JP4483173B2 - Manufacturing method of SOI substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a SIMOX (Separation by Implanted Oxygen) SOI (Silicon-On-Insulster) substrate manufacturing how having partially buried oxide film in the silicon substrate under the law.
[0002]
[Prior art]
Conventionally, an SOI substrate having a buried oxide film inside a silicon substrate is expected to be used as a device substrate for high speed and low power consumption. Among these, an SOI substrate (hereinafter referred to as a “partial SOI substrate”) having a partially buried oxide film, not the entire surface inside a silicon substrate, is an analog, logic, and memory mixed system LSI. It is regarded as important because it can be formed in the SOI region of the buried oxide film and a memory part can be manufactured in a bulk Si portion having no buried oxide film.
[0003]
As a method for manufacturing this type of partial SOI substrate, the following method has been proposed (for example, see Patent Document 1). That is, as shown in FIG. 2, first, a surface oxide film 4 is formed on the surface of a silicon substrate 2 (the substrate 2 is cut out in a plane perpendicular to the axis of the silicon single crystal rod) (FIG. 2A). Then, a resist layer 6 patterned by photolithography is formed on the surface of the surface oxide film 4 (FIGS. 2B and 2C). Next, the surface oxide film 4 is patterned by anisotropic etching (FIG. 2D), and after removing the resist layer 6 (FIG. 2E), the substrate 2 is washed. Next, oxygen ions 7 are implanted into the substrate 2 from a direction inclined by 7 degrees with respect to the normal to the surface of the substrate 2 (FIG. 2 (f)), and the substrate 2 is mixed with an ammonium hydrofluoric acid aqueous solution and hydrofluoric acid (etching solution). ) To remove the surface oxide film 4 (FIG. 2G). Then, the buried oxide film 3 is formed by annealing at a temperature of 1300 ° C. or higher for a predetermined time in an atmosphere of a mixed gas of argon and oxygen or a mixed gas of nitrogen and oxygen (FIG. 2H). Thereafter, the substrate 2 is again immersed in a mixed solution (etching solution) of an aqueous solution of ammonium fluoride and hydrofluoric acid, and the oxide film 5 formed on the surface of the substrate 2 is removed during annealing (FIG. 2 (i)). .
[0004]
[Patent Document 1]
JP-A-5-82525 (Claim 2)
[0005]
[Problems to be solved by the invention]
However, in the conventional method of forming the buried oxide film, when the buried oxide film 3 is formed by annealing, the volume expands to about 2.2 times and the surface of the substrate 2 swells, and FIG. And as shown to (i), there existed a malfunction that the level | step difference exceeding at least 30 nm produced in the surface of the board | substrate 2 in the part in which the embedded oxide film 3 was formed, and the part which is not formed. When a semiconductor device is formed on the surface of the substrate 2 having the step, there is a problem that the focus is shifted in the photolithography process.
An object of the present invention reduces the difference in level in the surface of the substrate 2 in the portion that does not form a part of forming the buried oxide film, to provide a manufacturing how the SOI substrate that can solve the problem that the focus is shifted in a photolithography process There is.
[0006]
[Means for Solving the Problems]
In the invention according to claim 1, as shown in FIG. 1, oxygen ions 22 are implanted with a first oxide film 17 having a thickness of 200 nm to 1000 nm partially formed on the surface of a substrate 12 made of silicon single crystal. a step of, seen including a step of forming a buried oxide film 13 inside the substrate 12 and the substrate 12 is annealed at 1300 ° C. or higher, oxide layer 23 is formed the surface of the substrate 12 at the time of annealing is oxidized that is an improvement of a method for manufacturing an SOI substrate.
The characteristic point is that the first oxide film 17 on the surface of the substrate 12 is thinned between the step of implanting the oxygen ions 22 and the step of annealing, and the second oxide film having a thickness of the buried oxide film 13 or more. 19 is formed or a second oxide film 19 having a thickness less than that of the first oxide film 17 and greater than or equal to the buried oxide film 13 is formed in place of the first oxide film 17 in the same portion as the first oxide film 17. step only contains, it is a step of removing the second oxide layer and the oxide layer 23 of the substrate 12 surface after annealing process including Mutokoro.
[0007]
In the method for manufacturing an SOI substrate according to claim 1, the surface of the substrate 12 is oxidized by annealing to form an oxide layer 23, and the oxide layer 23 is not masked by the second oxide film 19, that is, It progresses early in the portion where the buried oxide film 13 is formed and progresses later in the portion masked by the second oxide film 19. Therefore, in the state where the buried oxide film 13 is formed, the oxide layer 23 includes a thick film portion 23 a in a portion where the buried oxide film 13 is formed, and a thin film portion 23 b in a portion masked by the second oxide film 19. Have Therefore, although the oxide film 13 is expanded by the annealing process and the surface of the substrate 12 is expanded, the step is absorbed as a difference between the thick film portion 23a and the thin film portion 23b of the oxide layer 23 formed on the substrate 12 at that time. . As a result, after the buried oxide film 13 is formed by the annealing process, the buried oxide film 13 is expanded by removing the second oxide film 19 and the oxide layer 23 newly formed on the surface of the substrate 12 at the time of annealing. The step formed on the surface of the substrate 12 is removed together with the thick film portion 23a of the oxide layer 23, and when the thin film portion 23b of the oxide layer 23 is removed, the portion where the embedded oxide film 13 is formed and the portion where it is not formed. The level difference on the surface of the substrate 12 can be set to 0 to 30 nm .
[0008]
The invention according to claim 2 is the invention according to claim 1, wherein the second oxide film 19 is formed by anisotropically etching the first oxide film 17 to thin the first oxide film 17. This is a method for manufacturing an SOI substrate.
The invention according to claim 3 is the invention according to claim 2, wherein the anisotropic etching of the first oxide film 17 forms the resist layer 21 on the surface of the substrate 12 not masked by the first oxide film 17. was done after a manufacturing method of an SOI substrate you remove the resist layer 21 before annealing even after the anisotropic etching of the first oxide film 17.
In the method for manufacturing an SOI substrate according to the second aspect, the formation of the second oxide film 19 is relatively easy. In the method for manufacturing the SOI substrate according to the third aspect, the substrate 12 is etched when the first oxide film 17 is etched. It is possible to prevent the surface from being etched.
[0009]
The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the annealing treatment is held in an oxidizing atmosphere within a temperature range of 1300 to 1380 ° C. for 2 to 20 hours. This is a method for manufacturing an SOI substrate.
In the SOI substrate manufacturing method according to the fourth aspect, the amount of swelling of the surface of the substrate 12 caused by the expansion of the oxide film 13 by the annealing process, and the thick film portion 23a and the thin film portion of the oxide layer 23 formed on the substrate 12 are obtained. It is possible to effectively eliminate the level difference on the surface of the substrate 12 between the portion where the buried oxide film 13 is formed and the portion where the buried oxide film 13 is not formed by matching the difference with 23b.
Here, in this specification, the “oxidizing atmosphere” includes a mixed gas atmosphere of an inert gas and oxygen. The oxidizing atmosphere in this case contains 100% by volume of oxygen, the preferable oxygen content is 0.5 to 90% by volume, and the more preferable content is 40 to 70% by volume.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1K, the SOI substrate 11 has a silicon substrate 12 and a buried oxide film 13 formed inside the substrate 12. The substrate 12 is cut into a thin plate shape along a plane [(100) plane of the crystal structure of the silicon single crystal] perpendicular to the axis of the silicon single crystal rod grown by the Czochralski (CZ) method. The buried oxide film 13 is formed as follows. The substrate may be cut out from a silicon single crystal rod or a silicon single crystal plate grown by a floating zone (FZ) method or the like instead of the CZ method.
[0011]
First, a surface oxide film 14 is formed on the surface of the substrate 12 (FIG. 1A). The surface oxide film 14 is a silicon oxide film (SiO ₂ film), and is formed by thermally oxidizing the substrate 12 or by chemical vapor deposition (CVD). The thickness of the surface oxide film 14 is formed in the range of 200 nm to 1000 nm, preferably in the range of 500 nm to 800 nm. The reason why the thickness of the surface oxide film 14 is limited to the range of 200 nm to 1000 nm is that if it is less than 200 nm, oxygen ions 22 described later may be implanted into the substrate 12 through the surface oxide film 14. This is because ions can be sufficiently blocked. Next, a resist layer 16 having a predetermined pattern is formed on the surface of the surface oxide film 14 by photolithography (FIGS. 1B and 1C). The resist layer 16 is exposed using a photomask 18 (FIG. 1B), and after development and rinsing, a predetermined pattern is formed on the resist layer 16 (FIG. 1C).
[0012]
Using the resist layer 16 as a mask, the surface oxide film 14 is anisotropically etched in a direction perpendicular to the surface of the substrate 12 (FIG. 1D). The anisotropic etching is reactive ion etching in this embodiment. In the reactive ion etching, although not shown, a substrate is placed on the lower electrode of two counter electrodes installed in the reaction chamber, and a high frequency voltage is applied to these electrodes to induce plasma, whereby CF ₄ or A radical ion nuclide that is more reactive than an etching gas such as SF ₆ is formed, and the radical ion of several tens to several hundreds eV is incident on the substrate 12 due to a self-bias potential difference generated between the plasma and the substrate 12. Etching of the surface oxide film 14 proceeds by the effects of both sputtering and chemical reaction. Therefore, the inner peripheral edge of the surface oxide film 14 has a vertical etching shape with no undercut. Note that ECR plasma etching may be used as anisotropic etching. After the etching is completed, the resist layer 16 is removed with sulfuric acid / hydrogen peroxide or the like, and a first oxide film 17 having a thickness of 200 nm to 1000 nm formed of the surface oxide film 14 remaining on the substrate surface without being etched is partially formed on the surface of the substrate 12. (FIG. 1 (e)), and then washed.
[0013]
Next, oxygen ions 22 are implanted perpendicularly to the surface of the substrate 12 using the first oxide film 17 as a mask (FIG. 1F). Implantation conditions of the oxygen ions 22 at this time is the amount of implanted ^{1 × 10 17 / cm 2 ~2} × 10 18 / cm 2, preferably ^{2 × 10 17 / cm 2 ~5} × 10 1 7 / cm 2, The implantation energy is 20 keV to 200 keV, preferably 60 keV to 180 keV.
[0014]
Next, the first oxide film 17 on the surface of the substrate 12 is thinned to form a second oxide film 19 having a thickness equal to or greater than a buried oxide film 13 to be described later, or in the same portion as the first oxide film 17. Instead of the first oxide film 17, a second oxide film 19 having a thickness less than that of the first oxide film 17 and greater than or equal to the buried oxide film 13 is formed. In this embodiment, the first oxide film 17 on the surface of the substrate 12 is thinned to form the second oxide film 19 as shown in FIGS. The first oxide film 17 is thinned by anisotropically etching the oxide film 17. Then, the anisotropic etching of the first oxide film 17 is performed after the resist layer 21 is formed on the surface of the substrate 12 not masked by the first oxide film 17 (FIG. 1G). The formation of the resist layer 21 is performed by the same procedure as that for the resist layer 16 described above. More specifically, a resist layer 21 is formed on the entire surface of the substrate 12 partially formed with the first oxide film 17 by photolithography, and the resist layer 21 is exposed using a photomask (not shown) and developed. Then, the resist layer 21 formed on the first oxide film 17 is removed through rinsing, and the resist layer 21 is left on the surface of the substrate 12 not masked by the first oxide film 17. In this way, a resist layer 21 is formed on the surface of the substrate 12 that is not masked by the first oxide film 17.
[0015]
As shown in FIG. 1H, anisotropic etching is performed on the first oxide film 17 in a direction perpendicular to the surface of the substrate 12 using the resist layer 21 as a mask, and the first oxide film 17 is formed into a thin layer. Then, a second oxide film 19 having a thickness equal to or greater than the buried oxide film 13 described later is formed. The anisotropic etching is reactive ion etching in this embodiment. The reason why the thickness of the second oxide film 19 is limited to the buried oxide film 13 or more is that if it is less than the buried oxide film 13, the oxidation rate on the surface of the substrate 12 increases during annealing, which will be described later. This is because oxidation at the surface of the substrate 12 cannot be expected during annealing described later. After the first oxide film 17 is thinned to form the second oxide film 19, the resist layer 21 is removed and washed with sulfuric acid / hydrogen peroxide. In the above description, anisotropic etching is referred to as a means for thinning the first oxide film 17. However, this thinning is not limited thereto, and wet etching may be used.
[0016]
Next, an annealing process is performed in which the substrate 12 is held in an oxidizing atmosphere within a temperature range of 1300 to 1380 ° C. for 2 to 20 hours and then slowly cooled (FIG. 1 (j)). The oxidizing atmosphere includes a mixed gas atmosphere of an inert gas and oxygen, and a mixed gas atmosphere of argon and oxygen or a mixed gas atmosphere of nitrogen and oxygen is exemplified. The oxidizing atmosphere in this case contains 100% by volume of oxygen, the preferable oxygen content is 0.5 to 90% by volume, and the more preferable content is 40 to 70% by volume. This is because if the oxygen content is less than 0.5%, oxidation on the surface of the substrate 12 cannot be expected during annealing described later.
[0017]
By this annealing treatment, oxidation of the portion of the substrate 12 into which the oxygen ions 22 are implanted is promoted, and a buried oxide film 13 is formed inside the substrate 12. When the buried oxide film 3 is formed, the oxide film 13 expands and the surface of the substrate 12 swells. As shown in FIG. 1 (j), the substrate in the portion where the buried oxide film 3 is formed and the portion where it is not formed. A step is generated on the surface of 2.
[0018]
On the other hand, since the annealing process is performed by placing the substrate 12 horizontally in the furnace, the surface of the substrate 12 is oxidized to form an oxide layer 23. The oxide layer 23 progresses early in a portion not masked by the second oxide film 19, that is, in a portion where the buried oxide film 13 is formed, and progresses slowly in a portion masked by the second oxide film 19. As a result, when the buried oxide film 13 is formed, the oxide layer 23 includes a thick film portion 23a in the portion where the buried oxide film 13 is formed and a thin film portion 23b in the portion masked by the second oxide film 19. And have. Therefore, although the oxide film 13 is expanded by the annealing process and the surface of the substrate 12 is expanded, the step is absorbed as a difference between the oxidized thick film portion 23 a and the thin film portion 23 b formed on the substrate 12.
[0019]
After the buried oxide film 13 is formed by annealing, the substrate 12 is immersed in a mixed solution (etching solution) of an aqueous solution of ammonium fluoride and hydrofluoric acid to newly form the second oxide film 19 and the surface of the substrate 12 during annealing. The oxidized layer 23 is removed (FIG. 1 (k)). Then, the step formed on the surface of the substrate 12 by the expansion of the buried oxide film 13 is removed together with the thick film portion 23a of the oxide layer 23, and the buried oxide film is removed when the thin film portion 23b of the oxide layer 23 is removed. The step on the surface of the substrate 12 in the portion where 13 is formed and the portion where 13 is not formed can be 0 to 30 nm.
[0020]
That is, between the step of implanting oxygen ions 22 and the step of annealing, the first oxide film 17 on the surface of the substrate 12 is thinned to form the second oxide film 19 having a thickness of the buried oxide film 13 or more. Alternatively, a step of forming a second oxide film 19 having a thickness less than that of the first oxide film 17 and greater than or equal to the buried oxide film 13 in place of the first oxide film 17 in the same portion as the first oxide film 17 is included. Therefore, the step in the surface of the substrate 12 generated in the state where the buried oxide film 13 is formed by the annealing treatment is absorbed as a difference between the thick film portion 23a and the thin film portion 23b of the oxide layer 23 formed on the substrate 12 at that time. . As a result, after the buried oxide film 13 is formed by annealing, the second oxide film 19 and the oxide layer 23 newly formed on the surface of the substrate 12 at the time of annealing are removed, so that the buried oxide film 13 is formed. The step on the surface of the substrate 12 in the portion that is not formed can be 0 to 30 nm. The SOI substrate having a step of 0 to 30 nm can solve the problem that the focus shifts in the photolithography process.
[0021]
In the above-described embodiment, the example in which the first oxide film 17 on the surface of the substrate 12 is thinned to form the second oxide film 19 having a thickness greater than that of the buried oxide film 13 has been described. The film 19 may be formed in the same portion as the first oxide film 17 instead of the first oxide film 17.
In the above-described embodiment, the example in which the anisotropic etching of the first oxide film 17 is performed after the resist layer 21 is formed on the surface of the substrate 12 not masked by the first oxide film 17 is shown. The first oxide film 17 may be anisotropically etched without forming the resist layer 21 as long as the surface of the substrate 12 can be prevented from being etched during the etching of the first oxide film 17.
[0022]
【The invention's effect】
As described above, according to the present invention, between the step of implanting oxygen ions and the step of annealing, the first oxide film on the surface of the substrate is thinned to have a thickness equal to or greater than that of the buried oxide film. Forming an oxide film or forming a second oxide film having a thickness less than the first oxide film and greater than or equal to the buried oxide film in place of the first oxide film in the same portion as the first oxide film; Therefore, although the oxide film is expanded by the annealing process and the surface of the substrate is expanded, the step can be absorbed as a difference between the thick film portion and the thin film portion of the oxide layer formed on the substrate at that time. As a result, after the buried oxide film is formed by annealing, the buried oxide film is expanded and formed on the substrate surface by removing the second oxide film and the oxide layer newly formed on the substrate surface during the annealing. The step is removed together with the thick film portion of the oxide layer, and when the thin film portion of the oxide layer is removed, the step on the surface of the substrate in the portion where the buried oxide film is formed and the portion where it is not formed is set to 0 to 30 nm. In addition, it is possible to solve the problem that the focus shifts in the photolithography process.
[0023]
Further, if the step of forming the second oxide film is to thin the first oxide film by anisotropically etching the first oxide film, the formation of the second oxide film is relatively easy. Thus, if anisotropic etching of the first oxide film is performed after forming a resist layer on the surface of the substrate not masked by the first oxide film, the substrate surface during the etching of the first oxide film is etched. This can be prevented.
Further, if the annealing treatment is performed by holding in an oxidizing atmosphere within a temperature range of 1300 to 1380 ° C. for 2 to 20 hours, the amount of swelling of the substrate surface caused by the expansion of the oxide film by the annealing treatment By making the difference between the thick film portion and the thin film portion of the oxide layer formed on the substrate coincide with each other, the step on the surface of the substrate between the portion where the buried oxide film is formed and the portion where the buried oxide film is not formed can be surely set to 0 to 30 nm. it can.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a method for manufacturing an SOI structure element of an SOI substrate according to a first embodiment of the present invention in the order of steps;
FIG. 2 is a cross-sectional view corresponding to FIG. 1 showing a conventional example.
[Explanation of symbols]
11 SOI substrate 12 substrate 13 buried oxide film 17 first oxide film 19 second oxide film 21 resist layer 22 oxygen ion

Claims (4)

Implanting oxygen ions (22) in a state where a first oxide film (17) having a thickness of 200 nm to 1000 nm is partially formed on the surface of a substrate (12) made of silicon single crystal; and inside buried saw including a step of forming an oxide film (13), oxide layer surface by oxidation of the substrate (12) during said annealing treatment to be annealed at 1300 ° C. or more above the substrate (12) ( In the method for manufacturing an SOI substrate on which 23) is formed ,
Between the step of implanting oxygen ions (22) and the step of annealing, the first oxide film (17) on the surface of the substrate (12) is thinned to have a thickness of the buried oxide film (13 The above-described second oxide film (19) is formed, or the first oxide film (17) is formed in the same portion as the first oxide film (17) in place of the first oxide film (17). look including the step of forming the buried oxide film (13) over the second oxide layer (19) be less than,
The method for manufacturing an SOI substrate, wherein said substrate (12) the second oxide film and the oxide layer on the surface of the step of removing (23) including that after the annealing treatment. Formation of the second oxide layer (19) of claim 1 wherein is carried out by thinning the first oxide layer (17) by anisotropically etching the first oxide film (17) Manufacturing method of SOI substrate. The first anisotropic etching of the oxide film (17) is performed after forming the resist layer on the surface of the substrate not masked (12) and (21) in said first oxide film (17), said first claim 2 the method for manufacturing an SOI substrate according you remove the resist layer (21) was in before the annealing process after anisotropic etching of the first oxide film (17). 4. The method for manufacturing an SOI substrate according to claim 1, wherein the annealing treatment is performed by holding in an oxidizing atmosphere within a temperature range of 1300 to 1380 ° C. for 2 to 20 hours. 5.

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