Masking methods for ALD processes for electrode-based devices

Abstract

Masking methods for atomic-layer-deposition processes for electrode-based devices are disclosed, wherein solder is used as a masking material. The methods include exposing electrical contact members of an electrical device having an active device region and a barrier layer formed by atomic layer deposition. This includes depositing solder elements on the electrical contact members, then forming the barrier layer using atomic layer deposition, wherein the barrier layer covers the active device region and also covers the solder elements that respectively cover the electrical contact members. The solder elements are then melted, which removes respective portions of the barrier layer covering the solder elements. Similar methods are employed for exposing contacts when forming layered capacitors.

Claims

1. A method of exposing electrical contact members of an electrical device having an active device region and a barrier layer formed by atomic layer deposition (ALD), the method comprising: depositing solder elements on the electrical contact members; forming the barrier layer using ALD, wherein the barrier layer covers the active device region and also covers the solder elements that respectively cover the electrical contact members; and removing respective portions of the barrier layer covering the solder elements after melting the solder elements.

2. The method according to claim 1, wherein the barrier layer includes at least one of Al.sub.2O.sub.3, SiO.sub.2, TiO.sub.2 and ZrO.sub.2.

3. The method according to claim 1, wherein the solder elements are formed using solder-bump technology.

4. The method according to claim 1, wherein the electrical contact members are located around at least a portion of a perimeter of the active device region.

5. The method according to claim 1, wherein melting the solder elements includes applying heat to the solder elements through the barrier layer.

6. The method according to claim 5, wherein the heat is provided by a laser.

7. The method according to claim 1, further comprising removing the solder elements from the electrical contact members to expose the electrical contact members.

8. The method according to claim 1, wherein at least portions of each of the solder elements remain on the respective electrical contact members.

9. The method according to claim 1, wherein the active region includes at least one of: a light-emitter, a light sensor, a MEMS device, an electrolytic capacitor and a DMD device.

10. The method according to claim 1, further comprising establishing electrical contact with one or more of the electrical contact members.

11. The method according to claim 1, wherein the electrical contact members include electrical contact pads or electrical contact pins.

12. A method of providing at least one electrical contact for an electrode-based electrical device, comprising: a) depositing a first metal layer on a support substrate using an atomic layer deposition (ALD) process, wherein the first metal layer defines a first electrode; b) depositing at least one first solder element on the first metal layer; c) forming an insulating layer over the first metal layer and the at least one first solder element; d) forming at least one exposed portion of the first metal layer after melting the first solder element and removing a corresponding portion of the insulating layer; e) depositing at least one second solder element on the at least one exposed portion of the first metal layer; f) adding a second metal layer over the insulating layer and the at least one second solder element to define a second electrode; and g) defining at least one electrical contact for the first electrode after melting the at least one second solder element and exposing at the least one exposed portion of the first metal layer.

13. The method according to claim 12, wherein the electrode-based electrical device is a capacitor.

14. The method according to claim 12, wherein forming the insulating layer includes depositing an insulating material using an ALD process.

15. The method according to claim 14, wherein the insulating material is Al.sub.2O.sub.3.

16. The method according to claim 12, wherein the support substrate comprises a micro-capillary plate made of an insulating material.

17. The method according to claim 14, wherein at least one of the first and second metal layers is made of platinum.

18. The method according to claim 12, wherein the support substrate includes high-aspect-ratio features.

19. The method according to claim 12, wherein the electrode-based electrical device is a metal-oxide-metal capacitor.

20. The method according to claim 12, wherein the at least one first and second solder elements includes respective pluralities of the first and second solder elements.

21. The method according to claim 12, wherein act e) includes the at least one second solder element covering a portion of the insulating layer immediately adjacent the at least one exposed portion of the first metal layer, and wherein act g) exposes the portion of the insulating layer that was covered in act e).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the Detailed Description serve to explain principles and operation of the various embodiments. As such, the disclosure will become more fully understood from the following Detailed Description, taken in conjunction with the accompanying Figures, in which:

(2) FIG. 1A is a top-down schematic diagram of an example electronic device showing an active device region, electrical contact members surrounding a perimeter of the active device region, and an ALD barrier layer covering the surface of the electronic device;

(3) FIG. 1B is a cross-sectional view of the electronic device of FIG. 1A as taken along the line 1B-1B therein, showing solder elements formed on each of the electrical contact members, with the ALD barrier layer covering the solder elements;

(4) FIG. 1C is similar to FIG. 1B and illustrates the application of heat to the structure of FIG. 1B to melt the solder elements;

(5) FIG. 1D is similar to FIG. 1C and shows the solder elements having been melted, resulting in the local removal of portions of the ALD barrier layer from above the electrical contact members, thereby exposing the electrical contact members and allowing for electrical connection thereto;

(6) FIGS. 2A through 2G are schematic diagrams that illustrate an example method of processing a microcapillary plate to form a capacitor using the masking methods disclosed herein; and

(7) FIGS. 3A through 3H are cross-sectional views that show an example ALD-based process and masking method for substrate having high-aspect-ratio trench features such as used to form a metal-insulator-metal (MIM) capacitor.

DETAILED DESCRIPTION

(8) Reference is now made in detail to various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like parts. The drawings are not necessarily to scale, and one skilled in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure.

(9) The claims as set forth below are incorporated into and constitute part of this Detailed Description.

(10) The term solder is used herein to describe a material that has a melting temperature higher than ALD deposition temperatures but lower than that of the dielectric and metal layers that constitute the electrode-based devices that are subjected to the masking and processing techniques disclosed herein. The term solder thus includes but is not limited to relatively low-melting alloys, such as those that include tin or lead or brass or silver or copper or zinc or indium or bismuth or gallium or mercury, or combinations thereof. An example definition for solder as the term is used herein is a material with a melting point higher than ALD deposition temperatures and with low vapor pressure at ALD deposition temperatures, wherein the melting point is sufficiently low to allow for removal of the material from an electrode-based device via application of heat to the device where the material is located, without damaging the underlying layer or layers while also selectively removing corresponding portions of an overlying layer or layers.

(11) Example Electronic Device and Masking Process

(12) FIG. 1A is a top-down view of an example electronic device 10 that has a substrate 11 with a surface 12 on which is formed electrical contact members 20 and an active device region 30 having a perimeter 32. The electrical contact members 20 are shown in the form of contact pads, but can also be in the form of contact pins. The electrical contact members 20 are typically relatively large as compared to the other device features, e.g., 200 microns or larger. In an example, the electrical contact members 20 are located on the surface 12 adjacent the perimeter 32 of active device region 30. In an example, ALD is used to form a coating or barrier layer 50 that covers the surface 12 and encapsulates or seals the active device region 30 and also covers the electrical contact members 20.

(13) FIG. 1B is a cross-sectional side view of the structure of FIG. 1A and shows solder elements 22 formed on each of the electrical contact members 20, and also shows the substantially conformal barrier layer 50 that covers the surface features of the electronic device 10. The solder elements 22 serve as mask elements for the electrical contact members 20 and have a higher melting temperature than the ALD process temperature used to form the barrier layer 50 but a lower melting temperature than the metal (e.g., copper) that makes up the electrical contact members 20. The selective deposition of solder elements 22 can be accomplished using known solder-bump technology.

(14) FIG. 1C is similar to FIG. 1B and shows the structure of electronic device 10 as heat H is applied to the structure to melt the solder elements 22. In an example, heat H is applied using a heat source such as a laser. In another example, heat H is applied by a conventional heat source. In an example, the heat H is applied locally at the location of solder elements 22. The melting of solder elements 22 serves to locally remove the corresponding portion of barrier layer 50 above the electrical contact members 20, thereby exposing the electrical contact members 20 while leaving the other portion of the barrier layer 50 generally intact, as shown in FIG. 1D. The solder elements 22 thus act as low-temperature localized mask elements that are readily removed by the application of heat H, wherein the amount of heat H does not melt the electrical contact members 20 or damage the electronic device 10 if it is temperature sensitive.

(15) In an example, at least a portion of each solder elements 22 becomes part of the corresponding electrical contact member 20. This does not compromise the electrical contact member 20 because the solder material, like the electrical contact member 20, is conducting. In another example, the solder elements 22 are substantially entirely removed from the structure, leaving the exposed electrical contact members 20 without any substantial solder residue thereon. Removal of melted solder elements 22 can be accomplished using means well known in the art, such as a de-solder gun, a solder sucker, or a solder wick or braid.

(16) FIG. 1D also shows an electrical wire 60 used to establish electrical contact with one of the electrical contact members 20 once they are exposed as described above.

(17) Electrolytic Capacitor Example

(18) Dielectric ALD coatings are used in electrolytic capacitors to form a metal-dielectric electrode portion of the capacitor, while an electrolyte forms the second electrode. The dielectric ALD coating is used to cover the 3D structure but in the deposition process also covers the metal layer, making it difficult to access the metal electrode. Thus, in an example solder elements 22 is used as a mask to form an electrical contact in the flat (non-3D) metal region of the capacitor.

(19) Thus, another application of the methods disclosed herein is for an electronic device 10 in the form of an electrolytic capacitor. FIG. 2A is a top elevated view of an example micro-capillary plate 110 used to form the electrolytic capacitor. The example micro-capillary plate 110 is disk-shaped and has a body 111, a top surface 112, a bottom surface 114, an inner edge 116, a central axis AC and a plurality of cylindrical micro-holes 120 (hereinafter, capillaries). In an example, the body 111 is made of an insulating material such as glass. The capillaries 120 are open at the top and bottom surfaces 112 and 114 and run parallel to the central axis AC. Each capillary 120 has an inner surface 122 and diameter d, which in an example can be from about 2 microns to several hundred microns. The close-up inset of FIG. 2A is a top-down view of section of the micro-capillary plate 110 showing four of the capillaries 120.

(20) The formation of an electrolytic capacitor involves performing a number of process steps on the micro-capillary plate 110. FIG. 2B is similar to the close-up inset of FIG. 2A and shows four capillaries 120 in a section adjacent the inner edge 116 of the array of capillaries, and illustrates a first process step wherein a first metal layer 130 is deposited on the top surface 112 and the inner surface 122 of capillaries 120 using an ALD process. In an example, the first metal layer 130 is platinum. Note that the conformality of the ALD process allows for deposition of the first metal layer 130 so that it covers the inner surface 122 of capillaries 120 as well as the top surface 112. The first metal layer 130 serves as a first electrode for the electrolytic capacitor being formed.

(21) FIG. 2C illustrates as second process step wherein a small patch of solder 140 is deposited atop of the first metal layer 130 on the top surface 112 near the inner edge 116 of the array of capillaries 120. The solder 140 serves as a mask for the next step in the process.

(22) FIG. 2D illustrates a third process step wherein an insulating layer 150 is formed over the first metal layer 130 using an ALD process. An example material for the insulating layer 150 is a dielectric material such as Al.sub.2O.sub.3.

(23) FIG. 2E is a cross-sectional view of the micro-capillary plate 110 in FIG. 2D and further illustrates a fourth process step wherein a second metal layer 160 is formed on the bottom surface 114 of the micro-capillary plate 110 to serve as a second electrode. In an example, this is accomplished by partially inserting the micro-capillary plate 110 into an electrolytic solution.

(24) FIG. 2F is similar to FIG. 2D and shows the results fifth process step whereby the solder 140 is removed by melting it (e.g., by applying heat H as shown in FIG. 2E) so that the underlying portion of the first metal layer 130 is exposed to form an exposed portion 130E of the first metal layer portion 130, wherein the first metal layer 130 serves as a first electrode as noted above. The exposed portion 130E serves as an electrical contact for the resulting electrolytic capacitor. FIG. 2G is similar to FIG. 2E and shows the exposed portion 130E that defines an electrical contact in the first metal layer 130 for the resulting electrolytic capacitor device 200.

(25) In another example of the above process, the second metal layer 160 is formed using an ALD process rather than a more localized electrolytic deposition process. In this case, the process is modified to include additional solder elements formed on the dielectric layer prior to depositing the second metal layer 160 using ALD. The additional solder elements serve to define the second electrode while prevent a short-circuit path between the first and second metal layers 130 and 160.

(26) Another Example Electrode-Based Electrical Device and Masking Process

(27) The methods disclosed herein are generally applicable to electrode-based electrical devices where a portion of a metal layer of a device needs to be masked when forming the device so that it can later be exposed to provide a metal contact for making an external electrical connection. For example, high-surface-area capacitors with high-aspect-ratio features such as trenches or through holes (e.g., capillaries, such as discussed above) need to be processed to form electrodes that require electrical contacts.

(28) A general method of forming electrical contacts for an electrode-based device is now described with reference to FIGS. 3A through 3H. FIG. 3A is a cross-sectional view of a portion of a substrate 300 that has an upper surface 302 and a high-aspect-ratio (HAR) structure 310 in the form of a trench defined by sidewalls 312 and a bottom wall 314. The substrate 300 can be made of aerogel, anodic aluminum oxide, glass, etc. Here, a high-aspect-ratio means that the depth of the HAR structure 310 is greater than its width, e.g., by at least a factor of two, or at least a factor of 4, etc. Many HAR structures 310 can an aspect ratio of greater than 10 or greater than 100 or even greater than 1000.

(29) With reference to FIG. 3B, in a first step, a first metal layer 330 is conformally deposited on the sidewalls 312 and bottom wall 314 of HAR structure (trench) 310 using an ALD process. An example first metal layer 330 is made from platinum.

(30) With reference to FIG. 3C, in a second step, at least one first solder portion (e.g., patches) 340 is deposited on portions of the first metal layer 330 that will later serve as electrical contacts for an external connection.

(31) With reference to FIG. 3D, in a third step, a dielectric layer 350 is conformally deposited over the first metal layer 330, including the first solder portions 340, using an ALD process. An example material for the dielectric layer 350 is AL.sub.2O.sub.3.

(32) With reference to FIG. 3E, in a fourth step the first solder portions 340 are removed by the application of heat H (see FIG. 3D), which removes the overlying portion of dielectric layer 350 and leaves an exposed metal portion 330E of first metal layer 330.

(33) With reference to FIG. 3F, in a fifth step, second solder portions 340 are deposited on the exposed metal portions 330E as well as a small portion 350E of dielectric layer 350 that surrounds the exposed metal portions 330E.

(34) With reference to FIG. 3G, in a sixth step, a second metal layer 360 is deposited over the dielectric layer 350 and second solder portions 340. The dielectric layer 350 thus serves to electrically isolate the two metal layers 330 and 360.

(35) With reference to FIG. 3H, in a seventh step, heat H is applied to remove the second solder portions 340 (see FIG. 3G), which also removes select portions of the second metal layer 360 to expose portions 350E of the underlying dielectric layer 350 while also exposing the exposed metal portions 330E of first metal layer 330 that can serve as electrical contacts. The resulting structure is of the type used in MIM capacitors, for example, wherein the first and second metal layers 330 and 360 serve as first and second electrodes.

(36) It will be apparent to those skilled in the art that various modifications to the preferred embodiments of the disclosure as described herein can be made without departing from the spirit or scope of the disclosure as defined in the appended claims. Thus, the disclosure covers the modifications and variations provided they come within the scope of the appended claims and the equivalents thereto.