Time-Dependent Dielectric Breakdown in Thin Intrinsic SiO 2 Films
- PDF / 428,870 Bytes
- 9 Pages / 414.72 x 648 pts Page_size
- 88 Downloads / 231 Views
Mat. Res. Soc. Symp. Proc. Vol. 391 01995 Materials Research Society
The reciprocal-field model developed by Chen [4], Lee [5], and Moazzami [6] is based on Fowler-Nordheim electron injection into the oxide, and it is assumed that holes are injected or produced via impact ionization. These holes are trapped and alter the cathode electric field, leading to enhanced electron injection, hole generation, and eventual dielectric breakdown. The fieldacceleration parameter is also temperature dependent, and the thermal activation energy is assumed to be dependent on electric field as in the case of the linear field model. The results presented provide evidence that current-generation thin, intrinsic SiO2 films have similar and predictable electric field and temperature dependencies for TDDB stress conditions. Results from 6.5-to 22.5-nm-thick oxides show that the log(t.0) is linearly dependent on electricfield, with a field-acceleration parameter approximately equal to 1.0 decade/MV/cm. The field acceleration parameter is not sensitive to temperature.
All of the films exhibited a thermal
activation energy of approximately 0.7 to 0.9 eV at stress electric fields at or below 9 MV/cm. A description of the constant field stress test methodology is provided in Section II. Time-tofailure data obtained over a wide range of stress temperatures and electric fields are presented and discussed in Section El. Conclusions are given in Section IV.
EXPERIMENTAL Wafer-level TDDB data were collected from polysilicon gate test capacitors fabricated by several different technologies. The capacitors were fabricated on a p-type substrate and have an area of 0.001 cm2 . Oxide thickness ranged from 6.5 to 22.5 nm. The effect of positive and negative gate bias was also studied. An n' guard ring surrounded the devices to facilitate inversion testing. High-temperature stressing was implemented by using a specially designed wafer-level probe station capable of performing tests at temperatures as high as 400 'C [7, 8]. This station features a water-cooled probe card that utilizes a water jacket attached to a standard 10-cm (4-in.) probe card. The test devices are connected through a current-limiting series resistor to a constant voltage source. The voltage is monitored by scanning each device sequentially with a computer-controlled relay matrix system. The test system consists of equipment connected to a microcomputer via an IEEE interface bus. The system is capable of detecting a failure event in 100 ms. Stress temperatures varied from 60 to 400 "C, and electric fields were in the range from 5.5 to 12 MV/cm.
RESULTS AND DISCUSSION Figure 1 shows Fowler-Nordheim tunneling characteristics measured over the temperature range from 23 to 400 "C. Even at a temperature of 400 'C, the tunneling current is still qualitatively described by Fowler-Nordheim indicating that the high temperatures used to accelerate breakdown did not induce a failure mode that was significantly different than that which occurs at lower temperatures.
124
10-16 r
tox = 15
Data Loading...
