Dielectric etching
An etchant for dielectrics, such as silicon dioxide, that leaves monocrystalline silicon surface exposed by the etchant free of etch damage, such as etch pits, when the etch is done in the presence of transition metals, such as copper, tungsten, titanium, gold, etc. The etchant comprises hydrofluoric acid and a source of halide anion, such as hydrochloric acid or a metal-halide. The etchant is useful in microelectromechanical system device fabrication and in deprocessing integrated circuits or the like.
1. A method of etching, comprising the steps of: providing a device having a silicon layer with dielectric thereon; and etching the dielectric, in the presence of a material comprising at least one transition metal, with an etchant to expose at least a portion of the silicon layer; wherein the etchant consists of:
a first volume of about 49 percent by weight HF in a diluent;
a second volume of about 37 percent by weight transition metal sequestering agent in the diluent, the second volume being about the same as the first volume; and
a remaining volume of about 40 percent by weight buffering agent in the diluent, the remaining volume being about six times the first volume.
2. The method of claim 1 , wherein the transition metal sequestering agent is a halide anion from the group consisting of a chloride ion, a bromide ion, and an iodide ion, and the etchant has a halide anion to HF mole ratio of about 1:7 to about 100:1.
3. The method of claim 2 , wherein the halide anion is selected from the group of chlorine, iodine, and bromine, and the halide anion to HF mole ratio is from 0.21:1 to 0.84:1.
4. The method of claim 1 , wherein the transition metal sequestering agent is provided by a water-soluble metal-halide dissolved in water.
5. The method of claim 4 , wherein the metal in the water-soluble metal-halide is selected from the group of sodium, potassium, magnesium, and calcium, and the halide is selected from the group of chlorine, iodine, and bromine.
6. The method of claim 1 , wherein the transition metal sequestering agent is provided by HCl and the etchant has an HCl to HF mole ratio of about 1:7 to about 100:1.
7. The method of claim 1 , wherein the transition metal sequestering agent is provided by HCl and the etchant has an HCl to HF mole ratio of about 0.21:1 to about 0.84:1.
8. The method of claim 1 , wherein the transition metal is from the group of: Cu, Ti, W, Ni, Cr, Co, Ta, Pd, Pt, and Au.
9. The method of claim 1 , wherein the dielectric is silicon dioxide or a glass.
10. The method of claim 1 , wherein the buffering agent is ammonium fluoride and the etchant has an ammonium fluoride to HF mole ratio of about 100:1 to about 1:10.
11. The method of claim 1 , wherein the etchant is diluted with water, ethylene glycol, or a combination of water and ethylene glycol, wherein the etchant has an HF molarity of about 0.014 mol/l to about 22 mol/l.
12. The method of claim 1 , wherein the material is a nitride or a silicide of the transition metal.
13. A method of etching, comprising the steps of: providing a device having a layer of silicon with dielectric thereon; and etching the dielectric, in the presence of a material comprising at least one transition metal, with an etchant to expose at least a portion of the silicon wafer; wherein the etchant comprises HF, a transition metal sequestering agent, the transition metal sequestering agent comprising a halide anion provided by a water-soluble metal-halide dissolved in ethylene glycol, and over 10 percent by volume of a buffering agent.
14. The method of claim 13 , wherein the metal in the metal-halide is selected from the group of sodium, potassium, magnesium, and calcium, and the halide is selected from the group of chlorine, iodine, and bromine, and wherein the etchant has a halide anion to HF mole ratio of about 1:7 to about 100:1.
15. The method of claim 14 , wherein the halide anion to HF mole ratio ranges from about 0.21:1 to about 0.84:1.
16. The method of claim 13 , wherein the transition metal is from the group of: Cu, Ti, W, Ni, Cr, Co, Ta, Pd, Pt, and Au.
17. The method of claim 13 , wherein the dielectric is silicon dioxide or a glass.
18. The method of claim 13 , wherein the etchant includes a buffering agent of ammonium fluoride and the etchant has an ammonium fluoride to HF mole ratio of about 100:1 to about 1:10.
19. The method of claim 13 , wherein the etchant is further diluted with water, and wherein the etchant has an HF molarity of about 0.014 mol/l to about 22 mol/l.
20. A method of etching, comprising the steps of: providing a device having a silicon layer and a silicon dioxide layer on the silicon layer, the silicon dioxide layer including a layer of copper in contact therewith; etching the silicon dioxide layer, in the presence of the copper layer, using a mixture of BHF and HCl to expose at least a portion of the silicon layer, thereby leaving the exposed layer of silicon without significant etch-induced damage; wherein the etchant has an HCl to HF mole ratio of about 0.21:1 to about 0.84:1 and wherein the etchant consists of HCl, HF, a buffer, and water.