JPH11176824A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable formation of an oxide film for element isolation in a state in which the surface is polarized. SOLUTION: A selectively oxidized film 105 is etched selectively and eliminated by the use of a silicon nitride film 103 as a mask. In this etching treatment, a first etching treatment is performed by using BHF as an etching solution. Liquid treatment of aqueous solution (concentration range of is 0.01-0.05 wt.%) of surfactant such as polyoxyethylene alkylether is conducted as an intermediate treatment. After the intermediate treatment, continuously a second etching treatment using the same etching solution as in the first etching treatment is conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for manufacturing a semiconductor device in which elements are separated by an oxide film formed by selective oxidation.

[0002]

2. Description of the Related Art In a semiconductor integrated circuit using a silicon substrate, LOC is used to separate transistor elements.
A field oxide film formed by the OS method has been used. However, in the field oxide film formed by this selective oxidation, there is a step between the oxidized region and the non-oxidized region, and this surface step causes disconnection of the wiring formed in a subsequent step, and the yield of the integrated circuit is increased. Had been lowered. For this reason, in recent years, a technique for forming a field oxide film (buried selective oxide film) in which a surface oxide is eliminated by preliminarily forming a field oxide film formation region and thereafter performing selective oxidation has been developed.

Hereinafter, a technique for forming the buried selective oxide film will be described. FIG. 2 shows a conventional method of forming a field oxide film by buried type selective oxidation. In this buried type selective oxidation, first, as shown in FIG. 2A, an underlying oxide film 202 and a silicon nitride film 203 are formed on a silicon substrate 201.
Next, as shown in FIG. 2B, the silicon nitride film 103 is selectively etched using a resist pattern 204 formed by a known photolithography technique as a mask.

Next, after the resist pattern 204 is peeled off, as shown in FIG. 2C, selective oxidation is performed using the silicon nitride film 203 as a mask to form a selective oxide film 205 to a thickness of about 1.2 μm. . In this selective oxidation, 5kg
/ Cm ² by high-pressure steam (steam) oxidation at a temperature of about 950 ° C. Next, as shown in FIG. 2D, the selective oxide film 205 is removed by wet etching. This wet etching
The etching is performed under conditions in which silicon oxide is more easily etched than silicon nitride. Here, by removing the selective oxide film 205, the end of the silicon nitride film 203 is covered with the eaves 2
03a, and a gap which cannot be seen from above is formed underneath.

Then, as shown in FIG. 2E, an underlying oxide film 206 is formed on the exposed silicon substrate 201, and then a silicon nitride film 207 is formed by a CVD method. At this time, the silicon nitride film 207 is formed on all surfaces including the space below the eaves 203a. Next, as shown in FIG. 2F, the silicon nitride film 207 is selectively etched away by dry etching having vertical anisotropy such as reactive ion etching (RIE). As a result, the silicon nitride film 207a remains only in a region that cannot be seen from above under the eaves 203a. Next, the silicon nitride film 203 and the silicon nitride film 20 are formed.
By performing selective oxidation using 7a as a mask, an isolation oxide film 208 is formed as shown in FIG.

[0006]

However, the conventional method described above has a problem that a raised protrusion 209 is formed at the end of the isolation oxide film 208 as shown in FIG. there were. This projection 209 is
After the selective oxide film 205 is removed, as shown in FIG. 3, this occurs because the isolation oxide film residue 301 remains without being etched in the root portion under the eaves 203a. FIG. 3 is a partially enlarged view of FIG. 2D.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an oxide film for element isolation is provided.
It is an object of the present invention to enable the surface to be formed in a flat state.

[0008]

According to a method of manufacturing a semiconductor device of the present invention, when forming an isolation oxide film by buried selective oxidation, a selective oxide film is selectively removed to remove an edge of a first selective oxidation mask. The step of forming a gap below the warped portion as an eaves is performed by dipping the silicon substrate on which the selective oxide film is formed in an etching solution for etching silicon oxide preferentially for a predetermined time. And a second process of immersing the silicon substrate in an aqueous solution in which a surfactant is dissolved for a predetermined time following the first process;
The second process is followed by a third process in which the silicon substrate is immersed in an etchant for etching silicon oxide preferentially. Therefore, the surface tension (interfacial tension) of the etchant on the surface of the silicon substrate to be etched is reduced by the second process, so that the etchant easily reaches the interior of the eaves. Further, in the method of manufacturing a semiconductor device according to the present invention, when the isolation oxide film is formed by buried selective oxidation, the selective oxide film is selectively removed to cover the warped portion of the first selective oxidation mask end. The first step of dipping the silicon substrate on which the selective oxide film has been formed for a predetermined time in an etching solution that preferentially etches the silicon oxide includes the steps of: Subsequent to the treatment, the silicon substrate is immersed in an etching solution for preferentially etching the silicon oxide added with the surfactant for a predetermined time.
Processing. Therefore, in the etching by the second process, the surface tension (interfacial tension) of the etchant on the surface of the silicon substrate to be etched
And the etching liquid easily reaches the interior of the eaves.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram for explaining a method of manufacturing a semiconductor device according to an embodiment of the present invention, and particularly shows a step of forming an oxide film for element isolation. First, as shown in FIG.
An underlying oxide film (first underlying oxide film) 102 and a silicon nitride film 103 are formed on the substrate 01. Underlay oxide film 1
No. 02 is formed by thermal oxidation using steam at about 900 ° C. under normal pressure to have a film thickness of about 35 nm. The silicon nitride film 103 has a thickness of 120 nm by a CVD method.
Formed to the extent.

Next, as shown in FIG. 1B, the silicon nitride film 103 is selectively etched using a resist pattern 104 formed by a known photolithography technique as a mask. Next, after the resist pattern 104 is peeled off, as shown in FIG. 1C, selective oxidation is performed using the silicon nitride film (first selective oxidation mask) 103 as a mask, and the selective oxidation film 105 is formed to a thickness of 1. It is formed to about 2 μm. In this selective oxidation, the pressure was set to 5 kg / cm ² 9
This is performed by high-pressure steam oxidation at a temperature of about 50 ° C.

Next, as shown in FIG. 1D, the selective oxide film 105 is removed by wet etching. Hereinafter, this etching process will be described. First, buffered hydrofluoric acid (BHF) with NH ₄ F: HF = 6: 3 is used as an etching solution. In BHF, silicon nitride and silicon are hardly etched. Then, a first etching process is performed using BHF as an etchant. The first etching process is performed by immersing the substrate to be etched in the etchant for 17 minutes while keeping the etchant at room temperature. The etching is stopped by removing the substrate to be etched from the etching solution and then washing the substrate with pure water.

Next, as an intermediate treatment, a solution treatment of an aqueous solution of a surfactant such as polyoxyethylene alkyl ether (concentration: 0.01 to 0.05 w%) is performed. This intermediate treatment is performed by immersing the substrate to be etched in the aqueous solution of the surfactant for several seconds. Then, after the intermediate process, a second etching process using the same etching solution as the first etching process is subsequently performed. The second etching process is performed by immersing the substrate to be etched in the etching solution for 30 seconds while keeping the etching solution at room temperature. The stop of the etching is performed in the same manner as described above. The substrate to be etched is taken out of the etching solution and then washed with pure water.

By the above processing, as shown in FIG. 1D, the underlying oxide film 102 is not under the eaves 103a of the silicon nitride film 103, and
Will only remain under the flat part of the. Next, FIG.
As shown in (e), an underlying oxide film (second underlying oxide film) 10 is formed on the exposed silicon substrate 101 by thermal oxidation.
6 is formed to a thickness of about 35 nm, and then a silicon nitride film 107 is formed to a thickness of about 30 nm by a CVD method.
At this time, the silicon nitride film 107 is formed on all surfaces including the space below the eaves 103a.

Next, as shown in FIG. 1F, the silicon nitride film 107 is selectively removed by dry etching having vertical anisotropy such as RIE. As a result, the silicon nitride film (second selective oxidation mask) 107a remains only in a region that cannot be seen from above under the eaves 103a.
Next, as shown in FIG.
If the isolation oxide film 108 is formed by performing selective oxidation using the silicon nitride film 107 and the silicon nitride film 107a as a mask, from the underlying oxide film 102 to the isolation oxide film 108 formation portion,
It can be formed with a substantially flat surface.

Then, if the silicon nitride film 103 and the silicon nitride film 107a are removed and the silicon oxide is removed so as to eliminate the underlying oxide film 102, etching for element isolation from the silicon substrate surface in the element formation region is performed. Is formed almost flat over the oxide film forming portion. Thereafter, as is well known, an element such as a MOS transistor is formed in the element forming region,
If a wiring or the like is formed thereover with an interlayer insulating film interposed therebetween, a semiconductor device (integrated circuit) can be formed in a state where occurrence of a defect such as disconnection of the wiring is suppressed.

By the way, in the above description, the first etching process → intermediate process → second etching process is performed in order to obtain the state shown in FIG. 1 (d). The second etching process may be performed using an etching solution to which is added. in this way,
Even when the second etching process is performed using an etching solution to which a surfactant is added, the same as the above-described process is performed.

[0017]

As described above, according to the present invention, when the isolation oxide film is formed by the buried selective oxidation, the selective oxide film is selectively removed and the end of the first selective oxidation mask is warped. A step of immersing the silicon substrate on which the selective oxide film is formed for a predetermined time in an etchant that preferentially etches silicon oxide; Subsequent to the first treatment, the silicon substrate is immersed in an aqueous solution in which a surfactant is dissolved for a predetermined time, and after the second treatment, the silicon substrate is subjected to an etching solution for preferentially etching silicon oxide. And a third treatment of dipping. Therefore, the surface tension (interfacial tension) of the etchant on the surface of the silicon substrate to be etched is reduced by the second process, so that the etchant easily reaches the interior of the eaves. As a result, according to the present invention, there is an effect that an oxide film for element isolation can be formed with a flat surface without leaving any etching residue behind the eaves.

Further, according to the method of manufacturing a semiconductor device of the present invention, when forming an isolation oxide film by buried selective oxidation, the selective oxide film is selectively removed to warp the end of the first selective oxidation mask. A step of immersing the silicon substrate on which the selective oxide film is formed for a predetermined time in an etchant that preferentially etches silicon oxide; The first process is followed by a second process in which the silicon substrate is immersed in an etchant for preferentially etching the silicon oxide to which the surfactant is added for a predetermined time. Therefore, in the etching by the second process, the surface tension (interfacial tension) of the etchant on the surface of the silicon substrate to be etched is reduced, and the etchant is more likely to reach deep inside the eaves. As a result, according to the present invention, there is an effect that an oxide film for element isolation can be formed with a flat surface without leaving any etching residue behind the eaves.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for describing a method for manufacturing a semiconductor device according to an embodiment of the present invention;

FIG. 2 is an explanatory view showing a conventional method of forming a field oxide film by buried selective oxidation.

FIG. 3 is a partially enlarged cross-sectional view of FIG. 2 (d).

[Explanation of symbols]

101: silicon substrate, 102: underlying oxide film (first underlying oxide film), 103: silicon nitride film (first selective oxidation mask), 104: resist pattern, 105: selective oxide film 105, 106: underlying oxide film (Second underlying oxide film), 107: silicon nitride film, 107a: silicon nitride film (second selective oxidation mask), 108: isolation oxide film.

Claims (2)

[Claims] A first step of oxidizing a surface of the silicon substrate to form a first underlying oxide film on the surface of the silicon substrate; and depositing silicon nitride on the first underlying oxide film. A second step of forming a first selective oxidation mask by removing a predetermined portion; and selectively oxidizing by thermally oxidizing a surface of the silicon substrate in a region not covered by the first selective oxidation mask. A third step of forming a film, making the end portion of the selective oxide film penetrate below the end portion of the first selective oxidation mask, and bringing the end portion of the first selective oxidation mask into a warped state; A fourth step of selectively removing the oxide film so that the warped portion of the end of the first selective oxidation mask is used as an eaves and a gap is formed therebelow; Thermal oxidation of the silicon substrate surface Forming a second underlay oxide film by the step of: depositing silicon nitride so as to cover the surface of the second underlay oxide film and the exposed surface of the first selective oxidation mask. A sixth step of forming a silicon nitride film by dry etching having vertical anisotropy, thereby forming the silicon oxide film only on the end surface of the selective oxidation mask under the eaves and the surface of the second underlying oxide film under the eaves. A seventh step of forming a second selective oxidation mask while leaving a silicon nitride film; and a third step of thermally oxidizing the surface of the silicon substrate using the first and second selective oxidation masks as masks. Forming an isolation oxide film for element isolation in a region where the selective oxide film is formed, so that the surface of the isolation oxide film is substantially as high as the surface of the first underlying oxide film; Process and At least a ninth step of removing the first and second selective oxidation masks, wherein the fourth step comprises the steps of: A first process of immersing the silicon substrate on which the selective oxide film is formed for a predetermined time; and a second process of immersing the silicon substrate in an aqueous solution in which a surfactant is dissolved for a predetermined time following the first process A method for manufacturing a semiconductor device, comprising: a process; and a third process of immersing the silicon substrate in an etchant for etching silicon oxide preferentially subsequent to the second process. 2. A first step of forming a first underlay oxide film on the silicon substrate surface by oxidizing a surface of the silicon substrate, and depositing a silicon nitride on the first underlay oxide film. A second step of forming a first selective oxidation mask by removing a predetermined portion; and selectively oxidizing by thermally oxidizing a surface of the silicon substrate in a region not covered by the first selective oxidation mask. A third step of forming a film, making the end portion of the selective oxide film penetrate below the end portion of the first selective oxidation mask, and bringing the end portion of the first selective oxidation mask into a warped state; A fourth step of selectively removing the oxide film so that the warped portion of the end of the first selective oxidation mask is used as an eaves and a gap is formed therebelow; Thermal oxidation of the silicon substrate surface Forming a second underlay oxide film by the step of: depositing silicon nitride so as to cover the surface of the second underlay oxide film and the exposed surface of the first selective oxidation mask. A sixth step of forming a silicon nitride film by dry etching having vertical anisotropy, thereby forming the silicon oxide film only on the end surface of the selective oxidation mask under the eaves and the surface of the second underlying oxide film under the eaves. A seventh step of forming a second selective oxidation mask while leaving a silicon nitride film; and a third step of thermally oxidizing the surface of the silicon substrate using the first and second selective oxidation masks as masks. Forming an isolation oxide film for element isolation in a region where the selective oxide film is formed, so that the surface of the isolation oxide film is substantially as high as the surface of the first underlying oxide film; Process and At least a ninth step of removing the first and second selective oxidation masks, wherein the fourth step comprises the steps of: A first process of dipping the silicon substrate on which the selective oxide film is formed for a predetermined time; and, following the first process, the silicon substrate is added to an etchant that preferentially etches a silicon oxide added with a surfactant. A second process of immersing the semiconductor device for a predetermined period of time.