JPS63115358A - Manufacture of groove digging type capacitor - Google Patents

Abstract

PURPOSE:To improve the electric strength, prevent the breaking of wire at steps and make the capacitor very small by forming a capacitor in which the corners of the groove opening section are rounded. CONSTITUTION:After covering a silicon substrate 1 with an etching mask for forming a groove 6, oxygen ions 5a are obliquely implanted right below the opening end of the mask. Thereafter, the groove 6 is formed using the etching mask. Then a heat treatment is performed to form an oxide film 8, this oxide film is etched away, and thereafter an oxidation is performed. And an electrode is formed on the oxide film 8. By implanting oxygen ions 4, crystal defects occur in the substrate parts subjected to the driving-in. Also, when a heat treatment is performed for coexistence of silicon and oxygen in the parts subjected to the driving-in, the formation of a silicon oxide film becomes easy. And by applying this oxygen ion implantation to the corners of the groove and performing a heat treatment to round the corners, thereby improving the dielectric strength of the rounded parts.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for manufacturing a trench type capacitor with improved voltage resistance than the conventional capacitor.

(Prior Art) Capacitors constituting MOS dynamic memories (auA), etc., are becoming increasingly finer and more highly integrated in accordance with proportional reduction. However, since the capacitance of a capacitor is proportional to its area, as miniaturization progresses, there is a limit to its capacitance. Therefore, in order to ensure a certain certain capacity, a structure as shown in FIG. 3 is known. That is, it is a so-called trench-type capacitor in which a groove (2) is formed vertically in a silicon substrate (2) by reactive ion etching or the like, and the area is raked so that charges accumulate around the groove (2).

The grooves (1) are formed, for example, by a reactive ion etching method (hereinafter referred to as RIE method) using a gas mainly composed of CF, SF1, CC94, etc., or a gas containing H in this gas. Here, at the concave corner of the bottom of the groove ■,
It becomes rounded to some extent depending on the settings of conditions such as pressure. Thereafter, a gate oxide film (2) is formed in the groove part (2) by thermal oxidation, and then polycrystalline silicon (a) for a gate electrode is formed by a well-known method such as the CVD method to form a trench type capacitor. This polycrystalline silicon for gate electrode (A) is formed so as to be connected to the gate electrode of a MOS transistor (not shown).

However, according to this method, when forming the oxide film (3), the oxidation rate is slower at the corners of the groove (3), that is, at the convex corner (2) of the opening or at the concave corner (0) of the bottom surface than at the flat part. Therefore, in the gate oxide film (3), the corner portion 0. (If it is 0, the oxide film thickness will become thin locally. At the rough corners (c) and (2), heating of the electric field also occurs, resulting in a problem that the dielectric strength voltage decreases.

Therefore, before forming the oxide film (2), the substrate (2) is thermally oxidized, that is, rounded, to form an oxide film, and then this oxide film is removed by etching to give the silicon surface a rounded shape. A method has been proposed for locally thinning the oxide film and suppressing electric field concentration when the surface is oxidized. However, even with this method, when rounding oxidation is performed, oxidation of the convex portions or four corners of the trench is suppressed due to the stress accompanying the growth of the oxide film, making it difficult to obtain a sufficiently low pressure in those portions.

In particular, since the electrode (A) is also formed on the convex corner (2) of the opening, rounding of the convex corner (0) is an important problem in preventing step breaks and the like.

(Problems to be Solved by the Invention) The present invention improves the withstand voltage at the opening of the groove compared to the conventional grooved capacitor described above, and prevents breakage of the electrode formed on the groove. The purpose is to

[Structure of the invention]

(Means for solving the problems) 13= In order to achieve the above object, the present invention provides that after coating a silicon substrate with an etching mask for forming a groove, at least a portion immediately below the opening end of the mask is formed. A step of obliquely implanting oxygen ions into the substrate, a step of forming a groove in the substrate using the etching mask, a step of performing heat treatment to form an oxide film, and a step of once etching this oxide film. The present invention provides a method for manufacturing a trench type capacitor, which includes the steps of forming an oxide film by removing and then oxidizing the oxide film, and forming an electrode on the oxide film. Further, as another manufacturing method, the present invention includes the steps of: coating a silicon substrate with an etching mask for forming a groove, and then forming a groove on the substrate using this etching mask; After implanting oxygen ions into the trench opening obliquely with respect to the substrate,
A groove comprising a step of performing heat treatment, and a step of etching and removing the oxide film formed by the heat treatment, forming an oxide film on the opening and the substrate, and then forming an electrode on the oxide film. A method for manufacturing a trench type capacitor is provided.

(Function) The present invention utilizes the fact that when thermal oxidation is performed after oxygen ions are implanted into the surface of a silicon substrate, the oxidation rate of the ion-implanted portion is faster than that of other portions. It manufactures type capacitors. The increase in oxidation rate is thought to be due to the following reasons. In other words, by implanting oxygen ions, crystal defects are generated in the implanted part of the substrate, and a silicon oxide film is likely to be formed when heat treatment is performed due to the coexistence of silicon and oxygen in the implanted part. By becoming. According to the present invention, after this oxygen ion implantation is performed at the corners of the trench, heat treatment is performed to round the corners more than before, thereby making it possible to improve the dielectric strength of the rounded portions. .

(Example) Hereinafter, details of the present invention will be explained using the drawings.

FIG. 1 is a process sectional view showing an embodiment of the present invention.

First, as shown in FIG. 1(,), a resist mask (2) for groove trench etching is formed on a silicon substrate (2) to a thickness of 1 μm. Here, this region ■ has a non-line width of 1. The thickness of the resist (3) is determined by taking into consideration the area of this region, the implantation angle of the ion implantation process described later, and the resistance of the resist (3) so that it will not be etched to the substrate (2) during groove etching, which will also be described later. Next, this resist h (3) is etched to expose the region (2) where the groove is to be formed. The resist (2) also serves as a mask during ion implantation, which will be described later.

Next, as shown in FIG. 1(b), oxygen 0) is ion-implanted at an angle of 1, for example, 30 degrees to the vertical direction of the substrate (2), and ions of this oxygen are formed to form an oxygen ion-implanted layer (3). The implantation is performed, for example, at an acceleration voltage of 10, θV, and a dose of 1017.
/d conditions. Here, as mentioned above, the angle of ion implantation is related to the resist film thickness and the area of the groove, and can be changed accordingly, but at least oxygen is implanted into the substrate directly under the resist near the edges of the resist. make it possible to do so.

In addition, in this example, the substrate (2) is fixedly mounted on a substrate fixing table (not shown) at an angle of 30 degrees with respect to the horizontal direction, and ions are implanted at all azimuth angles by rotating the fixing table. I decided to do so.

Next, as shown in FIG. 1(c), the substrate 2 is etched by RIE or the like using the resist 2 as a mask to form a groove 0. By this etching, a part of the oxygen ion-implanted layer (5a) in the layer previously ion-implanted at the corner of groove 0 is removed.
remains. Thereafter, as shown in FIG. 1(d), after removing the resist (2), heat treatment is performed in a thermal oxidation atmosphere at approximately 850°C. The temperature of the heat treatment is approximately 850°C in this example.
The temperature was preferably about 800°C to 900°C. By this heat treatment, as shown in FIG. 1(e), an oxide film (2) is formed on the substrate (2) and in the groove 0, and the corners of the groove 0 into which oxygen ions have been implanted, that is, the convex corners of the openings, are oxidized. Despite the stress that occurs when oxidizing, it is more rounded than traditional rounding.

After that, after removing all the oxide film ①,
Add a new oxide film to the substrate ■''2 and groove 0 in an oxidizing atmosphere of
is formed to a thickness of about 150 people. Next, this oxide film (0
Polycrystalline silicon for electrodes on top! After forming J e) by CVD method etc., patterning is performed to obtain the shape shown in Fig. 1(f).
A trench-horizontal capacitor as shown in is completed. Here, the electrode may be a high melting point metal film or an aluminum film. In the trench type capacitor formed in this way, the convex corner of the opening of trench 0 can be rounded more than before, and also prevents breakage of the wiring on the oxide film that will be formed later. can.

In this example, oxygen ions were implanted before forming trench 0, but after trench 0 was formed by etching, a focused ion beam or the like was used to etch the convex corner of the opening of curved trench (2) into the substrate (2). A similar effect can be obtained by forming a trench-type capacitor by implanting oxygen ions obliquely.

Further, in Example 2, after oxygen ions were implanted into the opening of groove 0, heat treatment was performed in a thermal oxidation atmosphere, but it is not necessary to be in an oxygen atmosphere. For example, heat treatment is performed in a rare gas such as argon (Ar) gas to form an oxide film on the portion where oxygen ions have been implanted, and then this oxide film is removed by etching.

Then, an oxide film having a desired thickness may be formed on the opening (groove) portion 0 and the substrate (T) by exposing it to a thermal oxidation atmosphere.

In this case, the dose of oxygen ions implanted is preferably about 10''/d in order to form an oxide film.

Next, FIG. 2 shows an example in which the method for manufacturing a trench type capacitor according to the above embodiment is applied to a dRAM.

Portions common to those in FIG. 1 are denoted by the same reference numerals, and detailed explanations will be omitted.

Here, (8a) is an oxide film (8a) formed on the substrate O).
) is the gate oxide film left by etching away the oxide film in the source (10) and drain (11) regions. Then, using these oxide films (c) and (8a) as masks, impurity ions are implanted into the substrate as a source (10).
), a train (11) region was formed, and dRAl soil was fabricated. (12) is a gate electrode.

The present invention is not limited to the above-described embodiments, and can be modified as appropriate without departing from the gist of the present invention.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to form a capacitor with rounded corners of the groove opening, which improves the withstand voltage and prevents disconnection of the wiring formed on the groove. be able to.

Moreover, this allows miniaturization of the trench type capacitor.

[Brief explanation of the drawing]

FIG. 1 is a process sectional view showing a first embodiment of the present invention, FIG. 2 is a sectional view in the final process of applying the present invention to dRAM, and FIG. 3 is a diagram for explaining a conventional example. . 1... Silicon substrate, 3... Resist, 4
... Oxide ion, 5.5a... Oxygen ion implantation layer, 6... Groove, 7,8... Oxide film. Agent Patent Attorney Nori Ken Yudo Takehana Kikuojiku 1 M Thu l VN Gu m -1

Claims (2)

[Claims] (1) After covering a silicon substrate with an etching mask for forming a groove, a step of implanting oxygen ions obliquely into the substrate at least immediately below the open end of the mask, and then using the etching mask a step of forming a groove on the substrate using a heat treatment, a step of forming an oxide film by performing heat treatment, a step of removing the oxide film by etching, and then forming an oxide film on the groove portion and the surface of the substrate; A method for manufacturing a trench-horizontal capacitor, comprising the step of forming an electrode on a film. (2) After covering the silicon substrate with an etching mask for forming grooves, using this etching mask to form grooves in the substrate, and applying oxygen diagonally to the substrate directly under the open end of the mask. After ion implantation, a heat treatment step is performed, and after etching and removing the oxide film formed by the heat treatment, an oxide film is formed on the groove portion and the substrate, and then an electrode is formed on the oxide film. A method for manufacturing a trench-horizontal capacitor, comprising the steps of: