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Patent Issued for Semiconductor Device Provided with Photodiode, Manufacturing Method Thereof, and Optical Disc Device

August 27, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Yumoto, Hiroshi (Kagoshima, JP); Yoneda, Shuji (Kagoshima, JP); Mukai, Tomokazu (Kagoshima, JP); Takeuchi, Katsuhiko (Kanagawa, JP), filed on November 30, 2009, was published online on August 12, 2014.

The patent's assignee for patent number 8803272 is Sony Corporation (Tokyo, JP).

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to techniques of a semiconductor device provided with a photodiode, a manufacturing method thereof, and an optical disc device.

"In an optical disc device, a photodetector IC that receives light reflected from an optical disc and converts the light to an electric signal has been used. The photodetector IC is a semiconductor device including a photodiode, which is a light receiving element, and a semiconductor integrated circuit, such as a bipolar integrated circuit and a MOS (Metal Oxide Semiconductor) integrated circuit formed of transistors and the like, all of which are formed on the same substrate.

"In the semiconductor device including a photodiode and a semiconductor integrated circuit as above, incident light is converted to a current by the photodiode and the current is further converted to a voltage, and a predetermined processing is applied to the voltage to output a signal.

"FIG. 13 is a schematic cross section of a semiconductor device 100 in the related art including a photodiode and a semiconductor integrated circuit. The semiconductor device 100 includes a photodiode 101 and a circuit region having an NPN-type bipolar transistor 102 and so forth.

"To be more concrete, the semiconductor device 100 includes a P-type semiconductor substrate 110 and a heavily doped P-type semiconductor layer 111 is formed thereon, on which is further formed a lightly doped P-type epitaxial layer 112, which is a semiconductor layer having a lower impurity concentration than the heavily doped P-type semiconductor layer 111. Further, an N-type epitaxial layer 113 and a heavily doped N-type diffusion layer 114 are sequentially formed on the lightly doped P-type epitaxial layer 112 in a region of the photodiode 101. The heavily doped N-type diffusion layer 114 will form a charge extraction region to extract charges generated in the photodiode 101. It also plays a role of enhancing a frequency characteristic by lowering resistance of the cathode region in the photodiode 101. In addition, a heavily doped P-type diffusion layer 115 is formed adjacently to the heavily doped N-type diffusion layer 114 on the lightly doped P-type epitaxial layer 112. A lightly doped P-type diffusion layer 116 is formed adjacently beneath the heavily doped P-type diffusion layer 115.

"According to the structure in the related art as above, because not only the heavily doped N-type diffusion layer 114 but also the N-type epitaxial layer 113 is a cathode region in the region of the photodiode 101, an electric field is not applied to the vicinity of the PN junction sufficiently. Accordingly, a depletion layer on the bottom surface side does not extend sufficiently, which makes a parasitic capacitance larger. In addition, because the heavily doped N-type diffusion layer 114 in the cathode region and the heavily doped P-type diffusion layer 115 that will form an anode extraction region are joined directly, a parasitic capacitance is large.

"Consequently, a parasitic capacitance of the entire photodiode 101 becomes larger, which makes it difficult to make the photodiode 101 faster.

"To eliminate such an inconvenience, there has been proposed a semiconductor device that reduces a parasitic capacitance by extending the depletion layer in the anode region by changing an N-type epitaxial layer in the photodiode region to a lightly doped P-type semiconductor layer by means of ion implantation as described, for example, in JP-A-2007-317767. Also, there has been proposed a semiconductor device in which a photodiode is formed directly on a P-type semiconductor layer as described, for example, in JP-A-2006-210494."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "The technique described in JP-A-2007-317767, however, has a problem as follows. That is, in a case where a lightly doped P-type semiconductor layer is formed by means of ion implantation, it becomes difficult to control an impurity concentration and a depletion layer is not formed in a stable manner. A parasitic capacitance therefore becomes unstable, which causes the yields to decrease.

"The technique described in JP-A-2006-210494 has a certain effect in reducing a parasitic capacitance in comparison with the configuration of FIG. 13 in the related art. However, a reduction of the parasitic capacitance is insufficiently small in extent and no consideration is given to a parasitic resistance. Because a photodiode becomes faster in inverse proportion to the product of a parasitic capacitance and a parasitic resistance, there is a problem that the effect of reducing a CR time constant is too small to make the photodiode sufficiently faster.

"Thus, it is desirable to provide a semiconductor device capable of making a photodiode faster by reducing markedly a CR time constant determined by a parasitic capacitance and a parasitic resistance, a manufacturing method thereof, and an optical disc device.

"According to an embodiment of the present invention, there is provided a semiconductor device including: a P-type semiconductor substrate; a first P-type semiconductor layer formed on the P-type semiconductor substrate; a second P-type semiconductor layer formed on the first P-type semiconductor layer and having a lower P-type impurity concentration than the first P-type semiconductor layer; an N-type semiconductor layer, which will form a cathode region, formed on the second P-type semiconductor layer; a first P-type diffusion layer formed by diffusing a P-type impurity in a partial region of the second P-type semiconductor layer; a second P-type diffusion layer formed by diffusing a P-type impurity in the second P-type semiconductor layer so as to be present adjacently beneath the first P-type diffusion layer at a lower P-type impurity concentration than the first P-type diffusion layer; and a photodiode formed in such a manner that the N-type semiconductor layer and the first P-type diffusion layer are isolated from each other.

"The semiconductor device according to the embodiment of the present invention may be configured in such a manner that:

"(1) a distance from a side end of the N-type semiconductor layer to a side end of the first P-type diffusion layer, which is a distance in a direction parallel to a surface of the P-type semiconductor substrate, is set to a range of 3.0 .mu.m to 4.0 .mu.m;

"(2) a distance from a side end of the N-type semiconductor layer to a side end of the second P-type diffusion layer, which is a distance in a direction parallel to a surface of the P-type semiconductor substrate, is set longer than a distance from a side end of the N-type semiconductor layer to a side end of the first P-type diffusion layer;

"(3) a distance from the side end of the first P-type diffusion layer to the side end of the second P-type diffusion layer is set to a range of 1.0 .mu.m to 2.0 .mu.m; and/or

"(4) the P-type impurity concentration of the first P-type semiconductor layer is set to a range of 1.times.10.sup.17 atoms/cm.sup.3 to 1.times.10.sup.19 atoms/cm.sup.3, the P-type impurity concentration of the second P-type semiconductor layer is set to a range of 1.times.10.sup.13 atoms/cm.sup.3 to 5.times.10.sup.14 atoms/cm.sup.3, the P-type impurity concentration of the first P-type diffusion layer is set to a range of 1.times.10.sup.16 atoms/cm.sup.3 to 1.times.10.sup.18 atoms/cm.sup.3, the P-type impurity concentration of the second P-type diffusion layer is set to a range of 5.times.10.sup.14 atoms/cm.sup.3 to 1.times.10.sup.16 atoms/cm.sup.3, and an N-type impurity concentration of the N-type semiconductor layer is set to a range of 1.times.10.sup.18 atoms/cm.sup.3 to 1.times.10.sup.21 atoms/cm.sup.3.

"According to another embodiment of the present invention, there is provided a manufacturing method of a semiconductor device including the steps of: forming a first P-type semiconductor layer and a second P-type semiconductor layer having a lower P-type impurity concentration than the first P-type semiconductor layer sequentially on a P-type semiconductor substrate; forming a second P-type diffusion layer by diffusing a P-type impurity in a region which is a partial region of the second P-type semiconductor layer and in which a side end thereof is isolated from a side end of a cathode forming region on the second P-type semiconductor layer by a first distance in a direction parallel to a surface of the P-type semiconductor substrate; forming a first P-type diffusion layer having a higher impurity concentration than the second P-type diffusion layer by diffusing a P-type impurity in a region which is a partial region of the second P-type diffusion layer and a partial region of the second P-type semiconductor layer and in which a side end thereof is isolated from the side end of the cathode forming region by a second distance that is shorter than the first distance in the direction parallel to the surface of the P-type semiconductor substrate; and forming an N-type semiconductor layer in the cathode forming region.

"According to the embodiments of the present invention, it is possible to provide a semiconductor device capable of markedly reducing a CR time constant determined by a parasitic capacitance and a parasitic resistance and provided with a photodiode that can be made faster. Hence, data can be read and written at a high rate with an optical disc device employing, for example, a short-wavelength laser."

For additional information on this patent, see: Yumoto, Hiroshi; Yoneda, Shuji; Mukai, Tomokazu; Takeuchi, Katsuhiko. Semiconductor Device Provided with Photodiode, Manufacturing Method Thereof, and Optical Disc Device. U.S. Patent Number 8803272, filed November 30, 2009, and published online on August 12, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8803272.PN.&OS=PN/8803272RS=PN/8803272

Keywords for this news article include: Electronics, Semiconductor, Sony Corporation.

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Source: Electronics Newsweekly


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