# ETCHING SOLUTION, ETCHED ARTICLE AND METHOD FOR ETCHED ARTICLE 

The present invention relates to an etching solution, a method for producing an etched article and an etched article produced by the method, more specifically, an etching solu› tion and a method for producing an etched article for selec› tively etching a doped oxide film, particularly BSG or BPSG relative to an undoped oxide film, particularly THOX, and an etched article produced by the method. 

Conventionally, as etchants for silicon wafers and the like have been used buffered hydrofluoric acids comprising HF (50% by weight) and NH$_{4}$ F (40% by weight) at such a ratio that can achieve a desired etch rate. 

However, the buffered hydrofluoric acids etch not only doped oxide films such as BSG films, BPSG films, phospho› silicate glass (PSG) films, arsenic silicate glass (AsSG) films and the like, but also undoped oxide films such as USG including TEOS (oxide obtained by CVD method using tet› raethoxysilane gas) films, THOX and the like. Therefore, the buffered hydrofluoric acids can not selectively etch the doped oxide films. 

An object of the present invention is to provide an etching solution and an etching method for selectively etching oxide films doped with impurities relative to TEOS and THOX. 

DISCLOSURE OF INVENTION 

The present invention relates to the items 1-16 listed below. 

Item 1: An etching solution comprising hydrofluoric acid, wherein an a ratio of etch rate of a boron silicate glass film (BSG) or boron phosphosilicate glass / an etch rate of a thermal oxide film (THOX) at 25° C. is 10 or higher. 

Item 2: The etching solution according to item 1, wherein a solvent in the etching solution has a relative dielectric constant of 61 or lower. 

Item 3: The etching solution according to item 1, the solution containing at least one member selected from the group consisting of an organic acid and an organic solvent having a hetero atom. 

Item 4: The etching solution according to item 1, the solution containing (i) water and (ii) at least one member selected from the group consisting of an organic acid and an organic solvent having a hetero atom, the water being contained in a concentration of 70% by weight or lower. 

Item 5: The etching solution according to item 1, wherein the weight ratio ofHF:isopropyl alcohol:water is 0.1-50% by weight: 30-99% by weight: 0-70% by weight. 

Item 6: The etching solution according to item 1, wherein the weight ratio ofHF:acetic acid:water is 0.1-50% by weight: 30-99 .9% by weight: 0-70% by weight. 

Item 7: The etching solution according to item 1, wherein the weight ratio of HF:tetrahydrofuran:water is 0.1-50% by weight: 30-99.9% by weight: 0-70% by weight. 

Item 8: The etching solution according to item 1, wherein the weight ratio of HF: acetone:water is 0.1-50% by weight: 30-99 .9% by weight: 0-70% by weight. 

Item 9: The etching solution according to item 1, wherein the weight ratio of HF: methanol: water is 0.1-50% by weight: 30-99 .9% by weight: 0-70% by weight. 

TECHNICAL FIELD 

BACKGROUND ART 

Item 10: The etching solution according to item 1, wherein the weight ratio of HF:ethanol:water is 0.1-50% by weight: 30-99 .9% by weight: 0-70% by weight. 

Item 11: The etching solution according to item 1, the solu› tion comprising an inorganic acid. 

Item: 12 The etching solution according to item 11, wherein the inorganic acid has a pKa value at 25° C. of 2 or lower. 

Item 13: The etching solution according to item 11, wherein the weight ratio ofHF:HCl:water is 0.01-50% by weight: 1-36% by weight: 0-99% by weight. 

Item 14: The etching solution according to item 11, wherein the weight ratio ofHF:HNO$_{3}$:wateris 0.01-50% by weight: 1-70% by weight: 0-99% by weight. 

Item 15: A method for producing an etched article by etching an article to be etched with the etching solution as defined inanyofitems 1-14. 

Item 16: An etched article which is obtainable by the method of item 15. 

According to the etching solution of the invention, the ratio of BSG etch rate/TH OX etch rate and/or the ratio of BPSG etch rate/THOX etch rate at 25° C. is/are 10 or higher, pref› erably 20 or higher, more preferably 50 or higher, particularly 100 or higher. 

In case of using TEOS instead ofTHOX, the ratio ofBSG etch rate/TEOS etch rate and/or the ratio of BPSG etch rate/ TEOS etch rate at 25° C. is/are 5 or higher, preferably 10 or higher, more preferably 50 or higher, particularly 100 or higher. 

The etch rate of the etching solution of the invention can be calculated as the difference in thickness of a film (BSG; BPSG; THOX; TEOS and like USG, etc.) before and after etching divided by etch time. 

The water content is not higher than 70% by weight, pref› erably not higher than 30% by weight, more preferably about 30-5% by weight. The relative dielectric constant of the etch› ing solution expresses an arithmetic mean of the relative dielectric constants of the components of the etching solu› tions other than the HF and inorganic acid. 

Preferable examples of the inorganic acid include inor› ganic acids having a pKa value at 25° C. of 2 or lower, for example, hydrochloric acid (pKa =-8), nitric acid (pKa=- 1.8), hydrobromic acid (pKa=-9), hydroiodic acid (pKa=- 10) and perchloric acid (a pKa-unmeasurably strong acid). 

Examples of the organic acid include acetic acid (relative dielectric constant: 6.15 (20° C.)), propionic acid (relative dielectric constant: 3.4 ( 40° C.)), butyric acid (relative dielec› tric constant: 2.97(20° C.)), isobutyric acid (relative dielectric constant: 2.73( 40° C.)), valeric acid, caproic acid (relative dielectric constant: 2.63(71 ° C.)), caprylic acid (relative dielectric constant: 2.45(20° C.)), monochloroacetic acid (relative dielectric constant: 21 (20° C.)), dichloroacetic acid (relative dielectric constant: 8.08(20° C.)), trichloroacetic acid (relative dielectric constant: 4.6 (60° C.)), monofluoro› acetic acid, difluoroacetic acid, trifluoroacetic acid, a-chlo- robutyric acid, ~-chlorobutyric acid, y-chlorobutyric acid, lactic acid (relative dielectric constant: 22(70° C.)), glycolic acid, pyruvic acid, glyoxalic acid, acrylic acid and like mono› carboxylic acids, methanesulfonic acid, toluenesulfonic acid and like sulfonic acids, oxalic acid, succinic acid, adipic acid, tartaric acid, citric acid and like polycarboxylic acids. 

Examples of the organic solvent having a hetero atom include methanol (relative dielectric constant: 32.6 (25° C.)), ethanol (relative dielectric constant: 24.6 (25° C.)), isopro› panol (IPA, relative dielectric constant: 19.9 (25° C.)), 1-pro› panol (relative dielectric constant: 22.2 (25° C.)), 1-butanol (relative dielectric constant: 17.1 (25° C.)), 2-butanol (rela- tive dielectric constant: 15.5 (19° C.)), t-butanol (relative 

