GB2300000A

GB2300000A - Thin film forming using laser and activated oxidising gas

Info

Publication number: GB2300000A
Application number: GB9610969A
Authority: GB
Inventors: Keisuke Nanba; Koichi Ono; Mutsumi Tsuda; Taisuke Furukawa; Kenyu Haruta
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1992-11-30
Filing date: 1993-11-29
Publication date: 1996-10-23
Also published as: GB2300001A; GB2303379A; GB9611008D0; GB9610953D0; GB2303379B; GB9610969D0; GB2300426B; GB2300426A; GB2300001B; GB9611007D0

Abstract

A thin film forming apparatus using laser includes a chamber 1, a target 5 placed therein, a laser light source 10 for emitting laser beam to target 5, and a substrate holder 3. When target 5 is irradiated with laser beam 16, a plume 15 is generated, and materials included in plume 15 are deposited on the surface of a substrate 2 held by substrate holder 3. There is further provided means 363 for introducing activated oxidizing gas into the chamber. Therefore, oxygen defect generated during film deposition can be repaired immediately by oxygen ions supplied from the activated oxidizing atmosphere.

Description

Thin Film Forming Apparatus Using Laser This is a divisional application to application number 9324498.6, published as GB 2272912. The entirety of that specification as filed is incorporated herein by reference.

The present invention relates to a thin film forming apparatus using laser and, more specifically, to a film forming apparatus using laser used for forming thin film having functions and to form thin films having large areas.

Fig. 6 is a conventional thin film forming apparatus using laser disclosed, for example in, Japanese Patent Laying-Open No. 4-45263 which apparatus includes a chamber 1, a substrate 2, a substrate holder 3, a heater 4, a raw material target 5, a nozzle 6, an inlet window 7, a condenser lens 9, a laser unit 10, a turntable 11, an XY stage 12, a control apparatus 13, a motor 14, a plume 15 and an evacuating apparatus 17.

The operation will be described. Laser beam 16 emitted from laser unit 10 is condensed by condenser lens 9, passes through laser inlet window 7 of chamber 1, and irradiate raw material target 5 placed on turntable 11 in chamber 1. At this time, the turntable 11 can be rotated by means of motor 14. This is to make uniform laser irradiation by rotating raw material target 5 so as to prevent local generation of craters caused by sputtering of the same portion of raw material target 5.

At the portion of target 5 which is irradiated with the laser beam, plasma is generated abruptly, and in the process of cooling of the plasma in several ten ns, there are generated isolated excited atoms and ions. These groups of excited atoms and ions have the lives of at least several microseconds, which are emitted in this space to form a plume 15 which is like a candle flame.

Meanwhile, a substrate 2 is placed fixed on a substrate holder 3 opposing to raw material target 5, and the excited atoms and ions in the plume 15 reach substrate 2 and are deposited thereon, forming a thin film.

In substrate holder 3, a heater 4 for heating the substrate is provided, so as to enable post annealing in which the film deposited at a low temperature is annealed at a temperature higher than the temperature for crystallization to provide a thin film of superior quality, and allowing as-deposition in which the substrate itself is held at a temperature higher than the temperature for crystallization at the time of deposition so as to form crystallized thin film at the site. In the as-deposition method, sometimes an active oxygen atmosphere is used as well. For example, as shown in the figure, a nozzle 6 for supplying gas including oxygen is provided so that the atmosphere around the substrate 2 is made an oxygen atmosphere in forming a high temperature superconductive thin film, whereby generation of oxide on substrate 2 is promoted.

In view of enlargement of the area of thin film formation, substrate holder 3 is mounted on XY stage 12, so that the position of forming the thin film can be moved. First, a control signal corresponding to an oscillation pulse of laser unit 10 is transmitted to XY stage 12 through control apparatus 13. The XY stage 12 is driven based on the control signal, and moves the position of forming the thin film on the substrate 2 at every laser pulse. Consequently, a uniform thin film can be formed on a wide area. In the conventional example, when XY stage 12 is not driven, the area of thin film formation is limited to 10mum x 10mum (with the variation of film thickness distribution of +10%) and when the XY stage is driven, the area can be expanded to 35mm x 35my.

However, in the semiconductor industry, formation of a uniform thin film over 2 wafer of 6 to 8 inches in diameter has been desired, and conventional thin film forming apparatuses using laser could not meet such demand.

Fig. 7 shows another prior art example disclosed, for example, in Japanese Patent Laying-Open No. 4-114904.

Referring to the figure, 18 denotes an oxygen ion source, 19 denotes oxygen gas and 20 denotes oxygen ion beam. The process for forming a thin film in this example is the same as that of the above described prior art example. In such a thin film forming apparatus using laser, laser beam in the form of very short pulses of ten to about several ten ns is directed to the target, and the target material in the form of atoms, molecules or clusters are supplied onto the substrate only at the time of irradiation, so as to form a thin film.The excimer laser having extremely short pulse width and high energy has such advantage that (a) it allows generation of a large amount of target raw material to be deposited on the substrate so that the rate of thin film growth can be much increased, and that (b) a thin film of which composition is not very much changed from that of the raw material target can be obtained.

However, the excimer laser may degrade the quality of the film due to insufficient crystallization. In order to promote crystallization of the raw material in the form of atoms, molecules or clusters deposited on substrate 2, heating of substrate 2 by a heater provided in substrate holder 3 so as to keep the substrate at a temperature higher than the temperature for crystallization has been proposed. However, if the substrate is kept at a high temperature during thin film formation, it may induce degradation of the substrate or undesirable reaction, which is inconvenient for the functional thin film from electronic or mechanic point of view.Therefore, in this prior art example, in order to reduce problems accompanying heating of the substrate, oxygen gas 19 is introduced to ion source 18 when raw material target 5 is irradiated with laser beam 16 so that substrate 2 is irradiated with the generated oxygen ion beam 20, whereby oxygen is supplied to the thin film and the temperature of crystal growth is lowered by the oxygen bombardment.

Consequently, in this known example, a YlBa2Cu307x oxide superconductive thin film can be formed at the substrate temperature of 600"C.

However, the conventional thin film forming apparatus using laser has the problem of degradation of the substrate derived from high temperature of film formation and lower quality of the thin film caused by undesirable side reaction induced. In addition, when the film quality is to be improved by using active ion seeds, there has been possible damage of the substrate caused by ion beams, and therefore it has been difficult to improve the quality of the film.

One thin film forming apparatus using laser in accordance with the present invention includes, as basic components, a chamber having evacuating means, a target placed in the chamber, laser beam irradiating means for directing laser beams to the target, and substrate holding means holding a substrate on which a substance included in a plume generated from the target-by laser beam irradiation is deposited.

According to the present invention, the thin film forming apparatus using laser further includes means for introducing activated oxidizing gas into the chamber.

Therefore, oxygen defect generated during film deposition can be repaired immediately by oxygen ions supplied from the activated oxidizing atmosphere.

Therefore, at a relatively low substrate temperature, an oxide film with superior crystal property with less oxide defects can be obtained, and therefore degradation of the substrate derived from high temperature of film formation and degradation of thin film function caused by induced undesirable side reaction can be prevented. Further, since the activated oxidizing gas introduced in the chamber does not have such a high kinetic energy as ion beams, the damage to the substrate is negligible.

According to a particular embodiment the thin film forming apparatus using laser includes means for activating the oxidizing gas by silent discharge.

Since the thin film forming apparatus using laser includes means for introducing activated oxidizing gas in the chamber by silent discharge, ions are eliminated rapidly by impingement with the activated oxygen gas, and therefore active oxygen atoms having relatively low reactiveness are maintained at high concentration and applied to the substrate. Therefore, oxidation on the substrate surface is promoted.

The present invention provides a thin film forming apparatus using laser, comprising: a chamber having evacuating means; a target placed in said chamber; laser beam irradiating means for irradiating said target with a laser beam; substrate holding means for holding a substrate on which plume material generated from said target by laser beam irradiation is deposited; and means for introducing activated oxidizing gas to said chamber.

Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings in which: Fig. 1 is a cross sectional view showing a schematic structure of the thin film forming apparatus using laser in accordance with an embodiment of the present invention.

Fig. 2A is a cross sectional view showing one example of a silent discharge apparatus used in an embodiment of the present invention, and Fig.

2B is a cross section taken along the line B-B of Fig.

2A Fig. 3A is a cross sectional view showing another example of the silent discharge apparatus used in an embodiment of the present invention, and Fig.

ae is a cross section taken along the line B-B of Fig. 3A Fig.4 is a cross sectional view showing a schematic structure of the thin film forming apparatus using laser in accordance with a second embodiment of the present invention.

Fig.5 is a cross sectional view showing a schematic structure of the thin film forming apparatus using laser in accordance with a third embodiment of the present invention.

Fig.6 is a cross sectional view showing a schematic structure of a conventional thin film forming apparatus using laser disclosed in Japanese Patent Laying-Open No.

4-452263.

Fig.7 is a cross sectional view showing a schematic structure of another conventional thin film forming apparatus using laser disclosed in Japanese Patent Laying-Open No. 4-114904.

Referring to Fig.l, the apparatus of an embodiment of the present invention includes a laser unit 10, a lens 9 for condensing laser beam from laser unit 10 to the surface of a target, a vacuum chamber 1, a substrate 2, a substrate holder 3, a target 5, an optical transmission window 7, and a silent discharge apparatus 363. Figs.

2A, 2B and Figs. 3A and 3B show details of the silent discharge apparatus, which apparatus includes a dielectric cylinder 364 formed of quartz, ceramic or the like, an electrode 365 in contact with the outer portion of the dielectric cylinder, a high frequency power source 366, an oxygen gas cylinder 367, a gas flow rate adjusting valve 368 and an orifice 369.

The operation will be described. The laser beam emitted from laser unit 10 is condensed by lens 9 and focused on a target 5 so as to provide necessary light intensity. The laser beam passed through the lens 9 passes through transmission window 7 of the chamber 1 to be incident on target 5. By the high density laser beam incident on the target, a plasma is generated abruptly, and during the process of cooling the plasma rapidly, isolated excited atoms and ions are generated. These excited atoms and ions have the lives of several microseconds, forming a plume 15 which is like a flame.

Meanwhile, a substrate 2 is placed fixed on a substrate holder 3, opposing to target 5. Excited atoms and ions in plume 15 reach the substrate 2, and are deposited thereon to form a thin film.

Meanwhile, the oxygen gas supplied from oxygen gas cylinder 367 is set to an arbitrary flow rate by gas flow rate adjusting valve 368, so that a prescribed amount of oxygen gas is introduced to silent discharge apparatus 363. The side opposing to the gas inlet of the silent discharge apparatus 363 is connected to chamber 1 by means of an orifice 369, and by the function of orifice 369, the inside of silent discharge apparatus 363 is kept at a pressure in the range from 0.1 to 50 Torr. Silent discharge apparatus 363 includes a dielectric cylinder 364 and a pair of electrodes 365. A high voltage high frequency potential in the range of from 60 to 10kHz is applied from high frequency power supply 366, so that silent discharge occurs, and the supplied oxygen gas is excited to oxygen ions and oxygen atoms.However, if the gas pressure is in the range of 0.1 to 50 Torr, the life of the oxygen ions is short, so that most of the generated oxygen ions are eliminated, and the oxygen atoms are introduced to the chamber 3 through orifice 369 as the primary component of the excitation seeds. The oxygen atoms introduced in this manner oxidize the excited atoms and ions in plume 15 and, at the same time, oxidize the elements constituting the thin film deposited on the substrate 2, so that an oxide thin film is formed.

In this case, the excitation seeds for oxidation are mainly oxygen atoms, so that accumulation of charges on the surface and impact of high speed ions on the substrate surface can be avoided, and therefore the substrate is not damaged.

As for the structure of silent discharge apparatus 363, one electrode 365 may be provided outside the dielectric cylinder 364 to apply a high voltage high frequency potential, and the orifice 369 or chamber 1 may be used as the ground electrode as shown in Figs. 3 A and 3 B to obtain similar effect.

A second embodiment of the present invention will be described with reference to Fig. 4. The apparatus of this embodiment includes, referring to Fig.

4, an oxygen gas supply source 506 and an ECR plasma chamber 507. In this embodiment, a silicon substrate coated with platinum is used as the substrate 2, and BaTiO3 is used as raw material target 5. In the figure, the same reference characters as in Figs. 6 and 7 denote the same or corresponding portions.

The operation will be described. The oxygen gas supplied from the oxygen gas supply source first enters the ECR plasma chamber. There is an electrostatic field in the ECR plasma chamber, and microwave power is applied to this chamber. By the functions of these, a so-called ECR plasma derived from cyclotron movement of the oxygen gas is generated, and therefore active oxygen ions are generated. The oxygen gas activated in this manner is introduced to a film forming chamber. Under such a film forming atmosphere, BaTiO31 as the raw material target was irradiated with the laser, and a thin film was formed. A BaTiO3 thin film having smaller defects could be formed even when the substrate temperature was decreased to as low as about 5000C.

Though ECR plasma was used for ionizing the oxygen gas, similar effect is expected when RF plasma is used.

Similar effect is also expected when oxygen gas is excited by irradiation with W light. Though oxygen was used for oxidizing gas in this embodiment, an organic substance such as alcohol including oxygen may be used. Nitrogen gas may be used for oxidization in its broader meaning.

Further, such effect is obtained not only in forming BaTiO3 film but also in forming other oxide thin film.

As described above, the oxidizing gas in this embodiment is supplied from an oxidizing gas supply source and ionized in a preceding chamber provided for the purpose of activating the oxidizing gas such as an ECR plasma chamber, and then introduced to the thin film forming chamber. An oxide film is deposited by using laser in such an active oxidizing gas atmosphere. Since such active oxidizing gas is supplied to the film forming chamber, the oxygen defect generated during film deposition can be immediately repaired by the oxygen ions supplied from the active oxidizing atmosphere. Therefore, an oxide film having superior crystal properties with smaller oxygen defect can be obtained even at a low temperature.Accordingly, degradation of the substrate and degradation of the function of the thin film caused by undesirable side reaction derived from high temperature for film formation of the substrate can be prevented. The ionized oxidizing gas introduced to the film forming chamber do not have such high kinetic energy as the ion beam, and therefore the damage to the substrate is negligible.

Provision of an oxide film having superior quality at a low substrate temperature by introducing the oxidizing gas to the film forming chamber after the gas is activated, such as realized by the present embodiment, is especially advantageous in fabricating a perovskite type thin film mainly consisting of titanate such as BaTiO3 used as a dielectric film of a thin film capacitor of highly dielectric body. Conventionally, it has been difficult to form a highly insulative BaTiO3 thin film at a low temperature. This is because the oxygen defects generated during deposition of the film cannot be easily repaired when the film is deposited at a low temperature.When the film is formed at a high temperature, there have been problems of mutual diffusion of composition elements at the interface between the formed film and a platinum film which is mainly used as the lower electrode, and degradation of insulation derived therefrom.

A third embodiment of the present invention will be described with reference to Fig. 5 The apparatus of this embodiment includes, referring to Fig.

an an oxygen gas supplying source 506 and a DC power supply 508 for applying a DC voltage to the substrate. In this embodiment, a silicon substrate coated with platinum is used as substrate 2, and BaTiO3 is used as raw material target 5. In the figure, the same reference characters as in Figs. 6 and 7 denote the same or corresponding portions.

The operation will be described. First, while a prescribed positive bias is being applied to the substrate, the raw material target is irradiated with the laser beam, thus a plume is generated, and the film is deposited on the substrate placed near the plume. At this time, oxygen ions generated by the reaction with the plume are collected near the substrate as they are attracted by the positive potential of the substrate and these ions contribute to repair oxygen defect during film formation.

By such an operation, a BaTiO3 thin film could be obtained with smaller defects even when the substrate temperature was decreased to as low about 5000C.

Though a DC potential is applied to the substrate in this embodiment, an AC potential such RF may be applied.

Similar effect can be expected by excitation of the oxygen gas by W irradiation. Though oxygen was used as oxidizing gas in this embodiment, an organic substance containing oxygen such as alcohol may be used. Nitrogen gas may be used for oxidation in its broader meaning.

Further, such effect is provided not only in forming the BaTiO3 film but also in forming other oxide thin films.

As described above, the thin film forming apparatus using laser in accordance with this embodiment is structured such that at the time of depositing an oxide film, an oxidizing gas is introduced to the film forming chamber, and when the raw material target is irradiated with the laser beam and there is generated a plume between the raw material target and the substrate, a DC or RF potential is applied between the substrate and the ground potential or between the substrate and the raw material target. When a DC positive potential or the like is applied to the substrate, for example, the oxidizing gas which has been ionized by the reaction with the radical seeds and the like in the plume near the substrate will be incident on the substrate surface with an appropriate energy. Such ion seeds repair the oxygen defects which are caused during film deposition. Therefore, an oxide film having superior crystal property with smaller oxygen defects can be obtained even when the substrate temperature is low. Accordingly, degradation of the substrate and the degradation of the function of the thin film caused by undesirable side reaction derived from high temperature for film formation of the substrate can be prevented. In addition, the kinetic energy of the oxidizing gas which has been ionized and guided near to the substrate can be made small enough not to damage the substrate, by appropriately adjusting the substrate potential.

Provision of an oxide film having superior quality at low substrate temperature by applying a DC or RF potential to the substrate and by guiding ion seeds generated in the reaction with the plume to the substrate surface, such as realized by the present invention, is especially useful in fabricating perovskite type thin film may be consisting of titanate such as BaTiO3 which is used as a dielectric film of a thin film capacitor of a highly dielectric body.

Generally, it has been difficult to form a highly insulative Basic3 thin film at a low temperature. The reason for this is that the oxygen defects generated during film deposition is hardly repaired if the film is deposited at a low temperature. When the film is formed at a high temperature, there have been problems of mutual diffusion of composition elements at the interface between the film and the platinum film mainly used as the lower electrode, and degradation of insulation derived therefrom.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims

1. A thin film forming apparatus using laser, comprising: a chamber having evacuating means; a target placed in said chamber; laser beam irradiating means for irradiating said target with a laser beam; substrate holding means for holding a substrate on which plume material generated from said target by laser beam irradiation is deposited; and means for introducing activated oxidizing gas to said chamber.

2. A thin film forming apparatus using laser according to claim 1, wherein said means for introducing activated oxidizing gas includes at least one of ECR plasma, RF plasma and ultraviolet beam irradiation.

3. A thin film forming apparatus using laser according to claim 1, wherein said active oxidizing gas is oxygen or ozone or a mixed gas of oxygen and ozone, and said means for generating the active oxidizing gas is silent discharge.