A Mechanism of Field‐Oxide‐Ungrowth Phenomenon in Recessed Isolation Process and Practical Solution

Abstract

Field-oxide-ungrowth (FOU) phenomenon in recessed local oxidation of silicon (R-LOCOS) isolation process has been studied. Field oxidation temperature has been revealed to play a decisive role in the occurrence of FOU and nitrogen-containing polymers originated from the etching process are believed to be converted into oxidation barrier materials at a certain temperature and above. This transition temperature lies between 1000 and 1050°C, independent of the ambient in the furnace. Although field oxidation below the transition temperature can eliminate the FOU, it causes severe thinning of the field oxide at a small isolation spacing. In order to remove the FOU and at the same time to minimize the field oxide thinning, we propose a new field oxidation method which is a combination of a breakthrough field oxidation at below the transition temperature and a high temperature field oxidation.

Control of the Slope of Field Oxide Edge and Its Effects on Gate Oxide Reliability

“…This structure provides short bird's beak, high volume ratio, and relatively planar field oxide topology. 1,2 elsewhere. [1][2] All field oxides were grown with a target thickness of 3000 Å.…”

“…1,2 elsewhere. [1][2] All field oxides were grown with a target thickness of 3000 Å. The pad nitride and pad oxides were removed in a hot phosphoric acid and a diluted HF solution, respectively.…”

“…We proposed a mechanism of FOU occurrence where an oxidation barrier material is formed only above 1050ЊC from nitrogen-containing polymers produced during etch processes. 2 In order to avoid the FOU problem and at the same time incorporate high temperature field oxidation to mitigate field oxide thinning effect, 2,4 we proposed a two-step field oxidation recipe shown in Fig. 2c.…”

“…2c. 2 Figure 2d shows that a low temperature field oxidation carried out below 1050ЊC [named breakthrough field oxidation (BTFOX)] prior to a high temperature field oxidation (HTFOX) above 1050ЊC solves the FOU problem. It is believed that the oxide grown by the BTFOX provides oxidation paths before formation of the oxidation barrier at high temperature.…”

“…A number of modified local oxidation of silicon (LOCOS) structures have been used to meet the required profiles of field oxide. We reported that the recessed LOCOS with nitride spacer (R-LOCOS), [1][2] shown in Fig. 1, exhibited the suppressed bird's beak because of an oxidation blocking thin nitride spacer.…”