1. Field of the Invention
The present invention relates to a heat treatment apparatus and a method of manufacturing a semiconductor device using the heat treatment apparatus. In particular, the present invention relates to a heat treatment apparatus for heating a subject substrate with radiation from a light source such as a lamp, and a method of manufacturing a semiconductor device using the heat treatment apparatus is applied to a semiconductor device using a semiconductor film having a crystalline structure.
2. Description of the Related Art
Heat treatment is a process required for activating impurities added to a semiconductor and for forming contact between a semiconductor and an electrode. In particular, a hot-wall type horizontal or vertical annealing furnace is known as a typical heat treatment apparatus.
However, regarding a monolithic integrated circuit manufactured by using a semiconductor, there is an increasing demand for very high processing precision along with miniaturization. In particular, in order to form a shallow junction, a heat treatment technique is required for minimizing diffusion of impurities. It is considered that a method requiring a considerable time for heating and cooling as in an annealing furnace is not necessarily appropriate.
In contrast, as a heat treatment technique of rapid heating and rapid cooling, rapid thermal anneal (hereinafter, referred to as “RTA”) has been developed, and a heat treatment method has been developed, which is conducted by instantaneously supplying heat within tens of seconds to several microseconds. RTA is known as a method of rapidly heating a substrate mainly using an infrared lamp, thereby conducting heat treatment in a short period of time.
An integrated circuit is manufactured not only by using a semiconductor substrate such as a silicon wafer, but also by using a thin film transistor (hereinafter, referred to as “TFT”) formed on a substrate made of glass, quartz, or the like. Although depending upon the structure and manufacturing method, a TFT having more satisfactory electrical characteristics can be obtained by forming an active layer constituting a channel with a semiconductor film having a crystalline structure (hereinafter, referred to as a “crystalline semiconductor film”), rather than by forming the active layer constituting a channel with an amorphous semiconductor film.
When a quartz substrate is used, a resultant TFT can withstand heat treatment at 900° C., and a manufacturing technique based on a semiconductor substrate can be applied. On the other hand, in the case where the size of a substrate is enlarged as in a liquid crystal display device, the use of an inexpensive glass substrate is required for reducing a cost. As a glass substrate commercially available or mass-produced for electronic equipment such as a liquid crystal display device, aluminoborosilicate glass, barium borosilicate glass, or the like with the concentration of contained alkaline elements reduced is used. However, the heat resistant temperature of such a glass substrate is at most about 650° C., so that the upper limit of a heat treatment temperature is inevitably determined in the vicinity of that temperature.
For example, an amorphous silicon film requires heat treatment at 600° C. or higher for several to tens of hours for crystallization. In order to shorten a time for crystallization, a higher temperature is required. However, increasing a heat treatment temperature more than a strain point causes irreversible deformation of a glass substrate, which is not a practical method. Therefore, according to a laser annealing method to be adopted for that purpose, laser light with a high energy density condensed by an optical system is radiated for crystallization. Typically, an excimer laser that pulse-oscillates is used. In the case of an excimer laser, although an irradiation time of laser light is tens of nanoseconds, a semiconductor film melts to be in a liquid phase state and then, crystallized.
Although it is attempted to crystallize an amorphous semiconductor film by an RTA method, a longer heating time is required, compared with the laser annealing method. Furthermore, in terms of a heating temperature, crystallization by the RTA method has a problem. More specifically, crystallization by the RTA method is solid-phase growth; therefore, unlike the laser annealing method, satisfactory crystal cannot be obtained, and a substrate temperature is considerably increased. This requires that a quartz substrate having heat resistance be used. In the case of a glass substrate, it has been confirmed that a substrate temperature is increased by heating with lamp light irradiated for crystallization for tens of seconds, and strain and deformation are caused.
Crystallization by heat treatment of a semiconductor film and activation of added impurities have an optimum temperature range. However, reaction proceeds more rapidly with heating at a higher temperature, and heat treatment is conducted in a shorter period of time. Even with the RTA method, in the case of using a glass substrate with low heat resistance, treatment conditions for heating a glass substrate at a heat resistant temperature or higher cannot be applied. Therefore, it is required to prolong a treatment time, instead of lowering a treatment temperature. However, the RTA is based on a single wafer treatment, so that an increase in a heat treatment time causes a decrease in a throughput.
The RTA method is capable of conducting heat treatment up to a high temperature in a short period of time. Furthermore, although using a single wafer treatment, the RTA method potentially has higher treatment ability, compared with the furnace annealing method. However, according to the conventional RTA method, it is required to increase a heating temperature, instead of shortening a heating time. Therefore, in order to obtain desired effects in activation and gettering process, it is required to conduct heat treatment at a strain point or higher of glass, and in some cases, a softening point or higher of glass. For example, with heat treatment at 800° C. for 60 seconds for the purpose of gettering process, a glass substrate is curved and deformed with its dead weight.
The use of an annealing furnace for a batch treatment is also considered. However, in this case, an apparatus is enlarged with an increase in size of a subject substrate. This causes an increase in power consumption due to uniform heating in a furnace of large capacity, as well as an increase in a setting area.