The tilt effects of the mirror-lamp (M-L) system on the shape of the interface of the silicon molten zone formed during growth using the infrared convergent heating floating zone method were studied at various positions of the M-L system. The stability and the interfaces of the molten zone formed in the tilted condition were compared with those in the no tilt condition. The molten zone appeared to be more stabilized in the tilted condition than in the no tilt condition. However, the conventional parameters characterizing the interface shape such as convexities (h/r), gap and zone length (L) were almost independent of the tilt angle (theta) of the M-L system and insufficient to discuss the tilting effects on the molten zone shape. The curvature of the solid-liquid interface was affected by the theta. New characterizing parameters such as the growth interface and triple point angles (delta and TPA, respectively) were effective to quantitatively describe the tilting effects on the interface shape. With increase of the theta, the delta was decreased and the TPA was increased in both the feed and crystal sides. A silicon crystal of 45 mm in diameter was grown successfully in the tilted condition. (C) 2015 Elsevier B.V. All rights reserved.