JP2013249520A - Ge SPUTTERING TARGET FOR THIN FILM DEPOSITION - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Ge sputtering target for thin film deposition which can perform DC sputtering.SOLUTION: A Ge sputtering target for thin film deposition has the composition containing 0.001 to 0.1 wt.% of Al, with the balance consisting of Ge and inevitable impurities.

Description

  The present invention relates to a Ge sputtering target for thin film formation used for film formation in the manufacture of semiconductor memory elements and the like, and more particularly to a Ge sputtering target for thin film formation that enables direct current (DC) sputtering.

  Conventionally, for example, a phase-change random access memory (PRAM) has been used as a semiconductor memory device. This PRAM uses a characteristic that a phase change material such as GeSbTe changes to a crystalline state and an amorphous state due to local heat generation by an electric pulse, and stores binary information. It is an element. In such a PRAM, a memory cell that stores binary information includes a phase change layer, a heater, and a switch transistor. The transistor is generally provided on a silicon wafer, and the heater and the phase change layer are provided on the transistor. The phase change layer is a so-called GST (GeSbTe) based material.

  However, the conventional PRAM manufacturing process has a problem in that the adhesion between the GST thin film and the lower material layer is not excellent. As a result, after the GST thin film is deposited, a peeling phenomenon occurs in which the GST thin film constituting the phase change layer is detached from the lower material layer during the development / lift-off process for forming the phase change layer pattern. did. When the peeling phenomenon occurs, the subsequent manufacturing process of the PRAM may be difficult, and reliability and reproducibility may be deteriorated in the manufacturing process. In addition, the peeling phenomenon may deteriorate the switching characteristics of the PRAM, and in particular causes a problem that the initial resistance value may be increased during the switching operation of the PRAM. Therefore, in the manufacturing process of PRAM, the structure improvement of PRAM for suppressing the peeling phenomenon of the GST thin film has been required.

  The structure of the PRAM includes a switching element and a storage node connected to the switching element, and the storage node has a phase change material layer interposed between the lower electrode and the upper electrode. Accordingly, in order to improve the above-described problems, it has been proposed to interpose an adhesive interface layer between the lower electrode and the phase change material layer (see, for example, Patent Document 1). A thin film formed of a Ge—N or Ge—O—N material is used for the adhesive interface layer.

A thin film formed of a Ge—N or Ge—O—N material is used for the adhesive interface layer. This adhesive interface layer is formed by vapor deposition, for example, reactive sputtering. A Ge target is sputtered in a mixed gas atmosphere of Ar and N ₂ to form an adhesive interface layer.

  Various specific methods for forming an extremely thin thin film by sputtering have been proposed. There is a method of forming a film by direct current discharge sputtering having a pulse-like waveform (see, for example, Patent Document 2). In general, a direct current (DC) cathode has a higher voltage value applied than a radio frequency (RF) cathode, and therefore, the film formation rate is usually doubled. This is because the energy of the particles to be sputtered is high, and the electrode voltage does not reverse like RF. In order for the target material atoms to be sputtered from the target surface, an energy higher than a certain threshold energy is required, and a high voltage value is effective when sputtering a substance that is difficult to be sputtered.

  Further, in the RF in the boundary region of the threshold value to be sputtered, sputtering is performed due to the high voltage even when the spatter distribution is generated. However, if the film formation speed is increased, the film formation time is shortened, and there is a possibility that errors due to control of the film formation time and instability of the discharge state increase. Therefore, pulse DC sputtering is effective in which voltage application is pulsed and the time during which actual sputtering is actually performed is periodically canceled. Further, by pulsing, there is an effect that a self-triggering action is produced and the discharge is stabilized. In order to perform sputtering with DC, the specific resistance of the target must be 0.5 Ω · cm or less. If the specific resistance is higher than this, the target surface is charged up, so that stable DC discharge is difficult.

JP 2007-235128 A JP 2003-301263 A

As described above, in order to form a thin film by DC sputtering, it is necessary that the specific resistance of the target is low. The Ge target disclosed in Patent Document 1 has a high specific resistance, for example, 2 to 8 × 10 ² Ω · cm. As described above, since the Ge target has a high specific resistance, generally, when sputtering is performed using the Ge target, radio frequency (RF) sputtering is used. However, when this RF sputtering is used, there is a problem that the film forming speed is low.

  On the other hand, according to the pulse DC sputtering method proposed by the above-mentioned Patent Document 2, it is possible to increase the deposition rate even when sputtering with a Ge target. However, in order to perform this pulse DC sputtering method, it is necessary to provide a power source in which voltage application is pulsed, which increases costs. Therefore, it is expected that DC sputtering can be performed with a conventional DC sputtering apparatus even when sputtering with a Ge target without requiring such a special power source.

  Then, this invention aims at providing the Ge sputtering target for thin film formation which can perform DC sputtering by reducing the specific resistance of a target.

  The present inventors have found that it is effective to contain an appropriate amount of Al in order to reduce the specific resistance of the Ge sputtering target for forming a thin film. However, if a large amount of Al is contained, the specific resistance can be lowered. However, a thin film formed by sputtering contains a large amount of Al, and as a result, the characteristics of the thin film are affected. Therefore, if the Al content is sufficient to lower the specific resistance and does not affect the characteristics of the thin film, that is, if the amount of the thin film is within the allowable range of the characteristics, the conductive Ge sputtering capable of DC sputtering is possible. It turns out that you can get a target.

  Therefore, put a crushed powder of 5N purity Ge ingot and an Al lump of purity 5N weighed so as to be within the allowable range of the characteristics of the thin film, that is, Al: 0.001 to 0.1 wt%, into a quartz crucible. After melting and cooling the melted GeAl, the coarsely divided and pulverized GeAl fine powder was hot-press sintered. The sintered body was processed into a target to obtain an Al-containing conductive Ge sputtering target. And when DC sputtering was implemented using this Ge sputtering target, stable DC discharge was confirmed, without the target surface charging up.

Therefore, the present invention has been obtained from the above findings, and the following configuration has been adopted in order to solve the above problems.
(1) A Ge sputtering target for forming a thin film is characterized by containing Al: 0.001 to 0.1 wt%, with the balance being composed of Ge and inevitable impurities.

  In the present invention, the reason why the Al content is in the range of 0.001 to 0.1 wt% is that if it is less than 0.001 wt%, the Ge sputtering target cannot be imparted with conductivity, while 0.1 wt% is added. If it exceeds the upper limit, it will not change in conductivity even if it is added more, but it may affect the desired properties of the thin film formed by sputtering. Note that when the formed thin film is used for a semiconductor element or the like, Al indicates P type, and the present invention is advantageous for forming a P type semiconductor.

  As described above, according to the present invention, by adding 0.001 to 0.1 wt% of Al to the Ge sputtering target, the specific resistance of the Ge sputtering target is lowered and a conductive Ge sputtering target is realized. Therefore, the Ge thin film can be formed by DC sputtering, and the deposition rate of the Ge thin film can be improved. Therefore, for example, it contributes to the productivity improvement of semiconductor elements, optical discs, and the like.

  Next, the Ge sputtering target for forming a thin film of the present invention will be specifically described below with reference to examples.

〔Example〕
A Ge ingot having a purity of 99.999% was prepared, and the Ge ingot was roughly divided with a hammer to prepare a Ge coarsely pulverized powder. Furthermore, an Al lump having a purity of 99.999% was prepared. The Ge coarsely pulverized powder and the Al lump were weighed so as to have a predetermined ratio (wt%) shown in Table 1. Next, the weighed Ge coarsely pulverized powder and Al lump were placed in a quartz crucible and melted in an air melting furnace. Here, it was performed in an Ar flow atmosphere at a temperature of 1000 ° C. for 1 hour. After melting, it was poured out from a quartz crucible into an iron mold and cooled to produce a GeAl lump. The Ge ingot contains unavoidable impurities such as Fe, Cr, and Ni. In the preparation of this GeAl lump, an Al lump was used, but Al powder can be used instead of the Al lump.

  The GeAl lump was roughly divided and then placed in a vessel of a vibration mill (DISC MILL: manufactured by Kawasaki Heavy Industries) and pulverized. This ground GeAl powder was passed through a sieve having a mesh size of 90 μm. The GeAl powder having a powder particle size of 90 μm or less was sintered with a vacuum hot press apparatus. At this time, sintering was performed at 900 ° C. for 3 hours, and the GeAl sintered bodies of Examples 1 to 4 were manufactured. In the GeAl sintered bodies of Examples 1 to 3, the pressure was 24.5 MPa, whereas in the GeAl sintered body of Example 4, the pressure was 19.6 MPa. The GeAl sintered bodies of Examples 1 to 4 were dry-processed to produce GeAl sputtering targets of Examples 1 to 4 having a diameter of 125 mm and a thickness of 5 mm.

[Comparative example]
In the comparative example, a Ge sputtering target not containing Al was used for comparison with the example. First, a Ge ingot having a purity of 99.999% was prepared, and this Ge ingot was roughly divided with a hammer.

  Then, it put into the vessel attached to said vibration mill, and grind | pulverized. The ground Ge powder was passed through a sieve having a mesh size of 90 μm. The Ge powder having a powder particle size of 90 μm or less was sintered by a vacuum hot press apparatus. At this time, sintering was performed at a temperature of 900 ° C. for 3 hours, and a Ge sintered body of Comparative Example 1 was produced. In the Ge sintered body of this comparative example, the pressure was 19.6 MPa. The Ge sintered body of this comparative example was dry processed to produce a Ge sputtering target of Comparative Example 1 having a diameter of 125 mm and a thickness of 5 mm.

  Next, for the GeAl sputtering target of Examples 1 to 4 and the Ge sputtering target of Comparative Example 1, the density ratio was calculated from the theoretical density and the measured density, and the specific resistance was measured. The results are shown in Table 2.

  According to Table 2, in any of the GeAl sputtering targets of Examples 1 to 4, when 0.025 to 0.1 wt% Al was added, the specific resistance was much lower than that of Comparative Example 1. I understand that. By adding this Al, conductivity could be imparted to the Ge sputtering target. Even if DC sputtering is performed by mounting the Ge sputtering target to which 0.025 to 0.1 wt% Al is added to the DC magnetron sputtering apparatus, the surface of the target is not charged up, and stable DC discharge is maintained. We were able to.

Further, a Ge sputtering target to which 0.025 to 0.1 wt% Al was added was mounted on a DC magnetron sputtering apparatus, the distance between the sputtering target and the substrate was set to 70 mm, and the ultimate vacuum was 5 × 10 ^−5. Vacuuming is performed until the pressure becomes equal to or lower than Pa, and then Ar gas is supplied until the total pressure reaches 1.0 Pa, the substrate temperature is set to room temperature, and the input power is set to 100 W (0.8 W / cm ² ). When the film was formed on the substrate, it was confirmed that the formed thin film retained the desired characteristics, and if a small amount of Al was added, the characteristics were not affected.

Claims (1)

A Ge sputtering target for forming a thin film containing Al: 0.001 to 0.1 wt%, with the balance being composed of Ge and inevitable impurities.