JP3180404B2 - Method of forming capacitive element - 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 forming a capacitor in a semiconductor device, and more particularly to a method for forming an insulating film of the capacitor.

[0002]

2. Description of the Prior Art FIG.
FIG. 2 is a cross-sectional view of a stacked capacitor that is a capacitive element of a RAM (Dynamic Ramdom Access Memory).

In the capacitor shown in FIG. 3, a field oxide film 2 for element isolation is formed on a P-type silicon substrate 1, an N ⁺ diffusion layer 3, a word line 4 made of polysilicon, and a bit made of aluminum. Line 5, SiO ₂ film 6,
An interlayer insulating film 7, a lower electrode 8 of a capacitor made of polysilicon, and a first oxide film (Si
An upper electrode 13 of a capacitor made of O ₂ ) 9, Si ₃ N ₄ film 10 and polysilicon is formed.

FIG. 4 shows a lower electrode 8 / first oxide film (SiO ₂ ) 9, an Si ₃ N ₄ film 10 / an upper electrode 13 in FIG.
Of the lower electrode 8, the first oxide film 9, and the Si ₃ N ₄ film 10 in the step of forming the lower electrode 8 / the first oxide film 9 and the Si ₃ N ₄ film 10 It is sectional drawing.

A first oxide film (Si) formed on the surface of lower electrode 8 made of polysilicon shown in FIG.
O ₂ ) 9 is a natural oxide film that has grown in pure water for cleaning or during drying, even if a hydrofluoric acid treatment is performed to remove it.

As shown in FIG. 4B, in order to increase the capacitance of the capacitive element, Si ₃ N having a higher dielectric constant than SiO ₂ is used.
_{4 A} film 10 is formed on the upper surface of the first oxide film (SiO ₂ ) 9
Formed by Method D.

[0007]

However, in the above method, in the step of forming the Si ₃ N ₄ film 10 by the low pressure CVD method, oxygen is involved during loading into a furnace or the like, and as shown in FIG. As described above, the first oxide film 9 increases the thickness shown in FIG. 4A and grows to a thickness of 1 to 2 nm. In this case, no matter how much the thickness of Si ₃ N ₄ is reduced, the proportion of SiO ₂ having a low dielectric constant increases, and the capacity cannot be increased.

Therefore, the present invention removes the first oxide film such as a natural oxide film which becomes a bottleneck in increasing the capacitance by reducing the thickness of the capacitor insulating film, and instead has a higher dielectric constant than the first oxide film. In addition, an object of the present invention is to provide a method for forming a capacitance element with improved reliability by forming an oxide film having a large forbidden band width to increase capacitance and reduce leakage current.

[0009]

An object of the present invention is to form a natural oxide film having a low dielectric constant on one electrode surface of a capacitor composed of one electrode / a capacitor insulating film / the other electrode.
The first method of forming a capacitive element in a semiconductor substrate having an oxide film occurs, the pieces small material film of oxide formation free energy than the material film for forming the one electrode that
Forming a first oxide film surface on the square of the electrode, the oxygen
Heat treatment is performed on the semiconductor substrate while supplying the first oxide film, thereby modifying the first oxide film having a low dielectric constant to form the first acid film.
Forming a second oxide film having a higher dielectric constant than the oxide film, and thereafter , forming a silicon nitride film on the surface of the second oxide film.
And a forming step .

[0010]

Further, according to the present invention, according to the present invention, a material film forming one electrode is made of polycrystalline silicon, and a material film having a lower free energy of oxide generation than aluminum is used as a material film forming one electrode. It is preferably solved by a method for forming a capacitor, which is characterized in that

[0012]

According to the present invention, as shown in FIG. 2A, in a capacitor in which a first oxide film 9 is formed on the surface of one electrode (lower electrode) 8 of the capacitor, FIG. As shown in FIG. 2B, after forming a material film 11 having a smaller free energy of oxide generation than the material film of one electrode 8 on the surface of the first oxide film 9, FIG. By performing the heat treatment as described above, the first oxide film 9 reacts with the material film 11 to form the second oxide film 12. Since the free energy of oxide formation of the material film 11 is smaller than that of the material film of the one electrode 8, oxygen of the first oxide film 9 which is an oxide of the material film of the one electrode 8 is combined with the material film 11. The second oxide film 12 can be formed. Thus, the first oxide film is modified to form the second oxide film 12 having a larger dielectric constant than the first oxide film and a wide band gap as an insulating film of the capacitor, and And the reliability can be improved.

Further, according to the present invention, by performing the heat treatment while supplying oxygen, the material film 11 is completely oxidized, and the surface of one electrode 8 is suitably covered only by the second oxide film 12. be able to.

Further, according to the present invention, the material film forming one electrode 8 is made of polycrystalline silicon, and the material film 11 having a smaller free energy of oxide generation than the material film forming one electrode 8 is made of aluminum. By doing so, an insulating film having a higher dielectric constant and a wider band gap can be suitably formed in the aluminum oxide 12 as the second oxide film than in the SiO ₂ as the first oxide film.

[0015]

FIG. 1 is a cross-sectional view of a stacked capacitor of a DRAM formed according to one embodiment of the present invention. According to FIG. 1, a field oxide film 2, an N ⁺ diffusion layer 3, a word line 4 made of polysilicon, a bit line 5 made of aluminum, an SiO ₂ film 6, an interlayer insulating film 7, A lower electrode 8 of a capacitor made of silicon, a second oxide film (aluminum oxide) 12 and an Si ₃ N ₄ film 10 as an insulating layer of the capacitor, and an upper electrode 13 of a capacitor made of polysilicon are formed, respectively.

An embodiment according to the present invention will be described below with reference to the drawings.

FIG. 2 shows an embodiment according to the present invention, and comprises a DRAM composed of a lower electrode 8 / second oxide film (aluminum oxide) 12, a Si ₃ N ₄ film 10 / an upper electrode 13 in FIG. The lower electrode 8 in the step of forming the second oxide film (aluminum oxide) 12 and the Si ₃ N ₄ film 10 which are the insulating films of the capacitor.
FIG. 2 is a sectional view of a second oxide film (aluminum oxide) 12 and a Si ₃ N ₄ film 10.

FIG. 2A shows a state in which a first oxide film (SiO ₂ ) 9 is formed on the surface of a lower electrode 8 made of polysilicon. This first oxide film 9 is
This is a natural oxide film formed after the surface cleaning treatment of the electrode 8. As shown in FIG. 2 (b), aluminum metal 11, which is a substance having a lower free energy of oxidation generation than silicon, is replaced with C.
The first oxide film (SiO ₂ ) 9 is formed on the surface of the first oxide film 9 by the VD method.
It is formed to a thickness of about 2 nm.

Next, when heat treatment is performed by adding oxygen, FIG.
As shown in (c), oxygen in the first oxide film (SiO ₂ ) 9 reacts with aluminum 11 to form aluminum oxide as the second oxide film 12, and unreacted aluminum also reacts with the supplied oxygen. It becomes aluminum oxide. Furthermore, the first oxide film silicon (SiO ₂₎ 9 is deposited on the lower electrode 8, the first oxide film (SiO ₂₎ 9 is modified.

Next, as shown in FIG.
By the method D, a Si ₃ N ₄ film 10 is formed on the surface of the second oxide film (aluminum oxide) 12.

In this embodiment, aluminum is used as a substance having a lower free energy of oxide formation than silicon. However, aluminum oxide has a relative dielectric constant of about 8 which is larger than 7 of Si ₃ N ₄ and increases the capacity. be able to.

Further, the forbidden band width is about 10 eV, which is larger than that of SiO ₂ , thereby preventing a leak current and contributing to an improvement in reliability.

Materials having a lower free energy of oxide formation than silicon include Ti, Ce, Mg, Ca, etc., which are applicable due to the dielectric constant and bandgap properties of these oxides. It can be applied to the electrode forming material described above due to the nature of the oxide.

The present invention is also applicable to a capacitor having a structure in which one electrode / insulating film / the other electrode is arranged side by side.

[0025]

As described above, according to the present invention,
Oxide is produced more than the material film that forms one electrode of the capacitor.
A material film with low free energy of formation consists of a natural oxide film
After forming on the surface of the first oxide film, do not supply oxygen.
By subjecting the semiconductor substrate to heat treatment,
The second oxide film is modified to have a higher dielectric constant than the first oxide film.
Oxide film is formed on the surface of the second oxide film.
A cone film is formed . With this configuration,
A first oxide film made of a natural oxide film having a low dielectric constant
It can be modified into a second oxide film having a high dielectric constant.
A silicon nitride film is laminated on a second second oxide film.
Manufacture capacitors with capacitor insulation film with good reproducibility
Can be Moreover, the high dielectric of the capacitor insulating film
Increases the storage capacity and increases the Na ^{+ of} the second oxide film.
Improve the reliability of the capacitive element by barrier effect, etc.
Can be.

[Brief description of the drawings]

FIG. 1 shows a DR formed according to one embodiment of the present invention.
It is sectional drawing of an AM stacked capacitor.

FIG. 2 shows an embodiment according to the present invention, wherein the DR shown in FIG.
It is sectional drawing in the insulating film formation process of AM stacked capacitor.

FIG. 3 is a cross-sectional view of a DRAM stacked capacitor according to a conventional method.

FIG. 4 is a cross-sectional view illustrating a step of forming an insulating film of the DRAM stacked capacitor shown in FIG. 3;

[Explanation of symbols]

Reference Signs List 1 P-type silicon substrate 2 Field oxide film 3 N ⁺ diffusion layer 4 Word line (polysilicon) 5 Bit line (aluminum) 6 SiO ₂ film 7 Interlayer insulating film 8 One electrode (lower electrode) 9 First oxide film ( SiO ₂ ) 10 Si ₃ N ₄ film 11 Material film (aluminum) 12 Second oxide film (aluminum oxide) 13 The other electrode (upper electrode)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ identification code FI H01L 27/04 (58) Investigated field (Int.Cl. ⁷ , DB name) H01L 27/108 H01L 21/316 H01L 21/318 H01L 21/822 H01L 21/8242 H01L 27/04

Claims (2)

(57) [Claims] A dielectric is formed on the surface of one electrode of a capacitor composed of one electrode / capacitor insulating film / the other electrode.
A semiconductor in which a first oxide film made of a natural oxide film having a low rate is formed
A method of forming a capacitive element in the body substrate, forming a low material film of oxide formation free energy than the material film for forming the one electrode on the first surface of the oxide film on the one electrode Heat-treating the semiconductor substrate while supplying oxygen to modify the first oxide film having a low dielectric constant to form the first oxide film .
Forming a second oxide film having a dielectric constant higher than that of the second oxide film, and thereafter forming a silicon nitride film on the surface of the second oxide film. Element formation method. Wherein the material film for forming the one electrode and the polycrystalline silicon, the method of forming the capacitor element of claim 1, wherein the small material film with the oxide formation free energy, characterized in that the aluminum metal .