Deep trench capacitor and method of making same

The present invention relates to the field of integrated circuits; more specifically, it relates to deep trench capacitors for use in integrated circuits and a method of fabricating the deep trench capacitors.

The trend in integrated circuit technology is to increased circuit density and faster circuits. Current deep trench capacitor technology places limitations on the minimum pitch and minimum deep trench capacitor surface area based on the methods used contact the deep trench capacitors and the need to isolate the deep trench capacitor from other structures using trench isolation schemes. These restrictions increase the amount of space to be set aside for capacitors as well as increasing the series resistance to the outer plate of the capacitor. Therefore, there is a need for deep trench capacitors and methods of fabricating deep trench capacitors that are more compatible with the need for increased circuit density and faster circuits.

A first aspect of the present invention is a structure, comprising: a trench in a single-crystal silicon substrate, the trench extending from a top surface of the substrate into the substrate in a direction perpendicular to a top surface of the substrate, the trench having sidewalls and a bottom; a conformal dielectric liner on the sidewalls and the bottom of the trench, a top edge of the liner exposed at the top surface of the substrate; an electrically conductive polysilicon inner plate filling regions of the trench not filled by the liner; an electrically conductive doped outer plate in the substrate surrounding the sidewalls and the bottom of the trench and in direct physical contact with the dielectric liner, the outer plate extending from the top surface of the substrate to under the trench; a doped silicon region in the substrate, the doped silicon region extending from the top surface of the substrate into the substrate the direction perpendicular to the top surface of the substrate, the doped region physically and electrically contacting the outer plate; a first electrically conductive metal silicide layer on a surface region of the doped silicon region exposed at the top surface of the substrate; a second electrically conductive metal silicide layer on a surface region of the inner plate exposed at the top surface of the substrate; and an insulating ring on the top surface of the substrate between the first and second metal silicide layers.

A second aspect of the present invention is a method comprising: forming a trench in a single-crystal silicon substrate, the trench extending from a top surface of the substrate into the substrate in a direction perpendicular to a top surface of the substrate, the trench having sidewalls and a bottom; forming a conformal dielectric liner on the sidewalls and the bottom of the trench, a top edge of the liner exposed at the top surface of the substrate; filling regions of the trench not filled by the liner with an electrically conductive polysilicon inner plate; forming an electrically conductive doped outer plate in the substrate surrounding the sidewalls and the bottom of the trench and in direct physical contact with the dielectric liner, the outer plate extending from the top surface of the substrate to under the trench; forming a doped silicon region in the substrate, the doped silicon region extending from the top surface of the substrate into the substrate the direction perpendicular to the top surface of the substrate, the doped region physically and electrically contacting the outer plate; forming a first electrically conductive metal silicide layer on a surface region of the doped silicon region exposed at the top surface of the substrate; forming a second electrically conductive metal silicide layer on a surface region of the inner plate exposed at the top surface of the substrate; and forming an insulating ring on the top surface of the substrate between the first and second metal silicide layers.

The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

FIGS. 1A through 1D are cross-sectional drawings illustrating fabrication of a trench capacitor according to embodiments the present invention.

FIGS. 2A through 2C are schematic diagrams illustrated alternative alignments of the structure illustrated in FIG. 1D ;

FIG. 3 illustrates further fabrication steps of the trench capacitors according to embodiments of the present invention; and

FIG. 4 is a cross-sectional drawing illustrating an alternative method and structure for trench capacitors according to embodiments of the present invention.

FIGS. 1A through 1D are cross-sectional drawings illustrating fabrication of a trench capacitor according to embodiments the present invention. In FIG. 1A , formed in a single-crystal silicon substrate 100 , adjacent to a top surface 105 of the substrate is a doped region 110 . Substrate 100 may be a silicon-on insulator (SOI) substrate. Also formed in substrate 100 is a deep trench capacitor 115 . Deep trench capacitor 115 comprises an electrically conductive polysilicon core 120 (or inner plate 120 ), which may be doped or undoped, a dielectric layer (e.g. a silicon dioxide layer (SiO 2 )), and a diffused doped region 130 (or outer plate 130 ). Outer plate 120 surrounds the sidewalls and bottom of dielectric layer 125 and dielectric layer 125 surrounds the sidewall and bottom of inner plate 120 . Deep trench capacitor has a width W and extends from top surface 105 of substrate 100 a depth D into the substrate. In one example D is between about 0.5 microns to about 10 microns deep. In one example the ratio D/W is greater than or equal to about 2. When substrate 100 is a SOI substrate, deep trench capacitor may extend through a buried oxide (BOX) layer of the substrate as shown by the dashed line in FIG. 1A or terminate on the BOX layer. In a first example, inner plate 120 is doped P-type and outer plate 130 is doped N type. In a second example, inner plate 120 is doped N-type and outer plate 130 is doped P type. In a third example, inner plate 120 and outer plate 130 are both doped N-type. In a fourth example, inner plate 120 and outer plate 130 are both doped P-type. Region 110 is always doped the same type as outer plate 130 . Substrate 100 may be undoped, doped N type or doped P type.

In one example, the trench capacitor 100 may be formed by: (1) etching a trench into substrate 100 , (2) filling the trench with a doped polysilicon and heating the substrate to drive dopant out of the polysilicon fill into the regions of the substrate immediately surrounding the trench to form the outer plate, (3) removing the polysilicon fill and depositing a conformal dielectric material on the sidewalls or bottom of the trench or thermally oxidizing the sidewalls and bottom of the trench and (4) filling the trench with polysilicon, which may include overfilling the trench with polysilicon followed by a planarizing chemical-mechanical-polish (CMP).

In FIG. 1B , a gate dielectric layer has been formed on top surface 105 of substrate 100 , a gate polysilicon layer has been formed on top of the gate dielectric layer and then the gate polysilicon layer and the gate dielectric layer photolithographically masked and etched to leave rings of gate dielectric 135 and gate polysilicon 140 adjacent to the periphery of trench capacitor 115 .

In FIG. 1C , dielectric spacers 145 have been formed on the sidewalls of the rings of gate dielectric 135 and gate polysilicon 140 . Spacers 145 may be formed by depositing a thin conformal layer of dielectric (e.g. SiO 2 or silicon nitride (Si 3 N 4 )) followed by a directional reactive ion etch (RIE). The alignment of the composite ring formed of gate dielectric 135 , gate polysilicon 140 and sidewall spacers 145 relative to inner plate 120 and outer plate 130 is illustrated in FIGS. 2A through 2C .

In FIG. 1D , an electrically conductive metal silicide layer 150 A has been formed on doped region 110 , an electrically conductive metal silicide layer 150 B has been formed on inner plate 120 and an electrically conductive metal silicide layer 150 C has been formed on gate polysilicon 145 . Silicide layers 150 A, 150 B and 150 C may be formed simultaneously by: (1) blanket depositing or sputtering of a thin conformal metal layer, (2) heating the substrate and metal layer to a high enough temperature in a non-oxidizing or reducing atmosphere to cause the metal to react with silicon (but not with silicon oxide or silicon nitride) to form a metal silicide and (3) removing any unreacted metal (e.g. by wet etching).

FIGS. 2A through 2C are schematic diagrams illustrated alternative alignments of the structure illustrated in FIG. 1D . In FIGS. 2A , 2 B and 2 C, an insulating ring 155 represents the ring comprised of gate dielectric 135 , gate polysilicon 140 and spacers 145 of FIG. 1D . It should be understood that dielectric layer 125 is usually so thin as to allow bridging of silicide to short silicide layer 150 A and 150 B if ring 155 were not present, as ring 155 increases the distance along the surface of the substrate between the two silicide layers. In the examples of FIGS. 2A , 2 B and 2 C, at least one edge when viewed from above (either an inner edge or an outer edge) of dielectric layer 125 is aligned under ring 155 . This is not always necessary as long as ring 155 is formed on top surface 105 of substrate 100 (see FIGS. 1C and 1D ) between silicide layer 150 A and silicide layer 150 B.

FIG. 3 illustrates further fabrication steps of the trench capacitors according to embodiments of the present invention. In FIG. 3 , a blanket dielectric layer 160 is formed over substrate 160 and metal contacts 165 and 170 formed in the dielectric layer. Contacts 165 extend from a top surface of dielectric layer 160 to silicide layer 150 on doped region 110 . Contact 170 extends from the top surface of dielectric layer 170 to silicide layer 150 on inner plate 120 . In one example, contacts 165 and 170 are comprised of tungsten (W), titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), copper, (CU) or combinations thereof. Doping levels of doped region 110 and outer plate 130 are high enough so as to form a low resistance interface. Metal silicides generally provide very low resistance interfaces between metal contacts and silicon. Thus, a first low resistance electrically conductive path extends from contacts 165 through metal silicide layers 150 A to doped region 110 to outer plate 130 and a second low resistance path exists from contacts 170 through silicide layer 150 B to inner plate 120 .

FIG. 4 is a cross-sectional drawing illustrating an alternative method and structure for trench capacitors according to embodiments of the present invention. In FIG. 4 , instead of a ring comprised of gate dielectric 135 , gate polysilicon 140 and sidewall spacers 145 (see FIG. 1D ) or ring 155 (see FIGS. 2A , 2 B and 2 C), a dielectric ring 175 is substituted. Dielectric ring 175 prevents metal silicide layer 150 bridging to metal silicide layer just as ring 155 of FIGS. 2A , 2 B and 2 C did. In one example, dielectric ring 175 may comprise SiO 2 or Si 3 N 4 .

Thus, the present invention provides for deep trench capacitors and methods of fabricating deep trench capacitors that are more compatible with the need for increased circuit density and faster circuits.

The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.