JP3232161B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device having a structure in which source and drain diffusion layers are formed by diffusion from polysilicon on a semiconductor substrate.

[0002]

2. Description of the Related Art A conventional semiconductor device manufacturing method is disclosed in S. Kimura et al, IEDM Tech.dig., Pp. 950-952,199.
As described in 1), polysilicon is deposited on a semiconductor substrate, an oxide film is deposited on the entire surface of the polysilicon, patterning is performed, and then source and drain diffusions are formed near the semiconductor substrate surface by diffusion from the polysilicon. Layer was formed.

[0003]

In the conventional method of manufacturing a semiconductor device, in the step of patterning the polysilicon, when etching the polysilicon on the channel region, the semiconductor substrate is made of silicon having the same quality as the polysilicon. Therefore, it is difficult to detect the end point of the etching, and the semiconductor substrate is also scraped, thereby deteriorating the flatness of the channel surface, lowering the carrier mobility, and lowering the driving capability of the transistor. was there.

Therefore, the present invention provides a method of manufacturing a semiconductor device capable of realizing a channel surface having good flatness without etching a semiconductor substrate thereunder when etching polysilicon on a channel region. The purpose is to provide.

[0005]

According to a method of manufacturing a semiconductor device according to the present invention, a step of forming an element isolation oxide film on a semiconductor substrate of a first conductivity type, and after this step, a step of forming a polysilicon film on the semiconductor substrate. By depositing silicon and selectively oxidizing the polysilicon and removing the resulting oxide film, at least a part of the thickness of the polysilicon other than on the channel region is reduced by the thickness of the polysilicon on the channel. A step of making the polysilicon thinner than the film thickness, a step of introducing an impurity of the second conductivity type into the polysilicon by ion implantation after this step, and a step of resist coating and patterning after this step. By etching the polysilicon using the device isolation oxide film below the thin polysilicon portion as an etching end point detecting means, the polysilicon on the channel region is etched. Leaving a portion, after this step, oxidizing the polysilicon remaining on the channel region to remove the oxidized polysilicon, and diffusing the polysilicon from the polysilicon to form a second portion in the semiconductor substrate. Forming a two-conductivity type diffusion layer. In that case, it is preferable that the method further includes a step of forming a gate insulating film on the semiconductor substrate by oxidizing the semiconductor substrate in the channel region after removing the oxidized polysilicon.

[0006]

In the method of manufacturing a semiconductor device according to the present invention, the thickness of at least a portion of the polysilicon deposited on the semiconductor substrate other than on the channel region is made smaller than the thickness of the polysilicon on the channel region. By doing
When etching the polysilicon, the etching is terminated when the element isolation oxide film under the polysilicon in the thinned portion is exposed, so that the polysilicon on the channel region is partially left on the semiconductor substrate, Is oxidized to form an oxide film different from silicon which is a material of the semiconductor substrate, and then the oxide film is removed, thereby preventing the channel region of the semiconductor substrate from being scraped. Furthermore, after oxidizing the polysilicon on the channel region and removing the oxide film as described above, the gate insulating film is formed on the channel region again by oxidizing single crystal silicon, which is a material of the semiconductor substrate. Thus, a high-quality gate insulating film having a lower defect density than the oxide film obtained by oxidizing polysilicon can be realized.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing a semiconductor device according to the present invention will be described below with reference to FIGS. 1 to 3 are schematic sectional views showing a method of manufacturing a semiconductor device according to an embodiment in the order of steps.

[0008] First, as shown in FIG. 1 (a), is deposited as an element isolation film 2 made of SiO ₂ on the first conductivity type semiconductor substrate 1 is formed, the polysilicon film 3 with a thickness of about 300nm I do.

Next, as shown in FIG. 1B, for example, a silicon nitride film 4 is deposited on the polysilicon film 3 as an antioxidant, and is patterned into a predetermined shape by a known photolithography method.

Next, as shown in FIG. 1C, the portion of the polysilicon film 3 not covered with the silicon nitride film 4 is oxidized by annealing in an oxygen atmosphere to form an oxide film 5. At this time, the thickness of the oxide film 5 can be easily and accurately controlled by adjusting the oxidation time.

Next, as shown in FIG.
And the silicon nitride film 4 is removed.

Next, as shown in FIG. 2A, arsenic is ion-implanted as an impurity of the second conductivity type at, for example, 30 keV and 1 × 10 ¹⁶ / cm ^{2 over} the entire surface of the semiconductor device.
I do.

Next, as shown in FIG. 2B, a resist 7 is coated on the polysilicon film 3 and patterned by a known photolithography method, and then the polysilicon film 3 is used as a stopper by using the element isolation film 2 as a stopper. 3 is etched. At this time, for example, SF ₆ and Cl are used as etching gases.
₂ and the end point of the etching is detected by a known method. As a result, the polysilicon film 3 is not completely etched on the channel region, and a part 8 thereof remains.

Next, as shown in FIG. 2C, the remaining polysilicon film 3 is annealed in an oxygen atmosphere.
Is oxidized to form an oxide film 9. The oxidation conditions are, for example, Wet
Performed at 900 ° C. for 20 minutes in an O ₂ atmosphere. During this thermal oxidation, source and drain diffusion layers 10 of the second conductivity type are formed near the surface of the semiconductor substrate 1 by diffusion of arsenic ions from the polysilicon film 3.

Next, a resist is applied on the oxide film 9, patterned by a known photolithography method, and the oxide film is etched to remove the oxide film 9 on the channel region. After that, as shown in FIG.
The gate insulating film 11 is formed to have a thickness of about 6 nm by thermally oxidizing the semiconductor substrate 1 in the channel region.

Next, as shown in FIG.
A gate electrode 12 is formed of polysilicon on
Thereafter, an interlayer insulating film 13 is formed on the entire surface of the semiconductor device,
After that, the interlayer insulating film 13 is opened to reach the polysilicon film 3, and the source and drain lead electrodes 14 are formed.

[0017]

As described above, according to the present invention, when etching the polysilicon on the channel region, the end point of the etching can be reliably detected, so that the abrasion on the surface of the channel region of the semiconductor substrate is prevented. As a result, a channel surface having good flatness can be obtained, and a semiconductor device having desired characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view for explaining a method of manufacturing a semiconductor device according to one embodiment of the present invention.

FIG. 3 is a schematic sectional view illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 First conductivity type semiconductor substrate 2 Element isolation film 3 Polysilicon film 5 Oxide film by selective oxidation 6 Ion implantation 7 Resist 8 Part of polysilicon film left on channel region 9 Oxide film 10 Second conductivity type diffusion Layer 11 Gate insulating film

Claims (2)

(57) [Claims] A first step of forming an element isolation oxide film on a semiconductor substrate of a first conductivity type; and after the first step, depositing polysilicon on the semiconductor substrate; A second step of oxidizing the polysilicon and removing an oxide film formed thereby to make the thickness of the polysilicon partly smaller than the thickness of the polysilicon on the channel; After the step, a third step of introducing an impurity of the second conductivity type into the polysilicon by ion implantation, After the third step, after resist coating and patterning, the polysilicon portion having the thin film thickness A fourth step of etching the polysilicon using the lower element isolation oxide film as an etching end point detecting means to leave a part of the polysilicon on the channel region; and after the fourth step, A fifth step of oxidizing polysilicon remaining on the channel region and removing the oxidized polysilicon, and forming a second conductivity type diffusion layer in the semiconductor substrate by diffusion from the polysilicon. A method of manufacturing a semiconductor device, comprising: 2. The method of manufacturing a semiconductor device according to claim 1, wherein in the fifth step, the semiconductor substrate in a channel region is oxidized after removing the oxidized polysilicon. A method for manufacturing a semiconductor device, further comprising a step of forming a gate insulating film thereon.