JP2002020200A - Method of producing epitaxial silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing an epitaxial silicon wafer, by which the epitaxial silicon wafer almost free from occurrence of epitaxial defects can be produced without adding a new heat treatment process. SOLUTION: The method of producing the itaxial silicon wafer comprises cutting a silicon single crystal grown by a Czochralski method while doping nitrogen to obtain a wafer, then cleaning the wafer with an aqueous solution containing hydrogen fluoride(HF) and growing an epitaxial layer on the surface of the wafer. It is preferable that the cleaning mentioned above is carried out after subjecting the wafer to mirror polishing. In the method for producing the epitaxial silicon wafer, mentioned above, it is preferable to dope nitrogen in a concentration of 1×1013 to 1×1016 atom/cm3. Further, it is preferable to clean the wafer with an aqueous solution containing hydrogen fluoride(HF) in a concentration of 0.5 to 50%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an epitaxial silicon wafer used for a highly integrated device for a semiconductor, and more particularly, to a method for forming an epitaxial layer on a wafer obtained from a nitrogen-doped silicon single crystal. The present invention relates to a method for manufacturing an epitaxial silicon wafer in which defects such as stacking faults and dislocations (hereinafter referred to as “epitaxial defects”) generated in an epitaxial layer during growth are small.

[0002]

2. Description of the Related Art Conventionally, a silicon wafer used as a substrate of a highly integrated device is processed from a silicon single crystal grown by the Czochralski method (hereinafter referred to as "CZ method"). In the CZ method, after a silicon polycrystal filled in a crucible composed of an inner quartz container and an outer graphite container is heated and melted by a heater, a seed crystal is immersed in the surface of the melt, and this is melted. This is a method of growing while rotating, and growing a single crystal by pulling it up.

[0003] A silicon wafer grown by the CZ method contains microcavity defects generated by aggregation of point defects (vacancies) excessively introduced during crystal growth. When this cavity defect is exposed on the wafer surface by polishing, it becomes a small pit. The pits exposed on the wafer surface are detected as minute defects by a laser particle counter, and are referred to as Crystal Originated Particles (hereinafter “C”).
OP ”).

Since this COP lowers the yield of devices, it is necessary to reduce the COP density (the number of COPs per unit area) of the wafer. In addition, even if the micro-cavity defect is not exposed on the wafer surface, if it exists in the device active region near the wafer surface, the characteristics of the device are deteriorated. Therefore, in a silicon wafer used as a highly integrated device, it is necessary to reduce not only the COP detected on the surface but also the density of microcavity defects existing in a device active region near the wafer surface.

[0005] When growing a silicon single crystal by the CZ method, a temperature region (around 1100 ° C) in which minute cavity defects are formed.
Is recognized to exist. For this reason, in order to reduce the cavity defects formed in the wafer, a method of gradually cooling this temperature region has been performed. However, when this slow cooling method is employed, the number of defects per unit volume can be reduced, but the size of individual cavity defects increases. As recently, with the progress of high integration of devices, miniaturization of the pattern size is promoted.
The size of P and microcavity defects cannot be ignored, and a wafer without COP or microcavity defects on the surface and the device active region is required.

[0006] From such a demand, an epitaxial wafer in which an epitaxial layer having almost no COP or microcavity defects is grown on the wafer has been developed as a state-of-the-art device substrate, and is often used for highly integrated devices. Is being used. However, even if an epitaxial wafer having few defects and high crystal perfection is used, device characteristics deteriorate due to contamination of the epitaxial layer with metal impurities in a subsequent device process.

[0007] The contamination by such impurities of metallic elements becomes more complicated as the integration of devices becomes higher in density, and the chances and effects of the contamination increase.
The elimination of metal contamination is basically to clean the process environment and the materials used, but it is difficult to completely eliminate metal contamination in the device process, and it is important to develop gettering technology as a countermeasure. . This gettering technique is a means for capturing an impurity element that has entered due to contamination at a location (sink) outside the device active region and rendering it harmless in the device active region.

As a gettering technique, intrinsic gettering (hereinafter, simply referred to as "I"), which captures an impurity element by utilizing an oxygen precipitate caused by oxygen naturally induced during heat treatment in a device process.
G ”). However, when the wafer is subjected to a high-temperature heat treatment of 1050 ° C. to 1200 ° C. in the epitaxial process, the oxygen precipitation nuclei inherent in the wafer cut out of the silicon single crystal shrink and disappear, and in the subsequent device process, the inside of the wafer becomes It becomes difficult to sufficiently induce oxygen precipitates serving as gettering sources. Therefore, even if this gettering technique is applied, there arises a problem that a sufficient IG effect on metal impurities cannot be expected over the entire process.

Conventionally, in order to solve such a problem, nitrogen is doped when growing a single crystal by the CZ method, and oxygen precipitation nuclei which are hardly lost even by a high temperature heat treatment performed in an epitaxial process are formed in the wafer. A method for producing a silicon single crystal to be formed has been proposed (see, for example, JP-A-11-189493 and JP-A-2000-44389). That is, according to the proposed manufacturing method, the thermal stability of the oxygen precipitation nuclei in the crystal is increased by growing by doping with nitrogen by the CZ method, and the oxygen precipitation nuclei are reduced and disappear even by the epitaxial process. It is possible to produce a silicon wafer that does not need to be used.

[0010] The epitaxial layer formed on the wafer surface does not have any defect, but the epitaxial layer has a defect such as a stacking fault or a dislocation, that is, an epitaxial defect. In order to reduce this epitaxial defect, the method proposed above discloses performing a short-time high-temperature heat treatment in a hydrogen atmosphere or an inert gas atmosphere before the epitaxial treatment. However, if an attempt is made to reduce epitaxial defects by high-temperature heat treatment, it is necessary to perform heat treatment at a higher temperature or for a longer time than conventionally employed hydrogen baking. Applying such heat treatment conditions to the wafer can reduce epitaxial defects, but it causes new problems such as high-temperature heat treatment causing slip on the wafer and long-time heat treatment resulting in reduced throughput. become.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problem relating to the epitaxial defect accompanying nitrogen doping, and uses a wafer made of a silicon single crystal grown by doping with nitrogen. Even in such a case, it is an object of the present invention to provide an epitaxial silicon wafer manufacturing method capable of reducing the occurrence of epitaxial defects without adding a new heat treatment process or changing heat treatment conditions in a process of manufacturing an epitaxial wafer. It is an object.

[0012]

Means for Solving the Problems In order to solve the above problems, the present inventors investigated the causes of epitaxial defects while changing the conditions for doping nitrogen by the CZ method and the conditions for epitaxial processing. First, regarding the influence of the presence or absence of nitrogen doping, when epitaxial growth is performed under the same conditions, the number of epitaxial defects generated in a wafer is greater in an epitaxial wafer containing nitrogen than in an epitaxial wafer containing no nitrogen.
From this, it can be presumed that the epitaxial defects generated in the wafer doped with nitrogen are caused by the wafer.

In order to support the above estimation, defects detected on the wafer surface before and after epitaxial growth (Light Point Def.
ect, hereinafter referred to as “LPD”) was inspected with a laser particle counter. Next, when the coordinates of the LPD detected by the laser particle counter were compared,
There was a match between the two. From this inspection result, it is clear that the above-mentioned presumed epitaxial defects generated when the wafer doped with nitrogen is subjected to the epitaxial growth treatment are caused by the wafer, that is, the substrate itself before the epitaxial growth.

Therefore, to identify the cause of the epitaxial defect, an atomic force microscope (AtomicForce Microscope,
Nitrogen is converted to 1 × 10 ¹⁴ atom
The substance of LPD generated on the s / cm ³ -doped wafer was observed. As a result, LPD is a pit-like defect,
The COP can be determined by estimating the size or the in-plane distribution. In that case, since COP is observed even on a wafer not doped with nitrogen, it is difficult to presume that the pit itself is the cause of the epitaxial defect, and the results of both observations were compared in detail.

FIG. 1 shows the COP detected on the wafer surface.
5 is a photograph showing the result of observing the AFM by AFM. In FIG.
(a) is a photograph showing the result of AFM observation of COP detected on a wafer doped with nitrogen, while (b)
Is the COP detected on the wafer not doped with nitrogen
5 is a photograph showing the result of observation with AFM. In these observation results, the brightness (or black and white) contrast indicates the level of the object to be observed, and the brighter (or white) is higher.

A comparison between the two shows that the COP detected on the nitrogen-doped wafer shown in FIG. 1 (a) has projections around it. Then, it is presumed that the protrusion is a protrusion caused by the inner wall oxide film of the COP. On the other hand, such protrusions are not observed in the COP detected on the wafer not doped with nitrogen shown in FIG. From these observation results, it was presumed that epitaxial defects would be caused by protrusions around the COP.

On the basis of the above estimation, a method of removing a projection which causes a defect was examined. First, ammonia (NH), which is conventionally effective for removing adhered particles, is used.
_The wafer was cleaned using a cleaning solution containing ₄ OH) and hydrogen peroxide (H ₂ O ₂ ), but the protrusions around the COP could not be removed. However, hydrofluoric acid (FH)
When the wafer is cleaned using a cleaning solution containing
The protrusion existing around the OP could be removed.

FIG. 1 (c) shows the CP obtained when the COP shown in FIG. 1 (a) is cleaned using a cleaning solution containing hydrofluoric acid (1% HF-H ₂ O).
It is a photograph which shows the result of having observed OP by AFM. Figure 1
As shown in (c), the protrusions around the COP have been removed by cleaning using a cleaning solution containing hydrofluoric acid. As described above, the protrusions are easily removed by etching with hydrofluoric acid, and therefore, as described above, the protrusions around the COP are likely to be oxides.

Further, in order to confirm the cause of the epitaxial defect estimated above and the effect of the cleaning solution containing hydrofluoric acid, a wafer cleaned using an aqueous solution containing hydrofluoric acid was used.
The occurrence of epitaxial defects after epitaxial growth is compared using a wafer that has not been cleaned. As a result of this comparison, it was confirmed that the number of wafer defects cleaned using an aqueous solution containing hydrofluoric acid can be reduced to about half or less as compared with a wafer that was not subjected to the same cleaning, as shown in Examples described later. Therefore, it is clear that the generation of epitaxial defects can be reduced by removing the protrusions around the COP that cause defects by cleaning the wafer using an aqueous solution containing hydrofluoric acid before epitaxial growth.

The present invention has been completed based on the above findings, and has as its gist the following (1) and (2) methods for manufacturing an epitaxial silicon wafer. (1) A silicon single crystal doped with nitrogen is grown by the CZ method, and a wafer cut from the silicon single crystal is washed using an aqueous solution containing hydrofluoric acid (HF), and then an epitaxial layer is formed on the surface of the wafer. And a method for producing an epitaxial silicon wafer. The above cleaning is desirably performed after mirror polishing of the wafer. (2) In the method for manufacturing an epitaxial silicon wafer according to the above (1), the nitrogen concentration is set to 1 × 10 ¹³ atoms / cm ³ to 1 × 10 ¹⁶ at.
It is desirable to dope in the range of oms / cm ³ . Further, it is desirable to wash the wafer using an aqueous solution having a hydrofluoric acid concentration (% by mass) of 0.5% to 50%.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing an epitaxial silicon wafer according to the present invention, a silicon single crystal doped with nitrogen by the CZ method is grown, and a wafer cut out of the silicon single crystal is subjected to an aqueous solution containing hydrofluoric acid (HF). After cleaning in the wafer, an epitaxial layer is grown on the surface of the wafer.

The doping method employed in the present invention may be any method as long as the required concentration of nitrogen can be doped. For example, mixing of a nitride into a raw material or a melt, and addition into a furnace Single crystal growth while flowing nitrogen or nitrogen compound gas, spraying of nitrogen or nitrogen compound gas onto polycrystalline silicon at a high temperature before melting, use of a crucible made of nitride, and the like. In any case, the concentration of nitrogen doped in the crystal can be adjusted by adjusting the amount of nitride, the concentration of nitrogen gas, or the time for spraying them.

During the growth by the CZ method, by doping nitrogen into the silicon single crystal, the condensation of oxygen in the crystal is promoted, the density of oxygen precipitation nuclei is increased, and the thermal stability is increased. For this reason, the concentration of nitrogen to be doped is desirably in the range of 1 × 10 ¹³ atoms / cm ³ to 1 × 10 ¹⁶ atoms / cm ³ . Thereby, the thermal stability of the oxygen precipitation nuclei can be ensured. When the concentration of nitrogen to be doped is lower than 1 × 10 ¹³ atoms / cm ³ , formation of oxygen precipitation nuclei is not promoted, while the concentration of nitrogen is 1 × 10 ¹⁶ atoms / cm ^3.
When it exceeds m ³ , there is a problem that dislocation occurs in the single crystal. Further, since the occurrence of epitaxial defects becomes remarkable when the nitrogen concentration exceeds 1 × 10 ¹⁴ atoms / cm ³ ,
In particular, the hydrofluoric acid cleaning specified in the present invention is required.

The silicon single crystal grown by the CZ method is processed into a wafer according to an ordinary method. For example, after peripheral grinding and orientation flat processing,
Slicing is performed by cutting the wafer with an inner peripheral saw or a wire saw, followed by chamfering and lapping, followed by chemical etching to remove a work-affected layer, and further polishing to a mirror-finished wafer having optical gloss. The silicon wafer finished by mirror polishing is thereafter epitaxially grown.

In the manufacturing method of the present invention, cleaning is performed using an aqueous solution containing hydrofluoric acid before the above-mentioned epitaxial growth is performed. Since the purpose of the cleaning specified here is to remove projections around the COP which are exposed on the wafer surface by polishing and cause epitaxial defects, a mirror polishing step and an epitaxial growth step which are final polishing processes are performed. It is desirable to carry out between.

The concentration of hydrofluoric acid in the aqueous solution used for washing does not need to be particularly limited, but is preferably 0.5% to 50% by mass. Usually, since the concentration of high-purity hydrofluoric acid used for semiconductors is 50%, it is used as a stock solution or diluted with water (H ₂ O). If the concentration of hydrofluoric acid is less than 0.5% during the dilution, the time required for dissolving and removing the protrusions accompanying the COP becomes long, which is not practical.

After cleaning with an aqueous solution containing hydrofluoric acid, particles easily adhere to the wafer surface. Therefore, cleaning with an aqueous solution containing ammonia and hydrogen peroxide, which has an action of removing particles, so-called SC-1 cleaning is performed. It is desirable to do. Thereafter, if necessary, cleaning with an aqueous solution containing hydrochloric acid and aqueous hydrogen peroxide, which has an action of removing metal impurities, so-called SC-2 cleaning may be performed.

After a predetermined cleaning, an epitaxial layer is grown on the surface of the silicon wafer. The epitaxial growth treatment may be a method usually used as a device for a semiconductor, such as metal organic chemical vapor deposition (MOCVD), which is vapor phase epitaxy, or molecular beam epitaxy (MBE).
Method), any method can be applied as long as it is a method for forming an epitaxial layer without crystal defects.

[0029]

EXAMPLES The effects of the method for manufacturing an epitaxial silicon wafer of the present invention will be described in detail based on Examples 1 and 2 below. However, the content of the present invention is not limited to these examples. (Example 1) A silicon single crystal grown by doping with nitrogen by the CZ method so that the nitrogen concentration in the crystal becomes 2 × 10 ¹⁴ atoms / cm ³ , and the mirror surface after chamfering, lapping and chemical etching. Twenty polished wafers (wafer numbers: # 1 to # 20) were prepared. Of these 20
Wafer 10 sheets (♯11~20), compared to the wash for 10 minutes with an aqueous solution containing hydrofluoric acid of 5% HF-H ₂ O were carried out, the remaining 10 sheets (♯1~10) is 4% without hydrofluoric acid
_{H 2 O 2 -4% NH 4} SC-1 by OH-H ₂ O solution of
Washing and SC-2 washing with an aqueous solution of 4% H ₂ O ₂ -4% HCl-H ₂ O were performed. SC-1 cleaning and SC-
The cleaning time of the second cleaning was 10 minutes.

On the surfaces of the 20 cleaned silicon wafers, a 5 μm thick silicon epitaxial layer was grown at a processing temperature of 1200 ° C. For the epitaxial treatment, a leaf growth type growth furnace was used, SiHCl ₃ + H ₂ was introduced, and epitaxial growth was performed by a radiation heating method. Then, using a laser particle counter, LPD detected on the surface
The number was measured.

FIG. 2 is a diagram showing the result of measuring the number of LPDs detected on the surface after epitaxial growth in Example 1. For SC-1 and SC-2 cleaning, L
The average number of PDs is 9.9 / wafer, whereas when cleaning is performed using an aqueous solution containing hydrofluoric acid (5% HF), the average is 4.9 / wafer and the number of LPDs is reduced by half. You can see that. (Example 2) In Example 2, the nitrogen concentration in the crystal was 4 × 10
Twenty wafers (wafer number: # 1 to 1) cut out from a silicon single crystal grown by doping with nitrogen by the CZ method so as to have a concentration of ¹⁴ atoms / cm ³ and chamfered, wrapped, and chemically etched and then mirror-polished. 20) Prepared. As in the case of the first embodiment, 10 wafers ($ 11 to 20) are 5%
Using an aqueous solution containing hydrofluoric acid HF-H ₂ O while washing was carried out for 10 minutes, the remaining 10 sheets (♯1~10) does not contain hydrofluoric acid 4% H ₂ O ₂ -4% SC-1 washing with an aqueous solution of NH ₄ OH—H ₂ O, and 4% H ₂ O ₂ -4% HCl—
SC-2 washing with an aqueous solution of H ₂ O was performed.

Thereafter, under the same conditions as in Example 1, epitaxial growth was performed on the surface of the silicon wafer, and the number of LPDs detected on the surface was measured with a laser particle counter.

FIG. 3 shows the result of measuring the number of LPDs detected on the surface after epitaxial growth in Example 2. In the results shown in FIG. 3, the aqueous solution containing hydrofluoric acid (5
% HF), the number of LPDs was 5.2 / wafer on average, while the number of LPDs was 30.2 on average in SC-1 cleaning and SC-2 cleaning.
The number of wafers / wafer has increased significantly.

When the concentration of nitrogen to be doped is high as in Example 2, the number of LPDs detected on the surface of a wafer which has been subjected to SC-1 cleaning and SC-2 containing no hydrofluoric acid is as follows: Significantly increased compared to Example 1, but 5
The number of LPDs of the wafers cleaned using the% HF aqueous solution remains at substantially the same level as in Example 1. Thus, by performing cleaning using an aqueous solution containing hydrofluoric acid before the epitaxial growth, it is possible to eliminate the cause of the epitaxial defect caused by the nitrogen-doped wafer.

[0035]

According to the method for producing an epitaxial silicon wafer of the present invention, even if the epitaxial wafer is made of a silicon single crystal grown by doping with nitrogen, an aqueous solution containing hydrofluoric acid is used before the epitaxial growth. By performing the cleaning, generation of epitaxial defects can be suppressed. That is, it is possible to provide a high-quality epitaxial wafer with little occurrence of epitaxial defects without adding a new heat treatment process or changing heat treatment conditions in the epitaxial step.

[Brief description of the drawings]

FIG. 1 is a photograph showing the result of observation of COP detected on a wafer surface by AFM. (a) is a photograph showing the result of AFM observation of the COP detected on a wafer doped with nitrogen, and (b) is the result of observation of the COP detected on a wafer not doped with nitrogen by AFM. Further, (c) shows the COP shown in (a) above using a cleaning solution containing hydrofluoric acid.
9 is a photograph showing the result of observation at M.

FIG. 2 is a diagram showing the result of measuring the number of LPDs detected on the surface after epitaxial growth in Example 1.

FIG. 3 is a view showing the result of measuring the number of LPDs detected on the surface after epitaxial growth in Example 2.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/306 H01L 21/306 B (72) Inventor Eiichi Asayama 2201 Kamodada, Ehoku-cho, Kishima-gun, Saga Sumitomo (72) Inventor Yasuo Koike 2201 Kamioda, Ehoku-cho, Kishima-gun, Saga Prefecture Sumitomo Metal Industries Co., Ltd. Metallurgical Industry Co., Ltd. Sitix Business Division F-term (reference) 4G077 AA02 AB01 BB03 CF10 EB01 EE04 FE19 5F043 AA02 BB02 BB27 DD02 DD12 DD16 GG10 5F053 AA12 BB57 DD01 GG01 KK10 PP01 RR03 5F103 AA04 HA10 GG01

Claims (4)

[Claims] A silicon single crystal doped with nitrogen by the Czochralski method is grown, and a wafer cut from the silicon single crystal is washed with an aqueous solution containing hydrofluoric acid (HF), and then the surface of the wafer is cut. A method for manufacturing an epitaxial silicon wafer, comprising growing an epitaxial layer thereon. 2. The method of manufacturing an epitaxial silicon wafer according to claim 1, wherein cleaning using an aqueous solution containing hydrofluoric acid (HF) is performed after mirror polishing of the wafer. 3. A doped nitrogen concentration of 1 × 10 ¹³ atoms / c.
^{3. The} method for producing an epitaxial silicon wafer according to claim 1, wherein m ^{3 is} 1 × 10 ¹⁶ atoms / cm ³ . 4. The epitaxial silicon wafer according to claim 1, wherein the wafer is cleaned using an aqueous solution having a hydrofluoric acid concentration (% by mass) of 0.5% to 50%. Production method.