FIELD OF THE INVENTION
The invention relates to polishing layers and, more particularly, to polishing layers using a polishing pad.
BACKGROUND OF THE INVENTION
Making integrated circuits generally includes using chemical mechanical polishing (CMP) for polishing and thereby planarizing one or more of the deposited layers necessary for making the integrated circuit. Polishing pads used in CMP, typically made of polyurethane, are expended in the CMP process after some number of uses. Thus, in the course of a year, for example, a large number of polishing pads may need to be acquired. Thus, the cost of the polishing pads is relevant to the cost of making integrated circuits. Further, polishing pads are difficult to make perfectly.
One common way that polishing pads are patterned is to use a cutting approach in which a polishing pad is made to spin and a sharp object is applied to the rotating pad, analogous to a lathe operation. This often results in small strips of polyurethane, called stringers, dangling from the polishing pad. The stringers are not easily removed and, as a practical matter in a commercial environment, may not be possible to completely remove. Thus, a reduced quality of polishing pad is tolerated in the integrated circuit manufacturing process.
Another technique for patterning a polishing pad is to use a laser. One of the disadvantages of a laser is that it is difficult to form grooves with vertical walls. The walls are relatively more sloped than from the lathe approach. Another disadvantage is the high amount of local heat generated at the point where the laser hits the polishing pad.
Another technique is to use a small rotating cutting device, analogous to a router, that cuts a pattern into the polishing pad. The advantage of this approach is that the pattern does not have to be concentric circles which has been the only practical pattern for the lathe approach. The router approach, however, requires a relatively long time to form a pattern that greatly increases cost and also may leave small stringers as well. Thus, the patterns that are considered desirable than the concentric circle pattern have not been found to be practical due to high cost.
Thus, there is a need for a technique to make polishing pads and the subsequent polishing using the polishing pads that overcomes or improves upon the existing techniques described above.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and further and more specific objects and advantages of the invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment thereof taken in conjunction with the following drawings:
FIG. 1 is a pictorial of a polishing pad and a polishing pad apparatus useful in patterning the polishing pad according to an embodiment of the invention at a stage in processing;
FIG. 2 is a pictorial of the polishing pad and the polishing pad apparatus at a stage in processing subsequent to that shown in FIG. 1;
FIG. 3 is a pictorial showing the polishing pad of FIG. 2 with a completed pattern;
FIG. 4, in accordance with the invention, is a top view of a polishing pad having a desirable pattern useful in polishing a layer;
FIG. 5, in accordance with the invention, is a top view of a polishing pad having another desirable pattern useful in polishing a layer;
FIG. 6 is a pictorial of a semiconductor device structure and the polishing pad of FIG. 3 at a stage in processing;
FIG. 7 is a pictorial of the semiconductor device structure of FIG. 6 at a subsequent stage in processing; and
FIG. 8 is a pictorial of a polishing pad and an alternative polishing pad apparatus useful in patterning the polishing pad according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In one aspect a tool for forming a pattern on a polishing pad establishes a vibration that is coupled to the polishing pad. The vibration removes small portions of the polishing pad according to the desired pattern. The polishing pad is then used in a chemical mechanical polishing (CMP) step to polish a layer on a semiconductor device. This is better understood by reference to the drawings and the following description.
Shown in FIG. 1 is patterning apparatus 10 and a polishing pad 12. Apparatus 10 comprises a supporting table 14, a vibration generator 16 having pattern features 20 according to a pattern 18, a nozzle 22, and a nozzle 24. Nozzles 22 and 24 provide a liquid 26 to polishing pad 12. Polishing pads, such as polishing pad 12, typically have a thickness of about 1 centimeter and are preferably of polyurethane.
Vibration generator 16 establishes a vibration that is coupled to polishing pad according to pattern 18. In this example, the coupling is achieved through liquid 26. Liquid 26 has small particles that are moved linearly, up and down in FIG. 1, by the vibration of vibration generator 16. The vibration from vibration generator is established using piezo electric devices that are pulsed at a relatively high frequency, at least 10,000 hertz (10 KHz), and preferably about 20 KHz. The particles are caused to hit a major surface, which is the surface facing vibration generator 16, of polishing pad 12 by the vibration of vibration generator 16. The contact of a single particle only removes a very small portion of polishing pad 12, but at the rate of thousands of times per second the removal rate is quite high. The result is that the full depth of removal is achieved relatively quickly. Also, in this example, vibration generator has the whole pattern so that pattern 18 is applied to polishing pad 12 simultaneously.
Shown in FIG. 2 is pattern 18 being placed into polishing pad 12 by the vibration of vibration generator 16 being coupled to polishing pad 12 through liquid 26 and thereby removing selected portions of polishing pad 12 according to pattern 18.
Shown in FIG. 3 is polishing pad 12 after completion of forming pattern 18 in polishing pad 12. Grooves may be about a third of the thickness of polishing pad 12 or less. More than a third generally adversely impacts the character of the polishing pad.
Shown in FIG. 4 is a polishing pad 27 having a pattern made by the process described for FIGS. 1-3 that has radial spiral grooves in addition to concentric circle grooves. A pattern of concentric circles is the dominant pattern and perhaps the only pattern in commercial use but that is not necessarily the preferred pattern. The process described for FIGS. 1-3 not only can achieve the pattern of polishing pad 27 but can achieve it very quickly, typically less than a minute. The lathe approach with its quality problems and pattern limitations typically takes about 15 minutes.
Shown in FIG. 5 is a polishing pad 29 having a pattern made by the process described for FIGS. 1-3 that has what has been called a floral pattern that does not even have concentric circles. This is another pattern that is also believed to have advantages over the concentric circles pattern.
Shown in FIG. 6 is a semiconductor device 30 having a substrate 34, features 36, 38, and 40 over substrate 34, and a layer 42 over features 36, 38, and 40. Also shown in FIG. 6 is polishing pad 12 for polishing layer 42 using a CMP step.
Shown in FIG. 7 is semiconductor device 30 after the CMP step. The CMP step planarizes layer 42. Substrate 34 may include a major supporting layer, typically of silicon, in addition to other layers that are one or more of, dielectric layers, gate layers, and interconnect layers. Features 36, 38, and 40 may be gates or other features that have been patterned, typically according to a mask. Layer 42 may be a deposited layer that is either a dielectric or a conductor. Oxide is a common layer to polish.
Shown in FIG. 8 is an apparatus 40 and a polishing pad 42 to be patterned by apparatus 40. Apparatus 40 comprises position controller 44, a vibration generator 46, a nozzle 48, a liquid 50 for applying over polishing pad 42, a groove 52, a supporting table 54, and a turning drive 56. Apparatus 40 is similar to apparatus 10 of FIGS. 1-2 in that vibration is the source of removing material from polishing pad 42 to form the desired pattern. In this example, the pattern present in vibration generator 16 is far less than the pattern that will ultimately be on polishing pad 52. In fact in this example, vibration generator 46 may be a single point, and supporting table 54 is rotated by turning drive 56 so that a circular groove is formed in polishing pad 52 for a given position of vibration generator 46. Groove 52 is such a groove. Vibration generator 46 and liquid 50 may otherwise be like liquid vibration generator 16 and liquid 26 of FIGS. 1-2. On the other hand, vibration generator 46 may actually cause vibration of a diamond that is used to cut grooves such as groove 52. In such case, vibration generator 46 preferably spins and liquid 52 need not have particles.
Apparatus 10 of FIGS. 1-2 and apparatus 40 of FIG. 8 can be obtained from a company called Sonic Mill in Albuquerque, N.M. Examples of their equipment are model AP-1000, AP-10HCV, Rotary CNC Series 10 Bedmill, and Rotary Series 10.
Various other changes and modifications to the embodiments herein chosen for purposes of illustration will readily occur to those skilled in the art. For example, vibration frequencies other than those described, both lower and higher, may be found to be useful. To the extent that such modifications and variations do not depart from the spirit of the invention, they are intended to be included within the scope thereof which is assessed only by a fair interpretation of the following claims.
Patent Application
20070287361
