GB2300001A

GB2300001A - Thin film forming apparatus using plurality of lasers

Info

Publication number: GB2300001A
Application number: GB9611008A
Authority: GB
Inventors: Kenyu Haruta; Koichi Ono; Yoshio Saito; Akihiro Suzuki; Tomohiro Sasagawa
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
Anticipated expiration: 2013-11-29
Also published as: GB2300001B; GB2303379B; GB9611007D0; GB9610969D0; GB2300000A; GB2303379A; GB2300426B; GB9611008D0; GB2300426A; GB9610953D0

Description

2300001 1 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. 4 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-depos]-tion 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 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 35mm 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. 5 shows another prior art example disclosed, for example, in Japanese Patent Laying-Open No. 4-114904.

is 1- '.1.

4 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 1 1 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 Y,Ba2CU307-, oxide superconductive thin film can be formed at the substrate temperature of 600C.

However, the conventional thin film forming apparatus using laser has the following problem.

Since the area of film formation which can be formed by one plume is limited, it has been impossible to form uniform thin film over a large area such as over wafer having 6 to 8 inches in diameter required in the semiconductor industry.

1 6 According to the invention defined in appended claim 1, a thin film forming apparatus using laser includes means for irradiating a plurality of different positions on the target with a plurality of laser beams.

Therefore, film formation proceeds in parallel at plurality of positions on the substrate, and therefore thin f i lm can be formed over a wide area without moving the substrate over a wide range.

The means for irradiating a plurality of laser beams may include means for dividing one laser beam into a plurality of laser beams and for directing the laser beams to different positions on the target.

Embodiments of the invention will now be described, by way of example only with reference to the accompanying drawings in which:

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

Fig. 2 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. 3 is a section viewed f rom the top of a chamber of the thin film forming apparatus using laser in accordance with a second embodiment of the present invention.

7 Fig. 4 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. 5 is a cross sectional view showing a schematic structure of another conventional thin f ilm forming apparatus using laser disclosed in Japanese Patent Laying Open No. 4-114904.

A first embodiment of the present invention will be described with reference to Fig. 1. Referring to Fig.

1, the apparatus of this embodiment includes a half mirror 4001a transmitting 50% of laser beam 16, a mirror 4001b totally reflecting laser beam 16, and lenses 9a and 9b for condensing laser beams 16a and 16b.

The operation will be described. The laser beam 16 emitted from laser unit 10 is partially reflected by half mirror 4001a to be laser beam 16a, while the remaining part is transmitted as it is. The transmitted light is reflected by mirror 4001b to be laser beam 16b. The laser beams are condensed on target 5 by corresponding lenses 9a and 9b. Consequently, two plumes 15a and 15b are generated parallel to each other. Consequently, on substrate 2, thin films are formed in parallel at areas corresponding to these two plumes.

The effect of this beam division is proved from the 91 - Q - following fact. When laser beam 16 is condensed on the target 5 by lens 9, there is an optimal value of the,intensity of laser beam at the condense surface per unit area, as described, for example, in G. M. Davis and M. C. Gower, Appl. Phys. Lett., Vol. 55, No. 2, pp. 112-114 July 10, 1989. More specifically, sputtering does not occur and thin film is not formed until the intensity exceeds a certain threshold value. However, if the intensity becomes too strong, sputtered substances in the form of clusters are generated, and these substances are deposited as the thin film, which significantly degrades the quality of the thin film. From this fact, it is impossible to increase the rate of sputtering by increasing the laser beam intensity per unit area to increase the area of thin film formation stepwise.

Meanwhile, forming a thin film over a wide area by increasing the intensity of laser beam 16 and enlarging the cross section of the beam so that the area of laser beam irradiation is enlarged while maintaining the optimal laser intensity per unit area is impossible either, as described in, for example, R. K. Singh et al., Physical Review B, Vol. 41, No. 13, pp. 8843-8859 May 1, 1990.

In accordance with the description in this article, the higher the density of the generated plume becomes, the plume itself extends wider, and therefore even if the area of irradiation is enlarged to no purpose, it is apparent that a plume having larger cross section is not generated.

In view of these facts, in the present invention, a plurality of irradiation spots are provided by dividing the beam into a plurality of beam, rather than enlarging the cross section of the laser beam 16, to form a thin film having superior quality over large area rapidly at highest efficiency.

Though the beam is divided into two in the description of this embodiment, it is not limited thereto, and the beam may be divided into plural beams.

Therefore, reflectance (or transmittance) of the mirror used is not limited to the values of the embodiment above. When the nature or thickness of the thin film is to be controlled at various portions on the substrate, reflectance (or transmittance) of each of the mirrors for dividing the beam into a plurality beams may be positively changed, so as to generate plumes corresponding to the desired nature or thickness.

A second embodiment of the present invention will be described with reference to Fig. 2. In this embodiment, referring to Fig. 2, thelaser beam 16 is enlarged to the size corresponding to a condensing system 4004 at a beam enlarging portion 4002, and enters the condensing system 4004 as an enlarged laser beam 4003.

- The condensing system includes a plurality of concave mirrors, and corresponding to respective concave mirrors, laser beams 16a, 16b, 16c... are generated condensed by respective concave mirrors, which beams are generated to be incident on the target.

Though concave lenses are used for dividing the beam in this embodiment. A convex lens may be used, or concave and convex lenses may be used combined. Though division and condensing are both carried out by a single system, the division and condensing of the laser beam may be carried out by separate systems.

pig. 3 is a top view of the chamber of the thin film forming apparatus described above. The same numeral denote the same or corresponding portions. This embodiment is essentially the same as the first embodiment described above. However, the divided beams are adapted to enter the chamber through separate windows. By this structure, the load of the laser beam inlet window 7 is reduced.

In the described embodiments, one laser beam is divided. However, a plurality of laser units may be used so that a plurality of laser beams are emitted. However, as can be seen in the present embodiment, the advantage of the method using a laser beam divided into a number of beams is that all the resulting laser beams change commonly in accordance with the change of the characteristics of the laser beam. Therefore, as compared with a case in which a plurality of laser units are used, the reliability as the thin film forming apparatus is higher. From another view point, when the conditions of the laser beam are to be controlled in the step of forming a thin film, it has an advantage that all the divided beams can be controlled under the same condition.

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.

12

Claims

1. A thin f ilm forming apparatus user laser, comprising:

a chamber having evacuating means; a target placed in said chamber; means for irradiating a plurality of different positions of said target with a plurality of laser beams; and substrate holding means for holding a substrate on which a material included in a plurality of plumes generated from said target by irradiation with said plurality of laser beams is deposited.

2. Thin film forming apparatus according to claim 1, wherein said means for emitting a plurality of laser beams includes means for dividing one laser beam into a plurality of laser beams for irradiating different positions of said target with respective ones of said laser beams.