KR101078718B1 - Phase change RAM device and method of manufacturing the same - Google Patents

Abstract

The present invention discloses a phase change memory device and a method of manufacturing the same. The phase change memory device according to the present invention includes a semiconductor substrate having a lower pattern; A first insulating layer formed on the semiconductor substrate to cover the lower pattern; A contact plug formed in the first insulating layer to contact the lower pattern; A second insulating layer formed on the first insulating layer and having a trench for exposing a contact plug; A metal pad formed in the trench; A third insulating layer formed on the second insulating layer including the metal pad and having a contact hole exposing the metal pad; A lower electrode in a ring shape formed on the sidewall of the contact hole and a metal pad portion adjacent thereto; A fourth insulating layer embedded in the contact hole including the lower electrode; And a phase conversion film and an upper electrode sequentially formed on a ring-shaped lower electrode including the fourth insulating layer and a portion of the third insulating layer adjacent thereto.

Description

Phase change RAM device and method of manufacturing the same

1 is a graph for explaining the dependence of the set resistance and the reset resistance according to the size of the lower electrode.

2A through 2G are cross-sectional views illustrating processes of manufacturing a phase change memory device according to an embodiment of the present invention.

3 is a cross-sectional view illustrating a method of manufacturing a phase change memory device according to another embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

20 semiconductor substrate 21 first insulating film

22 contact plug 23 first nitride film

24: second insulating film 25: trench

26 metal pad 27 third insulating film

28: contact hole 29: conductive film for lower electrode

29a: lower electrode 30: second nitride film

30a: nitride film spacer 31: fourth insulating film

32: phase conversion film 33: upper electrode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change memory element, and more particularly, to a phase change memory element capable of securing a sensing margin and a manufacturing method thereof.

The memory device is a volatile random access memory (RAM) device that loses input information when the power supply is cut off, and a read only memory (ROM) device that maintains the storage state of the input information even when the power supply is turned off. It is largely divided. The volatile RAM devices may include DRAM and SRAM, and the nonvolatile ROM devices may include flash memory devices such as EEPROM (Elecrtically Erasable and Programmable ROM). have.

However, although the DRAM has a very good memory device as is well known, high charge storage capability is required, and for this purpose, it is difficult to achieve high integration since the electrode surface area must be increased. In addition, the flash memory device requires a high operating voltage compared to a power supply voltage in connection with a structure in which two gates are stacked, and thus requires a separate boost circuit to form a voltage required for write and erase operations. Therefore, there is a difficulty in high integration.

Accordingly, many studies are being conducted to develop a new memory device having a characteristic of the nonvolatile memory device and having a simple structure, and as an example, a phase change memory device (Phase Change RAM) Was proposed.

The phase change memory device utilizes a difference in resistance between crystalline and amorphous phases due to the phase change of the phase conversion film interposed between the electrodes from the crystal state to the amorphous state through the current flow between the lower electrode and the upper electrode. It is a storage element for determining stored information. In other words, the phase conversion memory device uses a chalcogenide film as a phase conversion film. The chalcogenide film is a compound film composed of germanium (Ge), stevidium (Sb), and tellurium (Te). Phase change occurs between the amorphous state and the crystalline state due to the applied current, that is, the joule heat, from which the resistivity of the phase change film having an amorphous state is higher than that of the phase change film having a crystalline state. In the read mode, the current flowing through the phase change layer is sensed to determine whether the information stored in the phase change memory cell is logic '1' or logic '0'.

Although not shown, such a phase conversion memory element is formed with a set transistor and a reset transistor on a semiconductor substrate, and then contact plugs are formed in contact with each transistor, and then damascene ( After forming a metal pad on each contact plug through a Damascene process, a lower electrode is formed in the form of a plug on the metal pad, and then a phase conversion film and an upper electrode are sequentially formed on the lower electrode. do.

On the other hand, the phase change memory device requires a current flow of 1 mA or more for stable phase change of the phase change film. Accordingly, the current required for the phase change of the phase change film is reduced by reducing the contact area between the bottom electrode and the phase change film. To this end, a method of reducing the size of the bottom electrode is used.

However, in the conventional stack structure, the method of reducing the size of the lower electrode in order to reduce the interface of the phase conversion film, as shown in Figure 1, the size of the lower electrode is reduced to 40nm or less as the cell size is smaller In this case, the reset current from crystalline to amorphous becomes small, but the set resistance increases rapidly, and as the set resistance increases, the difference between the reset resistance and the set resistance decreases. Sensing margin) is inevitably lowered.

As a result, the conventional phase change memory device has difficulty in securing a sensing margin due to high integration.

Accordingly, an object of the present invention is to provide a phase change memory device capable of securing a sensing margin despite high integration, and a method of manufacturing the same.

In order to achieve the above object, the present invention, a semiconductor substrate provided with a lower pattern; A first insulating layer formed on the semiconductor substrate to cover the lower pattern; A contact plug formed in the first insulating layer to contact the lower pattern; A second insulating layer formed on the first insulating layer and having a trench for exposing a contact plug; A metal pad formed in the trench; A third insulating layer formed on the second insulating layer including the metal pad and having a contact hole exposing the metal pad; A lower electrode in a ring shape formed on the sidewall of the contact hole and a metal pad portion adjacent thereto; A fourth insulating layer embedded in the contact hole including the lower electrode; And a phase conversion film and an upper electrode sequentially formed on a ring-shaped lower electrode including the fourth insulating film, and a portion of the third insulating film adjacent thereto.

The phase change memory device of the present invention further includes a nitride film interposed between the first insulating film and the second insulating film.

The phase change memory device of the present invention further includes a nitride film spacer interposed between the lower electrode and the fourth insulating film.

The lower electrode has a ring shape in which a lower width is larger than an upper width.

The contact hole has a size above the exposure limit.

In addition, in order to achieve the above object, the present invention, the step of providing a semiconductor substrate having a lower pattern; Forming a first insulating layer on an entire surface of the substrate to cover the lower pattern; Forming a contact plug in the first insulating layer to contact the lower pattern; Forming a second insulating film on the first insulating film including the contact plug; Etching the second insulating layer to form a trench for exposing a contact plug; Forming a metal pad in the trench; Forming a third insulating film on the second insulating film including the metal pad; Etching the third insulating layer to form a contact hole exposing a metal pad; Sequentially forming a lower electrode conductive film and a nitride film on the third insulating film including the contact hole; Etching the entire nitride film to form a nitride film spacer on the conductive film on the sidewall of the contact hole; Etching the entire conductive layer to form a ring-shaped lower electrode on the sidewall of the contact hole and the metal pad portion adjacent thereto; Embedding a fourth insulating layer in the contact hole; And sequentially forming a phase conversion film and an upper electrode on a ring-shaped lower electrode including the fourth insulating film and a third insulating film adjacent thereto.

Here, the method further includes the step of forming a nitride film after the forming of the contact plug and before the forming of the second insulating film.

The contact hole is formed to a size larger than the exposure limit.

The lower electrode is formed in a ring shape having a lower width than the upper width.

The filling of the fourth insulating layer in the contact hole may include forming a fourth insulating layer to fill the contact hole; And CMPing the fourth insulating layer to expose the third insulating layer, wherein the CMP of the fourth insulating layer is performed such that a part of the thickness of the third insulating layer, the lower electrode, and the nitride spacer is removed together.

The method may further include removing the nitride layer spacers after forming the lower electrode and before embedding a fourth insulating layer in the contact hole.

(Example)

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, in the case of implementing a phase conversion memory device of 256M or more with a conventional structure, it is expected that the amount of current required for phase change should be 0.3 mA or less and the size of the lower electrode should be 40 nm or less. When the thickness is less than or equal to nm, the set resistance is increased to decrease the resistance difference from the reset resistance, thereby lowering the sensing margin.

Accordingly, the present invention forms a phase change cell in a ring structure. In this way, the present invention can reduce the writing current from crystalline to amorphous while forming a phase conversion cell with the same area as in the prior art. The present invention also provides a plug-type lower electrode having a size of 40 nm or less. Since the contact interface with the phase change film can be made similar or smaller than the conventional one while forming stably in a certain size without forming, the process margin is also reduced from being affected by the exposure limit while securing the sensing margin by not increasing the set resistance. It can be secured.

In detail, FIGS. 2A to 2F are cross-sectional views illustrating processes of manufacturing a phase change memory device according to the present invention.

Referring to FIG. 2A, a first insulating layer 21 is formed on the semiconductor substrate 20 on which a lower pattern (not shown) including a transistor is formed to cover the lower pattern. Then, the first insulating layer 21 is etched to form a first contact hole exposing a lower pattern, specifically, a junction region of the transistor, and then a conductive film such as a silicon film or a metal film is formed in the first contact hole. A contact plug 22 is formed by being embedded.

Next, the first nitride film 23 and the second insulating film 24 are sequentially formed on the first insulating film 22 including the contact plug 22. Thereafter, the second insulating layer 24 and the first nitride layer 23 are etched to form a trench 25 defining a region in which the metal pad is to be formed.

Referring to FIG. 2B, after depositing a metal film on the second insulating film 24 including the trench 25, the metal film is chemically polished (CMP) to expose the second insulating film 24 in the trench 25. The metal pad 26 is formed.

Next, after the third insulating layer 27 is formed on the second insulating layer 24 including the metal pads 26, the lower electrode exposing the metal pads 26 by etching the third insulating layer 27. A forming second contact hole 28 is formed. In this case, the lower contact forming second contact hole 28 has a size greater than or equal to an exposure limit, for example, a size greater than or equal to 100 nm so that stable formation is achieved.

Referring to FIG. 2C, the conductive layer 29 for the lower electrode is thinned on the third insulating layer 27 including the second contact hole 28 by an atomic layer deposition (ALD) process or a metal organic CVD (MOCVD) process. After the deposition, the second nitride film 30 is similarly deposited on the lower electrode conductive film 29.

Referring to FIG. 2D, the nitride layer spacer 30a is formed on the lower electrode conductive layer 29 on the sidewall of the second contact hole 28 by etching the entire surface of the second nitride layer.

Referring to FIG. 2E, the entire surface of the lower electrode conductive layer is etched, thereby forming the lower electrode 29a on the surface of the second contact hole 28 and the metal pad portion adjacent thereto. At this time, the nitride film spacer 30a functions as an etch stop film during the etching of the conductive film for the lower electrode, so that the finally obtained lower electrode 29a has a ring shape.

Here, since the lower electrode 29a is formed in a ring shape and the lower electrode is wider than the upper part through the formation of the nitride film spacer 30a, the contact interface with the metal pad 28 can be stably formed. Can be.

Referring to FIG. 2F, after depositing the fourth insulating layer 31 to fill the second contact hole 28 on the third insulating layer 27 including the ring-shaped lower electrode 29a, the second contact hole is formed. The fourth insulating film 31 is CMP so as to remain only in (28). In this case, the CMP process with respect to the fourth insulating layer 31 is preferably performed so that a predetermined thickness of the third insulating layer 27, the nitride spacer 30a, and the lower electrode 29a is removed together. In the etching process for forming the lower electrode 29a, the sharply formed nitride spacer portion and the lower electrode portion are removed, and as a result, the contact interface with the phase change film to be formed subsequently is constant.

Referring to FIG. 2G, a phase change material film and an upper electrode conductive film are sequentially formed on the second insulating film and the fourth insulating film including the lower electrode and the nitride film spacer. Then, the upper electrode 33 is etched by etching the upper electrode conductive film, and the phase change film 32 is subsequently formed by etching the phase change material film to form a phase change cell having a ring structure.

Subsequently, although not shown, a series of known subsequent processes including a metallization process are sequentially performed to complete the manufacture of the phase change memory device according to the present invention.

As described above, the phase change memory device of the present invention forms a lower electrode in a ring shape and has a lower width than the upper width, thereby forming a stable contact interface with the metal pad and effectively reducing the contact interface with the phase change film. In this way, it is possible to prevent a sudden increase in the set resistance which appears as the device becomes smaller, and thus, the sensing margin can be increased.

Meanwhile, in the above exemplary embodiment of the present invention, the fourth insulating layer, the phase change layer, and the upper electrode are formed while the nitride spacer is left on the ring-shaped lower electrode sidewall, but as another embodiment of the present invention, shown in FIG. As described above, after the nitride film spacer is removed by wet etching, the fourth insulating film 31, the phase change film 32, and the upper electrode 33 may be formed.

In this case, it is possible to more stably form the contact interface with the phase change film 31 by removing the sharp portion generated in the process of forming the ring-shaped lower electrode (29a) in advance.

As described above, according to the present invention, by forming a phase conversion cell in a ring structure, the contact interface between the lower electrode and the phase conversion film can be made stable, and the contact hole for the lower electrode can be stably formed. Sensing margin can be increased by avoiding a sudden increase in set resistance.

Hereinbefore, the present invention has been described with reference to some examples, but the present invention is not limited thereto, and those skilled in the art to which the present invention pertains have many modifications and variations without departing from the spirit of the present invention. It will be appreciated that it can be added.

Claims (12)

A semiconductor substrate having a lower pattern; A first insulating layer formed on the semiconductor substrate to cover the lower pattern; A contact plug formed in the first insulating layer to contact the lower pattern; A second insulating layer formed on the first insulating layer and having a trench for exposing a contact plug; A metal pad formed in the trench; A third insulating layer formed on the second insulating layer including the metal pad and having a contact hole exposing the metal pad; A lower electrode in a ring shape formed on the sidewall of the contact hole and a metal pad portion adjacent thereto; A fourth insulating layer embedded in the contact hole including the lower electrode; And A phase conversion film and an upper electrode sequentially formed on a ring-shaped lower electrode including the fourth insulating film and a portion of the third insulating film adjacent thereto; Phase change memory device comprising a. Claim 2 has been abandoned due to the setting registration fee. The method of claim 1, And a nitride film interposed between the first insulating film and the second insulating film. Claim 3 was abandoned when the setup registration fee was paid. The method of claim 1, And the lower electrode has a ring shape in which a lower width is larger than an upper width. Claim 4 was abandoned when the registration fee was paid. The method of claim 1, And a nitride film spacer interposed between the lower electrode and the fourth insulating film. Claim 5 was abandoned upon payment of a set-up fee. The method of claim 1, And the contact hole has a size greater than or equal to an exposure limit. Preparing a semiconductor substrate having a lower pattern; Forming a first insulating layer on an entire surface of the substrate to cover the lower pattern; Forming a contact plug in the first insulating layer to contact the lower pattern; Forming a second insulating film on the first insulating film including the contact plug; Etching the second insulating layer to form a trench for exposing a contact plug; Forming a metal pad in the trench; Forming a third insulating film on the second insulating film including the metal pad; Etching the third insulating layer to form a contact hole exposing a metal pad; Sequentially forming a lower electrode conductive film and a nitride film on the third insulating film including the contact hole; Etching the entire nitride film to form a nitride film spacer on the conductive film on the sidewall of the contact hole; Etching the entire conductive layer to form a ring-shaped lower electrode on the sidewall of the contact hole and the metal pad portion adjacent thereto; Embedding a fourth insulating layer in the contact hole; And Sequentially forming a phase conversion film and an upper electrode on a ring-shaped lower electrode including the fourth insulating film and a third insulating film adjacent thereto; A method for manufacturing a phase change memory device comprising a. Claim 7 was abandoned upon payment of a set-up fee. The method of claim 6, And forming a nitride film after the forming of the contact plug and before the forming of the second insulating film. Claim 8 was abandoned when the registration fee was paid. The method of claim 6, The contact hole is a manufacturing method of a phase-change memory device, characterized in that formed in the size beyond the exposure limit. Claim 9 was abandoned upon payment of a set-up fee. The method of claim 6, And the lower electrode is formed in a ring shape having a lower width greater than an upper width. Claim 10 was abandoned upon payment of a setup registration fee. The method of claim 6, The filling of the fourth insulating layer in the contact hole may include: Forming a fourth insulating layer to fill the contact hole; And CMPing the fourth insulating film so that the third insulating film is exposed. Claim 11 was abandoned upon payment of a setup registration fee. 11. The method of claim 10, The CMP of the fourth insulating layer may be performed such that a partial thickness of the third insulating layer, the lower electrode, and the nitride spacer is removed together. Claim 12 was abandoned upon payment of a registration fee. The method of claim 6, And removing the nitride film spacer after the forming of the lower electrode and before embedding the fourth insulating film in the contact hole.

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