Program method of flash memory device

Abstract

The present invention relates to a method of programming a flash memory device. According to the present invention, after a program operation is completed, a program verify operation is repeatedly performed, wherein a threshold voltage of a programmed memory cell is also detected. If there are memory cells whose threshold voltage becomes low as a result of the detection, the program operation is again performed on a corresponding memory cell. It is thus possible to obtain a uniform distribution characteristic of a threshold voltage. Furthermore, a program verify operation is performed with a compare voltage being set higher than a target voltage initially so that a threshold voltage of a memory cell is sufficiently higher than the target voltage. The program verify operation is again performed while lowering the compare voltage according to the repetition number. It is thus possible to prevent normally programmed cells from being again excessively programmed.

1 . A programming method of a flash memory device, comprising:
 performing a first programming operation of memory cells;   performing a first program verify operation in order to discriminate first memory cells having a threshold voltage higher than a target voltage and second memory cells having a threshold voltage lower than the target voltage, of the programmed memory cells;   performing a second programming operation of the second memory cells; and   performing a second program verify operation for discriminating third memory cells having a threshold voltage lower than the target voltage by comparing the threshold voltages of the first and second memory cells with the target voltage.   
   
   
       2 . The programming method of  claim 1 , wherein if there is a memory cell having the threshold voltage lower than the target voltage, the second programming operation and the second program verify operation are performed repeatedly. 
   
   
       3 . The programming method of  claim 1 , wherein the second programming operation is performed by applying the second memory cells with a second program voltage higher than a first program voltage, which is applied to the memory cells during the first programming operation. 
   
   
       4 . A programming method of a flash memory device, comprising:
 performing a first programming operation of memory cells;   performing a first program verify operation for comparing a first comparison voltage higher than a target voltage with threshold voltages of the memory cells;   performing a second programming operation of memory cells having the threshold voltage lower than the first comparison voltage;   performing a comparison voltage resetting operation for changing the first comparison voltage to a second comparison voltage lower than the first comparison voltage; and   performing a second program verify operation for comparing the threshold voltage of the memory cells with the second comparison voltage.   
   
   
       5 . The programming method of  claim 4 , wherein if there is a memory cell having the threshold voltage lower than the second comparison voltage, the second programming operation, the comparison voltage resetting operation, and the second program verify operation are performed repeatedly. 
   
   
       6 . The programming method of  claim 5 , wherein whenever the second program verify operation is performed twice to six times repeatedly, the comparison voltage resetting operation is performed. 
   
   
       7 . The programming method of  claim 6 , wherein when the comparison voltage resetting operation is performed, a level of the comparison voltage is lowered by 0.02V to 0.03V. 
   
   
       8 . The programming method of  claim 4 , wherein:
 the first comparison voltage is set in the range of 1.15V to 1.25V, and the second comparison voltage is lowered in the range of 1.05V to 0.95V.   
   
   
       9 . The programming method of  claim 4 , wherein the second programming operation is performed by applying the memory cells with a second program voltage higher than a first program voltage, which is applied to the memory cells during the first programming operation. 
   
   
       10 . A programming method of a flash memory device, comprising:
 performing a first programming operation of memory cells;   performing a first program verify operation for comparing a first comparison voltage higher than a target voltage with threshold voltages of the memory cells;   performing a second programming operation on second memory cells having the threshold voltage lower than the first comparison voltage, of first memory cells having the threshold voltage higher than the first comparison voltage and the second memory cells;   performing a comparison voltage resetting operation for changing the first comparison voltage to a second comparison voltage lower than the first comparison voltage; and   performing a second program verify operation for discriminating third memory cells having the threshold voltage lower than the second comparison voltage by comparing the threshold voltages of the first and second memory cells with the second comparison voltage.   
   
   
       11 . The programming method of  claim 10 , wherein if there is a memory cell having the threshold voltage lower than the second comparison voltage, the second programming operation, the comparison voltage resetting operation, and the second program verify operation are performed repeatedly. 
   
   
       12 . The programming method of  claim 11 , wherein whenever the second program verify operation is performed twice to six times repeatedly, the comparison voltage resetting operation is performed. 
   
   
       13 . The programming method of  claim 12 , wherein when the comparison voltage resetting operation is performed, a level of the comparison voltage is lowered by 0.02V to 0.03V. 
   
   
       14 . The programming method of  claim 10 , wherein:
 the first comparison voltage is set in the range of 1.15V to 1.25V, and the second comparison voltage is lowered in the range of 1.05V to 0.95V.   
   
   
       15 . The programming method of  claim 11 , wherein the second programming operation is performed by applying the memory cells with a second program voltage higher than a first program voltage, which is applied to the memory cells during the first programming operation.