JPH09237784A - Element isolation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an element isolation method in which the oxidation time can be shortened by a method wherein, after the pattern of an Si3 N4 film has been formed, fluorine ions are implanted from the upper part of a pad oxide film on the surface of an Si substrate by using an ion implantation method, a pyrooxidation operation is performed, a pyrooxidation speed on the surface of the Si substrate is increased and an oxide film layer is formed. SOLUTION: A thin SiO2 pad oxide film 2 is formed on an Si film 1 by a thermal oxidation operation. After that, an Si3 N4 oxidation suppression film 3 is deposited on the pad oxide film 2 by a plasma CVD method. Then, a resist 4 in a prescribed shape is formed on the oxidation suppression film 3, the Si film is then dry-etched in the vertical direction, the Si3 N4 oxidation suppression film 3 is patterned, an oxidation suppression film 5 in a prescribed shape is left on the pad oxide film 2, and the resist is stripped. Then, fluorine 7 is ion- implanted into the surface of the Si film 1 from the upper part of the pad oxide film 2, the Si film containing the fluorine is pyrooxidized so as to be changed into a pyrooxide film 6, the Si3 N4 oxidation suppression film is etched in hot phosphoric acid, and an active-layer region is formed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to silicon (Si).
The present invention relates to an element isolation method for forming a plurality of fine elements on the same wafer.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor memory device, high integration is being advanced along with the miniaturization of processing dimensions. In order to integrate a large number of semiconductor elements on the same substrate, it is necessary to electrically insulate the individual semiconductor elements.

In the conventional element isolation method, semiconductor elements are isolated by the steps shown in FIG. 5, for example. FIG. 5 is a process sectional view of a conventional element isolation method by LOCOS. In this method, the surface of the Si film 1 of the Si substrate is previously thermally oxidized to form a thin pad oxide film 2 (FIG. 5a), and then Si ₃ N _{4 is formed} on the pad oxide film as a thermal oxidation inhibiting film for the Si film. After depositing an oxidation inhibiting film 3 made of silicon (FIG. 5b) and applying a resist on the oxidation inhibiting film, a resist having a predetermined shape is exposed and developed to leave the oxidation inhibiting film made of Si ₃ N ₄ only in the element formation region. 4 is formed (see FIG.
c), dry etching (eg, Reactive Ion Etchi) on the oxidation prevention film in the region where there is no resist.
etc.) to form an oxidation inhibiting film 5 having a predetermined shape on the pad oxide film 2 and then the resist is removed (FIG. 5d).

Further, the Si film on the surface of the region where the Si ₃ N ₄ film is removed by etching by the pyrooxidation is changed to a wavelength of 54
After converting to a thick pyro-oxide film 6 having a refractive index of 6452 to 1.462 at 6 nm (FIG. 5e), the oxidation inhibiting film made of Si ₃ N ₄ is removed by using hot phosphoric acid or the like to form an element. A region is formed (Fig. 5f). By the above manufacturing process, in FIG. 5, an element formation region is formed in the central Si film region, and an element isolation region is formed in the relatively thin Si film regions on the left and right of the element formation region.

[0005]

In the formation of such an element isolation region, a long thermal oxidation is required for pyrooxidation for a thick pyrooxide film, so that the processing time is shortened and L
It is necessary to shorten the SI manufacturing process. The present invention
The present invention has been made in view of the above point, and particularly aims to shorten the heat treatment time in the element isolation step.

[0006]

According to the element isolation method of the present invention, in the element isolation method by LOCOS of Si LSI, a step of forming an oxidation inhibiting film on a Si film and patterning the oxidation inhibiting film into a predetermined shape. After that, the method is characterized by including a step of ion-implanting fluorine into the Si film in a region other than the oxidation suppressing film having a predetermined shape, and a step of pyrooxidizing the Si film containing the injected fluorine.

Alternatively, the element isolation method of the present invention uses Si
In the element isolation method by LOCOS of the LSI manufactured by S,
A step of forming a pad oxide film and an oxidation inhibiting film in this order on the i film, and after patterning the oxidation inhibiting film formed on the pad oxide film into a predetermined shape, fluorine is applied to a region other than the oxidation inhibiting film having a predetermined shape. And a step of pyrolyzing the implanted Si film containing fluorine.

That is, according to the present invention, after the patterning of the Si ₃ N ₄ film, fluorine (F) ions are implanted from above the pad oxide film on the surface of the Si substrate by the ion implantation method, and then pyrooxidation is performed to perform the Si substrate oxidation. By increasing the rate of pyrooxidation on the surface, an oxide film layer is formed to shorten the oxidation time. As a mechanism, first, the F ions implanted on the surface of the Si substrate break the Si-Si bond, and Si on the surface of the Si substrate.
It is considered that the dangling bond and the Si—F bond are formed.

Next, this Si dangling bond and S
The i-F bond can be easily oxidized by thermal oxidation into Si-
It seems to change to O bond.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) A first embodiment of the present invention will be described with reference to FIG. FIG. 1 shows the LOCOS of the present invention.
6A to 6C are process cross-sectional views of the element isolation method by. (1) Formation of Oxidation Suppression Film A temperature of 110 is formed on the Si film 1 that will eventually become an LSI made of Si.
Pad oxide film 2 made of thin SiO ₂ by thermal oxidation at 0 ° C
After the formation (FIG. 1a), the oxidation inhibiting film 3 made of Si ₃ N ₄ is deposited on the pad oxide film by plasma CVD at a temperature of 500 ° C. for the LOCOS step of locally oxidizing (FIG. 1A).
b).

At this time, the thickness of the pad oxide film is 500
Å The thickness of the oxidation inhibiting film is 2000Å. (2) Patterning of oxidation inhibiting layer In order to leave the oxidation inhibiting film made of Si ₃ N ₄ only on the element formation region in the center of the figure, a predetermined shape is formed on the oxidation inhibiting film 3 by applying resist, exposing and developing. A resist 4 is formed (FIG. 1c).

Further, dry etching such as RIE is performed in a direction perpendicular to the Si film 1, and the oxidation inhibiting layer made of Si ₃ N ₄ is patterned into a predetermined shape in accordance with the shape of the resist to form an oxidation inhibiting film having a predetermined shape. 5 is left on the pad oxide film 2 and the resist is peeled off (FIG. 1d). (3) F ion implantation Fluorine 7 is ion-implanted from the pad oxide film 2 onto the surface of the Si film 1 (FIG. 1e).

The implantation conditions are ion species F ⁺ and accelerating voltage 1
It is 00 keV and the dose amount is 1 × 10 ¹⁶ atmscm ⁻² . At this time, although the ion implantation into the Si film 1 is alienated at the coating portion of the oxidation inhibiting film 5 made of Si ₃ N ₄ having a thickness of 2000 Å, the surface of the pad oxide made of SiO ₂ having a thickness of 500 Å is oxidized. In the non-coated portion of the oxidation inhibiting film where the film 2 is exposed,
F ions are implanted in the Si film 1.

Here, the implantation depth of F ions into the Si film 1 which is located on the left and right in FIG. 1 and later becomes the left and right element isolation regions is set to about 2000 Å. In this case, LOCO
The implantation depth of F ions into the Si ₃ N ₄ film during S formation is known in the literature, for example, James F. Gibbons,
William S. Johnson, Steven
W. "Projected" by Mylor et al.
RangeStatistics2nd Editi
Referring to "on" HALSTEAD PRESS (1975), the implantation depth of F ions into the Si substrate under the same conditions is about 1000Å and about 1/2.

From this, in the present embodiment, Si ₃ N _{4 is used.}
After removing the resist after dry etching of the film, F
Ion implantation was performed. (4) Pyrooxidation In a heat treatment furnace, the injected Si film containing fluorine is pyrooxidized to obtain a refractive index of 1.456 to 456 nm.
An element isolation layer is formed using the pyro oxide film 6 of 1.460 (FIG. 1f).

The refractive index values of 1.456 to 1.460 of the pyro oxide film produced by the element isolation method of the present invention are the same as those of the conventional pyro oxide film containing no fluorine as described above. It is equivalent to 1.462. The formation conditions are a temperature of 1000 ° C. and a flow rate of H ₂ : 3SLM and O ₂ : 3SLM (where STM is the number of liters of gas in a standard state per minute).

Pyrooxidation was performed for 130 minutes, and the device isolation formation conditions were set so that the oxide film thickness in the device isolation region was 6000 Å. When the Si film is pyrooxidized, the pyrooxidized film becomes 2 to 4 times or more as large as the oxidized Si film. Therefore, the implantation depth of F ions into the Si film may be smaller than the thickness of the pyro oxide film formed.

It should be noted that in this embodiment,
That is, the pyrooxidation rate is 70% higher than that of the conventional one. (5) Active layer formation After the element isolation regions are formed on the left and right sides, the oxidation inhibiting film made of Si ₃ N ₄ formed on the surface of the central active region is etched in hot phosphoric acid at 140 ° C. to form the active layer region ( Figure 1g).

As a result, according to the element isolation method of this embodiment, the pyro-oxide film is formed in a short time based on the ion-implanted fluorine. (Second Embodiment) In the above embodiment, the thickness of the oxidation inhibiting film is changed according to the ion implantation depth into the left and right Si films to be the element isolation regions. An element isolation method will be described in which a resist is used as a mask in addition to an oxidation prevention film at the time of ion implantation into silicon.

2A to 2C are sectional views of steps of another LOCOS element isolation method of the present invention. (1) Formation of Oxidation Suppression Film A temperature of 110 is formed on the Si film 1 that will eventually become an LSI made of Si.
After the pad oxide film 2 made of SiO ₂ having a thickness of 500 Å is formed by thermal oxidation at 0 ° C. (FIG. 2a), LO is locally oxidized.
For the COS process, an oxidation inhibiting film 3 made of Si ₃ N ₄ is deposited on the pad oxide film having a thickness of 1000 Å by plasma CVD at a temperature of 500 ° C (Fig. 2b).

Since the resist is used as the fluorine injection blocking film, the film thickness of the oxidation inhibiting film is as thin as 1000Å. (2) Patterning of oxidation inhibiting layer In order to leave the oxidation inhibiting film made of Si ₃ N ₄ only on the element formation region in the center of the figure, a predetermined shape is formed on the oxidation inhibiting film 3 by applying resist, exposing and developing. A resist 4 is formed (FIG. 2c).

Further, dry etching such as RIE is performed in a direction perpendicular to the Si film 1, and the oxidation inhibiting layer made of Si ₃ N ₄ is patterned into a predetermined shape in accordance with the shape of the resist to form an oxidation inhibiting film having a predetermined shape. 5 is left on the pad oxide film 2 (FIG. 2d). At this time, the resist 4 having a thickness of 6000Å remains on the oxidation inhibiting film 5 having a predetermined shape. (3) F ion implantation Fluorine 7 is ion-implanted from the pad oxide film 2 onto the surface of the Si film 1 (FIG. 2e).

The implantation conditions are ion species F ⁺ and accelerating voltage 1
It is 00 keV and the dose amount is 1 × 10 ¹⁶ atmscm ⁻² . At this time, a resist 4 having a thickness of 6000Å and a thickness of 10
Although the ion implantation into the Si film 1 is alienated in the coating portion of the oxidation inhibiting film 5 made of Si ₃ N _{4 of} 00 Å, the pad oxide film 2 made of SiO ₂ having a thickness of 500 Å is exposed on the surface. In the non-covered portion of the oxidation inhibiting film 5 having a predetermined shape, F ions are implanted into the Si film 1.

Here, the implantation depth of F ions into the Si film 1 which is located on the left and right in FIG. 1 and later becomes the left and right element isolation regions is set to about 2000 Å. In this case, Si ₃ N ₄
The F ions in the film are blocked by the resist and are not injected. After the fluorine ion implantation, the resist on the oxidation inhibiting film was peeled off.

This is because when the process of setting the film thickness of the Si ₃ N ₄ film to less than half the implantation depth of the F ions to be implanted, the F ions are removed before the resist is removed after the dry etching of the Si ₃ N ₄ film. This is because it is necessary to perform implantation so that F ions are not implanted into the element formation region. In the case of the present embodiment, even if the oxidation prevention film is thin, no adverse effect is exerted on the element formation region. Particularly, if the thickness is increased, a Si ₃ N ₄ film that is easily cracked can be formed under various ion implantation conditions. Will be available as. (4) Pyrooxidation In the heat treatment furnace, the injected Si film containing fluorine is pyrooxidized to form the pyrooxide film 6 to form the element isolation layer (FIG. 2f).

The formation conditions are a temperature of 1000 ° C. and a flow rate H ₂ :
3SLM, O ₂ : 3SLM (where STM is the number of liters per minute in the standard state of gas). 13
Pyro-oxidation is performed for 0 minutes and the oxide film thickness in the element isolation region is 60
The element isolation formation conditions were set so that the value was 00Å.
It should be noted that in the present embodiment, the pyrooxidation rate is 70% higher than that of the conventional one. (5) Active layer formation After the element isolation regions are formed on the left and right sides, the oxidation inhibiting film made of Si ₃ N ₄ formed on the surface of the central active region is etched in hot phosphoric acid at 140 ° C. to form the active layer region ( Figure 2g).

As a result, according to the element isolation method of this embodiment, since the oxidation inhibiting film 5 having a predetermined shape is thin, not only the oxidation inhibiting film 5 having a predetermined shape can be formed in a shorter time than in the first embodiment, but also fluorine is not formed. The Pyro oxide film is formed in a short time from the Si film containing Si. Although the above embodiment has described the manufacturing process of the pyro oxide film under a constant condition, various dose amounts and oxidation temperatures will be shown below as parameters as to how much the oxidation rate increases as the amount of fluorine increases. .

FIG. 3 shows the dependence of the oxidation rate on the oxidation temperature when the pyrooxide film is formed by changing the oxidation temperature after the F ion implantation to a depth of 2000 liters. The formation conditions are a temperature of 1000 ° C., a flow rate of H ₂ : 5 SLM, and a flow rate of O ₂ : 5 SLM (where STM is the number of liters of gas in a standard state per minute). The implantation conditions are ion species F ⁺ , accelerating voltage 100 keV, dose amount 1 × 10 ¹⁵ to 1 × 10 ¹⁶ a.
It is tmscm ^-2 .

In FIG. 3, the black circle indicates the oxidation rate without conventional ion implantation, and the white circle indicates the fluorine dose of the present invention of 1 × 10.
Oxidation rate at ¹⁵ atmscm ⁻² , ◆ is the fluorine dose amount of the present invention of 5 × 10 ¹⁵ atmscm ⁻² , and ◇ is the fluorine dose amount of the present invention of 1 × 10 ¹⁶ at
The oxidation rates at mscm ⁻² are shown.

The oxidation rate is generally higher than that in the case where ion implantation is not performed. Further, the oxidation rate has a correlation with the amount of fluorine ions implanted at the time of ion implantation, and in particular, the oxidation rate greatly changes at 950 ° C. or higher. This is Si-F formed by implantation of F ions.
Is considered to have changed to Si-O.

For example, in FIG. 3, the pyrooxidation temperature is 1000.
C, gas flow rate is H ₂ : 5 SLM, O ₂ : 5 SLM,
Oxidation rate without conventional ion implantation is 2400Å /
It is time, but the dose of fluorine is 1 × 10 ¹⁵
At atmscm ^-2 (expressed as 1E15 atms / cm ^{2 in the} figure), it is 2800Å / hour, which is an improvement of about 16%. Similarly, when the dose amount of fluorine is 5 × 10 ¹⁵ atmscm ⁻² (expressed as 5E15 atms / cm ^{2 in the} figure), it is 3500 Å
/ Hour, about 45% improvement.

Further, the dose of fluorine is 1 × 10 ¹⁶ a
At tmscm ^-2 (expressed as 1E16 atms / cm ^{2 in the} figure), it is 4200 Å / hour, which is an improvement of about 75%. Next, it will be described how such an improvement in the oxidation rate leads to a reduction in the time required to form an element isolation region having a constant thickness. FIG. 4 shows the oxidation time dependence of the oxide film thickness when pyrooxidation was performed under the same ion implantation conditions.

The conditions of the symbols in FIG. 4 are the same as the conditions of the same symbols in FIG. For example, (●) in this figure
It shows the oxidation time dependence of the oxide film thickness when the F ion implantation layer is not formed. The oxide film thickness monotonically increases with the oxidation time. On the other hand, in the samples (○), (◇), (◆) in which F ions were implanted and subjected to thermal oxidation, first, the thermal oxidation rate increased sharply as the F ion implantation amount increased. However, the increase in the oxide film thickness tends to saturate as the thermal oxidation time increases.

Then, fluorine ions are implanted at a concentration of 1 × 10 ¹⁶ atmscm ^{-2 to} a depth of 2000 Å.
It can be seen that when the oxide film of 00Å is formed, the time can be shortened by about 1.5 hours from the conventional 170 minutes to 60 minutes of the present invention, as compared with the case where the fluorine ion implantation is not performed. Therefore, as compared with the pyrooxidation of the conventional element isolation method, the pyrooxidation of the element isolation method of the present embodiment halves the thermal oxidation time.

In each of the above-described embodiments, the pad oxide film is provided on the surface of the Si film, but the pad oxide film 2 is the bird's beak of the pyro oxide film 6.
It is effective in suppressing the break), but is not particularly necessary in view of the purpose of shortening the pyrooxidation time.

[0036]

According to the element isolation method of the present invention, the thermal oxidation time in the step of forming the element isolation can be shortened. This allows TAT (Turn Around Ti)
(me: response time) can be shortened and lot throughput can be increased.

Furthermore, it is possible to reduce the consumption of thermal energy required for thermal oxidation.

[Brief description of drawings]

FIG. 1 is a process drawing of an element isolation method of implanting fluorine ions after peeling according to the present invention.

FIG. 2 is a process drawing of an element isolation method of implanting fluorine ions before peeling according to the present invention.

FIG. 3 is a correlation diagram between the amount of fluorine ions and the oxidation rate of the present invention.

FIG. 4 is a correlation diagram between the amount of fluorine ions and the oxide film thickness of the present invention.

FIG. 5 is a process chart of a conventional element isolation method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Si film 2 Pad oxide film 3 Oxidation inhibiting film 4 Resist 5 Oxidation inhibiting film of a predetermined shape 6 Pyro oxide film 7 Fluorine

Claims (2)

[Claims] 1. An LOCOS element isolation method for a Si LSI, comprising the steps of forming an oxidation inhibiting film on a Si film, patterning the oxidation inhibiting film into a predetermined shape, and then adding fluorine to a layer other than the oxidation inhibiting film having a predetermined shape. An element isolation method comprising: a step of implanting ions into a Si film in a region; and a step of pyrooxidizing the implanted Si film containing fluorine. 2. The device isolation method according to claim 1, wherein a pad oxide film is formed between the Si film and the oxidation inhibiting film.