JP2004363541A - Phase change recording film having high electrical resistance and sputtering target for forming the phase change recording film - Google Patents

Abstract

A phase change recording film having a high electric resistance and a sputtering target for forming the phase change recording film are provided.
Phase change recording with high electrical resistance having a composition containing Ge: 15-30%, Sb: 15-30%, C: 0.2-8 in atomic percent, the balance being Te and inevitable impurities A film and a sputtering target for forming the film.
[Selection figure] None

Description

  The present invention relates to a phase change recording film having a high electric resistance and a sputtering target for forming the phase change recording film.

In general, a phase change recording layer used in a phase change RAM, which is a kind of semiconductor nonvolatile memory, uses a phase change material in a crystalline state, and rewriting is rapidly heated by a heater and melted. Immediately cools and partially amorphizes, or the amorphous part is heated and held at a temperature below the melting point to return to the crystalline state, and reading is performed in the crystalline state and partially amorphous. It is also known that this phase change recording layer is formed by sputtering using a target made of an alloy having a component composition for phase change recording (for example, patents). References 1-3, and non-patent references 1-2).
JP-T-2001-502848 Japanese translation of PCT publication No. 2002-512439 Special Table 2002-540605 gazette "Applied Physics" Vol. 71 No. 12 (2002) pp. 1513-1517 Nikkei Microdevice, March 2002, pages 70-78

  However, as described in Non-Patent Document 1, the current phase change memory element has a large current value flowing through the circuit at the time of writing and erasing, power consumption is large, and because of the large current, the load on the circuit is very small. It has become an obstacle to conversion.

Therefore, the present inventors conducted research to reduce the value of the current flowing during the write / erase operation by increasing the resistance of the phase change recording film. as a result,
(A) In a normal Ge—Sb—Te phase change recording film, the phase change recording film containing C: 0.2 to 8% in atomic% (hereinafter,% indicates atomic%) is in a crystalline state. The electric resistance becomes high, and thereby the current value flowing during the write / erase operation can be reduced.
(B) A Ge—Sb—Te phase change recording film containing C: 0.2 to 8% is obtained by sputtering using a Ge—Sb—Te system target containing C: 0.2 to 8%. The result of the research was obtained.

The present invention has been made based on such research results,
(1) Ge: 15 to 30%, Sb: 15 to 30%, C: 0.2 to 8%, a phase change recording film having a high electrical resistance having a composition consisting of Te and inevitable impurities in the balance,
(2) Ge: 15 to 30%, Sb: 15 to 30%, C: 0.2 to 8%, with the balance being composed of Te and inevitable impurities, the electrical resistance according to (1) is high It is characterized by a sputtering target for forming a phase change recording film.

  Since the phase change recording film of the present invention has a reasonably high electrical resistance value, the current value during the write / erase operation is reduced, contributing to low power consumption and device miniaturization. It can improve the characteristics and reduce the cost, and can greatly contribute to the development of the new semiconductor memory industry.

  The reason why the component composition of the phase change recording film having high electrical resistance according to the present invention is limited as described above will be described.

(A) C
If the amount of the C component contained in the phase change recording film is less than 0.2%, the effect of increasing the resistance of the film is small, which is not preferable. On the other hand, if the content exceeds 8%, the increase in the crystallization temperature increases. It is not preferable. Therefore, the content of C is set to 0.2 to 8%.
An appropriate increase in the crystallization temperature increases the stability of the amorphous state and can be expected to improve the retention characteristics when used as a memory. However, if it is higher than necessary, crystallization becomes difficult. That is, unfavorable things such as a large electric power required for crystallization and a slow crystallization speed occur. Therefore, the more preferable range of the C content is set to 0.5 to 6%.

(B) Ge, Sb
Ge and Sb contained in the phase change recording film containing Al and Si having high electrical resistance according to the present invention are preferably Ge: 15-30% and Sb: 15-30%. The reason is that even if Ge is less than 15%, Sb is less than 15%, Ge is more than 30%, and Sb is more than 30%, the resistance value is lowered or the crystallization speed is decreased. This is due to the absence.

High electrical resistance phase change recording film of the present invention, the specific resistance value measured by the four point probe method after crystallization is 5 × 10 ^{- 2} Ω · cm or more (8 × 10 ^-2 Ω · cm or more and more preferably) The reason is that if the specific resistance value is less than 5 × 10 ⁻² Ω · cm, a large current flows through the circuit, which increases power consumption and is an obstacle to miniaturization. This is due to the absence. In addition, the specific resistance of the Ge—Sb—Te alloy in an amorphous state is usually about 1 × 10 ³ Ω · cm. It is preferable that there is a resistance difference. For this reason, the resistance value of the phase change recording film at the time of crystallization needs to be 5 × 10 ¹ Ω · cm or less. Therefore, the specific resistance value measured by the four-probe method after crystallization of the phase change recording film of the present invention. Was set to 5 × 10 ⁻² Ω · cm to 5 × 10 ¹ Ω · cm.

  In the sputtering target for forming the phase change recording film of the present invention, an alloy having a predetermined composition is dissolved in an Ar gas atmosphere, and then poured into an iron mold to produce an alloy ingot. An alloy powder is prepared by pulverization in an active gas atmosphere, and a mixed powder is prepared by mixing and mixing the C powder with the alloy powder so as to have the same component composition as that of the phase change recording film of the invention. It is produced by vacuum hot pressing the mixed powder. The vacuum hot press is performed under the conditions of pressure: 146 to 155 MPa, temperature: 370 to 430 ° C., holding for 1 to 2 hours, and then cooling rate: 1 to 1 when the temperature of the mold is lowered to 270 to 300 ° C. 3 ° C./min. More preferably, it is carried out by cooling to room temperature.

  An alloy ingot was prepared by melting and casting Ge, Sb, and Te in an Ar gas atmosphere, and by pulverizing the alloy ingot in an Ar atmosphere, an alloy powder having a particle size of 250 μm or less was prepared.

Commercially available C powder is blended with these alloy powders and mixed to produce a mixed powder, and this mixed powder is hot-pressed by vacuum hot pressing at a temperature of 400 ° C. and a pressure of 146 MPa. The present invention targets 1 to 1 having a component composition shown in Table 1 in the shape of a disk having a diameter of 125 mm and a thickness of 5 mm by grinding using a carbide tool under the condition of lathe rotation speed: 200 rpm. 10, Comparative targets 1-2 and Conventional target 1 were produced.

These inventive targets 1 to 10, comparative targets 1 and 2 and conventional target 1 are each soldered to a copper cooling backing plate with an indium brazing material having a purity of 99.999% by weight, and this is applied to a DC magnetron sputtering apparatus. After charging and setting the distance between the target and the substrate (Si wafer having a thickness of 100 nm of SiO ₂ on the surface) to be 70 mm, the ultimate vacuum is 5 × 10 ⁻⁵ Pa or less. Evacuated until Ar pressure is supplied until the total pressure is 1.0 Pa,
-Substrate temperature: room temperature,
-Input power: 50 W (0.4 W / cm ² ),
Sputtering was performed under the following conditions to form phase change recording films 1 to 10 of the present invention, comparative phase change recording films 1 and 2 and conventional phase change recording film 1 having a thickness of 300 nm on the surface of the substrate.
The component compositions of the phase change recording films 1 to 10 of the present invention, the comparative phase change recording films 1 and 2 and the conventional phase change recording film 1 thus obtained were measured by EPMA (electron probe microanalyzer), and the result Are shown in Table 2. In addition, in the composition analysis by EPMA, the amount of C detected from a film obtained by separately forming a film with a Ge—Sb—Te target to which C is not added in consideration of the influence of the C component due to surface adsorption from the atmosphere. A value obtained by subtracting (corresponding to the amount of adsorption from the atmosphere) from the analysis value of each film was defined as the C amount of the film.
Further, after crystallizing the obtained phase change recording films 1 to 10, comparative phase change recording films 1 and 2 and conventional phase change recording films 1 of the present invention at 300 ° C. for 5 minutes in a vacuum, four probes are used. The specific resistance was measured by the above method, and the film was formed on a polycarbonate substrate having a diameter of 120 mm at a thickness of 3 μm under the same conditions as described above. The crystallization temperature was measured under the conditions of a heating rate of 10 ° C./min in an Ar flow of 200 ml per minute, and the results are shown in Table 2. The sample used for this measurement was unified at 15 mg. Here, the exothermic peak appearing in the vicinity of 150 to 350 ° C. was defined as the crystallization temperature.

  From the results shown in Tables 1 and 2, the crystallized phase change recording films 1 to 10 of the present invention obtained by sputtering using the targets 1 to 10 of the present invention are obtained by sputtering using the conventional target 1. It can be seen that the specific resistance is higher than that of the obtained crystallized conventional phase change recording film 1. However, the comparative phase change recording films 1 and 2 crystallized by sputtering using the comparative targets 1 and 2 having component compositions that deviate from the conditions of the present invention have a low specific resistance or are crystallized. It turns out that the temperature rises too much, which is undesirable.

Claims (3)

Atomic% (hereinafter,% indicates atomic%) Ge: 15-30%, Sb: 15-30%, C: 0.2-8%, with the balance being Te and inevitable impurities A phase change recording film having a high electrical resistance. 3. The phase change recording film having a high electrical resistance according to claim 2, wherein a specific resistance value measured by a four-probe method after crystallization is 5 × 10 ^{−2 to} 5 × 10 ¹ Ω · cm. 3. Electricity according to claim 1 or 2, characterized in that it contains Ge: 15-30%, Sb: 15-30%, C: 0.2-8%, with the balance being Te and inevitable impurities. A sputtering target for forming a phase change recording film having high resistance.