GB2300426A

GB2300426A - Thin film forming apparatus using laser and secoindary sputtering means

Info

Publication number: GB2300426A
Application number: GB9611007A
Authority: GB
Inventors: Koichi Ono; Mutsumi Tsuda; Taisuke Furukawa; Kenyu Haruta; Takaaki Kawahara
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1992-11-30
Filing date: 1993-11-29
Publication date: 1996-11-06
Anticipated expiration: 2013-11-29
Also published as: GB2303379A; GB9610969D0; GB9611008D0; GB2300426B; GB9610953D0; GB9611007D0; GB2300001B; GB2300001A; GB2303379B; GB2300000A

Description

2300426 Thin Film Forming Apparatus Using Laser

This is a divisional application to application number 9324498.6, published as GB 2 272 912. The entirety of that specification as filed is incorporated herein by reference.

The present ILAvention 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. 2 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 chainber 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 25- irradiation by rotating raw material target 5 so as to 1 1 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 10mm x 10mm (with the variation of film thickness distribution of 10%), and when the XY stage is driven, the area can be expanded to 35min x 35mm.

However, in the semiconductor industry, formation of a uniform thin film over a 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. 3 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 f ilm grow-th 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 YBa2CU307-x oxide superconductive thin film can be formed at the substrate temperature of 600'C.

is one thin film forming apparatus using accordance with the present invention includes components, a chamber having evacuating nlaced in the cha ber laser laser in as basic a target 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.

means beam irradiating According to the present invention, this thin film forming apparatus further includes at least one of RF sputtering means, DC sputtering means and ion beam sputtering means.

Therefore, a DC voltage or a high frequency voltage can be applied as preprocessing of the substrate and the target or as an assistance to the laser beam. For example, by applying a high frequency voltage to the substrate or the target, the surface of the substrate or the target can be made clean. when a DC voltage or a high frequency voltage is applied or ion beam sputtering is used to assist the laser beam, the rate of film formation can be improved, and thin film can be formed uniform over wider area.

The present invention provides a thin film forming apparatus using laser, comprising: a chamber having evacuating means; a target placed in said chamber; 5 laser beam irradiating means f or irradiating said target with at least one laser beam; substrate holding means for holding a substrate on which a material included in a plume generated from said target by laser beam irradiation is deposited; and secondary sputtering means comprising at least one of RF sputtering means, DC sputtering means or ion beam sputtering means. An embodiment of the present invention will now be described 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. 2 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.

9 Fig. 3 '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.

- The apparatus of an embodiment of the invention includes, referring to Fig.1, a mirror moving apparatus 220, an XY6 stage 221 for moving the target, a sample moving apparatus 222, a DC sputtering apparatus 223, an RF sputtering apparatus 224, an RF reverse sputtering apparatus 225, a shutter 226, a movement controlling apparatus 227 and an ion beam sputtering apparatus 228.

The operation will be described. By setting the distance between target 5 and substrate 2 wider than the diameter of target 5, plume 15 comes to be extended more easily, so that the film can be made uniform over wider area. If this distance is shorter than the diameter of the target, the space in which the plume is generated becomes elongate and therefore the plume hardly extends. However, if the distanceis longer than the diameter of the target, the space in which the plume is generated will be wide in the lateral direction Fig.1 11 - Therefore, the plume expands easily, so that film can be easily made uniformed over wider area.

In Fig. 1 a plurality of lasers are used to increase the number of nlumes cenerated at one time This f acilitates unif orm. f ilm f ormation over wider area. Since the rate of film formation is increased as the number of lasers is increased, the throughput is improved.

In the structure of Fig. 1 the mirror, the target and the sample can be moved. By moving these, film can be f ormed unif ormly. Such movement is controlled by movement control apparatus 227 which allbws movement at random, simple rotation as well as rotation and revolution.

In the structure of Fig.1 DC or RF can be applied so as to assist the laser or as the pre-processing of the substrate and the target. When RF is applied to the substrate with the shutter 226 closed, the substrate can be cleaned, and the surface of the target can be cleaned. By such operation, a highly pure thin film can be formed. When DC or RF is applied so as to assist the laser, or by utilizing ion beam sputtering as well, the rate of film formation can be improved, and the film can be made uniform over wider area.

12 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.

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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 at least one laser beam; substrate holding means for holding a substrate on which a material included in a plume generated from said target by laser beam irradiation is deposited; and secondary sputtering means comprising at least one of RF sputtering means, DC sputtering means or ion beam sputtering means.

2. An apparatus according to claim 1 wherein said secondary sputtering means comprises RF sputtering means.

3. An apparatus according to claim 1 wherein said secondary sputtering means comprises DC sputtering means.

4. An apparatus according to claim 1 wherein said secondary sputtering means comprises ion beam sputtering means.

5. An apparatus according to any preceding claim wherein said laser beam irradiating means comprises a plurality of laser beam sources.

6. An apparatus according to any preceding claim wherein said secondary sputtering means is adapted so as to assist laser sputtering.

7. An apparatus according to any one of claims 1 to 5 wherein said secondary sputtering means is adapted for preprocessing of the substrate.

is

8. An apparatus according to claim 7 wherein said preprocessing effects cleaning of the substrate.

9. An apparatus according to any one of claims 1 to 5 wherein secondary sputtering means is adapted for preprocessing of the target.

10. An apparatus according to claim 9 wherein said preprocessing effects cleaning of the target.

11. A method of forming a thin film on a substrate, wherein a target placed in an evacuated chamber is irradiated with at least one laser beam so as to generate from said target a plume of material, and material included in the plume is deposited on the substrate, further comprising the use of secondary sputtering means, wherein the secondary sputtering means includes at least one of RF sputtering means, DC sputtering means and ion beam sputtering means.

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12. A method according to claim 11 wherein said secondary sputtering means is used for cleaning of the substrate or the target.

13. A method according to claim 11 or 12 wherein said secondary sputtering means is used to assist the laser.

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