Application Study Of Some Chelating Agents For Reducing Copper Contamination On Silicon Wafer Surface In Microelectronics Solution Process

Along with the characteristic size reducing and the integration rapidly enhancement in ULSI,the metal impurities harm appears specially prominently. The request for metal tarnish on silicon substrate surface will be slower and slower, but the metal tarnish is nearly inevitable.This paper proceeded with the inevitable contact and reaction betwwen silicon and some kinds of aqueous solution used in microelectronic craft. The method here is adding chelating agent in solutions. On the one hand, it can reduce metal depositon opportunity as far as possible; on the other hand it can eliminate the already metal pollution as far as possible.The stability constants of Cu(II) and Fe (III) with the FA/O chelating agent were first determined, which was invented by Professor Liu Yuling in Hebei university of technology. The results showed that the FA/O chelating agent has at least ten coordinating atoms; the FA/O chelating agent suits for using in alkaline solution with pH >10 prefentially pH >12. The chelate stability constants logK of Cu(II) and Fe (III) with FA/O are 9.69 and 18.7 respectively.With copper as the example, the reducing effect of Cu contamination was also determined in this paper for FA/O chelating agent and other kinds of chelating agents in DHF cleaning solution, the RCA cleaning solution as well as the polishing slurry of silicon substrate. The copper concentration on silicon surface was determined by GFAAS joint with one-drop sandwich etching method.In the alkaline SC1 cleaning solution (NH4OH/ H2O2/H2O) and the alkaline polishing slurry, the results indicated that FA/O was better than the traditional chelating agent EDTA with reduction of copper pollution on silicon wafer surface. Moreover, compared with EDTA, FA/O has other advantages: not containing Na+, easily soluble in water, convenient to use and so on.When NH4OH in SC1 cleaning solution was substituted by FA/O, copper concentration on silicon wafer could meet the request of microelectronic process only by one step clean.The Cu contamination reducing effects of several kinds of acidic chelating agent were also studied in DHF cleaning solution and the acidic polishing slurry. Adding chelating agent in DHF cleaning solution to reduce metal deposition on the silicon surface was first proposed by author. The data showed that phosphonic acid chelating agent DTPMP was better in DHF solution and carboxylic acid chelating agent PAA was better in acidic polishing slurry.The metal pollution reducing mechanism of different chelating agent was also analysized in this paper. The effect of chelating agents on reducing Cu contamination on silicon wafer surface was carried out by two ways: reducing free metallic ions in the solution by coordinating equillirm and reducing adsorption opportunities on silicon surface of metal ions by competitive adsorption. When the chelating agent was large in polarity and large in size, it would preferentially adsorped on silicon surface and the adsorption way could be the leading role.