JP2002009051A - Dry etching method of semiconductor wafer and manufacture of epitaxial wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technology for removing damage caused by the dry etching (reactive ion etching) of an insulating film even in a fine pattern, and to provide a method for manufacturing an epitaxial wafer where the occurrence of a crystal defect is suppressed even if an epitaxial layer is formed on a surface after etching. SOLUTION: The insulating film is formed on the surface of a semiconductor wafer and a dry etching mask having a prescribed opening part on the surface of the insulating film is formed. The insulating film exposed to the opening part of the mask is removed by first dry etching and second dry etching for removing an etching damage layer by first dry etching, which exists on the surface of the semiconductor wafer, is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dry etching a semiconductor wafer (hereinafter, may be simply referred to as a wafer) and a method for manufacturing an epitaxial wafer using the method, and more particularly to a method for dry etching a silicon oxide film. The present invention relates to a method for manufacturing a silicon epitaxial wafer having few crystal defects by removing damage to a silicon wafer caused by the above.

[0002]

2. Related Art When forming an opening in an insulating film such as a silicon oxide film or a silicon nitride film, there are cases where wet etching is used and cases where dry etching is used.
When the pattern of the opening to be formed is extremely fine, dry etching is often used.

Conventionally, reactive ion etching has been used for dry etching of a silicon nitride film or a silicon oxide film. Reactive ion etching is a process in which a wafer to be processed such as a semiconductor wafer having a thin film to be etched is placed in a vacuum vessel having parallel plate electrodes, and a reactive gas is introduced into the vacuum vessel. In this method, a reactive gas is discharged by applying high-frequency power, and a target wafer is etched by reactive ions in generated plasma to obtain a desired shape.

As dry etching methods other than the reactive ion etching method, there are an ECR type plasma etching method, an ion beam etching method, etc., depending on a difference in a plasma generation method, a control method, an electrode shape and the like. The method also activates the reactive gas introduced into the wafer to be processed in the vacuum vessel and performs etching, and in this regard, it can be considered to be the same as reactive ion etching.

[0005] Etching of a silicon oxide film using the above-described dry etching apparatus is performed by increasing the density of a semiconductor integrated circuit.
With high integration, wet etching, which was conventionally performed with hydrofluoric acid-based chemicals, cannot respond to fine structures by side etching (undercutting) etc., so oxide films used as contact hole formation and diffusion masks Widely used for etching.

Various etching gases used for etching an oxide film have been reported.
A mixed gas system of / Ar + CHF ₃ + CF ₄ is often used. It is known that when etching is performed by activating these gases, active species for etching are mainly ions, and the collision of these ions progresses the etching, so that the base of the film to be etched is damaged. I have. In particular, when an oxide film is formed on bare silicon as a diffusion mask and is etched, damage (plasma damage) due to this etching occurs on the underlying silicon surface, which may affect the next process. In particular, it has been clarified that when the epitaxial growth is performed after the etching, a defect occurs in the epi layer due to the damage.

A conventional method for manufacturing an epitaxial wafer is generally performed in the order of steps shown in FIG. First, a semiconductor wafer W, for example, a silicon wafer is prepared [Step (a) in FIG. 8]. Next, as a mask for forming a diffusion layer before the epitaxial growth, a silicon oxide film 10 serving as a mask is formed on a silicon wafer by a method such as thermal oxidation or CVD (Chemical Vapor Deposition) [step (FIG. b)).

Then, in order to form a predetermined pattern (opening) by etching this silicon oxide film 10,
Mask 12 for etching using photoresist
Is formed [step (c) of FIG. 8 and FIG. 3).

The wafer W where the silicon oxide film 10 is exposed in the opening 14 of the photoresist mask 12 is subjected to dry etching to form an opening 16 in the silicon oxide film 10 [step (d) in FIG. FIG. 4]. Since this etching needs to completely remove the oxide film 10, damage to the surface of the silicon wafer W is caused by the damage.
8 enters.

Next, a predetermined impurity is diffused from the opening 16 of the oxide film 10 formed by dry etching to form a diffusion layer 20 (step (e) in FIG. 8). The diffusion is performed by a commonly used ion implantation method, thermal diffusion method, or the like. In the case of the ion implantation method, the photoresist 12 on the oxide film can be used as a mask, so that the photoresist 12 may be left as it is. However, when the thermal diffusion method is used, the photoresist 12 is removed. FIG. 8E shows a case where the photoresist 12 is removed.

After the diffusion layer 20 is formed, the oxide film 10 (and the photoresist 12 when the photoresist 12 remains) on the surface of the silicon wafer W is removed (step (f) in FIG. 8). . Next, the epitaxial layer 22 is formed on the surface of the silicon wafer W (step (g) in FIG. 8). The epitaxial layer 22 is affected by the damage 18, resulting in a defect 24.

In order to remove the damage 18, a method of removing the damaged layer by wet etching after dry etching can be considered, but it is difficult to adapt to a fine pattern in consideration of side etching. .

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems.
Dry etching of insulating film (reactive ion etching)
Provided is a technique for removing a damage caused by a fine pattern even if the pattern is a fine pattern, and a method for manufacturing an epitaxial wafer in which generation of crystal defects is suppressed even when an epitaxial layer is formed on a surface after etching. It is in.

[0014]

According to the present invention, there is provided a first dry etching (reactive ion etching) which is performed when an insulating film is formed on a surface of a semiconductor wafer and a predetermined opening is formed on the surface of the insulating film. ) Is to remove the damaged layer of the underlying semiconductor wafer by the second dry etching so as not to cause damage. In the case of a silicon wafer, such a second
If a plasma having fluorine radicals is used as dry etching, the fluorine radicals react with silicon,
By generating highly volatile SiF ₄ , the damaged layer is efficiently etched. In addition, O ₂ is added to the reactive gas.
Is included, the etching rate is improved, so that etching can be performed in a short time.

By using such a dry etching method, a damaged layer on the surface of a semiconductor wafer can be removed, so that when an epitaxial layer is formed thereon, crystal defects can be suppressed, and a high quality epitaxial wafer can be obtained. Is obtained. Note that the second dry etching before the epitaxial layer growth is performed by using an insulating film (or a photoresist) having an opening after the first dry etching.
May be used as a mask as it is, or may be applied to the entire surface of the semiconductor wafer after the insulating film and the photoresist are all removed.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 5 in the attached drawings, but the present invention is not limited to these illustrated examples. Needless to say.

FIG. 1 is a flow chart showing a process sequence of a method for manufacturing an epitaxial wafer according to the present invention. As described above, the present invention is directed to dry etching performed when an insulating film is formed on a surface of a semiconductor wafer and a predetermined opening is formed on the surface of the insulating film (in the present invention, the first dry etching is performed). The damage layer of the underlying semiconductor wafer caused by the
Is removed by dry etching. That is, in the method of the present invention, the first and second dry etchings are performed twice to newly introduce a damaged layer caused by the first dry etching (which is the same as the dry etching of the conventional method). The point that it is removed by the second dry etching is different from the conventional method.

Therefore, steps (A) to (C) of the method of the present invention in FIG. 1 are the same as steps (a) to (c) of the conventional method in FIG. 6, and a description thereof will not be repeated.

Next, in the method of the present invention, the first dry etching (reactive ion etching) is performed on the wafer W in which the silicon oxide film 10 is exposed at the opening 14 of the photoresist 12, as in the conventional method. 4
An opening 16 is formed in the silicon oxide film 10 as described above [Step (D) in FIG. 1]. Although various conditions are known as etching conditions at this time, CF ₄ / CHF ₃ /
He gas or CH ₄ / CHF ₃ / Ar gas is used. Since this etching needs to completely remove the oxide film 10, the surface 18 of the underlying silicon wafer W is damaged 18 as in the conventional case.

Therefore, in the present invention, the damaged layer 18 is removed by the second dry etching, and the surface of the wafer W is made a layer 19 without damage (step (E) in FIG. 1 and FIG. 5). At this time, since the object of the present invention cannot be achieved if the second dry etching itself causes etching damage, radicals such as fluorine radicals are mainly used without using reactive ions which are considered to be easily damaged. Perform etching. It is considered that since etching is mainly performed by radicals, etching by chemical reaction rather than ion collision becomes dominant and damage is not caused. CF ₄ , CHF ₃ , C ₂ F ₆ , C ₂ H ₄ F ₄ , and the like, which are reaction gases that generate fluorine radicals and are suitable for damage-free etching.

Next, a predetermined impurity is diffused from the opening 16 of the oxide film 10 formed by dry etching in the same manner as in the conventional method shown in FIG. 8 to form a diffusion layer 20 [step of FIG. F)]. The diffusion is performed by a commonly used ion implantation method, thermal diffusion method, or the like. In the case of the ion implantation method, the photoresist on the oxide film can be used as a mask so that the photoresist may be left as it is. However, when using the thermal diffusion method, the removal is performed. When forming the diffusion layer,
Although heat treatment for recovering irradiation damage due to ion implantation and heat treatment during thermal diffusion are added, damage due to the etching cannot be completely removed.

After forming the diffusion layer, the oxide film 10 (and the photoresist 1) on the surface of the silicon wafer W is formed.
If the epitaxial layer 22 is formed after removing 2), an epitaxial wafer having few crystal defects can be obtained [Steps (G) and (H) in FIG. 1].

In the above embodiment, after the first dry etching, the second dry etching is performed with the oxide film (and the photoresist) on the wafer surface left as a mask, and thereafter, a diffusion layer is formed. Although the process has been described, as shown in FIG. 2, after performing the first dry etching [step (D) in FIG. 2], a diffusion layer is formed [step (E ') in FIG. It is also possible to remove the oxide film (and the photoresist) entirely (step (F ′) in FIG. 2), and then perform a second dry etching on the entire surface of the wafer (step (G ′) in FIG. 2). is there.

[0024]

The present invention will be described in more detail with reference to the following Examples, which are illustrative only and should not be construed as limiting.

(Comparative Examples 1 to 3) A silicon wafer having a diameter of 200 mm having a photoresist opening as shown in FIG. 3 was prepared, and CF ₄ /
The oxide film at the resist opening was removed by reactive ion etching mainly using CF ₃ ⁺ ions using CHF ₃ / He gas. At this time, the calculated etching time for just removing the oxide film by etching is 1 minute (Comparative Example 1).
Then, a wafer subjected to overetching for 2 minutes (Comparative Example 2) was produced. Reference (Comparative Example 3)
A wafer prepared by removing an oxide film with an aqueous solution containing hydrofluoric acid was also prepared.

After removing the resist and oxide film from these wafers, washing them, and performing epitaxial growth of 5 μm at 1125 ° C., the surface of the epitaxial wafers was inspected using a surface inspection apparatus (SP-1 manufactured by KLA Tencor).
LPD (Light Point Defect) with a size of 0.16 μm or more
The result of counting s) is shown in FIG. As shown in FIG. 6, almost no LPD was observed in the reference wafer (Comparative Example 3), but in the above-described dry-etched wafers (Comparative Examples 2 and 3), about 800 to 800 in the wafer plane. 1200 LPDs were detected. Also, if the over-etching time is longer, LPD
It was found that the numbers tended to increase. On the other hand, the LPDs of the reference wafers not subjected to the dry etching treatment were 10 or less.

As described above, in the reactive ion etching of the silicon oxide film when the base is made of silicon, damage due to the etching remains on the silicon wafer, and this causes crystal defects in the epitaxial layer during epitaxial growth. You can see that there is.

(Examples 1 and 2) Next, Comparative Examples 1 and 2
CF ₄
A second dry etching (plasma etching mainly based on fluorine radicals) using / O ₂ was performed for 1 minute. That is,
Example 1 is over-etching for 1 minute + second dry etching, and Example 2 is over-etching for 2 minutes +
The second dry etching is performed. afterwards,
After removing the resist and the oxide film and performing epitaxial growth after cleaning the wafer, LPD was performed in the same manner as in Comparative Examples 1 and 2.
The result of counting was shown in FIG. As shown in FIG. 7, when the second dry etching was performed, only about 10 LPDs were detected in the wafer surface, and the reference wafer (Comparative Example 3) not subjected to the dry etching process It was equivalent.

Therefore, the etching damage remaining on the silicon wafer by the etching of the silicon oxide film was removed by the etching of CF ₄ / O ₂ , and no crystal defects occurred in the epitaxial layer even after the epitaxial growth. You can see that.

Example 3 A silicon wafer used as a sample was a p-type wafer 200 mm in diameter, crystal orientation <100>, and boron doped as a conductivity type. After forming a 300 nm thermal oxide film on the surface of this wafer,
A predetermined pattern was formed by applying a photoresist, and the silicon oxide film was etched using the resist as a mask.

The following conditions were used as the first dry etching conditions for the silicon oxide film. Reaction gas: CF ₄ / CHF ₃ / He gas flow rate (per ^{minute): 50cm 3 / 50cm 3/} 2
00cm ³ High frequency output: 1000W Reaction pressure: 0.3 Torr (about 40 Pa)

Under the above conditions, an etching rate of about 200 nm / min can be obtained, so that the etching time is set at 2 mi.
After the silicon oxide film in the resist opening was completely removed, the second dry etching was performed as the damage removal etching under the following conditions.

The reaction gas: CF ₄ / O ₂ gas flow rate (per minute): 170cm ³ / 30cm ³ frequency output: 300 W Reaction Pressure: 0.3 Torr (about 40 Pa)

The surface of the wafer subjected to the above-mentioned etching has P
After a diffusion layer is formed in the opening by ion implantation of (phosphorus) ions, the resist and oxide film on the surface are completely removed and then washed, and a 4 μm epitaxial layer is grown at 1130 ° C. to form a 0.16 μm The above LPD was counted.

As a result, 8 LPDs / wafer were observed on the epitaxial surface, and it was found that defects on the epitaxial layer surface were extremely small.

Comparative Example 4 An epitaxial wafer was prepared under the same conditions as in Example 3 except that the second dry etching was not performed, and LPDs of 0.16 μm or more on the surface of the epitaxial layer were counted.

As a result, the number of LPDs observed on the epitaxial surface was approximately 500 / wafer, and the number of defects on the surface of the epitaxial layer was considerably larger than that in the example.
It is presumed that damage due to oxide film etching remains.

[0038]

As described above, according to the present invention, the damage caused by the dry etching of the insulating film can be removed even in the case of a fine pattern, and even if an epitaxial layer is formed on the etched surface. A large effect that generation of crystal defects is suppressed is achieved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing one process sequence of a method for manufacturing an epitaxial wafer of the present invention.

FIG. 2 is a flowchart showing another process sequence of the method for manufacturing an epitaxial wafer of the present invention.

FIG. 3 is an explanatory sectional view showing a state in which an oxide film and a photoresist are formed on a silicon wafer, and an opening is provided in the photoresist.

4 is an explanatory cross-sectional view showing a state in which an oxide film has been removed by etching (first etching) from the state of FIG. 3;

5 is an explanatory cross-sectional view showing a state where damage has been removed by a second etching from the state of FIG. 4;

FIG. 6 is a graph showing LPD counts in Comparative Examples 1 to 3.

FIG. 7 is a graph showing LPD counts in Examples 1 and 2 together with Comparative Example 3.

FIG. 8 is a flowchart showing one process sequence of a conventional epitaxial wafer manufacturing method.

[Explanation of symbols]

10: oxide film, 12: photoresist, 14, 16: opening, 18: damage, 19: undamaged layer, 2
0: diffusion layer, 22: epitaxial layer, 24: defect W:
Wafer.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F004 AA07 BA04 DA00 DA01 DA02 DA16 DA22 DA23 DB01 DB03 EA06 FA03 FA08 5F045 AD15 AF03 BB12 HA03 HA05 HA10

Claims (5)

[Claims] An insulating film is formed on a surface of a semiconductor wafer, a dry etching mask having a predetermined opening is formed on the surface of the insulating film, and the insulating film exposed at the opening of the mask is formed as a first film. After removing by dry etching,
A dry etching method for a semiconductor wafer, comprising: performing a second dry etching for removing an etching damage layer existing on a surface of the semiconductor wafer due to the first dry etching. 2. The method for etching a semiconductor wafer according to claim 1, wherein said semiconductor wafer is a silicon wafer, said insulating film is a silicon oxide film, and said dry etching mask is a photoresist. 3. The method according to claim 2, wherein the second dry etching is performed by dry etching using plasma having fluorine radicals. 4. The method according to claim 2, wherein the second dry etching is performed by using a reactive gas containing O ₂ . 5. A step of forming an insulating film on a surface of a semiconductor wafer, a step of forming a predetermined opening in the surface of the insulating film by dry etching, and a step of forming a diffusion layer on the surface of the semiconductor wafer exposed in the opening. Forming an epitaxial layer on the surface of the semiconductor wafer including the surface of the diffusion layer, wherein a predetermined opening is formed on the surface of the insulating film by dry etching. 5. A method for manufacturing an epitaxial wafer, comprising using the dry etching method according to claim 1 as a step.