JPH0575184B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a trench capacitor, and particularly to increasing the radius of curvature of a trench corner portion.

(Prior Art) FIGS. 3A to 3F are process diagrams showing a conventional method of manufacturing a trench capacitor. As shown in FIG.
For example, CVD (Chemical Vapor
A photoresist 3 is coated on this to form a window 3a, and then,
As shown in Figure B, a window 2a for digging a trench is formed in the mask material 2, and the photoresist 3 is removed. Next, as shown in FIG. 3c, a trench 1a of the required depth is formed in the silicon substrate 1 by anisotropic etching such as ion etching, and the mask material 2 is removed by an appropriate post-processing. Remove the damaged layer during silicon etching. Next, as shown in Figure D, an impurity layer 4 is formed on the surface of the trench by ion implantation or solid-phase diffusion to make the part that will become a capacitor D (Depression), and then gate oxidation is performed. An insulating film 5 is formed as shown in Figure E. Finally, polysilicon or the like is deposited on the insulating film 5 to form an electrode film 6, thereby forming a trench capacitor as shown in FIG.

(Problems to be Solved by the Invention) The trench capacitor described above is produced by digging a trench on a silicon substrate by anisotropic etching.
Since an insulating film is formed on the surface including the inside of this trench, compared to a planar capacitor, electric field concentration at the corners can cause a drop in breakdown voltage and reduce reliability. For this purpose, after etching the inner surface of the trench, the surface is once oxidized to give rounded corners.

Such oxidation treatments require the establishment of special conditions. In other words, when a trench is formed in a silicon substrate with a "1.0.0" plane orientation and the inner surface of this trench is oxidized, horn-shaped protrusions are generated at the corners, which instead of suppressing electric field concentration, actually promotes electric field concentration. Often.

Therefore, in a water vapor atmosphere of 1000℃ or more, the thickness
When special conditions are used to form an oxide film with a thickness of 1000 Å or more, the corners are rounded and electric field concentration is avoided, but this high-temperature atmosphere can cause crystal defects and changes in impurity distribution. There was a problem.

This invention was made in order to solve the above problems, and it is possible to easily increase the radius of curvature of the corner portion of a trench under safe conditions, thereby significantly improving withstand voltage and reliability. It is an object of the present invention to provide a method for manufacturing a trench capacitor that can be improved.

[Structure of the invention]

(Means for Solving the Problems) The present invention first forms a trench in a silicon substrate, and then the surface of the silicon substrate including the inside of the trench is filled with amorphous silicon or amorphous silicon doped with impurities. Depositing polysilicon, then oxidizing the amorphous silicon or polysilicon and a part of the silicon substrate to form an impurity layer inside and an oxide film layer on the surface, and then is removed by etching, then an insulating film is formed on the surface of the impurity layer, and then an electrode film is deposited on the insulating film.

(Operation) In the present invention, when amorphous silicon or polysilicon is deposited on a silicon substrate, its corner portions are rounded. When amorphous silicon or polysilicon is oxidized in this state, the boundary between the oxide film and the Si substrate becomes rounded to follow the surface shape of the corner of the amorphous silicon or polysilicon. after this,
If the oxide film is removed by etching, the corners of the trench will become rounded, and at the same time, impurities will be stirred into the Si substrate. Therefore,
Compared to conventional manufacturing methods that require special processing conditions to be established in order to round the trench corners, the radius of curvature of the trench corners can be easily increased under stable conditions. .

(Example) FIGS. 1A to 1F are process diagrams showing an example of the present invention. Here, first, as shown in FIG. 1A, a mask material 2 is formed on the surface of a silicon substrate 1 to open a window 2a for forming a trench, and then, as shown in FIG. A trench 1a is dug in the silicon substrate 1 by etching, and the mask material 2 is peeled off. Next, amorphous silicon doped with 1×10 ¹⁸ cm ^-3 of arsenic is applied to the surface of the silicon substrate, including the inner surface of trench 1a.
Deposit 500-2000Å. Next, this wafer is subjected to oxidation of the amorphous silicon 7 and a part of the silicon substrate 1, for example, the surface layer with a depth of 500 to 1000 Å, by hydrogen combustion oxidation in an atmosphere of 950° C. As a result, as shown in FIG. 1D, an oxide film layer 8 is formed, and the impurity layer 4 is formed by diffusing the impurities doped into the amorphous silicon into the silicon substrate. .
Subsequently, as shown in FIG. E, the impurity layer 4 is exposed by etching the oxide layer 8.
Here, an insulating film 5 is formed. In this case, the corner portions of the silicon substrate 1 are rounded with a radius of curvature of 100 Å or more, reflecting the shape of the amorphous silicon deposit, and form a base for a trench capacitor in which electric field concentration is unlikely to occur. Finally, as shown in FIG. F, an electrode film 6 of polysilicon or the like is formed to complete the trench capacitor.

Figure 2 is a diagram showing the relationship between electric field strength and current for a trench capacitor manufactured using this process, together with that for a trench capacitor manufactured using a conventional method. According to the curve Y, this process is adopted. Here, assuming that the silicon substrate 1 is of N type, by applying a positive voltage to the electrode, for example, 10 ^-6 A
When compared when a current of
While the electric field strength was 5.7 MV/CM, when the process shown in Figure 1 was followed, it was 7.0 MV/CM.

Thus, according to this embodiment, the radius of curvature of the trench corner can be greatly increased by a simple method, and as a result, the withstand voltage can be increased to 1.0 MV/
CM can also be raised.

In this embodiment, the oxide layer 8 is formed by depositing amorphous silicon, but the same oxide layer 8 and impurity layer 4 as described above can be formed by using polysilicon instead.

On the other hand, in this example, impurity diffusion treatment is performed at the same time during the oxidation process of the amorphous silicon doped with impurities and the silicon substrate, and the product yield is lower than that of the conventional method that includes the D conversion process. can be improved.

[Conventional configuration]

As is clear from the above description, according to the present invention, when amorphous silicon or polysilicon is deposited on a silicon substrate, the corner portions are rounded. Because it forms a rounded impurity layer,
Under stable conditions, the radius of curvature of the corner portion of the trench can be easily increased, which has the effect of significantly improving voltage resistance and reliability.

[Brief explanation of the drawing]

Fig. 1 is a process diagram showing an embodiment of the present invention, and Fig. 2 shows the relationship between electric field strength and current of a product manufactured by the same embodiment in comparison with a product manufactured using a conventional method. FIG. 3 is a process diagram showing a conventional trench capacitor manufacturing method. 1...Silicon substrate, 2...Mask material, 4...
Impurity layer, 5... Insulating film, 6... Electrode film, 7...
Amorphous silicon, 8... oxide layer.

Claims (1)

[Claims] 1 First, a trench is formed in a silicon substrate, then amorphous silicon or polysilicon doped with impurities is deposited on the surface of the silicon substrate including the inside of the trench, and then amorphous silicon or polysilicon doped with impurities is deposited. Polysilicon and a portion of the silicon substrate are oxidized to form an impurity layer inside and an oxide layer on the surface, then the oxide layer is removed by etching, and then the impurity layer is etched. A method for manufacturing a trench capacitor, comprising forming an insulating film on the surface, and then depositing an electrode film on the insulating film.