JPS63133562A - Manufacture of groove type capacitor - Google Patents

Abstract

PURPOSE:To realize a groove type capacitor whose film thickness of an oxide film for capacitor use is uniform and whose capacitive characteristic is stable by a method wherein a diffused region having the uniform concentration of an impurity over the whole inside wall of a groove is obtained by separately implanting ions of the impurity into the sidewall and the bottom of the groove. CONSTITUTION:A silicon oxide film 2 is formed on a silicon substrate 1, and a groove 3 is made inside the silicon substrate 1. While the silicon substrate is being turned, a solution of silanol is dropped so as to form a silanol film 4. During this process, the bottom of the groove is coated with the solution, but the sidewall of the groove is hardly coated with the solution. Ions 5 of arsenic are implanted by making use of the silanol film as a mask for the bottom part of the groove. An ion-implanted layer 6 is formed at the sidewall of the groove, but no ion-implanted layer is formed at the bottom. After that, the silanol film is removed, and ions 7 of arsenic are implanted again. During a second ion implantation process an ion-implanted layer 8 is formed only at the bottom of the groove while the ions are hardly implanted into the sidewall.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a trench capacitor, which involves digging a trench in a semiconductor substrate and uniformly implanting impurities into the inner wall of the trench.

2. Description of the Related Art In conventional methods of manufacturing trench capacitors, ion implantation is often used to form diffusion regions along the inner walls of trenches.

The method for manufacturing this trench capacitor is to form a trench, then perform ion implantation by tilting the ion beam at an angle of about 5 to 9 degrees from the perpendicular direction to the substrate surface in order to implant impurities into the inner wall of the trench, followed by heat treatment. A diffusion region is formed on the sidewalls and bottom of the trench, and then a dielectric film for a capacitor and a conductive film to be one electrode of the capacitor are sequentially formed on the inner wall of the trench. Note that the inclination of the ion beam from the direction perpendicular to the substrate surface during ion implantation is referred to as a tilt angle.

Problems to be Solved by the Invention As described above, in the conventional manufacturing method, when a tilt angle is set during ion implantation, impurities are implanted into the side walls of the trench, but more impurities are implanted into the bottom of the trench. In order to
The impurity concentration at the bottom of the trench is extremely high.As a result, when an oxide film for a capacitor is formed inside the trench, the thickness of this oxide film becomes non-uniform, and ions are generated at the bottom of the trench. Since the damage caused by the implantation is large, the quality of the oxide film in this area is poor, and leakage current increases, causing instability in the capacitance characteristics.

Means for Solving the Problems In order to solve these problems, impurity ions are implanted into the sidewalls and bottom of the trench separately. For this purpose, before the first ion implantation into the sidewalls, a film that shields the ion beam is deposited on the bottom of the groove, and this film is used as a mask for the 5-
Ions are implanted into the sidewalls of the trench with a tilt angle of 100 degrees. Next, after removing the film deposited on the bottom of the trench, ions are implanted into the bottom of the trench.

By applying a silanol film to the bottom of the working groove and using this film as a mask for ion implantation into the bottom, ion implantation into the sidewalls and bottom of the groove can be performed separately, resulting in a uniform coating on the inner wall of the groove. A diffusion region with impurity concentration can be formed.

Embodiment An embodiment of the method for manufacturing a trench capacitor according to the present invention will be described with reference to the process cross-sectional diagram shown in FIG.

First, a silicon oxide film 2 is formed on a silicon substrate 1, and an opening of 1 μm x 1 μm is formed in the silicon oxide film 2 by photolithography. Dry etching is performed through this opening to form an inside of the silicon substrate 1. Form groove 3 with a depth of 4μ in (
Figure 1 a).

While rotating the silicon substrate 1 at a speed of 7000 r, p, - or more, a silanol solution is dropped to form a silanol film 4. At this time, the solution is applied to the bottom of the groove, and is hardly applied to the side walls of the groove (FIG. 1b).

Using this silanol film as a mask at the bottom of the groove, arsenic ions (As'') 5 are implanted at a high acceleration voltage of 200 KeV with a tilt angle of 5 to 9 degrees (Fig. 1C). An ion implantation layer 6 is formed at the bottom, but no ion implantation layer is formed at the bottom.

After that, the silanol film 4 is removed with a solution prepared by diluting hydrofluoric acid with ultrapure water, and arsenic ions (As") 7 are implanted again at a low acceleration voltage of about 20 KeV (Fig. 1d). Second time In the ion implantation, the ion implantation layer 8 is formed only at the bottom of the groove, and is hardly implanted into the sidewalls.

Thereafter, a heat treatment is performed to form a diffusion region 9 having a uniform impurity concentration and a shallow diffusion length on the inner wall of the groove.

(Figure 1e).

Next, 100 ml was applied to the surface of the silicon substrate 1 and the inner wall of the groove 3.
After growing a silicon oxide film 10 with a thickness of about 500 Å to form a dielectric film for a capacitor, a polysilicon film 11 that will become one electrode of the capacitor is grown on top of the silicon oxide film 10 with a thickness of about 300 Å.
By forming 00A, a trench capacitor is completed (FIG. 1f).

Note that the other electrode of the capacitor is the diffusion region 9. Furthermore, although a silanol film was used in the embodiment as a film for shielding the ion beam, a resist film may also be used.

Effects of the Invention As described above, according to the present invention, a diffusion region with a uniform impurity concentration can be obtained throughout the inner groove, so that an oxide film for a capacitor can have a uniform thickness and a good quality. A trench capacitor with stable capacitance characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a process sectional view showing an embodiment of the method for manufacturing a trench capacitor according to the present invention. 1... Silicon substrate, 2, 10... Silicon oxide film, 3... Groove, 4... Silanol coating, 5, 7...・Arsenic ion (As”)
, 6.8... ion implantation layer, 9...
Diffusion region, 11... Polysilicon film. Name of agent: Patent attorney Toshio Nakao and one other person

Claims (3)

[Claims] (1) A process of forming a groove in a semiconductor substrate, a process of depositing a film to shield the ion beam on the bottom of the groove, and an ion implantation method using the film as a mask at a tilt angle to implant impurities into the groove. a step of implanting an impurity into the side wall portion, a step of implanting an impurity into the bottom of the trench again by ion implantation after removing the film, a dielectric film for a capacitor on the inner wall of the trench, and one electrode of the capacitor. 1. A method for manufacturing a trench capacitor, comprising the step of sequentially laminating conductive films. (2) The method for manufacturing a trench capacitor according to claim 1, wherein the film that shields the ion beam is a silanol film. (3) The method for manufacturing a trench capacitor according to claim 1, wherein the film that shields the ion beam is a photoresist film.