JP2004505435A - Orbital polishing equipment - Google Patents

Abstract

The present invention is an apparatus and a method for planarizing the front surface of a wafer. The invention includes a hard platen (221) for supporting the polishing pad (207), which is connected to a support having means for orbiting the platen, or connected to said means for orbiting. . The carrier (215) is preferably a front reference carrier having a plurality of individually controllable pressure zones (204, 228), wherein the carrier supports the polishing pad (207) while orbiting the hard platen. It can be used to hold and press a wafer. The planarization step can be further optimized by orbiting the polishing pad with a radius of less than 4 mm and / or orbiting the polishing pad at a rate of greater than 400 revolutions / minute.

Description

[0001]
(Industrial applications)
The present invention relates generally to semiconductor manufacturing, and more particularly to the field of chemical mechanical polishing (CMP) methods and polishing equipment for planarizing and removing thin films used in semiconductor manufacturing.
[0002]
(Conventional technology)
Flat disks, or wafers, of single crystal silicon are the substrate materials on which integrated circuits are made in the semiconductor industry. Semiconductor wafers are typically made by growing single crystal silicon in a long cylindrical or bowl shape, and then slicing the cylinder into individual wafers. Due to this slicing, both surfaces of the wafer become extremely rough. The front side of the wafer, on which the integrated circuits are fabricated, must be extremely flat to achieve a highly reliable semiconductor bond with each layer of material later provided on the wafer. Also, during the construction of integrated circuit interconnects, the material layers provided on the wafer (usually metal for conductors, and oxides for insulators) are deposited to a uniform thickness. Must be made.
[0003]
Integrated circuits manufactured today consist of literally millions of active elements, such as transistors and capacitors formed in a semiconductor substrate. Integrated circuits rely on advanced metallization systems to connect active devices to functional circuits. FIG. 1 illustrates a typical multilayer interconnect 100. Active devices such as MOS transistors 107 are formed on a silicon substrate or in the well 102. SiO ₂ An interlayer dielectric (ILD) 104 such as is formed over the silicon substrate 102. ILD 104 is used to electrically isolate a first level of metallization, typically aluminum, from active devices formed in substrate 102. Metallized contacts 106 electrically couple active devices formed in substrate 102 with first level metallization interconnects 108. In a similar manner, metal via 112 electrically couples second level metallization interconnect 114 with first level metallization interconnect 108. Contacts 106 and vias 112 typically comprise a metal 116, such as tungsten (W), surrounded by a barrier layer metal 118, such as titanium nitride (TiN). Further, the ILD / contact and the metallization layer can be stacked on top of each other to achieve the desired interconnect.
[0004]
Planarization is a process that removes protrusions and other defects, both locally and globally, to create a planar planar surface, and / or removes material to achieve a uniform thickness of the deposited thin film layer on the wafer. It is to remove. After the semiconductor wafer has been planarized or polished to achieve a smooth and flat finish, the process steps for making integrated circuits or interconnects on the wafer are performed. A significant portion of the effort to manufacture modern complex, high density, multi-layer interconnects is spent on planarizing individual layers of the interconnect structure. If the surface is not flat, the optical resolution in the subsequent photolithography process will be poor. Poor optical resolution hinders printing of dense lines. Another problem associated with uneven surface shapes is the step coverage of subsequently formed metallization layers. If the step is too large, there is a serious problem that an open circuit (open circuit) occurs. The fabrication of modern high-density integrated circuits requires a flat interconnect surface layer. For this reason, CMP tools have been developed for adjusting the planarization of both structured and unstructured wafers.
[0005]
In a conventional CMP tool for planarizing a wafer, the wafer is held in a carrier connected to a shaft. The shaft is typically connected to mechanical means for transporting the wafer between a loading or unloading station and a location adjacent to a polishing pad mounted on a platen. Pressure is applied to the backside of the wafer via the carrier to press the wafer against the polishing pad. At this time, it is usual to interpose a slurry. Subsequently, using a motor connected to a shaft and / or a platen, the wafer and / or the polishing pad are relatively moved to remove the material from the front surface of the wafer in a flat state.
[0006]
The relative movement between the carrier and the polishing pad is an important factor in the planarization process. As new requirements and materials are used in semiconductor manufacturing processes, there is a continuing need to improve the movement of carriers and polishing pads. One of the goals of the planarization process is to remove material at a uniform rate over the entire front surface of the wafer. One method of attempting to remove material at a uniform rate is to have any point on the front side of the wafer move relative to the polishing pad relative to other points. The orbital tool orbits the orbital movement of the polishing pad about an axis offset from the center of the polishing pad while continuously maintaining the rotational direction of the polishing pad throughout the trajectory. One possible way to accomplish this. Orbital tools are desirable because any point on the front side of the wafer can cause the polishing pad to make the same circular motion as the other points.
[0007]
Conventional orbital tools use a polishing pad supported by a diaphragm. A front-reference carrier is known in the art as supporting a wafer with a fluid or flexible diaphragm / septum. The front reference carrier can uniformly apply pressure to the back surface of the wafer, regardless of the shape of the back surface. Applicants have discovered that the use of a front reference carrier with conventional orbital tools, i.e., having a polishing pad supported by a diaphragm, results in a lack of stability in the planarization process. Although the reasons for the lack of stability are not fully understood, applicant believes that it may have been caused by the lack of a fixed reference plane.
[0008]
Another problem with conventional orbital tools is that there is a tendency for bands to remain in the peripheral area on the front side of the wafer where material is being removed at a faster rate. Applicants have noted that the width of this band is typically the same as the orbit diameter of the polishing platen. Applicants believe that this band may be caused by the residue from the planarization process accumulating in the center of the polishing pad while the periphery of the polishing pad is slightly conditioned by the retaining ring. As a result, the polishing rate is reduced at the center of the wafer corresponding to the polishing pad in which the residue is accumulated, while the polishing rate is increased in the peripheral region of the wafer corresponding to the peripheral portion where the condition of the polishing pad is adjusted.
[0009]
Therefore, there is a need for a system for precisely flattening the front surface of a wafer that provides stable processing while minimizing bands due to uneven material removal at the periphery of the wafer.
[0010]
(Summary of the Invention)
The present invention is an apparatus and a method for planarizing the front surface of a wafer. The present invention includes a hard platen, ie, does not use a diaphragm or diaphragm to support the polishing pad as in the prior art. The platen is connected to a supporting base having means for orbiting the platen, or is connected to the means for orbiting the platen. The carrier is preferably a front reference carrier, which holds and presses the wafer against the polishing pad while the support orbits the platen.
[0011]
Also, the carrier can be connected to a motor via a shaft to rotate or otherwise move the wafer during the planarization process. Further, by using a carrier on the backside of the wafer that can apply a plurality of different pressure zones, more flexibility is obtained for the planarization process. By adjusting the orbit radius and / or orbit velocity, the planarization process can be optimized for various wafers and thin films deposited on the wafer. By orbiting the polishing pad with a radius smaller than the conventional orbital radius, or by orbiting the polishing pad at a speed higher than the conventional orbital speed, preferably by combining the two, the planarization result can be improved. Applicant has found.
[0012]
The invention can be practiced by loading the wafer in a carrier, preferably a front reference carrier, and placing the wafer in proximity to a polishing pad mounted on a substantially rigid platen. The wafer is planarized by pressing the wafer against the polishing pad while orbiting the polishing pad, preferably at a radius of less than 4 mm, at a speed greater than 400 orbits / minute. Also, the carrier can be rotated to smooth and remove patterns that are often formed on the front side of the wafer. Alternatively, the carrier can be rotated in a clockwise and counterclockwise direction, preferably at an angle of less than 360 degrees, to simplify the supply of fluid to the carrier.
[0013]
If a front reference carrier with a plurality of individually controllable pressure zones is used, a further improvement is obtained for the planarization process. The pressure applied in contact with the back surface of the wafer can be increased or decreased according to the region on the front surface of the wafer where the material to be removed is large or small. The wafer planarization process can be terminated by removing the wafer from the polishing pad or by stopping relative movement between the wafer and the polishing pad.
[0014]
(Description of the preferred embodiment)
The present invention will be described below with reference to the accompanying drawings. In the drawings, like numbers represent like elements.
[0015]
An improved polishing apparatus and polishing method used for polishing a semiconductor substrate and a thin film formed thereon will be described. In the following, numerous specific details are set forth in order to elucidate the best mode of practice of the present invention by applicant, and enable any person skilled in the art to make and use the invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well known machines and process steps have not been described in detail in order to avoid unnecessarily obscuring the present invention.
[0016]
With reference to FIG. 2, consider an apparatus embodying the present invention. Front reference carrier 215 can be used to hold wafer 216 and press the wafer against polishing pad 207 during the planarization process. The front reference carrier applies a substantially uniform pressure to the back surface of the wafer 216, even if the back surface of the wafer 216 has protrusions. This avoids the problems associated with the protrusions of the back-reference carrier, i.e., the occurrence of locally strong pressure on the spot on the front surface of the wafer opposite to those protrusions. The front reference carrier typically uses a pressurized fluid (eg, filtered air, deionized water, etc.) and / or a flexible membrane / diaphragm 203 to uniformly apply pressure to the back of the wafer 216. Some examples of front reference carriers that can be used to practice the present invention include US Pat. No. 5,423,716 (Strasbaugh), US Pat. No. 5,449,316 (Strasbaugh), US Pat. No. 083 (Breivogel et al.), US Pat. No. 5,851,140 (Barns et al.), US Pat. No. 6,012,964 (Arai et al.) And US Pat. No. 6,024,630 (Shendon et al.). And these are hereby incorporated by reference.
[0017]
The carrier 215 can have a plurality of regions 204, 228 or zones, which are typically concentric with each other and can be individually pressurized to produce a plurality of uniform pressure regions. In other words, different pressures are applied to each area, but the pressure in each area is substantially uniform. The multi-zone carrier 215 can be advantageously used to quickly remove excess material from a concentric area having a bulge on the front side of the wafer 216. In particular, the multi-zone carrier 215 can apply a higher uniform pressure to the backside of the wafer 216 opposite the bulge. At the same time, lower uniform pressure is applied in other areas of the wafer backside, for example, between the bulges. Examples of multi-zone front reference carriers that can be used to practice the present invention are U.S. Pat. No. 5,941,758 (Mack), U.S. Ser. No. 09 / 540,476 and U.S. Pat. 686, all of which are incorporated herein by reference.
[0018]
FIG. 2 shows one embodiment of a front reference carrier 215 having individually controllable uniform pressure regions 204, 228, together with an apparatus for implementing the present invention. The pressure source 227 can supply pressure to the two pressure regulators 223 and 224 via the manifold 229. The pressure regulators 223, 224 are preferably computer controlled and can be connected to the control system 230. Pressure regulators 223, 224 can deliver pressurized fluid to a corresponding rotating coupler (not shown) in carrier shaft 201. The rotating coupler can then direct pressurized fluid through tubes or channels 225, 226 in shaft 201 to corresponding tubes or channels in carrier 215. The tubes or channels in the carrier 215 then direct the pressurized fluid through the plenums 204, 228 in the carrier 215 to control the pressure applied to a corresponding area on the backside of the wafer 216. The plenums 204, 228 are separated by one or more ring-shaped barriers 205 so that each plenum can have a distinct internal pressure. Thus, in this embodiment of the present invention, the control system 230 can individually control the pressure applied to the two regions 204, 228 on the back surface of the wafer 216. It should be understood that various other carriers can be used to facilitate applying the desired pressure on the backside of the wafer. In particular, the front reference carrier 215 is described in detail, and the present invention is desirably implemented using the front reference carrier. However, the present invention can be implemented using various front and rear reference carriers.
[0019]
The carrier 215 can be held stationary or have various movements, for example, can have a linear, orbital, oscillating or rotational movement on a polishing pad. For example, the carrier 215 can be rotated by the motor 222 via the shaft 201. When the carrier 215 rotates, it is desirable to rotate at about 10 to 20 rpm. By rotating the carrier 215, it has been found that the periodicity of the orbital movement of the polishing pad 207 smoothes or removes a pattern that tends to occur on the front surface of the wafer. In addition, the carrier 215 can be alternately rotated clockwise and counterclockwise. This is particularly advantageous when using a front reference carrier with multiple chambers. All chambers require an additional fluid communication path to operate. When the carrier 215 rotates in only one direction, complicated fluid supply means such as a rotary coupling is required. However, if the carrier 215 alternately rotates clockwise and counterclockwise, and more preferably does not rotate up to 360 degrees, a less complicated fluid supply means such as a conventional tube can be used.
[0020]
During the planarization process, the front side of the wafer 216 is pressed against a polishing pad 207 secured to a hard platen 221 typically in the presence of a slurry. Polishing pad 207 may be, for example, an IC 1000 or an IC 1000 supported by a Suba IV polishing pad. Both products are available from Rodel Inc., headquartered in Phoenix, Arizona. Manufactured and provided commercially. The specific polishing pad 207 used can vary depending on the characteristics of the wafer 216, but is typically made of a urethane-based material. As shown in FIG. 3, the polishing pad 207 may include holes 322 for supplying a slurry to the surface of the polishing pad 207. The slurry is generally a silica-based solution with different additives depending on the type of material being polished. The polishing pad 207 may also include a groove (not shown) to assist in spreading the slurry over the entire surface of the polishing pad 207.
[0021]
Referring back to FIG. 2, the platen 221 can be made from a hard material having a substantially flat surface for mounting the polishing pad 207. The platen 221 of the present invention should be harder than the conventional platen of prior art orbital tools that use a pressure diaphragm or diaphragm to support the polishing pad. For example, platen 221 is comprised of aluminum, stainless steel, ceramic, titanium or other hard and preferably non-corrosive materials.
[0022]
During the planarization process, the platen 221 can be orbited by the support 220. The orbital movement of the polishing pad will be described in detail with reference to FIG. The polishing pad moves to positions 207a, 207b, 207c, and 207d at time 1, time 2, time 3 and time 4, respectively, so that "X" on the polishing pad moves in a circle 400a. Note that the polishing pad does not rotate during orbital motion. The orbital radius is the same as the radius of circle 400a or another circle drawn by one orbital movement point on the polishing pad. The magnitude of the orbital motion indicated by circle 400a is larger than is normally desired to facilitate the description of the orbital motion.
[0023]
Referring to FIG. 4b, wafer 216 is shown with a plurality of circular motions 400b. Circular motion 400b represents the motion that each point on the front surface of wafer 216 follows during orbital motion. The radius of the trajectory that produces circular motion 400b is significantly smaller than the radius of the trajectory that produces circular motion 400a. The orbit radius can be controlled by the mechanism used to produce the orbital motion, several examples of which are discussed here.
[0024]
U.S. Patent No. 5,582,534 (Shendon) and U.S. Patent No. 5,938,884 (Hoshizaki et al.) Disclose several mechanisms for producing orbital motion of a carrier. The principles of these mechanisms disclosed to produce orbital motion can be applied by one of ordinary skill in the art to create a support 220 capable of orbiting the platen 221 and are hereby incorporated by reference. .
[0025]
FIG. 5 is a cross-sectional view of an exemplary support 220 that can be used to cause orbital movement of the platen 211. This support is generally disclosed in U.S. Pat. No. 5,554,064 (Breivogel et al.), Which is hereby incorporated by reference. The support base 220 includes a rigid frame 502 that can be firmly fixed to the ground. The fixed frame 502 is used to support and balance the motion generator 502. The outer ring 504 of the lower bearing 506 is firmly fixed to the fixed frame 502 by a clamp. The fixed frame 502 prevents the outer ring 504 of the lower bearing 506 from rotating. A wave generator 508 formed by a round, hollow, hard stainless steel body is attached to the inner ring 510 of the lower bearing 506. The wave generator 508 is also mounted on the outer ring 512 of the upper bearing 514. Wave generator 508 places upper bearing 514 parallel to lower bearing 506. Wave generator 508 offsets center axis 515 of upper bearing 514 from center axis 517 of lower bearing 506. The aluminum circular platen 211 is symmetrically disposed with respect to the inner ring 519 of the upper bearing 514 and is securely fixed thereto. The polishing pad or polishing pad assembly can be securely secured to a ridge 525 formed around the outer edge of the upper surface of the platen 211. A universal joint 518 having two pivot points 520a, 520b is fixedly secured to the fixed frame 502 and the lower surface of the platen 211. The lower portion of the wave generator 508 is rigidly connected to a hollow and cylindrical drive spool 522, which in turn is connected to a hollow and cylindrical drive pulley 523. Drive pulley 523 is coupled to motor 526 by belt 524. Motor 526 may be a variable speed three-phase two-horsepower AC motor.
[0026]
The orbital movement of the platen 211 is caused by spinning the wave generator 508. The wave generator 508 is rotated by a variable speed motor 526. As the wave generator 508 rotates, the center axis 515 of the upper bearing 514 rotates about the center axis 517 of the lower bearing 506. The orbit radius of the upper bearing 517 is equal to the offset (R) 526 between the center axis 515 of the upper bearing 514 and the center axis 517 of the lower bearing 506. The upper bearing 514 rotates about the central axis 517 of the lower bearing 506 at a speed equal to the rotation of the wave generator 508. Note that as wave generator 508 rotates, outer ring 512 of upper bearing 514 orbits and rotates (spins) at the same time. The function of the universal joint 518 is to prevent torque due to rotation or spin of the platen 211. The two pivot points 520a, 520b of the universal joint 518 allow the platen 211 to move in all directions except the direction of rotation. By connecting the platen 211 to the inner ring 519 of the upper bearing 514 and connecting the universal joint 518 to the platen 211 and the fixed frame 502, the rotational movement of the inner ring 519 and the platen 211 is hindered, and Orbital motion only. The orbital speed of the platen 211 is equal to the rotational speed of the wave generator 508, and the orbital radius of the platen 211 is equal to the offset of the center 515 of the upper bearing 514 from the center 517 of the lower bearing. It should be understood that various other known means may be used to facilitate the orbital movement of the polishing pad. Although specific methods of orbiting have been described in detail, the present invention can be implemented using various techniques for orbiting the polishing pad on platen 211.
[0027]
With reference to FIGS. 2 and 6, a typical operation method of the present invention will be described. The first step is to load the wafer 216 on the carrier 215 (step 600). Although the back reference carrier 215 can be used, in the present invention, the use of the front reference carrier 215 provided good results. If the wafer 216 has one or more concentric bulges on its front surface, it is appropriate to use a front reference carrier 215 having a plurality of individually controllable pressure zones. The individually controllable pressure regions can apply a higher pressure to the backside of the wafer abutting the bulge than to a pressure applied to a recess or lower point on the wafer. The number and location of the bulges can be determined, for example, by taking measurements in situ or by knowing the general wafer shape resulting from the pre-processing step.
[0028]
Next, the wafer 216 is placed close to the polishing pad 207 fixed to the hard platen 221 (step 601). Mechanical means for moving the wafer 216 to a position proximate to the polishing pad 207 are known in the art and are not mentioned to avoid unnecessarily obscuring the present invention. The pressure applied to the backside of wafer 216 presses the wafer against polishing pad 207 (step 604). The optimal pressure applied to the backside of wafer 216 can vary depending on the characteristics of wafer 216, polishing pad 207, slurry, desired removal rate, and other factors. However, pressures between about 3 psi and about 7 psi have yielded very good results. However, the invention can easily be used at lower or higher pressures.
[0029]
At about the same time that the wafer 216 is pressed against the polishing pad 207 (step 604), the polishing pad 207 can begin orbiting (step 602) and the carrier can begin to rotate (step 603). The polishing pad 207 desirably orbits at a speed of more than 400 revolutions / minute, and the applicant obtained extremely good flattening at an orbital radius of 16 mm and an orbital speed of about 600 times / minute. Also, the orbital radius of the polishing pad can be less than 6 mm, and the applicant has obtained extremely good flattening at an orbital rotation frequency of about 6400 revolutions / minute and an orbital radius of about 1.5 mm. Smaller orbital radii generally require higher orbital periods to maintain a given rate of material removal from the front of the wafer. The carrier can rotate at speeds below 30 rpm, with speeds between about 10 to about 20 rpm being desirable. When the carriers 215 rotate alternately in the clockwise or counterclockwise direction without rotating to 360 degrees, the fluid supply passages 225 and 226 can be simplified.
[0030]
The wafer 216 can be removed from the polishing pad 207 based on input from an end point detection system or based on the time required for a particular planarization step determined by experience, and the planarization step can be terminated.
[0031]
Although the present invention has been described with respect to particular embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a standard multilayer interconnect structure used in semiconductor integrated circuits.
FIG. 2 is a cross-sectional view of a front reference carrier that holds a wafer against a polishing pad attached to a hard platen.
FIG. 3 is a plan view of a wafer in proximity to an orbiting polishing pad.
FIG. 4a is a plan view of a stationary wafer shown with the orbiting polishing pad at four different times during the orbiting of the polishing pad.
FIG. 4b is a front view of the wafer showing the motion experienced at every point on the front of the wafer by orbital motion only.
FIG. 5 is a cross-sectional view of one possible mechanism for causing orbital movement of the polishing pad.
FIG. 6 is a flowchart illustrating one possible method of implementing the present invention.

Claims (15)

An apparatus for planarizing a wafer, comprising:
a) a hard platen;
b) a support connected to the platen for orbiting the platen;
c) a polishing pad mounted on the platen; and d) a carrier configured to hold and press a wafer against the polishing pad;
An apparatus comprising: The device further comprises:
a) a shaft connected to the carrier; and b) a motor connected to the shaft for rotating the shaft and the carrier;
The apparatus of claim 1 comprising: The device of claim 1, wherein the carrier is a front reference carrier. The apparatus of claim 1, wherein the carrier is a back reference carrier. The apparatus of claim 3, wherein the carrier is adjustable to provide a plurality of individually controllable pressure zones on the backside of the wafer. The apparatus of claim 1, wherein the support is configured to orbit the polishing pad with an orbital radius of less than about 4 mm. The apparatus of claim 1, wherein the support is configured to orbit the polishing pad at an orbital speed greater than about 400 revolutions / minute. A method for planarizing a wafer, comprising:
a) loading the wafer into the carrier;
b) placing the wafer in proximity to a polishing pad attached to a hard platen;
c) pressing the wafer against the polishing pad;
d) orbiting the polishing pad; and e) removing the wafer from the polishing pad;
A method that includes The method further includes:
a) rotating the wafer before removing the wafer from the polishing pad;
The method of claim 8, comprising: The method further includes:
a) rotating the wafer alternately clockwise and counterclockwise before removing the wafer from the polishing pad;
The method of claim 8, comprising: The pressing step further includes:
Applying a first pressure to a central area on the back side of the wafer; and applying a second pressure different from the first pressure to a peripheral area concentric with the central area;
The method of claim 8, comprising: The method of claim 8, wherein the polishing pad orbits at a speed greater than about 400 revolutions / minute. The method of claim 8, wherein the polishing pad orbits with a radius less than about 4 mm. 9. The method of claim 8, wherein the polishing pad orbits with a track radius of less than about 4 mm and at a speed greater than about 400 revolutions / minute. The method of claim 8, wherein the carrier is a front reference carrier.

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