JP2011054879A - Epitaxial substrate for back-illuminated image sensor and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epitaxial substrate for a back-illuminated image sensor and a manufacturing method thereof, capable of suppressing metal contaminations and reducing occurrence of a white spot defect of the image sensor, by maintaining a sufficient gettering performance in a device process. <P>SOLUTION: The method for manufacturing the epitaxial substrate includes steps of forming a gettering sink immediately below a surface of a carbon-added silicon substrate of 5.0×10<SP>15</SP>to 10×10<SP>16</SP>atom/cm<SP>3</SP>in carbon concentration, forming a first epitaxial layer on the surface of the carbon-added silicon substrate, and forming a second epitaxial layer on the first epitaxial layer. In the step of forming the gettering sink, the carbon-added silicon substrate is subjected to long-time heat treatment at 600-1150°C to form a carbon-oxygen-based precipitate region. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a back-illuminated image sensor epitaxial substrate and a manufacturing method thereof, and more particularly to a back-illuminated image sensor epitaxial substrate used in a digital video camera, a mobile phone, and the like and a manufacturing method thereof.

  The back-illuminated image sensor has a wiring layer, etc., that is placed below the sensor unit, so that light from outside can be directly taken into the sensor, and clearer images and videos can be taken even in dark places. In recent years, it has been widely used. When manufacturing such a back-illuminated image sensor, a semiconductor may be mixed with metal as an impurity. The metal mixed in the semiconductor substrate increases the dark current of the image sensor and causes a defect called a white defect.

  The factor that metal is mixed into the semiconductor substrate is in the process of forming the semiconductor epitaxial substrate and the process of forming the image sensor. Metal contamination in the former process for forming a semiconductor epitaxial substrate is considered to be caused by heavy metal particles generated by the metal corrosion of the piping material due to the use of heavy metal particles from the components of the epitaxial growth furnace or chlorine-based gas. It is done. In recent years, these metal contaminations have been improved by efforts such as replacing the components of the epitaxial growth furnace with corrosion-resistant materials, but it is difficult to completely avoid metal contamination in the process of forming a semiconductor epitaxial substrate. It is. On the other hand, in the latter image sensor formation process, there is a concern about heavy metal contamination of the semiconductor substrate during each process such as ion implantation, diffusion, and oxidation heat treatment.

  Therefore, conventionally, a gettering sink for capturing a metal is formed on a semiconductor substrate, or a substrate having a high metal capture capability (gettering capability) such as a high-concentration boron substrate is used. The metal contamination was avoided.

  Here, in order to form a gettering sink on a semiconductor substrate, an intrinsic gettering (IG) method in which oxygen precipitates are formed inside the semiconductor substrate, or an excinx that forms a gettering sink on the back surface of the semiconductor substrate. The trick gettering (EG) method is generally used. However, when the EG method is used, since damage such as backside damage is formed on the back surface, particles are generated from the back surface during the process of forming the semiconductor epitaxial substrate or the image sensor, which causes further defects in the image sensor. There was a problem of forming.

  Patent Document 1 discloses a technique for forming a gettering sink by forming a carbon implantation region in a semiconductor substrate using a carbon ion implantation method, which is one of the IG methods, and then performing a heat treatment in an image sensor formation process. It is disclosed.

  However, this technique forms a gettering sink by heat treatment in the image sensor formation process, and there is a problem that the gettering capability in this process is not sufficient. In Patent Document 1, when a high-temperature heat treatment is performed on a semiconductor substrate in which a carbon implantation region is formed, crystal defects (such as crystal lattice strain) formed by carbon implantation are alleviated and the function as a gettering sink is reduced. There is also a problem that an upper limit is set for the processing temperature.

JP 2002-353434 A

  The object of the present invention is to solve the above-mentioned problems and maintain sufficient gettering capability during the device process, thereby suppressing metal contamination and reducing the occurrence of white defects in the image sensor. An object of the present invention is to provide an epitaxial substrate for a type image sensor and a manufacturing method thereof.

In order to achieve the above object, the gist of the present invention is as follows.
(1) forming a gettering sink immediately below the surface of the carbon-added silicon substrate having a carbon concentration in the range of 5.0 × 10 ¹⁵ to 10 × 10 ¹⁶ atom / cm ³ ; A step of forming a first epitaxial layer; and a step of forming a second epitaxial layer on the first epitaxial layer, wherein the step of forming the gettering sink comprises forming 600 to 1150 on the carbon-added silicon substrate. A method of manufacturing an epitaxial substrate for a backside illuminated image sensor, comprising forming a carbon / oxygen-based precipitate region by performing a heat treatment for a long time at a temperature of ° C.

  (2) The long-time heat treatment is performed by heating the carbon-added silicon substrate at a rate of 0.5 to 3 ° C./min to 600 ° C. to 900 ° C. and maintaining this state for 20 minutes to 4 hours, The manufacturing method of the epitaxial substrate for backside illumination type image sensors as described in said (1) including high temperature heat processing which heats to 1000-1150 degreeC at the speed of -5 degreeC / min, and hold | maintains this state for 0.5 to 4 hours.

  (3) The step (1) or (2) further comprising a step of polishing and cleaning the carbon-added silicon substrate after the step of forming the gettering sink and before forming the first epitaxial layer. A manufacturing method of an epitaxial substrate for back irradiation type image sensors given in 2.

(4) A back-illuminated image sensor epitaxial substrate manufactured by the method for manufacturing a back-illuminated image sensor epitaxial substrate according to (1), (2) or (3) above, wherein the carbon / oxygen-based The carbon concentration in the precipitate region is in the range of 5.0 × 10 ¹⁵ to 10 × 10 ¹⁶ atom / cm ³ , and the oxygen concentration is in the range of 1.0 × 10 ^{18 to} 1.0 × 10 ¹⁹ atom / cm ^3. An epitaxial substrate for a back-illuminated image sensor.

(5) After the step of forming the gettering sink and before forming the first epitaxial layer, the density of carbon / oxygen-based precipitates in the carbon / oxygen-based precipitate region is 1 × 10 ⁵ The epitaxial substrate for backside illumination type image sensor according to (4) above, which is ˜1 × 10 ⁷ / cm ² .

(6) The back-illuminated image sensor epitaxial substrate according to (4) or (5), wherein the impurity concentration of the first epitaxial layer is in the range of 1 × 10 ¹⁶ to 1 × 10 ¹⁹ atom / cm ³ .

(7) The back-illuminated image sensor according to (4), (5), or (6), wherein the impurity concentration of the second epitaxial layer is in the range of 1 × 10 ¹⁴ to 1 × 10 ¹⁶ atom / cm ^3. Epitaxial substrate.

  According to the present invention, the carbon-added silicon substrate is subjected to heat treatment for a long time, so that sufficient gettering ability is maintained during the device process, thereby suppressing metal contamination and generating white defects in the image sensor. It is possible to provide a back-illuminated image sensor epitaxial substrate that can be reduced and a method for manufacturing the epitaxial substrate.

It is typical sectional drawing for demonstrating the manufacturing method of the epitaxial substrate for backside illumination type image sensors according to this invention.

  Next, an embodiment of an epitaxial substrate for backside illuminated image sensor and a method for manufacturing the same according to the present invention will be described with reference to the drawings. 1A to 1C are schematic cross-sectional views for explaining a method for manufacturing a backside illuminated image sensor according to the present invention. FIG. 1 shows the thickness direction exaggerated for convenience of explanation.

  As shown in FIGS. 1A to 1C, the back-illuminated image sensor epitaxial substrate 100 according to the present invention is provided with a carbon-added silicon substrate 1 (FIG. 1A), and gettering is performed immediately below the surface. The step of forming the sink 2 (FIG. 1B), the step of forming the first epitaxial layer 3 on the surface of the carbon-added silicon substrate 1, and the second epitaxial layer 4 on the first epitaxial layer 3 The step of forming the gettering sink 2 (FIG. 1 (b)) includes the step of forming the gettering sink 2 (FIG. 1 (b)) by subjecting the carbon-added silicon substrate 1 to heat treatment for a long time. Forming a system precipitate region, and having such a configuration maintains sufficient gettering ability during the device process, thereby suppressing metal contamination and reducing white defects in the image sensor. Generation can be reduced Epitaxial substrate and a manufacturing method thereof for a surface-illuminated image sensor is capable of providing.

  Here, the carbon-oxygen-based precipitate means a precipitate that is a carbon-oxygen complex (cluster) containing carbon, and the device process is an epitaxial layer growth in a semiconductor epitaxial substrate forming process. It means a process and a process for forming an image sensor.

The carbon concentration of the carbon-added silicon substrate 1 is in the range of 5.0 × 10 ¹⁵ to 10 × 10 ¹⁶ atom / cm ³ . If the carbon concentration is less than 5.0 × 10 ¹⁵ atom / cm ³ , carbon / oxygen-based precipitates acting as gettering sinks 2 cannot be sufficiently formed, while the carbon concentration is 10 × 10 ¹⁶ atom / cm ^3. This is because the size per carbon / oxygen-based precipitate is less than 50 nm, and sufficient gettering ability cannot be maintained. The carbon-added silicon substrate 1 can contain carbon in a solid solution state. Thereby, carbon can be introduced into the silicon lattice in a form that replaces silicon. Since the atomic radius of carbon is shorter than that of silicon atoms, when carbon is coordinated at the substitution position, the stress field of the crystal becomes a compressive stress field, and interstitial oxygen and impurities are easily trapped in the compressive stress field. When a predetermined heat treatment is performed starting from this substitutional position carbon, precipitates with oxygen accompanied by dislocations are easily expressed at high density, and a high gettering effect can be imparted to the carbon-added silicon substrate 1. is there.

  The long-time heat treatment is in the range of 600 to 1150 ° C. In particular, the long-time heat treatment is performed by heating the carbon-added silicon substrate 1 to 600 to 900 ° C. at a rate of 0.5 to 3 ° C./min and maintaining this state for 20 minutes to 4 hours, and thereafter 3 to 5 ° C. It is preferable to include a high-temperature heat treatment that heats to 1000 to 1150 ° C. at a rate of / min and maintains this state for 0.5 to 4 hours. By this treatment, the carbon / oxygen-based precipitate is deposited as described above, and a carbon / oxygen-based precipitate region is formed on the carbon-added silicon substrate 1.

The carbon concentration of the carbon / oxygen-based precipitate region thus formed is in the range of 5.0 × 10 ¹⁵ to 10 × 10 ¹⁶ atom / cm ³ , and the oxygen concentration is 1.0 × 10 ^{18 to} 1.0 × 10 ¹⁹ atom. The range is / cm ³ . If the carbon concentration is less than 5.0 × 10 ¹⁵ atom / cm ³ , the precipitation of oxygen is not promoted and the precipitation density of the carbon / oxygen-based precipitate is lowered, and there is a possibility that sufficient gettering ability cannot be obtained. On the other hand, if it exceeds 10 × 10 ¹⁶ atom / cm ³ , the density of carbon / oxygen-based precipitates becomes too high, and the size of carbon-oxygen-based precipitates becomes extremely small and sufficient strain effects cannot be obtained. There is a risk that ability will decline. In addition, if the oxygen concentration is less than 1.0 × 10 ¹⁸ atom / cm ³ , the precipitation of oxygen is suppressed, and the precipitation density of carbon / oxygen-based precipitates is lowered, so that sufficient gettering ability may not be obtained. On the other hand, when the oxygen concentration exceeds 1.0 × 10 ¹⁹ atom / cm ³ , the density of carbon / oxygen-based precipitates becomes too high, the size of the carbon / oxygen-based precipitates increases, and secondary dislocations enter the epitaxial layer. This is because there is a risk of extension.

The density of carbon / oxygen-based precipitates in the carbon / oxygen-based precipitate region is preferably 1 × 10 ⁵ to 1 × 10 ⁷ / cm ² . This is because increasing the oxygen precipitation density is effective in improving the gettering ability. However, if the density of the oxygen precipitates exceeds 1 × 10 ⁷ / cm ² , the size of the oxygen precipitates tends to decrease, and the strain energy may be relaxed and the gettering ability may be reduced.

  In addition, after the step of forming the gettering sink (FIG. 1B) and before the step of forming the first epitaxial layer (FIG. 1C), the carbon-added silicon substrate 1 is polished and polished. Preferably, the method further comprises a washing step. In addition, as a washing | cleaning method, the RCA washing | cleaning etc. which combined SC-1 and SC-2 are mentioned.

The impurity concentration of the first epitaxial layer is preferably in the range of 1 × 10 ¹⁶ to 1 × 10 ¹⁹ atom / cm ³ . If the impurity concentration is less than 1 × 10 ¹⁶ atom / cm ³ , the resistance may be too high, while if the impurity concentration exceeds 1 × 10 ¹⁹ atom / cm ³ , lattice distortion occurs and misfit dislocations occur. This is because it may occur. Moreover, as an additive element, it is preferable to use B, P, etc., for example.

The impurity concentration of the second epitaxial layer is preferably in the range of 1 × 10 ¹⁴ to 1 × 10 ¹⁶ atom / cm ³ . If the impurity concentration is less than 1 × 10 ¹⁴ atom / cm ³ , when the PN junction is formed, the space charge layer may come into contact with the first epitaxial layer and adversely affect the electrical characteristics, while the impurity concentration is 1 × This is because if it exceeds 10 ¹⁶ atom / cm ³ , misfoot dislocation may occur at the interface between the first epitaxial layer and the second epitaxial layer. Moreover, as an additive element, it is preferable to use B, P, etc., for example.

  FIG. 1 shows examples of typical embodiments, and the present invention is not limited to these embodiments.

  Next, an epitaxial substrate for backside illuminated image sensor according to the present invention was prepared as a sample and its performance was evaluated, which will be described below.

Example 1
In Example 1, as shown in FIG. 1, a carbon-added silicon substrate (carbon concentration: 1 × 10 ¹⁶ atom / cm ³ ) was heated to 900 ° C. at a rate of 1 ° C./minute for a long time. Is kept for 1 hour and then heat treated at a low temperature, then heated to 1000 ° C. at a rate of 3 ° C./minute, and this state is kept for 1 hour) to give a carbon / oxygen-based precipitate region (carbon concentration: 1 × 10 ¹⁶ atom / cm ³ , oxygen concentration: 15 × 10 ¹⁷ atom / cm ³ , carbon / oxygen-based precipitate density: 1 × 10 ⁶ / cm ² ) to form a getter directly under the surface of the carbon-added silicon substrate After forming the ring sink and polishing and cleaning the carbon-added silicon substrate, the first epitaxial layer (B-added, B concentration: 1 × 10 ¹⁶ atom / cm ³ ) and the second are formed on the surface of the carbon-added silicon substrate. Epitaxial layers (B addition, B concentration: 1 × 10 ¹⁵ atom / cm ³ ) were formed in order, and an epitaxial substrate for a back-illuminated image sensor as a sample was obtained. .

(Example 2)
In the above long-time heat treatment, the carbon-added silicon substrate is heated to 850 ° C. at a rate of 3 ° C./min, this state is maintained for 2 hours, low-temperature heat treatment is performed, and then heated to 1150 ° C. at a rate of 5 ° C./min. Then, a back-illuminated image sensor wafer as a sample was obtained by the same process as in Example 1 except that this state was maintained for 2 hours.

(Example 3)
A back-illuminated image sensor wafer serving as a sample was obtained by the same process as in Example 1 except that the carbon-added silicon substrate was not polished and washed.

Example 4
A back-illuminated image sensor wafer serving as a sample was obtained by the same process as in Example 1 except that the first epitaxial layer with P addition and P concentration: 1 × 10 ¹⁶ atom / cm ³ was formed.

(Example 5)
A back-illuminated image sensor wafer serving as a sample was obtained by the same process as in Example 1 except that the second epitaxial layer with P addition and P concentration: 1 × 10 ¹⁵ atom / cm ³ was formed.

(Comparative Example 1)
A back-illuminated image sensor wafer serving as a sample was obtained by the same process as in Example 1 except that a carbon-added silicon substrate having a carbon concentration of 1 × 10 ¹⁵ atom / cm ³ was used.

(Comparative Example 2)
A back-illuminated image sensor wafer serving as a sample was obtained by the same process as in Example 1 except that a non-doped carbon-added silicon substrate was used.

(Comparative Example 3)
A back-illuminated image sensor wafer serving as a sample was obtained by the same process as in Example 1 except that the heat treatment was not performed for a long time.

(Evaluation)
For each of the samples prepared in Examples 1 to 5 and Comparative Examples 1 to 3, the carbon concentration in the carbon / oxygen-based precipitate region, the oxygen concentration, and the density of the carbon / oxygen-based precipitate were determined by infrared absorption spectroscopy (FT- IR: Furie infrared spectroscopy, transform coefficients old ASTM: f _c = 4.81) results obtained by, as well as Table 1 shows the results of evaluating the metal contamination and white defects. The evaluation method is as follows.

(Metal contamination)
The obtained sample was contaminated with nickel (1.0 × 10 ¹² atoms / cm ² ) by spin coating contamination method, and then heat-treated at 900 ° C. for 1 hour, and then the sample surface was selectively etched. Thus, the defect density (pieces / cm ² ) on the sample surface was measured and evaluated according to the following criteria.
No metal contamination: Less than 0 / cm ² Metal contamination: 10 / cm ² or more

(White scratch defect)
Using the obtained sample, a back-illuminated image sensor was manufactured, and then, for this back-illuminated image sensor, the dark current leakage of the photodiode was measured using a semiconductor parameter analyzer, and pixel data (white defect) The number of white scratch defects per unit area (1 cm ² ) was measured.

  From the result of Table 1, Examples 1-5 can suppress generation | occurrence | production of metal contamination and a white-scratch defect compared with Comparative Examples 1-3, and maintain sufficient gettering capability during a device process. Recognize.

  According to the present invention, the carbon-added silicon substrate is subjected to heat treatment for a long time, so that sufficient gettering ability is maintained during the device process, thereby suppressing metal contamination and generating white defects in the image sensor. It is possible to provide a back-illuminated image sensor epitaxial substrate that can be reduced and a method for manufacturing the epitaxial substrate.

DESCRIPTION OF SYMBOLS 1 Carbon addition silicon substrate 2 Gettering sink 3 1st epitaxial layer 4 2nd epitaxial layer 100 Epitaxial substrate for back irradiation type image sensors

Claims (7)

Forming a gettering sink directly under the surface of the carbon-added silicon substrate having a carbon concentration in the range of 5.0 × 10 ¹⁵ to 10 × 10 ¹⁶ atom / cm ³ ;
Forming a first epitaxial layer on the surface of the carbon-added silicon substrate;
Forming a second epitaxial layer on the first epitaxial layer,
The step of forming the gettering sink includes forming a carbon / oxygen-based precipitate region by subjecting the carbon-added silicon substrate to heat treatment at a temperature of 600 to 1150 ° C. for a long time. A method of manufacturing an epitaxial substrate for a backside illuminated image sensor.   In the long-time heat treatment, the carbon-added silicon substrate is heated to 600 to 900 ° C. at a rate of 0.5 to 3 ° C./min, and this state is maintained for 20 minutes to 4 hours, and then 3 to 5 ° C. / The method for producing an epitaxial substrate for a backside illuminated image sensor according to claim 1, further comprising a high temperature heat treatment in which heating is performed at a rate of minutes to 1000 to 1150 ° C. and this state is maintained for 0.5 to 4 hours.   3. The backside illumination type according to claim 1, further comprising a step of polishing and cleaning the carbon-added silicon substrate after the step of forming the gettering sink and before forming the first epitaxial layer. Manufacturing method of epitaxial substrate for image sensor. A backside illuminated image sensor epitaxial substrate manufactured by the method for manufacturing a backside illuminated image sensor epitaxial substrate according to claim 1, 2, or 3,
The carbon concentration in the carbon / oxygen-based precipitate region is in the range of 5.0 × 10 ¹⁵ to 10 × 10 ¹⁶ atom / cm ³ , and the oxygen concentration is in the range of 1.0 × 10 ^{18 to} 1.0 × 10 ¹⁹ atom / cm ³ . An epitaxial substrate for a backside illuminated image sensor, characterized in that: After the step of forming the gettering sink and before forming the first epitaxial layer, the density of the carbon / oxygen-based precipitate in the carbon / oxygen-based precipitate region is 1 × 10 ⁵ to 1 × The epitaxial substrate for backside illumination type image sensor according to claim 4, which is 10 ⁷ / cm ² . 6. The epitaxial substrate for a backside illuminated image sensor according to claim 4, wherein the impurity concentration of the first epitaxial layer is in the range of 1 × 10 ¹⁶ to 1 × 10 ¹⁹ atom / cm ³ . 7. The back-illuminated image sensor epitaxial substrate according to claim 4, wherein an impurity concentration of the second epitaxial layer is in a range of 1 × 10 ¹⁴ to 1 × 10 ¹⁶ atom / cm ³ .

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