Semiconductor device with a protection element and method for manufacturing the same

Abstract: At least one power output element (10) made of an insulated gate semiconductor element, a surge protection element (9) for an input electrode of the power output element (10), and a circuit element block (11) for controlling the power output element (10), are formed on the same semiconductor substrate (P-Sub). The power output element (10), surge protection element (9), and circuit element block (11) are partially connected to each other, and a predetermined electrode of the power output element (10) and one end of the surge protection element (9) are connected to each other. In this state, first, second, and third electrode wiring layers (13, 15, 14) are connected to an output terminal of the circuit element block (11), the input electrode of the power output element (10), and the other end of the surge protection element (9), respectively, and the first to third electrode wiring layers (13, 15, 14) are formed separately from one another. In order to connect the first to third electrode wiring layers (13, 15, 14) to each other, a fourth electrode wiring layer (18) is formed thereon. Thus, a characteristic of the power output element (10) is previously evaluated before the fourth electrode wiring layer (18) is formed, using at least the second electrode wiring layer (15).

Description: The present invention relates to a method for manufacturing a semiconductor device, for example a monolithic semiconductor device including one or plural power output elements and circuit blocks for controlling the power output elements both formed on one chip, more particularly though not exclusively to a semiconductor device whose gate oxide film is improved in reliability when an insulated gate semiconductor element is used as a power output element. In a conventional monolithic semiconductor device wherein one or plural power output elements and circuit blocks for controlling these elements are formed on one chip, all the elements and circuit blocks are electrically connected to one another by metal wiring using aluminum (Aℓ) electrodes and the like so as to serve as a single functional device and, in this state, screening is performed to determine whether the chip is defective or not. However, in the screening of the chip, it is impossible to sufficiently determine whether the respective power output elements and circuit blocks are defective or not. For example, as shown in FIG. 3, in a functional device comprising an output element 1 of a power metal oxide silicon FET (power MOSFET), circuit blocks 2, 3 and 4 for controlling the output element 1, and a Zener diode 5 for protecting a gate-to-source path of the output element 1, as shown in FIG. 3, a considerably high voltage has to be applied between the gate and source of the output element 1 in order to evaluate the withstand voltage of a gate oxide film of the output element 1. However, the Zener diode 5 makes it difficult to apply such a high voltage between the gate and source of the output element 1. This drawback will be described in detail. Normally, as shown in FIG. 4, the Zener diode 5 has a voltage of 10V enough to turn on the output element 1 in order to protect the gate-to-source path of the output element 1 from its breakage when a surge voltage higher than a predetermined value is applied between the gate and source of the output element 1. The gate oxide film of the power MOSFET has a time dependent dielectric breakdown (TDDB) mode in which the gate oxide film is broken in connection with time and temperature when a voltage is applied thereto for a long time, even though the voltage is lower than the breakdown voltage. FIG. 5 is a graph showing a relationship between a temperature and an estimated lifetime of the gate oxide film for each voltage to be used. Calculating the lifetime of the gate oxide film by means of the Anolick's model which is widely used as a formula for the TDDB, a voltage of about 20V has to be applied to the gate oxide film at the time of probe cut in order to secure the lifetime of 15 years when the used voltage is 10V and the temperature is 90°C. Therefore, a voltage of 20V has to be applied to the gate of the output element 1 for chip screening. Since, however, the Zener diode 5 for protecting the gate-to-source path of the output element 1 has a characteristic as shown in FIG. 4, if the voltage of 20V is applied, an overcurrent of nearly 20 mA flows through the Zener diode 5. The overcurrent causes the Zener diode 5 to be burnt and broken, and adversely affects the characteristic of the functional device. The present invention has been developed in consideration of the above situation, and its object is to provide a method of manufacturing a semiconductor device wherein the characteristics of power MOSFET output elements and circuit blocks connected to the output elements are evaluated before they are connected to serve as a functional device, which was difficult in the conventional semiconductor device, to thereby improve the reliability of a gate oxide film. IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 13, No. 10, March 1971, page 2844 discloses a method to allow gate oxides of MOSFETS to be tested independently of their protective diodes. In order to perform certain gate tests, the diode is disconnected firstly from its associated FET gate. After testing, a conductive spot is deposited to reconnect the diode and FET gate. Reference is also made to PROCEEDINGS OF THE 3RD INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES AND IC'S April 1991, Baltimore; Maryland; pages 242-247, XP220813, in which is discussed an intelligent power switch comprising a power MOSFET, control circuit and Zener diodes. According to the present invention, there is provided a method of manufacturing a semiconductor as defined in claim 1. In a preferred way of performing the invention, in a monolithic semiconductor device wherein a power MOSFET serving as one or more power output elements, a Zener diode serving as a surge protection element for the power MOSFET, and a circuit block (including an element for protecting a gate-to-source path of the power MOSFET) for controlling the power MOSFET are formed on one chip, the power MOSFET, Zener diode, and circuit block are connected to constitute a single functional device after an amount of withstand voltage of the gate of the power MOSFET is confirmed. This invention can be more fully understood from the following detailed description, given by way of example and when taken in conjunction with the accompanying drawings, in which: FIGS. 1A and 1B are a cross-sectional view and a block diagram of a semiconductor device in the intermediate manufacturing process according to one way of performing the present invention; FIGS. 2A and 2B are a cross-sectional view and a block diagram of a finished semiconductor device resulting from the manufacturing process; FIG. 3 is a block diagram of a conventional monolithic semiconductor device; FIG. 4 is a graph showing a characteristic of a Zener diode; and FIG. 5 is a graph showing a relationship between a temperature and an estimated lifetime of a gate oxide film for each voltage to be used. One way of performing the present invention will now be described in detail, with reference to FIGS. 1A, 1B, 2A, and 2B. Let us suppose in this embodiment that the connection of elements and circuit blocks is performed by metal wiring using aluminum electrodes. As shown in FIG. 1A, small signal elements 6 and 8 of small signal NPN transistors and a resistor 7, which serve as a control circuit block, a Zener diode 9 serving as a surge protection element, and a power MOSFET 10 serving as a power output element, are formed on one chip of a P-type semiconductor substrate P-Sub by a well-known technique, and surfaces of these elements are protected by an oxide film 3-1 formed thereon. Next, contact holes are formed in the oxide film 3-1, and an aluminum electrode 3-2 is formed by evaporation as a first metal wiring layer. The elements are then connected to one another by the etching technique. The small signal elements 6 and 8 and the resistor 7 are connected to constitute a control circuit block 11. While the anode of the Zener diode 9 and the source of the power MOSFET 10 are connected to each other as shown in FIG. 1A, no elements are connected between the gate of the former and the cathode of the latter. Then, an insulation film 3-3 is formed, and openings 12-17 are formed therein as chip screening pads. By doing so, a semiconductor device having the circuit arrangement shown in FIG. 1B is achieved in the intermediate manufacturing process. When the first metal wiring layer is formed, the Zener diode 9 is not virtually connected between the gate and source of the power MOSFET 10. In this state, element evaluation and chip screening are performed by a well-known die sorter. More specifically, a probe of a die sorter (not shown) is applied to the bonding pads 12 and 13 to evaluate the control circuit block 11. Similarly, the probe is applied to the bonding pads 14 and 16 to evaluate the Zener diode 9, and the probe is applied to the bonding pads 15, 16 and 17 to evaluate the power MOSFET 10 (including screening of a gate film). If the chip is judged as defect-free by the above evaluation, as shown in FIG. 2A, the control circuit block 11, Zener diode 9, and power MOSFET 10 are connected to one another by an aluminum electrode 3-4 (18). An insulation film 3-5 is then formed, and openings 12, 16 and 17 are formed as bonding pads, thereby obtaining a finished semiconductor functional device as shown in FIG. 2B. In FIGS. 1A, 1B, 2A, and 2B, reference numerals 12 and 13 indicate an input terminal and an output terminal of the control circuit block 11, respectively, numeral 14 denotes a cathode of the Zener diode 9, and numerals 15, 16, and 17 show a gate electrode, a source electrode, and a drain electrode of the power MOSFET 10, respectively. More specifically, as shown in FIGS. 1A, 1B, 2A, and 2B, the semiconductor device comprises: at least one power output element 10 made of an insulated gate semiconductor element, a circuit element block 11 for controlling the power output element 10 and a surge protection element 9 for an input electrode of the power output element 10, the circuit element block 11, the power output element 10, and the surge protection element 9 being formed on a single semiconductor substrate; first, second and third electrodes 13, 14, and 15 connected to an output terminal 13 of the circuit element block 11, the input electrode 15 of the power output element 10, and one end 14 of the surge protection element 9, respectively, while the power output element 10, the surge protection element 9, and the circuit element block 11 are partially connected to one another and a predetermined electrode of the power output element 10 is connected to another end of the surge protection element 9, the first, second and third electrodes being formed separately from one another; a fourth electrode wiring layer 18 formed on the first, second and third electrodes 13, 14, and 15 for connecting the first, second and third electrodes 13, 14, and 15 to each other, wherein a withstand voltage of the gate region of the power output element 10 is previously evaluated by applying a predetermined voltage between the gate and the source electrodes before the fourth electrode wiring layer 18 is formed. According to the present manufacturing method described above in detail, the characteristics of output elements (e.g., power MOSFET) and circuit blocks can sufficiently be evaluated before they are connected to serve as a single function device, which was difficult in the conventional semiconductor device. Therefore, the reliability of the entire semiconductor device can be enhanced More specifically, in the present method, since a surge protection diode is connected between the gate and source of the power MOSFET not when the first metal wiring layer is formed but when the second metal wiring layer is formed, screening of a gate film of the power MOSFET can be performed, without applying an overvoltage to the surge protection diode.

Claims: A method of manufacturing a semiconductor device, having at least one power output element (10), constituted by an insulated gate semiconductor element having gate, drain and source regions, and a surge protection diode (9) having cathode and anode regions, the power output element (10) and surge protection diode both being formed on a semiconductor substrate (P-Sub), said method comprising the steps of: forming a first metal wiring layer (3-2) to connect the source region of the power output element (10) and the anode or cathode region of the surge protection diode (9) and to forming gate, drain and source electrodes (15, 17, 16) on the gate, drain and source regions of the power output element (10) and a cathode or anode electrode (14) on the cathode or anode region of the surge protection diode (9) ; evaluating a withstand voltage of the gate region of the power output element (10) by applying a predetermined voltage between the gate and source electrodes (15, 16) of the power output element (10); and subsequently forming a second metal wiring layer (3-4) to connect the gate electrode (15) of the power output element (10) and said cathode or anode electrode (14) of the surge protection diode (9). The method according to Claim 1, characterized in that: said first forming step further forms a circuit element block (11) for controlling the power output element (10), the surge protection diode (9), and the circuit element block (11) being formed on the same semiconductor substrate (P-Sub); said second forming step further forms pads (12, 13) connected to input and output terminals of the circuit element block (11), respectively, by using the first metal wiring layer (3-2); said evaluating step further evaluates the circuit element block (11) by using the pads (12, 13); and said third forming step further connects the gate electrode (15) of the power output element (10) and the pad (13) connected to the output terminal of the circuit element block (11) by using the second metal wiring layer (3-4). The method according to Claim 1 or 2, characterized in that said power output element (10) is a power MOSFET, and the surge protection diode (9) is a Zener diode. The method according to any one of Claims 1 to 3, characterized in that said third forming step further forms pads (17, 16) connected to the drain and source electrodes (17, 16) of the power output element (10), respectively, by using the second metal wiring layer (3-4).

Inventors: KITAHARA KOICHI, OHATA YU, TAKAGI YOSUKE, KITAHARA, KOICHI, OHATA, YU, TAKAGI, YOSUKE, KITAHARA, KOICHI, C/O INTELLECTUAL PROPERTY DIV., OHATA, YU, C/O INTELLECTUAL PROPERTY DIV., TAKAGI, YOSUKE, C/O INTELLECTUAL PROPERTY DIV.
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1993
Main classification: H01L27
IPC codes: H01L27, H01L21