Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2001-10-25
2004-08-03
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S680000, C438S681000, C427S255120, C118S715000
Reexamination Certificate
active
06770562
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a film formation apparatus and a film formation method, which are used when a film formation material is purified by sublimation to form a film using the purified material in forming an EL element over a substrate.
2. Description of the Related Art
In recent years, there has been an active study of a light emitting device which has an EL element as a self light emitting element, and in particular, a light emitting device using an organic material as an EL material has attracted attention. This light emitting device is also called an organic EL display (OELD) or an organic light emitting diode (OLED).
Note that the EL element has a layer containing an organic compound in which electro luminescence is generated by applying electric field (hereinafter referred to as EL layer), an anode, and a cathode. The electro luminescence in the organic compound includes luminescence produced in returning from a singlet excitation state to a ground state (fluorescence) and luminescence produced in returning from a triplet excitation state to a ground state (phosphorescence). A light emitting device manufactured by a film formation apparatus and a film formation method according to the present invention can be applied to the case where either luminescence is used.
A light emitting device has a characteristic that a problem with respect to an angle of a field of view is not caused because it is a self light emitting type which is different from a liquid crystal display device. That is, it is more suitable than the liquid crystal display device when a display is used in the outdoors, and thus various ways of use are proposed.
The EL element has a structure in which an EL layer is interposed between a pair of electrodes. The EL layer generally has a laminate structure. Typically, there is a laminate structure called “hole transport layer/light emitting layer/electron transport layer”, which is proposed by Tang, et al. of Eastman Kodak Company. Light emitting efficiency is very high in this structure, and thus, this structure is adapted to most of the light emitting devices which have been researched and developed at present.
In addition, a structure in which a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer are laminated in this order on the anode is preferable. Also, a structure in which a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer are laminated in this order on the anode is preferable. The light emitting layer may be doped with a fluorescent pigment or the like. These layers may be formed using a low molecular system material or a polymer system material.
Note that all layers provided between the cathode and the anode in this specification is generically called the EL layer. Thus, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, and the electron injection layer, which are described above, are all included in the EL layer.
Also, in this specification, a light emitting element formed of a cathode, an EL layer, and an anode is called the EL element. There are two types, that is, a type in which an EL layer is formed between two kinds of stripe-shaped electrodes provided to intersect each other (simple matrix type) and a type in which an EL layer is formed between a pixel electrode which is connected with a TFT and arranged in matrix and a counter electrode (active matrix type).
The most serious problem in putting the EL element to practical use is the insufficiency of the element life. Also, deterioration of the element is recognized in the form that a non light emitting region (dark spot) is expanded with light emission for a long period of time due to deterioration of the EL layer which eventually becomes a problem.
An EL material for forming the EL layer is deteriorated by an impurity such as oxygen, water, or the like. Also, when other impurity is included in the EL material, there arises a fear that the deterioration of the EL layer is adversely influenced.
Conventionally, when film formation is performed by an evaporation method, an evaporated material is used without being processed. However, it is considered that an impurity is mixed into the evaporated material at evaporation. That is, there is a possibility that oxygen, water, and other impurity are mixed as one reason for the deterioration of the EL element.
Also, when the evaporated material has been purified in advance, the purity can be increased. However, there is a possibility that an impurity is mixed during a period until the evaporation is completed.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems, and an object of the present invention is therefore to provide a film formation apparatus with which an impurity included in an EL material at film formation is separated and removed, film formation is performed using an EL material with the increased purity, and thus an EL layer with high purity can be formed. Also, another object of the present invention is to provide a film formation method using the film formation apparatus of the present invention.
The present invention is characterized in that the EL material is purified by sublimation using a sublimation temperature of the pure EL material immediately before the film formation to remove plural impurities included in the EL material, and then a thin film is formed using the purified EL material (hereinafter referred to as high purity EL material) as an evaporation source.
In
FIG. 1
, it will be described that in the case where the EL material in which plural impurity substances are included is evaporated from a solid and a temperature is changed, plural substances can be separated from the EL material in accordance with different sublimation temperatures of respective substances. Note that an ordinate is given by a temperature and an abscissa is given by the total amount of precipitation. In this specification, a substance (impurity) which has a higher sublimation temperature than the high purity EL material is called a high temperature material, and a substance (impurity) which has a lower sublimation temperature is called a low temperature material. Also, the high purity EL material which is sublimated at a middle temperature located between a high temperature and a low temperature is called a middle temperature material. Note that, with examining a material precipitated at every temperature in advance by an analysis such as a mass analysis (GC-MS), a sublimation temperature of the pure EL material can be examined.
First, a temperature at which all substances (high purity EL material and impurity) included in the EL material are evaporated (hereinafter referred to as complete sublimation temperature) is set. Thus, there are all substances included in the EL material as gases in a complete sublimation region
100
. Thereafter, when a temperature is gradually decreased, a high temperature material which has a high sublimation temperature is precipitated as a solid in a high temperature material precipitation region
101
shown in FIG.
1
.
Further, when a temperature is decreased, a middle temperature material (high purity EL material) as a main product is precipitated in a middle temperature material precipitation region
102
shown in FIG.
1
. Then, a temperature is again decreased, a low temperature material is precipitated in a low temperature material precipitation region
103
.
That is, according to the present invention, there are provided a film formation apparatus and a film formation method for separating an impurity precipitated at a high temperature (high temperature material) or an impurity precipitated at a low temperature (low temperature material) from the high purity EL material (middle temperature material) based on a precipitation temperature difference and performing film formation using only the high purity EL material. Further, i
Konuma Toshimitsu
Nishi Takeshi
Yamazaki Shunpei
Berry Renee R.
Nelms David
Semiconductor Energy Laboratory Co,. Ltd.
LandOfFree
Film formation apparatus and film formation method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Film formation apparatus and film formation method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Film formation apparatus and film formation method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3362179