JP4934987B2 - Semiconductor X-ray detection element and method for manufacturing semiconductor X-ray detection element - Google Patents

Description

  The present invention relates to a semiconductor X-ray detection element for detecting X-rays. This semiconductor X-ray detection element is used, for example, in a detector of an analyzer such as an energy dispersive X-ray fluorescence analyzer or an X-ray microanalyzer.

  2. Description of the Related Art Conventionally, a semiconductor X-ray detection element using Si or Ge as a base material has been used for an energy dispersive X-ray detector. In particular, a lithium drift type semiconductor X-ray detection element (Si (Li) X-ray detection element) formed by drifting Li (lithium) on a P-type silicon substrate has excellent energy resolution and is widely used as a detection element. (For example, refer to Patent Document 1).

FIG. 5 is a diagram showing the structure of a conventional Si (Li) X-ray detection element. In this element, an i layer 102 made of a Li diffusion layer (Li drift layer) and an n layer (preferably an n ⁺ layer doped with an n-type impurity at a high concentration) 103 are formed on a p-type Si substrate forming the p layer 101. This is a so-called top-hat type detection element having a pin structure semiconductor layer. A p-plane ring electrode 104 made of Au (gold) and a p-plane electrode 105 made of Ni (nickel) are formed on the p-side, and an n-plane electrode 106 having a Ni / Au laminated structure is formed on the n-side. The partial region 102a of the i layer, the n layer 103, and the n-plane electrode 106 form a top hat portion 107 that protrudes into a cylindrical convex shape. The top hat portion 107 is covered with a protective film 108 (for example, a resin) except for the central portion of the outer surface of the n-plane electrode 106.

  A window region 109 for X-ray incidence is formed immediately below the top hat portion 107, and when X-rays enter from the window region 109, electron / hole pairs are generated in the i layer 102. Electron / hole pairs are separated by a reverse bias voltage applied to this region and generate electric charges. The energy required to generate this electron / hole pair is about 3.9 eV, and a number proportional to the energy of the incident X-ray is generated.

This Si (Li) X-ray detection element is used in a state of being cooled to liquid nitrogen temperature in a vacuum in order to remove the influence on electron-hole pairs due to thermal energy and suppress leakage current and thermal noise. Thereby, the charge amount is measured in a stable state. By performing arithmetic processing such as voltage conversion and time differentiation on the measured charge amount, fluorescent X-ray energy (incident X-ray energy) from the sample is derived. Since this is a physical property value specific to the element, the element contained in the sample can be specified.
Japanese Patent Laid-Open No. 10-335691

In the Li diffusion layer (i layer 102), a depletion layer region is formed by compensating holes due to B (boron) as a p-type impurity in Si and electrons due to Li as an n-type impurity. In particular, in the depletion layer region (i layer 102a) in the top hat portion, the impurity concentration other than B-Li is reduced as much as possible, and the number of impurity atoms excluding Li-B is approximately 10 ⁹ to 10 ¹⁰ / cm. Generally, it is maintained at about ³ .
However, for some reason during the manufacturing process, dirt such as heavy metal may adhere to the surface of the top hat portion 107 during the element forming process. In this case, the leakage current increases due to the attached impurities. Further, when the dirty surface is n-layered (n ⁺ layered) and a reverse bias is applied, a uniform electric field cannot be generated.

  FIG. 6 is a diagram for explaining an electric field state when a reverse bias voltage is applied to the element in which the metal contamination region 110 is formed on the surface of the top hat portion. As a result of the n-layer formation on the side surface of the top hat portion 107, the electric field is distorted in the vicinity of the metal contamination region 110. In an element having such an electric field curve, electrons or holes generated by incident X-rays in this vicinity reach a channel derived from the side wall portion. This charge is trapped in the middle, and as a result, when energy spectrum data is obtained, a tail is drawn to the low energy side of the spectrum peak. Also, background noise increases.

Further, it is necessary to measure the degree of diffusion of Li to the p-plane side during the element manufacturing process. This measurement is performed by plating with a saturated copper sulfate solution (CuSO ₄ ) added with thin hydrofluoric acid (HF). This method is convenient because it is easy to determine whether the Li diffusion region is formed up to the p-plane, but it is difficult to remove even by etching if Cu ions adhere to the surface of the top hat portion. Cu becomes an impurity, and the characteristics are deteriorated in the same manner as described above.

Therefore, the present invention provides a semiconductor X-ray detection element capable of accurate and stable measurement by reducing leakage current due to heavy metal contamination on the element surface and preventing n ⁺ layering of the contaminated surface. The purpose is to provide.

The semiconductor X-ray detection element of the present invention, which has been made to solve the above-mentioned problems, joins an n layer to a p layer region and diffuses Li from the n layer side to the p layer region to form i in a part of the p layer region. A layer is formed, the remainder is a p-layer, an n-plane electrode is formed on the n-layer surface, a p-plane electrode is formed on the p-layer surface, and a reverse bias is applied between the n-plane electrode and the p-plane electrode. A semiconductor X-ray detection element that detects by converting a X-ray incident on an i-layer region into an electron / hole pair by applying a voltage, wherein the semiconductor X-ray detection element is formed on a planar portion and a planar portion. It has a top hat type structure having a protruding portion protruding on a cylinder, and a p-plane electrode and a p-layer are formed in the plane portion, and an n-plane electrode, an n-layer, and an i layer near the n-layer are formed in the protruding portion. together, n surface electrode peripheral portion, n layer peripheral edge, i layer peripheral end portion of the n layer near to form protrusions sidewall, n surface of the projecting portion side wall Part of the element surface leading to i layer peripheral edge through the n layer peripheral portion is removed from the poles of the peripheral end portion, the partially removed portion of the element surface, there is no contamination by heavy metals It is configured as follows.

According to the present invention, the semiconductor X-ray detection element has a top hat type structure having a planar portion and a projecting portion projecting on a cylinder on the planar portion, and a semiconductor layer having a pin structure is formed. electrode, the n-layer, i layer of the n layer vicinity has a layered structure in the element peripheral end portion of the protruding portion, in the element peripheral end portion of the protruding portion, the protruding portion of the cross section surface (element these layers are stacked Exposed on the side wall surface). The laminated structure portion exposed at the peripheral edge of the element (the corner portion extending from the peripheral edge portion of the n-plane electrode to the peripheral edge portion of the i-layer region through the peripheral edge portion of the n-layer region) is contaminated by heavy metal during manufacturing. Even if the material adheres, the contaminant is finally removed so that the contaminant does not exist. This completely cuts the conductive path formed in the surface portion from the n-plane electrode to the i-layer through the n-layer, thereby increasing the leakage current due to the adhesion of heavy metals, etc., or generating a non-uniform electric field. lose.

Here, it is preferable to use a p-type Si or Ge wafer for the p-layer region, and it is particularly preferable to use a p-type Si wafer. The n layer for forming a pn junction first is preferably formed by doping Li as an impurity.
Formation of the i layer by diffusing Li into the p layer region is preferably performed by a drift process in which thermal diffusion of Li is performed with a reverse bias voltage applied between the p-plane electrode and the n-plane electrode.

According to the present invention, when the i layer surface portion which is the Li diffusion layer is contaminated with heavy metal or the like for some reason during the manufacturing process, or plating with a saturated copper sulfate solution (CuSO ₄ ) during the device manufacturing process. In this case, even if Cu ions are attached to the surface of the device , the contaminants are not finally present, so that the characteristics of the device due to the metal attached to the surface can be reduced. Thus, it is possible to obtain a semiconductor X-ray detection element capable of removing the influence of the above and capable of performing stable and accurate measurement.

(Means and effects for solving other problems)
In addition, the method for manufacturing a semiconductor X-ray detection element according to another aspect of the present invention, which is made from another viewpoint, joins an n layer to a p layer region and diffuses Li from the n layer side to the p layer region to form a p layer. Of the semiconductor X-ray detection element in which the i layer is formed on a part of the substrate, the rest is the p layer, the n plane electrode is formed on the surface of the n layer, and the p plane electrode is formed on the surface of the p layer. In this method, by removing a part of the element surface from the peripheral edge of the n-plane electrode through the n-layer region peripheral edge to the i-layer region peripheral edge in a tapered or stepped manner by ultrasonic processing, The surface after the removal is made free from heavy metal contaminants.

According to which this, by removing a portion of the peripheral end portion of the n surface electrode via the n layer region peripheral edge i layer region peripheral end surface of the device leading to the tapered or stepped by ultrasonic machining The surface after removal is made free from contaminants due to heavy metals. As a result, the conductive path formed on the surface can be completely separated, and an increase in leakage current due to adhesion of heavy metal or the like or generation of a non-uniform electric field can be eliminated. Further, by using ultrasonic processing as the removing means, the corner portion of the element can be processed into a tapered shape or a staircase shape easily and accurately.

  In the above manufacturing method, a part of the element may be removed in a taper shape or a step shape by ultrasonic processing, and then the removed portion may be etched. This makes it possible to completely remove scratches on processing parts and contaminants during ultrasonic processing after processing into a tapered or stepped shape. It becomes possible to form.

Hereinafter, the semiconductor X-ray detector of the present invention will be specifically described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a semiconductor X-ray detector according to an embodiment of the present invention.
In this element 10, a p-type Si substrate for forming a p layer 11 is doped with an i layer 12 made of a Li diffusion layer (Li drift layer) in which Li as an n type impurity is diffused, and an n type impurity is doped at a high concentration. This is a so-called top hat type detection element having a pin structure semiconductor layer composed of the n ⁺ layer 13. On the p side, an Au p-plane ring electrode 14 and an Ni p-plane electrode 15 are formed, and on the n-side, an n-plane electrode 16 having a Ni / Au laminated structure is formed. The partial region 12a of the i layer, the n ⁺ layer 13, and the n-plane electrode 16 form a cylindrical top hat portion 17 protruding in a convex shape. The top hat portion 17 is covered with a protective film (resin) 18 except for the central portion of the surface of the n-plane electrode 16.
A window region 19 for incident X-rays is formed immediately below the top hat portion 17. When X-rays enter from the window region 19, electron / hole pairs are generated in the i layer 12. The electron / hole pairs are separated by a reverse bias voltage applied between the p-plane electrode 19 and the n-plane electrode 16 to generate charges (and holes).

  Further, on the upper side of the top hat portion 17, the corner portion 20 extending from the peripheral end portion of the n-plane electrode 16 through the peripheral end portion of the n layer region 13 to the peripheral end portion of the i layer region is removed. Even if contaminants such as heavy metals adhere to the surface of this part during the manufacturing process, the contaminants are finally removed. And the surface protective film 18 is formed so that the clean surface after removing the corner part 20 may be covered.

FIG. 2 shows an electrolysis state when a reverse bias voltage is applied to the semiconductor X-ray detection element 10 thus formed. Even if the metal contamination portion 21 remains on the side wall of the i-layer portion of the top hat portion 17, the n-layer region 13, the n-plane electrode 16 and the i-layer 12a can be completely cut at the corner portion 20, As a result, even when a reverse bias voltage is applied, the electrolytic curve is not curved.
Therefore, when energy dispersion is measured, there is no influence such as a tail appearing on the low energy side of the spectrum peak or a background becoming large.

  Next, a method for processing the corner portion 20 will be described. 3 and 4 are diagrams for explaining a processing method. The element 10 to be processed is set in an ultrasonic processing machine ((FIG. 3A), FIG. 4A)), and an appropriate tool that matches the processing shape from above the n electrode 16 is attached to the corner portion of the n electrode 16 peripheral end. The contact surface is processed while being pressed against 20 and supplying slurry (a processing liquid containing abrasive grains). Specifically, when machining the corner portion 20 into a tapered shape, the inner surface of the tool 23 is opposed to the tool 23 (FIG. 3 (b)), and when machining into a stepped shape, the inner surface of the tool 24 is cylindrical. It is made to oppose (FIG.4 (b)). Thereby, the corner part 20 can be accurately processed into an arbitrary shape.

Further, the corner portion 20 after ultrasonic processing is left behind and covered with a mask, and an etching process is performed (FIGS. 3C and 4C). Thereafter, the mask 10 is removed and a cleaning process is performed to obtain the element 10 in which the corner portion 20 has a clean surface (FIGS. 3D and 4D).
Subsequently, by forming a surface protective film, a semiconductor X-ray detection element is completed.

  The present invention can be used for manufacturing a semiconductor X-ray detection element.

The figure which shows the structure of the semiconductor X-ray detection element which is one Embodiment of this invention. The figure which shows an electric field curve when a reverse bias voltage is applied to the semiconductor X-ray detection element of FIG. The figure explaining the processing method of the corner part in the semiconductor X-ray detection element of FIG. The figure explaining the other processing method of the corner part in the semiconductor X-ray detection element of FIG. The figure which shows the structure of the conventional semiconductor X-ray detection element. The figure which shows an electric field curve when a reverse bias voltage is applied to the semiconductor X-ray detection element of FIG.

Explanation of symbols

10: Semiconductor X-ray detection element 11: p layer 12, 12a: i layer (Li diffusion layer)
13: n layer 14: p layer ring electrode 15: p surface electrode 16: n surface electrode 17: top hat portion 19: window region 20: corner portion

Claims (3)

The n layer is joined to the p layer region, and Li is diffused from the n layer side to the p layer region to form an i layer in a part of the p layer region, and the rest is formed as a p layer. A plane electrode is formed, a p-plane electrode is formed on the p-layer surface, a reverse bias voltage is applied between the n-plane electrode and the p-plane electrode, and X-rays incident on the i-layer region are converted into electrons and holes. A semiconductor X-ray detection element that detects by converting into a pair,
The semiconductor X-ray detection element has a top hat type structure having a flat part and a protruding part protruding on a cylinder on the flat part, a p-plane electrode and a p-layer are formed in the flat part, and an n-plane electrode, n The i-layer near the n-layer is formed at the protrusion, and the peripheral edge of the n-plane electrode, the n-layer peripheral edge, and the i-layer peripheral edge near the n-layer form a protrusion side wall. Part of the device surface from the peripheral edge of the n-plane electrode to the peripheral edge of the i-layer through the peripheral edge of the n-layer is removed, and the removed part of the surface of the element is contaminated with heavy metal A semiconductor X-ray detection element, characterized in that it does not exist. The n layer is joined to the p layer region and Li is diffused from the n layer side to the p layer region to form an i layer in a part of the p layer, and the rest is used as a p layer. A method for manufacturing a semiconductor X-ray detection element comprising forming an electrode and forming a p-plane electrode on a p-layer surface,
By removing a part of the element surface from the peripheral edge of the n-plane electrode through the peripheral edge of the n-layer region to the peripheral edge of the i-layer region by ultrasonic processing, the surface after the removal A method for producing a semiconductor X-ray detection element, characterized in that no contaminants due to heavy metals exist in the substrate. 3. The method of manufacturing a semiconductor detection element according to claim 2 , wherein a part of the element is removed in a taper shape or a step shape by ultrasonic processing, and then the removed portion is etched.

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