Abstract:
An HSG-Si layer is formed on a wafer under a uniform temperature condition. An apparatus for forming the HSG-Si layer includes a housing forming a process chamber, a first heater on which the wafer is positioned fixed in place at the bottom of the process chamber, a second heater at the top of the process chamber, and a thermal insulator which prevents the heat generated by the first heater from being transferred to the outside of the process chamber. A temperature control system regulates the temperature of the heaters. A method of forming the HSG layer includes steps of placing the wafer on the first heater, using the heaters to remove moisture from the wafer, injecting a source gas of the HSG-Si toward the upper surface of the wafer to form amorphous silicon on the wafer, and annealing the wafer for a predetermined period of time to transform the amorphous silicon into an HSG-Si layer. During the steps of forming the HSG-Si layer, the temperatures of the first and second heaters are regulated to maintain the surface temperature of the wafer constant.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to method and apparatus for forming an HSG-Si (hemispherical grained silicon) layer. More particularly, the present invention relates to a method and apparatus for forming an HSG-Si layer on a wafer in the manufacturing of semiconductor memory devices. 
     2. Description of the Related Art 
     In general, semiconductor devices are manufactured by coating a silicon wafer with a thin film having predetermined electrical characteristics, using a semiconductor manufacturing apparatus. The thin film is typically formed on the wafer by executing a series of semiconductor processes such as lithography, chemical and physical vapor deposition, plasma etching, HSG-Si manufacturing processes or the like. The wafer coated with the thin film is used for manufacturing semiconductor devices and chips. 
     Among the above-mentioned semiconductor manufacturing processes, the HSG-Si manufacturing process is widely used to increase the surface area of a capacitor, thereby increasing the capacitance. HSG-Si is commonly manufactured by depositing silicon under a predetermined deposition condition or by depositing amorphous silicon and transforming the silicon into HSG-Si. These types of HSG-Si manufacturing methods are disclosed in U.S. Pat. No. 5,885,869 (issued to Charles Turner et al. on Mar. 23, 1999) and U.S. Pat. No. 5,759,864 (issued to Homg-Huei Tseng et al. on Jun. 2, 1998). 
     FIG. 1 shows a semiconductor processing system  500  for carrying out a conventional HSG-Si manufacturing process. As shown in FIG. 1, the conventional semiconductor processing system  500  includes a process chamber  510 . A first heater  520  for heating a wafer  400  is installed in the process chamber  510 . The lower surface of the first heater  520  is supported by a support member  522 . The wafer  400  is introduced into the process chamber  510  through a guide slot  514  formed on one side of the process chamber  510  and is positioned on the first heater  520 . 
     A thermocouple  525  for detecting the temperature of the first heater  520  and a current supplying line  523  for supplying a current to the first heater  520  are provided beneath the first heater  520 . The thermocouple  525  and the current supplying line  523  are connected to a controller (not shown). The controller supplies the current to the first heater  520  through the current supplying line  523  based on the temperature of the first heater  520  detected by the thermocouple  525 , thereby maintaining the temperature of the first heater  520  within a predetermined range. 
     The wafer  400  is fed into the process chamber  510  by a handler (not shown), and a control section (not shown) operates a valve device  516  to open/close the guide slot  514  so that the wafer  400  can be guided into the process chamber  510 . 
     The process chamber  510  includes a dome-shaped roof  512 , and a second heater  521  is installed on an upper portion of the dome-shaped roof  512  in such a manner that it surrounds the dome-shaped roof  512 . The radiant heat created in the process chamber  510  by the first and second heaters  520  and  521  is directed to the wafer  400  by the dome-shaped roof  512 . 
     An RF (Radio Frequency) electrode  540  to which an RF current is applied is installed between the dome-shaped roof  512  and the second heater  521 . When a gas such as silane, disilane, or the like is injected from a gas injector  530 , RF electric waves are irradiated into the process chamber  510  through the RF electrode  540  to activate the gas. The gas injector  530  is connected to a gas supplying line  538 , and the gas is supplied to the gas injector  530  through the gas supplying line  538  from a gas source (not shown). 
     One side of the process chamber  510  communicates with a discharging port  532 . The discharging port  532  is connected to a vacuum pump  535  so that a vacuum can be created in the process chamber  510 . 
     A wafer holder  560 , which receives the wafer  400  guided toward first heater  520  and places the wafer  400  on the upper surface of the first heater  520 , is installed in the process chamber  510 . The wafer holder  560  includes a first arm portion  562  disposed at a peripheral portion of the upper surface of the first heater  520 , a second arm portion  564  engaged with a wafer holder driving apparatus  570 , and a support  566  connecting the first arm portion  562  and the second arm portion  564 . Although only one first arm portion  562 , one second arm portion  564 , and one support  566  are shown in FIG. 1, the wafer holder  560  comprises three or more sets of such components. 
     The wafer holder driving apparatus  570  comprises a cylinder  572  provided below the process chamber  510 . A bellows  580  provides a seal between the cylinder  572  and the process chamber  510  so that the vacuum state of the process chamber  510  is maintained. 
     A plunger  574  is disposed in the cylinder  572  and is movable in upward and downward directions. A shaft  576  is engaged with the upper surface of the plunger  574 , and the upper end portion of the shaft  576  is engaged with the end portion of the second arm portion  564 . A hydraulic pressure supplying section  578  supplies hydraulic pressure to the cylinder  572  to move the plunger  574  in the cylinder  572 . 
     In addition, the conventional semiconductor processing system  500  includes a heater moving apparatus  600  for moving the first heater  520  upward and downward. The heater moving apparatus  600  comprises a motor  608  generating a driving force and a lift  610  which is connected to the motor  608  in such a manner that it can move up and down. 
     The lift  610  is fixed to the lower surface of a bellows cover  620 , and moves the bellows cover  620  upward and downward when the motor  608  is operated. The bellows cover  620  includes an upper cover  622  fixedly attached to the bottom of the process chamber  510  and a lower cover  624  which is moved upward and downward by the lift  610 . When the lift  610  is moved upward, the upper cover  622  is maintained in a fixed state and the lower cover  624  is moved into the upper cover  622 . Further, the support member  522  of the first heater  520  is mechanically connected to the lower cover  624  so as to move together with the lower cover  624 , so that the first heater  520  can be moved upward and downward in the process chamber  510 . 
     Hereinafter, the operation of the of the above-described conventional semiconductor processing system  500  for manufacturing an HSG-Si will be explained. 
     When the HSG-Si manufacturing process starts, the valve device  516  opens the guide slot  514  whereupon the wafer  400  is moved into the process chamber  510  by the handler. 
     When the wafer  400  has been moved into a position over the upper surface of the first heater  520 , the wafer holder  560  is moved upward by the wafer holder driving apparatus  570  to receive the wafer  400 , and then is moved downward to position the wafer  400  on the upper surface of the first heater  520 . At the same time, the controller applies operation signals to the first and second heaters  520  and  521  so as to operate the first and second heaters  520  and  521 . At this time, the temperature of the first heater  520  is about 700 to 750° C., the temperature of the second heater  521  is about 315 to 325° C., and the temperature of the wafer  400  is about 600 to 610° C. 
     Then, the controller applies operation signals to the heater moving apparatus  600  in order to move the first heater  520  upward to a first position A in the process chamber  510 . Placing the first heater  520  at the first position A in the process chamber  510  improves the efficiency of heating the wafer  400 . At the first position A the first heater  520  is at a level corresponding to that of the gas injector  530 , and is vertically displaced upwardly from its initial position by about  80 mm. 
     At this time, the temperatures of the first and second heaters  520  and  521  are maintained constant, but the temperature of the wafer  400  is raised to 615-625° C. due to the heat radiating in the process chamber  510 . 
     Thereafter, the first heater  520  is left at the first position A for about one minute. The time period of one minute is required for removing foreign substances such as moisture from the wafer  400 . 
     After one minute has passed, a gas is injected on the wafer  400 . The gas acts as a source for forming HSG-Si on the wafer  400 , and for this purpose a reactive gas such as silane or disilane or the like is used. Then, the RF current is applied to the RF electrode  540  so that the RF electric waves are irradiated into the process chamber  510 , to activate the source gas. 
     When the gas injecting process has been completed, the controller operates the heater moving apparatus  600  to move the first heater  520  upward to a second position B in the process chamber  510 . Placing the first heater  520  to the second position B in the process chamber  510  accelerates the growth rate of the HSG-Si by raising the temperature of the wafer  400 . 
     At the second position B, the first heater  520  is displaced vertically upward from its initial position by about 100 mm. At this time, the heating temperatures of the first and second heaters  520  and  521  remain constant, but the temperature of the wafer  400  is raised to 625-635° C. by the heat radiating in the process chamber  510 . The gas injected on the wafer  400  is thermally decomposed when the heater  520  is at the second position B, whereby the HSG-Si layer is formed on the wafer  400 . 
     After the formation of the HSG-Si layer has been completed, the controller operates the heater moving apparatus  600  to return the first heater  520  to its initial position, and then opens the valve device  516 . Then the handler moves into the process chamber  510  and feeds the wafer  400  to the next stage of the semiconductor device fabrication equipment. 
     However, in the conventional semiconductor processing system  500 , the temperature in the process chamber  510  varies as the first heater  520  is moved in the process chamber  510  while the HSG-Si process is proceeding. As it is known that HSG-Si forms best under a uniform temperature condition, the unstable temperature condition occurring due to the movement of the first heater  520  can produce defects in the HSG-Si layer. 
     Furthermore, the heater moving apparatus  600  for moving the first heater  520  upward and downward renders the overall structure of the apparatus complex, and contributes significantly to the manufacturing cost of the apparatus. 
     Furthermore, moving the first heater  520  upward and downward during the forming of the HSG-Si layer takes time, thereby detracting from the productivity of the manufacturing process. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the above-described problems. 
     Accordingly, one object of the present invention is to provide a method of forming an HSG-Si layer in a relatively short amount of time and under a uniform temperature condition, thereby preventing defects from occurring in the HSG-Si layer and contributing to the overall efficiency and productivity of a semiconductor device manufacturing process. Another object of the present invention is to provide an apparatus of a relatively simple structure for forming an HSG-Si layer under a uniform temperature condition, thereby preventing defects from occurring in the HSG-Si layer and reducing equipment costs associated with a semiconductor device fabrication facility. 
     In order to achieve the first object, the present invention provides a method of forming an HSG-Si layer wherein the temperature of the ambient in a process chamber is maintained constant by regulating the temperature of a first heater fixed in place at the bottom of the process chamber and a second heater surrounding the upper portion of the process chamber. A wafer having a silicon layer is placed on a central portion of the first heater and foreign substances are removed from the wafer by using the first and second heaters and the heat radiating within the process chamber. Thereafter, a source gas is injected onto the silicon layer of the wafer and the wafer is annealed for a predetermined time, while the first heater remains fixed in place and temperatures of the heaters are regulated to maintain the surface temperature of the wafer constant, so that a uniform HSG-Si layer is formed from the silicon layer. 
     In order to achieve the second object, the present invention provides a semiconductor processing apparatus having a housing constituting a process chamber in which the HSG-Si manufacturing process is performed, a first heater fixed in place at the bottom of the process chamber, a gas injector disposed at the same level as the first heater, and a thermal insulator which insulates the process chamber to prevent the loss of heat from the process chamber. 
     A second heater for raising the temperature in the process chamber may be provided at the top of the process chamber. The upper portion of the housing constituting the process chamber is preferably dome-shaped so that the heat radiating from the first heater is directed toward the wafer. 
     A temperature control system allows the temperature of the first and second heaters and, hence, the temperature of the ambient within the process chamber and the surface temperature of the wafer itself, to be regulated. The temperature control system includes at least one temperature sensor, such as a thermocouple, and a current supply line attached to the first heater. 
     The gas injector injects a gas onto the upper surface of the wafer positioned on the first heater so that an HSG-Si layer can be grown on a silicon layer of the wafer. An RF electrode may be provided between the upper portion of the process chamber and the second heater. RF electric waves are irradiated into the process chamber when the gas is injected toward the upper surface of the wafer, thereby activating the gas. 
     The insulator preferably includes a quartz member extending over the inner surface of a wall of the housing at the lower portion of the process chamber. The wall has an interior space, which is preferably in the state of a vacuum to prevent the transfer of heat from the inner wall surface at the bottom of the process chamber to the outer wall surface at the bottom of the process chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description thereof made with reference to the accompanying drawings, of which: 
     FIG. 1 is a schematic diagram of a conventional semiconductor processing system used to form an HSG-Si layer on a wafer; 
     FIG. 2 is a schematic diagram of a semiconductor processing system used to form an HSG-Si layer on a wafer according to the present invention; 
     FIG. 3 is a schematic diagram of a portion of the semiconductor processing system comprising a thermocouple and a power supplying line installed on the bottom of a heater; 
     FIG. 4 is a cross-sectional view of a wafer fed into a process chamber; 
     FIG. 5 is a cross-sectional view of the wafer showing an HSG-Si layer formed on the wafer; and 
     FIG. 6 is a flow chart of an HSG-Si manufacturing process according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a preferred embodiment of the present invention will be explained in detail with reference to the attached drawings. 
     Referring to FIG. 2 an apparatus  100  for forming an HSG-Si layer on a wafer according to the present invention includes a housing  101  forming a process chamber  110  therein. The housing  101  includes a bottom wall  117  extending along the bottom of the process chamber  110 . 
     A first heater  102  for heating a wafer  200  is fixed in place in the process chamber  110 . More specifically, the bottom surface of the first heater  102  is supported by a support member  125  fixed to the bottom wall  117  of the housing  101 . The wafer  200  is introduced into the process chamber  110  through a guide slot  114  formed at one side of the process chamber  110  and is positioned on the upper surface of the first heater  102 . 
     Referring to FIG. 3, first and second thermocouples  122  and  123  for detecting temperatures of the central and peripheral portions of the first heater  102  and a current supplying line  124  for supplying a current to the first heater  102  are attached to the bottom surface of the first heater  102 . The first thermocouple  122  is attached to a central portion of the bottom surface of the first heater  102  and extends downwardly therefrom, and the second thermocouple  123  is attached to the peripheral portion of the bottom surface of the first heater  102  at one side thereof and extends downwardly therefrom. 
     The first and second thermocouples  122  and  123  and current supplying line  124  are connected to a controller  300 . The controller  300  supplies a current to the first heater  102  through the current supplying line  124  based on the temperature of the first heater  102  detected by the first and second thermocouples  122  and  123  so that the temperature of the first heater  102  is maintained within a predetermined range. 
     It is preferable that the temperature of the first heater  102  is maintained at a temperature of from 700 to 750° C. More particularly, the controller  300  maintains the temperature of the central portion of the first heater  102  at 700 to 710° C. based on the temperature data inputted from the first thermocouple  122  and maintains the temperature of the peripheral portion of the first heater  102  at 740 to 750° C. based on the temperature data inputted from the second thermocouple  123 . Here, the central portion of the first heater  102  refers to that portion on which the wafer  200  is positioned. Because the temperature of the central portion of the first theater  102  is lower than the temperature of the peripheral portion of the first heater  102 , and the peripheral portion of the first heater  102  is disposed remotely from the wafer  200 , the effect that the peripheral portion of the first heater  102  has on heating the wafer is less than the effect that the central portion of the first heater  102  has. 
     The central portion of the first heater  102  protrudes upwardly by a predetermined distance from the upper surface of the peripheral portion of the first heater  102 . As such, a wafer holder  160  (shown in FIG. 2) can be positioned on the periphery of the upper surface of the first heater  102 . 
     As shown in detail in FIG. 4, a silicon layer  210  is formed on the upper surface of the wafer  200  which is positioned on the first heater  102 . The wafer  200  formed with the silicon layer  210  is fed into the process chamber  110  by a handler (not shown), and the control section  300  operates a valve device  116  (shown in FIG. 2) to open the guide slot  114  so that the wafer  200  can be easily guided into the process chamber  110 . 
     Referring again to FIG. 2, the process chamber  110  includes a dome-shaped roof  112 . A second heater  105  surrounding the dome-shaped roof  112  is disposed at an upper portion of the dome-shaped roof  112 . The radiant heat in the process chamber  110  is efficiently directed toward the wafer  200  by the dome-shaped roof  112 . 
     The temperature of the second heater  105  is controlled by the controller  300 . The controller  300  controls the temperature of the second heater  105  to within a range of 300 to 320° C. The controller  300  also controls the temperatures of the first and second heaters  102  and  105  such that the surface temperature of the wafer  200  is maintained within a range of 625 to 630° C. considering also the heat radiating toward the wafer in the process chamber  110 . For this purpose, the temperatures of the second heater  105  and the process chamber  110  are inputted to the controller  300  by a sensor device (not shown). 
     The apparatus  100  also includes an RF electrode  140  disposed between the dome-shaped roof  112  and the second heater  105 . When a gas such as silane, disilane, or the like is injected from the gas injector  130 , RF electric waves are irradiated into the process chamber  110  through the RF electrode  140 , thereby activating the gas. The gas injector  130  is installed at the same level (with respect to the vertical) as the first heater  102  and is connected to a gas supplying line  138  for receiving the gas from a supply  139  of source gas. 
     Furthermore, the apparatus  100  according to the present invention includes an insulating member  180  which insulates the interior of the process chamber  110  from the environment outside the process chamber  110  so that the heat in the process chamber  110  is prevented from transferring to the outside of the process chamber  110 . The insulating member  180  covers the inner wall surface of the bottom portion of the process chamber  110 . The insulating member  180  is of quartz. 
     A space  118  is formed in the bottom wall  117  of the process chamber  110 . The space  118  is in a vacuum state to prevent heat from being transferred from the inner wall surface of the bottom of the process chamber  110  to the outer wall surface of the bottom of the process chamber  110 . According to another form of the present invention, an insulating material such. as quartz can occupy the space  118 . 
     The vacuum within the space  118  reduces the temperature loss in the process chamber  110  so that the temperature in the process chamber  110  is stably maintained, and prevents the outer wall of the process chamber  110  from becoming hot, thereby protecting operating personnel. 
     One side of the process chamber  110  communicates with a discharge port  132 . The discharge port  132  is connected to a vacuum pump  135  controlled by the controller  300  to allow the process chamber  110  to be evacuated. 
     In the process chamber  110 , the wafer holder  160  receives the wafer  200  guided toward the first heater  102  in order to place the wafer  200  on the upper surface of the first heater  102 . The wafer holder  160  includes a first arm portion  162  disposed at a peripheral portion of the upper surface of the first heater  102 , a second arm portion  164  connected to a wafer holder driving apparatus  170 , and a support  166  which connects the first arm portion  162  to the second arm portion  164 . Although only one first arm portion  162 , one second arm portion  164 , and one support  166  are shown in the figure, the wafer holder comprises three or more sets of such components. 
     The wafer holder driving apparatus  170  comprises a cylinder  172  integral with and disposed at the central portion of the bottom of the process chamber  110 . 
     A plunger  174  is disposed in the cylinder  172  in such a manner that it can move upward and downward. An operation rod  176  is engaged with the upper surface of the plunger  174  and the upper end portion of the operation rod  176  is connected to an end of the second arm portion  164 . A hydraulic pressure supplying section  178  controlled by the controller  300  supplies the cylinder  172  with hydraulic pressure to cause the plunger  174  to move upward and downward in the cylinder  172 . 
     Hereinafter, the operation of the HSG-Si layer forming apparatus  100  of the present invention will be described with reference to FIG.  6 . 
     When the HSG-Si manufacturing process starts, the controller  300  causes current to be supplied to the first heater  102  fixed in place in the process chamber  110  and to the second heater  105  surrounding the upper portion of the process chamber  110  until the temperature in the process chamber  110  reaches a constant value (Step S 1 ). Then, the controller  300  regulates the temperature of the first heater  102  so as to be within a range of 700 to 750° C. and regulates the temperature of the second heater  105  so as to be within a range of 300 to 320° C. 
     Thereafter, the valve device  116  is commanded by signals received from the controller  300  to open the guide slot  114  whereupon the wafer  200  is moved into the process chamber  110  by the handler. 
     When the wafer  200  is moved to a position over the upper surface of the first heater  102 , the first arm portion  162  of the wafer holder  160  positioned on the peripheral portion of the upper surface of the first heater  102  is moved upwardly by the wafer holder driving apparatus  170  and thereby receives the wafer  200 . The first arm portion  162  is then moved downward and places the wafer  200  on the central portion of the upper surface of the first heater  102  (Step S 2 ). 
     The wafer  200  remains there in a stationary state (is fixed on the first heater  102 ) for a predetermined time (Step S 3 ). During this time foreign substances, such as moisture formed on the wafer  200 , are removed by the heat generated by the first and second heaters  102  and  105  and the radiant heat in the process chamber  110 . At this time, the temperature of the wafer  200  is maintained within the range of 625 to 630° C. 
     Thereafter, gas is injected onto the silicon layer of the wafer  200  by gas injector  130  to form amorphous silicon (Step S 4 ). The gas is a source gas of the amorphous silicon, such as silane, disilane, trisilane, and dichlorosilane. During this injecting step, the RF electric waves are irradiated into the process chamber  110  by the RF electrode  140  to activate the gas. The gas injected onto the wafer  200  is thermally decomposed, thereby forming the amorphous silicon layer on the wafer  200 . The amorphous silicon layer is formed on the wafer  200  by rapid thermal chemical vapor deposition or low pressure chemical vapor deposition. 
     Thereafter, the wafer  200  is annealed for a predetermined time so that the amorphous silicon layer formed on the upper portion of the silicon layer is transformed into an HSG-Si layer (Step S 5 ). The HSG-Si layer  220  is shown in FIG.  5 . 
     During Steps S 1  to S 5 , the temperature in the process chamber  110  and the temperatures of the first and second heaters  102  and  105  are detected by the sensor device and the first and second thermocouples  122  and  123 . Also, during Steps S 3  to S 5 , the controller  300  finely controls the amount of current supplied to the first and second heaters  102  and  105  based on the detected temperatures to thereby maintain the temperature of the wafer  200  within a range of 625 to 630° C. 
     In addition, during Steps S 1  to S 5 , the temperature in the process chamber  110  is maintained constant, whereby the temperature of the wafer  200  is also maintained constant (from 625 to 630° C.). 
     When the formation of the HSG-Si layer  220  has been completed, the controller  300  opens the valve device  116  and applies operation signals to the handler to feed the wafer  200  to the next stage of the semiconductor fabrication equipment. 
     As described above, the HSG-Si layer can be uniformly formed on the wafer according to the present invention, because the temperature in the process chamber is maintained constant during the HSG-Si manufacturing process. Furthermore, the HSG-Si layer forming apparatus has a comparatively small number of working parts and hence, a correspondingly simple structure. Thus, it is economical to manufacture. Still further, the present invention can form the HSG-Si layer in less time than the prior art, and thus contributes to the efficiency in the manufacturing process of the semiconductor devices. 
     Although the present invention has been described above in connection with the preferred embodiment thereof, it is to be understood that various changes and modifications can be made to the present invention within the spirit and scope of the present invention as defined by the appended claims.