TWI226137B - Structure of dual-pad high speed photodiode - Google Patents

Abstract

A structure of a high-speed reach-through photodiodes, which is made on a thick and high-resistivity layer grown by epitaxy method on a high-conductivity substrate of the same semiconductor type, has both P and N electrodes of the photodiode formed on its upper surface, so that the bottom electrode is accessible for wire bonding from the die surface in specific packages whenever applications are necessary. The structure is characterized by having a deeply etched hole or holes on the surface and down below the substrate boundary, so that the electrical contact from a pad to the high-conductivity substrate, either P- or N-type, can be connected directly through metallization over the surfaces of the etched hole or holes. Therefore the high series resistance of the photodiode device, which is associated with the thick epitaxial layer, can be eliminated, exempting from the conventional method of deep and expensive drive-in diffusion. The performance of the photodiode, both bandwidth and sensitivity, hence can be upgraded.

Description

1226137 V. Description of the invention (1) --- [Technical field to which the invention belongs] The present invention relates to a dual-pad type photodiode, and more particularly to a high-speed dual-solder with a very small time constant. Pad type photodiode. I. [Xianru Technology] At present, the popularization of high-speed optical fiber communication requires a large number of photodiodes. In this application field, a good look at bandwidth and sensitivity are two important indicators for measuring the performance of a photodiode. Both of these factors are degraded by the junction capacitance and the series resistance parasitic to the photodiode structure. The capacitance and the series resistance are shown as CD and dagger in Figure 1. In addition, FIG. 2 is an equivalent circuit diagram of the photodiode and its matched transfer impedance amplifier (TIA), in which the series resistance Rs, the input resistance Rin of the TIA, and the junction capacitance of the diode (Junction depletion capacitance) CD will cause the RC time delay of the photo-induced current flowing to the amplifier T IA, thus affecting the bandwidth. Due to the stability of the circuit, the Rin property of the design TIA is usually very small, so once Rs is too large relative to Rin, it will cause serious RC time delay phenomenon and decrease in signal processing sensitivity, which will be hindered by the series resistance Rin The light-induced charge flows to the TIA, causing the current to flow only through the empty capacitor CD, thereby reducing the sensitivity of the light detection function. Therefore, in order to manufacture high-speed and sensitive photodiodes, the size of the series resistance Rs relative to Rin must be minimized to meet the actual needs; especially under the requirements of high-speed transmission.

1226137

So far, ι have been used, and there have been a variety of photodiode structure conditions for decades; never before, however, each structure is usually only suitable for its specific application and general purpose A? Suitable for all photodiode detection. The present invention proposes an innovative and inexpensive production of optical communication optical two-frame structure, which has the characteristics of high speed and high sensitivity, which can meet specific requirements. One feature of this special structure is that a surface of a photodiode crystal electrode plate is provided with P for wire bonding, and a bonding pad of the middle electrode is formed by a special method. ^ One of the bonding wires 连接 is connected to the lower electrode of the component to reduce the series I resistance of the component and the parasitic capacitance caused by the bonding wire; this dual wire pad structure & can meet the requirements of some specific packaged components Special pin ordering; J. If a substrate electrode under a polar die must be electrically isolated from the electrode seated on the lead frame and cannot conduct electricity. 3. Summary of the Invention A feature of the present invention is to provide a photovoltaic diode with a low junction capacitance with a Reach-through depletion region structure. This penetrating empty region structure has a thick high-resistance epitaxial layer, which is obtained by using an epitaxial method to grow on a high-conductivity semiconductor substrate of the same type. The photodiode formed on this epitaxial circle (Wafer) therefore has a penetrating space charge region and a small junction capacitance equal to the epitaxial thickness. The bonding pads of the P and N electrodes of the device are all formed on the surface of the die, and

Page 10 1226137 V. Description of the invention (3) One of the pads is connected to the metal connected to the grain. The base part with deep rhyme cut holes on its surface, the boring layer directly makes the solder joint and the remote crystal layer bring the bandwidth and sensitivity of the inner body of the component according to the present invention. In addition, according to the scope of the present invention and other applications of the Group 315 compound invention, when the substrate electrode forms an electrical phase, the photodiode is characterized by a component table that passes through downwards. The high-resistance epitaxial layer reaches a low-resistance value, and an excellent electrical connection is formed between the metal deposition bases formed on the surface of the deep-recessed engraved hole, so as to eliminate the high series resistance from the thick part, thereby improving the photoelectric diode In the aspect, the photodiode has a layer structure. In another embodiment, the photodiode system is composed of a semiconductor material. The purpose and advantages will be made clearer by the detailed description and the ensuing details. 4. Embodiment First, referring to FIG. 1, in order to have high speed and high photoelectric sensitivity, a photodiode must use a thick, high-resistance substrate to increase the depth of the empty region 11 to achieve the purpose. The reason is that the width of the empty region is inversely proportional to the capacitance value of the joint surface of the element. A wider empty region has a smaller bonding capacitance. In addition, the deeper empty region has a higher efficiency of absorbing incident light and Have better photoelectric conversion sensitivity. However, 'when using an over-thick, high-resistance substrate that exceeds the empty required thickness', the neutral substrate region located outside the empty region will be provided with a comparable internal string such as a resistor, as shown in Figure ^ . If this internal series resistance is too high,

1226137 V. Description of the Invention (4) "-Will seriously degrade the speed and sensitivity of the device. Therefore, in the production of high-speed optoelectronic components, epitaxial substrates will be used to improve, as shown in Fig. 3. That is, the epitaxial method is used to form a high-resistance epitaxial layer 31 of a desired thickness on a substrate having the same conductivity type and high dopant production and high conductivity (low value). When a photodiode is manufactured with such an epitaxial structure, the series resistance value brought by the above substrate can be greatly reduced. In addition, when there is an empty region with a constant & type, the series connection to the lower electrode substrate will be completely eliminated. In order to prevent the high-resistance material and the structure's intrinsic purity from occurring during the epitaxial process, Spontaneous doping (Auto-doping) phenomenon, and contamination by high-concentration impurities on the back of the wafer, generally a better method is to use the anti-doping high-concentration substrate 32 with a small diffusion to simplify the process, as shown in the figure 3 shown. Since the antimony element is valence of one to five, this type of substrate is N-type. ', ·,' However, in some established packaging specifications, such as To shlink's fiber optic connectors' | ^ The metal substrate 44 (see Figure 4) for mounting die is required to have f and negative bias, so Under the condition that the photodiode must withstand reverse bias when operating, the above-mentioned antimony-doped N-type substrate 32 cannot be electrically connected directly to the metal substrate 44. As shown in FIG. 4, the solution to this problem is to bond the photodiode wafer to the metal substrate 44 by bonding the non-conductive resin 43, so both can be avoided Between the electrical connections. However, in this case, the lower base electrode must also be connected to a pad on the upper surface of the photodiode to provide a bonding wire to form a circuit. Among such photodiodes currently on the market, a deep penetration diffusion process such as N-type phosphorus doping is usually used to make the upper surface

1226137 V. Description of the invention (5) The substrate pad 46 can electrically pass through the high-resistance epitaxial layer to the N-type substrate 41 with a different high conductivity. However, the Shixi Photodiode with fast performance has a stupid thickness of tens of micrometers. The required drive-u diffusion process is very time-consuming and therefore extremely costly. In addition, the long-term high temperature drive-in process will cause an out-diffusion effect, as shown by the dashed line 42 in FIG. 4. That is, it causes the substrate with a high concentration of antimony impurities to diffuse toward the epitaxial layer, thereby making the effective thickness of the high-resistance layer thin and difficult to control. In this way, the width of the empty region will be reduced, and the capacitance value will be increased accordingly, so the response speed is designed. 1 thousand, regarding the high level of gallium arsenide or other arsenic in the constituent materials will greatly affect the final performance of the component composition, resulting in no unsuitable deep driving. The present invention proposes a polar structure and its process. The locally doped substrate trenches are followed by the upper pads 4 6 of the external wiring on the surface of the remaining trenches. With this structure, the resistance value can be close to none. For vacuum coating and tempering (Out-diffusion), as far as the Danish process is concerned, the deep-diffusion process is formed by the components of the potential diode and therefore the photoelectric two, and the excellent conductive inside of the package is connected in series. Due to the gold's outward expansion therapy pressure, the high temperature drives the expansion of the electrical properties and the light related to this expected result, so the gallium is incorporated into the diffusion process. An innovation that is sufficient to improve the above disadvantages is shown in Fig. 5, which replaces the conventional deep-layer drive-in cover metal layer by an etching process to make it electrically connected. Since the covering metal greatly reduces the photodiode, since the post-processing can be performed at extremely low temperatures, the above-mentioned antimony impurities on the substrate can be almost ignored at the same time.

Page 13 1226137 V. Description of the invention (6) In order to maintain the thickness of the epitaxial layer originally specified. The v-shaped face-etched grooves can be formed by the well-known anisotropic relief (A η-is s 0 t r 0 p i c), as shown in FIG. 5. In the case of the Shixun photodiode, an etching solution such as potassium hydroxide (κ〇ίΙ) can be used to etch an inverted pyramid-shaped V-shaped groove on the silicon wafer surface, and its Opening and depth dimensions can be precisely controlled. On the (11) surface of the trench, the eight-member slope can be fully covered by the metal deposition layer when the electron beam is plated on the metal film 'without the problem of step coverage. As far as gallium arsenide-based materials are concerned, other well-known anisotropic etching solutions can also be used. Its knowledge is widely found in textbooks on related semiconductor processes. In addition to the above-mentioned etching method of forming trenches by using anisotropic relief, the method of etching will not make the surface of the grooves after money engraving too steep and can be fully covered with metal layer deposition. For example, as shown in FIG. 6, the isotropic Shi Xijin K 2 !! Shi Xizhen speed (approximately 7.4 micrometers per minute) is performed using a well-known CD-8 etching solution consisting of = 03, CHgCOOH, and " . But for 70% in the vertical direction 7T with: a certain degree of lateral etching effect (approximate., &Quot; so it can form a tilted bowl-shaped curved surface to cover ^ = t = the description, only for It is convenient to explain any changes made by the preferred embodiments of the present invention.] Narrower than the examples ^ ^ It is within the scope of the present invention to apply for a patent.

1226137 Brief description of the diagram 5. Simple explanation of the diagram Figure 1 is a conventional high-speed photovoltaic diode with a P + -r junction structure, in which the high-resistance neutral region outside the empty region has poor internal series resistance value. Fig. 2 is an equivalent circuit diagram of the photodiode and its matched amplifier. 'I4 is the effective signal current flowing through the TIA. FIG. 3 is a high-speed photodiode structure with an epitaxial substrate. Fig. 4 shows the structure of a two-pad p-n photodiode, which has the characteristics that the crystal grains and the negative-pressure metal substrate 44 are adhered to each other but are electrically insulated. FIG. 5 is an innovative high-speed photodiode structure according to the present invention, which is characterized by eliminating conventional series resistance by anisotropic etching. FIG. 6 is another innovative high-speed photodiode structure of the present invention, which is characterized by eliminating the conventional series resistance by isotropic etching. Description of symbols of standing pieces: D Dep 1 eti on reg i on or Space charge region 12 Neutral region 13 Active bonding pad 14 Substrate lower electrode electrode) 15 Reach-through empty area interface (Junet i on) 16 Oxidation layer 31 High resistivity stupid layer (H i gh res i st ivi ty ep i tax ia 1 layer)

1226137 on page 15 Brief description of drawings 32 High doping conductive substrate 41 Dr i ve-i ndiff used conduct or 42 Substrate out diffusion interface boundary) 43 Non-conductive epoxy 46 + 4. +, u,., Substrate connected bonding pad

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Claims (1)

1226137 6. Scope of patent application 1. A local-speed photodiode with a Reach-through space charge region. The structure of this penetrating space-charge region uses the epitaxial method to grow thick and high The resistivity epitaxial layer is on a highly doped conductive semiconductor substrate of the same conductivity type, in which the P and N electrodes of the photodiode are arranged on the surface of the die, and one of the substrate pads has a lead to the The metal layout of the high-conductivity substrate connected to the photodiode is characterized in that: the upper surface has deep-etched holes that pass through the high-resistance epitaxial layer and reach the substrate portion below the epitaxial layer. A metal layer structure deposited on the surface of the deep hole is directly electrically connected between the pad and the base electrode, so the high series resistance caused by the thick stupid crystal layer can be eliminated, thereby improving the photoelectricity. Bandwidth and sensitivity of the diode. 2. The high-speed photodiode with a Reach-through space charge region as described in item 1 of the patent, wherein the deep-etched hole refers to an inclined V-shaped recess formed by anisotropic etching technology. The groove is characteristic. 3. The high-speed photodiode with a Reach-through space charge region as described in item 1 of the patent, wherein the deep-etched hole refers to an inclined bowl-shaped curved surface formed by an isotropic etching technique. The groove is characteristic. 4. The photovoltaic diode with a Reach-through space charge region as described in item 1 of the patent, wherein the photovoltaic diode system refers to a P-N or N-P junction. Page 12 1226137 Page 18