JP5183840B2 - Chemical mechanical polishing apparatus and method using cylindrical rollers - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates generally to chemical-mechanical polishing (CMP) of a semiconductor wafer surface, and more particularly to a chemical-mechanical polishing system that can achieve a desired film thickness profile on the wafer surface after polishing and Regarding the method.
[0002]
[Prior art]
A semiconductor device is manufactured by forming a circuit on a semiconductor substrate using metal wiring. Specifically, the metal wiring forms an integrated circuit by interconnecting a plurality of elements that exist discretely in the device, and is insulated from other layers using an interlayer insulating film. For electrical connection between layers, a contact hole penetrating the insulating film is formed, and electrical connection is provided through the contact hole. Recently, as the density of integrated circuits has increased due to technological advances, it has been required to increase the number of wirings and elements stacked on a semiconductor substrate.
[0003]
When metal wiring is formed on a substrate, its surface is generally roughened. However, when multiple layers are used, each layer, including interlayer insulation films and wiring, is used to accurately form contact holes and metal films to improve device yield and maintain the reliability of the final integrated circuit. Is very important.
[0004]
A chemical mechanical polishing method (CMP) is currently widely used as a process for the planarization. As an example, there is an oxide film CMP which is a step of planarizing an interlayer insulating film of an oxide film (SiO ₂ ). In an apparatus for performing CMP, a semiconductor wafer is held between a wafer carrier and a polishing cloth (pad), and the carrier and the polishing table are rotated at a predetermined rotational speed, respectively, so that the semiconductor wafer is interposed between the semiconductor wafer and the polishing pad. A polishing pressure is applied. At this time, a polishing liquid (slurry) in which solid abrasive grains (silica particles, alumina particles, cerium oxide, etc.) are dispersed in an alkaline solution is dropped and impregnated on a pad affixed on the polishing table. By performing the polishing, mechanical polishing by the abrasive grains and chemical softening of the wafer surface by the alkaline solution proceed simultaneously on the wafer surface, and the wafer surface is flattened. In the slurry, the dispersion and agglomeration state of the abrasive grains are controlled according to the abrasive grains and the material to be polished, and the components are chemically adjusted to optimize the chemical effect of the polishing. . Due to the combined chemical and mechanical effect of this polishing, excellent planarization of the polishing surface is achieved.
[0005]
FIG. 1 shows a typical apparatus configuration for performing CMP. The wafer 101 is fixed with a constant pressure 106 between the wafer carrier 102 and the polishing pad 104 on the polishing table 103. In such a configuration, actual polishing is performed by rotating both the polishing table 103 and the wafer carrier 102 while supplying the slurry 105. In CMP, three values of (1) polishing rate, (2) polishing pressure, and (3) relative velocity between the polishing table and the wafer carrier are expressed as “the polishing rate is the difference between the polishing pressure and the relative velocity. It is known that the relationship “proportional to product” holds. This relationship is called the Preston's Equation.
[0006]
[Problems to be Solved by the Invention]
Recently, a multi-zone control type wafer carrier has begun to be provided in a CMP apparatus. As one of the multi-zone control methods, different air pressures are applied to the back surface (surface opposite to the polishing surface) of the wafer according to the wafer position (zone) to generate relatively different polishing pressures. The control means that the polishing rate changes for each position on the wafer. In conventional polishing equipment where the polishing pressure is uniform across the entire wafer, the film thickness profile from the center of the wafer to the edge is similar to the film thickness profile in the film before polishing, even after polishing. The target film thickness profile may not always be properly achieved. On the other hand, in a multi-zone control type carrier capable of providing a plurality of pressures, the polishing rate is increased by applying a larger polishing pressure to a region to be polished more than a region not to be polished (from the Preston equation). Guided) better film thickness profile flattening than with single pressure wafer carriers is achieved.
[0007]
As a problem in conventional CMP, there is a phenomenon called rebound in which a convex portion is formed in a peripheral region near the edge of the wafer surface after polishing. FIG. 2A shows the principle that rebound occurs. FIG. 2B shows the rebound situation. The rebound phenomenon is caused by the fact that the wafer is elastically deformed when polishing pressure is applied to the wafer surface from the polishing pad in the vertical direction while the circumferential portion of the wafer is fixed horizontally by the wafer carrier. To do. If the rebound phenomenon occurs, the wafer flattening is naturally not achieved in that region, so the wafer region where the rebound occurs cannot be used, leading to a decrease in yield.
[0008]
In the conventional polishing method, since a large-diameter polishing pad and a wafer carrier are used, a stable high-rotation polishing process is not practically used. In addition, a high polishing pressure process is employed to ensure a certain amount of apparatus throughput. Due to this combination of high pressure / low speed, the polishing pad is severely deformed, the relative speed between the polishing pad and the carrier is lowered, and excellent flatness on the wiring is not obtained. (In general, the flatness on the device is proportional to the relative speed, but inversely proportional to the polishing pressure.)
In a general CMP apparatus, as shown in FIG. 1 and already described, a wafer carrier holding a wafer is pressed from above onto a circular turntable on which a polishing pad is installed by a vacuum chuck or the like. It is normal to perform polishing. As a polishing device with a completely different configuration, a cylindrical roller is provided on the lower surface of the wafer carrier that holds the wafer, and a polishing pad is placed on the surface, and is in contact with the wafer carrier through a narrow linear region. There has also been proposed so far that polishing is carried out by using a metal. For example, JP-A-2-269552, JP-A-7-66160, and JP-A-2000-218518 disclose a CMP apparatus having such a configuration.
[0009]
In the CMP apparatus and method according to the present invention, the polishing is performed in such a manner that different polishing rates are generated depending on the region of the wafer, as in the multi-zone control type polishing described above. However, the polishing rate is not changed by changing the polishing pressure, but the polishing rate is controlled by the cylindrical polishing pad capable of high rotation with a small diameter opening according to the present invention and the conditioning method thereof. Accordingly, it is an object of the present invention to execute a multi-zone control type CMP using a cylindrical roller to solve the problems existing in the conventional CMP.
[0010]
[Means for Solving the Problems]
According to one embodiment of the present invention, an apparatus for performing chemical mechanical polishing of a semiconductor wafer, comprising: (1) a wafer carrier for holding a semiconductor wafer to be polished with its polished surface exposed And (2) a polishing roller having a cylindrical shape and having a polishing pad affixed on the surface thereof, wherein the polishing pad is composed of a plurality of strip-like portions having different polishing characteristics along the long axis direction of the cylinder A polishing roller that is in contact with the surface to be polished of the semiconductor wafer via a line segment in the longitudinal direction of the cylinder, (3) slurry supply means, and (4) a controller. Mechanical polishing apparatus is provided. In this apparatus, the polishing roller divides the central axis of the cylinder and the length of the long axis direction of the cylinder into two, and has two axes perpendicular to the surface to be polished perpendicular to the central axis. Two rotational movements are performed as the rotating shaft, and simultaneously, a translational movement is performed over the entire surface to be polished, and polishing is performed while the slurry is supplied from the slurry supply means to the contact portion with the surface to be polished. The polishing pressure applied from the roller to the surface to be polished, the two rotational movements, and the translational movement are controlled by the controller in accordance with the target polishing.
[0011]
According to another embodiment of the present invention, a method for performing chemical mechanical polishing of a semiconductor wafer is provided. This method can also be provided in the form of a computer program stored in a computer-readable storage medium or transmitted via a communication medium. This method includes (1) a step in which a wafer carrier holds a semiconductor wafer to be polished with its polished surface exposed, and (2) a cylindrical shape having a polishing pad affixed on the surface. A polishing roller comprising a plurality of strip-like portions having different polishing characteristics along a major axis direction of the cylinder, the polishing roller being connected to a surface to be polished of the semiconductor wafer and the cylinder. (3) contacting the polishing roller with the center axis of the cylinder and the length of the cylinder in the major axis direction, and perpendicularly intersecting the center axis. Two rotational movements are performed with the axis perpendicular to the surface to be polished as two rotation axes, and at the same time, translational movement is performed over the entire surface to be polished, and a slurry is applied to the contact portion with the surface to be polished. Perform polishing while receiving supply A polishing pressure applied from the roller to the surface to be polished, the two rotational movements, and the translational movement are controlled by the controller according to a target polishing; It is constituted by.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
3 and 4 illustrate an overview of a polishing system according to the present invention. FIG. 3 is a cross-sectional view in the direction along the long axis of the cylindrical roller, and FIG. 4 is a cross-sectional view in the direction orthogonal to the long axis.
[0013]
As shown in FIG. 3, a wafer 301 to be polished is placed on a wafer carrier 303. The device side (surface to be polished) faces upward, and on the opposite side is a backing film 302, which is held via a vacuum hole provided in the wafer carrier 303 and the backing film 302. The roller is, for example, a hollow metal rod. The rod is provided with a plurality of slurry holes, and the slurry is supplied to the pad surface via these slurry holes. The slurry can be supplied from an external source according to the actual situation of polishing, rather than being supplied via the pad. This external source is shown in the figure as tube 306 external to the roller pad device. For example, in JP-A-7-66160 and JP-A-2000-218518 cited above, the slurry is supplied to the polishing surface through holes provided on the roller surface rather than dropping the slurry from above the polishing surface. Thus, there are described effects such as that the slurry is evenly distributed over the entire wafer, and that it is possible to prevent the polishing from proceeding due to the hydroplane phenomenon. However, the supply mode of the slurry is not a characteristic part of the present invention, and since such contents are well known to those skilled in the art, further details are omitted.
[0014]
In FIGS. 3 and 4, the wafer carrier is shown on the lower side and the polishing roller is shown on the upper side. However, this is merely an example, and the positional relationship shown in FIG. Is not important to the apparatus and method. Therefore, it can be rotated 90 degrees or rotated 180 degrees and turned upside down. However, when the top and bottom are reversed, there is a possibility that some consideration may be necessary for the supply mode of the slurry. This is because, unlike conventional polishing in which the surfaces are in contact with each other, some technique may be required to appropriately supply the slurry to the straight portion where the polishing occurs.
[0015]
The polishing pad 304 affixed to the surface of the cylindrical roller may be a single polishing pad, or may be a stack composed of two layers having different materials and compressibility. This pad or pad stack is deposited on a roller to form a polishing pad. A roller having a polishing pad affixed to its surface is disposed above the wafer carrier and performs CMP of the wafer by descending and rotating. It is important that the length of the cylindrical roller in the major axis direction does not exceed the diameter of the wafer. This length feature of the roller allows the polishing pad having different polishing characteristics to be pressed against different areas of the wafer according to the position of the roller by moving the roller two-dimensionally on the wafer surface. It is. Also, in order to reduce the rebound phenomenon described above, it is important that the roller does not protrude from the wafer edge, and that it takes only a short time to protrude.
[0016]
On the roller, a film having pad conditioning abrasive grains attached to a pad conditioning cover is attached. This film is divided into a plurality of strip-like portions parallel to each other along the major axis direction, and the abrasive particles and density are different in each portion, and therefore the polishing characteristics are different. These portions are shown in FIG. 3 as dressers n, n + 1, n + 2, n + 3. Of course, it may be divided into more parts than the four parts shown in FIG. 3, or may be divided into, for example, three parts smaller than that. The polishing characteristics at each portion can be set so that the user can obtain a target film thickness profile according to the purpose of polishing.
[0017]
When polishing is commanded, the wafer carrier 303 starts rotating at a speed set by the user. At this time, a straight line AA (FIG. 3) that is the center of the wafer carrier becomes a rotation axis. The roller 304 with the polishing pad attached to the surface rotates around the center line BB of the cylinder (FIG. 3) as the rotation axis while applying a polishing pressure set by the user downward with respect to the wafer surface. Run. The wafer surface and the roller come into contact via a line segment corresponding to the length of the roller. While the roller is in contact with the wafer via a line segment, the entire wafer surface is polished to achieve flatness while performing a translational movement in the X-axis direction and the Y-axis direction over the entire wafer surface. Make two rotational movements. The two rotational movements are a rotation about the central axis B-B of the roller in the horizontal direction and a rotation about the vertical axis AA at the center of the roller pad device. The rotational speed and the linear speed can all be set by the user according to the purpose of polishing. All of the rotation axes are shown in FIGS.
[0018]
When the wafer is polished, conditioner strips with different particle sizes and densities for portions n, n + 1, n + 2, n + 3 condition the pad surface. Due to the varying nature of the conditioning material from part to part of the roller pad 304, the pad surface has different polishing properties and therefore the polishing rate varies from part to part. By using such a method, the polishing rate on the wafer surface can be adjusted according to the thickness profile of the wafer before polishing, and a desired thickness profile can be generated after polishing.
[0019]
As described above, the roller 304 in charge of polishing rotates in two directions and simultaneously performs a two-dimensional translation movement over the entire wafer surface. These complex movements of the roller 304 are controlled by a controller (not shown) built into the polishing apparatus of the present invention. In conventional CMP, the number of control parameters related to polishing is very small. However, in the polishing apparatus according to the present invention, the number of control parameters is dramatically increased because the roller itself to which a pad having a plurality of different polishing characteristics is attached moves in a complicated manner. If the number of control parameters increases, it becomes possible to cope with various polishing required at present and in the future.
[0020]
The adjustment of conditioning in the polishing method according to the present invention will be supplemented. Combinations of conditioning abrasive grains, density, and the like are experimentally determined according to the film thickness profile in the wafer surface. Experiments with conditioning abrasives and density as factors if we know the various conditions (various habits such as thick, thin, almost flat on the entire surface) of the equipment used for the formation of the insulating film (deposition) This will determine the polishing conditioning process. In this case, if the deposition apparatus is unstable, a variety of conditioning strips must be prepared.
[0021]
【Effect of the invention】
When the polishing method according to the present invention is used, the rebound phenomenon can be reduced. The reason is as follows. As long as the wafer edge is polished, it is impossible to avoid rebounding completely. In particular, in the conventional polishing technique, since the polishing pad is larger than the wafer (including the carrier), it protrudes from the wafer edge, and the wafer edge is polished with the protruding pad portion remaining deformed. Therefore, the occurrence of rebound was remarkable. In contrast, in the polishing according to the present invention, by appropriately controlling the movement of the roller pad in the X-axis and Y-axis directions, the time when the pad does not protrude from the edge of the wafer or protrudes can be shortened. Therefore, rebound can be reduced.
[0022]
Further, according to the polishing method of the present invention, the polishing time can be shortened. The reason is as follows. First, according to the Preston equation described above, the amount of cutting is proportional to the product of pressure and relative speed. Since the roller pad according to the present invention is smaller than the conventional polishing pad, it can be adjusted to high rotation. Accordingly, the relative speed increases, the amount of cutting per unit time increases even when the pressure is the same, and the polishing time can be shortened.
[0023]
A significant feature of the present invention is that the user can achieve the desired flatness and film thickness profile by combining a roller pad having two rotational axes and pad processing using multiple types of conditioning abrasives. It is. As the number of layers formed on a wafer substrate increases, the surface profile of the surface to be polished before polishing can become increasingly diverse. Therefore, in order to realize planarization on the premise of such various profiles, it is necessary to provide different polishing rates for each region of the wafer.
[0024]
In such a case, by using the polishing apparatus and method according to the present invention, it is possible to provide a wide variety of polishing rates by performing polishing while appropriately controlling many parameters. The surface to be polished can be appropriately handled. With the apparatus and method according to the present invention, it is possible to polish only the area that needs to be polished on the wafer, so that excessive polishing does not occur and the cost of consumables such as slurry can be minimized. It is.
[0025]
Furthermore, according to the apparatus and method of the present invention, excellent flattening on the wiring can be obtained by high relative speed polishing, the DOF margin in photolithography can be expanded, and the flatness of the laminated metal can be improved. And excessive etching can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic of a general CMP apparatus according to the prior art.
FIG. 2 is an example of a rebound phenomenon that occurs at an edge portion of a wafer.
FIG. 3 is a sectional view of a polishing apparatus according to the present invention.
FIG. 4 is a sectional view from another direction of the polishing apparatus according to the present invention.

Claims (4)

An apparatus for performing chemical mechanical polishing of a semiconductor wafer,
A wafer carrier for holding a semiconductor wafer to be polished with its polished surface exposed;
A polishing roller having a cylindrical shape and having a polishing pad affixed on a surface thereof, wherein the polishing pad is composed of a plurality of band-shaped portions having different polishing characteristics along the long axis direction of the cylinder, and the semiconductor wafer A polishing roller that is in contact with the surface to be polished via a line segment in the lengthwise direction of the cylinder,
Slurry supply means;
A controller,
The polishing roller divides the central axis of the cylinder and the length of the long axis direction of the cylinder into two, and two axes perpendicular to the surface to be polished perpendicular to the central axis. While performing two rotational movements as a rotation shaft , simultaneously performing the two rotational movements, performing a translational movement over the entire surface to be polished, while receiving slurry from the slurry supply means to the contact portion with the surface to be polished The polishing pressure applied from the roller to the surface to be polished, the two rotational movements, and the translational movement are controlled by the controller in accordance with the target polishing. Chemical mechanical polishing equipment. A method for performing chemical mechanical polishing of a semiconductor wafer, comprising:
A wafer carrier holding a semiconductor wafer to be polished with its polished surface exposed;
A polishing roller having a cylindrical shape and having a polishing pad affixed on the surface thereof, wherein the polishing pad is composed of a plurality of belt-like portions having different polishing characteristics along the long axis direction of the cylinder Contacting the surface to be polished of the semiconductor wafer with a line segment in the longitudinal direction of the cylinder, and
The polishing roller is divided into two rotation axes with a center axis of the cylinder and a length in the major axis direction of the cylinder divided into two, and an axis perpendicular to the surface to be polished perpendicular to the center axis. Performing a rotational movement, simultaneously with the two rotational movements, performing a translational movement over the entire surface to be polished, and performing polishing while receiving a supply of slurry to the contact portion with the surface to be polished, A polishing pressure applied from a roller to the surface to be polished, the two rotational movements, and the translational movement are controlled by the controller according to a target polishing;
A chemical mechanical polishing method comprising: A computer-readable storage medium storing a computer program comprising instructions for causing a computer to execute the steps included in the method according to claim 2 . A computer program comprising instructions for causing a computer to execute the steps included in the method according to claim 2 .

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