JP3192673B2 - 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 for manufacturing a semiconductor device, and more particularly, to a method for forming a capacitor on a semiconductor substrate such as a DRAM cell, and more particularly, to a method for manufacturing a lower electrode of a capacitor.

[0002]

2. Description of the Related Art As disclosed in the 1990 Spring Society of Applied Physics manuscripts, P583 29a-SB-4,
The polysilicon film is formed in a temperature region where the transition from the amorphous state to the polycrystalline state occurs, so that the unevenness of the film surface becomes large.
By using the polysilicon film formed in this temperature region for the lower electrode of the capacitor of the DRAM cell, 620 ° C.
The capacity is increased by about 30% as compared with the case where the film is formed by the above method.

[0003]

However, a rough-surface polysilicon film formed in a temperature region where a transition is made from amorphous to polycrystalline is a porous (porous) film (a very coarse film having a gap as a film). Therefore, there is a problem in that the underlying film is damaged during the post-cleaning and that the polysilicon film is peeled off. That is, when forming the lower electrode of the capacitor with the rough polysilicon film, first, the rough polysilicon film is formed, and As is ion-implanted into the rough polysilicon film.
After the As is diffused into the whole by N ₂ annealing, the polysilicon film is patterned to form a lower electrode. At the time of the N ₂ annealing, the surface of the polysilicon film is about 50 ° An oxide film is formed. Therefore, before the patterning step, post-cleaning is performed with 5% HF (hydrofluoric acid) for 20 to 30 seconds to remove the oxide film.
At this time, since the rough polysilicon film is a porous film, HF penetrates and the underlying oxide film is etched. Also, when the underlying oxide film is etched, lift-off causes the upper rough polysilicon film to be peeled off.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and provides a method of manufacturing a semiconductor device capable of forming a capacitor lower electrode capable of increasing a capacitor capacity by preventing damage to a base and peeling of a film. With the goal.

[0005]

According to the present invention, a rough-surfaced polysilicon film having large surface irregularities and a silicon film having a dense film quality (a silicon film having no gap) are laminated on a semiconductor substrate in an arbitrary order. The lower electrode of the capacitor is formed from these two layers.

[0006]

According to the present invention, the penetration of HF into the substrate during the post-cleaning is prevented by the silicon film having a dense film quality. Therefore, etching of the base and, as a result, peeling of the two-layer film are prevented. When the rough polysilicon film is located in the upper layer, the roughness of the surface of the rough polysilicon film is increased. On the other hand, when the dense silicon film is located in the upper layer, the lower polysilicon film is formed of the lower layer. The surface area of the capacitor lower electrode can be increased by the unevenness of the surface of the dense silicon film affected by the unevenness of the surface. Therefore, the capacitance of the capacitor can be increased.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a first embodiment of the present invention. In this figure, reference numeral 1 denotes a silicon substrate. First, an oxide film 2 is formed on the surface of the substrate 1 by oxidation at a temperature of 950 ° C. at 1000 °. Next, on the oxide film 2, 100
% SiH ₄ gas as the source gas under reduced pressure CVD method.
At 2 Torr and at a temperature of 570 ° C., a rough polysilicon film 3 having large irregularities on the film surface is formed at 1000 ° as a lower layer film of a capacitor lower electrode. Then, on top of that, 100% SiH ₄
Pressure of 0.2 Torr by low pressure CVD method using gas as raw material gas
r, at a temperature of 620 ° C., 5
At 00 °, a film is formed as an upper layer film of the capacitor lower electrode. Thereafter, an n-type impurity is ion-implanted into the polysilicon films 3 and 4, and a heat treatment is performed in N ₂ so that the n-type impurity is diffused into the entire polysilicon films 3 and 4. At this time, an oxygen film of about 50 ° is formed on the surface of the polysilicon film 4 due to oxygen that has entered the heat treatment apparatus. Then, post-cleaning is performed for 20 to 30 seconds with 5% HF to remove the oxide film.
At this time, even if the polysilicon film 3 is a very coarse film having a gap, in the first embodiment, the upper layer film quality of the polysilicon film 4 prevents the penetration of HF into the oxide film 2. This prevents the oxide film 2 from being etched, and prevents the polysilicon films 3 and 4 from peeling off due to the etching.

Next, the polysilicon films 3 and 4 are patterned to form a lower electrode having a two-layer structure of the capacitor. Thereafter, a silicon nitride film 5 was formed on the entire surface including the surface of the lower electrode as a capacitor insulating film at a pressure of 0.15 Torr and a temperature of 650 ° C. by a reduced pressure CVD method using SiH ₂ Cl ₂ gas and NH ₃ gas as source gases. To form Further thereon, as a capacitor upper electrode film, reduced pressure CVD using SiH ₄ gas as a source gas.
The polysilicon film 6 is formed at a pressure of 0.2 Torr and a temperature of 620 ° C. by 1000 °. Then, an n-type impurity is ion-implanted into the polysilicon film 6, and a heat treatment is performed so that the impurity is diffused all over. Then, the polysilicon film 6 is patterned to form an upper electrode of the capacitor. Further, the silicon nitride film 5 is also patterned in the same pattern as the upper electrode. Thus, the capacitor is completed. In this capacitor, the surface of the polysilicon film 4 (the surface of the lower electrode having the two-layer structure) becomes uneven due to the influence of the unevenness of the surface of the polysilicon film 3, and the surface area of the lower electrode can be increased. The capacity of the capacitor can be increased.

FIG. 2 shows a second embodiment of the present invention. In the second embodiment, the order of forming the coarse polysilicon film 3 having large unevenness on the film surface and the polysilicon film 4 having the dense film quality are reversed from those of the first embodiment. First, a dense polysilicon film 4 is formed as a capacitor lower electrode lower layer film, and a rough polysilicon film 3 is formed thereon as a capacitor lower electrode upper layer film.

[0010] Even in this case, the penetration of HF into the oxide film 2 when the thin oxide film formed on the surface of the polysilicon film 3 is removed with 5% HF is prevented by the dense polysilicon film 4. In addition, the surface area of the capacitor lower electrode can be increased by the unevenness of the surface of the rough polysilicon film 3. The second embodiment is the same as the first embodiment except for the order in which the polysilicon films 3 and 4 are formed.

In the first and second embodiments, a dense silicon film is formed at a pressure of 0.2 Torr and a temperature of 620 ° C. by a low pressure CVD method using 100% SiH ₄ gas as a source gas. Although the polysilicon film is formed at 500 °, an amorphous silicon film may be formed. In the case of an amorphous silicon film, for example, the same gas as above,
An amorphous silicon film is formed at a pressure of 0.2 Torr and at a temperature of 500 ° C. by the same CVD method at a temperature of 500 °.

[0012]

As described above in detail, according to the manufacturing method of the present invention, the lower electrode of the capacitor is formed by the two layers of the rough polysilicon film having large surface irregularities and the dense silicon film. Accordingly, it is possible to prevent damage to the base and peeling of the film during the post-cleaning, and increase the capacitance of the capacitor.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a method for manufacturing a semiconductor device according to the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 oxide film 3 polysilicon film 4 polysilicon film 5 silicon nitride film 6 polysilicon film

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-64-42161 (JP, A) JP-A 2-1154 (JP, A) JP-A 3-263370 (JP, A) JP-A 3- 272165 (JP, A) JP-A-4-280463 (JP, A) JP-A-5-67730 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 27/108 H01L 21 / 822 H01L 21/8242 H01L 27/04

Claims (1)

(57) [Claims] 1. A semiconductor device comprising: a semiconductor substrate having a rough surface polysilicon film having large surface irregularities and a dense silicon film laminated on the semiconductor substrate in an arbitrary order;
Thereafter, a capacitor insulating film is formed, and an upper electrode is formed on the capacitor insulating film.