Patent Publication Number: US-2011049383-A1

Title: Ion implanter and ion implant method thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an ion implanter and implant method, and more particularly, relates to an ion implanter and an ion implant method that achieves a two-dimensional scan by moving a wafer and an aperture for filtering an ion beam along different directions separately. 
     2. Description of the Prior Art 
     Ion implantation is a popular and important processing step performed during semiconductor manufacture. To effectively implant a wafer with a required dose distribution, a two-dimensional scan path is typically used. 
       FIG. 1A  is a simplified diagram of a conventional ion implanter  100 . The conventional implanter  100  includes an ion source  110  and a mass analyzer  120 . The ion source  110  is used to generate ions that are analyzed by the mass analyzer  120  before the required ions are implanted into the wafer  10 . 
       FIG. 1B  shows a top view of the wafer  10  depicted in  FIG. 1A . Several popular ion implant methods exist for achieving a two-dimensional scan of the ion beam  20  on the wafer  10 . If the wafer  10  is fixed, the ion beam  20  can be moved along both the X-axis and the Y-axis. If the ion beam  20  is fixed, the wafer  10  can be moved along both the X-axis and the Y-axis. Also, both the ion beam  20  and the wafer  10  can be moved along the X-axis and the Y-axis simultaneously. 
     When the ion beam  20  is movable, it is difficult to precisely control the properties of the implantation on the wafer  10 . For example, the incident angle between the implanted ion beam and the surface of the wafer varies among different portions of the wafer  10 . This variance causes the wafer  10  to be non-uniformly implanted whereby an additional step may be required to improve the uniformity. 
     Hence, a popular implementation involves fixing the ion beam and moving the wafer to achieve the two-dimensional scan, regardless of whether a spot ion beam or a ribbon ion beam is used. 
     However, when the size of the wafer  10  is increased, the required movement distance of the wafer  10  must also be increased to ensure proper implantation of the whole wafer  10 . Hence, the cost and complexity of the mechanism for moving the wafer  10  are correspondingly increased. Of course, a solution is to increase the height of the ion beam  20 , such that the wafer  10  can be properly implanted by the ion beam  20  without having to significantly move the wafer  10 . However, increasing the height of ion beam  20  causes the uniformity of the ion beam  20  to be decreased, so that the problem of meeting the required movement distance of the wafer  10  still persists and remains significant. 
     For the disadvantages mentioned above, there is a need to propose a novel ion implanter and a novel ion implant method for achieving the two-dimensional scan. 
     SUMMARY OF THE INVENTION 
     The present invention provides a new approach for achieving a two-dimensional scan. According to a feature of the invention, conventional two-dimensional movement of the wafer is replaced by a one-dimensional movement of the wafer and a one-dimensional movement of an aperture for filtering an ion beam before the wafer is implanted. Hence, when the wafer and the aperture are moved along different directions respectively, a two-dimensional scan of a projection of the ion beam on the wafer can be achieved without using the conventional two-dimensional movement of the wafer. 
     One embodiment is an ion implant method. The ion implant method includes the following steps. Initially, a wafer and an ion beam are provided. Also an aperture mechanism (e.g., panel) is provided with an aperture capable of filtering the ion beam before the wafer is implanted, especially to filter out partial ion beam and only allow other portions of the ion beam to be implanted. Next, the wafer is moved along a first direction, and the aperture mechanism is moved along a second direction intersecting with the first direction respectively, such that a projection of the ion beam is two-dimensionally scanned over the wafer. 
     Another embodiment is an ion implanter. The ion implanter includes one or more of an ion source, a mass analyzer, a wafer driving mechanism (e.g., advancer), an aperture mechanism, and an aperture driving mechanism (e.g., advancer). The ion source is capable of generating an ion beam, and the mass analyzer is capable of analyzing the ion beam. The wafer driving mechanism is configured to drive a wafer to be implanted by the ion beam, wherein the wafer is, is capable of being, is operated to be, or is configured to be, movable only along a first direction. The aperture mechanism has an aperture that is configured to filter an ion beam before the wafer is implanted. The aperture driving mechanism is used for driving the aperture mechanism, wherein the aperture is, is capable of being, is operated to be, and/or is configured to be, movable along a second direction. A two-dimensional scan of the ion beam on the wafer is achieved by both the wafer driving mechanism and the aperture driving mechanism driving the wafer and the aperture along different directions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a simplified diagram of a conventional ion implanter; 
         FIG. 1B  shows a top view of the wafer depicted in  FIG. 1A ; 
         FIG. 2A  is a sectional view of an ion implanter with an aperture mechanism in accordance with an embodiment of the present invention; 
         FIG. 2B  and  FIG. 2C  show sectional and top views respectively of the aperture mechanism depicted in  FIG. 2A ; 
         FIG. 3  shows a flow diagram of an ion implant method in accordance with an embodiment of the present invention; 
         FIG. 4A  to  FIG. 4G  show ion implant steps as an example of the method depicted in  FIG. 3 ; 
         FIG. 5A  to  FIG. 5G  show ion implant steps as another example of the method depicted in  FIG. 3 ; and 
         FIG. 6A  and  FIG. 6B  show steps of optionally adjusting the filtered ion beam according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A detailed description of the present invention will be discussed in connection with the following embodiments, which are intended not to limit the scope of the present invention but rather to be adaptable for other applications. While the drawings are illustrated in detail, it is appreciated that the quantity of the disclosed components may be greater or less than that disclosed except for instances expressly restricting such components. 
       FIG. 2A  is a sectional view of an ion implanter  200  in accordance with an embodiment of the present invention. The ion implanter  200  includes an ion source  210 , a mass analyzer  220 , a wafer driving mechanism (e.g., advancer)  230 , an aperture mechanism (e.g., panel)  240 , and an aperture driving mechanism (e.g., advancer)  250 . The ion source  210  is capable of generating an ion beam, and the mass analyzer  220  is capable of filtering out ions without desired kinds/energies from the ion beam  20 . A combination of both the ion source  210  and the mass analyzer  220  can be regarded as an ion beam assembly, because their function is generating the ion beam to be implanted into the wafer. The aperture mechanism  240  has an aperture  241  such that only a portion of the ion beam is allowed to be implanted into the wafer  10 . Moreover, the wafer driving mechanism  230  and the aperture driving mechanism  250  are configured to move the wafer  10  and the aperture mechanism  240  separately. Note that the embodiment is not intended to particularly limit the details of the wafer driving mechanism  230  and the aperture driving mechanism  250 , except for limiting their functions. Hence,  FIG. 2A  shows only their existence without providing particular details such as their positions or sizes. 
       FIG. 2B  and  FIG. 2C  show sectional and top views of the operation of the aperture mechanism  240  depicted in  FIG. 2A  respectively. The X-axis is perpendicular to the Y-axis. The wafer driving mechanism  230  is used for driving a wafer  10  only along the X-axis. The aperture driving mechanism  250  is used for driving the aperture mechanism  240  such that the aperture  241  is moved along only the Y-axis. Accordingly, a two-dimensional scan of the ion beam  20  on the wafer  10  is achieved by the movements of the wafer  10  and the aperture  241 . Herein, the aperture  241  is only moved across the ion beam  20  along the Y-axis, and the wafer  10  is only moved across the ion beam  20  along the X-axis. Hence, a two-dimensional scan on the X-Y plane, intersecting with the ion beam  20 , is achieved. 
     By comparison with the conventional two-dimensional scan, one advantage of the embodiment is clear. In the prior art, the wafer is moved along both the X-axis and the Y-axis. In contrast, in the inventive embodiment, the wafer is moved along the X-axis, and the aperture  241  is moved along the Y-axis. Clearly, the size of the aperture mechanism  240  can be significantly smaller than that of the wafer  10 , especially the size along the X-axis. Note that the aperture mechanism  240  is used only to provide the aperture  241 , in other words, to block portions of the ion beam  20  other than the portion directly passing through the aperture  241 . Hence, along the Y-axis, the mechanism for driving the aperture mechanism  240  provided by the embodiment can be significantly simpler, even cheaper, than that of the mechanism for driving the wafer  10  required by the prior art. 
     Although  FIG. 2A  to  FIG. 2C  show the situation where the movement direction of the wafer  10  is perpendicular to the movement direction of the aperture  241 , the invention need not be so limited. Indeed, the only requirement is that the wafer  10  and the aperture  241  be moved along different directions. According to another aspect, to effectively achieve two-dimension scanning, it is better that one or more of the wafer  10  and the aperture  241  be moved in a direction of a long axis of the projection of the ion beam (e.g., as shown). That is, it may be advantageous to perform such movement parallel to the longer dimension of the two-dimensional cross-section of the ion beam. 
     Furthermore, according to an optional feature, the wafer  10  is moved with a first velocity and the aperture mechanism  240  is moved with a second velocity, wherein the first velocity is independent of the second velocity, and one or more (e.g., both) of the first velocity and the second velocity are adjustable. Therefore, the ion beam projection can be scanned through different points of the wafer  10  by an adjustable velocity, such that different portions of the wafer  10  can be scanned with different velocities. When a non-uniform implantation over the wafer  10  is required, or when a different scan rate is an important factor of implantation over the wafer  10 , the option is valuable. 
     By analogy, the function of the aperture  241  can be likened to that of a raster, whereby for instance only a portion of the wafer  10  exposed by the aperture  241  is implanted. Therefore, when the aperture  241  is moved, different portions of the wafer  10  can be implanted without corresponding movement of the wafer  10  or adjusting of the mass analyzer  220 . 
     Owing to its movability over the wafer  10 , another advantage of the embodiment is the motion of the aperture  241  being flexible such that one or more of the scan path and the scan rate of the aperture  241  over the wafer  10  are adjustable. Therefore, depending on the kind of dose distribution over the wafer  10  that is required, each of the scan path and the scan rate of the aperture  241  may be adjusted correspondingly to achieve the required dose distribution. Of course, the scan path and the scan rate of the wafer  10  also may be adjusted correspondingly to further elastically adjust the motion of the projection of the ion beam  20  on the wafer  10 . Furthermore, the size of the aperture  241  may be significantly smaller than the diameter of the wafer  10 , such that the unit size of the filtered ion beam projection over the wafer  10  can be significantly reduced. Therefore, to compare with the conventional two-dimensional scan where the unit size is the size of the whole ion beam projection, the embodiment is more effective for implanting a wafer with non-uniform dose distribution. 
     One further advantage of the embodiment is that the dose rate control of different portions of the wafer  10  can be achieved separately. As well known, different scan rates of the ion beam  20  may induce different effects on the semiconductor structures formed in and on the wafer  10 . Therefore, as discussed above, when the unit size of the projection of the filtered ion beam  20  is smaller than the size of the ion beam  20 , it is easy to adjust the dose rate effect over different portions of the wafer  10 . 
     Moreover, it is well-known that an aperture can be used to adjust the ion beam to be implanted into the wafer  10 , wherein the aperture has a fixed shape and is located in a fixed position. Hence, details of the aperture  241  are omitted herein, except for main characteristics being briefly introduced. For example, a shape of the aperture  241  may be adjusted to ensure a beam current distribution of a filtered ion beam dropping to zero gradually at the edge of the aperture  241 , or to ensure a current distribution of the filtered ion beam having a Gaussian distribution. As may be typical, the shape of aperture  241  may comprise one or more (e.g., combination or complex shape) of a circle, oval, ellipse and diamond. Also, the material of the aperture mechanism  240 , especially the material of a part of the aperture mechanism  240  close to the aperture  241 , may be graphite to minimize the possible pollution induced by collision with the ion beam  20 . Besides, to further minimize possible pollution, a shield capable of preventing the aperture driving mechanism  250  from being implanted by the ion beam  20  optionally may be implemented. According to a non-illustrated embodiment, the shield may be made of graphite and located between the aperture mechanism  240  and the mass analyzer  220  for covering most of the aperture mechanism  240  and exposing essentially only the aperture  241 . 
     As may be typical, calculation of the scan rate and the scan path, and/or even other scan parameters, can be based on an assumption that the whole aperture  241  is filled by the ion beam  20  and the whole filtered (i.e., passing through the aperture  241 ) ion beam is implanted into the wafer  10 . The assumption almost is correct when the aperture  241  is located over the wafer  10 . However, when the aperture  241  is located nearby the ends of the cross-section of the ion beam  20 , the aperture  241  may not be completely filled by the ion beam. However, when the aperture  241  is located near the edge of the wafer  10 , the filtered ion beam passing through the aperture  241  may not be completely projected onto the wafer  10 . In such case, it is desired to correct the scan path and the scan rate, and/or even other scan parameters, according to the real ion beam passing through the aperture  241  and arriving on the wafer  10 , to thereby provide what usually is referred to as an “edge correction factor.” 
       FIG. 3  shows a flow diagram of an ion implant method in accordance with an embodiment of the present invention. The ion implant method includes a step as shown in block  301  of providing a wafer, an ion beam, and an aperture mechanism (e.g., panel) having an aperture for filtering the ion beam before the wafer is implanted. As shown in block  302 , the wafer is moved along a first direction and the aperture mechanism is moved along a second direction intersecting with the first direction separately, such that a projection of the ion beam is two-dimensionally scanned over the wafer. 
     Two practical examples for block  302  are briefly discussed below with reference to  FIGS. 4A-4G  and  FIGS. 5A-5G  separately. In the embodiments, the ion beam  20  is a ribbon ion beam, and the beam height is larger than the diameter of the wafer  10 . However, another non-illustrated embodiment may use a spot ion beam or a ribbon ion beam whose height is smaller than the diameter of the wafer. Of course, if the wafer diameter is smaller than the ion beam height, an additional step of moving either or both of the wafer  10  and the beam  20  in a direction of the long axis (e.g., dimension) of the ion beam projection is included to ensure proper implantation of the whole wafer  10 . Herein, the additional movement of the wafer  10  or the ion beam  20  is used only to change the relative geometric relation between the wafer  10  and the ion beam  20  rather than alter the essential mechanism of the embodiment. 
     Referring to  FIG. 4A  and  FIG. 4B , the aperture  241  is located in a first position of the Y-axis, and the wafer  10  is located on a side of the aperture  241  along the X-axis. 
     Here, as examples, the height of the ribbon beam is 350 mm if the wafer  10  is a 300 mm wafer, the uniformity of the ribbon beam is about 5% and usually not less than 1%, and the aperture  241  has an oval shape or diamond shape. To ensure that the current density of the ion beam  20  has a Gaussian distribution, the lengthwise dimension L of the aperture  241  is about 150 mm, and the lateral dimension W of the aperture  241  is about 60 mm. 
     Considering aperture  241 ,  FIG. 4C  and  FIG. 4D  show its relative movement across the ion beam  20  along the Y-axis whereby only the filtered part of ion beam  20  passing through aperture  241  is implanted into the wafer  10 . As examples, the scan speed may be a function of one or more of a predefined dose, a scan number, and the edge correction factor. Continuing with  FIG. 4E  and  FIG. 4F , the aperture  241  is further moved across the ion beam  20  until it arrives on the other side of the wafer  10 . Thus, a first one-dimensional scan (e.g., in the drawing, from left to right) of the ion beam  20  on the wafer  10  is achieved (e.g., with neither the wafer  10  nor the ion beam  20  being moved). Then, optionally, the ion beam current can be measured followed by calculation of a scan parameter, such as scan rate, for the next one-dimensional scan of the ion beam  20  on the wafer  10 . 
     Thereafter, the aperture  241  can be moved to a second position (or, alternatively, held at its current position) of the Y-axis, and the wafer  10  is positioned (e.g., in the drawing, moved up in the X-direction) for the next step. As shown in  FIG. 4G , by repeating the ion implant steps mentioned above, a second one-dimensional scan (e.g., in the drawing, from right to left) of the ion beam  20  on the wafer  10  is achieved. Additional one-dimensional scans can of course be implemented. Accordingly, by implementing the one-dimensional scans, two-dimensional scanning on the wafer  10  is achieved. While not shown, alternative but not interchangeable or equivalent implementations of the invention for  FIGS. 4C-4F  may include movement of the wafer  10  along the X-axis (e.g., in one or more of a simultaneous, intermittent, prior, or post fashion relative to movement of the aperture  241 ). The one-dimensional scans can be repeated until, for example, the wafer  10  has been scanned (e.g., the entire wafer has been two-dimensionally scanned) by projection of the filtered ion beam. 
     Another practical embodiment is now briefly described. Referring to  FIG. 5A , locate the wafer  10  in a first position of the X-axis, and locate the aperture  241  on a side of the wafer  10  along the Y-axis. Now, considering wafer  10 ,  FIGS. 5B ,  5 C, and  5 D show its relative movement across the ion beam  20  along the Y-axis whereby only the part of the ion beam  20  passing through aperture  241  is implanted into the wafer  10 . 
     Referring to  FIG. 5E  and  FIG. 5F , move the wafer  10  across the ion beam  20  until it arrives on the other side thereof. Thus, a first one-dimensional scan of the ion beam  20  on the wafer  10  is achieved (e.g., without movement of the ion beam  20 ). Again, it is optional to measure the ion beam current and calculate a scan parameter, such as scan rate, for the next one-dimensional scan of the ion beam  20  on the wafer  10 . Subsequently, move the wafer  10  to a second position of the X-axis and move the aperture  241  to the position for the next step. Therefore, as shown in  FIG. 5G , by repeating the ion implant steps mentioned above, a second one-dimensional scan of the ion beam  20  on the wafer  10  is achieved. As with the above example, additional one-dimensional scans of course can be implemented. Accordingly, when some one-dimensional scans are executed, two-dimensional scanning on the wafer  10  is achieved. While not shown, alternative but not interchangeable or equivalent implementations of the invention for  FIGS. 5B-5F  may include movement of the aperture  241  along the X-axis (e.g., in one or more of a simultaneous, intermittent, prior, or post fashion relative to movement of the wafer  10 ). The one-dimensional scans can be repeated until, for example, the wafer  10  has been scanned (e.g., the wafer has been fully two-dimensionally scanned) by projection of the filtered ion beam. 
     Furthermore, to more elastically adjust the shape of the filtered ion beam, the aperture  241  optionally can be slightly moved around the ion beam  20 . For example, keep the aperture  241  in a fixed point of the Y-axis but slightly move aperture  241  along the x-axis. Hence, as shown in  FIG. 6A  and  FIG. 6B , the projection of the ion beam  20  on the wafer  10  may be deformed or totally blocked. Then, different portion(s) of the wafer  10  may be implanted by different implanted ion beam(s) or even may not be implanted. Clearly, the option may be more suitable for particular situations such as non-uniform two-dimensional implantation on the wafer  10 . 
     Although specific embodiments have been illustrated and described, it will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the present invention, which is intended to be limited solely by the appended claims.