# US 12,217,968 B2 · Atomic layer etching for smoothing of arbitrary surfaces > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,217,968 B2 - Document ID: US12217968B2 - Status: Granted - Kind: B2 - Application number: 17/224,037 - Filed: 2021-04-06 - Published: 2021-10-07 - Granted: 2025-02-04 - Earliest claimed: 2020-04-06 - Assignees: California Institute of Technology - Applicants: California Institute of Technology - Inventors: Harold Frank Greer - Web page: https://patentgrep.com/patent/US12217968B2 ## CPC - H10P 50/266: {by vapour etching only} - H10P 50/642: {Chemical etching} - H10P 50/242: {of Group IV materials} - H10P 50/283: {by chemical means} - H10P 72/0422: {for wet etching} - H10P 72/32: {between different workstations} - H10P 72/33: {into and out of processing chamber} - H10P 95/04: {Planarisation of conductive or resistive materials} - H10P 95/064: {the removal being chemical etching} - H10P 72/0424: {using mainly spraying means, e.g. nozzles} - H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10 ## Abstract A method for etching a surface including obtaining a substrate comprising a material; reacting a surface of a substrate with a reactant, comprising a gas or a plasma, to form a reactive layer on the substrate, the reactive layer comprising a chemical compound including the reactant and the material; and wet etching or dissolving the reactive layer with a liquid wet etchant of solvent that selectively etches or dissolves the reactive layer but not the substrate. ## Claims ### Claim 1 An apparatus: a reactor tool comprising a source of a reactant for reacting with a surface of a substrate so as to form a reactive layer on the substrate, wherein the reactant comprises is generated by a plasma, the substrate comprises a material comprising a semiconductor, a metal, or a dielectric, and the reactive layer comprises a chemical compound including the reactant and the material; and an etching tool comprising a source of a liquid wet etchant for removing the chemical compound; and a computer tool comprising a non-transitory computer readable medium storing a plurality of instructions, the plurality of instructions comprising: outputting the reactant in the reactor tool, transferring the substrate between the reactor tool and the etching tool, and outputting the liquid wet etchant in the etching tool to remove the chemical compound at a higher rate than the material so as to smoothen the surface of the substrate and form the surface having a root mean square surface roughness of less than 1 nm. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein: the reactive layer comprises at least one of: protrusions having sidewalls and the removing comprising wet etching the protrusions laterally through the sidewalls so as to planarize the surface and remove or shrink the protrusions, the protrusions having a height or width in a range of 1-100 nm; or valleys having sidewalls and the removing comprising wet etching the valleys laterally through the sidewalls so as to planarize the surface and remove or connect the valleys. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the reactant comprises at least one of a halogen that halogenates the surface, a sulphide so as to form the reactive layer comprising a sulphide, hydrogen or a hydride so as to form the reactive layer comprising a hydride, or a nitride or nitrogen or nitrogen containing species so as to form the reactive layer comprising a nitride. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein the reactant forms the reactive layer comprising a salt. ### Claim 5 (depends on 1) The apparatus of claim 1, further comprising a computer controlling output of the reactant and the wet etchant suitable for smoothing the material comprising a semiconductor comprising a III-V material or a metal comprising copper. ### Claim 6 (depends on 1) The apparatus of claim 1, further comprising a computer controlling output of the reactant and the wet etchant so as to form the reactive layer forming a polycrystalline metal including grain boundaries so that the wet etching is isotropic so as to remove grain boundaries in both lateral and vertical directions. ### Claim 7 (depends on 1) The apparatus of claim 1, further comprising the: computer programmable to: (a) instruct the output of the reactant so as to form the reactive layer; and (b) instruct the output of the liquid wet etchant, wherein: the step (a) forming the reactive layer further comprises at least one of: a pre-cleaning step prior to forming the reactive layer, or an activating step so as to make the reactive layer more amenable for the removing, and the computer is programmable to instruct repeating the step (a) prior to performing step (b). ### Claim 8 (depends on 7) The apparatus of claim 7, wherein the computer is programmable to instruct that the step (b) is performed only once. ### Claim 9 (depends on 1) The apparatus of claim 1, further comprising a tool configured to contact the liquid wet etchant with the reactive layer and so that the liquid wet etchant removes the reactive layer using a self-limiting process. ### Claim 10 (depends on 9) The apparatus of claim 9, wherein the tool comprises a bath or tank comprising the liquid wet etchant or a spray system spraying the liquid wet etchant. ### Claim 11 (depends on 9) The apparatus of claim 9, further comprising a tool configured to control contact of the liquid wet etchant on the reactive layer so as to controllably wet etch the reactive layer. ### Claim 12 An apparatus, comprising: a source of a reactant reacting with a surface of a substrate so as to form a reactive layer on the substrate, wherein the reactant is in gaseous form or is generated by a plasma, the substrate comprises a material, and the reactive layer comprises a chemical compound including the reactant and the material; a source of a treatment that removes the chemical compound at a higher rate than the material; and a computer programmable to: (a) instruct output of the reactant so as to form the reactive layer; (b) instruct performance of the treatment, and (c) instruct a repeat of steps (a) and (b) so as to perform a first cycle and a second cycle each comprising the step (a) and the step (b), wherein: the second cycle forms the reactive layer having a thickness that is thinner as compared to the reactive layer formed in the first cycle, so that the treatment in the second cycle removes the reactive layer with a finer resolution as compared to in the first cycle. ### Claim 13 (depends on 12) The apparatus of claim 12, further comprising a conveyor conveying the substrate between a first region wherein the reactant reacts with the surface of the substrate, and a second region wherein the treatment removes the reactive layer. ### Claim 14 (depends on 12) The apparatus of claim 12, further comprising: one or more reactor tools; one or more etching tools; a load lock chamber for loading the substrate comprising the material into the apparatus; a transfer chamber for transferring the substrate between the load lock, the reactor tools, and the etching tools; one or more arms positioned to transfer the substrate between the load lock, the reactor tools, and the etching tools; and a computer programmable to: (a) instruct the one or more arms to move the substrate to one of the reactor tools and controlling the one of the reactor tools so as to form the reactive layer; and′ (b) instruct the one or more arms to move the substrate to one of the etching tools and controlling the one of the etching tools so as to perform the treatment comprising a wet etch of the reactive layer. ### Claim 15 (depends on 12) The apparatus of claim 12, wherein the reactant comprises at least one of a halogen that halogenates the surface, a sulphide so as to form the reactive layer comprising a sulphide, hydrogen or a hydride so as to form the reactive layer comprising a hydride, a nitride or nitrogen or nitrogen containing species so as to form the reactive layer comprising a nitride, or oxygen or an oxide so as to form the reactive layer comprising an oxide. ### Claim 16 (depends on 12) The apparatus of claim 12, further comprising one or more chambers comprising first regions, wherein the chambers each comprise a vacuum or a pressure below atmospheric pressure during the reacting. ### Claim 17 (depends on 12) The apparatus of claim 12, further comprising: one or more reactor tools each comprising a first region, an outlet connected to a source of the reactant, the outlet for outputting the reactant towards the substrate in the first region, and electrodes and/or coils or wires electrically connected to a voltage supply for accelerating the reactant comprising charged particles towards the substrate; and one or more etching tools each comprising a bath, tank, or spray system, wherein: the treatment comprises a liquid wet etchant, the spray system comprises a spray nozzle for spraying the reactive layer with the wet etchant, and the spray system comprises or is coupled to a reservoir containing the wet etchant. ### Claim 18 (depends on 12) The apparatus of claim 12, wherein the treatment smoothens the surface of the substrate and forms the surface having a root means squared (RMS) surface roughness of less than 1 nm for an optical, mechanical, or assembly application. ### Claim 19 (depends on 12) The apparatus of claim 12, further performing a thermal treatment, a plasma treatment, or an ultraviolet (UV) treatment of the reactive layer. ### Claim 20 (depends on 19) The apparatus of claim 19, wherein the removing comprises performing the thermal treatment, the plasma treatment, or the UV treatment. ### Claim 21 An apparatus, comprising: a reactor tool for reacting a reactant with a surface of a substrate so as to form a reactive layer on the substrate, wherein the reactant comprises a plasma, and the reactive layer comprises a chemical compound including the reactant and the material; an etching tool for applying a treatment for removing the chemical compound at a higher rate than the material; a transfer chamber for transferring the substrate between the reactor tool and the etching tool; a computer programmable to instruct the apparatus to: (a) instruct the reactor tool to form the reactive layer and at least perform: a cleaning of the surface of the substrate prior to forming the reactive layer, or activating of the reactive layer so as to make the reactive layer more amenable for the removing; (b) repeat the step (a) in a presence of the reactive layer previously formed; and (c) instruct the etching tool to perform the treatment of the reactive layer to remove the reactive layer, such that the substrate is smoother after the reactive layer is removed. ### Claim 22 (depends on 21) The apparatus of claim 21, wherein the step (a) comprises the activating. ### Claim 23 (depends on 21) The apparatus of claim 21, wherein the activating comprises ion bombardment. ### Claim 24 (depends on 21) The apparatus of claim 21, wherein the activating changes at least one of a stoichiometry or oxidation state of the reactive layer. ### Claim 25 (depends on 21) The apparatus of claim 21, wherein the step (a) comprises the pre-cleaning. ### Claim 26 (depends on 21) The apparatus of claim 21, wherein the step (a) comprises the pre-cleaning and the activating. ### Claim 27 (depends on 21) The apparatus of claim 21, wherein the computer is programmable to instruct the apparatus to perform the treatment of the reactive layer only once. ### Claim 28 An apparatus comprising: a reactor tool comprising a source of a reactant, wherein the reactor tool is configured to ignite a plasma comprising the reactant; an etching tool comprising a source of a liquid wet etchant; and a substrate with a reactive layer disposed in the etching tool, wherein: the substrate comprises a material comprising a semiconductor, a metal, or a dielectric, the reactive layer was formed by reacting a surface of the substrate with the reactant and the plasma in the reactor tool, the reactive layer comprises a chemical compound including the reactant and the material, and the liquid wet etchant is configured to remove the chemical compound at a higher rate than the material in order to smoothen the surface of the substrate and to form the surface having a root mean square surface roughness of less than 1 nm.