The present invention relates to the field of integrated circuit devices. More specifically, it relates to testing and sorting individual integrated circuit devices according to their operational characteristics.
Integrated circuit devices, or dies, are manufactured through a multi-step process during which transistors and other electronic circuit components are formed in areas on a thin silicon wafer. After the circuit fabrication is completed, the individual dies are cut from the silicon wafer.
The manufacturing process for integrated circuits is imprecise; minor variations during each step of the manufacturing process affect vital performance characteristics of individual dies. These variations impact the speed at which a particular die operates, which directly impacts the commercial value of each individual die. It is therefore desirable to the manufacturer to determine the speed at which individual dies can operate so the manufacturer can then sort them accordingly.
Typical integrated circuit test devices consist of bench setups utilizing standard lab equipment including an oscilloscope or frequency meter to directly or indirectly measure the operating frequency (speed) of the circuit. In some setups such outboard test equipment is used to test the speed of a device, such as an oscillator, which is fabricated in association with a die but which is not materially part of the operational die circuit. The tested frequency of the oscillator is representative of the operational speed of the die. All these systems, however, require expensive specialized and sometimes bulky frequency measurement equipment to be provided with the test setup.
What is needed is a simplified method and apparatus for determining the operating speed of the die.
The present invention provides a method and apparatus for characterizing an integrated circuit device based on device switching speed on an individual die or lot-by-lot basis by measuring frequency in a digital domain. An oscillator, integrated in association with the die and capable of generating pulses, and a counter are used during a test period to count the pulses from the oscillator to a predetermined value. A pulse generator is initiated at the beginning of a test which resets the counter to a known state and starts the oscillator. When the counter reaches its predetermined maximum count value a signal is issued. The elapsed time between the initiation of the oscillator and when the counter full signal is issued represents the summation of many oscillator periods. The period of the oscillator may then be determined by the formula: oscillator period=elapsed time/capacity of counter. The determined oscillator period provides an indication of the operating speed of electronic devices on the die. A digital tester which performs other tests on the die can be used to record the elapsed time and thereby determine the operating speed of a die.
These and other features of the invention will be more clearly understood from the following detailed description of the invention which is provided in connection with the accompanying drawing.