Sgs-thomson Microelectronics S.r.l.

Stmicroelectronics S.r.l.

Leonardo Ravazzi

Lorenzo Fratin

Paolo Giuseppe Cappelletti

Carlo Riva

Giuseppe Paolo Crisenza

Carlo Severgnini

Piero Pansana

Paolo Cappeletti

A flash EEPROM having an array of memory cells which include a common source line connecting together source electrodes of the memory cells. A resistive feedback element is coupled in series between the common source line and a positive potential when the memory cells must be electrically erased. The Flash EEPROM includes a voltage limiting circuit coupled to the common source line for limiting the potential of the common source line to be prescribed maximum value lower than the positive potential.

Flash EEPROM with integrated device for limiting the erase source voltage

Method for localizing point defects causing column leakage currents in a non-volatile memory device including a plurality of memory cells arranged in rows and columns in a matrix structure, source diffusions, and metal lines which connect said source diffusions to each other. Such a method includes the steps of: modifying the memory device in order to make source diffusions independent of each other and each one electrically connected to a respective row; sequentially biasing the single columns of the matrix; localizing the column to which at least one defective cell belongs, as soon as the leakage current flow occurs in the biased column; by keeping biased the localized column, biasing sequentially the single rows of the matrix to the same potential as that of the localized column; localizing a couple of cells, wherein at least one of them involves the point defects, as soon as the leakage current flow does not occur.

Method for localizing point defects causing leakage currents in a non-volatile memory device

Flow process for producing non-volatile memories with differentiated removal of the sacrificial oxide in the NO-DPCC diagram including a series of steps that permit the removal of the oxide in two distinct moments from the matrix area and from the circuitry area. In this manner the active circuitry areas are preserved from the danger of breaking the tunnel oxide, thus avoiding the degradation of the quality of the oxides and increasing, in addition, the level of reliability of the device itself.

Flow process for producing non-volatile memories with differentiated removal of the sacrificial oxide

Method for localizing point defects causing column leakage currents in a non-volatile memory device, said device including a plurality of memory cells arranged in rows and columns in a matrix structure, the columns being connected to drain regions by first contacts, source diffusions, and metal lines which connect the source diffusions to each other by second contacts. The method includes the steps of modifying the memory device in order to eliminate a part of the first contacts and all the second contacts, and to form third contacts, which connect the metal lines to drain regions in rows wherein the first contacts have been eliminated, making the source diffusions independent of each other and halving the initial number of the memory cells; sequentially biasing the single columns of the matrix; sequentially biasing the single rows of the matrix, keeping biased one column; localizing a memory cell which presents the point defects, when the leakage current flow occurs.

Method and apparatus for localizing point defects causing leakage

A nonvolatile memory having a cell comprising an N.sup.+ type source region and drain region embedded in a P.sup.- type substrate and surrounded by respective P-pockets. The drain and source P-pockets are formed in two different high-angle boron implantation steps designed to optimize implantation energy and dosage for ensuring scalability of the cell and avoiding impairment of the snap-back voltage. The resulting cell also presents a higher breakdown voltage as compared with known cells.

Method of making asymmetric nonvolatile memory cell

A method employing a test structure identical to the memory array whose gate oxide quality is to be determined, except for the fact that the cells are connected electrically parallel to one another. The test structure is so stressed electrically as to extract electrons from the floating gate of the defective-gate-oxide cells and so modify the characteristic of the cell while leaving the charge of the non-defective cells unchanged. In this way, only the threshold of the defective cells is altered. A sub-threshold voltage is then applied to the test structure, and the drain current through the cells, which is related to the presence of at least one defective cell in the structure, is measured. Measurement and analysis of the current-voltage characteristic provides for determining the number of defective cells. The method is suitable for in-line quality control of the gate oxide of EPROM, EEPROM and flash-EEPROM memories.

Method of evaluating the gate oxide of non-volatile EPROM, EEPROM and

A method employing a test structure identical to the memory array whose gate oxide or interpoly dielectric quality is to be determined, except for the fact that the cells are connected electrically parallel to one another. The test structure is subjected to electrical stress of such a value and polarity as to extract electrons from the floating gate of the defective-gate-oxide or defective-interpoly-dielectric cells and so modify the characteristic of the cell while leaving the charge of the non-defective cells unchanged. In this way, only the threshold of the defective cells is altered. A subthreshold voltage is then applied to the test structure, and the drain current through the cells, which is related to the presence of at least one defective cell in the structure, is measured. Measurement and analysis of the current-voltage characteristic provides for determining the number of defective cells. The method is suitable for in-line quality control of the gate oxide or interpoly dielectric of EPROM, EEPROM and flash-EEPROM memories.

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Dalmine, Italy

Leonardo Ravazzi