number: US-2006016396-A1

Title: Apparatus for depositing a thin film on a substrate

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      The present application claims the benefit of priority of Korean Patent Application 2004-57760, filed Jul. 23, 2004, the disclosure of which is hereby incorporated herein by reference in its entirety.  
     FIELD OF THE INVENTION  
      The present invention relates to apparatus for manufacturing semiconductor devices and, more particularly, to an apparatus for depositing a thin film on a substrate.  
     BACKGROUND OF THE INVENTION  
      A semiconductor memory device may include a volatile memory device that loses data in its memory cells when electric power supplied to the device is interrupted or suspended, and a nonvolatile memory device that retains data in its memory cells even when the electric power supplied to the device is shut down. Recently, a phase change storage device having excellent characteristics has been suggested as an example of a new nonvolatile memory device.  
      The phase change storage device uses a phase change material as a storage medium for data. The phase change material has two stable states, namely, an amorphous state and a crystalline state. The phase change material has a higher resistivity when in the amorphous state than in the crystalline state. Logical information stored in a unit cell of the phase change storage device can be discriminated by sensing a difference in the amount of a current flowing through the phase change material.  
      A compound containing germanium Ge, tellurium Te, and antimony Sb (which may be referred to as GST or Ge—Te—Sb) is an example of a widely known phase change material. The GST compound is deposited on a wafer by means of a sputtering device. However, upon depositing the phase change material on the wafer using a conventional sputtering device, the compound may not be deposited on the wafer with sufficiently uniform thickness or concentrations of the germanium Ge, the tellurium Te, and the antimony Sb across the regions of the wafer.  
     SUMMARY OF THE INVENTION  
      The present invention is directed to a deposition apparatus capable of depositing a layer or film of a phase change material such as a compound of germanium, tellurium, and antimony on and across an entire prescribed surface or region of a wafer such that the layer is uniform in thickness and composition.  
      According to embodiments of the present invention, an apparatus for depositing a thin film on a substrate includes a housing, a substrate support portion, a securing member, a heater, a target member and a plasma generator. The housing defines a process chamber. The substrate support portion is disposed in the process chamber to support the substrate. The securing member is adapted to non-electrically secure the substrate to the substrate support portion during performance of a process. The heater is provided to maintain the substrate supported by the substrate support portion at a process temperature. The target member faces the substrate support portion and includes materials to be deposited on the substrate. The plasma generator is adapted to excite a process gas supplied into the process chamber into a plasma state.  
      The apparatus may further include a magnet member disposed above the target member and including a plurality of magnets to increase a density of a plasma in the vicinity of the target member. An electrode portion can be provided in the substrate support portion to draw ionized particles separated from the target member to the substrate supported by the substrate support portion.  
      According to some embodiments, the substrate support portion includes a support plate that includes: an upper plate having the electrode portion disposed therein; and a lower plate disposed below the upper plate and having the heater disposed therein. The upper plate can be made of aluminum nitride. The upper plate may include a first plate having the electrode portion disposed therein and a second plate disposed on the first plate and formed of aluminum nitride. In some embodiments, the support plate includes a sheet portion disposed between the upper plate and the lower plate and being formed of carbon and/or copper. According to some embodiments, a groove is formed in an upper surface of the upper plate, and a gas supply path is provided within the support plate to supply gas to the groove. The electrode portion may include only a single electrode or, alternatively, a plurality of electrodes.  
      According to some embodiments, the apparatus is adapted to deposit a phase change material layer on the substrate. The phase change material layer may include a compound layer containing germanium, tellurium, and antimony.  
      According to some embodiments, the securing member is adapted to mechanically secure the substrate to the substrate support portion during performance of the process. In some embodiments, the securing member includes a cover portion, the cover portion being positioned at an upper edge portion of the substrate supported by the substrate support portion during the performance of the process.  
      According to some embodiments, the substrate support portion includes a support plate and a moving portion adapted to raise and lower the support plate, the process chamber housing includes a processing room housing defining a processing room for performance of a deposition process, a through hole is formed in the processing room housing to receive the support plate therethrough, and the securing member is disposed on a lower surface of the processing room housing to engage a side portion of the substrate mounted on the support plate when the support plate is moved into the processing room. The securing member may include a cover portion adapted to engage an upper edge surface of the substrate mounted on the support plate during performance of the process. In some embodiments, a tip end of the cover portion is tapered in a direction toward a center portion of the substrate. The securing member may be formed in a ring shape.  
      According to further embodiments of the present invention, an apparatus for depositing a phase change material on a substrate includes a process chamber housing defining a process chamber and a substrate support portion disposed in the process chamber to support the substrate. The substrate support portion is adapted to be raised and lowered in the process chamber and includes lower and upper plates. The upper plate is formed of aluminum nitride. A heater is disposed in the lower plate. An electrode is disposed in the upper plate. The apparatus further includes a securing member adapted to non-electrically secure the substrate to the substrate support portion. A target member faces the substrate support portion and includes materials to be deposited on the substrate. A plasma generator is provided which is adapted to excite a process gas supplied into the process chamber into a plasma state. A magnet member is disposed above a target member and includes a plurality of magnets to increase a density of a plasma in the vicinity of the target member.  
      According to some embodiments, the process chamber housing includes a processing room housing defining a processing room for performing a deposition process. A through hole is formed in a bottom surface of the processing room housing. The substrate support portion further includes a support plate and a moving portion adapted to raise and lower the support plate in the process chamber. The securing member is located in a lower portion of the processing room and is adapted to surround at least a portion of a circumference of the substrate mounted on the support plate when the support plate is inserted into the through hole. In some embodiments, the securing member includes a cover portion positioned at an upper edge portion of the substrate mounted on the support plate during performance of the process. A tip end of the cover portion may be tapered in a direction toward a center portion of the substrate.  
      The electrode portion may include only a single electrode or, alternatively, a plurality of electrodes.  
      Further features, advantages and details of the present invention will be appreciated by those of ordinary skill in the art from a reading of the figures and the detailed description of the preferred embodiments that follow, such description being merely illustrative of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain principles of the present invention. In the drawings:  
       FIG. 1  is a schematic cross-sectional view showing a deposition apparatus according to embodiments of the present invention;  
       FIG. 2  is a bottom view of a magnet member of the apparatus of  FIG. 1 ;  
       FIG. 3  is a schematic side view showing problems occurring when a deposition apparatus of the prior art is used;  
       FIG. 4  is a schematic side view showing a line of magnetic force formed when a magnet member according to the present invention is employed in the deposition apparatus of  FIG. 1 ;  
       FIG. 5  is a schematic side view showing paths of movement of particles from a target of the deposition apparatus of  FIG. 1 ;  
       FIG. 6  is a schematic side view showing a construction of a substrate support portion of the deposition apparatus of  FIG. 1 ;  
       FIG. 7  is a schematic side view showing an alternate construction of a substrate support portion of the deposition apparatus of  FIG. 1 ;  
       FIG. 8  is a schematic cross-sectional view of a wafer mounted on a substrate support portion of the deposition apparatus of  FIG. 1  and secured thereto by a securing member;  
       FIG. 9  is an enlarged cross-sectional view showing the securing member of  FIG. 8  in accordance with embodiments of the present invention;  
       FIG. 10  is an enlarged cross-sectional view showing the securing member of  FIG. 8  in accordance with further embodiments of the present invention;  
       FIG. 11  is a schematic side view showing an exemplary construction and materials of a support plate in accordance with embodiments of the present invention; and  
       FIG. 12  is a schematic side view showing a further exemplary construction and materials of a support plate in accordance with further embodiments of the present invention. 
    
    
     Detailed Description of Embodiments of the Invention  
      The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. In the drawings, the relative sizes of regions or features may be exaggerated for clarity. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.  
      It will be understood that when an element is referred to as being “coupled” or “connected” to another element, it can be directly coupled or connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly coupled” or “directly connected” to another element, there are no intervening elements present. Like numbers refer to like elements throughout. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items.  
      In addition, spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. Thus, the exemplary term “under” can encompass both an orientation of over and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.  
      Well-known functions or constructions may not be described in detail for brevity and/or clarity.  
      The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.  
      Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.  
      With reference to  FIG. 1 , a deposition apparatus  1  according to embodiments of the present invention is shown therein. The deposition apparatus  1  can be used to deposit and form a predetermined thin layer or film on a wafer W via a sputtering operation. The apparatus  1  may be used to form a thin film of a phase change material such as a compound layer containing germanium (Ge), tellurium (Te), and antimony (Sb) on the wafer W. The deposition apparatus  1  may also be used to deposit materials other than phase change materials on the wafer W as well.  
       FIG. 1  is a schematic cross-sectional view of the apparatus  1 . The deposition apparatus  1  includes a process chamber housing  100  for receiving the wafer W and providing a process chamber or space for performance of the deposition process. The process chamber housing  100  includes a processing room housing  120  defining a subchamber or processing room  120 A for performing the process and a housing  140  surrounding the housing  120  and the processing room  120 A. The processing room  120 A is located at an upper portion within the housing  140 .  
      A through hole  122  is formed in a bottom wall of the housing  120 . A support plate  202  of a substrate support portion or assembly  200  is movable through the through hole  122  so that the wafer W when mounted on top of the support plate  202  can be positioned in the processing room  120 A. The housing  140  defines a lower subchamber or chamber  140 A under the processing room  120 A. An entrance port  142  is formed in a sidewall of the housing  140 . The entrance port  142  functions as a passage for moving the wafer W into and out of the process chamber  100 .  
      A gas supply tube  160  is connected to a sidewall of the housing  120  and a process gas is introduced into the processing room  120 A through the gas supply tube  160 . A valve  162  is provided in the gas supply tube  160 . The valve  162  is operable to open/close an internal passage and adjust the amount of gas supplied. One or more gas supply tubes  160  may be provided. A discharge tube (not shown) is connected to a lower wall or a sidewall of the housing  120  and is connected with a pump. The pump is used to maintain a pressure suitable for a process in the processing room  120 A. Process by-products occurring in the processing room  120 A are discharged or exhausted from the processing room  120 A through the discharge tube. According to some embodiments, while the process is being performing, a relatively high pressure of from 13 mTorr to 75 mTorr is maintained in the processing room  120 A. According to some embodiments, a pressure of from 40 mTorr to 75 mTorr is maintained in the processing room  120 A.  
      A target  300  is located at an upper portion within the processing room  120 A and is made of materials to be deposited on the wafer W. The substrate support portion  200  is located at a lower portion within the process chamber housing  100 . The wafer W is mounted on the substrate support portion  200 . The target  300  has a size and a shape similar to the size and shape of the wafer W. The target  300  is positioned to face the wafer W mounted on the substrate support portion  200 . The substrate support portion  200  is adapted to move vertically up and down. The substrate support portion  200  is also adapted to rotate. Prior to performing the process, an upper surface of the substrate support portion  200  is positioned at a waiting position under the processing room  120 A in the lower chamber  140 A defined by the housing  140 . After the wafer W is mounted on a support plate  202 , the substrate support portion  200  ascends until an upper surface of the substrate support portion  200  is moved to a process position in the processing room  120 A. The wafer W can be loaded/unloaded to and from the substrate support portion  200  by a transfer robot (not shown) through the entrance port  142 , respectively, when the substrate support portion  200  is positioned in the waiting position.  
      According to some embodiments, the target  300  is composed of a compound containing Ge, Te, and Sb. An energy source  500  is connected to the target  300  and excites the process gas supplied into the processing room  120 A into a plasma state. The energy source  500  includes a first power supply section  520  for applying a high frequency alternating current power and a second power supply section  540  for applying a direct current (DC) power. A matching device  560  is provided between the target  300  and the energy source  500 . According to some embodiments, the first power supply section  540  supplies a high frequency power of about 60 MHz and about 5 kW, and the second power supply section  540  supplies a DC power of about 6 kW.  
      A magnet member  400  is provided above the target  300 . The magnet member  400  increases the density of a plasma in the vicinity of the target  300 .  FIG. 2  is a bottom view of the magnet member  400 . With reference to  FIG. 2 , the magnet member  400  has a plate  420  and a plurality of magnets  440 . The magnets  440  protrude downwardly from a lower surface of the plate  420 , and adjacent magnets  440  can be arranged to have different polarities. The magnets  440  may be uniformly spaced apart. According to one embodiment of the present invention, the magnets  440  are arranged to form a plurality of rows and columns under the plate  420 . The plate  420  may be rotated about a center axis during performance of the process.  
      With reference to  FIG. 3 , in a device of the prior art, the magnet member includes a first magnet and a second magnet. The first magnet has a first polarity and is arranged at the center of the magnet member. The second magnet has a second polarity, and is arranged at an edge of the magnet member in a ring shape. During the performance of a process, a low pressure of from 1 mTorr to 2 mTorr is maintained within the processing room. When the deposition apparatus of the aforementioned construction is used, a line of magnetic force extends a long distance to an adjacent area of the wafer W. Particles separated from the target  300  travel to the wafer W along a slope at a predetermined angle under the influence of the magnetic force line and therefore have a long mean free path to the adjacent surface of the wafer. Accordingly, as shown in  FIG. 3 , a contact hole may be filled asymmetrically, with a film at a center portion ‘a’ and an edge portion ‘b’ of the wafer W.  
      By contrast, using the deposition apparatus  1  or other deposition apparatus in accordance with embodiments of the present invention and as shown in  FIG. 4 , a strong magnetic field is formed at an area in the vicinity of the target  300 , while little or no magnetic field is formed in the vicinity of or proximate the wafer W. Due to the arrangement of the aforementioned magnets  440  and the relatively high pressure in the processing room  120 A as discussed above, the ionization ratio of particles separated from the target  300  is high. As shown in  FIG. 5 , each of the particles has a short mean path and the particles travel generally perpendicularly to the surface of the wafer W. For this reason, the particles are deposited in the contact hole symmetrically about the center portion ‘a’ and the edge portions ‘b’ of the wafer W. Furthermore, the target  300  is uniformly eroded or depleted due to the configuration of the magnets and rotation of the target  300 .  
       FIG. 6  is a schematic view showing the construction of the substrate support portion  200  shown in  FIG. 1 . Referring to  FIG. 6 , a rotating shaft  204  is connected to a rear side of the support plate  202 . A driving unit  206  is connected to the rotating shaft  204  and rotates and vertically moves the rotating shaft  204 . The rotating shaft  204  may be vertically moved by a hydraulic/pneumatic cylinder or by a mechanism having a pump for precise position control, for example.  
      A heater  700  is installed within the support plate  202 . The heater  700  provides heat to the wafer W mounted on the substrate support portion  200  so that the wafer W maintains a prescribed process temperature during performance of the process. The heater  700  may include a hot plate or a coil-shaped hot wire.  
      An electrode portion or assembly  600  draws or directs particles separated from the target  300  to the wafer W in a direction perpendicular to the wafer W. According to embodiments of the present invention, for example, a power supply source can supply a high frequency power of about 13.56 MHz and about 1 kW. As shown in  FIG. 6 , the electrode portion  600  includes a first electrode  620  and a second electrode  640 . The shapes and positions of the first and second electrodes  620  and  640  can vary according to process conditions.  
      Alternatively, the electrode portion  600  may have a single electrode  660  as shown in  FIG. 7 . As a further alternative, the electrode portion  600  can have three or more electrodes.  
      A securing member  900  ( FIG. 8 ) is provided to secure the wafer W to prevent the wafer W from being separated from the substrate support portion  200  and, more particularly, from the support plate  202 . Electrically securing the wafer W to the substrate support portion  200  may have advantages and disadvantages as follows. An energy source has a first power supply source and a second power supply source composed of one circuit. The first power supply source applies a radio frequency (RF) power to the electrode portion  600  in order to draw the ionized particles separated from the target to the wafer. The second power supply source applies a DC power to the electrode portion  600  so that the wafer W is stably held to the substrate support portion  200 . When the wafer W is electrically held, a uniform temperature is maintained throughout the wafer W. However, a thin film is not deposited in uniform thickness on all regions of the wafer W. Moreover, when the deposited material is a phase change material composed of a compound containing Ge, Te, and Sb, the composition ratio of the deposited material varies as between different regions of the wafer W.  
      Non-uniformities in the deposition thickness and the composition ratio occur due to a non-uniform field formed on an upper portion of the wafer W. A field is formed on an upper region of the wafer W by the energy source  500  applied to the target  300 . The field formed on the aforementioned region by the energy source  500  resonates with the field formed by the energy applied to the electrode portion  600  and thereby causes the non-uniformity. The non-uniform field is caused by the DC voltage applied to the electrode portion  600  to hold the wafer W electrically. According to experimental results, a thick layer having a large amount of Ge forms on a region of the wafer W in the vicinity of the second electrode  640  when a positive voltage is applied thereto. In contrast, a thin film having small amounts of Ge and Sb forms on a region of the wafer W in the vicinity of the first electrode  620  when a negative voltage is applied thereto.  
      In accordance with the embodiments of the present invention, the securing member  900  fixes the wafer W in a non-electric manner. Preferably, the securing member  900  mechanically holds or secures the wafer W using a mechanical structure.  FIG. 8  is a view showing the wafer W secured or coupled to the substrate support portion  200  by the securing member  900 . The securing member  900  is fixed and installed on a lower surface of the housing  120  in a lower region of the processing room  120 A. The securing member  900  includes a cover member or portion  920  and a sidewall portion  940 . When the support plate  202  is set at the process position, the cover portion  920  is positioned at an edge of the wafer W mounted on the support plate  202 . Referring to  FIG. 9 , the sidewall portion  940  extends downwards from a tip end  922  of the cover portion  920 . The sidewall portion  940  is arranged to be adjacent to the side portion of the wafer W. The cover portion  920  is arranged to engage and push or positively locate an upper edge surface of the wafer W mounted on the support plate  202  into the process position. The securing member  900  can have a ring shape. Alternatively, a plurality of the securing members  900  can be arranged to wrap the wafer W at predetermined spaced apart locations. As shown in  FIG. 9 , the end  922  of the cover portion  920  is shaped such that the upper surface thereof extends parallel to the top surface of the wafer W. Alternatively, and as shown in  FIG. 10 , in order to improve deposition uniformity at the edge of the wafer W, a tip end  922 ′ of the cover portion  920  can be shaped such that it tapers inwardly (i.e., in the direction of the center of the wafer W) with the top surface of the tip end  922 ′ sloping downwardly. Although the aforementioned shapes and structures of the securing member  900  may be preferred for mechanically supporting the wafer W, the invention is not limited thereto. It will be apparent to those skilled in the art that the securing member  900  may have various shapes and structures.  
      When the wafer W is mechanically supported and the upper plate upon which the wafer W is mounted is formed of stainless steel (SUS), variation in the temperature of the wafer W will increase in accordance with the area of wafer W. The deviation in the temperature of the wafer W may have a significant effect on the uniformity of the deposition thickness. In accordance with embodiments of the invention, the substrate support portion  200  is provided to mechanically support the wafer W to provide a uniform temperature distribution throughout the wafer W.  
      With reference to  FIG. 6 , the support plate  202  includes an upper plate  220  and a lower plate  240 . The upper plate  220  includes a first plate  224  and a second plate  222 . The electrode portion  600  is located within the first plate  224 . The second plate  222  is disposed on the first plate  224  and is formed in a disc shape having a size similar to that of the wafer W.  
      A groove  222   a  ( FIG. 6 ) is formed in the upper surface of the second plate  222 . A gas supply path or line  282  ( FIG. 1 ) extends through the support plate  202  and serves as a gas flow path through which gas is supplied to the groove  222   a . The gas supply line  282  is connected to an external gas supply tube. An inert gas such as argon is used at the gas. The gas introduced into the groove  222   a  through the gas supply line  282  causes the heat generated by the heater  700  to be uniformly transferred to the wafer W.  
      With reference to  FIG. 11 , according to some embodiments of the present invention, a support plate  220  may be constructed and formed of materials as follows. The second plate  222  may be formed of materials having good or excellent thermal conduction. For example, the second plate  222  may be formed from aluminum nitride (AlN) having excellent thermal conduction. Although the first plate  224  can be made of SUS or AlN, it is preferably made of the same material (e.g., AlN) as the second plate  222  to improve temperature uniformity across the entirety of the wafer W.  
      Alternatively and as shown in  FIG. 12 , the first and second plates  224  and  222  can be integrally formed of AlN to form the upper plate  220 .  
      The aforementioned heater  700  is installed within the lower plate  240 . The lower plate  240  may be made of SUS. A sheet portion  260  is inserted between the upper plate  220  and the lower plate  240 . The sheet portion  260  may be made of carbon or copper to provide effective transfer of heat from the lower plate  240  to the upper plate  220 .  
      According to experimental results, in the case where the upper plate  220  was made of the SUS and the temperature of the wafer W was maintained at 200° C. to 300° C., the temperature deviation across the wafer W was about 3% to 4%.  
      However, in accordance with an embodiment of the present invention, upon mechanically fixing the wafer W to support portion  200 , the temperature deviation across the wafer W was reduced to about 1% to 2% under the same conditions. In this embodiment, because the wafer W was mechanically secured to the substrate support portion  200 , the formation of a non-uniform electric field at an upper portion of the wafer W was avoided. The second plate  222  contacting with the wafer W was made of AlN, thereby reducing the temperature deviation between different regions of the wafer W. By adhering a copper or carbon sheet  260  on the lower plate  240  in which the heater  700  was installed, the heat from the heater  700  was substantially uniformly transferred to the wafer W.  
      In accordance with embodiments of the present invention, a substrate support portion is adapted to mechanically hold a wafer W to a deposition apparatus of the present invention to provide a more uniform electrical field on the wafer W as compared with the conventional method of electrically securing the wafer. Temperature uniformity across the entire width of the wafer W can be improved by forming the part of the substrate support portion contacting the wafer W of AlN having good thermal conduction characteristics. Therefore, when depositing a phase change material layer containing Ge, Te, and Sb on the wafer, a deposition having a uniform thickness and a uniform composition ratio of respective materials can be formed across the entirety of the wafer.  
      The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the invention.