Methods of Forming Three-Dimensional Structures Having Reduced Stress and/or Curvature

• US 20140238865A1
• Filed: 02/28/2014
• Published: 08/28/2014
• Est. Priority Date: 05/07/2002
• Status: Active Grant

• Current Assignee: Microfabrica Incorporated (Technoprobe S.P.A.)
• Original Assignee: Microfabrica Incorporated (Technoprobe S.P.A.)
• Inventors: Kumar, Ananda H., Cohen, Adam L., Kim, Kieun, Lockard, Michael S., Frodis, Uri, Smalley, Dennis R., Alberron, Jorge S.
• Granted Patent: US 9,540,233 B2
• Time in Patent Office: Days
• US Class Current: 205/135
• CPC Class Codes: B81C 1/00666 Treatments for controlling internal stress or strain in MEMS structures
• CPC Class Codes: C25D 5/022 using masking means

Abstract

Electrochemical fabrication processes and apparatus for producing single layer or multi-layer structures where each layer includes the deposition of at least two materials and wherein the formation of at least some layers includes operations for reducing stress and/or curvature distortion when the structure is released from a sacrificial material which surrounded it during formation and possibly when released from a substrate on which it was formed. Six primary groups of embodiments are presented which are divide into eleven primary embodiments. Some embodiments attempt to remove stress to minimize distortion while others attempt to balance stress to minimize distortion.

Claims

1. In a method of forming a multi-layer three-dimensional structure, including:

(A) forming a plurality of successive layers of the structure with each successive layer, except for a first layer, adhered to a previously formed layer and with each successive layer comprising at least two materials, one of which is a structural material and the other of which is a sacrificial material, and wherein each successive layer defines a successive cross-section of the three-dimensional structure, and wherein the forming of each of the plurality of successive layers includes;

(i) depositing a first of the at least two materials;

(ii) depositing a second of the at least two materials; and

(B) after the forming of the plurality of successive layers, separating at least a portion of the sacrificial material from the structural material to reveal the three-dimensional structure, wherein the improvement comprises;

in association with the formation of at least one of the successive layers, dividing the layer into a first thin sublayer and a second thicker sublayer and depositing a primary structural material in a lateral region of the first sublayer to form at least a portion of the sublayer, and thereafter planarizing the primary structural material to a height that bounds the first sublayer, where the thickness of the first sublayer is similar to a known or estimated effective work hardened thickness (e.g. preferably having a thickness between ⅓ and

3 times that of the estimated or known effective work hardened thickness, more preferably between ½ and

2 times that of the estimated or known effective work hardened thickness, even more preferably within 2/3 and 3/2 times that of the estimated or known effective work hardened thickness, even more preferably between 4/5 and 5/4 times that of the estimated or known effective work hardened thickness, and most preferably between 9/10 and 10/9 times that of the estimated or known effective work hardened thickness) or less than a known or estimated effective work hardened thickness induced by the planarization operation, and thereafter depositing the primary structural material in a lateral region of the second sublayer, and thereafter planarizing the primary structural material of the second sublayer.

6. The method of claim 1 where curvature during formation of the structure is reduced by forming the structure on a thick rigid substrate.

7. The method of claim 1 where curvature during formation of the structure is reduced by plating material periodically on the back side of the substrate as a thickness of deposited material on the front side of increase.

8. The method of claim 7 wherein the material plated on the back side of the substrate is planarized after it is deposited.

2. In a method of forming a multi-layer three-dimensional structure, including:

(A) forming a plurality of successive layers of the structure with each successive layer, except for a first layer, adhered to a previously formed layer and with each successive layer comprising at least two materials, one of which is a structural material and the other of which is a sacrificial material, and wherein each successive layer defines a successive cross-section of the three-dimensional structure, and wherein the forming of each of the plurality of successive layers includes;

(i) depositing a first of the at least two materials;

(ii) depositing a second of the at least two materials; and

(B) after the forming of the plurality of successive layers, separating at least a portion of the sacrificial material from the structural material to reveal the three-dimensional structure, wherein the improvement comprises;

in association with the formation of at least one of the successive layers, depositing a primary structural material in a lateral region of the layer to form at least a majority of the one successive layer in the lateral region, and thereafter planarizing the primary structural material to a height that bounds or exceeds the desired height of the at least one successive layer and such that at least a portion of the primary structural material is work hardened, etching into the primary structural material to form one or more openings that extend into the one successive layer in a least a portion of the lateral region to remove at least a portion of the work hardened primary structural material.

3. The method of claim 2 further comprising depositing structural material into the one or more openings after etching.

4. The method of claim 3 wherein the depositing of structural material into the one or more openings occurs during deposition associated with formation of a subsequent successive layer.

5. The method of claim 3 wherein the depositing of structural material into the one or more openings occurs prior to being a deposition associated with formation of a subsequent successive layer.

9. In a method of forming a multi-layer three-dimensional structure, including:

(A) forming a plurality of successive layers of the structure with each successive layer, except for a first layer, adhered to a previously formed layer and with each successive layer comprising at least two materials, one of which is a structural material and the other of which is a sacrificial material, and wherein each successive layer defines a successive cross-section of the three-dimensional structure, and wherein the forming of each of the plurality of successive layers includes;

(i) depositing a first of the at least two materials;

(ii) depositing a second of the at least two materials; and

(B) after the forming of the plurality of successive layers, separating at least a portion of the sacrificial material from the structural material to reveal the three-dimensional structure, wherein the improvement comprises;

forming at least one layer such that a primary structural material on the layer is provided with an upper surface configuration, planarizing the upper surface, and thereafter forming notches in the planarized surface in a desired pattern where the notches provide decoupling of stress located in separated regions of structural material.