Patent Application
20050287032
1. Field
Substrate cleaning.
2. Background
Chemical mechanical polishing (“CMP”) processes are widely used in manufacturing of semiconductor circuits for planarization and/or removing excess of dielectric and metal materials. Many commercially available rotary and orbital polishers may be used to perform a CMP process. One example is the Reflexion™300 mm CMP system, which is available from Applied Materials, Inc.
A chemical mechanical process involves application of a polymer-based polishing pad(s) and abrasive slurries. After the CMP process is completed, a substrate (e.g., wafer) may be covered with residuals of abrasives, pads, or polished out metal/oxide layers. Residual slurry and polished out layers should be removed to avoid such particles/contaminants inhibiting subsequent processing. To remove particles/contaminants, the substrate may be subjected to one or a series of cleaning and scrubbing operations. Many commercially available tools, e.g., the Reflexion system mentioned above, integrate CMP modules with the post CMP cleaning modules that perform those cleaning and scrubbing functions. Such tools may include one or more high porosity foam (such as poly vinyl (alcohol) (“PVA”)) brushes, for example, included in a brush box. In the presence of deionized water or a dilute cleaning agent rinse, such brush(es) contact a surface of the substrate and remove the particles/contaminants through mechanical action. An additional cleaning technique includes sonic or ultrasonic cleaning that may be used in conjunction with a brush treatment.
One current technology trend is the substitution of traditional dielectric materials such as silicon dioxide with a dielectric material having a dielectric constant less than silicon dioxide (a “low-k” dielectric material). Certain materials that may be used to form low-k dielectric layers (e.g., carbon doped oxides) may have surface energies different than traditional silicon dioxide. Post-CMP cleaning solutions may seek to match these surface energies. Current brushes, however, do not provide capabilities to adjust their surface energies to make it close to that of the cleaning solution to effectively clean a substrate. In other words, surface energy synergism in the system solution-brush-substrate to improve effectiveness of the substrate cleaning cannot be achieved.
Bacteria growth in polymer materials that constitute the working portion of a post-CMP brush can dramatically change physical and mechanical properties of the brush, such as compressive stress, or destroy the polymer after prolonged storage. Currently, post-CMP brushes from different suppliers are shipped in sealed bags with a wet chemical (transient) anti-bacterial treatment. Typical wet chemical treatments include ammonium hydroxide, or oxalic acid, or other treatments. A typical wet chemical treatment involves dipping the brush in the chemical and then removing the excess (e.g., squeezing out the excess) and sealing the brush in a bag. A major problem with wet treatments is that a polymer material of the brush can be degraded when exposed to a liquid ambient, such as water, ammonium hydroxide, oxalic acid. Those changes occur due to polymer plastisizing that affect mechanical properties. Moreover, these changes depend on brush storage time, temperature conditions, other external factors, and such. Another problem is that the amount of wet chemical (e.g., ammonium hydroxide, oxalic acid) is not quantified and therefore the excess chemical tends to change the properties of the polymer of the brush in an uncontrolled and unpredictable manner.
Features, aspects, and advantages of embodiments will become more thoroughly apparent from the following detailed description, appended claims, and accompanying drawings in which:
Brush 110 and brush 120 are made of a relatively soft, porous foam polymer such as poly vinyl (alcohol) (PVA).
Referring again to
As noted above, a typical material for a cleaning brush in a post-CMP system is a foam polymer such as PVA. PVA is known to be susceptible to biodegradation. Current methods to minimize biodegradation include storing a brush in transient chemical solutions such as ammonia or oxalic acid. These chemical solutions, however, tend to affect mechanical properties of a brush such as compressive stress. Additionally, the amount of time a brush is stored in a chemical solution may affect the mechanical properties of a brush leading to an unpredictable change of brush properties.
Referring to process flow 400, at block 410 a post-CMP cleaning brush is formed. In one embodiment, a brush is formed of a relatively soft and porous PVA material as known in the art. The brush may be either of the knobby type or ridged (splined) type or other configurations.
Once a brush is formed, the brush may be treated to impart a residual bacteria-inhibiting property to the brush. Such treatment may be done by the brush manufacturer or other entity. Referring to block 420, in a first process, a polymer brush may be radiated with, for example, an ultraviolet (UV) radiation source. The UV radiation penetrates the polymer and essentially sterilizes the brush. In one embodiment, a brush may be exposed to UV radiation for a period of seconds (e.g., 10-20 seconds) to modify the brush. One application of ultraviolet radiation to inhibit bacteria is described in “Bioactive assessment and bacteria test for the varied degrees of ultraviolet radiation onto the collagen-immobilized polypropylene non-woven fabric” by J. D. Liao and Y. C. Tyan, Biomedical Engineering Application Basis Communication, v. 4, no. 1 2002, pgs. 20-30.
Block 430 shows another technique to impart a residual bacteria-inhibiting property to a post-CMP brush. In this technique, a coating is applied to the brush surface. One type of coating is chemically modifying the polymer with an anti-bacterial monomer such as diallyldimethylammonium chloride (DADMAC) (block 440). The monomer may be connected to the polymer of the brush by activating the polymer surface (e.g., applied activation to generate radicals). The monomers, such as DADMAC, may be grafted to the surface by radical polymerization. According to another technique, the polymer surface of the brush is plasma treated to create oxygen functionalities. Co-polymers such as DADMAC co-polymers are then connected to the activated surface. Studies of polyammonium compounds as an anti-bacterial coating are reported in “Ultrathin antibacterial polyammonium coatings on polymer surfaces,” by J. Thome et al, Surface & Coatings Technology, vol. 174-175, September-October 2003, pgs. 584-7.
A second type of coating may be used to chemically modify a polymer-based post-CMP brush to impart a residual bacteria-inhibiting property is a thiocyanate. One technique for coating a post-CMP brush of PVA is to immerse the brush in an aqueous solution of sodium thiocyanate possibly in the presence of an intermediate such as tetrabutylammonium hydroxide (TBAH). One example is to immerse a brush in a solution of sodium thiocyanate (3 moles/dm3) in the presence of TBAH (0.15 moles/dm3) at 80° C. for 5 hours. After immersion, the post-CMP brush may be rinsed and dried. An additional sterilization operation may be performed using ethylene oxide (ETO). Studies of thiocyanate coatings as an anti-bacterial coating on a polymer are reported in “Surface thiocyanation of plasticized poly(vinyl chloride) and its effect on bacterial adhesion,” by N. R. James and A. Jayakrishnan, Biomaterials, v. 24, issue 13, 2003, pgs. 2205-2212.
Block 460 shows another technique to impart a residual bacteria-inhibiting property to a post-CMP brush. In one embodiment, a post-CMP brush of a PVA material is treated with an oxygen-plasma to impart a residual anti-bacterial property to the brush. A study of oxygen-plasma treatment of polymers to provide anti-bacterial coatings are reported in “Adhesion of Pseudomonas aeruginosa strains to untreated and oxygen-plasma treated poly(vinyl chloride) (PVC) from endotracheal intubation devices,” by Triandafillu, K. et al., Biomaterials, v. 24, no. 8, 2003, pgs. 1507-18. The oxygen plasma treatment conditions to modify the polymer surface can be set up at, for example, treatment time of 60 seconds, plasma pressure of 650 mTorr with an oxygen gas flow rate of 900 sccm, and radio-frequency (rf) power of 110 W, as per “CMP of Low-k Methylsilsesquiazane with Oxygen Plasma Treatment for Multilevel Interconnect Applications,” by T. C. Chang, T. M. Tsai, P. T. Liu, C. W. Chen, S. T. Yan, H. Aoki, Y. C. Chang, and T. Y. Tseng, published in Electrochemical and Solid-State Letters, 2004, Vol. 7, No. 6, pp. G122-G124.
A second type of plasma treatment to impart a residual bacteria-inhibiting property to a post-CMP brush is an acetylene plasma immersion ion implantation. One study of this technique is described in “Surface characterization and antibacterial adhesion of poly(ethylene-therephtalate) modified by acetylene plasma immersion ion implantation” by J. Wang et al., Proceedings of 2002 IEEE International Conference on Plasma Science, Piscataway, N.J., IEEE, 2002, pg. 311.
In addition to imparting a residual bacteria-inhibiting property to a post-CMP brush, in another embodiment, a surface energy of a brush may also be modified. Many low-k films tend to have low hydrophobicity. Post-CMP cleaning solutions seek to match the surface energy of the film. It is advantageous if surface energies (that determine hydrophobicity) of the brush surface and post CMP cleaning solutions are close. Certain of the above techniques for imparting a residual anti-bacteria coating also tend to make the surface of a post-CMP brush more hydrophilic. For example, the UV treatment described with reference to block 420, the thiocyanate coating described with reference to block 450, and the oxygen-plasma treatment with reference to block 460 described with reference to in
In the preceding paragraphs, specific embodiments are described. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.
