JPS62113466A - Manufacture of semiconductor memory device - Google Patents

Abstract

PURPOSE:To increase the area of a charge storage capacitor in the base section of a groove in addition to the increase of the area only of the side surface section of the capacitor by previously coating a predetermined section in a groove forming section with a substance having an etching rate slower than an silicon substrate and forming a projecting section to the base of the groove after etching. CONSTITUTION:Field oxide films 12 are shaped previously (a), (b) at the same time even in prescribed sections in a groove forming section 12. A mask layer 15 for silicon etching is applied onto the whole surface, and the mask layer 15 in the groove forming section 13 is removed (c). The groove forming section 13 is etched until the field oxide film 12 in the groove forming section 13 is all removed, thus forming a groove for a capacitor, the base thereof has a trapezoid projecting section (d). A capacitor oxide film layer 16 is shaped into the groove for the capacitor, and a polycrystalline silicon electrode 17 is formed, thus obtaining a device having the groove type capacitor (e). The ratio of the etching rates of an silicon substrate 14 and the field oxide film 12 in conditions at the time of etching is kept previously at the ratio or less of desired silicon etching-depth to field oxide film thickness. Accordingly, the groove type capacitor, the base thereof has the projecting section, can be formed simply, and the increase of 30-40% of a charge storage area can be expected in the groove type capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application IP) The present invention relates to a semiconductor memory device, and particularly to a method for manufacturing a semiconductor memory device having a trench type capacitor.

(Prior Art) Regarding a semiconductor memory device having a trench-type capacitor, there is a device shown in Japanese Patent Publication No. 12739/1983, in which a trench is dug in a silicon substrate to increase the storage capacitance. A capacitor is formed along the line.

To outline the method for manufacturing a semiconductor memory device having this trench type capacitor, first, as shown in FIG. An etching mask layer is provided on the entire surface except for the etching mask layer. Thereafter, the silicon substrate 1 exposed in the groove forming part 13 is etched using a well-known etching technique.
4 (or field oxide film 12),
Form a groove. Next, as shown in FIG. 3(b), a capacitor oxide film layer 16 is provided on the surface inside the trench, and a polycrystalline silicon electrode 17 is further formed to obtain a trench type capacitor.

(Problem to be solved by the invention) However, the trench capacitor obtained by the above method is
Compared to a capacitor with a planar structure, the area of only the side portions was increased, and a sufficient charge storage capacitor area could not be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a semiconductor memory device that increases the area of a charge storage capacitor not only at the side surfaces of the capacitor but also at the bottom surface of the trench.

(Means for Solving the Problems) In the method for manufacturing a semiconductor memory device of the present invention, when forming a trench capacitor, a predetermined portion within the trench forming portion is covered in advance with a material whose etching rate is slower than that of the silicon substrate. This is characterized in that a convex portion is later provided on the bottom surface of the groove. Here, a silicon oxide film is most suitable as a material whose etching rate is slower than that of a silicon substrate, and it is formed at the same time as the field oxide film is formed.

(Function) According to the method of the present invention, a convex portion is provided on the bottom surface of the capacitor groove, and the charge storage area within the groove is further increased compared to the conventional method. This makes it possible to obtain a storage device of up to 100 days.

(Example) The present invention will be explained below based on the drawings.

FIGS. 1A to 1C show a first embodiment of the present invention. First, the active region 11 is separated by a well-known oxide film separation method. At the same time, a field oxide film 12 is also formed at a predetermined portion in the groove forming portion 13 (see FIG. The layer 15 is removed (see FIG. 1(e)). Thereafter, the exposed silicon substrate 14 and the field oxide film 12 are simultaneously etched by a well-known dry etching method, until all the field oxide film 12 in the groove forming part 13 is etched. Etching is performed until it is removed, and a capacitor groove having a platform-shaped convex portion on the bottom is formed (see Fig. 1 (dl)).
reference).

Among the etching conditions, the etching rate ratio between the silicon substrate 14 and the field oxide film 12 is kept below the desired silicon etching depth to field oxide film thickness ratio. For example, set the silicon etching depth to 3μ.
If the m1 field oxide film thickness is 5,000, the etching rate ratio should be 6:1 or less, ie, 5:1 or 4:1.

Thereafter, a capacitor oxide film layer 16 is provided in the capacitor groove by a well-known thermal oxidation method, and a polycrystalline silicon electrode 17 is further formed to obtain a semiconductor memory device having a groove type capacitor (see tel in FIG. 1). .

FIGS. 2(a) and 2(b) show a second embodiment of the present invention. Almost the same as the first embodiment, but
In the second embodiment, field oxidation Wj in the groove forming portion 13
412 is formed as shown in FIG. 2 (al), and in the groove after etching, a step-shaped convex portion connecting the - side and the opposite side is formed on the bottom surface (see FIG. 2 (b)). However, in this case, the following conditions must be satisfied regarding the dimensions of the convex portion.That is, since the present invention is characterized in that the surface area inside the groove is larger than that of the conventional groove type capacitor, 2 m with the symbol in Figure 2 (b)
# -2mk> 0 Therefore, the j)k condition is essential for the finished shape of the groove.

(Effects of the Invention) As explained above, according to the manufacturing method of the present invention, a coating layer of a substance having a slower etching rate than the silicon substrate is formed in advance in a part of the capacitor formation region, and then the silicon substrate and the coating layer are formed in advance. Since the layers are etched at the same time, it is possible to easily form a groove-type capacitor having a convex portion on the bottom surface.
Since the charge storage area can be expected to increase, it becomes possible to realize a semiconductor memory device having excellent signal output characteristics, noise resistance, and η-no-alpha characteristics.

[Brief explanation of drawings]

FIG. 1 (al and FIG. 1 (bl to (el) are the first
A plan view and a sectional view showing an example of
bl is a plan view and a perspective view showing a second embodiment of the present invention,
FIG. 3 (al and (bl) are a plan view and a cross-sectional view showing a conventional trench capacitor. 11. Active region, 12. Field oxide film, 13. Groove (capacitor) forming portion, 14.・Silicon substrate, 15. Mask layer, 16... Capacitor oxide film layer, 17. Polycrystalline silicon electrode.

Claims (3)

[Claims] (1) When manufacturing a semiconductor memory device having a trench type capacitor, (a) forming a covering layer of a substance whose etching rate is slower than that of the silicon substrate in a part of the trench type capacitor forming region on the silicon substrate; (b) forming an etching mask layer covering other areas except the trench capacitor formation region; and (c) etching the silicon substrate and the covering layer in the trench capacitor formation region at the same time. (d) forming a capacitor oxide film and an electrode polycrystalline silicon layer inside the formed groove; manufacturing method. (2) The method of manufacturing a semiconductor memory device according to claim (1), wherein the material having a slower etching rate than the silicon substrate is an oxide film layer. (3) The method of manufacturing a semiconductor memory device according to claim (2), wherein the oxide film layer is formed at the same time as a field oxide film formed in an oxide film isolation step.