JP4491449B2 - Molecular beam source cell for thin film deposition - Google Patents

Description

  In the present invention, by heating the film forming material, the film forming material is sublimated or melted and evaporated to generate molecules of the film forming material, and the molecules of the film forming material are released toward the solid surface. The present invention relates to a molecular beam source cell for thin film deposition used for growing a film by depositing molecules on a solid surface and a thin film deposition method using the same.

  A thin film deposition apparatus called a molecular beam epitaxy apparatus installs a substrate in a vacuum chamber that can be depressurized to a high vacuum, heats it to a required temperature, and moves molecules such as Knudsen cells toward the thin film growth surface of the substrate. A source cell is installed. The film forming material stored in the crucible of the molecular beam source cell is heated by a heater to be sublimated or melted and evaporated, and the generated evaporated molecules are incident on the thin film growth surface of the substrate, and the thin film is epitaxially grown on the surface. Thus, a film of the film forming material is formed.

  The molecular beam source cell used in such a thin film deposition apparatus is formed in a crucible made of, for example, quartz glass or PBN (pyrolytic boron nitride) having high thermal and chemical stability. The material is stored, and this film forming material is heated by an electric heater provided outside the crucible, whereby the film forming material is sublimated or melted and evaporated to generate film forming molecules.

In recent years, research and development of organic electroluminescence elements (organic EL elements) have been promoted in fields such as displays and optical communications. This organic EL element is an element in which a light-emitting layer is formed of an organic low-molecular or organic polymer material having EL light-emitting ability, and has attracted attention as a self-luminous element. For example, the basic structure is that a film of a hole transport material such as triphenyldiamine (TPD) is formed on a hole injection electrode, and a fluorescent material such as an aluminum quinolinol complex (Alq ₃ ) is laminated thereon as a light emitting layer. Further, a metal electrode having a small work function such as Mg, Li, or Ca is formed as an electron injection electrode.

  As for recent displays, a large screen has become a demand of the times. Therefore, even in the display using the organic EL as described above, it is required to form an organic EL film on a large-area substrate. In particular, in a display using an organic EL, it is required to form a homogeneous organic EL film on a substrate.

  As such an organic EL material, a powdery material is used as a material serving as an evaporation source, and the powdery evaporation source material is sublimated to generate molecules thereof. However, at this time, the so-called spitting phenomenon, in which the molecules of the film forming material are aggregated, clustered and scattered, is likely to occur. Then, the clusters are scattered and attached to the solid film formation surface to be formed. The clusters adhering to the film formation surface cause non-uniformity and discontinuity of the film and cause film defects. Therefore, it is necessary to separate the film formation surfaces to such a distance that the clusters do not fly, and the film formation efficiency is poor.

  Therefore, for example, as described in the following cited document, the molecule is not released directly from the opening of the crucible, and the molecule is released toward the film formation surface from the exit port which is a small hole provided in the lid or the wall. Measures are taken to suppress scattering of the cluster and to release only molecules from the exit port toward the film formation surface.

However, in such a molecular beam source cell provided with an exit port, if the amount of released molecules is increased in order to increase the film formation rate, the temperature of the exit port decreases due to rapid expansion of the molecules at the exit port. As a result, the molecules become solid around the exit port and the exit port is clogged, and the film formation due to the release of the molecule does not continue. This is a so-called cold wall phenomenon. In order to prevent this phenomenon, it is desirable to maintain the emission port at a certain temperature higher than the crucible side, specifically, at a high temperature of about 20 ° C. However, for that purpose, in addition to the heater for heating the crucible, a heater for heating the periphery of the emission port and its temperature control means are required, and there is a problem that the molecular beam source cell becomes complicated and large.
JP 2004-162108 A JP 2004-18997 A JP 2003-301255 A JP 2003-113465 A

In view of the problems in the conventional thin film deposition molecular beam source cell, it is possible to maintain the temperature around the exit opening slightly higher temperature than the crucible at the same heater, thereby, at the exit port It is an object of the present invention to provide a molecular beam source cell for thin film deposition in which released molecules are hardly solidified and the exit port is not easily clogged.

  In the present invention, in order to achieve the above object, the heater 3 is brought close to the crucible 1, while the heat transfer member 4 that directly receives heat from the heater 3 and the member provided with the outlet 7 are integrated. By doing or connecting, the heat of the heater 3 is easily transmitted to the member provided with the emission port 7. On the other hand, the crucible 1 has a structure in which heat is hardly transmitted as compared with the member provided with the emission port 7.

That is, a molecular beam source cell for thin film deposition according to the present invention includes a crucible 1 for storing a film forming material and a heater for generating molecules by heating and sublimating or evaporating the film forming material stored in the crucible 1. 3 and an emission port 7 which is provided on the opening side of the crucible 1 and emits molecules toward the film formation surface. Then, although to close the heat transfer member 4 which receives the transmission of heat directly from the heater 3 in the crucible 1, provided with a gap therebetween, the shielding member 6 provided with the exit opening 7 and the heat transfer member 4 Are integrated or connected.

In such a molecular beam source cell for thin film deposition according to the present invention, the heater 3 is brought close to the crucible 1, and the heat transfer member 4 that directly receives heat from the heater 3 and the shielding member 6 provided with the emission port 7. preparative due to the linked or an integral, can be heated both the member provided with the crucible 1 and an exit port 7 in the same heater 3. In this structure, the heat of the heater 3 is transmitted more greatly from the crucible 1 side to the shielding member 6 side where the emission port 7 is provided. As a result, even if the temperature of the exit port 7 is about to drop due to the rapid expansion of the molecules emitted from the exit port 7, heat is transferred from the heater 3 accordingly, so the temperature of the exit port 7 is kept higher. Is done. Thereby, solidification of molecules at the emission port 7 does not occur, and the emission port 7 is not blocked by the solidified film forming material.

  In particular, an orifice provided with a gap g between the heat transfer member 4 and the crucible holder 5 containing the crucible 1, and further provided with a molecule passage hole 11 for adjusting the flow of molecules to be released between the crucible 1 and the exit port 7. By arranging 2, the heat of the heater 3 is not directly transferred from the heat transfer member 4 to the crucible holder 5 but is transferred from the shielding member 6 through the orifice 2. And by making the thickness of the contact portion 2a between the orifice 2 and the heat transfer member 4 thinner than other portions, it becomes difficult to transfer heat from the shielding member 6 to the orifice 2, and the area around the emission port 7 and the crucible 1 is easy to form a temperature difference.

As described above, according to the present invention, the same heater 3 makes it possible to generate a molecule with sublimation or evaporation of the film forming material was heated crucible 1. Further, since the exit port 7 can be maintained at a slightly higher temperature than the crucible 1 to prevent clogging due to solidification of molecules at the exit port 7, the structure of the crucible 1 and its heater 3 is not complicated or enlarged. Molecular radiation is possible.

In the present invention, the heat transfer path between the heater 3 and the crucible 1 and the member forming the outlet is reexamined, and by adopting a structure in which the heat of the heater 3 is more easily transferred from the crucible 1 to the outlet. The objective has been achieved.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

FIG. 1 is a longitudinal side view showing an embodiment of a molecular beam source cell for thin film deposition according to the present invention, and FIG. 2 is a plan view thereof.
A cylindrical container-shaped crucible 1 made of quartz glass or the like whose outer shape is slightly smaller than its inner diameter is fitted in a cylindrical container-shaped crucible holder 5. A film forming material is stored in the crucible 1.

  A cylindrical cup-shaped orifice 2 is fitted on the upper part of the crucible holder 5 so as to close the opening of the crucible 1, and a molecular passage hole 11, which is a small hole, is opened at the bottom of the orifice 2. From the central part of the bottom wall of the orifice 2, a shaft-like member is suspended downward, and a partition plate 10 projects from the shaft-like member into the crucible 1. The partition plate 10 rectifies the upward flow of molecules generated by sublimation or evaporation of the film forming material stored in the bottom of the crucible 1 and raises only the molecules, and the clusters are released toward the film forming surface. It is intended to prevent this.

  A lid-shaped shielding member 6 is provided so as to close the opening of the orifice 2, and an emission port 7, which is a small hole, is provided at a position corresponding to the center of the opening of the shielding member 6 orifice 2. Accordingly, the internal space of the orifice 2 is a small space, and the molecule passage hole 11 on the bottom wall of the orifice 2 and the emission port 7 of the shielding member 6 communicate with each other through the internal space of the orifice 2. ing. The contact portion 2a of the upper half that is in contact with the shielding member 6 of the orifice 2 is thinner than the portion below it. As a result, the contact area of the orifice 2 with the shielding member 6 is narrow, and the cross-sectional area of the contact portion 2a that conducts heat is narrow, so that heat transfer from the shielding member 6 side to the orifice 2 side is difficult.

  A rod-shaped heater 3 is provided on the side of the crucible holder 5, and a heat transfer member 4 made of cylindrical stainless steel or the like having a good heat conductivity is fitted into the heat generating portion at the tip. The upper end portion of the heat transfer member 4 is integrated with the shielding member 6. The heat transfer member 4 and the shielding member 6 are not necessarily integrated, but they may be directly joined or indirectly joined via a member having good heat conduction. In short, the structure is such that the heat of the heater 3 easily conducts heat around the emission port 7 via the heat transfer member 4 and the shielding member 6.

On the other hand, the heat transfer member 4 fitted into the heat generating portion of the heater 3 is close to the crucible holder 5, but a gap g is provided between the heat transfer member 4 and the crucible holder 5. Thereby, the heat applied to the crucible 1 is not directly transmitted to the crucible holder 5.
Temperature measuring contacts of the first thermocouple T / C1 and the second thermocouple T / C2 are attached to the upper surface of the shielding member 6 and the bottom surface of the crucible holder 5, respectively.
Note that the film thickness meter 12 shown in FIG. 1 measures the film thickness when a film formation test to be described later is performed, and a substrate having a film formation surface is actually placed at this position.

Using such a molecular beam source cell for thin film deposition, 1.8 cc of Alq ₃ was stored as a film forming material in a crucible in a vacuum chamber, and the heater 3 was heated to perform a molecular emission test. .
Table 1 shows the temperatures measured by the first thermocouple T / C1 and the second thermocouple T / C2, respectively, when the heater 3 is heated to heat the crucible 1 and the shielding member 6 and raise the temperature. Indicates. Measured at 50 ° C. intervals until the temperature measured by the first thermocouple T / C1 reaches 100 ° C. to 350 ° C., and the temperature measured by the second thermocouple T / C2 at that time is shown in the right column. ing. As is apparent from Table 1, the temperature measured by the second thermocouple T / C2 when the temperature of the first thermocouple T / C1 is 350 ° C. is 322.3 ° C., and the temperature difference is It was 27.6 ° C.

  Table 2 shows the temperature control so that the temperature measured by the first thermocouple T / C1 is maintained at 350 ° C., and the second after 5 minutes, 10 minutes and 15 minutes after the temperature is reached. The temperature measured by the thermocouple T / C2 and the film formation rate, the total film thickness accumulated up to each time, and the degree of vacuum at each time are shown. The film thickness meter 12 was placed at a distance of 400 mm from the emission port 7. As is apparent from Table 2, the temperature difference between the temperatures measured by the first thermocouple T / C1 and the second thermocouple T / C2 is 23 ° C. to 20.8 ° C., and the film formation rate is 10 After a minute, it became stable at 2.7 to 2.8 Å / s.

  Table 3 shows that the temperature measured by the first thermocouple T / C1 is controlled so that the temperature is maintained at 360 ° C., and measured by the second thermocouple T / C2 after 5 minutes from that temperature. Temperature, film formation rate, total film thickness up to each time, and degree of vacuum at each time are shown. The distance from the emission port 7 to the film thickness meter 12 is 400 mm, which is the same as in Table 2. As apparent from Table 3, the temperature difference between the temperatures measured by the first thermocouple T / C1 and the second thermocouple T / C2 is 22.5 ° C., and the film formation rate is 4 Å / s. stable.

  Table 4 shows temperature control so that the temperature measured by the first thermocouple T / C1 is maintained at 370 ° C., and the second thermocouple T 5 minutes and 10 minutes after the temperature is reached. The temperature measured at / C2, the film formation rate, the total film thickness up to each time, and the degree of vacuum at each time are shown. The distance from the emission port 7 to the film thickness meter 12 is 400 mm, which is the same as in Table 2. As apparent from Table 4, the temperature difference between the temperatures measured by the first thermocouple T / C1 and the second thermocouple T / C2 is about 25.5 ° C., and the film formation rate is 5 minutes later. It is estimated that the maximum peak is reached and the maximum is around 5.5 Å / s.

Next, for comparison, a molecular beam source cell for thin film deposition shown in FIG. 3 is used, and 1.2 cc of Alq ₃ is housed in a crucible as a film forming material in a vacuum chamber, and the heater 3 is heated. A molecular emission test was performed. In the molecular beam source cell for thin film deposition shown in FIG. 3, the heat transfer member 4 and the shielding member 6 fitted in the heat generating portion of the heater 3 are separated, while the heat transfer member 4 and the crucible holder 5 are separated from each other. A structure in which the copper plate 13 is sandwiched therebetween and the heat of the heater 3 can be transmitted to the crucible 1 through the heat transfer member 4, the copper plate 13, and the crucible holder 5. Heat is transferred to the shielding member 6 provided with the emission port 7 through the orifice 2. The upper half of the orifice 2 is not thinned so that heat can be transferred from the orifice 2 to the shielding member 6. This heating method is the same as the conventional heating method. The rest is the same as the molecular beam source cell for thin film deposition according to the present invention described above with reference to FIGS. 1 and 2, and the same parts are indicated by the same reference numerals, and the description thereof will be omitted.

  Table 5 shows that the first thermocouple T / C1 and the second thermoelectric for 45 minutes every 5 minutes from the start of heating when the heater 3 is heated to heat the crucible 1 and the shielding member 6 and raise the temperature. The temperature, the film formation rate, the total film thickness accumulated until each time, and the degree of vacuum at each time are shown as measured against T / C2. The distance from the emission port 7 to the film thickness meter 12 is 400 mm, which is the same as in Table 2.

  As apparent from Table 5, when the temperature rises, the temperature of the first thermocouple T / C1 is higher than the temperature measured by the second thermocouple T / C2, but the temperature of the first thermocouple T / C1 When the temperature measured by the second thermocouple T / C2 from the vicinity where the temperature exceeds 300 ° C. becomes substantially the same as the temperature of the first thermocouple T / C1, and the film formation is started, the first thermocouple The temperature of the pair T / C1 is about 2 ° C. lower than the temperature measured by the second thermocouple T / C2. This is presumably because the temperature around the exit port 7 decreased due to the rapid expansion of the molecules emitted from the exit port 7. As a result of the observation, due to the temperature decrease, some of the molecules were solidified and the emission port 7 was clogged.

It is a vertical side view which shows one Example of the molecular beam source cell for thin film deposition by this invention. It is a top view which shows the said Example of the molecular beam source cell for thin film deposition by this invention. It is a vertical side view which shows the comparative example which uses the conventional heating system for comparing with one Example of the molecular beam source cell for thin film deposition by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crucible 2 Orifice 2a Contact part with orifice shielding member 3 Heater 4 Heat transfer member 6 Shielding member 7 Outlet 11 Molecule passage hole g Gap between heat transfer member and crucible holder

Claims (3)

A crucible (1) for storing a film forming material, a heater (3) for heating and sublimating or evaporating the film forming material stored in the crucible (1) to generate molecules, and a crucible (1) In a molecular beam source cell for thin film deposition, which is provided on the opening side and has an emission port (7) that emits molecules toward the film formation surface, a heat transfer member that directly receives heat from the heater (3) ( 4). However is closer to the crucible (1), provided with a gap therebetween, the heat transfer member (4) and said exit (7) is provided with shielding members (6) and the or an integral A molecular beam source cell for thin film deposition characterized by being connected. The molecular beam source cell for thin film deposition according to claim 1, wherein a gap (g) is provided between the heat transfer member (4) and the crucible holder (5) containing the crucible (1). Between the crucible (1) and the exit port (7), an orifice (2) provided with a molecule passage hole (11) for adjusting the flow of molecules to be released is arranged. The orifice (2) and the shielding member (6) The molecular beam source cell for thin film deposition according to claim 1 or 2, characterized in that the thickness of the contact portion (2a) is made thinner than other portions .

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