US20010012656A1

US20010012656A1 - Method of forming dram trench capacitor with metal layer over hemispherical grain polysilicon

Info

Publication number: US20010012656A1
Application number: US09/339,890
Authority: US
Inventors: Howard E. Rhodes; Lyle D. Breiner; Philip J. Ireland; Trung Tri Doan; Gurtej S. Sandhu; Sujit Sharan
Original assignee: Individual
Current assignee: Mosaid Technologies Inc
Priority date: 1999-06-25
Filing date: 1999-06-25
Publication date: 2001-08-09
Anticipated expiration: 2019-06-25
Also published as: US6388284B2; US20010001210A1; US6291289B2

Abstract

Integrated circuitry capacitors and methods of forming the same are described. In accordance with one implementation, a capacitor plate is formed and a conductive layer of material is formed thereover. Preferably, the conductive layer of material is more conductive than the material from which the capacitor plate is formed. In a preferred implementation, the conductive layer of material comprises a titanium or titanium-containing layer. In another preferred implementation, the capacitor plate comprises an inner capacitor plate having an outer surface with a generally roughened surface area. In one aspect of this implementation, the roughened surface area comprises hemispherical grain polysilicon. Capacitors formed in accordance with the invention are particularly well suited for use in dynamic random access memory (DRAM) circuitry.

Description

TECHNICAL FIELD

This invention relates to integrated circuitry capacitors and methods of forming the same.

BACKGROUND OF THE INVENTION

One common goal in capacitor fabrication is to maximize the capacitance for a given size capacitor. It is desirable that stored charge be at a maximum immediately at the physical interface between the respective electrodes or capacitor plates and the capacitor dielectric material between the plates. Typical integrated circuitry capacitors have electrodes or plates which are formed from doped semiconductive material such as polysilicon. The polysilicon is usually heavily doped to impart a desired degree of conductivity for satisfactory capacitor plate operation.

One drawback of heavily doping polysilicon is that during operation a charge depletion region develops at the interface where charge maximization is desired. Hence, a desired level of charge storage is achieved at a location which is displaced from the interface between the capacitor plate and the dielectric material.

Another drawback of heavily doping the polysilicon capacitor plates is that during processing, some of the dopant can migrate away from the polysilicon and into other substrate structures. Dopant migration can adversely affect the performance of such structures. For example, one type of integrated circuitry which utilizes capacitors are memory cells, and more particularly dynamic random access memory (DRAM) devices. Migratory dopants from doped polysilicon capacitor plates can adversely impact adjacent access transistors as by undesirably adjusting the threshold voltages.

As the memory cell density of DRAMs increases there is a continuous challenge to maintain sufficiently high storage capacitance despite decreasing cell area. Additionally there is a continuing goal to further decrease cell area. The principal way of increasing cell capacitance heretofore has been through cell structure techniques. Such techniques include three dimensional cell capacitors such as trench or stacked capacitors.

This invention arose out of concerns associated with improving integrated circuitry capacitors. This invention also grew out of concerns associated with maintaining and improving the capacitance and charge storage capabilities of capacitors utilized in memory cells comprising DRAM devices.

SUMMARY OF THE INVENTION

Integrated circuitry capacitors and methods of forming the same are described. In accordance with one implementation, a capacitor plate is formed and a conductive layer of material is formed thereover. Preferably, the conductive layer of material is more conductive than the material from which the capacitor plate is formed. In a preferred implementation, the conductive layer of material comprises a titanium or titanium-containing layer. Other materials can be used such as chemical vapor deposited platinum, TiN, and the like. In another preferred implementation, the capacitor plate comprises an inner capacitor plate having an outer surface with a generally roughened surface area. In one aspect of this implementation, the roughened surface area comprises hemispherical grain polysilicon. Capacitors formed in accordance with the invention are particularly well suited for use in dynamic random access memory (DRAM) circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below with reference to the following accompanying drawings. [0008]
FIG. 1 is a view of a semiconductor wafer fragment undergoing processing in accordance with the invention. [0009]
FIG. 2 is a view of the FIG. 1 wafer fragment at a processing step subsequent to that shown in FIG. 1. [0010]
FIG. 3 is a view of the FIG. 1 wafer fragment at a processing step subsequent to that shown in FIG. 2. [0011]
FIG. 4 is a view of the FIG. 1 wafer fragment at a processing step subsequent to that shown in FIG. 3. [0012]
FIG. 5 is a view of the FIG. 1 wafer fragment at a processing step subsequent to that shown in FIG. 4. [0013]
FIG. 6 is a view of the FIG. 1 wafer fragment at a processing step subsequent to that shown in FIG. 5. [0014]
FIG. 7 is a view of the FIG. 1 wafer fragment at a processing step subsequent to that shown in FIG. 6. [0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8). [0016]
Referring to FIG. 1, a semiconductor wafer fragment in process is indicated generally at [0017] 10 and includes a semiconductor substrate 12. In the context of this document, the term “semiconductor substrate” is defined to mean any construction comprising semiconductor material, including, but not limited to, bulk semiconductor materials such as a semiconductor wafer (either alone or in assemblies comprising other materials thereon), and semiconductor material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductor substrates described above.
[0018] Isolation oxide regions 14 are formed relative to substrate 12 and define therebetween a substrate active area over which a plurality of capacitors are to be formed. Conductive lines 16, 18, 20, and 22 are provided over substrate 12. Such lines typically include, as shown for line 16, a thin oxide layer 24, a conductive polysilicon layer 26, a silicide layer 28, a protective insulative cap 30, and sidewall spacers 32. A plurality of diffusion regions 17, 19, and 21 are received within substrate 12 and constitute source/drain regions for transistors which serve as access transistors for the capacitors to be formed. Diffusion regions 17, 19 and 21 define substrate node locations with which electrical communication is desired. An insulative layer 34 is formed over substrate 12 and typically comprises an oxide such as borophosphosilicate glass. Of course, other materials such as phosphosilicate glass, borosilicate glass, and the like can be used. Subsequently, insulative layer 34 is patterned and etched to define openings 36, 38 over diffusion regions 17, 21 respectively, and relative to which capacitors are to be formed. Insulative layer 34 defines a substrate outer surface 35.
A [0019] first layer 40 is formed over substrate outer surface 35. An exemplary and preferred material for layer 40 comprises a conductive or semiconductive material such as conductively doped polysilicon. Layer 40 defines at least a portion of a first or inner capacitor plate. Layer 40 also has a first conductivity and defines a capacitor plate which is operably adjacent and in electrical communication with the node locations defined by diffusion regions 17 and 21. Accordingly, layer 40 is electrically connected with the node locations defined by diffusion regions 17, 21.
Referring to FIG. 2, a [0020] second layer 42 is formed over first layer 40. In a preferred implementation, second layer 42 comprises a conductive material which constitutes roughened or rugged polysilicon. An exemplary and preferred roughened or rugged polysilicon is hemispherical grain polysilicon. Such is, in one aspect, substantially undoped as formed over first layer 40. Subsequently, and through suitable processing, outdiffusion of dopant from conductively doped polysilicon layer 40 into layer 42 renders second layer 42 conductive. Together, layers 40 and 42 constitute a doped semiconductive material having a first average conductivity. Accordingly, layers 40 and 42 constitute a first or inner capacitor plate having an outermost surface 44 of hemispherical grain polysilicon. Accordingly, outermost surface 44 defines a generally roughened surface area.
Referring to FIG. 3, a [0021] layer 46 is formed over substrate 12 and outer surface 44 of layer 42. According to one aspect, layer 46 constitutes a conductive material having a second average conductivity which is greater than the first average conductivity of layers 40, 42. A preferred manner of forming layer 46 is through suitable chemical vapor deposition thereof over layer 42. Accordingly, such forms a generally conformal layer over the roughened surface area of the preferred hemispherical grain polysilicon layer 42. Hence, layer 46 is disposed over and operably adjacent layers 40, 42.
Suitable materials for [0022] layer 46 include conductive metal compounds, metal alloys, and elemental metals. Other suitable materials include those which are preferably not conductively doped semiconductive material such as polysilicon. Accordingly, layer 46 constitutes a material other than doped semiconductive material. An exemplary and preferred material for layer 46 is elemental titanium which is chemical vapor deposited over layer 42. Other materials can be used such as chemical vapor deposited platinum, TiN, and the like. Layer 46 is preferably chemical vapor deposited directly onto the hemispherical grain polysilicon material of layer 42.
Referring to FIG. 4, layers [0023] 40, 42, and 46 are planarized to electrically isolate the layers within respective opening 36, 38. Exemplary planarization techniques include mechanical abrasion of the substrate as by chemical mechanical polishing. Other techniques are possible.
Referring to FIG. 5, a [0024] capacitor dielectric layer 48 is formed operably proximate the first capacitor plate, over layer 46 and within openings 36, 38. Accordingly, layer 48 is spaced from the material of layers 40, 42 a distance which is defined by layer 46. Exemplary materials for layer 48 are Si₃N₄and SiO₂alone, or in combination. Other materials such as tantalum pentoxide (Ta₂O₅), barium strontium titanate (BST), and other dielectric materials can be used.
Alternately considered, the [0025] preferred metal layer 46 is formed intermediate conductive capacitor plate 40, 42 and capacitor dielectric layer 48 preferably by chemical vapor deposition prior to providing capacitor dielectric layer 48. As formed, metal layer 46 is at least in partial physical contacting relationship with capacitor dielectric layer 48. Accordingly, layer 46 is interposed between capacitor plate 40, 42 and dielectric layer 48. In a most preferred aspect, conductive layer 46 consists essentially of non-semiconductive material such as titanium, or titanium silicide.
Referring to FIG. 6, a second [0026] capacitor plate layer 50 is formed over dielectric layer 48 and operatively proximate layer 46. In a preferred implementation, layer 50 defines an outer capacitor plate which defines a cell plate layer of a DRAM storage capacitor. An exemplary material for capacitor plate layer 50 is polysilicon.
Referring to FIG. 7, individual storage capacitors are patterned and etched to form [0027] capacitors 52, 54. An insulative layer 56 is formed thereover and is subsequently patterned and etched to form an opening which outwardly exposes diffusion region 19. Subsequently formed conductive material 58 provides a conductive bit line contact plug, and a subsequently formed conductive layer 60 provides a bit line in operative electrical contact therewith. Accordingly, such defines, in the illustrated and preferred embodiment, DRAM storage cells comprising storage capacitors 52, 54. The FIG. 7 construction illustrates but one example of DRAM storage cell constructions. Of course, other constructions which utilize the inventive methodology are possible The above-described methodology and capacitor constructions provide a desirable solution to concerns associated with charge depletion effects at the interface between a capacitor plate and a dielectric layer. The interpositioning of a layer of conductive material relative to the capacitor plate and the dielectric layer, which is more conductive than capacitor plate, effectively relocates the location of the capacitor's stored charge to a more desirable location. In addition, in implementations where doped semiconductive material is utilized for an inner capacitor plate and the “more conductive” interposed layer is formed thereover, a lesser degree of doping can be utilized such that dopant migration into other substrate structures is reduced. This is particularly useful when the capacitor plate includes an additional layer which is generally undoped as formed and subsequently rendered suitably conductive by outdiffusion of dopant from an adjacent layer.
In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents. [0028]

Claims

1. A method of forming a capacitor comprising:

forming a conductive capacitor plate;

forming a capacitor dielectric layer operably proximate the capacitor plate; and

forming a metal layer intermediate the conductive capacitor plate and the capacitor dielectric layer.

2. The method of

claim 1

, wherein the forming of the metal layer comprises chemical vapor depositing an elemental metal layer over the conductive capacitor plate prior to providing the capacitor dielectric layer.

3. The method of

claim 1

, wherein the forming of the metal layer comprises chemical vapor depositing a titanium layer over the conductive capacitor plate.

4. The method of

claim 1

, wherein the forming of the metal layer comprises chemical vapor depositing a titanium silicide layer over the conductive capacitor plate.

5. The method of

claim 1

, wherein the forming of the metal layer comprises chemical vapor depositing a platinum layer over the conductive capacitor plate.

6. The method of

claim 1

, wherein the forming of the metal layer comprises chemical vapor depositing a TiN layer over the conductive capacitor plate.

7. The method of

claim 1

, wherein the conductive capacitor plate comprises polysilicon and the forming of the metal layer comprises chemical vapor depositing the metal layer onto the polysilicon.

8. The method of

claim 1

, wherein the conductive capacitor plate comprises hemispherical grain polysilicon and the forming of the metal layer comprises chemical vapor depositing a titanium layer onto the hemispherical grain polysilicon.

9. A method of forming a capacitor comprising:

forming a conductive capacitor plate comprising polysilicon;

forming a capacitor dielectric layer operably proximate the conductive capacitor plate; and

10. The method of

claim 9

, wherein the metal layer is formed to be at least in partial physical contacting relationship with the capacitor dielectric layer.

11. The method of

claim 9

, wherein the forming of the metal layer comprises chemical vapor depositing the metal layer over the conductive capacitor plate.

12. The method of

claim 9

further comprising:

prior to the forming of the metal layer, forming a doped polysilicon layer over a substrate and a layer comprising roughened polysilicon over the doped polysilicon layer to form the conductive capacitor plate; and

wherein the forming of the metal layer comprises chemical vapor depositing the metal layer over the roughened polysilicon layer.

13. The method of

claim 9

further comprising:

prior to the forming of the metal layer, forming a doped polysilicon layer over a substrate and a layer comprising undoped hemispherical grain polysilicon over the doped polysilicon layer to form the conductive capacitor plate;

outdiffusing dopant from the doped polysilicon layer into the hemispherical grain polysilicon layer; and

wherein the forming of the metal layer comprises chemical vapor depositing a titanium layer over the hemispherical grain polysilicon layer.

14. A method of forming a capacitor comprising:

forming a capacitor plate layer comprising conductively doped roughened polysilicon;

forming a dielectric material layer operably proximate the capacitor plate layer; and

interposing a conductive layer between the capacitor plate layer and the dielectric material layer, the conductive layer being more conductive than the capacitor plate layer.

15. The method of

claim 14

, wherein the conductive layer consists essentially of non-semiconductive material.

16. The method of

claim 14

, wherein the conductive layer comprises titanium.

17. The method of

claim 14

, wherein the roughened polysilicon comprises hemispherical grain polysilicon and the interposing of the conductive layer comprises chemical vapor depositing a titanium-containing layer over the hemispherical grain polysilicon.

18. A method of forming a capacitor comprising:

forming a conductive capacitor plate comprising roughened polysilicon;

forming a metal layer consisting essentially of titanium intermediate the conductive capacitor plate and the capacitor dielectric layer.

19. The method of

claim 18

, wherein the forming of the metal layer comprises chemical vapor depositing the layer over the capacitor plate.

20. The method of

claim 18

, wherein the roughened polysilicon layer comprises hemispherical grain polysilicon and the forming of the metal layer comprises chemical vapor depositing the layer over the layer comprising hemispherical grain polysilicon.

21. A method of forming a capacitor comprising:

forming a first layer comprising conductive material over a substrate outer surface;

forming a second layer comprising conductive material over the first layer of conductive material;

forming a layer comprising conductive metal over the second layer; and

forming a layer of dielectric material and a cell plate layer operatively proximate the conductive metal layer to form a capacitor.

22. The method of

claim 21

, wherein:

the forming of the first layer comprises forming conductively doped polysilicon over the substrate outer surface; and

the forming of the second layer comprises forming a layer comprising roughened polysilicon over the first layer and outdiffusing dopant from the first layer into the second layer.

23. The method of

claim 21

, wherein:

the forming of the second layer comprises forming a layer comprising hemispherical grain polysilicon over the first layer and outdiffusing dopant from the first layer into the second layer.

24. The method of

claim 21

, wherein the forming of the layer comprising the conductive metal comprises chemical vapor depositing the metal over the second layer.

25. The method of

claim 21

, wherein:

the forming of the second layer comprises forming a layer comprising hemispherical grain polysilicon over the first layer; and

the forming of the layer comprising the conductive metal comprises chemical vapor depositing elemental titanium over the layer comprising hemispherical grain polysilicon.

26. A method of forming a capacitor comprising:

forming a doped semiconductive material over a substrate, the material having a first average conductivity;

forming a conductive material over the doped semiconductive material, the conductive material having a second average conductivity which is greater than the first average conductivity;

forming a capacitor dielectric layer over the conductive material; and

forming an outer capacitor plate over the capacitor dielectric layer.

27. The method of

claim 26

, wherein the conductive material is not conductively doped semiconductive material.

28. The method of

claim 26

, wherein the forming of the conductive material comprises forming a material other than doped semiconductive material over the doped semiconductive material.

29. The method of

claim 26

, wherein the forming of the conductive material comprises forming a layer of elemental metal over the doped semiconductive material.

30. The method of

claim 26

, wherein the forming of the conductive material comprises forming a metal alloy layer over the doped semiconductive material.

31. The method of

claim 26

, wherein the forming of the conductive material comprises forming a metal compound layer over the doped semiconductive material.

32. The method of

claim 26

, wherein:

the forming of the doped semiconductive material comprises forming a layer comprising doped polysilicon over the substrate and forming a layer of hemispherical grain polysilicon over the layer comprising doped polysilicon; and

the forming of the conductive material comprises chemical vapor depositing a layer of titanium over the layer of hemispherical grain polysilicon.

33. A method of forming a capacitor comprising:

forming a first capacitor plate comprising an outer surface of hemispherical grain polysilicon;

forming an elemental titanium layer over the outer surface;

forming a capacitor dielectric layer over the elemental titanium layer;

forming a second capacitor plate over the capacitor dielectric layer.

34. The method of

claim 33

, wherein the forming of the elemental titanium layer comprises chemical vapor depositing the layer over the hemispherical grain polysilicon.

35. The method of

claim 33

, wherein the forming of the first capacitor plate comprises:

forming a layer of conductively doped polysilicon over a substrate;

forming a layer of hemispherical grain polysilicon over the layer of conductively doped polysilicon; and

outdiffusing dopant from the conductively doped polysilicon into the hemispherical grain polysilicon.

36. A method of forming a DRAM storage capacitor comprising:

forming a capacitor opening relative to insulative layer formed over a substrate, the capacitor opening being disposed elevationally over a node location with which electrical connection is to be made;

forming a first polysilicon material layer within the capacitor opening and in electrical communication with the node location, the first polysilicon material layer having a first conductivity;

forming a second polysilicon material layer over the first polysilicon material layer, the second polysilicon material layer having an outermost surface with a generally roughened surface area;

forming a layer comprising a metal material over the second polysilicon material layer's outermost surface, the metal material layer having a second conductivity which is greater than the first conductivity;

forming a layer comprising a dielectric material over the metal material layer; and

forming a cell plate layer over the dielectric material layer to form a storage capacitor.

37. The method of

claim 36

, wherein the forming of the second polysilicon material layer comprises forming a layer of hemispherical grain polysilicon over the first polysilicon material layer.

38. The method of

claim 36

, wherein the forming of the layer comprising a metal material comprises chemical vapor depositing a layer comprising titanium over the second polysilicon material layer's outermost surface.

39. A capacitor comprising:

a substrate having a node location;

an insulative layer disposed over the substrate and having an opening over the node location;

a first polysilicon material layer having a first conductivity, the layer being disposed within the opening and operably connected with the node location;

a second polysilicon material layer over the first polysilicon material layer, the second polysilicon material layer having an outermost surface with a generally roughened surface area;

a non-polysilicon conductive layer over the second polysilicon material layer's outermost surface, the conductive layer having a second conductivity which is greater than the first conductivity;

a capacitor dielectric layer over the conductive material layer; and

a capacitor plate over the capacitor dielectric layer.

40. The capacitor of

claim 39

, wherein the capacitor plate comprises a cell plate layer which constitutes a portion of DRAM circuitry.

41. The capacitor of

claim 39

, wherein the second polysilicon material comprises hemispherical grain polysilicon.

42. The capacitor of

claim 39

, wherein the conductive material layer comprises elemental titanium or a titanium alloy.

43. The capacitor of

claim 39

, wherein the conductive material layer comprises TiN.

44. The capacitor of

claim 39

, wherein the conductive material layer comprises platinum.

45. A capacitor comprising:

a substrate having a node location;

a doped semiconductive material capacitor plate operably proximate the node location;

a metal layer disposed over and operably proximate the first capacitor plate;

a capacitor dielectric layer disposed over the metal layer and spaced from the semiconductive material capacitor plate; and

a capacitor plate over the capacitor dielectric layer.

46. A capacitor comprising:

a substrate having a node location;

a conductive inner capacitor plate comprising polysilicon operably proximate the node location;

a metal layer disposed over and in physical contact with the conductive capacitor plate;

a capacitor dielectric layer disposed over the metal layer and in physical contact therewith; and

an outer capacitor plate over the capacitor dielectric layer.

47. A capacitor comprising:

a substrate having a node location;

an inner conductive capacitor plate having a doped roughened polysilicon outer surface, the plate being connected with the node location and having a first average conductivity;

a conductive layer connected with the inner conductive capacitor plate and having a second average conductivity which is greater than the first average conductivity;

a dielectric layer connected with the conductive layer; and

an outer conductive capacitor plate connected with the dielectric layer.

48. A capacitor comprising:

a substrate having a node location;

an inner conductive capacitor plate having a roughened outer surface comprising hemispherical grain polysilicon;

a metal layer consisting essentially of titanium conformally proximate the roughened outer surface and connected with the capacitor plate;

a capacitor dielectric layer over the metal layer; and

an outer conductive capacitor plate connected with the dielectric layer.

49. A capacitor comprising:

a substrate having an outer surface;

a first layer comprising conductive material over the outer surface;

a second layer comprising conductive material over the first layer of material, the first and second layers being different from one another, the second layer having an outer roughened surface;

a conductive titanium-containing layer disposed in conformal physical contacting relation with the second layer;

a dielectric layer over the titanium-containing layer; and

a cell plate layer operatively proximate the dielectric layer.

50. A capacitor comprising:

a substrate having an outer surface;

a doped semiconductive material over the outer surface and having a first average conductivity;

a conductive material over the doped semiconductive material, the conductive material having a second average conductivity which is greater than the first average conductivity, the doped semiconductive material and the conductive material comprising an inner capacitor plate;

a capacitor dielectric layer over the conductive material; and

an outer capacitor plate over the capacitor dielectric layer.

51. A capacitor comprising:

a first capacitor plate comprising an outer surface of hemispherical grain polysilicon;

an elemental titanium layer over the outer surface;

a capacitor dielectric layer over the elemental titanium layer; and

a second capacitor plate over the capacitor dielectric layer.