1. Field of the Invention
The present invention relates to a thermal processing method and a thermal processing apparatus for heating a precision electronic substrate (hereinafter simply called a “substrate”) shaped as a thin plate such as a semiconductor wafer of a circular plate shape by irradiating the substrate with a flash, and a susceptor on which the substrate is placed.
2. Description of the Background Art
Impurity introduction performed to form a pn junction in a semiconductor wafer is an essential step in manufacturing process of a semiconductor device. At present, impurities are introduced generally by ion implantation process and subsequent annealing process. The ion implantation process is a technique of implanting impurities physically by ionizing an impurity element such as boron (B), arsenic (As) or phosphorous (P) and making the impurity ions collide with the semiconductor wafer at a highly accelerated voltage. The implanted impurities are activated by the annealing process. If the annealing takes about several seconds or more, the implanted impurities are diffused deeply by heat and a resultant junction reaches a depth greater than is necessary. This might become an obstacle to favorable formation of the device.
Flash lamp annealing (FLA) has attracted attention in recent years as an annealing technique of heating a semiconductor wafer within an extremely short time. The flash lamp annealing is a thermal processing technique of increasing the temperature only of a surface containing implanted impurities of a semiconductor wafer within an extremely short time (several milliseconds or less) by irradiating the surface of the semiconductor wafer with a flash using a xenon flash lamp (in the below, a lamp simply called a “flash lamp” means a xenon flash lamp).
The spectral distribution of light emitted from a xenon flash lamp ranges from an ultraviolet region to a near-infrared region, has a shorter wavelength than light from a conventional halogen lamp, and substantially agrees with the base absorption band of a silicon semiconductor wafer. Thus, irradiating a semiconductor wafer with a flash from the xenon flash lamp does not produce much transmitted light so that the temperature of the semiconductor wafer can be increased rapidly. Additionally, it has become known that irradiation with a flash within an extremely short time of several milliseconds or less can increase the temperature only of a surface and its vicinity of the semiconductor wafer selectively. As a result, increasing a temperature within an extremely short time with the xenon flash lamp can realize only activation of impurities without causing deep diffusion of the impurities.
US 2009/0175605 discloses a thermal processing apparatus using such a xenon flash lamp. In this thermal processing apparatus, the flash lamp and a halogen lamp are arranged above and below a chamber respectively and desirable thermal processing is realized by a combination of these lamps. In the thermal processing apparatus of US 2009/0175605, a semiconductor wafer placed on a susceptor is preheated to a certain temperature with the halogen lamp, and is then heated to a desirable processing temperature by being irradiated with a flash from the flash lamp.
In the thermal processing apparatus of US 2009/0175605, six bumps (support pins) in total are provided on the quartz susceptor while being spaced at intervals of 60 degrees along the circumference of a circle of a given radius. A target semiconductor wafer is placed on the susceptor while being supported by point contact with the six bumps (six-point support). When the semiconductor wafer is placed on the susceptor with the six bumps and irradiated with a flash from the flash lamp, the temperature only of the upper surface of the wafer increases instantaneously to expand rapidly by heat. Hence, the semiconductor wafer warps such that the upper surface of the wafer becomes convex. This makes an edge portion of the semiconductor wafer contact the upper surface of the susceptor so the quartz in the contact area is scraped against the semiconductor wafer. This phenomenon disadvantageously causes a scar in the susceptor and makes the scraped quartz scatter as particles.