JP2020038937A - Method for manufacturing epitaxial wafer - Google Patents

Abstract

To provide a method with which an epitaxial wafer having a silicon epitaxial layer can be manufactured, which can prevent the generation of a white scratch defect when especially used for manufacture of an image pick-up device.SOLUTION: There is provided a method for manufacturing an epitaxial wafer by performing vapor phase growth of a silicon epitaxial layer by supplying a material gas and a carrier gas onto a silicon single crystal substrate. When a growth temperature of the silicon epitaxial layer is T(°C), and an air converted flow rate of the carrier gas during growth is X(SLM), an epitaxial wafer is manufactured by performing the vapor phase growth with a growth condition having the growth temperature T of 1000°C or more and 1200°C or less and satisfying T<23X+885.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing an epitaxial wafer, and more particularly to a method for manufacturing an epitaxial wafer by vapor-phase growing a silicon epitaxial layer on a silicon single crystal substrate.

  As a substrate for manufacturing a semiconductor integrated circuit, a silicon wafer mainly manufactured by a CZ (Czochralski) method is used. Some of the defects in recent state-of-the-art imaging devices are considered to be caused by a trace amount of metal impurities in the device active region. Specifically, metal impurities in the wafer form deep levels, causing white defects. On the other hand, in the device process, there is an ion implantation process, and point defects occur. Point defects generated by the ion implantation react with carbon in the wafer to form a CiCs complex. Since the CiCs complex forms a level, it is expected to contribute to poor white flaws.

On the other hand, an epitaxial wafer is often used for an imaging device. Therefore, as the carbon concentration of the epitaxial layer is lower, the occurrence of white flaws can be reduced. However, the growth conditions for reducing the carbon concentration in the epitaxial layer are not clear.
Patent Document 1 discloses a method for manufacturing an epitaxial wafer having a silicon epitaxial layer having an impurity concentration equal to or lower than a target value. However, it is necessary to manufacture an epitaxial wafer in advance by using growth gases having different impurity concentrations.

By the way, to measure the carbon concentration in the wafer, an FT-IR method (Fourier Transform Infrared Spectroscopy: Fourier Transform Infrared Spectroscopy), SIMS (Secondary Ion Mass Spectroscopy: low-temperature electron beam mass spectroscopy), PL (Photoluminescence) measurement is mentioned.
The FT-IR method is a method of transmitting infrared light to a wafer and quantifying a carbon concentration from an infrared absorption peak at a position of 1106 cm ^-1 (Non-Patent Document 1). However, the analysis by the FT-IR method is based on the absorption of transmitted light, so that the entire evaluation is performed in the depth direction of the wafer, and the extreme surface layer as the device active layer cannot be evaluated.

  SIMS is capable of performing elemental analysis by irradiating a sample surface with primary ions and performing mass spectrometry on the released secondary ions. SIMS analysis can measure the distribution of carbon concentration in the depth direction, but the lower limit of detection is about 0.002 ppma, so that extremely low carbon analysis is difficult.

  In the electron beam irradiation + low-temperature PL measurement method, a point defect introduced into the wafer by electron beam irradiation reacts with carbon to form a complex of interstitial carbon and substituted carbon (CiCs complex). This is a method of quantifying the carbon concentration from the emission intensity of the complex (Non-Patent Document 2). This technique has good sensitivity and a low detection lower limit, but a CiCs complex is formed in the entire wafer depth direction, and the CiCs complex detected by the low-temperature PL method depends on the carrier diffusion depth at the time of low-temperature PL measurement. . For example, in Non-Patent Document 2, it is about 10 μm, and the carbon concentration in a shallower region cannot be measured. For example, it is not possible to evaluate a surface layer of 1 to 2 μm, which is a photodiode region of an image sensor.

  On the other hand, in the ion implantation + PL method, a point defect can be introduced only at a specific depth position to form a CiCs complex, so that the carbon concentration in the surface layer can be measured.

JP 2012-9581 A

JEITA EM-3503 Applied Physics Vol. 84, No. 11, (2015) p. 976 Japan Society of Applied Physics

  Since the influence of the difference in the growth conditions on the carbon concentration in the epitaxial layer has not been clarified, the growth conditions with the reduced carbon concentration are unknown, and an epitaxial wafer for an imaging device cannot be stably provided.

  The present invention has been made in view of the above problems, and in particular, a method capable of manufacturing an epitaxial wafer having a silicon epitaxial layer that can suppress the occurrence of white spot defects when used for manufacturing an imaging device. The purpose is to provide.

In order to achieve the above object, the present invention is a method for producing an epitaxial wafer by supplying a source gas and a carrier gas on a silicon single crystal substrate to vapor-grow a silicon epitaxial layer,
When the growth temperature of the silicon epitaxial layer is T (° C.) and the flow rate of the carrier gas during growth is X (SLM),
A method for producing an epitaxial wafer, characterized in that the growth temperature T is 1000 ° C. or more and 1200 ° C. or less and vapor phase growth is performed under a growth condition satisfying T <23X + 885.

Thus, if the vapor phase growth is performed under the growth conditions satisfying the above inequality, a silicon epitaxial layer having a low carbon concentration can be easily and stably grown. Then, by using the manufactured epitaxial wafer, it is possible to obtain an imaging device in which the occurrence of the white defect is suppressed.
Further, by setting the growth temperature to 1000 ° C. or higher, the productivity can be increased without the growth rate being excessively lowered. By setting the temperature to 1200 ° C. or lower, uniformity of the in-plane temperature distribution of the growing wafer can be easily maintained.

ここで、Ｘ：キャリアガスの空気換算流量（ＳＬＭ）、
Ｘ_０：実際に使用しているガスでの流量（ＳＬＭ）、
γ_０：流体密度（ｋｇ／ｍ^３）、Ｔ_０：使用温度（℃）、
Ｐ_０：使用圧力×９．８７（ＭＰａ）である。 Here, the air-equivalent flow rate X (SLM) of the carrier gas (also referred to as air-equivalent carrier gas flow rate) can be obtained by the following conversion formula.

Here, X: air equivalent flow rate (SLM) of the carrier gas,
X ₀ : flow rate (SLM) in the gas actually used,
γ ₀ : fluid density (kg / m ³ ), T ₀ : operating temperature (° C.),
P ₀ : Working pressure × 9.87 (MPa).

  At this time, the silicon epitaxial layer having a carbon concentration of 0.0015 ppma or less can be vapor-phase grown by performing vapor-phase growth under the above-described growth conditions.

  According to the manufacturing method of the present invention, a silicon epitaxial layer having a low carbon concentration of 0.0015 ppma or less as described above can be easily grown. The lower the carbon concentration in the silicon epitaxial layer is, the more the occurrence of white defects in the image sensor can be reduced. Therefore, the manufacturing method of the present invention makes it possible to stably supply an epitaxial wafer suitable for an image sensor.

  As described above, according to the present invention, it is possible to easily and stably grow a silicon epitaxial layer having a low carbon concentration, and to obtain an epitaxial wafer for an imaging device in which white defects are less likely to occur. it can.

5 is a graph showing the relationship between the carbon concentration in the epitaxial layer and the growth temperature for each air-equivalent carrier gas flow rate. 6 is a graph showing the relationship between the carbon concentration in the epitaxial layer and the flow rate of carrier gas in air at each growth temperature. FIG. 4 is a correlation diagram showing a relationship between a growth temperature, an air-equivalent flow rate of a carrier gas, and a white flaw level. FIG. 3 is a schematic view of a vapor phase growth apparatus that can be used in the method for manufacturing an epitaxial wafer of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings as an example of an embodiment, but the present invention is not limited to this.
First, FIG. 4 shows an example of a vapor phase growth apparatus that can be used in the method for producing an epitaxial wafer of the present invention.
The vapor phase growth apparatus 1 includes a chamber 2 for performing vapor phase growth therein, and a gas introduction pipe 3 communicating with the inside of the chamber 2 and introducing various gases G such as a source gas and a carrier gas into the chamber 2. , A gas discharge pipe 4 communicating with the inside of the chamber 2 and discharging gas from the inside of the chamber 2, and a susceptor 5 disposed in the chamber 2 and mounting a wafer W thereon.

  In addition, the vapor phase growth apparatus 1 appropriately includes a susceptor rotation mechanism 6 for rotating the susceptor 5, a heating unit 7 for heating the wafer W, and the like. Further, the chamber 2 is usually composed of a plurality of members. For example, it comprises a chamber upper member 8 and a chamber lower member 9 made of transparent quartz. The gas inlet 3 is provided with a gas inlet 10 and the gas outlet 4 is provided with a gas outlet 11. The susceptor 5 is supported by a main column 13 having a shaft 12 and a sub column 14. The susceptor 5 has a counterbore 15 on which the wafer W is placed.

Next, a method for manufacturing an epitaxial wafer of the present invention will be described.
First, a silicon single crystal substrate is prepared. As this silicon single crystal substrate, one manufactured by, for example, the CZ method can be prepared. 2. Description of the Related Art An epitaxial wafer, particularly for an image sensor, is manufactured using a CZ silicon single crystal substrate.
Note that the method is not limited to the CZ method, and can be prepared by another method such as an FZ (Floating Zone) method.

Next, using a vapor phase growth apparatus 1 as shown in FIG. 4, a silicon epitaxial layer is vapor-phase grown on a silicon single crystal substrate (wafer W).
In this epitaxial growth step, hydrogen is supplied as a carrier gas through the gas introduction pipe 3, and the temperature is raised to the growth temperature of the silicon epitaxial layer in the hydrogen atmosphere. Thereafter, a source gas such as TCS (trichlorosilane) is supplied together with a carrier gas to grow the silicon epitaxial layer for a predetermined time.
In addition, in addition to trichlorosilane, monosilane, monochlorosilane, dichlorosilane, carbon tetrachloride, or the like can be used as a source gas. In addition to the source gas, a dopant gas such as diborane (B ₂ H ₆ ) or phosphine (PH ₃ ) can be supplied together with the hydrogen gas.

  After the epitaxial layer was thus vapor-grown, the supply of the source gas and the dopant gas was stopped, and the temperature in the reaction vessel was lowered while maintaining the atmosphere of hydrogen as the carrier gas. Take out the epitaxial wafer.

  Note that various growth conditions such as a growth temperature, a growth time, and a carrier gas flow rate in the epitaxial growth step can be appropriately determined in consideration of a desired thickness of the silicon epitaxial layer. However, in the present invention, the following conditions are satisfied for the growth temperature and the carrier gas flow rate.

  First, the growth temperature T (° C.) of the silicon epitaxial layer is 1000 ° C. or more and 1200 ° C. or less. If the growth temperature is lower than 1000 ° C., the growth rate is reduced and the productivity is deteriorated. On the other hand, if the temperature exceeds 1200 ° C., it becomes difficult to maintain the uniformity of the in-plane temperature distribution of the growing wafer. With such a growth temperature, an epitaxial wafer having a uniform thickness and characteristics of a silicon epitaxial layer in a plane can be manufactured with high productivity.

Further, as the relationship between the growth temperature T and the flow rate of the carrier gas, more specifically, the relationship between the growth temperature T (° C.) and the air-equivalent flow rate X (SLM) of the growing carrier gas, an inequality of T <23X + 885 holds. To do.
That is, as the growth conditions, the growth temperature and the flow rate of the carrier gas are set such that the above inequality holds within the range of the growth temperature, and the epitaxial growth step is performed based on the set conditions.

  According to such a manufacturing method, a low-carbon-concentration silicon epitaxial layer can be easily and stably grown on a silicon single crystal substrate. In particular, a silicon epitaxial layer having a low carbon concentration of 0.0015 ppma or less can be grown. Further, since an epitaxial wafer having such a silicon epitaxial layer with a low carbon concentration can be supplied stably with high productivity, white defect defects may occur when an imaging device is manufactured using the epitaxial wafer. Can be stably supplied.

Here, a description will be given of how the inventors have found the above inequality and experimental results.
First, an epitaxial wafer having a diameter of 300 mm was prepared by epitaxially growing a silicon epitaxial layer on a prepared silicon single crystal substrate under a growth condition in which the growth temperature was 1040 to 1180 ° C. and the air flow rate of the carrier gas was changed to 3 to 13 SLM. The thickness of the epitaxial layer is 9 μm. In the fabrication, the vapor phase growth apparatus shown in FIG. 4 was used, and TCS was used as a source gas, and hydrogen gas was used as a carrier gas.

After He ions were implanted into these epitaxial wafers (the range of ion implantation was about 0.5 μm), the emission intensity of CiCs was measured by low-temperature PL measurement to estimate the carbon concentration.
Furthermore, an image sensor was manufactured using epitaxial wafers having different carbon concentrations in the silicon epitaxial layer, and white defect defects were evaluated.

As a result, FIG. 1 shows the relationship between the carbon concentration in the epitaxial layer and the growth temperature for each flow rate of air-equivalent carrier gas. The case where the air-equivalent flow rate of the carrier gas is 5, 8, and 10 SLM is summarized as an example. FIG. 2 shows the relationship between the carbon concentration in the epitaxial layer and the air-equivalent flow rate of the carrier gas at each growth temperature. The case where the growth temperature is 1090, 1130, or 1170 ° C. is summarized as an example.
The marks in FIGS. 1 and 2 and FIG. 3 described later represent white defect levels. ○ is good, X is bad, and △ is intermediate. ○, ×, and Δ are indices relating to the number of white defect defects in all chips. When ○ is set to “1”, × is equal to or more than “3.0”, and △ is larger than 1.0 and 3 0.0.

From these results, it is preferable that the carbon concentration in the silicon epitaxial layer is particularly 0.0015 ppma or less in order to prevent the white flaw level from becoming defective (that is, to make it good or intermediate). I understood.
Therefore, based on the results of FIGS. 1 and 2, the conditions under which the white flaw level does not become defective (especially, the conditions under which the carbon concentration in the epitaxial layer becomes 0.0015 ppma or less) were examined. Specifically, first, epitaxial growth is performed under growth conditions in which the growth temperature is 1030 to 1170 ° C., and the air-equivalent flow rate of the carrier gas is changed to 3 to 13 SLM. The scratch level was evaluated.

FIG. 3 shows the relationship among the growth temperature, the air-equivalent flow rate of the carrier gas, and the level of white spots (or carbon concentration). From the relationship between the white flaw level, the growth temperature, and the carrier gas flow rate thus obtained, the growth condition of growth temperature T (° C.) <23 × growing carrier gas flow rate (air conversion flow rate) X (SLM) +885 is satisfied. In the region (the shaded region on the right side of the straight line of T = 23X + 885 in FIG. 3), it was found that the white flaw level was reliably improved. Furthermore, it was found that in the region satisfying the inequality, the carbon concentration in the epitaxial layer was 0.0015 ppma or less.
Note that FIG. 3 shows the evaluation results when the growth temperature is in the range of 1030 to 1170 ° C. as described above. Similarly, at around 1000 ° C. and around 1200 ° C., the straight line of T = 23X + 885 is similarly obtained. It has been confirmed that the white scratch level is good in the region on the right side of the figure.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
(Example 1-2, Comparative Example 1)
A silicon single crystal wafer having a diameter of 300 mm was prepared, and the vapor phase growth apparatus shown in FIG. 4 was used (source gas: TCS, carrier gas: hydrogen), the growth temperature was 1050 ° C., and the carrier gas air equivalent flow rate was 2 SLM (Comparative Example 1). ), 8 SLM (Example 1), and 18 SLM (Example 2), and a 10 μm thick epitaxial layer was grown. An image sensor was manufactured using these epitaxial wafers, and white defect defects were evaluated.
After He ions were implanted into the epitaxial wafer grown under the same conditions, the emission intensity of CiCs was measured by low-temperature PL measurement to estimate the carbon concentration.

  As a result, when the carrier gas air equivalent flow rate was 2 SLM, the carbon concentration was 0.006 ppma, and the white flaw level was poor. On the other hand, when the carrier gas air equivalent flow rates were 8 SLM and 18 SLM, the carbon concentration was 0.0010 ppma and 0.00025 ppma, respectively, and the white flaw level was good.

  When the growth temperature and the carrier gas air-equivalent flow rate are substituted for the inequality in the present invention, when the carrier gas air-equivalent flow rate is 2 SLM, “growth temperature 1050 <931” is satisfied, and the inequality in the present invention is not satisfied. Thus, the white scratch level becomes poor. On the other hand, when the carrier gas air-equivalent flow rates are 8 SLM and 18 SLM, “growth temperature 1050 <1069” and “growth temperature 1050 <1299” are satisfied, respectively, and the condition of the inequality expression in the present invention is satisfied, and the white spot level is good.

(Example 3, Comparative Example 2-3)
A silicon single crystal wafer having a diameter of 300 mm was prepared and the vapor phase growth apparatus shown in FIG. 4 was used (source gas: TCS, carrier gas: hydrogen), the growth temperature was 1100 ° C., and the carrier gas air conversion flow rate was 2 SLM (Comparative Example 2). ), 8 SLM (Comparative Example 3), and 18 SLM (Example 3), and a 10 μm thick epitaxial layer was grown. An image sensor was manufactured using these epitaxial wafers, and white defect defects were evaluated.
After He ions were implanted into the epitaxial wafer grown under the same conditions, the emission intensity of CiCs was measured by low-temperature PL measurement to estimate the carbon concentration.

  As a result, the carbon concentration was 0.01 ppma when the carrier gas air-equivalent flow rate was 2 SLM, and 0.0016 ppma when the carrier gas air-equivalent flow rate was 8 SLM. On the other hand, when the carrier gas air equivalent flow rate was 18 SLM, the carbon concentration was 0.00047 ppma or less, and the white flaw level was good.

  When the respective growth temperatures and the carrier gas air-equivalent flow rates are substituted into the inequality in the present invention, when the carrier gas air-equivalent flow rates are 2 SLM and 8 SLM, “growth temperature 1100 <931” and “growth temperature 1100 <1069” are obtained. Does not satisfy the condition of the inequality in, and the white flaw level becomes poor. On the other hand, when the carrier gas air-equivalent flow rate is 18 SLM, “growth temperature 1050 <1299” is satisfied, which satisfies the inequality condition of the present invention, and the white flaws are good.

  Table 1 below summarizes the growth conditions and the evaluation results of the white flaw level in Example 1-3 and Comparative Example 1-3. Even at the same growth temperature, the evaluation of the white flaw level changes depending on the carrier gas air-equivalent flow rate. Further, even at the same carrier gas flow rate, the evaluation of the white flaw level changes depending on the growth temperature.

  By setting the temperature range of the growth temperature in the present invention, an epitaxial wafer having high productivity and uniformity can be obtained. In addition, by setting the growth temperature and the carrier gas air-equivalent flow rate so as to satisfy the inequality in the present invention and performing epitaxial growth, the epitaxial growth is excellent for an imaging device having a low carbon concentration and capable of reducing the occurrence of white spot defects. It is possible to easily and stably supply the wafer.

  As described above, it was confirmed that, when the inequality in the present invention was satisfied, the carbon concentration was reduced and the white spot level was improved. Therefore, as a growth condition when a silicon epitaxial layer is vapor-phase grown on a silicon single crystal substrate, a condition that satisfies the relationship of the inequality of the growth temperature and the carrier gas flow rate in air (and the temperature range of the growth temperature) in the present invention is set. If a vapor phase growth is performed under the set conditions, the concentration of carbon in the epitaxial layer is low, and the occurrence of white defects is suppressed, and a silicon epitaxial wafer useful for an imaging device can be easily and stably obtained. be able to.

  Note that the present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the claims of the present invention, and any device having the same function and effect can be realized by the present invention. It is included in the technical scope of the invention.

1 ... vapor phase growth apparatus, 2 ... chamber, 3 ... gas introduction pipe,
4 ... gas exhaust pipe, 5 ... susceptor, 6 ... susceptor rotation mechanism,
7: heating means, 8: upper chamber member,
9: lower chamber member, 10: gas inlet, 11: gas outlet,
12: shaft, 13: main support, 14: sub-support, 15: counterbore W: wafer, G: gas.

Claims (2)

A method for producing an epitaxial wafer by supplying a source gas and a carrier gas on a silicon single crystal substrate to vapor-grow a silicon epitaxial layer,
When the growth temperature of the silicon epitaxial layer is T (° C.) and the flow rate of the carrier gas during growth is X (SLM),
A method for manufacturing an epitaxial wafer, wherein the growth temperature T is 1000 ° C. or more and 1200 ° C. or less, and a vapor phase growth is performed under a growth condition satisfying T <23X + 885. 2. The method according to claim 1, wherein the silicon epitaxial layer having a carbon concentration of 0.0015 ppma or less is vapor-phase grown by performing vapor-phase growth under the growth condition.

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