Grooved polishing pads for chemical mechanical planarization

Details Grooved polishing pads for chemical mechanical planarization Grooved polishing pads for chemical mechanical planarization

2000-08-03

2004-05-18

Rachuba, M. (Department: 3723)

Abrading

Machine

Rotary tool

C451S527000, C451S529000, C451S530000, C451S539000

Reexamination Certificate

active

06736709

ABSTRACT:

The present invention relates generally to improved polishing pads used to polish and/or planarize substrates, particularly metal or metal-containing substrates during the manufacture of a semiconductor device. Specifically, this invention relates to pads manufactured with an optimized combination of physical properties and a grooved surface engineered to a specific design to provide improved polishing performance.
Chemical-mechanical planarization (“CMP”) is a process currently practiced in the semiconductor industry for the production of flat surfaces on integrated circuits devices. This process is discussed in (“
Chemical Mechanical Planarization of Microelectronic Materials
”, J. M. Steigerwald, S. P. Murarka, R. J. Gutman, Wiley, 1997, which is hereby incorporated by reference in its entirety for all useful purposes. Broadly speaking, CMP involves flowing or otherwise placing a polishing slurry or fluid between an integrated circuit device precursor and a polishing pad, and moving the pad and device relative to one another while biasing the device and pad together. Such polishing is often used to planarize: i. insulating layers, such as silicon oxide; and/or ii. metal layers, such as tungsten, aluminum, or copper.
As semiconductor devices become increasingly complex (requiring finer feature geometries and greater numbers of metallization layers), CMP must generally meet more demanding performance standards. A relatively recent CMP process has been the fabrication of metal interconnects by the metal damascene process (see for example, S. P. Murarka, J. Steigerwald, and R. J. Gutmann, “
Inlaid Copper Multilevel Interconnections Using Planarization by Chemical Mechanical Polishing
”, MRS Bulletin, pp. 46-51, June 1993, which is hereby incorporated by reference in its entirety for all useful purposes).
With damascene-type polishing, the polished substrate is generally a composite rather than a homogenous layer and generally comprises the following basic steps: i. a series of metal conductor areas (plugs and lines) are photolithographically defined on an insulator surface; ii. the exposed insulator surface is then etched away to a desired depth; iii. after removal of the photoresist, adhesion layers and diffusion barrier layers are applied; iv. thereafter, a thick layer of conductive metal is deposited, extending above the surface of the insulator material of the plugs and lines; and v. the metal surface is then polished down to the underlying insulator surface to thereby produce discrete conductive plugs and lines separated by insulator material.
In the ideal case after polishing, the conductive plugs and lines are perfectly planar and are of equal cross-sectional thickness in all cases. In practice, significant differences in thickness across the width of the metal structure can occur, with the center of the feature often having less thickness than the edges. This effect, commonly referred to as “dishing”, is generally undesirable as the variation in cross-sectional area of the conductive structures can lead to variations in electrical resistance. Dishing arises because the harder insulating layer (surrounding the softer metal conductor features) polishes at a slower rate than the metal features. Therefore, as the insulating region is polished flat, the polishing pad tends to erode away conductor material, predominantly from the center of the metal feature, which in turn can harm the performance of the final semiconductor device.
Grooves are typically added to polishing pads used for CMP for several reasons:
1. To prevent hydroplaning of the wafer being polished across the surface of the polishing pad. If the pad is either ungrooved or unperforated, a continuous layer of polishing fluid can exist between the wafer and pad, preventing uniform intimate contact and significantly reducing removal rate.
2. To ensure that slurry is uniformly distributed across the pad surface and that sufficient slurry reaches the center of the wafer. This is especially important when polishing reactive metals such as copper, in which the chemical component of polishing is as critical as the mechanical. Uniform slurry distribution across the wafer is required to achieve the same polishing rate at the center and edge of the wafer. However, the thickness of the slurry layer should not be so great as to prevent direct pad-wafer contact.
3. To control both the overall and localized stiffness of the polishing pad. This controls polishing uniformity across the wafer surface and also the ability of the pad to level features of different heights to give a highly planar surface.
4. To act as channels for the removal of polishing debris from the pad surface. A build-up of debris increases the likelihood of scratches and other defects.
The “Groove Stiffness Quotient” (“GSQ”) estimates the effects of grooving on pad stiffness and is hereby defined as Groove Depth (D)/Pad Thickness (T). Hence, if no grooves are present, the GSQ is zero, and at the other extreme (if the grooves go all the way through the pad) the GSQ is unity. The “Groove Flow Quotient” (“GFQ”) estimates the effects of grooving on (pad interface) fluid flow and is hereby defined as Groove Cross-Sectional Area (Ga)/Pitch Cross-Sectional Area (Pa), where Ga=D×W, Pa=D×P, P=L+W; D being the groove depth, W being the groove width, L being the width of the land area, and P being the pitch. Since D is a constant for a particular groove design, the GFQ may also be expressed as the ratio of groove width to pitch Groove Width (W)/Groove Pitch (P).
The present invention is directed to (i) polishing pads for CMP having low elastic recovery during polishing, while also exhibiting significant anelastic properties relative to many known polishing pads; and (ii) polishing pads with defined groove patterns having specific relationships between groove depth and overall pad thickness and groove area and land area. In some embodiments, the pads of the present invention further define: i. an average surface roughness of about 1 to about 9 micrometers; ii. a hardness of about 40 to about 70 Shore D; and iii. a tensile Modulus up to about 2000 MPa at 40° C. In one embodiment, the polishing pads of the present invention define a ratio of Elastic Storage Modulus (E′) at 30 and 90° C. being 5 or less, preferably less than about 4.6 and more preferably less than about 3.6. In other embodiments of the present invention, the polishing pad defines a ratio of E′ at 30° C. and 90° C. from about 1.0 to about 5.0 and an Energy Loss Factor (KEL) from about 100 to about 1000 (1/Pa) (40° C.). In other embodiments, the polishing pad has an average surface roughness of about 2 to about 7 micrometers, a hardness of about 45 to about 65 Shore D, a Modulus E′ of about 150 to about 1500 MPa at 40° C., a KEL of about 125 to about 850 (1/Pa at 30° C.) and a ratio of E′ at 30° C. and 90° C. of about 1.0 to about 4.0. In yet other embodiments, the polishing pads of the present invention have an average surface roughness of about 3 to about 5 micrometers, a hardness of about 55 to about 63 Shore D, a Modulus E′ of 200 to 800 MPa at 40° C., KEL of 150 to 400 (1/Pa at 40° C.) and a ratio of E′ at 30° C. and 90° C. of 1.0 to 3.6.
In another embodiment, the present invention is directed to polishing padshaving a groove pattern with a groove depth in a range of about 75 to about 2,540 micrometers (more preferably about 375 to about 1,270 micrometers, and most preferably about 635 to about 890 micrometers), a groove width in a range of about 125 to about 1,270 micrometers (more preferably about 250 to about 760 micrometers, and most preferably about 375 to about 635 micrometers) and a groove pitch in a range of about 500 to about 3,600 micrometers (more preferably about 760 to about 2,280 micrometers, and most preferably about 2,000 to about 2,260 micrometers). A pattern with this configuration of grooves further provides a Groove Stiffness Quotient (“GSQ”) in a range of from about 0.03 (more preferably about 0.1, and most

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