JPH08153717A - Element isolation insulation film and its formation - Google Patents

Abstract

PURPOSE: To prevent a circuit from lowering in operation speed by making the dielectric constant of element isolation insulation film of a semiconductor device low in order to reduce its parasitic capacity. CONSTITUTION: An element isolation insulation film 1 is formed of an oxide film, which includes a fluorine atom of at least 5 atomic % and less 20 atomic %. When an oxide film is subjected to be formed on a silicon substrate 11 by a selective oxidation method using a silicon nitride film (not shown in the Fig.) as an oxidation preventive mask, a fluorine gas or a gas containing fluorine is introduced as a selective oxidation atmosphere for forming an oxide film, to perform selective oxidation, and the oxide film is formed on the substrate 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element isolation insulating film of a semiconductor device and a method of forming the same, and more particularly to an element isolation insulating film having a low dielectric constant used for a semiconductor integrated circuit of a memory element which has been further miniaturized. And a method for forming the same.

[0002]

2. Description of the Related Art Most of element isolation insulating films of semiconductor devices are
It is formed by the LOCOS oxidation method. This LOCO
In the S oxidation method, a pad silicon oxide film is formed on the surface of a silicon substrate, and then the silicon nitride film is patterned to form an oxidation prevention mask. After that, a LOCOS oxide film is formed by selectively oxidizing the surface of the silicon substrate.

In the LOCOS oxidation method, the oxide film extends in the substrate surface direction at the edge portion of the silicon nitride film, and a so-called bird's beak is generated. This bird's beak is one of the factors that hinder the miniaturization of semiconductor devices. As shown in FIG. 6, a part of the surface layer of the silicon substrate 101 is oxidized by the LOCOS method. Especially about 0.35μ
Since the bird's beaks 112B and 113B of the LOCOS oxide films 112 and 113, which grow from the lower sides of both ends of the silicon nitride film 111a (111), overlap the narrow active region 102 of m or less, the film thickness d at that portion is reduced.
1 becomes thicker than the film thickness d2 of the pad silicon oxide film 114 already formed.

Therefore, after the silicon nitride film 111 is removed by etching, in order to form the active region 102 on the silicon substrate 101 below the portion where the bird's beaks 112B and 113B extend, the bird's beak is exposed until the surface of the silicon substrate 101 is exposed. 112B and 113B were removed by etching.

[0005]

However, as shown in FIG. 7, the bird's beaks 112B and 113B (portions indicated by the two-dot chain line) extending in the region where the active region 102 is formed do not extend in thickness. It is thicker than the film thickness of the pad silicon oxide film 114 (portion indicated by a chain line). Therefore, when the bird's beaks 112B and 113B are removed by etching together with the pad silicon oxide film 114, the upper layers (portions indicated by broken lines) of the LOCOS oxide films 112 and 113 are also bird's beaks 112B and 113B.
A thickness approximately equal to the thickness of is removed. As a result, the film thickness D2 of the LOCOS oxide films 112 and 113 is the design value D.
It becomes thinner than 1. Although not shown, there is also a method of reducing the film thickness itself of LOCOS oxidation in order to form a narrow active region. However, the thickness of the LOCOS oxide film formed by this method is thin. As the thickness of the LOCOS oxide film is reduced, the parasitic capacitance increases. Therefore, the delay time becomes long and the operation speed of the circuit is lowered.

An object of the present invention is to provide an element isolation insulating film excellent in miniaturization and low parasitic capacitance and a method for forming the same.

[0007]

SUMMARY OF THE INVENTION The present invention is an element isolation insulating film and a method of forming the same for achieving the above object. That is, the element isolation insulating film is made of an oxide film, and the oxide film contains 5 atomic% or more and 20 atomic% or less of fluorine atoms.

In the first method for forming the oxide film, when forming an oxide film on a silicon substrate by a selective oxidation method using a silicon nitride film as an oxidation prevention mask, a fluorine gas or a selective oxidation atmosphere for forming the oxide film is used. An oxide film is formed on the silicon substrate by introducing a gas containing fluorine and performing selective oxidation.

In the second method, after forming an oxide film on a silicon substrate by a selective oxidation method using a silicon nitride film as an anti-oxidation mask, fluorine ions or ions containing fluorine are selectively introduced into the oxide film. .

In the third method, when an oxide film is formed on a silicon substrate by a selective oxidation method using a silicon nitride film as an oxidation prevention mask, after the oxidation prevention mask is formed and before the selective oxidation is performed, Fluorine ions or ions containing fluorine are selectively introduced into a region of the silicon substrate where the oxide film is to be formed. After that, selective oxidation is performed to form an oxide film in a region of the silicon substrate where the oxide film is to be formed.

[0011]

[Function] In the above element isolation insulating film, 5 atomic is contained in the oxide film.
% Or more and 20 atomic% or less of fluorine atoms, the dielectric constant (4.
It has a lower dielectric constant than 2). Its dielectric constant is about 3.0 to 3.5, though it depends on the content of fluorine. An oxide film containing less than 5 atomic% of fluorine does not have a sufficiently low dielectric constant. On the other hand, when the content of fluorine exceeds 20 atomic%, the fluorine in the film becomes close to the saturated state, and the fluorine reacts with hydrogen in the atmosphere to generate hydrogen fluoride. In such a case, the generated hydrogen fluoride corrodes the aluminum wiring formed on the element isolation insulating film. Or it will be corroded and lead to disconnection. Therefore, the content of fluorine atoms is set within the above range.

As a method of forming the element isolation insulating film, in the first method, when the oxide film is formed on the silicon substrate by the selective oxidation method using the silicon nitride film as an oxidation prevention mask, a fluorine gas is used in a selective oxidizing atmosphere. Alternatively, since a gas containing fluorine is introduced to perform selective oxidation, fluorine atoms are contained in the oxide film formed on the silicon substrate.

In the second method, an oxide film is formed on a silicon substrate by a selective oxidation method using a silicon nitride film as an oxidation prevention mask, and then fluorine ions or ions containing fluorine are selectively introduced into the oxide film. Therefore, the oxide film contains fluorine atoms. In the above-mentioned ion implantation, since the oxidation mask serves as an ion implantation mask, fluorine is not introduced into the silicon substrate portion which is the active region covered with the oxidation mask.

In the third method, when an oxide film is formed on a silicon substrate by a selective oxidation method using a silicon nitride film as an oxidation prevention mask, after the oxidation prevention mask is formed and before the selective oxidation is performed, Fluorine ions or ions containing fluorine are selectively introduced into a region of the silicon substrate where the oxide film is to be formed.
After that, selective oxidation is performed, so that the silicon substrate is oxidized in a state in which fluorine atoms are contained and an oxide film containing fluorine atoms is formed. In the above-mentioned ion implantation, since the oxidation mask serves as an ion implantation mask, fluorine is not introduced into the silicon substrate portion which is the active region covered with the oxidation mask.

In each of the above methods, since the oxide film contains fluorine, the dielectric constant of the oxide film becomes low. Therefore, even if the oxide film is thinned, the insulating property required for element isolation is secured. Therefore, when removing the oxide film in the portion where the bird's beaks formed in the fine active region have grown, the element isolation insulating film is removed. Even if the surface layer of the oxide film to be removed is removed, the oxide film has a low dielectric constant, so that the insulating property as the element isolation insulating film is ensured.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the schematic configuration diagram of FIG. As shown in the figure, an element isolation insulating film 1 formed by a selective oxidation method using an oxidation prevention mask is provided on the surface of a silicon substrate 11. The element isolation insulating film 1 is made of a silicon oxide film (oxide film) containing 5 atomic% or more and 20 atomic% or less of fluorine atoms. The selective oxidation method is performed by, for example, a LOCOS oxidation method, an improved LOCOS oxidation method, or the like.

Since the element isolation insulating film 1 contains 5 atomic% or more and 20 atomic% or less of fluorine atoms in the silicon oxide film, the dielectric constant (4.2) of the silicon oxide film containing no fluorine atoms is used. Also has a low dielectric constant. Its dielectric constant varies depending on the content of fluorine, but is 3.0 to 3.
It will be about 5. For example, the element isolation insulating film 1 having a dielectric constant of 3.0 has a film thickness approximately 30% thinner than that of the conventional element isolation insulating film made of silicon oxide, and has the same insulating property as that of the conventional element isolation insulating film. Have. Therefore, it is 3
No parasitic capacitance is generated even if the film thickness is about 0%. In addition,
A silicon oxide film containing less than 5 atomic% of fluorine does not have a sufficiently low dielectric constant. On the other hand, when the content of fluorine exceeds 20 atomic%, the fluorine in the element isolation insulating film 1 becomes close to a saturated state, and the fluorine reacts with hydrogen in the atmosphere to generate hydrogen fluoride. In such a case, the aluminum fluoride wiring (not shown) formed on the element isolation insulating film is corroded by the generated hydrogen fluoride. Alternatively, the aluminum-based wiring is corroded resulting in disconnection. Therefore, the content of fluorine atoms is set within the above range.

Next, an embodiment of the first invention relating to the method for forming the element isolation insulating film will be described with reference to the process chart of FIG.

As shown in FIG. 2A, the pad silicon oxide film 12 is formed on the surface of the silicon substrate 11 to have a film thickness of, for example, 10 nm by the thermal oxidation method. After that, the silicon nitride (Si ₃ N ₄ ) film 1 is formed by the low pressure CVD method.
3 is formed to have a film thickness of 100 nm, for example. Further, after applying a resist film, patterning is performed by lithography to form a resist mask 14.

Then, as shown in FIG. 2B, the portion indicated by the chain double-dashed line is removed from the silicon nitride film 13 by dry etching, and the remaining silicon nitride film (13) is used to form an anti-oxidation mask 15. . At this time, the pad silicon oxide film 12 may be left as it is. The figure shows the case where the pad silicon oxide film 12 is etched. In the dry etching, for example, a single wafer type magnetron reactive ion etching apparatus is used. The etching atmosphere is composed of octafluorocyclobutane (C ₄ F ₈ ) having a flow rate of 5 sccm, oxygen (O ₂ ) having a flow rate of 4 sccm, and argon (Ar) having a flow rate of 100 sccm, and the pressure of the etching atmosphere is 2.7 Pa. , RF
Set the power to 1kW. After that, the resist mask 14 is removed by oxygen ashing or wet processing.

Next, as shown in FIG. 2C, a surface of the silicon substrate 11 except for the region covered with the anti-oxidation film 15 is selected by introducing a fluorine gas or a gas containing fluorine into the selective oxidizing atmosphere. Oxidation and silicon oxide film 16
To form. The selective oxidizing atmosphere has a flow rate of 10 for example.
It is composed of oxygen (O ₂ ) of SLM, hydrogen (H ₂ ) with a flow rate of 10 SLM, and fluorine (F) with a flow rate of 5 SLM.
Set the oxidation temperature to 950 ° C. The selective oxidizing atmosphere may be, for example, a mixed gas atmosphere of oxygen (O ₂ ) and fluorine (F) or a mixed gas atmosphere of water vapor and fluorine (F).

After that, the anti-oxidation mask 15 and the pad silicon oxide film 12 are removed. The antioxidant mask 15 is
Since it is made of silicon nitride, it is removed by wet etching with hot phosphoric acid, for example. The pad silicon oxide film 12 is removed by light etching. The light etching is performed using hydrofluoric acid: H ₂ O = 1:
It is performed by immersing it in a hydrofluoric acid solution of about 100 for 1 to 2 minutes. The light etching also removes the upper layer of the silicon oxide film 16. In this way, as shown in (4) of FIG. 2, the element isolation insulating film 1 made of the silicon oxide film (16) is formed on the surface side of the silicon substrate 11.

In the embodiment of the first invention, the surface of the silicon substrate 11 is oxidized in a mixed atmosphere of oxygen, hydrogen and fluorine, so that the element isolation insulating film 1 produced is a silicon oxide film containing fluorine atoms. Become 16. Therefore, the dielectric constant of the element isolation insulating film 1 is reduced to about 3.0 depending on the amount of fluorine contained in silicon oxide. In addition,
The amount of fluorine atoms contained in the silicon oxide film 16 is adjusted by controlling the flow rate of fluorine introduced into the selective oxidizing atmosphere.

Next, an embodiment of the second invention relating to the method of forming the element isolation insulating film will be described with reference to the process chart of FIG. In the figure, the same components as those described with reference to FIG.

As shown in (1) of FIG. 3, the pad silicon oxide film 12 (for example, a film thickness of 10 nm is formed on the surface of the silicon substrate 11 in the same manner as described in (1) and (2) of FIG. 2 above. ) Is formed, and a silicon nitride film 13 (having a film thickness of 100 nm, for example) is formed thereon. After applying a resist film, a resist mask (not shown) is formed by lithography. After that, a portion indicated by a chain double-dashed line is removed from the silicon nitride film 13 by dry etching, and the remaining silicon nitride film (13) is used as the anti-oxidation mask 1.
5 is formed. At this time, the pad silicon oxide film 12
The portion (shown by the one-dot chain line) is also etched. Then, the resist mask is removed by oxygen ashing or wet treatment.

Then, as shown in FIG. 3B, the silicon substrate 11 excluding the region covered with the anti-oxidation film 15 in a selective oxidizing atmosphere consisting of oxygen and hydrogen, for example.
The surface of is selectively oxidized to form a silicon oxide film 16 containing fluorine atoms. The selective oxidizing atmosphere is composed of, for example, oxygen (O ₂ ) having a flow rate of 10 SLM and hydrogen (H ₂ ) having a flow rate of 10 SLM, and the oxidation temperature is set to 950 ° C.

Next, as shown in (3) of FIG. 3, fluorine (F ⁺ ) ions are introduced into the silicon oxide film 16 by an ion implantation method using the oxidation prevention mask 15 made of silicon nitride as an ion implantation mask. . The ion implantation conditions are, for example, an implantation energy of 30 keV,
The dose amount is set to 10 P (peta) cm ⁻² .

After that, the anti-oxidation mask 15 and the pad silicon oxide film 12 are removed. The anti-oxidation mask 15 and the pad silicon oxide film 12 are removed by the same method as described in the first embodiment. Thus, as shown in (4) of FIG. 3, on the upper layer of the silicon substrate 11,
The element isolation insulating film 1 made of a silicon oxide film (16) containing fluorine atoms is formed.

In the embodiment of the second invention, since fluorine ions are introduced into the silicon oxide film 16 by the ion implantation method, the element isolation insulating film 1 contains fluorine atoms. Therefore, the dielectric constant of the element isolation insulating film 1 is 3.0.
It is reduced to the extent. Further, in the above ion implantation, since the active region of the silicon substrate 11 is covered with the oxidation preventing mask 15 made of silicon nitride, the oxidation preventing mask 15 serves as an ion implantation mask. Therefore, fluorine ions are not introduced into the active region. In addition,
The amount of fluorine atoms contained in the silicon oxide film 16 is adjusted by controlling the dose amount of fluorine ion-implanted.

Next, an embodiment of the third invention relating to the method of forming the element isolation insulating film will be described with reference to the process chart of FIG. In the figure, the same components as those described with reference to FIG.

As shown in FIG. 4A, the pad silicon oxide film 12 (for example, with a film thickness of 10 μm) is formed on the surface of the silicon substrate 11 in the same manner as described in (1) and (2) of FIG. 10 nm) and silicon nitride (Si ₃
N ₄ ) film 13 (for example, a film thickness of 100 nm) is formed.
After applying a resist film, patterning is performed by lithography to form a resist mask 14. Then, a silicon nitride film 1 is formed by dry etching.
A portion indicated by a chain double-dashed line in 3 is removed, and an oxidation preventing mask 15 is formed by the remaining silicon nitride film (13). At this time, the pad silicon oxide film 12 may be left as it is. The figure shows the case where the pad silicon oxide film 12 is etched.

Then, as shown in FIG. 4B, with the resist mask 14 left, fluorine (F ⁺ ) ions are added to the silicon substrate by an ion implantation method using the resist film and the oxidation prevention mask 15 as ion implantation masks. The silicon oxide film 11 is introduced into the region 17 where the silicon oxide film is to be formed. As the ion implantation conditions, the implantation energy is set to 40 keV and the dose amount is set to 10 P (peta) cm ⁻² . As a result, fluorine ions are introduced only into the region 17 where the silicon oxide film is to be formed, and fluorine ions are not introduced into the active region covered with the resist mask 14.

After that, the resist mask 14 is removed by oxygen ashing or wet processing. Then in FIG.
(3), the surface of the silicon substrate 11 excluding the region covered with the anti-oxidation film 15 is selectively oxidized in a selective oxidizing atmosphere of oxygen and hydrogen,
A silicon oxide film 16 containing fluorine atoms is formed. The selective oxidizing atmosphere is, for example, oxygen (O 2) having a flow rate of 10 SLM.
₂₎ the flow is constituted out with hydrogen 10 SLM (H _2), it sets the oxidation temperature to 950 ° C..

After that, the oxidation prevention mask 15 and the pad silicon oxide film 12 are removed. The oxidation prevention mask 15 and the pad silicon oxide film 12 are removed by the same method as described in the first embodiment. As a result, as shown in FIG. 4D, the element isolation insulating film 1 made of the silicon oxide film 16 is formed on the silicon substrate 11.

In the third embodiment of the present invention, since fluorine is introduced into the region where the silicon oxide film is to be formed by the ion implantation method, when the region is selectively oxidized, the silicon oxide film 16 containing fluorine is formed. Are produced, and this silicon oxide film becomes the element isolation insulating film 1. Therefore, the dielectric constant of the element isolation insulating film 1 is reduced to about 3.0. Further, in the above ion implantation, since the active region of the silicon substrate 11 is covered with the oxidation prevention mask 15 made of at least silicon nitride, the oxidation prevention mask 15 serves as an ion implantation mask. Further, when ion implantation is performed with the resist mask 14 left, this resist mask 14 serves as an ion implantation mask. Therefore, fluorine ions are not introduced into the active region covered with the oxidation prevention mask 15. The amount of fluorine atoms contained in the silicon oxide film 16 is adjusted by controlling the dose amount of fluorine ion-implanted into the silicon substrate 11.

As described above, in each of the above-described first to third inventions, the silicon oxide film 16 serving as the element isolation insulating film 1 is formed in a state containing fluorine atoms. Therefore, the dielectric constant of the element isolation insulating film 1 is reduced to about 3.0. The conventional silicon oxide film made of silicon dioxide had a dielectric constant of about 4.2. Therefore, the element isolation insulating film 1 having a dielectric constant reduced to about 3.0 as in this embodiment is equivalent to the conventional LOCOS oxide film thickness increased by about 30%.

As described above, since the dielectric constant of the element isolation insulating film 1 becomes low, the insulation required for element isolation can be secured even if the element isolation insulating film 1 is thinned. Therefore, as shown in FIG. 5, bird's beaks 31B and 32B portions grown from the element isolation insulating films 1 and 2 formed on both sides of the fine active region 21 (for example, width 0.35 μm) formed on the silicon substrate 11 ( When the part (shown by the chain double-dashed line) is removed, each surface layer of the element isolation insulating films 1 and 2 (the part shown by the single-dot chain line) is also removed. However, since the element isolation insulating films 1 and 2 have a low dielectric constant of, for example, about 3.0, the parasitic capacitance does not become larger than that of the element isolation insulating film made of only silicon oxide without removing the surface layer. Therefore, the operating speed of the device is not significantly affected.

[0038]

As described above, according to the element isolation insulating film of the present invention, since the dielectric constant of the element isolation insulating film is low, the parasitic capacitance is large even if the element isolation insulating film is thin. I won't. Therefore, the operating speed of the element does not decrease. According to the invention of claim 2, the oxide film can be formed in a state containing fluorine during the selective oxidation. According to the invention of claim 3, after forming the oxide film, fluorine can be introduced into the oxide film. Further claim 4
According to the invention, the oxide film can be formed in a state containing fluorine. Therefore, whichever method is used,
Since the oxide film contains fluorine atoms, it is possible to form an element isolation insulating film made of an oxide film having a low dielectric constant.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an element isolation insulating film of the present invention.

FIG. 2 is a process drawing of an embodiment of the first invention.

FIG. 3 is a process drawing of an embodiment of the second invention.

FIG. 4 is a forming process diagram of the embodiment of the third invention.

FIG. 5 is an explanatory diagram of an operation of the present invention.

FIG. 6 is an explanatory diagram of a conventional forming method.

FIG. 7 is an explanatory diagram of a problem.

[Explanation of symbols]

 1 Element Isolation Insulating Film 11 Silicon Substrate 13 Silicon Nitride Film 15 Antioxidant Mask 16 Silicon Oxide Film 17 Oxide Film Formation Area

Claims (4)

[Claims] 1. An element isolation insulating film made of an oxide film used for element isolation of a semiconductor device, wherein the oxide film contains fluorine atoms of 5 atomic% or more and 20 atomic% or less. 2. A method for forming an element isolation insulating film for forming an oxide film on a silicon substrate by a selective oxidation method using a silicon nitride film as an oxidation prevention mask, wherein fluorine gas or fluorine is used in a selective oxidation atmosphere for forming the oxide film. A method for forming an element isolation insulating film, comprising forming an oxide film on the silicon substrate by introducing a gas containing the material and selectively oxidizing the silicon substrate. 3. A method of forming an element isolation insulating film, wherein an oxide film is formed on a silicon substrate by a selective oxidation method using a silicon nitride film as an oxidation prevention mask, wherein the silicon substrate is selectively oxidized to be oxidized on the silicon substrate. After forming the film, a method for forming an element isolation insulating film, which comprises selectively introducing fluorine ions or ions containing fluorine into the oxide film. 4. A method for forming an element isolation insulating film, wherein an oxide film is formed on a silicon substrate by a selective oxidation method using a silicon nitride film as an oxidation prevention mask, wherein the selective oxidation is performed after the oxidation prevention mask is formed. Before performing, fluorine ions or ions containing fluorine are selectively introduced into a region of the silicon substrate where the oxide film is to be formed,
After that, selective oxidation is performed to form an oxide film in a region where the oxide film is to be formed.