Semiconductor structure and method of forming the same

Abstract

A semiconductor structure and a method of forming the same are provided. In the semiconductor structure, contact spacers are formed at least on sidewalls of contact trenches in the substrate, so that the distance between the gate and the silicide layers disposed only on the bottom surfaces, rather than on the sidewalls and the bottom surfaces, of the contact trenches can be increased, and thus the current leakage induced by gate can be decreased.

Claims

1. A method of forming a semiconductor, the method comprising: forming a gate structure on a substrate; forming a source and a drain in the substrate on two sides of the gate structure; forming a dielectric layer on the substrate and the gate structure; forming two contact openings in the dielectric layer to respectively expose the source and the drain; forming a hard mask layer on the dielectric layer between the step of forming the dielectric layer and the step of forming the contact openings, wherein the hard mask layer is used as an etching mask; forming two contact trenches in the source and drain and under the two contact openings, respectively; forming two contact spacers to respectively cover sidewalls of the contact trenches for avoiding current leakage induced by the gate structure; forming two silicide layers under the bottom surface of the contact trenches; and forming two contact plugs to fill the contact trenches and the contact openings, wherein the hard mask layer is removed between the step of forming the silicide layers and the step of forming the contact plugs.

2. The method of claim 1, wherein the step of forming the contact spacers comprises: forming contact dielectric layers respectively on surfaces of the contact trenches by thermal oxidation or thermal nitridation; and anisotropically etching the contact dielectric layers to form the contact spacers on the sidewalls of the contact trenches and expose the substrate.

3. The method of claim 1, wherein the step of forming the contact spacers comprises: forming a contact dielectric layer conformally covering exposed surfaces of the dielectric layer, the contact openings and the contact trenches; and anisotropically etching the contact dielectric layer to form the contact spacers on the sidewalls of the contact openings and the contact trenches and expose the substrate.

4. The method of claim 3, wherein the contact dielectric layer is formed by chemical vapor deposition.

5. The method of claim 3, wherein the contact dielectric layer is a silicon oxide layer or a silicon nitride layer.

6. The method of claim 1, wherein a material of the silicide layers comprises TiSi.sub.2, NiSi.sub.2, or CoSi.sub.2.

7. The method of claim 1, wherein the step of forming the gate structure comprises: forming a gate dielectric layer on the substrate; forming a gate layer on the gate dielectric layer; forming a gate mask layer on the gate layer; and sequentially patterning the gate mask layer, the gate layer and the gate dielectric layer to form the gate structure.

8. The method of claim 7, further comprising forming two gate spacers on sidewalls of the gate structure between the step of forming the gate structure and the step of forming the source and the drain.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A-1B and 2A-2B are schematic cross-sectional views showing a process of forming a semiconductor structure according to an embodiment of this invention.

(2) FIGS. 1A-1B and 3A-3B are schematic cross-sectional views showing a process of forming a semiconductor structure according to another embodiment of this invention.

DESCRIPTION OF THE EMBODIMENTS

(3) FIGS. 1A-1B and 2A-2B are schematic cross-sectional views showing a process of forming a semiconductor structure according to an embodiment of this invention. FIGS. 1A-1B and 3A-3B are schematic cross-sectional views showing a process of forming a semiconductor structure according to another embodiment of this invention.

(4) In FIG. 1A, a gate dielectric layer 102, a gate layer 104 and a gate mask layer 106 are sequentially formed on a substrate 100. Next, the gate dielectric layer 102, the gate layer 104, and the gate mask layer 106 are patterned by a patterning process, such as photolithography and etching, to form a gate structure having the gate dielectric layer 102, the gate layer 104 and the gate mask layer 106. In this step, the gate mask layer 106 is used as an etching mask when the gate layer 104 and the gate dielectric layer 102 are etched. The gate dielectric layer 102 may be a silicon oxide layer, or a high-k dielectric layer such as a hafnium oxide layer or a zirconium oxide layer. The gate layer 104 is a conductive layer, such as a doped polysilicon layer or a metal layer (e.g. a tungsten layer). The gate mask layer 106 may be a silicon oxide layer.

(5) Next, an insulating layer, such as a silicon oxide layer, is conformally formed on the substrate 100 and the gate structure, and then anisotropically etched to form gate spacers 108 on sidewalls of the gate structure. Subsequently, source/drain 110 are formed in the substrate 100 on two sides of the gate structure by ion implantation. A dielectric layer 112 and a hard mask layer 114 are sequentially formed on the substrate 100. The dielectric layer 112 may be a silicon oxide layer or a low-k dielectric layer, such as a fluorine-doped silicon oxide layer, a carbon-doped oxide layer (CDO), a porous silicon oxide layer, or a spin-on glass layer. The hard mask layer 114 may be a silicon nitride layer.

(6) In FIG. 1B, the hard mask layer 114 and the dielectric layer 112 are patterned, such as photolithography and etching, to form contact openings 116a and a gate opening 118a in the dielectric layer 112. Then, the exposed substrate 100 under the contact openings 116a and the exposed gate mask layer 106 under the gate opening 118a are subsequently over etched to form contact trenches 116b in the source/drain 110 in the substrate 100 and a gate trench 118b in the gate mask layer 106. In this etching process, the hard mask layer 114 is used as an etching mask.

(7) Next, there are two choices may be made to complete the rest of the process of forming the semiconductor structure. The first choice is depicted in FIGS. 2A and 2B, the second choice is depicted in FIGS. 3A and 3B.

(8) In FIG. 2A of the first choice, a contact dielectric layer 120a is conformally formed on the exposed surfaces of the substrate 100, the dielectric layer 112, and the hard mask layer 114. The contact dielectric layer 120a may be a silicon oxide layer or a silicon nitride layer, and the method of forming the contact dialectic layer may be chemical vapor deposition (CVD).

(9) In FIG. 2B of the first choice, the contact dielectric layer 120a is then anisotropically etched to respectively form contact spacers 122a on the sidewalls of the contact openings 116a and the contact trenches 116b to expose the substrate 100, as well as gate contact spacers 124a on sidewalls of the gate opening 118a and the gate trench 118b to expose the gate mask layer 106. Please note that the exposed sidewall of the contact trenches 116b are covered by the contact spacers 122a, only the bottom surface of the contact trenches 116b are not covered by the contact spacers 122a to expose the substrate 100.

(10) Then, metal silicide layers 126 are formed on the exposed substrate 100 by a salicidation process, which comprises depositing a metal layer and then performing a thermal process to allow the metal layer react with the exposed substrate 100 to form the silicide layers 126. The metal silicide layers may be TiSi.sub.2, NiSi.sub.2, or CoSi.sub.2, for example.

(11) In this step, since contact spacers 122a cover the sidewalls of the contact trenches 116b, the metal silicide layers 126 may be formed only on the bottom surface of the contact trenches 116b, and no metal silicide can be formed on sidewalls of the contact trenches 116b. Therefore, the distance between the conductive metal silicide layers 126 and the gate layer 104 can be kept at a distance far enough to avoid current leakage induced by the gate layer 104.

(12) Next, the hard mask layer 114 is removed, and a metal layer is deposited to fill the contact openings 116a, the contact trenches 116b, the gate opening 118a and the gate trench 118b, and then etched back. Thus, contact plugs 128 are formed in the contact openings 116a and the contact trenches 116b, and a gate plug 130 is formed in the gate opening 118a and the gate trench 118b. The metal layer may be a tungsten layer.

(13) In FIG. 3A of the second choice, a contact dielectric layer 120b is formed only on the exposed surfaces of the contact trenches 116b in the substrate 100. The contact dielectric layer 120b may be a silicon oxide layer or a silicon nitride layer, and may be formed by a thermal oxidation process or a thermal nitridation process.

(14) In FIG. 3B of the second choice, the contact dielectric layer 120b is then anisotropically etched to form contact spacers 122b on the sidewalls of the contact trenches 116b in the substrate 100 to expose the substrate 100. Please note that the exposed sidewall of the contact trenches 116b are covered by the contact spacers 122b, only the bottom surface of the contact trenches 116b are not covered by the contact spacers 122b to expose the substrate 100.

(15) Then, metal silicide layers 126 are formed on the exposed substrate 100 by a salicidation process, which comprises depositing a metal layer and then performing a thermal process to allow the metal layer react with the exposed substrate 100 to form the silicide layers 126. The metal silicide layers may be TiSi.sub.2, NiSi.sub.2, or CoSi.sub.2, for example.

(16) In this step, since contact spacers 122b cover the sidewalls of the contact trenches 116b, the metal silicide layers 126 may be formed only on the bottom surface of the contact trenches 116b, and no metal silicide can be formed on sidewalls of the contact trenches 116b. Therefore, the distance between the conductive metal silicide layers 126 and the gate layer 104 can be kept at a distance far enough to avoid current leakage induced by the gate layer 104.

(17) In light of the foregoing, since the contact spacers are formed at least on sidewalls of the contact trenches in the substrate, so that the distance between the gate and the silicide layers below the bottom surfaces, rather than on the sidewalls and the bottom surfaces, of the contact trenches can be increased, and thus the current leakage induced by gate can be decreased.

(18) Although implementations of the present invention have been described above in detail in combination with the attached drawings, the above-described implementations could not be interpreted as limitation to the present invention. Various modifications can be made by those skilled in the art within their knowledge without departing from the spirit and scope of the present invention.