BaxSr1-xTiO3-y target materials for sputtering

Details BaxSr1-xTiO3-y target materials for sputtering BaxSr1-xTiO3-y target materials for sputtering

1998-09-29

2001-06-12

Gupta, Yogendra (Department: 1751)

Chemistry: electrical and wave energy

Apparatus

Coating, forming or etching by sputtering

C204S298120, C204S192100, C252S519100, C252S519120, C252S520200

Reexamination Certificate

active

06245203

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to sputtering target materials of perovskite type composite oxide represented by the compositional formula Ba
x
Sr
1−x
TiO
3−y
, for use in depositing highly dielectric capacitor thin films of MOS-ULSI by sputtering process. This invention relates, more particularly, to sputtering target materials capable of remarkably decreasing the leakage current in the deposited Ba
4
Sr
1−x
TiO
3
thin film or to sputtering target materials capable of forming thin films with a minimum of particle defect and also with enhanced mechanical strength.
Research has in recent years been made on the use of high-dielectric-constant thin films of SrTiO
3
and Ba
x
Sr
1−x
TiO
3
that are obtained by substituting part of the Sr site of SrTiO
3
with Ba for the capacitors of semiconductor memories. As a method of depositing such highly dielectric thin films, sputtering is commonly used. In order to impart desirable dielectric properties to the thin films formed by sputtering, a heat treatment to enhance their crystallinity is necessary. In that case, it is known that if the thin films contain alkali metal impurities such as Na and K, crystal growth will force these impurities to come out along the grain boundaries with a consequent increase of leakage current through these impurities. It is also known that U, Th, and other radioactive elements, if present as impurities, will emit alpha rays which can induce software error.
For instance, Japanese Patent Application Kokai No. 7-70747 clarifies that in a target material of a perovskite type titanate compound, what is responsible for leakage current is alkali metal that contributes largely to the migration of charges and teaches that the alkali metal content should be kept 1 ppm or less. It also proposes that the total amount of the radioactive elements such as U and Th that can cause software error by their alpha rays be limited to 10 ppb or less.
Patent Application Kokai No. 7-173621 discloses that on a sintered target material for sputtering composed of Ba
x
Sr
1−x
TiO
3−y
an upper limit of 10 ppm is put to the alkali metal impurity content so that high speed film deposition can be realized.
Patent Application Kokai No. 7-3444 suggests that in order to improve the resistance to cracking due to thermal strain of sintered target materials for sputtering composed of (Ba, Sr)O.TiO
2
, the total content of inevitable impurities such as Na and Ca, and also Al, Si, and Fe should be 90 ppm or less
Other problems associated with SrTiO
3
and Ba
x
Sr
1−x
TiO
3
that is obtained by substituting part of the Sr site of SrTiO
3
with Ba are that since these materials tend to give rise to abnormal grain growth during sintering, they can hardly provide sputtering targets of dense structure. Sintering them at higher temperatures for obtaining denser structure will encourage the abnormal grain growth until sintered structures with grain diameters as large as 20 &mgr;m or upwards result. When such a sintered body is used as a sputtering target, a large number of defects known as particles (clusters of minute particulates released from the target) develop on the deposited thin film, resulting in a serious decrease in the yield. Moreover, when sintered bodies are machined to target dimensions, those of low density or large grain size have such low mechanical strength that they present problems of low yield, contamination with impurities, etc.
OBJECTS OF THE INVENTION
In the prior art there has been no clear knowledge yet of the influence upon leakage current of transition metals such as Fe, Ni, Co, Cr and Cu or of impurity elements such as Mg and Al. This invention has for its object to impart enhanced dielectric properties to sputtering target materials of the perovskite type composite oxide sintered bodies represented by the general formula Ba
x
Sr
1−x
TiO
3−y
(where 0≦x<1 and 0≦y<0.5) while, at the same time, decreasing the leakage current that has been a problem of the prior art and further preventing the occurrence of software error.
Another object of this invention is to allow such sputtering target materials of the perovskite type composite oxide sintered bodies to produce thin films with far few particle defects than heretofore, simultaneously with enhanced mechanical strength.
No attempt has been made in the art to tackle squarely the problems of particle defect and mechanical strength that arise from the use of the sputtering target materials of the perovskite type composite oxide sintered bodies.
SUMMARY OF THE INVENTION
In view of the above, the present inventors have closely investigated impurities in the target materials for sputtering represented by the compositional formula Ba
x
Sr
1−x
TiO
3−y
so as to decrease the leakage current in highly dielectric thin films of the composition Ba
1−x
Sr
x
TiO
3−y
deposited by sputtering. As a result we have now found that a remarkable decrease in leakage current in the Ba
x
Sr
1−x
TiO
3−y
film thus deposited is made possible by restricting the contents of alkali metal elements such as Na and K in the target material to 1 ppm or less each and, moreover, limiting the contents of transition metals Fe, Ni, Co, Cr, and Cu and also of Mg and Al to 1 ppm or less each. It has also been found possible to put more strict limitations to the contents of the radioactive elements such as U and Th to 1 ppb or less each than those proposed by Patent Application Kokai No. 7-70747, i.e., a total radioactive element content of 10 ppb or less, so that the software error of semiconductor memories can more positively be precluded.
The present inventors have also searched for means to realize the second object and have just found that the particle defect can be decreased to fewer than one particle per square centimeter and the machining yield be markedly improved by adjusting the relative density of a sintered body of the compositional formula Ba
x
Sr
1−x
TiO
3−y
to 97% or above and also adjusting the grain diameter of the sintered body to 3 &mgr;m or below. High-temperature sintering for close packing usually promotes abnormal grain growth, resulting in a sintered structure of large grain diameters. Nevertheless, this invention has successfully realized the normally incompatible achievements through adequate control of the manufacturing method.
On the basis of the above findings, this invention in its first aspect provides a target material for sputtering composed of a perovskite type composite oxide sintered body of the general formula Ba
x
Sr
1−x
TiO
3−y
(where 0≦x<1 and 0≦y<0.5), characterized in that the content of each element in the group consisting of Na, K, Mg, Fe, Ni, Co, Cr, Cu and Al is 1 ppm or less and the content of each element of U and Th is 1 ppb or less.
This invention in its second aspect provides a target material for sputtering composed of a perovskite type composite oxide sintered body of the general formula Ba
x
Sr
1−x
TiO
3−y
(where 0≦x<1 and 0≦y<0.5), characterized in that the relative density of the sintered body is 97% or above and the average grain diameter of the sintered body is 3 &mgr;m or below.
Putting these together, this invention further provides a target material for sputtering composed of a perovskite type composite oxide sintered body of the general formula Ba
x
Sr
1−x
TiO
3−y
(where 0≦x<1 and 0≦y<0.5), characterized in that the content of each element in the group consisting of Na, K, Mg, Fe, Ni, Co, Cr, Cu, and Al is 1 ppm or less and the content of each element of U and Th is 1 ppb or less and that the relative density of the sintered body is 97% or above and the average grain diameter of the sintered body is 3 &mgr;m or below.
DETAILED DESCRIPTION OF THE INVENTION
(1) A sputtering target material in which the content of each element in the group consisting of Na, K, Mg, Fe, Ni, Co, Cr, Cu, and Al is 1 ppm or less and the content of each element of U and Th i

Affiliated with

Also associated with

Rating

BaxSr1-xTiO3-y target materials for sputtering does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with BaxSr1-xTiO3-y target materials for sputtering, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and BaxSr1-xTiO3-y target materials for sputtering will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2464437