Electrical Characterization of Oxynitrided Gate Dielectrics under Constant‐Current Fowler‐Nordheim Stress

Abstract

Charge defects in metal oxide semiconductor capacitors formed with N,O oxynitrides are analyzed by Fowler-Nordheim tunneling injection stress. These oxides are found to incur fewer interface states and lower flatband voltage shifts, the higher the oxynitridation temperature, between 850 and 1050°C. Analysis of oxide traps during constant-current Fowler-Nordheim stress uncovers complex phenomena in oxide trap creation. Several features of the data indicate an optimum at an oxynitridation temperature of 850 to 950°C, including initial net-positive oxide trap creation, and changes in rates of oxide trap creation. However, the net-negative oxide trapping at high cumulative injected charge simply decreases with higher oxynitridation temperatures. There is evidence that "slow" donor states (or anomalous positive charge) near the Si/SiO 2 interface may be suppressed by this oxide process. ' 3-1 radiation impact-ionization,' 0 charge breakdown,"' Fowler-Nordheim stress -6 8 0, ' 6'18 and deep level transient spectroscopy.'9Several previous studies have shown that the oxynitrides have greater charge-to-breakdown, Qbd, than thermal oxides. Okada et al." 6 show that, the higher the concentration of N,O in the oxynitridation ambient (in the range 0% to 100%), the higher the charge to breakdown, Qbd, and that the Qbd of oxynitrides is two to four times larger (0.5 to 0.9 C/cm 2 ) than the control (thermal) case (0.2 to 0.6 C/cm 2 ). According to Hwang et al., 2 0 if the oxynitridation temperature is high (1000 to 1200°C), the shift of the interface trap density, D,, under a constant current Fowler-Nordheim (CCFN) stress of 10 mA/cm 2 , at high fluence (0.1 to 10 C/cm 2 ) is an order of magnitude lower than the control case. For example, for samples oxynitrided at 1000, 1100, and 1200°C, at a fluence of 1C/cm 2 , Dt at midgap is 4 x 10", 2 x 10", and 6 x 10 cm-2eV-', respectively, while the control has a Dt at midgap of >1.5 x 1012 cm-2 eV-'.Using Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and electrical characterization, Hori et al. 9 , have formed a semiempirical formula to explain the dramatic reduction of flatband voltage shift, AV,,, and * Electrochemical Society Active Member.