Semiconductor structure and manufacturing method thereof

Abstract

A semiconductor structure including a substrate, a dielectric layer and a polysilicon layer is provided. The dielectric layer is disposed on the substrate. The polysilicon layer is disposed on the dielectric layer. A fluorine dopant concentration in the polysilicon layer presents Gaussian distributions from a top portion to a bottom portion of the polysilicon layer. Fluorine dopant peak concentrations of the Gaussian distributions are progressively decreased from the top portion to the bottom portion of the polysilicon layer.

Claims

1. A semiconductor structure, comprising: a substrate; a dielectric layer, disposed on the substrate; and a polysilicon layer, disposed on the dielectric layer, wherein a fluorine dopant concentration in the polysilicon layer presents Gaussian distributions from a top portion to a bottom portion of the polysilicon layer, fluorine dopant peak concentrations of the Gaussian distributions are progressively decreased from the top portion to the bottom portion of the polysilicon layer, and the fluorine dopant peak concentrations are 810.sup.15 ions/cm.sup.2 to 110.sup.16 ions/cm.sup.2, 510.sup.15 ions/cm.sup.2 to 710.sup.15 ions/cm.sup.2, and 110.sup.15 ions/cm.sup.2 to 410.sup.15 ions/cm.sup.2 from the top portion to the bottom portion of the polysilicon layer, wherein an uppermost part of the top portion of the polysilicon layer is at minimum in the fluorine dopant concentration.

2. The semiconductor structure as claimed in claim 1, wherein the substrate comprises a silicon substrate.

3. The semiconductor structure as claimed in claim 1, wherein a material of the dielectric layer comprises silicon oxide.

4. The semiconductor structure as claimed in claim 1, wherein a material of the polysilicon layer comprises doped polysilicon or undoped polysilicon.

5. The semiconductor structure as claimed in claim 1, wherein the fluorine dopant peak concentrations comprise: a first fluorine dopant peak concentration, close to the bottom portion of the polysilicon layer; and a second fluorine dopant peak concentration, close to the top portion of the polysilicon layer.

6. The semiconductor structure as claimed in claim 5, wherein the fluorine dopant peak concentrations further comprise: a third fluorine dopant peak concentration, wherein compared to the second fluorine dopant peak concentration, the third fluorine dopant peak concentration is closer to the top portion of the polysilicon layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

(2) FIG. 1A to FIG. 1C are cross-sectional views of a process of manufacturing a semiconductor structure according to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

(3) FIG. 1A to FIG. 1C are cross-sectional views of a process of manufacturing a semiconductor structure according to an embodiment of the invention. Moreover, in FIG. 1A to FIG. 1C, relationship curve diagrams of depth positions and fluorine dopant concentrations are also illustrated.

(4) Referring to FIG. 1A, a dielectric layer 102 is formed on a substrate 100. The substrate 100 may be a semiconductor substrate, for example, a silicon substrate. A material of the dielectric layer 102 is, for example, oxide (for example, silicon oxide). A method for forming the dielectric layer 102 is, for example, thermal oxidation or chemical vapor deposition.

(5) A polysilicon layer 104 is formed on the dielectric layer 102. A material of the polysilicon layer 104 is, for example, doped polysilicon or undoped polysilicon. A method for forming the polysilicon layer 104 is, for example, the chemical vapor deposition.

(6) Ion implantation processes are performed to the polysilicon layer 104 by using a fluorine dopant, where implantation depths of the ion implantation processes are different. A fluorine dopant concentration of the ion implantation process with a deeper implantation depth is smaller than a fluorine dopant concentration of the ion implantation process with a shallower implantation depth. Implantation energy of the ion implantation process with the deeper implantation depth is, for example, greater than implantation energy of the ion implantation process with the shallower implantation depth. The ion implantation processes performed to the polysilicon layer is, for example, performed before a lightly doped drain (LDD), a source region or a drain region is formed.

(7) In this way, the fluorine dopant concentration in the polysilicon layer 104 may present Gaussian distributions from a top portion to a bottom portion of the polysilicon layer 104. Fluorine dopant peak concentrations of the Gaussian distributions are progressively decreased from the top portion to the bottom portion of the polysilicon layer 104. The top portion of the polysilicon layer 104 is the portion of the polysilicon layer 104 located away from the dielectric layer 102. The bottom portion of the polysilicon layer 104 is the portion of the polysilicon layer 104 located close to the dielectric layer 102.

(8) For example, the ion implantation processes performed to the polysilicon layer 104 by using the fluorine dopant may include a first ion implantation process 110 and a second ion implantation process 112 performed to the polysilicon layer 104, and may further include a third ion implantation process 114 performed to the polysilicon layer 104. In the present embodiment, the first ion implantation process 110, the second ion implantation process 112 and the third ion implantation process 114 are sequentially performed as an example. In another embodiment, the first ion implantation process 110, the second ion implantation process 112 and the third ion implantation process 114 may not be sequentially performed.

(9) In the first ion implantation process 110, the second ion implantation process 112 and the third ion implantation process 114, the implantation depth of the first ion implantation process 110 is the deepest, the implantation depth of the second ion implantation process 112 is shallower, and the implantation depth of the third ion implantation process 114 is the shallowest. A first fluorine dopant concentration of the first ion implantation process 110 is smaller than a second fluorine dopant concentration of the second ion implantation process 112. The second fluorine dopant concentration of the second ion implantation process 112 is smaller than a third fluorine dopant concentration of the third ion implantation process 114. The first fluorine dopant concentration may be 110.sup.15 ions/cm.sup.2 to 410.sup.15 ions/cm.sup.2, for example, 310.sup.15 ions/cm.sup.2. The second fluorine dopant concentration may be 510.sup.15 ions/cm.sup.2 to 710.sup.15 ions/cm.sup.2, for example, 610.sup.15 ions/cm.sup.2. The third fluorine dopant concentration may be 810.sup.15 ions/cm.sup.2 to 110.sup.16 ions/cm.sup.2, for example, 810.sup.15 ions/cm.sup.2.

(10) First implantation energy of the first ion implantation process 110 may be greater than second implantation energy of the second ion implantation process 112. The second implantation energy of the second ion implantation process 112 may be greater than third implantation energy of the third ion implantation process 114. The first implantation energy may be 27 KeV to 33 KeV, for example, 30 KeV. The second implantation energy may be 18 KeV to 22 KeV, for example, 20 KeV. The third implantation energy may be 9 KeV to 11 KeV, for example, 10 KeV.

(11) Therefore, referring to a relationship curve diagram of the depth position and the fluorine dopant concentration of FIG. 1A, the fluorine dopant concentration in the polysilicon layer 104 may present a third Gaussian distribution G3, a second Gaussian distribution G2 and a first Gaussian distribution G1 from the top portion to the bottom portion of the polysilicon layer 104. The first Gaussian distribution G1, the second Gaussian distribution G2 and the third Gaussian distribution G3 respectively have a first fluorine dopant peak concentration P1, a second fluorine dopant peak concentration P2 and a third fluorine dopant peak concentration P3. The first fluorine dopant peak concentration P1 may be close to the bottom portion of the polysilicon layer 104. The second fluorine dopant peak concentration P2 may be close to the top portion of the polysilicon layer 104. Moreover, compared to the second fluorine dopant peak concentration P2, the third fluorine dopant peak concentration P3 may be closer to the top portion of the polysilicon layer 104. The second fluorine dopant peak concentration P2 may be greater than the first fluorine dopant peak concentration P1. The third fluorine dopant peak concentration P3 may be greater than the second fluorine dopant peak concentration P2.

(12) Referring to FIG. 1B, a patterning process may be performed to the polysilicon layer 104 and the dielectric layer 102 to form patterned polysilicon layer 104a and dielectric layer 102a. The polysilicon layer 104a may serve as a gate. The dielectric layer 102a may serve as a gate dielectric layer. The patterning process is, for example, a combination of a lithography process and an etching process.

(13) In the present embodiment, after the ion implantation processes are first performed to the unpatterned polysilicon layer 104, the polysilicon layer 104 is then patterned, though the invention is not limited thereto. In another embodiment, after the polysilicon layer 104 is first patterned, the ion implantation processes are then performed to the patterned polysilicon layer 104a.

(14) Referring to a relationship curve diagram of depth positions and fluorine dopant concentrations of FIG. 1A and FIG. 1B, the fluorine dopant concentration distribution in the polysilicon layer 104a and the fluorine dopant concentration distribution of the polysilicon layer 104 are substantially the same.

(15) Referring to FIG. 1C, after the ion implantation processes are performed, a thermal process 120 is performed to the polysilicon layer 104a. The thermal process 120 may be a subsequent thermal process used for forming the source region or the drain region or an additionally perform thermal process.

(16) After the thermal process 120 is performed, the fluorine dopant concentration in the polysilicon layer 104a may still present the Gaussian distributions. Since after the thermal process 120 is performed, the fluorine dopant is diffused into the dielectric layer 102a, oxide traps of the whole dielectric layer 102a may be filled by the fluorine dopant. Therefore, after the thermal process 120 is performed, the fluorine dopant concentration in the polysilicon layer 104a is decreased.

(17) For example, referring to a relationship curve diagram of depth positions and fluorine dopant concentration of FIG. 1C, after the thermal process 120 is performed, the fluorine dopant concentration in the polysilicon layer 104a may still present the first Gaussian distribution G1, the second Gaussian distribution G2 and the third Gaussian distribution G3, where the first fluorine dopant peak concentration P1 of the first Gaussian distribution G1 is decreased to a first fluorine dopant peak concentration P1a, the second fluorine dopant peak concentration P2 of the second Gaussian distribution G2 is decreased to a second fluorine dopant peak concentration P2a, and the third fluorine dopant peak concentration P3 of the third Gaussian distribution G3 is decreased to a third fluorine dopant peak concentration P3a.

(18) In the present embodiment, it is assumed that three ion implantation processes are performed, such that the fluorine dopant concentration may present three Gaussian distributions in the polysilicon layer 104a, though the invention not limited thereto. It is considered to be within a protection range as long as two or more ion implantation processes are performed to make the fluorine dopant concentration to present two or more Gaussian distributions in the polysilicon layer 104a.

(19) Based on the above description, it is known that in the method for manufacturing the semiconductor structure, since the fluorine dopant concentration of the ion implantation process with the deeper implantation depth is smaller than the fluorine dopant concentration of the ion implantation process with the shallower implantation depth, a specific fluorine dopant concentration distribution is formed in the polysilicon layer 104a. In this way, after the thermal process is performed to the polysilicon layer 104a, since the fluorine dopant in the polysilicon layer 104a is diffused into the dielectric layer 102a, the oxide traps in the whole dielectric layer 102a can be filled by the fluorine dopant in the specific fluorine dopant concentration distribution, so as to mitigate the flicker noise of both of the high frequency portion and the low frequency portion.

(20) The semiconductor structure of the aforementioned embodiment is described below with reference of FIG. 1B.

(21) Referring to FIG. 1B, the semiconductor structure includes the substrate 100, the dielectric layer 102a and the polysilicon layer 104a. The dielectric layer 102a is disposed on the substrate 100. The polysilicon layer 104a is disposed on the dielectric layer 102a. A fluorine dopant concentration in the polysilicon layer 104a presents Gaussian distributions (for example, the third Gaussian distribution G3, the second Gaussian distribution G2 and the first Gaussian distribution G1) from the top portion to the bottom portion of the polysilicon layer 104a. Fluorine dopant peak concentrations (for example, the third fluorine dopant peak concentration P3, the second fluorine dopant peak concentration P2 and the first fluorine dopant peak concentration P1) of the Gaussian distributions are progressively decreased from the top portion to the bottom portion of the polysilicon layer 104a. Moreover, materials, configuration methods, forming methods and effects of various components of the semiconductor structure have been describe in detail in the aforementioned embodiment, and details thereof are not repeated.

(22) Based on the aforementioned embodiment, it is known that in the semiconductor structure, since the fluorine dopant peak concentrations of the Gaussian distributions are progressively decreased from the top portion to the bottom portion of the polysilicon layer 104a, the specific fluorine dopant concentration distribution is formed in the polysilicon layer. In this way, after the thermal process is performed to the polysilicon layer 104a, since the fluorine dopant in the polysilicon layer 104a is diffused into the dielectric layer 102a, the oxide traps in the whole dielectric layer 102a may be filled by the fluorine dopant in the Gaussian distributions with different fluorine dopant peak concentrations, so as to mitigate the flicker noise of both of the high frequency portion and the low frequency portion.

(23) In summary, in the semiconductor structure and the manufacturing method thereof of the invention, by adjusting the fluorine dopant concentration distribution in the polysilicon layer, the flicker noise of both of the high frequency portion and the low frequency portion is mitigated.

(24) It will be apparent to those skilled in the art that various modifications and variations may be made to the structure of the invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.