JP4606721B2 - Phase change recording film with high electrical resistance - Google Patents

Description

The invention is by electrical resistance is high resistance heat relates to a semiconductor non-volatile memory for phase change recording film for writing and erasing.

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 a large current causes a minute load from being applied to the circuit. It has become an obstacle to conversion.

Therefore, the present inventors have studied to reduce the value of the current flowing during the write / erase operation by increasing the resistance of the phase change recording film on which writing / erasing is performed by resistance heating. as a result,
(A) In a normal Ge—Sb—Te phase change recording film, the phase change recording film containing 0.2% to 0.81 % in atomic% (hereinafter,% indicates atomic%) is in a crystalline state. The electric resistance at the time becomes higher, thereby reducing the current value flowing during the write / erase operation.
(Ii) C: a Ge-Sb-Te-based phase-change recording film containing from 0.2 to .81 percent is obtained by sputtering using a a Ge-Sb-Te-based target containing a C, studies in which The result was obtained.

The present invention has been made based on such research results, and contains Ge : 15-30%, Sb: 15-30%, C: 0.2-0.81%, with the balance being Te and A semiconductor nonvolatile semiconductor having a composition composed of inevitable impurities and having a specific resistance value of 5 × 10 ^{−2 to} 5 × 10 ¹ Ω · cm measured by a four-probe method after crystallization, and having high electrical resistance to write and erase by resistance heating It is characterized by a phase change recording film for memory.

  The phase change recording film for semiconductor non-volatile memory to which data is erased by resistance heating according to the present invention has a reasonably high electric resistance value. This contributes to the improvement of the characteristics of the phase change nonvolatile memory film and the cost reduction, 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 for semiconductor nonvolatile memory in which writing and erasing is performed by resistance heating with 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. In the present invention, the C content is 0.2 to 0.81%.
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 occur, such as requiring large electric power for crystallization or slowing down the crystallization .

(B) Ge, Sb
Ge and Sb electrical resistance is contained in the semiconductor nonvolatile memory for phase change recording film to write erased by high resistance heating of the present invention, Ge: 15% to 30%, Sb: preferably 15% to 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.

Semiconductor non-volatile memory for phase change recording film to write erased by electrical resistance is high resistance heat 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 (more preferably 8 × 10 ⁻² Ω · cm or more), because the specific resistance value is less than 5 × 10 ⁻² Ω · cm, a large current flows through the circuit, which increases power consumption. Moreover, it is because it becomes an obstacle at the time of refinement | miniaturization, and is because it is not preferable. 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.

  A sputtering target for forming a phase change recording film for a semiconductor nonvolatile memory to be written and erased by resistance heating according to the present invention is prepared by dissolving an alloy having a predetermined component composition in an Ar gas atmosphere, and then pouring it into an iron mold. An ingot is prepared, and the alloy ingot is pulverized in an inert gas atmosphere to prepare an alloy powder. The alloy powder is mixed with C powder so as to have the same component composition as that of the phase change recording film of the invention. A mixed powder is produced by mixing, and this mixed powder is produced by vacuum hot pressing. 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. 3. Comparative targets 1 and 2 and conventional target 1 were produced.

The present invention targets 1 to 3 , comparative targets 1 to 2 and the 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 3 of the present invention, comparative phase change recording films 1 to 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 3 , comparative phase change recording films 1 and 2 and the conventional phase change recording films 1 thus obtained were measured by EPMA (electron probe microanalyzer). 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 3 , comparative phase change recording films 1 and 2 and the 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 3 of the present invention obtained by sputtering using the targets 1 to 3 of the present invention were sputtered using the target 1 of the prior art. 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 (1)

A composition containing Ge: 15 to 30%, Sb: 15 to 30%, C: 0.2 to 0.81% in atomic% (hereinafter,% represents atomic%), with the balance being Te and inevitable impurities. And a specific resistance value measured by the four-probe method after crystallization is 5 × 10 ^{−2 to} 5 × 10 ¹ Ω · cm. Phase change recording film for memory.