Study on La 2 O 3 Wet Clean by pH Controlled Functional Water

Introduction For the dimensional scaling and performance enhancement of upcoming semiconductor devices, some novel materials have been implemented. In the high-k metal gate (HKMG) of logic and memory periphery transistors, some lanthanides and alkaline earth metal or their oxides, e.g. lanthanum oxide (La 2 O 3 ) and magnesium oxide (MgO), have been proposed as a zero-thickness work function shifter [1-7]. These dielectric films are typically patterned by wet processing to enable a multiple threshold voltage [6,7]. However, the wet processes on the new materials are challenging because they dissolve easily in de-ionized wafer (DIW). In this paper, the impact of functional water rinsing on the dissolution and passivation of La 2 O 3 films have been investigated. Experimental detail Coupon testFirst, the effect of etching due to pH was tested. The pH of the solution was adjusted by ammonia or hydrochloric acid. Moreover, O3, H2, H2O2 was added to the ammonia water which dissolution suppression has confirmed, and the effects of their solutions were tested.(2) Wafer test We tested using 10 mm × 10 mm coupon which was cut from 300 mm La 2 O 3 wafers. And the La 2 O 3 coupon was immersed in various dilute solutions under open air conditions. After immersion, the La concentration in the solution was analyzed by ICP-MS. And we calculated the La dissolution amount from these results. The DIW and some functional waters, e.g. CO 2 dissolved water (CO 2 Water), ultra-diluted NH 4 OH (NH 4 OH water) , ultra-diluted NH 4 OH and ultra-diluted H2O2 (NH 4 OH/H 2 O 2 water), were prepared by using a Kurita functional water unit (HS-13, Kurita Water Industries), which has the capability of injection and mixing CO 2 (1 – 40 ppm) and NH 4 OH (1 – 100 ppm). The 300 mm blanket La 2 O­ 3 wafers were processed on a single wafer wet cleaning tool (SU-3200, SCREEN Semiconductor Solutions) connected with the functional water unit. First, We had cleaning tests using CO 2 water, DIW, NH 4 OH water, NH4OH/H2O2 water. Moreover, in order to clarify the dissolution suppression mechanism, the wafer surfaces after cleaning with each solution were analyzed by XRR. Results and discussion Coupon test La 2 O 3 + 6H + → 2La 3 + +3H 2 O (1). La 2 O 3 + 3H 2 O → 2La(OH) 3 (2).In addition, when H 2 , O 3 and H 2 O 2 were added to ammonia water of pH 10.4, Suppression effects were confirmed by H 2 O 2 added, but we did not have the effect by H 2 and O 3 gases added(2) Wafer test Several functional wa