Abstract:
A semiconductor wafer chemical mechanical treatment apparatus having a sectional extended arm carrying a head. The sectional arm is comprised of a fixed yoke and an elongated arm positioned in said yoke on a pivot. The elongated arm carries a first means thereon for establishing and maintaining a given loading or pressure on the head. A second means, is positioned on the yoke, adjacent to the elongated arm for temporarily altering the given loading or pressure on the head established by the first means without disturbing the setting of the first means such that when the second means is reset the given head load or pressure established by said first means is automatically restored.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to an apparatus used to treat semiconductor wafer surfaces. More particularly, the present invention is an apparatus, for treating spinning semiconductor wafer surfaces, in which there is provided a head, for contacting the surface of the wafer, having attached thereto a first means for setting the head against the wafer surface with a selected predetermined force and a second means for temporarily and selectively altering the selected predetermined force set by the first means without altering the setting established by said first means. 
     BACKGROUND OF THE INVENTION 
     Production of semiconductor devices requires the treatment of a semiconductor wafer with a number of chemical, mechanical or chemical-mechanical processing steps. 
     During these processing steps, even minute changes or variations in the wafer surface can produce effects that can adversely affect later processing steps and thus affect the reliability of the devices formed in the wafer. For example, such changes and variations can fail to remove contaminants or otherwise fail to appropriately condition the surface of the semiconductor wafer such that later processing steps are interfered with. When such processing steps fail they usually result in either instant or premature failure or long term degradation and shortened life of some or all or the devices produced in the wafer. 
     Certain of these processing steps require the use of an apparatus that can place a head, carrying a pad or brush, steeped in a suitable chemical such as a cleansing agent, adjacent to or against the surface of the wafer to treat, e.g., clean, or otherwise condition, the surface of the wafer. 
     In all such presently available apparatuses the force between the brush or pad carrying head and the surface, i.e., the head pressure, is substantially unknown and uncontrolled. Further the prior art apparatuses lack any means for consistently setting, maintaining or monitoring the head pressure. This lack of control of the head pressure is inherent in the prior art apparatuses because their rigid design renders them incapable of either achieving or consistently maintaining a known head pressure. 
     The present inventors have now found that many of such wafer processing steps require, for optimum results, that distinct head pressures be maintained and that for most process steps that the head pressure be, at least, a selected minimum pressure. The present inventors have also found that by doing so more consistent production results can be obtained. 
     The present inventors have also found that while many steps require this minimum head pressure other steps require that the head pressure be altered from this minimum pressure. 
     Therefore, it is most desirable that such semiconductor devices be fabricated using an apparatus that is capable of producing and maintaining different selected head pressures as required by the process steps. 
     It is also desirable, for many process steps, that the apparatus be readily and quickly capable of returning the applied head pressure to a preselected minimum head pressure. 
     SUMMERY OF THE PRESENT INVENTION 
     The present invention provides a head processing apparatus having a first means that can be set to establish and provide a selected head loading or pressure, i.e., the loading or pressure between a brush or pad carrying head and a wafer surface, and a second means that can be activated to temporarily alter or adjust the selected head pressure without affecting the setting of the said first means that establishes the selected head pressure such that when said second means is deactivated, the apparatus will instantly return to the selected head pressure established by said first means. 
     The present invention by providing said first and second head loading means maintains better processing conditions thus causing all the processing steps performed by the apparatus to be performed under optimum and repeatable conditions. 
     In this way, the present invention, achieves better more consistent results and a lower defect or scrap rate. 
     More particularly, the present invention accomplishes these desirable results in a semiconductor wafer chemical mechanical treatment apparatus having a sectional extended arm carrying a head. The sectional arm is comprised of a fixed yoke and an elongated arm positioned in said yoke on a pivot. The elongated arm carries a first means thereon for establishing and maintaining a given loading or pressure on the head. A second means, is positioned on the yoke, adjacent to the elongated arm for temporarily altering the given loading or pressure on the head established by the first means without disturbing the setting of the first means such that when the second means is reset the given head load or pressure established by said first means is automatically restored. 
     Therefore it is an object of the present invention to provide a new wafer treatment apparatus which is provided with first means that can be set to create a selected head pressure between a brush and pad carrying head and a wafer surface and with second means for altering the selected head pressure as required by the process without altering the setting of the first means. 
     These objects, features and advantages of the present invention will be become further apparent to those skilled in the art from the following detailed description taken in conjunction with the accompanying drawings wherein: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric top view of the wafer processing apparatus of the present invention. 
     FIG. 2 is an isometric view of the bottom of the head assembly of the wafer processing apparatus of the present invention as shown in FIG.  1 . 
     FIG. 3 is a partial sectional view of the head assembly of FIG.  1 . 
     FIG. 4 shows the wafer holding chuck of FIG. 1 having a special load cell plate thereon. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to FIGS. 1,  2  and  3  a wafer processing apparatus  10  employing the present invention will be described. 
     The apparatus  10  includes a rotary chuck  12  supported by the shaft  14  of motor  16  as is well known to the art. A semiconductor wafer  18  is supported on chuck  12  and maintained centrally thereon by a plurality of clips or edge supports  20 . The wafer chuck is mounted on the motor  16  so that the wafer  18  can be spun around its axis as shown by arrow  19 . 
     Adjacent the chuck  12  there is positioned a hollow vertical post  22  coupled to a reciprocating motor  24  via a shaft  25  which extends from the motor  24 , up through the post  22 , to connect to one end of a cantilevered assembly  26  supported on the post  22 . The other end of the cantilevered assembly  26  is provided with a brush head assembly  27  formed of a descending rod  30  having a passage extending along its vertical axis. The rod  30  carries, at its lower end, a head  32  provided with means  34  for mounting either a brush or pad  35  thereon. 
     The motor  24  is designed to move the assembly  26  in a reciprocating arcuate path across the surface of the wafer  18 , as shown by the double headed arrow  36 , and to step the assembly  26  up and down, as shown by the double headed arrow  37  so that the brush  35  can be positioned with respect to the wafer surface as required by the process. 
     When the wafer is being spun by the motor  16  turning the chuck  12 , the brush  35 , is stepped, by the motor  24 , into position so as to touch the wafer surface and then moved, by the same motor  24 , back and forth in a series of reciprocating arcuate paths across the spinning wafer surface. Because the wafer is spinning and the brush or pad is being moved across the surface of the wafer, the entire surface of the wafer will pass under the head and is thus treated as required by the process. 
     In the prior art, the assembly  26  was rigid, and therefore the amount of pressure applied by the brush  35  to the wafer surface was solely based on position of the brush  35  with respect to the wafer surface as determined by the stepping motor  24 . As is well known to the art, the stepping motor  24  moves the head assembly toward the surface of the wafer in fixed incremental steps. To assure that the head did not crush the wafer surface the prior art limited the position of the head to a preset position above where the surface the wafer was expected to be. 
     Because the stepping motor moves only with incremental steps, these limits would in some instances cause the motor to stop the head so that the brush  35  was above and not touching the wafer surface, in other cases the limits would cause the brush  35  to barely touch the wafer surface and in still other case the brush  35  would be stopped in full contact with the surface but without knowing if what pressure, if any, was being applied to the wafer surface. Thus, in the first above described case, little or no pressure would exist between the brush  35  and the wafer surface and, in the other cases, the pressure applied would be unknown. Further, in those cases where the head did contact the wafer surface if the surface was warped or undulating the applied head pressure would vary as the head passed over the warped or undulating surface. 
     If the treatment being performed required a minimum amount of pressure greater than that actually being applied, the treatment could either take substantially longer than expected or could even be ineffective. On the other hand if head was positioned such that too much pressure was applied to the wafer surface the wafer surface could be damaged. 
     Because of this uncontrolled reliance on the positioning of the head by the stepping motor the pressure applied between the head and the wafer surface was effectively uncontrollable. 
     Later techniques attempted to more accurately position the bead with respect to the wafer surface by using proximity senors such as laser beams but again, because of the limiting incremental steps imposed by the stepping motor, the pressure applied by the head arm remained unknown and indeterminable. 
     The present invention avoids these problems of the prior art by designing the assembly  26  as a yoke supported pivoting arm carrying a pivoting head assembly and a primary means for providing the brush  35  with a selected brush to wafer pressure or loading whenever the brush is placed in contact with a wafer surface. Once this primary mean has established the selected brush to wafer pressure, then whenever the stepping motor places the brush  35  anywhere within a specified distance from the wafer surface that the brush  35  will bear on the wafer surface with the known preestablished loading or pressure. 
     Still further the present invention provides secondary means which when activated, can selectively alter the loading or pressure between the brush and the wafer surface established by the primary means without disturbing the setting of the primary means that established the preload. This means that the brush to wafer loading or pressure can be altered on the fly at any time during the process and also means that when the secondary means is deactivated that the pre-loaded brush head to wafer pressure established by the primary means will automatically be restored. 
     The head assembly  26 , of the present invention, achieves these desirable results by use of a cantilevered, sectional assembly  40  maintained at a right angle to the post  22  and extending horizontally therefrom. This sectional assembly  40  comprises a yoke  41 , having a body portion  41   a  and bifurcated arms  41   b  and  41   c , and a pivoting, extended, brush head carrying, elongated bar arm  42 . Preferably both the yoke  41  and the arm  42  are made of stainless steel. This bar arm  42  is positioned between and supported in the yoke arms  41   b  and  41   c  by a pivot pin  43  passing through the center of the bar arm  42  and the end of the yoke arms,  41   b  and  41   c . Thus the bar arm  42  has a proximal end  42   a  generally positioned between the bifurcated arms  41   b  and  41   c  and a distal end extending past the ends of the bifurcated arms  41   b  and  41   c . It is of course understood that the pivot pin  43  is made such that the bar arm  42  can rotate within the yoke arms  41   b  and  41   c . The yoke body  41   a  is also provided with an opening  41   d  therein so that the yoke may be secured to the shaft  25  of the motor  24  passing up through the hollow center of the post  22 . 
     As shown in the FIGS. 1,  2 ,  3 , and  4 , the bar arm  42  has its proximal end  42   a  enclosed between the bifurcated arms  41   b  and  41   c  and its distal end  42   b  extending, i.e.; cantilevered, past the ends of the bifurcated arms  41   b  and  41   c . The distal end  42   b  of the bar arm  42  is provided with an opening  42   d  in which there is positioned a descending shaft  30  having the head  32  thereon. The top of the descending shaft  30  is connected to a cross bar  44  located in the opening  42   d . This crossbar is supported in the opening  42   d  by locating it between a pair of shoulder screws  45 . These shoulder screws  45  are designed to permit the shaft  30  to swing or pivot in the opening  42   d.    
     As especially shown in FIG. 2, the bar  42  has a first means for applying a selected force on the brush head  32  when the brush head is brought close to a wafer positioned on the chuck  12 . These first means comprise the one or more sliding weights such as weights  46   a  and  46   b  hung on the bottom of the bar  42 . Each of these weights  46   a  and  46   b  is provided with a pair of inwardly projecting ears  47  that hang in longitudinal grooves  49  positioned along the lower edge of the bar  42 . The weights  46   a  and  46   b  are further provided with screws  48   a  and  48   b  passing there through so that the weights may be locked in position anywhere along the bar  42  as will be further explained below. 
     The proximal end  42   a  of the bar arm  42  is positioned between the bifurcated arms  41   b  and  41   c  such that is beneath and spaced from a second means, such as an electromagnet  49 , for selectively altering the amount of head pressure applied by the weighs  46   a  and  46   b . The electromagnet  49  is supported a fixed height above the proximal end  30   a  of the bar arm  30  by hangers  60 , which are secured atop the yoke arms  41   b  and  41   c . Because stainless steel is nonmagnetic, it is necessary that an iron plate  42   e  be secured to the proximal end  42   a  of the bar  42 . With this plate  42   e  is in position and the electromagnet is activated the plate will be pulled up causing the distal end  42   b  of the bar  42  to press harder against the surface of the wafer  18 . If, instead of being made out of iron, the plate  42   e  is formed of magnetic material then the electromagnet can, by selecting the direction of current flow there though, be used to either attract or repel the proximal end of arm  42  and thereby increase or decrease the pressure applied by the head  32  on the wafer surface. The length of the entire head assembly  26 , i.e., the yoke  41  and the arm  42 , is, as shown in the FIG. 1, sufficient to position the head  32  over the center of the rotary chuck  12 . 
     Positioned on the distal end of the arm  42  is a “T” shaped drip arm  51  having an extended leg end  51   a  cantilevered over the brush head. This cantilevered end  51   a  supports a hose  52  coupled to a suitable source  52   a  of the fluids required in the wafer treatment process as is well known to the art. The cross bar Sib of the T shaped drip arm  51  spans across and is fixed between the bifurcated arms  41   b  and  41   c  of the yoke  41 . The extended leg of the “T” is of a length as to position the hose  52  over the port  30   a  passing along the axis of the shaft  30  such that the fluids passing through the hose  52  will be delivered through the brush  35  onto the surface of the wafer being treated, as will be discussed further below. 
     The operation of the equipment will now be described. In present day wafer treatment processes, ideal brush to wafer pressures for various steps have been established either empirically or by calculation. When the apparatus of the invention is to be used for a selected process, the brush head locking screws  50  and  51  are loosened to allow the head  32  to swing in the pivot screws  45 . The wafer chuck  14  has a special load cell plate  62  placed thereon. This plate  62  is designed to have, in its center, a load cell  63  electrically coupled to a detection meter  64  by wires  65 . The plate  62  is designed to carry the load cell  63  such that the upper surface of the load cell  63  is positioned at same height as the surface of a wafer  18  placed on the chuck  12 . The head  32  is then moved vertically so that it is placed in contact with the surface of the pressure detector or load cell  63 . Once the head  32  is in the desired position the weights  46   a  and  46   b  are moved along the arm  42  to pivot the bar  42  and establish a selected head to surface pressure. 
     For example, it has been found that, for effective cleaning of a wafer surface, a head to surface pressure of 0.75 ounces/inch 2  is especially beneficial. It is, of course, understood that for other processes a greater or lessor pressure may be required. 
     One acceptable pressure sensor that has been used for measuring the head to wafer surface pressure is a 0 to 5 pound/inch 2  load cell, model LCGC-5, sold by Omega Engineering Inc. of Stamford, Conn. This load cell is used in conjunction with a model DP25S load cell meter also sold by Omega Engineering Inc. 
     Although, for purposes of illustration and ease of description, the pressure sensor  63  is, as shown in FIG. 1, positioned adjacent the chuck  12 , in production conditions, it is preferred to use a special pressure sensor holder that can be substituted for the wafer  18  on the chuck  12 . 
     Once the desired head to wafer surface pressure has been established, by moving the weights  46   a  and  46   b , the weights are locked in position, the head raised off the surface of the pressure sensor. If the sensor is on the chuck  12  then the entire pressure sensor holder is removed off the chuck  12  and replaced thereon by the wafer that is to be treated. 
     Because the pressure sensor, whether used in the pressure sensor holder positioned on the chuck  12  or positioned adjacent the chuck  12 , has its upper surface in the same plane as the surface of a wafer  18  held in chuck  12  the brush will be, when the assembly  26  is again positioned over a wafer in the chuck as it was positioned over the pressure sensor, in contact with the wafer surface with the same force as it contacted the pressure detector  63 . 
     Thus once a wafer  18 , to be treated, is placed on the chuck  12 , the chuck is set spinning, the assembly  26  is swung over the spinning wafer and the desired fluid is passed through the hose as the brush is lowered against the wafer surface. Because this lowering of the brush is accomplished by the same stepping motor used to set the brush in position over the pressure sensor surface, the brush  35  will be positioned at the same distance from the wafer surface as it was positioned from the surface of the pressure head. Thus the brush will bear on the wafer surface with the same pressure that it bore against the pressure head, i.e., the pressure established by positioning the sliding weighs  45  and  46  on the arm  42 . In this way a known brush to wafer pressure can be established and maintained during the process steps. 
     Once the brush arm  35  is in contact with the rotating surface of the wafer  18 , the brush is moved, in the above described arcuate path, so that it will treat the entire wafer surface at the preestablished pressure. 
     If we now assume that the next process step requires an increase in the pressure applied between the brush and the wafer surface, such an increase can easily be achieved by activating the electromagnet so as to attract the iron plate  42   e . By attracting the plate  42   e  the proximal end of the arm  42  is raised and the distal end is pivoted down placing the brush against the wafer surface with greater force. 
     If it is found desirable to either increase or decrease the pressure applied between the brush and the wafer surface the iron plate  42   e  should be replaced by a fixed magnet. By so substituting a fixed magnet for the iron plate and by changing the direction and amount of current through the electromagnet  49  the applied head to surface pressure can be either increased or decreased. As is well known, when a current is passed through an electromagnet it creates magnetic forces that will either attract to or repel another adjacent magnet. In this way the fixed magnet, substituted for iron plate  42   e  can be either pulled up toward the electromagnet  49  or repelled therefrom. These forces either pull or push the proximal end  42   a  of arm  42 , positioned beneath the electromagnet, thus pivoting the distal end  42   b  in the opposite direction. By so pivoting the bar  42  around the pin  43 , the brush will be either pushed harder against the wafer thus increasing the brush to wafer surface pressure or be pulled away from the wafer surface thus reducing the brush to wafer pressure. 
     In this way the electromagnet  49  in conjunction with a magnetic plate can be used to alter the pressure between the brush head and the wafer surface established by the weights  46   a  and  46   b.    
     Once this altered pressure is no longer required, the current, applied to the electromagnet is cut off and causing the preestablished pressure created by the weights to be automatically restored. 
     This completes the description of the preferred embodiment of the invention. Since changes may be made in the above construction without departing from the scope of the invention described herein, it is intended that all the matter contained in the above description or shown in the accompanying drawings shall be interpreted in an illustrative and not in a limiting sense. Thus other alternatives and modifications will now become apparent to those skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims.