WO1997036020A1

WO1997036020A1 - Ceramic target for thin film deposition

Info

Publication number: WO1997036020A1
Application number: PCT/IL1997/000108
Authority: WO
Inventors: Gad Koren
Original assignee: Technion Research and Development Foundation Ltd
Current assignee: Technion Research and Development Foundation Ltd
Priority date: 1996-03-26
Filing date: 1997-03-26
Publication date: 1997-10-02
Anticipated expiration: 1998-09-26
Also published as: IL117657A0; AU1938397A

Abstract

A tiled sputtering target (10) prepared from ceramic tiles (12), for use in a vapor deposition process, and affording large target areas (10) and small spaces (18) between tiles (12) for the uniform introduction of the sputtering gases. In the preferred embodiment, the tiled sputtering target (10) is comprised of many small ceramic tiles (12), which are attached to the backing plate (14) by a soft solder such as indium. The tiles (12) are arranged close to one another, but spaces (18) are formed therebetween. The backing plate (14) has holes (15) formed therein, and the holes (15) and spaces (18) enable uniform introduction of the sputtering gas into the plasma developed in the vapor deposition process, and enhances control of the plasma uniformity, with resulting films being uniform. Each of the small ceramic tiles (12) can be fabricated very densely and uniform as pressed pellets.

Description

CERAMIC TARGET FOR THIN FILM DEPOSITION

FIELD OF THE INVENTION

The invention relates to vacuum deposition systems and components thereof for thin film deposition, such as by DC and RF sputtering techniques, and more particularly, to a novel tiled target assembled from materials composed of sma 11 ceramic t i les .

BACKGROUND OF THE INVENTION

Sputtering targets are used in wafer fabrication systems to grow a thin film on a substrate via a vapor deposition technique involving an exchange of ions, atonii and molecules in a vacuum between the target and the substrate. For example, for targets formed of a ceramic material, a very high pressure is applied to press the target material into a pellet. Because of this, the size of the target is problematic, since application of a high pressure to a large area typically causes cracks in the target, since uniform pressure intensity is impossible to achieve.

There are known sputtering targets fabrication techniques. Examples include a planar magetron cathode target as described in US Patent 4,200,510 to Nichols et al, consisting of a number of target tiles arranged in an abutting fashion to form a continuous and enclosed length of consumable metal , with partially consumed tiles being severed and reassembled for further use.

In Japanese patent JP 63307264 to Kawaguchi et al, a target construction is disclosed having pieces of two compositions, with beveled edges on the sputtering surface for 1 of the compositions to suppress breakage of the edge portions in contact with adjacent different target pieces due to thermal expansion.

A mosaic composite target is disclosed in Japanese patent JP 63307265 to Kawaguchi et al, and is constructed from pieces of two compositions. Gaps between adjacent pieces, which cause no contact during sputtering, act to suppress dust formation from breakage of the edges due to thermal expansion.

In Japanese patent JP 63183170 to Mizoguchi et al, there is disclosed a target for magnetron sputtering constructed as an arrangement of metal blocks on the cathode with gaps between the without causing discharge between them.

The problems associated with fabrication of large area sputtering targets formed of ceramic materials have not been adequately solved by the prior art. Presently, there are limitations in fabricating large area targets, since large, dense homogeneous pellets are difficult to fabricate. Therefore, it would be desirable to provide a method of fabricating large area ceramic sputtering targets without cracks. SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention to overcome the disadvantages of the prior art and provide a tiled sputtering target prepared from ceramic tiles, affording large target areas and small spaces between tiles for the uniform introduction of the sputtering gases .

In a preferred embodiment, there is provided a target for use in a vapor deposition process, said target co pri s i ng : a plurality of individual ceramic tiles proximately disposed one another on a backing plate and bonded thereon, forming spaces between said tiles, said backing plate having holes formed therein, for gas introduction via said holes and spaces.

In the preferred embodiment, the tiled sputtering target is comprised of many small ceramic tiles, which are attached to the backing plate by a soft solder such as indium. The tiles are arranged close to one another, but spaces are formed therebetween. The backing plate has holes formed therein, and the holes and spaces enable introduction of the sputtering gas into the plasma developed in the vapor deposition process. This greatly enhances uniform introduction of the sputtering gas into the plasma and enhances control of the plasma uniformity.

Each of the small ceramic tiles can be fabricated very densely and uniform as pressed pellets, approximately 1 square cm, since the size does not prevent application of high pressure. As a result, uniform large area targets can be assembled, of any shape and size. The holes in the backing plate and spaces between the tiles assist gas flow input into the plasma, and the resulting films are therefore un i form.

Other features and advantages of the invention will become apparent from the following drawings and descri pt ion .

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is made to the following drawings, in which like numerals designate corresponding elements or sections throughout, and in which:

Fig. 1 is a perspective view of a tiles sputtering target constructed in accordance with the principles of the present invention;

Fig. 2 is a cross-sectional view of the target of Fig. 1;

Fig. 3 is a graph illustrating the resistivity vs. temperature of a high temperature superconducting thin film of YBa Cu 0 produced using the inventive target; and 2 3 7-x

Fig. 4 ia an enlargement of a graph illustrating the transition temperature region of Fig. 3 together with the critical current density of the thin film produced using the inventive target. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to Figs. 1-2, there are shown, respec ively, perpective and cross-sectional side views of a tiled sputtering target 10 constructed in accordance with the principles of the present invention. Target 10 comprises ceramic tiles 12, each on the order of 1 x 1 sq. cm. , which are easily prepared as pressed pellets, at high pressures, enabing them to exhibit properties of unparalleled homogeneity and density. Tiles 12 are the building blocks of target 10, and because of their small area, the high pressure does not cause cracks, and tiles 12 are relatively uniform. Standard materials and a press are needed for fabrication of the inventive target 10 design.

Tiles 12 are attached to a backing plate 14 by a soft solder 16 such as indium. As best seen in Fig. 2, backing plate 14 has formed therein a plurality of holes 15. To enhance the bonding between backing plate 14 and tiles 12 in the case of high temperature superconductors (HTS), the tiles are alloyed on their back side with silver prior to the soldering step.

An advantage of the inventive design of tiled sputtering target 10 is that tiles 12 are spaced apart from one another. As shown in Fig. 2, the spaces 18 between tiles 12 enable gases used in the sputtering process to be introduced via holes 15 in backing plate 14. For example, in the case of high temperature superconductors, oxygen is used, and it is important to use active oxygen, ionic or atomic, not just oxygen molecules. When introducing the oxygen through the plasma, it is ionized and becomes d i s sassoc i ated into atomic species, which is important for the superconductor. Also, by adding a series resistor to each tile 12, better control of the plasma uniformity can be obta ined .

Referring now to Figs. 3-4, there are shown, respectively, graphs illustrating resistivity vs. temperature of a thin film produced using the inventive target 10 in DC sputtering.

The graphs of Figs. 3-4 indicate a sharp superconducting transition, and in Fig. 4, this is indicated at between 89.5-90.5 degrees Kelvin, which is 1 degree. The other important number is the critical current density (Jc).

This was measured at 79 degrees Kelvin, which is 2 degrees above the temperature of liquid nitrogen, and the value obtained was 5 million amps/sq. cm. This value is among the best of the state of. the art values, for current density in

YBa Cu 0 films and was obtained using the inventive tiled

2 3 7-x target 10.

Large area scaling up of the tiled target 10 is not difficult, so that any area or shape can be designed, by increasing the number of tiles 12 in the target 10 structure. In microwave devices, it is important to have large area uniform thickness, uniform quality films. The largest known target areas using ceramic materials are 6 inches in diameter for high temperature superconductors, and these cost about $20 thousand per target, and are difficult to use since they tend to have cracks in them. The present inventive target design, by contrast, would cost about $1000. A target of 10 inches diameter could be fabricated easi ly .

Another advantage of the inventive design is that using the small ceramic tiles 12, it is relatively easy to replace damaged tiles without discarding the whole target which could be very expensive if it is of large area.

It will be appreciated by those skilled in the art that the ceramic target can also be used in laser ablation deposition systems, or in electron gun or ion gun evaporation systems. The above techniques may be employed for the deposition of thin films of metals, insulators, semiconductors, and superconductors.

Having described the invention in connection with certain specific embodiments thereof, it is to be understood that the description is not meant as a limitation, since further modifications will now suggest themselves to those skilled in the art, and it is intended to cover such modifications as fall within the scope of the appended claims.

Claims

CLAIMS:

1. A target for use in a vapor deposition process, said target comprising: a plurality of individual ceramic tiles proximately disposed one another on a backing plate and bonded thereon, forming spaces between said tiles, said backing plate having holes formed therein, for gas introduction via said holes and spaces.

2. The target of claim 1 wherein said tiles are assembled as uniform large area targets having any desired shape and size.

3. The target of claim 1 wherein said backing plate holes and spaces between the tiles assist gas flow input into the vapor deposition process, resulting in uniform films.

4. The target of claim 1 wherein said tiles are fabricated as dense and uniform pressed pellets.

5. The target of claim 1 for use in a DC sputtering system.

6. The target of claim 1 for use in a RF sputtering system.

7. The target of claim 1 for use in a laser ablation deposition system.

8. The target of claim 1 for use in an electron gun evaporation system.

9. The target of claim 1 for use in an ion gun evaporation system.

10. The target of claim 1 used for deposition of thin fi 1ms of metal .

11. The target of claim 1 used for deposition of thin films of i nsul ators .

12. The target of claim 1 used for deposition of thin films of semiconductors.

13. The target of claim 1 used for deposition of thin films of superconductors.

14. A target for use in a vapor deposition process substantially as described herein by way of example and with reference to the drawings.