X-Ray Assisted Etching of Insulators

Abstract

The invention is a method of electrochemical etching of a non-conductive insulator. The method entails inducing a current in the insulator by exciting electrons into the conduction band by supplying the needed energy through irradiation of the insulator. Alternatively, electrons may be supplied externally from an electron gun. The insulator is subject to an electrical bias, and the induced or supplied electrons then create a current in the insulator that effects the etch rated.

1 . A method of forming a device comprising: providing a substrate having a electronic band structure with an electronic band gap greater than about 3 eV, exposing a section of the substrate's surface to an electrolyte, applying an electrical bias between a region of the substrate and the electrolyte; and exposing a portion of the substrate to radiation produced from a radiation source having energy sufficient to generate mobile charge carriers within the substrate, thereby generating a current within the substrate to etch portions of said section of the substrate's surface exposed to said etchant. 
     
     
         2 . The method of  claim 1  in which the radiation source is an X-ray radiation source. 
     
     
         3 . The method of  claim 2  wherein said X-ray radiation has an energy level in excess of 100 eV. 
     
     
         4 . The method of  claim 2  further comprising positioning a patterned radiation-opaque mask between the substrate and the radiation source. 
     
     
         5 . The method of  claim 1  further comprising forming a patterned etch mask on the substrate's surface exposed to said electrolyte. 
     
     
         6 . The method of  claim 5  further comprising applying a reverse bias between a second region of the substrate and the electrolyte. 
     
     
         7 . The method of  claim 6  where said substrate has at least two opposing sides, and said region and second region are on opposing sides of the insulator. 
     
     
         8 . The method of  claim 1  wherein the electrical bias is applied between the region of substrate and the electrolyte by connecting a voltage source between a reference electrode in said electrolyte and a bias contact positioned on the surface of the substrate. 
     
     
         9 . A method of forming a device comprising: providing substrate, exposing a portion of the substrate's surface to an electrolyte, applying a first electrical bias between a first region of the substrate and the electrolyte and applying a second electrical bias between a second region of the substrate and the electrolyte, and exposing a portion of the substrate to radiation produced from a radiation source having energy levels exceeding 100 eV, and sufficient to generate mobile charge carriers within the substrate, thereby generating a current in portions of the substrate to etch portions of said substrate surface. 
     
     
         10 . The method of  claim 1  wherein said substrate consists essentially of quartz, or Lithium Niobate or Lithium Tantalate or Silicon Carbide or Lithium Tetraborate, or combinations thereof. 
     
     
         11 . The method of  claim 10  wherein said electrolyte comprises hydrofluoric acid (HF) or ammonium fluoride (NH4F) or ammonium bifluoride (NH4HF2) or other solution containing fluoride (F) ions. 
     
     
         12 . The method of  claim 1  wherein said device is a resonator. 
     
     
         13 . A method of electrochemical etching of substrate, comprising the step of supplying electrons to said substrate from an external electron source, exposing a portion of the substrate's surface to an electrolyte, applying a first electrical bias between a first region of the substrate and the electrolyte, thereby generating a current in portions of the substrate to etch portions of said substrate surface. 
     
     
         14 . The method of  claim 9  wherein said substrate has a band gap greater than 3 eV. 
     
     
         15 . The method of  claim 9  wherein said created current has a current density greater than 10 pA/cm2 at a region on a surface of said substrate exposed to said electrolyte. 
     
     
         16 . The method of  claim 2  wherein said x-ray radiation has an intensity of greater than 1 uW/cm 2 . 
     
     
         17 . A method of electrochemical etching of substrate having a electronic band structure with an electronic band gap greater than about 3 eV, comprising the step of generating free carriers in the substrate, exposing a portion of the substrate's surface to an electrolyte, applying a first electrical bias between a first region of the substrate and the electrolyte, thereby generating a current in portions of the substrate to etch portions of said substrate surface, said current having a current density greater than 10 pA/cm2 at a region on a surface of said substrate exposed to said electrolyte. 
     
     
         18 . A method of forming a device comprising a series of resonator precursers, comprising the steps of providing a substrate having a electronic band structure with an electronic band gap greater than about 3 eV, exposing a section of the substrate's surface to an electrolyte, applying a series of electrical biases, each applied between an associated region of the substrate and the electrolyte; and exposing a portion of the substrate to radiation produced from a radiation source having energy sufficient to generate mobile charge carriers within the substrate, thereby generating a series of currents within the substrate to etch a series of portions of said section of the substrate's surface exposed to said etchant. 
     
     
         19 . The method of  claim 18  further comprising the step of monitoring the etch rate or sample thickness at a plurality of said series of portions of said section of the substrate's surface exposed to said etchant, and modifying a plurality of said series of electrical biases in response to said monitoring step. 
     
     
         20 . A method of creating a series of resonators comprising creating a series of resonator precursers according to the method of  claim 18 , each resonator precursor having at two sides, forming conductive leads on each side of said series of resonator precursers, and physically separating said series on said substrate into a series of resonators. 
     
     
         21 . The method of  claim 2  wherein said X-ray radiation source comprises a Xenon flash lamp, a plasma source, an X-ray tube, or a synchrotron x-ray source. 
     
     
         22 . The method of  claim 18  wherein said series of electrical biases each applied between an associated region of the substrate and the electrolyte are applied through a series of electrodes positioned on said substrate and a reference electrode positioned in said electrolyte. 
     
     
         23 . The method of  claim 21  wherein said series of biases comprises at least two different bias values. 
     
     
         24 . The method of  claim 17  wherein said substrates consists essentially of Silicon Carbide, Galium Nitride, Lithium Niobate, Tantalum Pentoxide, Aluminum Oxide, Diamond, Titanium Oxide, Silicon nitride, Lithium Tantalate, quartz, or combinations thereof.