Patent Publication Number: US-2020298365-A1

Title: Polishing apparatus and polishing method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-052786, filed on Mar. 20, 2019, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a polishing apparatus and a polishing method. 
     BACKGROUND 
     Chemical mechanical polishing (CMP) is a method for polishing the face of a substrate. In CMP, a polishing agent is supplied onto a rotating turntable, and then a substrate being rotated is pressed against a polishing pad provided on the turntable in order to polish the face of the substrate. The face of the substrate is thus chemically and mechanically polished and planarized. 
     In CMP, the polishing rate sometimes differs between the central area and the circumferential area of a substrate, which may cause nonuniform polishing of the face of the substrate. Under the circumstances, a method for adjusting the polishing rate across the face of a substrate has been required. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are schematic diagrams of a polishing apparatus according to a first embodiment; 
         FIG. 2  is a schematic diagram of a polishing apparatus according to a second embodiment; and 
         FIG. 3  is a schematic diagram of a polishing apparatus according to a third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A polishing apparatus according to an embodiment includes a polishing table; a polishing pad provided on the polishing table; a first rotating mechanism configured to rotate the polishing table on a first rotation axis; a substrate holding unit configured to hold a substrate and press the substrate against the polishing pad; a second rotating mechanism configured to rotate the substrate holding unit on a second rotation axis; and a tilting mechanism configured to change the angle between the first rotation axis and the second rotation axis. In the apparatus, the circumferential edge of the substrate is always kept inside the circumferential edge of the polishing pad during polishing of the substrate. 
     With reference to the drawings, embodiments of the disclosure will now be described. In the following description, the same or similar components are provided with the same reference numerals and repeated description of the same or similar components may be omitted. 
     With reference to the drawings, polishing apparatuses and polishing methods according to embodiments will now be described. 
     First Embodiment 
     A polishing apparatus according to a first embodiment includes a polishing table; a polishing pad provided on the polishing table; a first rotating mechanism configured to rotate the polishing table on a first rotation axis; a substrate holding unit configured to hold a substrate and press the substrate against the polishing pad; a second rotating mechanism configured to rotate the substrate holding unit on a second rotation axis; and a tilting mechanism configured to change the angle between the first rotation axis and the second rotation axis. In the apparatus, the circumferential edge of the substrate is always kept inside the circumferential edge of the polishing pad during polishing of the substrate. 
     A polishing method according to a first embodiment includes rotating a polishing pad on a first rotation axis; and pressing a substrate rotating on a second rotation axis tilted with respect to the first rotation axis, against the polishing pad to polish the substrate while always keeping the circumferential edge of the substrate inside the circumferential edge of the polishing pad. 
       FIGS. 1A and 1B  are schematic diagrams of the polishing apparatus according to the first embodiment.  FIG. 1A  is a side view of the polishing apparatus and  FIG. 1B  is a top view of the polishing apparatus. The polishing apparatus of the first embodiment is a CMP apparatus  100  configured to polish the face of a substrate such as a semiconductor wafer. 
     The CMP apparatus  100  of the first embodiment includes a turntable  10  (the polishing table), a polishing pad  12 , a first supporting shaft  14 ; a first rotating mechanism  18 , a top ring  20  (the substrate holding unit), a second supporting shaft  22 , a second rotating mechanism  24 , a top ring tilting mechanism  26  (the tilting mechanism), and a polishing agent supplying nozzle  28 . 
     The turntable  10  rotates on a first rotation axis RA 1 . The turntable  10  rotates on its own axis that is the first rotation axis RA 1 . The turntable  10  is an example of the polishing table. 
     The polishing pad  12  is provided on the turntable  10 . The polishing pad  12  is fixed on the turntable  10 . As in the turntable  10 , the polishing pad  12  rotates on the first rotation axis RA 1 . The polishing pad  12  rotates in the circumferential direction. 
     The polishing pad  12  is an elastic body. The polishing pad  12  contains resin or nonwoven fabric, for example. The polishing pad  12  is made of polyurethane resin, for example. 
     The first supporting shaft  14  supports the turntable  10  at the center of the turntable  10 . 
     The first rotating mechanism  18  is designed to rotate the turntable  10 . The first rotating mechanism  18  rotates the first supporting shaft  14 . The first rotating mechanism  18  includes a motor, and a bearing configured to rotatably hold the first supporting shaft  14 , for example. 
     The top ring  20  is designed to hold a semiconductor wafer W to be polished. The top ring  20  is designed to press the semiconductor wafer W being held against the polishing pad  12 . 
     The top ring  20  rotates on a second rotation axis RA 2 . The top ring  20  rotates on the second rotation axis RA 2 . As in the top ring  20 , the semiconductor wafer W held by the top ring  20  rotates on the second rotation axis RA 2 . The top ring  20  is an example of the substrate holding unit. 
     The second supporting shaft  22  supports the top ring  20  at the center of the top ring  20 . 
     The second rotating mechanism  24  is designed to rotate the top ring  20 . The second rotating mechanism  24  rotates the second supporting shaft  22 . The second rotating mechanism  24  includes a motor, and a bearing configured to rotatably hold the second supporting shaft  22 , for example. 
     The first rotating mechanism  18  and the second rotating mechanism  24  rotate the turntable  10  and the top ring  20 , respectively, in one direction. In  FIGS. 1A and 1B , for example, both the turntable  10  and the top ring  20  rotate in the counterclockwise direction. 
     The top ring tilting mechanism  26  is designed to change the angle between the first rotation axis RA 1  and the second rotation axis RA 2  (the angle θ in  FIG. 1A ) for polishing of the semiconductor wafer W. The top ring tilting mechanism  26  supports the second rotating mechanism  24 , for example. The top ring tilting mechanism  26  is designed to fix the angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  at a constant angle during polishing of the semiconductor wafer W. 
     The top ring tilting mechanism  26  moves the top ring  20 , the second supporting shaft  22 , and the second rotating mechanism  24  using a motor, for example, and tilts these components with respect to the vertical direction. 
     The top ring tilting mechanism  26  is designed to change the angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  within the range of 0° to 5°, for example. 
     The top ring tilting mechanism  26  is designed to tilt the second supporting shaft  22  by an angle θ with respect to the vertical direction, for example. Tilting the second supporting shaft  22  changes the inclination of the second rotation axis RA 2 . 
     Tilting the second supporting shaft  22  tilts the face of the semiconductor wafer W being polished by the angle θ with respect to the face of the turntable  10 . This makes the face of the semiconductor wafer W being polished not in parallel with the face of the turntable  10 . 
     The polishing agent supplying nozzle  28  is designed to supply slurry onto the face of the polishing pad  12 . The slurry contains abrasive grains. The abrasive grains are particles containing silicon oxide, aluminum oxide, or cerium oxide, for example. 
     The CMP apparatus  100  is configured to polish the semiconductor wafer W while always keeping the circumferential edge of the semiconductor wafer W (shown by We in  FIG. 1B ) inside the circumferential edge of the polishing pad  12  (shown by  12   e  in  FIG. 1B ). 
     In the CMP apparatus  100 , the first rotation axis RA 1  of the turntable  10  and the second rotation axis RA 2  of the top ring  20  do not move relative to each other during polishing of the semiconductor wafer W. In the CMP apparatus  100 , the relative position of the turntable  10  and the top ring  20  does not change during polishing of the semiconductor wafer W. Also, the relative position of the first supporting shaft  14  and the second supporting shaft  22  does not change during polishing of the semiconductor wafer W. 
     The CMP method according to the first embodiment will now be described. A case where the CMP apparatus  100  of the first embodiment is used will be described as an example. 
     In the CMP method of the first embodiment, the face of the semiconductor wafer W is polished and planarized. The semiconductor wafer W to be polished has a circuit pattern formed by repeated layer deposition and etching of the film, for example. The semiconductor wafer W to be polished has at least one of a dielectric film and a conductive film exposed on its face. 
     First, the semiconductor wafer W is put into the CMP apparatus  100 . 
     The turntable  10  is then rotated on the first rotation axis RA 1  by the first rotating mechanism  18 . The polishing pad  12 , which is fixed on the turntable  10 , is also rotated on the first rotation axis RA 1 . 
     The polishing agent supplying nozzle  28  is then operated to supply slurry onto the face of the polishing pad  12 . 
     The face of the semiconductor wafer W held by the top ring  20  is then pressed against the polishing pad  12 . The top ring  20  is rotated on the second rotation axis RA 2  by the second rotating mechanism  24 . The semiconductor wafer W, which is held by the top ring  20 , is also rotated on the second rotation axis RA 2 . 
     The top ring tilting mechanism  26  tilts the second supporting shaft  22  by an angle θ with respect to the vertical direction. The second rotation axis RA 2  is tilted by the angle θ with respect to the first rotation axis RA 1 . The second rotation axis RA 2  is tilted by the angle θ with respect to the vertical direction. 
     Tilting the second supporting shaft  22  tilts the face of the semiconductor wafer W by the angle θ with respect to the face of the turntable  10 . This makes the face of the semiconductor wafer W not in parallel with the face of the turntable  10 . 
     While the face of the semiconductor wafer W is kept not in parallel with the face of the turntable  10 , the semiconductor wafer W is pressed against the polishing pad  12 . The face of the semiconductor wafer W is thus polished while the face of the semiconductor wafer W is kept not in parallel with the face of the turntable  10 . 
     The angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  is more than 0° and equal to or less than 5°, for example. The angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  is fixed at a constant angle during polishing. 
     After the face of the semiconductor wafer W has been polished, the supply of slurry onto the polishing pad  12  is stopped. The semiconductor wafer W is then taken out of the CMP apparatus  100 . 
     The functions and effects of the CMP apparatus  100  and the CMP method of the first embodiment will now be described. 
     In CMP, a polishing agent is supplied onto a rotating turntable, and then a semiconductor wafer being rotated is pressed against a polishing pad provided on the turntable in order to polish the face of the semiconductor wafer. The face of the semiconductor wafer is thus chemically and mechanically polished and planarized. 
     The rotation axis of the turntable and the rotation axis of the semiconductor wafer W are generally kept in parallel with each other so that the face of the semiconductor wafer W is uniformly polished. In other words, the face of the semiconductor wafer W and the face of the turntable  10  are kept in parallel with each other during polishing. 
     However, there is a case where the polishing rate differs between the central area and the circumferential area of the semiconductor wafer W and the face of the semiconductor wafer W may be polished nonuniformly. For example, there is a case where the polishing rate in the central area of the semiconductor wafer W is higher than the polishing rate in the circumferential area of the semiconductor wafer W. The difference in the polishing rate is thought to be caused depending on the type of the film and the pattern formed on the face of the semiconductor wafer W. 
     The CMP apparatus  100  of the first embodiment includes the top ring tilting mechanism  26 . The top ring tilting mechanism  26  is designed to change the angle between the first rotation axis RA 1  and the second rotation axis RA 2  (the angle θ in  FIG. 1A ) for polishing of the semiconductor wafer W. 
     The top ring tilting mechanism  26  keeps the face of the semiconductor wafer W not in parallel with the face of the turntable  10  during polishing of the face of the semiconductor wafer W. Keeping the face of the semiconductor wafer W not in parallel with the face of the turntable  10  causes different forces for pressing the semiconductor wafer W against the polishing pad  12  across the face of the semiconductor wafer W. The force for pressing the semiconductor wafer W against the polishing pad  12  is greater in the circumferential area of the semiconductor wafer W than in the central area of the semiconductor wafer W. Accordingly, the polishing rate in the circumferential area of the semiconductor wafer W becomes higher than the polishing rate in the central area of the semiconductor wafer W. 
     The top ring tilting mechanism  26  enables adjustment of the polishing rate across the face of the semiconductor wafer W. 
     For example, the face of the semiconductor wafer W can be polished uniformly by fixing the angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  at an appropriate angle depending on the type of the film and the pattern formed on the face of the semiconductor wafer W. For example, fixing the angle θ at a large angle will make the polishing rate in the circumferential area of the semiconductor wafer W higher than the polishing rate in the central area of the semiconductor wafer W. 
     The top ring tilting mechanism  26  should preferably change the angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  within the range of 0° to 5°. There is a case where uniform polishing is achieved at an angle θ of 0°. An angle θ more than 50 makes uniform polishing difficult irrespective of the type of the film and the pattern. During polishing of the semiconductor wafer W, the angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  should preferably be more than 0° and equal to or less than 5°, more preferably equal to or more than 0.5° and equal to or less than 5°, and much more preferably equal to or more than 1° and equal to or less than 4°, for example. 
     The face of the semiconductor wafer W can be polished uniformly by always keeping the circumferential edge of the semiconductor wafer W inside the circumferential edge of the polishing pad  12  during polishing of the semiconductor wafer W. 
     In view of uniform polishing of the face of the semiconductor wafer W, the relative position of the first rotation axis RA 1  of the turntable  10  and the second rotation axis RA 2  of the top ring  20  should preferably be fixed. In other words, the relative position of the first supporting shaft  14  and the second supporting shaft  22  should preferably be fixed during polishing of the semiconductor wafer W. 
     In view of uniform polishing of the face of the semiconductor wafer W, the turntable  10  and the top ring  20  should preferably be rotated in one direction. 
     As described above, the first embodiment provides the polishing apparatus and the polishing method that can adjust the polishing rate across the face of the semiconductor wafer W by keeping the face of the semiconductor wafer W not in parallel with the face of the turntable  10 . The apparatus and the method thus enable uniform polishing of the face of the semiconductor wafer W. 
     Second Embodiment 
     The polishing apparatus of the second embodiment differs from that of the first embodiment in that the tilting mechanism changes the inclination of the first rotation axis instead of the inclination of the second rotation axis. In the following, the description overlapping with the description of the polishing apparatus and the polishing method of the first embodiment will partly be omitted. 
       FIG. 2  is a schematic diagram of a polishing apparatus according to the second embodiment.  FIG. 2  is a side view of the polishing apparatus. The polishing apparatus of the second embodiment is a CMP apparatus  200  configured to polish the face of a substrate such as a semiconductor wafer. 
     The CMP apparatus  200  of the second embodiment includes the turntable  10  (the polishing table), the polishing pad  12 , the first supporting shaft  14 , the first rotating mechanism  18 , the top ring  20  (the substrate holding unit), the second supporting shaft  22 , the second rotating mechanism  24 , a turntable tilting mechanism  27  (the tilting mechanism), and the polishing agent supplying nozzle  28 . 
     The turntable tilting mechanism  27  is designed to change the angle between the first rotation axis RA 1  and the second rotation axis RA 2  (the angle θ in  FIG. 2 ) for polishing the semiconductor wafer W. The turntable tilting mechanism  27  supports the first rotating mechanism  18 , for example. The turntable tilting mechanism  27  is designed to fix the angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  at a constant angle during polishing of the semiconductor wafer W. 
     The turntable tilting mechanism  27  tilts the turntable  10 , the first supporting shaft  14 , and the first rotating mechanism  18  using an oil pressure mechanism, for example, with respect to the vertical direction. 
     The turntable tilting mechanism  27  is designed to change the angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  within the range of 0° to 5°, for example. 
     The turntable tilting mechanism  27  is designed to tilt the first supporting shaft  14  by an angle θ with respect to the vertical direction, for example. Tilting the first supporting shaft  14  changes the inclination of the first rotation axis RA 1 . 
     Tilting the first supporting shaft  14  tilts the face of the turntable  10  by the angle θ with respect to the face of the semiconductor wafer W being polished. This makes the face of the semiconductor wafer W being polished not in parallel with the face of the turntable  10 . 
     A CMP method according to the second embodiment will now be described. A case where the CMP apparatus  200  of the second embodiment is used will be described as an example. 
     First, the semiconductor wafer W is put into the CMP apparatus  200 . 
     The turntable tilting mechanism  27  tilts the first supporting shaft  14  by an angle θ with respect to the vertical direction. The first rotation axis RA 1  is tilted by the angle θ with respect to the second rotation axis RA 2 . The first rotation axis RA 1  is tilted by the angle θ with respect to the vertical direction. 
     The turntable  10  is then rotated on the first rotation axis RA 1  by the first rotating mechanism  18 . The polishing pad  12 , which is fixed on the turntable  10 , is also rotated on the first rotation axis RA 1 . 
     The polishing agent supplying nozzle  28  is then operated to supply slurry onto the face of the polishing pad  12 . 
     The face of the semiconductor wafer W held by the top ring  20  is then pressed against the polishing pad  12 . The top ring  20  is rotated on the second rotation axis RA 2  by the second rotating mechanism  24 . The semiconductor wafer W, which is held by the top ring  20 , is also rotated on the second rotation axis RA 2 . 
     While the face of the semiconductor wafer W is kept not in parallel with the face of the turntable  10 , the semiconductor wafer W is pressed against the polishing pad  12 . The face of the semiconductor wafer W is thus polished while the face of the semiconductor wafer W is kept not in parallel with the face of the turntable  10 . 
     The angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  is more than 0° and equal to or less than 5°, for example, and fixed at a constant angle during polishing. 
     After the face of the semiconductor wafer W has been polished, the supply of slurry onto the polishing pad  12  is stopped. The semiconductor wafer W is then taken out of the CMP apparatus  200 . 
     As described above, the second embodiment provides the polishing apparatus and the polishing method that can adjust the polishing rate across the face of the semiconductor wafer W by keeping the face of the semiconductor wafer W not in parallel with the face of the turntable  10 , as in the first embodiment. The apparatus and the method thus enable uniform polishing of the face of the semiconductor wafer W. 
     Third Embodiment 
     The polishing apparatus of the third embodiment differs from that of the first embodiment in that the apparatus further includes a control unit configured to control the tilting mechanism and change the angle between the first rotation axis and the second rotation axis during polishing of the substrate. In the following, the description overlapping with the description of the polishing apparatus and the polishing method of the first embodiment will partly be omitted. 
       FIG. 3  is a schematic diagram of a polishing apparatus according to the third embodiment.  FIG. 3  is a side view of the polishing apparatus. The polishing apparatus of the third embodiment is a CMP apparatus  300  configured to polish the face of a substrate such as a semiconductor wafer. 
     The CMP apparatus  300  of the third embodiment includes: the turntable  10  (the polishing table); the polishing pad  12 ; the first supporting shaft  14 ; the first rotating mechanism  18 ; the top ring  20  (the substrate holding unit); the second supporting shaft  22 ; the second rotating mechanism  24 ; the top ring tilting mechanism  26  (the tilting mechanism); the polishing agent supplying nozzle  28 ; and a tilting mechanism controlling unit  30  (the control unit). 
     The tilting mechanism controlling unit  30  controls the top ring tilting mechanism  26 . The tilting mechanism controlling unit  30  is designed to control the top ring tilting mechanism  26  and change the angle between the first rotation axis RA 1  and the second rotation axis RA 2  (the angle θ in  FIG. 3 ) during polishing of the semiconductor wafer W. 
     The tilting mechanism controlling unit  30  is hardware such as a circuit board, or a combination of such hardware and software such as a control program stored in the hardware and a memory, for example. 
     A CMP method according to the third embodiment will now be described. A case where the CMP apparatus  300  of the third embodiment is used will be described as an example. 
     First, the semiconductor wafer W is put into the CMP apparatus  300 . 
     The turntable  10  is then rotated on the first rotation axis RA 1  by the first rotating mechanism  18 . The polishing pad  12 , which is fixed on the turntable  10 , is also rotated on the first rotation axis RA 1 . 
     The polishing agent supplying nozzle  28  is then operated to supply slurry onto the face of the polishing pad  12 . 
     The face of the semiconductor wafer W held by the top ring  20  is then pressed against the polishing pad  12 . The top ring  20  is rotated on the second rotation axis RA 2  by the second rotating mechanism  24 . The semiconductor wafer W, which is held by the top ring  20 , is also rotated on the second rotation axis RA 2 . 
     The top ring tilting mechanism  26  keeps the second supporting shaft  22  in parallel with the vertical direction. In other words, the top ring tilting mechanism  26  keeps the second rotation axis RA 2  in parallel with the first rotation axis RA 1 . The angle between the first rotation axis RA 1  and the second rotation axis RA 2  (the angle θ in  FIG. 3 ) is 0°. The face of the semiconductor wafer W and the face of the turntable  10  are kept in parallel with each other during polishing. 
     After the face of the semiconductor wafer W has been polished for a predetermined period of time, the tilting mechanism controlling unit  30  controls the top ring tilting mechanism  26  to tilt the second supporting shaft  22  with respect to the vertical direction. The second rotation axis RA 2  is tilted by an angle θ (θ&gt;0°) with respect to the first rotation axis RA 1 . The second rotation axis RA 2  is tilted by the angle θ with respect to the vertical direction. 
     The second supporting shaft  22  is tilted while the turntable  10  is being rotated. 
     Tilting the second supporting shaft  22  tilts the face of the semiconductor wafer W by the angle θ with respect to the face of the turntable  10 . This makes the face of the semiconductor wafer W not in parallel with the face of the turntable  10 . 
     While the face of the semiconductor wafer W is kept not in parallel with the face of the turntable  10 , the semiconductor wafer W is pressed against the polishing pad  12 . The face of the semiconductor wafer W is polished for a predetermined period of time while the face of the semiconductor wafer W is kept not in parallel with the face of the turntable  10 . 
     After the face of the semiconductor wafer W has been polished, the supply of slurry onto the polishing pad  12  is stopped. The semiconductor wafer W is then taken out of the CMP apparatus  300 . 
     According to the CMP method of the third embodiment, a first polishing step in which the face of the semiconductor wafer W is kept in parallel with the face of the turntable  10  is followed, without a break, by a second polishing step in which the face of the semiconductor wafer W is kept not in parallel with the face of the turntable  10 . The polishing rate in the circumferential area of the semiconductor wafer W is higher in the second polishing step than in the first polishing step. 
     According to the CMP apparatus  300  and the CMP method of the third embodiment, the polishing rate across the face of the semiconductor wafer W can minutely be adjusted by changing the angle between the first rotation axis RA 1  and the second rotation axis RA 2  (the angle θ in  FIG. 3 ) during polishing. The apparatus and the method thus further facilitate uniform polishing of the face of the semiconductor wafer W. In addition, since the angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  is changed without a break during polishing, the throughput in the polishing process is improved compared to the case with a break between two polishing steps, for example. 
     In the above CMP method, the angle θ between the first rotation axis RA 1  and the second rotation axis RA 2  is changed from an angle θ of 0θ in the first polishing step to an angle θ more than 0° in the second polishing step. The CMP method, however, is not limited to this example. For example, the method may include a first polishing step with an angle θ more than 0° and a second polishing step with an angle θ of 0°. Alternatively, the method may include a first polishing step with an angle θ more than 0° and a second polishing step with an angle θ more than the angle θ of the first polishing step. Alternatively, the method may include a third polishing step with an angle θ different from those of first and second polishing steps. Alternatively, the method may include a first polishing step with an angle θ, a second polishing step with an angle θ more than the angle θ of the first polishing step, and a third polishing step with an angle θ less than the angle θ of the second polishing step. 
     As described above, the third embodiment provides the polishing apparatus and the polishing method that can adjust the polishing rate across the face of the semiconductor wafer W by keeping the face of the semiconductor wafer W not in parallel with the face of the turntable  10 , as in the first embodiment. The apparatus and the method thus enable uniform polishing of the face of the semiconductor wafer W. In addition, the apparatus with the control unit enables minute adjustment of the polishing rate across the face of the semiconductor wafer W. The apparatus and the method thus further facilitate uniform polishing of the face of the semiconductor wafer W. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the polishing apparatuses and the polishing methods described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatuses and methods described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.