Source: {"pile_set_name": "USPTO Backgrounds"}

1. Field
The described technology relates generally to a substrate processing apparatus that simultaneously forms thin films or applies heat treatment to a plurality of substrates, and more particularly, to a substrate processing apparatus that can uniformly process a plurality of substrates by uniformly heating the substrates stacked on a boat disposed in a processing chamber.
2. Description of the Related Art
Flat panel displays have replaced cathode ray tube displays, due to superior characteristics, including light weight and small size. Typical examples of flat panel displays are liquid crystal displays (LCD) and organic light emitting diode (OLED) displays. Organic light emitting diode displays have excellent luminescence characteristics and viewing angle characteristics, as compared with liquid crystal displays (LCD) and do not need a backlight, such that they can be implemented in very small sizes.
The organic light emitting diode display generates light having a specific wavelength by energy from excitons produced by recombination of electrons injected from the cathode to an organic thin film and holes injected from the anode. Organic light emitting displays are classified into a passive matrix type and an active matrix type in accordance with the operation method, in which the active matrix type includes a circuit using a thin film transistor (TFT).
The flat panel displays are manufactured by forming a thin film with a predetermined pattern, which has electrical properties, from an organic substance or an inorganic substance on a substrate or performing heat treatment on the formed thin film. Methods of forming the thin film include physical vapor deposition (PVD), in which sputtering is used to apply and deposit plasma on a target and chemical vapor deposition (CVD), in which a reaction gas containing a source material is ejected onto a substrate, chemically forming a film on the substrate. Further, the chemical vapor deposition method is divided by the deposition type into low pressure chemical vapor deposition (LPCVD), plasma chemical vapor deposition (PECVD), and atomic layer deposition (ALD), which forms a source material in an atomic layer unit. The atomic layer deposition (ALD) method provides good uniformity of a thin film and step coverage, as compared with the physical vapor deposition method, such that it is increasingly used in the semiconductor process.
The chemical vapor deposition method uses batch type equipment that puts a plurality of substrates into a deposition chamber at one time and simultaneously forms thin films on the substrates, because the forming speed of a thin film is low when plasma is not used.
In general, substrate processing apparatuses that simultaneously form thin films on a plurality of substrates and perform heat treatment using the lower pressure chemical vapor deposition or the atomic layer deposition include a process chamber providing a space for processing, a boat including a plurality of stacked substrates, a heating unit disposed outside the process chamber, and a conveying unit that carries the boat into/out of the process chamber. In this configuration, the substrate processing apparatuses may further include substrate holders that are seated on the substrates and stacked in the boat, in order to prevent the substrates stacked in the boat from sagging.
In the substrate processing apparatuses, since the inside of the process chamber is heated by the heating unit at the outside of the process chamber and since a large process chamber is needed to accommodate the boat with stacked substrates, it is difficult to uniformly heat the inside of the process chamber only with the heating unit at the outside of the process chamber. Therefore, the portions stacked in the boat, particularly, the center portion and the edges are heated at different temperatures in the substrate, the time for performing heat treatment to the substrates increases, non-uniformity occurs in the formed film due to the non-uniform temperature distribution and non-uniformity occurs in the device characteristics due to differences in the heat treatment temperature. If temperature non-uniformity is excessive, substrate warpage may occur, such that following processes are impossible.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.