Abstract:
A wafer treatment apparatus includes a wafer heating device having a wafer-load region at an upper portion, a shower head opposing the wafer-load region for ejecting/directing a source gas toward the wafer surface, and a reflecting apparatus positioned between the shower head and the heating device for reflecting thermal energy radiated from the heating device back toward the wafer-load region. The reflecting apparatus includes a reflector positioned above and opposing the wafer-load region, and a supporter for supporting the reflector. The reflector may have a flattened reflecting surface facing toward the wafer-load region, or may be a semi-spherical type reflector having a concave mirror facing toward the wafer-load region. The reflector can be controlled to move vertically relative to the wafer.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an apparatus for treating semiconductor wafers, and more particularly, the present invention relates to an apparatus for treating a wafer in which a thermal reflector is provided above a wafer support.  
           [0003]    2. Description of the Related Art  
           [0004]    Thin films comprised of various types of materials are formed on wafers during the sequential processes for manufacturing a semiconductor device. To ensure high yields and operationally superior devices, the thin film materials should exhibit good step coverage, that is, a uniform thickness over every region, regardless of the surface pattern of an underlying layer.  
           [0005]    Uniform step coverage requires that all process conditions employed in the formation of thin films be uniformly maintained, from source gas supply to wafer temperature. Moreover, the structure of the thin film forming apparatus itself may affect the uniformity of the thin film.  
           [0006]    [0006]FIG. 1 is a cross sectional schematic view of a conventional thin film forming apparatus. The conventional apparatus includes a chamber  10  for housing the wafers to isolate them from the outside environment during a process of forming thin films. The apparatus also includes a susceptor  16  formed on the bottom surface of the chamber  10 , and a shower head  18 . The susceptor  16  supports the wafer  24  along a wafer-load region  20 , and a heater  22  is provided under the wafer-load region  20 . The heater  22  maintains the wafer  24  at a preferred temperature conducive to the formation of a thin film on the wafer  24 . In addition, the heater  22  may be used to anneal the wafer  24  after forming the thin film thereon.  
           [0007]    The shower head  18  directs the source gas, which is needed to form the thin film material, toward the wafer  24  on the wafer load region  20 . Any residual gases are discharged through an outlet  28  formed at the bottom of the chamber  10  by a pump  26  provided outside of the chamber  10 . Inlet/outlet region  30  allows the wafer  24  to be transported into and out of the chamber  10 .  
           [0008]    With the conventional thin film forming apparatus, by-products are created during the process and these by-products adhere to the chamber wall and aggregate to become particles  32 . In addition, if a multi-chamber apparatus is used, when the wafer is transferred within the confines of the multi-chamber apparatus, the by-products or the thin film materials which exist near the wafer-load region of the susceptor may also be transferred.  
           [0009]    Accordingly, with the conventional film forming apparatus, particles  32  adhered to the chamber wall may break apart and be deposited on the wafer, or by-products created by transfer of the wafer may be adhered to the wafer, resulting in undesirable impurities being included on the thin film deposited on the wafer. This degrades the thin film characteristics, and ultimately degrades the semiconductor device function when the inferior thin film is applied on the semiconductor device.  
           [0010]    Another problem with the conventional apparatus concerns the heating/annealing of the wafer. After the thin film material is formed on the wafer, an annealing step to stabilize the thin film is performed at a temperature higher than that used for forming the thin film. The wafer temperature is a function of the thermal energy supplied from a heater block (e.g.,  22  in FIG. 1), but the thermal energy distribution is not uniform when the heater block is initially heating up. Accordingly, the temperature distribution along the wafer is not uniform. When the temperature of the wafer is increased by using the heater, the temperature only stabilizes after oscillating above and below the preferred temperature. Thus it takes time to obtain a uniform temperature distribution along a wafer during the annealing process, which reduces the throughput.  
         SUMMARY OF THE INVENTION  
         [0011]    Accordingly, it is an object of the present invention to provide an apparatus for surface treatment of a wafer which prevents impure particles from being deposited onto the wafer, especially during the formation of a thin film.  
           [0012]    It is another object of the present invention to quickly obtain a uniform wafer-temperature distribution during an annealing process after the formation of a thin film, thereby improving the performance and increasing the productivity of semiconductor devices.  
           [0013]    To achieve these and other objects, the present invention provides a wafer heating device having a wafer-load region at an upper portion, a shower head opposing the wafer-load region for ejecting/directing a source gas toward the wafer surface, and a reflecting apparatus positioned between the shower head and the heating device for reflecting thermal energy radiated from the heating device back toward the wafer-load region. There is also provided a pumping device for controlling the air pressure in the chamber and for discharging by-products formed within the chamber.  
           [0014]    The reflecting apparatus includes a reflector positioned above and opposing the wafer-load region, and a supporter for supporting the reflector. The reflector may have a flattened reflecting surface facing toward the wafer-load region, or a semi-spherical type reflector having a concave mirror facing toward the wafer-load region.  
           [0015]    The reflector can be controlled to move upward and downward in response to the thin film formation process and the annealing process. The movable reflector is connected via the supporter to a driver outside the chamber. The supporter includes a first cylinder connected to the driver and a second cylinder connected to the driver through the first cylinder at one end, and connected to the reflector at the other end. The supporter is symmetrically arranged around the shower head or the heating device.  
           [0016]    The thin film forming apparatus according to the present invention is provided therein with a reflecting apparatus above the susceptor, thereby preventing particles from being deposited on the wafer during the formation of the thin film. In addition, even without applying additional power to the heater during the thin film forming process to the annealing process, the wafer temperature can be increased and stabilized in preparation for the annealing, and is uniformly maintained. Furthermore, even if additional temperature controls are necessary, the reflector shortens the time required to reached a stabilized increased temperature, thereby increasing the productivity of the semiconductor device manufacturing process. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The objects and advantages of the present invention will become better understood form the following detailed description that follows, with reference to the accompanying drawings, in which:  
         [0018]    [0018]FIG. 1 is a cross sectional schematic view of a conventional thin film forming apparatus;  
         [0019]    [0019]FIG. 2 is a cross sectional schematic view of a thin film forming apparatus according to a first embodiment of the present invention;  
         [0020]    [0020]FIGS. 3 and 4 are plan views of a reflecting apparatus provided in the thin film forming apparatus according to a first embodiment of the present invention;  
         [0021]    [0021]FIG. 5 is a perspective view of a reflecting apparatus having a semi-spherical type of reflector; and  
         [0022]    [0022]FIG. 6 is a cross sectional schematic view of a thin film forming apparatus according to a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    The preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. Throughout the drawings, like reference numerals and nomenclature designate like or equivalent parts. In the drawings, layers or thicknesses in various regions may be exaggerated for clarity.  
       First Embodiment  
       [0024]    Referring to FIG. 2, a heating apparatus  40  is located in the lower portion of the chamber  38 . A wafer-load region  43  for supporting a wafer (W) is provided on the upper portion of the heating apparatus  40 . After loading the wafer (W) in the chamber, the heating apparatus  40  enables the wafer (W) to be heated to a temperature appropriate for formation of a thin film on the wafer (W). After the wafer temperature for forming the thin film is stabilized, the heating apparatus  40  serves to maintain the wafer at the stabilized temperature until the thin film is formed on the wafer (W). In addition, the heating apparatus  40  can be used in the wafer-annealing process for stabilizing the thin film after the thin film material is formed on the wafer (W). That is, the heating apparatus  40  may be used to increase the wafer temperature to a stabilized temperature appropriate to the annealing temperature, and can also be used to maintain the stabilized temperature until the annealing process is completed.  
         [0025]    A heater  42  is disposed below the wafer (W) and housed in the upper portion of the heating apparatus  40 , and supplies thermal energy to the wafer. A typical heater  42  includes a number of heater blocks, and the portion of the wafer in contact with the heater block is heated first, which causes a non-uniform temperature distribution in the wafer.  
         [0026]    In the present invention, however, a reflecting apparatus  44  is disposed above the wafer-load region  43 . The reflecting apparatus  44  reflects thermal energy radiated from the heater  42  back toward the wafer-load region  43 . Therefore, the entire surface of the wafer (W) at the wafer-load region  43  is uniformly heated due to this additional heating mechanism deployed in the chamber. A so-called “heat island” (HI) is thus formed by the reflecting apparatus  44 , which provides a uniform distribution of thermal energy on the wafer-load region  43 , both during the thin film forming and annealing processes, thereby resulting in a thin film material with uniform thickness and good characteristics being formed on the wafer (W).  
         [0027]    The reflecting apparatus  44  includes a reflector  46  for reflecting the thermal energy radiated from the heating apparatus toward the wafer (W) and a supporter  48  for supporting the reflector  46 . In one embodiment, the reflector  46  has a flat planar mirror facing the wafer (W). At a minimum, the area of the reflector mirror facing the wafer-load region  43  is equal to that of the wafer. Preferably, the area of the planar mirror is larger than the wafer. Since the wafer has a circular shape, the planar mirror is preferably a circular shape as well as shown in FIG. 3, with the supporters  48  disposed 180 degrees apart as shown. Alternatively, a rectangular shaped mirror having a wider coverage area than the wafer may also be employed, like the reflector  60  of the reflecting apparatus shown in FIG. 4. In this case, the supporters  62  may be disposed at the four edges of the reflector  60 , respectively. However, only two supporters  62  may be used instead.  
         [0028]    Also, rather than employing a planar mirror as in FIG. 2, it is preferable that the reflecting surface of the mirror be concave  64  as shown in FIG. 5, taking into consideration the heat island formed in the wafer-load region  43  and the reflection efficiency of the concave mirror  64 . The reflecting surface of the concave mirror  64  facing the heating apparatus  40  thus exhibits a semi-spherical shape. As before, it is preferable that the area of the concave mirror  64  be larger the wafer. As shown in FIG. 5, two opposite supporters  66  are connected to the two edges of the reflector  64 , respectively. Only two supporters  66  may be used to support the reflector  64  and enable it to move up and down, but three or more supporters may also be provided for more stabilization in the movement. The supporters  66  may also include two cylinders, which are identical to the first and second cylinders  48   a ,  48   b  comprising supporters  48  as shown in FIG. 2, and described further below.  
         [0029]    The supporters  48  are positioned around the heating apparatus  40 . The number of the supporters  48  is determined according to the shape of the reflector  46  and the desired stability of movement. Keeping the supporters  48  to a minimum reduces the likelihood that the flow of source gas toward the wafer would be obstructed.  
         [0030]    In this embodiment, the supporters  48  are comprised of first and second cylinders  48   a ,  48   b . The first cylinder  48   a  is connected through the chamber  38  to the driver  50  beneath the chamber  38 . The connection though the chamber is tightly sealed to maintain the proper pressure in the chamber without leakage. The first cylinder  48   a  acts as a guide for second cylinder  48   b , which slides within first cylinder  48   a . One side of the second cylinder  48   b  is connected to the driver  50  via the first cylinder  48   a  to receive the driving power generated by the driver  50 , and the other side of the second cylinder  48   b  is connected to an edge of the reflector  46 . Accordingly, under action of the driver  50 , the reflector  46  can move up and down while facing the wafer-load region  43 .  
         [0031]    The reflector  46  can be located at an appropriate position between the shower head  52  and the wafer (W) during the formation of the thin film material (for example, an insulating layer or conductive layer) on the wafer, as indicated by the elevated position in FIG. 2. Since the pressure in the chamber  38  is very low, in the range of 0-10 −7  torr during the formation of the thin film, the source gas ejected from the shower head  52  can easily reach the wafer (W) without any disturbances, even though the reflector  46  is located between the shower head  52  and the wafer (W). However, if the distance between the reflector  46  and the wafer (W) is too small, the reflector  46  may affect the source gas supply.  
         [0032]    In the annealing step after the formation of the thin film material, the reflector  46  is moved to a position lower than the position for the thin film formation step, as indicated with the dotted lines in FIG. 2, so that the distance between wafer (W) and the reflector  46  may be minimized as much as possible. With such a close distance between the reflector  46  and the wafer (W), the wafer temperature can be increased to a temperature necessary for the annealing, and be uniformly distributed along the surface of the wafer, without an additional heating process.  
         [0033]    In either the thin film forming step or the annealing step, since the reflector  46  is located above the wafer-load region  43 , particles (P) which fall off the chamber wall are prevented from being deposited on the wafer (W).  
         [0034]    To complete the description of the embodiment of the present invention, an exhaust outlet  54  discharges by-products created during the formation of the thin film material, and the outlet  54  is connected to the pump  56 , which is preferably a turbo pump, although other type of pumps may be used, to regulate the pressure condition or process condition in the chamber. Wafer inlet  57  allows the wafer (W) to be transferred into and out of the chamber  38  for processing.  
       Second Embodiment  
       [0035]    In this second embodiment, the positions of the supporters and the driver are different from the first embodiment. Referring to FIG. 6, the driver  70  is located on top of the chamber  39 , rather than under the chamber  38  as in the first embodiment. The reflecting apparatus  80  consists of the reflector  82  and the supporters  84 , which function in a manner identical to the reflector  46  and supporters  48  in the first embodiment. The only difference is they move in an opposite direction to those in FIG. 2.  
         [0036]    The supporter  84  includes the first cylinder  84   a  connected to the driver  70 , and acts as a guide for second cylinder  84   b , which is in turn connected to the reflector  82 . The supporters  84  are positioned around the shower head  52 . Preferably, the supporters  84  are arranged symmetrically around the shower head  52  so that there is an unobstructed flow of source gas ejected from the shower head  52  toward the wafer (W) to ensure a uniform distribution of the gas. The driver  70  functions the same as the driver  50  in FIG. 2. The reflector  82  may be planar or concave as in the first embodiment, and the variable spacing of the reflector and the wafer (W) should be the same as described in the first embodiment (i.e., a closer spacing for the annealing process than the thin film forming process).  
         [0037]    As described above, the thin film forming apparatus according to the present invention includes a reflecting apparatus for reflecting thermal energy radiated from the susceptor toward the wafer, thereby preventing impurities from being deposited on the wafer during the formation of the thin film. In addition, the wafer temperature is increased to a higher and stabilized temperate for the annealing process without additional power being supplied to the heater. Both of these attributes contribute to the uniformity of the thin film material formed on the surface of the wafer.  
         [0038]    The above description should not be construed as limited to the exact embodiments set forth. For example, by way of illustration and not limitation, one skilled in this field could provide a different support structure, or different types of drivers, or reflectors that incorporate horizontal as well as vertical movement, and still be considered within the scope of the invention as set forth in the appended claims.