Solid state image pickup device and its manufacture

#The present invention relates to a solid state image pickup device and its manufacture method, and more particularly to a solid state image pickup device having the structure that a gate insulating film has therein a nitride film and its manufacture method.

#FIG. 4A is a block diagram showing a main portion of a solid state image pickup apparatus assembling a solid state imaging pickup device, and FIGS. 4B and 4C are schematic plan views showing the structure of the solid state image pickup device. FIG. 4D is a schematic cross sectional view showing a portion of a pixel area of a solid state pickup device.

#Referring to FIG. 4A, the structure of a solid state image pickup apparatus will be described. A solid state imaging pickup device 51 generates signal charge corresponding to an amount of light incident upon each pixel and supplies an image signal corresponding to the generated signal charge. A drive signal generator 52 generates drive signals (transfer voltage, etc.) for driving the solid state image pickup device 51 and supplies them to the solid state image pickup device 51. An analog front end (AFE) 53 subjects an output signal from the solid state imaging unit 51 to correlation double sampling, amplifies the sampled signal at an externally set gain, converts it into a digital signal, and outputs the digital signal. A digital signal processor (DSP) 54 processes an image signal supplied from the analog front end 53, such as recognition process, data compression and network control, and outputs the processed image data. A timing generator (TG) 55 generates timing signals for the solid state image pickup device 51, drive signal generator 52 and analog front end 53, to control the operations thereof.

#FIGS. 1A to 1E are schematic cross sectional views illustrating a manufacture method for a characteristic portion of a solid state image pickup device according the preliminary study.

#FIGS. 2A to 2E are diagrams explaining problems, newly found by the present inventors, of a solid state image pickup device manufactured by the method illustrated in FIGS. 1A to 1E.

#FIGS. 3A to 3J are schematic cross sectional views illustrating a manufacture method for the characteristic portion of a solid state image pickup device according to an embodiment.

#The present inventors manufactured the characteristic portion of a solid state image pickup device by the following manufacture method. The manufacture method for the other portion of the solid state image pickup device is similar to that described with reference to FIGS. 5A and 5B.

#FIGS. 1A to 1E are schematic cross sectional views illustrating a manufacture method for a characteristic portion of a solid state image pickup device according to the invention.

#Referring to FIG. 1A, in a semiconductor substrate 81, e.g., an n-type silicon substrate, p-type impurities, e.g., boron ions, are implanted to form a p-type well 82. In a surface layer of the well 82, n-type impurities, e.g., phosphorus or arsenic ions, are implanted to form a vertical transfer channel 73. A read gate 72 and the like are formed by implanting p-type impurities, e.g., boron ions. An insulating film 74 is formed on the surface of the p-type well 82, the insulating film including a thermally oxidized silicon oxide film (bottom oxide film) 74a having a thickness of 25 nm, a silicon nitride film 74b having a thickness of 50 nm and formed through CVD and a silicon oxide film (top oxide film) 74c having a thickness of 5 nm and formed by thermally oxidizing the surface of the silicon nitride film, respectively formed in this order from the bottom.