Abrading – Accessory – Dressing
Reexamination Certificate
2001-07-16
2003-01-21
Nguyen, George (Department: 3723)
Abrading
Accessory
Dressing
C451S444000, C451S056000, C451S456000, C451S285000
Reexamination Certificate
active
06508697
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of semiconductor fabrication, microelectromechanical systems (MEMS) fabrication or precision polishing; more specifically to apparatuses and methods for Chemical Mechanical Polishing (CMP) and planarization.
2. Description of Related Art W/R to Semiconductor Fabrication
An integrated circuit generally consists of a silicon wafer substrate typically produced on fabricated as a disc with a diameter of 100 to 300 millimeters and a thickness of 16 to 40 mils. Metallic dielectric and insulator depositions forming interconnected circuits are created on a wafer by a series of processes (lithography, vapor deposition, oxydation) producing the desired electrical circuitry. An electrical insulating layer, up to one-micron in thickness, is then deposited over the electrical circuit layer. With each layer, a multiplicity of undesired irregularities occur on the surface. These irregularities are on the order of 0.1 to 0.5 microns but it is critically important that they be removed so that processing can continue to develop new layers of circuitry without loss of focus in lithography and whereby accurate interconnections can be formed between layers.
Various techniques have been developed and used to effect the removal of these irregularities. Chemical Mechanical Polishing (CMP) (planarity) process has become a key technology to remove irregularities and achieve required planarity and layer geometries of microelectronic devices. A CMP system generally consists of the following components:
1) a polishing pad mounted on a rotating platen or belt;
2) a stream of polishing slurry (oxidizer and abrasive) whose chemistry is important to polishing performance;
3) large amounts of ultra pure water (UPW) used as a lubricant or flushing medium/agent;
4) slurry components and flushing agent. To adjust chemistry or fluid properties during processing;
5) an end effector arm with a diamond impregnated head at the free end that controls the asperity surface of the polishing pad, and;
6) a rotating carrier head that contains the wafer and exerts a force on the wafer against the polishing pad.
Irregularities on the wafer are removed with the polishing pad that has slurry of oxydating chemicals and very fine abrasive particles continually poured on its surface. Polishing or planarity is generally accomplished with the silicon wafer placed face down on the polishing pad that is rotating beneath the wafer that is itself rotating around a central axis.
Polishing pads are generally made of a plastic (urethane) material and the removal rate of wafer irregularities is affected by the pressure applied to the wafer against the polishing pad, the relative speed of the slurry on the wafer, the amount of fresh slurry presented to the surface of the polishing pad, and the circuit pattern of the wafer. The introduction of slurry under the wafer, and the removal of waste products from the polishing process are dependent on centrifugal force of the rotating pad, the action of the end effector, and the flow of slurry and components and ultra-pure water. This type of flushing does not always remove the waste. Large settled abrasive particles from the slurry, and agglomerated slurry and wastes form in the pores and grooves of the pad and between diamond particles on the conditioners. Commercial applications have large volumes of UPW used in production and significant amounts of wastewater that must be treated.
The rate of wafer polishing depends upon the slurry and diamond head on the end effector arm to roughen or condition the polishing pad, providing a consistent asperity profile. In cross-section, the pad has regions of peaks and valleys which both carry slurry and provide pressure to the abrasive particles therein). The pad generally consists of a hard or soft urethane material with pores and/or fibers dispersed throughout the active layer. The fibers and/or urethane give the pad rigidity, provides pressure to the abrasive/wafer interface, and aids in the removal of material from the surface of the wafer. The pores act as a reservoir for the slurry facilitating the chemical contact and interaction with the wafer surface. The chemical interaction is an important ‘accelerator’ over an abrasive only polishing situation and therefore is critical to overall process performance and control.
The diamond end effector generally consists of diamond particles embedded in a metal matrix in the form of a rotating disk. The disk is principally used to texture the polishing pad so that a sustainable rate of planarization can occur on the wafer and wafer to wafer. It is also used to remove used slurry and debris from the pad. The used slurry and debris often occurs as large hard agglomerations which consists of silicon dioxide (SiO
2
), dielectric and metals that become embedded in the polishing pad. These materials reduce removal or polishing rates and repeatability and can produce defects in the form of scratches that damage the wafer surface and device performance (opens, shorts). Data from the semiconductor industry reveal that 60% of chip loss is due to contamination. The CMP process has been reported to be a major source of this contamination.
The uncontrolled delivery and removal (flushing) of process fluids can also cause polishing waste to build-up on many surfaces within the tooling. When dislodged, these dried/agglomerated compounds can lead to additional defects. Slurry has proven to be “unstable” prone to agglomeration due to shear forces in delivery systems, heat, and age effects. There is also potential for diamond particles to fracture or be torn from the metal matrix of the end effector disk and scratch the wafer surface. Within typical polishing times, from 60-600 seconds, there is significant causal mechanisms for scratching and more control of the process is required.
Presently this debris is removed from the pad with copious flushing of the pad with ultra-pure water and/or slurry. This method relies on centrifugal force of the liquid to carry off the waste and agglomerates. This is a very uncontrolled method of removal because the flushing cannot breakup the static layer of slurry on the pad surface nor is it able to dislodge the slurry in the holes of the pad. This could lead to additional agglomerates of slurry becoming deposited in holes and recesses of the pad. This slurry can be dislodged, at a later time, and damage subsequent wafers. The reliance of centrifugal force to present new slurry to the wafer/pad interface is also less controlled or repeatable than required causing variation in removal rates and uniformity.
Polishing pad surfaces, which typically contain pores, holes or grooves for channeling the slurry between the wafer and the pad require conditioning to create a consistent polishing interface. Slurry and debris from the wafer must be removed by continually “abrading” or “conditioning” the pad surface. Additionally, oxidizing slurries sometimes used in this process contribute to the contamination of the pad by interacting with metals that come in close proximity to the pad causing potential contamination of the wafer. A variety of apparatuses and methods are presently in use to condition polishing pads. Diamond in one form or another is most often used as the conditioning apparatus because of its wear resistance, chemical inertness and reduced propensity to contaminate the pad/wafer.
One such apparatus is described in Breivogel et al U.S. Pat. No. 5,216,843 in which the pad conditioning apparatus comprises a diamond block holder having a plurality of conical ground diamond tipped, stainless steel, threaded rods embedded into a substantially planar surface of the block. The diamond points are manually adjusted with the threaded rods to position them to the desired depth as shown in FIG.
1
. The holder containing the diamond points is pressed into the pad until the holder contacts the pad. A conditioner arm is coupled at one end to the diamond block holder and at the other end to a variable speed oscill
Benner Robert L.
Benner Robert Lyle
Benner Stephen J.
Benner Virginia A.
Benner Virginia A.
Chovanes Eugene
Nguyen George
LandOfFree
Polishing pad conditioning system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polishing pad conditioning system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polishing pad conditioning system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3026898