Selective etching of silicate

Abstract: A silicate glass is selectively etched employing a composition containing a fluoride containing compound and certain organic solvents. Preferred compositions also include water.

Description: The present invention is concerned with selectively etching a silicate and particularly selectively etching a silicate at a rate greater than for silicon dioxide. In the fabrication of microelectronic components, a number of the steps involved, for instance, in preparing integrated circuit chips and the packaging for the chips (articles to which the chips are attached and protected), are etching processes. Accordingly, over the years, a number of vastly different types of etching processes to remove material, sometimes in selective areas, have been developed and are utilised to varying degrees. Moreover, the steps of etching different layers which constitute, for instance, the finished integrated circuit chip are among the most critical and crucial steps. One method widely employed for etching is to overlay the surface to be etched with a suitable mask and then immerse the surface and mask in a chemical solution which attacks the surface to be etched, while leaving the mask intact and while only etching other materials of the article to at most, a minimum extent. The problem of selectivity is especially pronounced when silicon dioxide is present on the same article as a silicate glass and is also exposed to the composition used to etch the silicate glass. This requires superior cleaning or etching solutions that exhibit extremely high selectivities in etching between the silicate glass and the silicon dioxide material. It would therefore be desirable to provide a selective etching procedure that exhibits high selectivity for the silicate as well as achieving excellent removal. Methods for selective etching of materials relative to SiO 2 , making use of a fluoride in an organic solvent, are described in DD-A-238.622, US-A-4.395-304, WO-A-9 702 950, US-A-5.320.709 and US-A-4.269.654. The present invention is concerned with a method for selectively etching a silicate glass, which comprises contacting an article that contains silicate glass and silicon dioxide with an etching composition that consists essentially of 0.05 to 3 molar of one of hydrofluoric acid and ammonium fluoride in propylene carbonate to thereby selectively etch the silicate glass at a rate greater than the rate for the silicon dioxide. The method of the present invention uses certain preferred etching compositions that are capable of selectively etching silicate glass at a rate greater than the rate for silicon oxides; the preferred compositions used contain 0.05 to 3 molar of a fluoride containing compound, proplylene carbonate, and 0.05 to 3 molar of water. The propylene carbonate employed in the method of present invention typically has relatively high flash point and provide low viscosity compositions. Other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realised, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, as defined in the claims. The present invention is concerned with selectively etching a silicate glass and especially a silicate glass that has been doped with boron, arsenic, antimony and/or phosphorous. The doped silicate glass to be etched, according to the method of the present invention, typically contains about 0.5 to about 10 percent by weight and preferably about 3 to about 7 percent by weight of the dopant. Moreover, the silicate is present in an article that also includes silicon dioxide, wherein both the silicate and silicon dioxide will come in contact with the etching composition. The present invention provides for selectively etching the silicate glass at a rate of at least about 100 times the rate for the silicon dioxide. The silicon dioxide is preferably high density silicon dioxide. High density silicon dioxide refers to thermally grown silicon dioxide or silicon dioxide that is chemically vapour deposited (CVD) or physically vapour deposited (PVD) followed by thermal annealing. The etching compositions employed pursuant to the method of the present invention consist essentially of hydrofluoric acid or ammonium fluoride and propylene carbonate. The amount of the fluoride containing compound in the composition is 0.05 to 3 molar, and preferably 0.2 to 2.5 molar, and most preferably 0.25 to 1.5 molar. The organic solvent is propylene carbonate. The organic solvent employed in the method of the present invention provides for low viscosity compositions, which in turn render the compositions more workable and providing for better etch uniformity. According to preferred aspects of the method of the present invention, the compositions used therein also include water. Typically, when present, the water is employed in an amount of 0.05 to 3.5 molar, preferably 0.2 to 2.9 molar, and most preferably 0.1 to 1.7 molar. However, it should be understood that compositions used in the method of the present invention do not require water. The etching process of the present invention is typically carried out at temperatures of 20°C to 90°C, and preferably 30°C to 70°C. Employing increased temperature results in increasing the etch rates of the silicate and the silicon dioxide. The increase in the etch rate due to increased temperature will be somewhat greater for the silicate glass than for the silicon dioxide, thereby somewhat increasing the selectivity of the etching of the silicate glass. The following non-limiting examples are presented to further illustrate the present invention. Example 1 - An etching composition is prepared by admixing one part by volume of a 49 percent by weight aqueous solution of HF with about 28 parts by volume of propylene carbonate to provide a one molar HF solution in propylene carbonate. A blanket silicon wafer having a layer of thermally grown silicon dioxide beneath a layer of silicon nitride which in turn is beneath a layer of 6 weight percent boron doped silicate glass is contacted with this etching composition. The article includes vias thereby exposing the walls of the vias of the underlying layers, i.e. silicon nitride and silicon dioxide, to the etchant. The etching is carried out at room temperature. The etching solution etches the boron doped silicate glass at a rate of about 125 nanometers/minute and the silicon dioxide at a rate of only about 0.6 nanometers per minute. This results in a selectivity of boron silicate glass etching relative to the silicon dioxide of over 200:1. Example 2 - Example 1 is repeated except that the water content of the solution is twice as much as in Example 1. This composition etches the boron doped silicate glass at a rate of about 140 nanometers/minute and the silicon dioxide at a rate of about 1.2 nanometers per minute. Accordingly, the selectivity of the etch rate is about 115:1. Example 3 - Example 1 is repeated except that the composition is prepared by admixing about 1 part by volume of 49 percent by weight of an aqueous HF solution and about 115 parts by volume of propylene carbonate, and the etching is carried out at about 60°C. The etch rate for the silicate glass is 615 angstroms per minute and for the silicon dioxide is 3.6 angstroms per minute. Accordingly the selectivity of the etch rate is about 170:1.

Claims: A method for selectively etching a silicate glass which comprises contacting an article containing said silicate glass and a silicon dioxide with an etching composition characterised by the etching composition consisting essentially of 0.05 to 3 molar of one of hydrofluoric acid and ammonium fluoride, in propylene carbonate to thereby selectively etch said silicate glass at a rate greater than said silicon dioxide. The method of claim 1 wherein said silicate glass is a silicate glass doped with at least one member selected from the group consisting of boron, arsenic, antimony and phosphorous. The method of claim 1 or claim 2 wherein said silicon dioxide is high density silicon dioxide. The method of claim 3 wherein said silicon dioxide is selected from the group consisting of thermally grown silicon dioxide, chemically vapour deposited thermally annealed silicon dioxide and physically vapour deposited thermally annealed silicon dioxide. The method of any previous claim wherein said composition further contains water, preferably in the amount of 0.05 to 3.5 molar; more preferably in the amount of 0.2 to 2.9 molar; most preferably in the amount of 0.25 to 1.7 molar. The method of any previous claim wherein the amount of said fluoride is 0.2 to 2.5 molar, preferably 0.25 to 1.5 molar. The method of any previous claim wherein the contacting with said composition is carried out at a temperature of 20°C to 90°C, preferably 30°C to 70°C.

Inventors: JAGANNATHAN RANGARAJAN, MADDEN KAREN P, MCCULLOUGH KENNETH J, OKORN-SCHMIDT HARALD F, POPE KEITH R, RATH DAVID L, JAGANNATHAN, RANGARAJAN, MADDEN, KAREN P., MCCULLOUGH, KENNETH J., OKORN-SCHMIDT, HARALD F., POPE, KEITH R., RATH, DAVID L.
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES
Application year: 1998
Main classification: C03C15
IPC codes: C09K13, C03C15, H01L21