JP2008267988A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device capable of easily and efficiently evaluating AC characteristics. <P>SOLUTION: The semiconductor device has a ring oscillator, constituted using a MOSFET element formed in the same manufacturing process as a MOSFET constituting an installed internal circuit, and a frequency counter formed to start and stop counting of oscillation signals of the ring oscillator by a timing signal supplied from an external terminal. At evaluation, the count of the frequency counter is output by an output circuit. A control determining circuit is provided to control the frequency counter, to determine whether the count output is within an allowable value and to output the determined result. Timing signals are set to different time so that the counted value of the frequency counter lies within a maximum count value corresponding to each of a plurality of ring oscillators. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor device and a semiconductor device evaluation method, and relates to a technology that is effective when applied to development design of a semiconductor device and AC characteristic determination technology for mass-produced products.

Japanese Laid-Open Patent Publication No. 2005-009923 discloses a semiconductor integrated circuit device that can perform high-speed and high-frequency characteristic evaluation at low cost in an on-wafer state. In the technique of this publication, since the LD driver IC for optical communication includes a driver stage having a three-stage differential amplifier circuit and a differential output unit, a dummy buffer chain is provided on the driver stage. In the measurement, the driver stage-differential output unit-dummy buffer chain is operated as a ring oscillator.
JP 2005-009923 A

  In general, a semiconductor device uses a plurality of types of MOSFETs such as a MOSFET having a relatively high withstand voltage for input / output and a MOSFET operating at an internal low voltage. In order to evaluate the AC characteristics of the internal circuit composed of these MOSFETs, the inventors of the present application have formed an evaluation ring oscillator composed of the MOSFET in the semiconductor device LSI as shown in FIG. Then, it was examined that the oscillation signal A was taken out and measured by a frequency counter. That is, as shown in the waveform diagram of FIG. 6, the oscillation signal A of the ring oscillator is taken out as an external signal B, and measured by a frequency counter to determine the frequency, that is, the gate delay time per stage of the ring oscillator. It is. Such an AC characteristic evaluation method has a problem that it takes time to prepare a frequency counter outside the chip and to read out the result of the frequency counter.

  An object of the present invention is to provide a semiconductor device capable of simple and efficient AC characteristic evaluation. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  One embodiment in the present application is as follows. Start and stop counting of the oscillation signal of the ring oscillator by the timing signal supplied from the ring oscillator and external terminal configured using the MOSFET element formed by the same manufacturing process as the MOSFET constituting the mounted internal circuit A frequency counter is formed. At the time of evaluation, the output circuit counts the frequency counter. In another embodiment, a control determination circuit is provided to control the frequency counter and determine whether the count output is within an allowable value and output the determination result. In still another embodiment, the timing signal is set at a different time so that the count value of the frequency counter falls within the maximum count value corresponding to each of the plurality of ring oscillators.

  Since only the count output or the determination result is obtained, the AC characteristic can be evaluated easily and efficiently. The frequency counter can be simplified by controlling the measurement time.

  FIG. 1 is a schematic block diagram showing an embodiment of a semiconductor device according to the present invention. The semiconductor device LSI is directed to development and design of a semiconductor device. In addition to the original circuit, an evaluation circuit for performing AC evaluation of the original circuit is provided as shown in FIG. The ring oscillator is composed of a MOSFET formed in the same manufacturing process as the MOSFET constituting the original circuit. The timing control circuit transmits the oscillation signal A of the ring oscillator as the input signal C of the frequency counter in response to the timing signal B supplied from the external terminal STM. The output signal of the frequency counter is stored in the result register. As a result, the output signal D of the register is output from the output terminal ROUT. The external terminal RST is provided for resetting the frequency counter and the result register.

  FIG. 2 shows a timing chart of the AC evaluation operation of the semiconductor device of FIG. The ring oscillator performs an oscillating operation in a state where a power supply voltage is supplied to the semiconductor device, and forms an oscillation signal A. The frequency counter and the result register are reset by the external terminal RST. When the timing signal B supplied from the external terminal STM is set to a high level, the pulse C corresponding to the oscillation signal A is input to the frequency counter, and the counting operation is started. When the timing signal B supplied from the external terminal STM becomes low level, the timing control circuit stops the input of the oscillation signal A to the frequency counter. As a result, the input signal C is maintained at a low level. The timing control circuit controls the result register to hold the count value D of the frequency counter. As a result, the count value D (d0 to d7) of the frequency counter is output to the output terminal ROUT through the result register.

  In this embodiment, the frequency counter is built in the semiconductor device as described above, and it is only necessary to input the timing signal B, the frequency counter, and the reset signal for resetting the result register from the outside. Since the measurement result is automatically output corresponding to the low level of the signal B, time is saved for preparing a frequency counter outside the chip for AC evaluation of the semiconductor device and reading the result of the frequency counter. It is possible to easily and efficiently evaluate the AC characteristics. Such an AC evaluation circuit can be formed in a mass-produced product in addition to the prototype for the development and design of the semiconductor device as described above, and can be used for the performance test.

  FIG. 3 is a schematic block diagram showing an embodiment of the semiconductor device according to the present invention. In this embodiment, the inside of the frequency counter is described in more detail. In this embodiment, a plurality of ring oscillator blocks corresponding to the evaluation target circuits 1 to N are provided. For example, the evaluation target circuit 1 is a ring oscillator composed of a relatively high voltage MOSFET used in an input / output circuit of a semiconductor device LSI. The evaluation target circuit N is a ring oscillator formed of a MOSFET that operates at a low voltage that constitutes an internal logic circuit. In addition, if there is a charge pump that generates a boosted voltage that is equal to or higher than the power supply voltage, or an internal circuit that operates with such a boosted voltage, a ring oscillator configured with a high-breakdown-voltage MOSFET is provided. For example, in a semiconductor device such as a system LSI incorporating a dynamic RAM, a ring oscillator composed of an address selection MOSFET for a dynamic memory cell is provided. As described above, a plurality of ring oscillators mounted on the semiconductor device LSI and corresponding to the AC characteristic evaluation target circuit are provided.

  One of the ring oscillators is selected by the selection circuit and input to the synchronization circuit. A timing signal input from the external terminal STM is taken in through the input / output circuit I / O and input to the synchronization circuit. The external terminal PC [0] is used for reset input, is similarly taken in through the input / output circuit I / O, and is transmitted as a reset signal to the synchronous circuit and the synchronous frequency counter. The synchronization circuit synchronizes the timing signal input from the external terminal STM with the oscillation signal of the ring oscillator transmitted through the selection circuit. That is, the synchronization circuit generates a clock signal CLK in which the timing signal STM input asynchronously with the oscillation signal of the ring oscillator is synchronized with the oscillation signal, and supplies the clock signal CLK to the synchronous frequency counter. The synchronous frequency counter is not particularly limited, but includes a 14-bit counter.

  The synchronous frequency counter of this embodiment transmits an overflow signal OF to the timing control circuit. When the timing control circuit detects the overflow signal OF, it does not form the capture signal SET. As a result, the result register remains reset, and a defective output is performed. For example, even if the oscillation frequency of the ring oscillator is higher than an appropriate value and the synchronous frequency counter overflows, if the signal OF does not exist, the counter outputs a count value that is rotated by 1 as a count value. Occurs. Such malfunction can be prevented by detecting the presence or absence of the overflow signal OF and controlling the result register.

  The timing signal input from the external terminal STM is set to the high level for a certain period (reference time), and the oscillation signal of the ring oscillator selected by the selection circuit is counted by the synchronous frequency counter during that period. The timing control circuit supplies the control signal SET to the result register at the end of the counting operation, using the timing signal STM and the pulse of the ring oscillator that has passed through the synchronization circuit. The result register captures and holds a 14-bit count output. The count value of the result register is output from the external terminal PQ [17: 4] through the input / output circuit. By sequentially switching the selection circuits, it is possible to sequentially obtain evaluation outputs for each of the evaluation target circuits 1 to N.

  Although not particularly limited, in the embodiment shown in the figure, the oscillation signal of the ring oscillator through the selection circuit can be output from the external terminal PQ [0]. For example, when there is a defect in an internal circuit such as a frequency counter, measurement becomes impossible, and this is output to enable external frequency measurement. For the selection operation of the selection circuit, a selection signal may be supplied from an external terminal, and the terminal PQ [17: 4] due to the output operation from the result register is used only temporarily. A selection signal is input using the input function of the terminal PQ [17: 4] using a period during which no operation is performed. For example, if the ring oscillator can oscillate when the test mode is set, useless current consumption due to the oscillation of the ring oscillator can be reduced.

  The AC evaluation operation is performed when the original circuit operation of the semiconductor device is being performed. Therefore, the input / output circuit I / O can be used together with the input / output circuit of the original circuit. When a specific test terminal and a test command are provided and the test mode is set, if a part of the input / output circuit I / O used for the regular circuit can be used as the external terminal for AC evaluation as described above, Terminals and input / output circuits can be simplified.

  As described above, when the evaluation target circuits 1 to N are various, the width of the oscillation frequency in each ring oscillator is widened. Therefore, when a timing signal is supplied from the external terminal STM using a fixed time as a reference time, it is necessary to set the number of bits of the synchronous frequency counter corresponding to the maximum frequency so as to cover the width of the oscillation frequency. . As a result, an increase in the number of bits of the synchronous frequency counter is inevitable. The configuration in which the measurement time is controlled by the timing signal from the external terminal STM can be arbitrarily set from the outside. Therefore, for the measurement of a ring oscillator with a high frequency, the measurement time can be shortened by the timing signal from the external terminal STM, and the measurement with a synchronous frequency counter with a small number of bits is possible. As described above, the evaluation method for setting the measurement time corresponding to the frequency of the circuit to be evaluated can reduce the circuit scale of the frequency counter provided in the semiconductor device.

  FIG. 4 is a schematic block diagram showing another embodiment of the semiconductor device according to the present invention. In this embodiment, a result determination register for output operation is omitted and a control determination circuit is provided. The control determination circuit has a data holding register equivalent to the result register, holds the count output of the synchronous counter, and determines whether or not it is within the expected value. For this determination, the overflow signal OF is referred to. The determination result is output as OVF or VLD from the output terminals PQ [2] and PQ (3), which means OVF and failure, and VLD means a non-defective product.There are a plurality of ring oscillators as described above. In some cases, the determination outputs OVF and VLD are output corresponding to each selection operation, and the other configurations are the same as those in the embodiment of FIG.

  The determination output may output GO (good) / NOG (bad) from one terminal. Alternatively, a result register for output as in the embodiment of FIG. 3 may be provided to output the frequency measurement result together.

  Although the invention made by the inventor has been specifically described based on the above embodiment, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the invention. For example, a ring oscillator is configured by using an odd number of stages of inverter circuits, and using a 2-input logic gate, one terminal is used as a control terminal, and the gate of the logic gate is opened at the time of evaluation. In other words, it may be substantially operated as an inverter circuit. In this case, it is possible to prevent the oscillation operation from being performed by supplying an active level to the control terminal at the time of evaluation and closing the gate of the logic gate circuit otherwise. Specific configurations of the frequency counter, the timing control circuit, the control determination circuit, and the like may be anything as long as they perform the operations described above. The present invention can be widely used for development design of semiconductor devices, mass-produced products, and evaluation methods thereof, which are composed of MOSFETs.

1 is a schematic block diagram showing an embodiment of a semiconductor device according to the present invention. FIG. 2 is a timing diagram of an AC evaluation operation of the semiconductor device of FIG. 1. 1 is a schematic block diagram showing an embodiment of a semiconductor device according to the present invention. It is a schematic block diagram which shows another Example of the semiconductor device which concerns on this invention. It is a block of a semiconductor device for performing AC characteristic evaluation studied prior to the present invention. FIG. 6 is a timing diagram of an AC evaluation operation of the semiconductor device of FIG. 5.

Explanation of symbols

  STM, RST, ROUT ... external terminals, A to D ... signal, OF ... overflow signal, SET ... capture signal, LSI ... semiconductor device,

Claims (5)

A ring oscillator configured using a MOSFET element formed in the same manufacturing process as the MOSFET constituting the mounted internal circuit;
A frequency counter that starts and stops counting the oscillation signal of the ring oscillator by a timing signal supplied from an external terminal;
A semiconductor device having an output circuit for outputting a count of the frequency counter; In claim 1,
The mounted internal circuit is composed of a plurality of types of MOSFETs having different characteristics from each other,
The ring oscillator includes a plurality of ring oscillators corresponding to a plurality of types of MOSFETs,
A selection circuit for selecting an oscillation signal of the plurality of ring oscillators;
The frequency counter is a semiconductor device that counts one oscillation signal through the selection circuit. A ring oscillator configured using a MOSFET element formed in the same manufacturing process as the MOSFET constituting the mounted internal circuit;
A frequency counter that starts and stops counting the oscillation signal of the ring oscillator by a timing signal supplied from an external terminal;
A semiconductor device comprising: control of the frequency counter corresponding to the timing signal; and a control determination circuit for determining whether the count output is within an allowable value and outputting a determination result. In claim 3,
The mounted internal circuit is composed of a plurality of types of MOSFETs having different characteristics from each other,
The ring oscillator includes a plurality of ring oscillators corresponding to a plurality of types of MOSFETs,
A selection circuit for selecting an oscillation signal of the plurality of ring oscillators;
The frequency counter is a semiconductor device that counts one oscillation signal through the selection circuit. A plurality of ring oscillators having an internal circuit composed of a plurality of types of MOSFETs having different characteristics from each other, and configured using MOSFET elements formed in the same manufacturing process as the plurality of types of MOSFETs;
A selection circuit for selecting the oscillation signals of the plurality of ring oscillators;
A frequency counter that starts and stops counting of an oscillation signal of one ring oscillator selected by a timing signal supplied from an external terminal;
The method for evaluating a semiconductor device, wherein the timing signal is set at different times so that the count value of the frequency counter falls within the maximum count value corresponding to each of the plurality of ring oscillators.

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