Patent Application: US-56246595-A

Abstract:
a process for suppressing boron penetration in bf 2 + - implanted p + - poly - si gates provides a nitrided layer between the oxide layer and poly - si through use of inductively - coupled nitrogen plasma to form an energy barrier which the boron ion can hardly penetrate . the process includes the steps of growing an oxide layer by washing the silicon , introducing nitrogen gas into the inductively - coupled plasma system and carrying out nitrogen plasma surface treatment at rf power of 150w to 250w ; stacking polysilicon of 3000 å low pressure chemical vapor deposition system ; implanting bf 2 + at 5 × 10 15 atom / cm 2 and 50 kev ; removing the surface oxide layer by annealing at 900 ° c . for a time ; and plating al to form a mos capacitor and measuring electric properties .

Description:
the preferred process , as illustrated in fig1 is implemented as follows : substrate 1 and thick oxide 2 are formed from a silicon wafer according to conventional cmos production methods . the silicon wafer is then washed and placed in a high temperature furnace , where an oxide layer 3 of 50 - 120 å is grown by introducing oxygen at 900 °- 1000 ° c ., again according to conventional production methods . next , a nitrided barrier layer is formed by placing the silicon wafer in an icnp system and introducing nitrogen at power of 100 - 300 w for 1 - 30 minutes at the surface of the substrate , after which one or more layers 4 of polysilicon or polycrystalline silicon of approximately 1000 - 3000 å thickness are stacked , bf 2 + ions 5 are implanted at an energy of 30 - 70 kev and amount of 1 × 10 15 - 1 × 10 16 atom / cm2 with layer 3 preventing penetration , and the silicon wafer is washed again and placed into a high temperature furnace again , at which time nitrogen or oxygen is introduced at 800 °- 1000 ° c . and annealed for 10 - 30 minutes . subsequent steps are the same as those in conventional double gate cmos production . referring to fig2 a comparison of nitrogen contents in the space between the oxide layer formed and the polysilicon substrate after various icnp treatments shows that after icnp treatment , more nitrogen was stacked in the space between the oxide layer formed and the polysilicon substrate , the nitrogen content at 500w , 21 , being higher than that at 250w , 22 , whereas when the sample at 250w was annealed in high temperature nitrogen of 900 ° c ., its nitrogen content , 23 , became less and about the same as that of control sample , 24 . thus , this secondary - ion mass spectrum ( sims ) can demonstrate that a layer of nitrogen atoms is indeed formed at the interface between the oxide layer and the polysilicon substrate . referring to fig3 the flatband voltage ( vfb ) of annealed ( 900 ° c .) samples which have been treated , respectively , with icp 150w for 10 minutes , icp 250w for 10 minutes , and without icp , after treatment for 20 minutes , the vfb of the sample treated with icp 150w , 31 , is the lowest , while that of the sample treated with icp 250w , 32 , is the same as that of control , 33 , and after annealing for 60 minutes , the vfb of the sample treated with icp 150w , 31 , is still the lowest , but in this case , the vfb of the sample treated with icp 250w , 32 , is higher than that of control , 33 . this result occurs because the power of icp 250w is too strong , causing the quality of the oxide layer to be degraded so as to be unable to prevent the diffusion of boron ions . fig4 shows the relationship of the ratio of low frequency capacitance to oxide layer capacitance versus gate voltage of those three samples after annealing at 900 ° c . for 60 minutes , while fig5 shows their high frequency capacitance - voltage relationship . it can be seen that the shift of the sample treated with icp 150w , 31 , like its vfb , is the lowest , indicating that its boron diffusion is the lowest . the invention has been described in detail with reference to the above embodiments in order to illustrate the objects , features and functionalities thereof . however , a person having ordinary skill in the art will readily recognize that , according to the above description of the invention , partial variations and modifications to the embodiment can be made without departing from the scope and spirit of the invention . accordingly , the intellectual property rights to this invention are defined only by the appended claims . . g . j . hu , and r . h . bruce , &# 34 ; 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