METHODS AND APPARATUS FOR DEVICES HAVING IMPROVED CAPACITANCE
Some embodiments of the invention include a capacitor in which a dielectric of the capacitor is formed by oxidizing at least a portion of a metal layer. Other embodiments are described and claimed.
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This application is a Divisional of U.S. application Ser. No. 10/946,770, filed Sep. 22, 2004, which is a Divisional of U.S. application Ser. No. 09/246,918, filed Feb. 9, 1999, now U.S. Pat. No. 6,838,353, which is a Divisional of U.S. application Ser. No. 08/676,708, filed Jul. 8, 1996, now U.S. Pat. No. 6,660,610, all of which are incorporated herein by reference.
BACKGROUNDAlthough there have been attempts to deposit metal oxides, such as TiO2 and SrTiO3, during semiconductor fabrication, thermal oxidation of metals in the fabrication of capacitors has been limited since an initial oxide layer prohibits further diffusion during thermal oxidation. As a result the use of high dielectric constant oxidized metals has been limited in semiconductor capacitor fabrication. One such metal, titanium dioxide, has a dielectric constant 2-15 times greater than present semiconductor capacitor dielectrics such as silicon nitride, while titanates are 2-1000 times greater.
In the Jan. 1996 issue of Material Research, Vol. 11, No. 1, an article entitled ELECTROCHEMICAL SYNTHESIS OF BARIUM TITANATE THIN FILMS, R. R. Bacsa et al. describes the synthesizing of polycrystalline films of barium titanate on titanium substrates by the galvanostatic anodization of titanium to form a material which has a dielectric constant of 200.
BRIEF DESCRIPTION OF THE DRAWINGS
In
Following the deposition and isolation of portions of the first conductive layer 25 a conformal metal layer 30 is deposited by chemical vapor deposition to overlie the first conductive layer 25 and exposed portions of silicon dioxide layer 5, see
In
Although in an embodiment, a three electrode potentiostat controls the electrochemical oxidation process, a two electrode rheostat control device may also be used. However, the oxidation is less controllable using the two electrode rheostat. When using the rheostat the second electrode 45 is eliminated and the electrochemical reaction changes the counter electrode chemistry. When this happens the potential changes. Thus the oxidation of the metal layer 30 is uncontrolled. In the three electrode embodiment, the existence of the reference electrode provides better control of the oxidation process.
In the first embodiment substantially all of the metal layer 30 is oxidized during the electrolytic process to form a metal oxide 35, titanium dioxide in the example embodiment, see
Following the oxidation step the metal oxide is chemically mechanically planarized and a second conductive layer 55 is deposited to overlie the metal silicon dioxide layer 5, the silicon oxide 50 and the metal oxide 35, see
In
In an alternate embodiment it is only necessary to oxidize a portion of the metal layer 30 to create a metal/metal oxide layer, or in the example embodiment a titanium/titanium dioxide layer. In this case the unoxidized metal layer 30 and the polysilicon layer 25 form the first capacitor plate while the thin layer of titanium oxide forms the dielectric.
In a still further alternate embodiment multiple layers of metal are deposited and at least a portion of each metal layer is electrochemically oxidized prior to the deposition of a subsequent metal layer. In this case the dielectric comprises alternate layers of oxide and metal. In this embodiment the second conductive layer 55 is deposited on the last metal oxide created.
In a second embodiment of the invention, shown in
Alternately the metal layer 75 is planarized to expose the silicon dioxide prior to oxidation and formation of the first metal oxide 80, see
Following the first oxidation a second metal layer 85,
In the alternate embodiment, shown in
Following the oxidation of the second metal layer 85 a third metal layer 95 is sputter deposited to overlie the second metal oxide layer 90, and capacitors are defined by a mask 100, see
Exposed first, second and third metal layers 75, 85, and 95 and exposed first and second metal oxide layers 80 and 90 are etched to form the capacitors 105 of an embodiment of the invention, see
In further conceived embodiments the metal layer 30 (in this embodiment titanium) may be alloyed with a material, such as Strontium. In this case SrTiO3 is formed during the oxidation performed by the method of an embodiment of the invention. Other titanates may also be formed depending on the alloy used in combination with titanium. For Example, Ba or Pb may be combined with Ti to form BaTiO3 and PbTiO3, respectively, during oxidation. The process also works for TiO3−2 complexes. In a still further embodiment the metal layer 30 (in this embodiment titanium) may be oxidized in a supersaturated Sr+2 solution such as Sr(OH)2 to form SrTrO3, in an example embodiment.
The capacitors 65 and 105 shown in
Methods and apparatus for devices having improved capacitance are described. In one exemplary embodiment, the capacitor of an embodiment of the invention is formed by a process using only two deposition steps. The capacitor has first and second conductive plates and a dielectric is formed from the first conductive plate. In one exemplary process in accordance with and embodiment of the invention, a metal layer is deposited and at least partially oxidized in an electrolytic solution. The metal oxide formed during this oxidation forms the dielectric of the capacitor. Portions not oxidized may form at least a portion of a capacitor plate. In one exemplary implementation in accordance with an embodiment of the invention, a metal layer is deposited to overlie a first capacitor plate fabricated on a semiconductor wafer. The wafer is placed in an electrolyte conducive to forming an oxide with the metal. A potential is applied across the electrolyte and the metal, and at least a portion of the metal oxidizes. In an embodiment the metal is titanium and titanium dioxide is formed during the electrochemical reaction. The capacitor fabrication is completed with the formation of a second capacitor plate overlying the oxidized metal layer. The oxidized metal layer functions as the dielectric of the capacitor and has a high dielectric constant.
It will be evident to one skilled in the art that many different combinations of materials, deposits and etch steps may be used to fabricate the capacitor and dielectric according to example embodiments of the invention without departing from the scope of the embodiments of the invention as claimed. The method for forming the dielectric according to an embodiment of the invention is equally applicable to any type of capacitor structure, such as trench, container, and stacked and ministacked or variations thereof.
Claims
1. A method of forming capacitor, the method comprising:
- forming a capacitor plate over a substrate;
- forming a metal layer over the substrate;
- applying a potential across the metal layer; and
- oxidizing at least a portion of the metal layer to form an oxidized layer, wherein the oxidized layer forms a dielectric of the capacitor.
2. The method of claim 1, wherein the conductive layer is formed from a first material, and wherein the metal layer is formed from a second material different from the first material.
3. The method of claim 2, wherein the capacitor plate is formed from metal.
4. The method of claim 3 further comprising:
- forming a diffusion barrier layer between the capacitor plate and the metal layer.
5. The method of claim 1, wherein the metal layer is formed from one of titanium, copper, gold, tungsten and nickel.
6. The method of claim 5, wherein the capacitor plate is formed from polysilicon.
7. The method of claim 1, wherein the metal layer is formed from an alloy of a metal and an additional material of one of strontium, barium, and lead.
8. The method of claim 7, wherein the metal of the metal layer is titanium.
9. The method of claim 1, wherein oxidizing the portion of the metal layer includes contacting the portion of the metal layer with an Sr+2 solution.
10. The method of claim 1, wherein oxidizing the portion of the metal layer includes contacting the portion of the metal layer with a solution of one part NH4OH to ten parts water.
11. The method of claim 1, wherein oxidizing the portion of the metal layer includes contacting the portion of the metal layer with a solution of, and wherein the solution is a 0.1 molar solution of HClO4.
12. The method of claim 1, wherein the capacitor plate is formed to a thickness of approximately 200 to 400 angstroms.
13. The method of claim 12, wherein the metal layer is formed to a thickness of approximately 16 to 100 angstroms.
14. The method of claim 13, wherein the oxidized layer has a thickness of approximately 10 to 1000 angstroms.
15. A method of forming a capacitor, the method comprising:
- forming a capacitor plate over a substrate;
- forming a metal layer over the substrate;
- applying a potential across the metal layer;
- oxidizing a portion of the metal layer to form an oxidized layer, wherein the oxidized layer forms at least a portion of a dielectric of the capacitor;
- mechanically planarizing the oxidized layer to form a planarized oxidized layer; and
- forming a second capacitor plate over the planarized oxidized layer.
16. The method of claim 15, wherein the capacitor plate is formed from a first material, and wherein the metal layer is formed from a second material different from the first material.
17. The method of claim 15, wherein the second conductive layer includes a metal layer.
18. The method of claim 15, wherein the second capacitor plate includes a polysilicon layer.
19. The method of claim 15, wherein the metal layer is formed from one of titanium, copper, gold, tungsten and nickel.
20. A method of forming capacitor, the method comprising:
- forming a first metal layer over a substrate;
- applying a potential across the first metal layer;
- oxidizing at least a portion of the first metal layer to obtain an oxidized portion and a non-oxidized portion of the first metal layer;
- forming a second metal layer over the first metal layer;
- oxidizing at least a portion of the second metal layer to obtain an oxidized portion and a non-oxidized portion of the second metal layer; and
- forming a third metal layer over the second metal layer.
21. The method of claim 20, wherein oxidizing at least the portion of the first metal layer includes contacting the portion of the first metal layer with an electrolytic solution.
22. The method of claim 20, wherein the first, second, and third metal layers are formed from titanium.
23. The method of claim 22, wherein the titanium of at least one of the first and second metal layers is alloyed with strontium.
24. The method of claim 22, wherein the titanium of at least one of the first and second metal layers is alloyed with barium.
25. The method of claim 22, wherein the titanium of at least one of the first and second metal layers is alloyed with lead.
26. A capacitor comprising:
- a first metal layer over a substrate, the first metal layer including an oxidized portion and a non-oxidized portion;
- a second metal layer over the first metal layer, the second metal layer including an oxidized portion and a non-oxidized portion; and
- a third metal layer over the second metal layer.
27. The capacitor of claim 26 further comprising a diffusion barrier layer between the first metal layer and the second metal layer.
28. The capacitor of claim 27 further comprising a diffusion barrier layer between the second metal layer and the third metal layer.
29. The capacitor of claim 26, wherein the oxidized portion of one of the first and second metal layers has a dielectric constant between 86 and 170.
30. The capacitor of claim 26, wherein the first, second, and third metal layer include titanium.
Type: Application
Filed: May 16, 2006
Publication Date: Sep 7, 2006
Applicant:
Inventor: Karl Robinson (Boise, ID)
Application Number: 11/383,717
International Classification: H01G 9/00 (20060101);