KR20080032841A - Method for manufacturing flash memory device having blocking oxide film - Google Patents

Abstract

A method of manufacturing a charge trapping flash memory device in which a deposition process is performed under a temperature condition high enough to obtain a crystallized blocking oxide film in forming a blocking oxide film for blocking electrons from moving to a gate electrode. In the method of manufacturing a flash memory device according to the present invention, a tunneling oxide film is formed on a semiconductor substrate. A charge storage layer is formed on the tunneling oxide film. A crystallized blocking oxide film is formed on the charge storage layer. A gate electrode is formed over the blocking oxide film.

Description

Method of manufacturing flash memory device having blocking oxide film

1 to 5 are cross-sectional views illustrating a method of manufacturing a flash memory device according to a preferred embodiment of the present invention in a process sequence.

FIG. 6 is a graph illustrating Vth characteristics of a programming operation time and an erase operation time evaluated for flash memory devices including a blocking oxide film formed under various temperature conditions.

FIG. 7 is a graph illustrating a result of evaluating a difference between Vth during programming and Vth during an erase operation, that is, a Vth window, of flash memory devices including a blocking oxide film formed under various temperature conditions.

8A is a graph illustrating a result of evaluating HTS characteristics of a flash memory device according to a comparative example.

8B is a graph showing the results of evaluating HTS characteristics for an exemplary flash memory device manufactured according to the method of the present invention.

9A is a graph illustrating a result of evaluating HTS characteristics of a flash memory device according to a comparative example.

9B is a graph showing the results of evaluating HTS characteristics for another exemplary flash memory device manufactured according to the method of the present invention.

<Explanation of symbols for the main parts of the drawings>

100: semiconductor substrate, 110: tunneling oxide film, 120: charge storage layer, 130: blocking oxide film, 132; Annealing, 140: gate electrode, 150: gate stack structure, 162, 164: source / drain regions.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor memory device, and more particularly, to a method of manufacturing a charge trap type flash memory device having a blocking oxide film for blocking electrons from moving to a gate electrode.

Recently, a charge trap type flash memory device has been developed as one of nonvolatile memory devices and has been widely used in various fields such as a mobile communication system and a memory card.

A typical charge trapping flash memory device has a gate stack structure in which a tunneling oxide film, a charge storage layer, a blocking oxide film, and a gate electrode are sequentially stacked on a semiconductor substrate. The tunneling oxide film is in contact with a source and a drain formed of an impurity region formed in the semiconductor substrate, and the charge storage layer includes a trap site for storing charge passing through the tunneling oxide film. The blocking oxide layer blocks electrons from escaping to the gate electrode in the process of being trapped in the trap site of the charge storage layer, and blocks the charge of the gate electrode from being injected into the charge storage layer.

In the charge trapping flash memory device having the above structure, electrons passing through the tunneling oxide film by the voltage application are trapped at the trap site of the charge storage layer. In the charge trapping nonvolatile semiconductor memory device, the threshold voltage (Vth) varies depending on whether electrons are trapped in the charge storage layer and when they are not trapped.

Typically, the deposition process for forming the blocking oxide film on the charge storage layer is performed under relatively low temperature conditions around 400 ° C. As such, impurities such as C or H are present in the blocking oxide film formed under the low temperature condition, thereby causing a leakage current. In addition, when an Al ₂ O ₃ film is employed as the blocking oxide film, an uncrystallized Al ₂ O ₃ film is obtained by depositing at a relatively low temperature as in a normal process, and thus the electrical properties to HTS (high temperature stress) due to such film quality are obtained. This can be easily degraded. In particular, more stress is applied to a cell for a multi-level cell (MLC) operation in which a plurality of pieces of information are stored in one cell in order to implement a high-capacity memory device, and thus, electrical deterioration of HTS becomes more severe.

SUMMARY OF THE INVENTION The present invention seeks to solve the above problems in the prior art, by minimizing the deterioration of electrical characteristics for HTS and improving the film quality of the blocking oxide film to prevent leakage current due to impurities in the blocking oxide film. It is to provide a method of manufacturing a flash memory device that can improve the characteristics.

In order to achieve the above object, in the method of manufacturing a flash memory device according to the present invention, a tunneling oxide film is formed on a semiconductor substrate. A charge storage layer is formed on the tunneling oxide layer. A crystallized blocking oxide film is formed on the charge storage layer under a first temperature condition. A gate electrode is formed on the blocking oxide film.

The first temperature may be selected within the range of 500 to 1000 ° C.

The blocking oxide film may be made of at least one material selected from the group consisting of Al ₂ O ₃ , SiO ₂ , HfO ₂ , ZrO ₂ , LaO, LaAlO, LaHfO, and HfAlO.

In the method of manufacturing a flash memory device according to the present invention, after forming the crystallized blocking oxide film, the method may further include annealing the crystallized blocking oxide film under a second temperature higher than the first temperature. The second temperature may be selected in the range of 950 ~ 1200 ℃.

The charge storage layer may be formed of a silicon nitride film, a metal oxide film, a metal nitride film, or a combination thereof. In addition, the gate electrode may be made of at least one material selected from the group consisting of TaN, TiN, W, WN, HfN, and tungsten silicide.

According to the present invention, the deposition process for forming the blocking oxide film constituting the flash memory device is performed under a temperature condition sufficiently high to obtain a crystallized film quality, thereby improving the film quality of the blocking oxide film and minimizing the deterioration of the electrical characteristics of the HTS. By preventing leakage current caused by impurities in the blocking oxide layer, a flash memory device having improved program and erase operation characteristics can be implemented.

Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 to 5 are cross-sectional views illustrating a method of manufacturing a flash memory device according to a preferred embodiment of the present invention in a process sequence.

Referring to FIG. 1, a tunneling oxide layer 110 is formed on a semiconductor substrate 100 such as a silicon substrate. The tunneling oxide film 110 may be formed of, for example, a silicon oxide film, and may be formed to a thickness of about 20 to about 70 kPa.

The charge storage layer 120 is formed on the tunneling oxide layer 110. The charge storage layer 120 may be formed of a silicon nitride film or a high-k film having a higher dielectric constant. For example, the charge storage layer 120 may be formed of a Si ₃ N ₄ film, a metal oxide film, a metal nitride film, or a combination thereof. The charge storage layer 120 may be formed to a thickness of about 40 ~ 120 Å.

Referring to FIG. 2, a blocking oxide layer 130 is formed on the charge storage layer 120. The deposition process for forming the blocking oxide film 130 is performed under a first temperature condition sufficient for the constituent material of the blocking oxide film 130 to crystallize. Preferably, the first temperature is selected in the range of about 500 to 1000 ° C.

The blocking oxide layer 130 may be formed by, for example, physical vapor deposition (PVD), atomic layer deposition (ALD), or chemical vapor deposition (CVD).

The blocking oxide layer 130 may be formed of at least one material selected from the group consisting of Al ₂ O ₃ , SiO ₂ , HfO ₂ , ZrO ₂ , LaO, LaAlO, LaHfO, and HfAlO, for example.

Referring to FIG. 3, the blocking oxide layer 130 is annealed 132 under a second temperature higher than the first temperature.

The second temperature may be selected in the range of about 950 ~ 1200 ℃. The annealing 132 may be performed for about 30 seconds to 4 minutes. The film quality of the blotting oxide layer 130 may be further improved by the annealing 132. However, in some cases, the annealing process 132 may be omitted.

The blocking oxide layer 130 serves to block electrons from moving to the upper gate electrode while electrons passing through the tunneling oxide layer 110 are trapped in the charge storage layer 120.

Referring to FIG. 4, a gate electrode 140 is formed by depositing a conductive material on the blocking oxide layer 130.

The gate electrode 140 may be made of at least one material selected from the group consisting of TaN, TiN, W, WN, HfN, and tungsten silicide.

Referring to FIG. 5, the gate electrode structure 140, the blocking oxide layer 130, the charge storage layer 120, and the tunneling oxide layer 110 are sequentially patterned to form a gate stacked structure 150. Thereafter, an impurity is implanted into the surface of the semiconductor substrate 100 exposed on both sides of the gate stacked structure 150 and heat-treated to form source / drain regions 162 and 164.

In the method of manufacturing the flash memory device according to the exemplary embodiment described above, the deposition process for forming the blocking oxide film 130 is performed under high temperature conditions sufficient for the constituent material to crystallize, thereby blocking the blocking oxide film 130. Impurity content can be minimized in the inside, and the blocking oxide film 130 formed of the crystallized material is obtained, thereby improving the film quality of the blocking oxide film 130 to prevent the occurrence of leakage current due to impurities in the blocking oxide film 130. In addition, a flash memory device having improved program and erase operation characteristics may be implemented.

Evaluation example 1

In order to evaluate the operating characteristics of a flash memory device including a blocking oxide film formed according to an exemplary embodiment of the present invention, a tunneling oxide film composed of a silicon oxide film having a thickness of 40 mW and a silicon nitride film having a thickness of 70 mW is formed on a silicon substrate. after forming a blocking oxide layer formed of a charge storage layer and formed of, Al ₂ O ₃ film of 150 Å thick, the resultant formed by the blocking ring in the oxide film was 1200 ℃ annealing for 2 minutes. Thereafter, a gate electrode was formed on the blocking oxide layer to manufacture flash memory devices. Here, the gate electrode was formed in a structure in which TaN having a thickness of 200 mW, WN having a thickness of 50 mW, and W having a thickness of 300 mW were sequentially stacked.

In this evaluation example, in order to evaluate the resulting Vth characteristics according to the formation temperature of the blocking oxide film, each of the blocking oxide films formed by the ALD method at deposition temperatures of 250 ° C, 300 ° C, 450 ° C and 500 ° C, respectively In this case, the Vth characteristics of the programming operation and the erasing operation time were evaluated.

FIG. 6 is a graph illustrating Vth characteristics of a programming operation time and an erase operation time evaluated for flash memory devices including a blocking oxide film formed under the various temperature conditions described above.

In FIG. 6, the dotted line (………) is when the deposition temperature is 250 ° C. when forming the blocking oxide film (sample 1), and the dashed dash line (− · −) is when the deposition temperature is 300 ° C. when the blocking oxide film is formed (sample). 2), the double-dot chain line (---) is when the deposition temperature is 450 deg. C when forming the blocking oxide film (sample 3), and the solid line (-) is when the deposition temperature is 500 deg. C when forming the blocking oxide film (sample 4) is shown.

For the evaluation of FIG. 6, a voltage of 17 V was applied for 100 kV as the programming voltage for each of Samples 1-4. Vth in the programming operations of Samples 1 to 4 were 2.3 V, 4.0 V, 4.0 V, and 4.1 V, respectively. In addition, a voltage of −19 V was applied for 10 ms as the erase voltage for each of Samples 1 to 4. Vth in the erase operation of Samples 1 to 4 was -0.4 V, -2.7 V, -3.7 V, and -3.9 V, respectively.

FIG. 7 is a graph showing a result of evaluating the difference between the Vth during programming and the Vth during the erase operation, that is, the Vth window from the result of FIG. 6.

In FIG. 7, "■" indicates a deposition temperature when forming the blocking oxide film is 250 ° C, "●" indicates a deposition temperature when forming the blocking oxide film is 300 ° C, and "▲" indicates a deposition temperature when forming the blocking oxide film. In the case of 450 ° C., and “▼” denotes a case where the deposition temperature is 500 ° C. in forming the blocking oxide film.

In the results of FIG. 7, when the blocking oxide film is formed at a temperature of 500 ° C. according to the method of the present invention, a larger Vth window is obtained at the same level of equivalent oxide thickness (Toxeq) than when the blocking oxide film is formed under a relatively low temperature. It can be confirmed that is obtained.

Table 1 shows the results of measuring breakdown voltages of each of the flash memory devices evaluated in Evaluation Example 1. FIG.

As can be seen from the results of Table 1, it can be seen that the blocking oxide film was formed at a temperature of 500 ° C. according to the method of the present invention as compared with the case where the blocking oxide film was formed at a relatively low temperature. .

Evaluation example 2

In order to evaluate the high temperature stress (HTS) characteristics of the flash memory device including the blocking oxide film formed according to another exemplary embodiment of the present invention, a flash memory device including the blocking oxide film by a method as prepared in Evaluation Example 1 Were prepared. However, here, the case where the deposition temperature at the time of forming the said blocking oxide film was set to 450 degreeC and 600 degreeC was evaluated.

8A shows, as a comparative example, 1200 cycles of programming and erasing operations for a flash memory device including a blocking oxide film made of Al ₂ O ₃ formed at a deposition temperature of 450 ° C., followed by a temperature of 200 ° C. for the resultant. Is a graph showing the drain current (Ids) change according to the measured gate voltage (V _G ) before and after baking for 2 hours at (...).

FIG. 8B is a 1200 cycle of programming and erasing operations for a flash memory device including a blocking oxide film made of Al ₂ O ₃ formed under a deposition temperature of 600 ° C. according to the method of the present invention, and then 200 ° C. for the resultant. It is a graph showing the change of the drain current (Ids) according to the change of the gate voltage (V _G ) measured before (-) and after (......) for 2 hours at the temperature of.

For the evaluation of FIGS. 8A and 8B, a voltage of 16.6 V was applied for 100 mV as a programming voltage, and a voltage of -18.1 V was applied for 10 ms as an erase voltage, respectively.

8A and 8B show that when the blocking oxide film is formed at a temperature of 600 ° C. according to the method of the present invention, when the blocking oxide film is formed at 450 ° C., which is a relatively low temperature, the program operation before and after the baking process is performed. It can be seen that the Vth difference (ΔVth) is improved by about 0.08V.

FIG. 9A shows, as a comparative example, only one programming operation and one erasing operation for a flash memory device including a blocking oxide film made of Al ₂ O ₃ formed at a deposition temperature of 450 ° C., and then at 200 ° C. for the resultant. It is a graph showing the change of drain current (Ids) according to the change of the gate voltage (V _G ) measured before (-) and after (-...) baking process for 2 hours at temperature.

FIG. 9B shows only one programming operation and one erasing operation for a flash memory device including a blocking oxide film made of Al ₂ O ₃ formed under a deposition temperature of 600 ° C. according to the method of the present invention, and then 200 for the resultant. It is a graph showing the change of the drain current (Ids) according to the change of the gate voltage (V _G ) measured before (-) and after (-...) baking for 2 hours at the temperature of ° C.

For the evaluation of FIGS. 9A and 9B, a voltage of 16.6 V was applied for 100 mV as a programming voltage, and a voltage of -18.1 V was applied for 10 ms as an erase voltage, respectively.

9A and 9B show that when the blocking oxide film is formed at a temperature of 600 ° C. according to the method of the present invention, compared to the case where the blocking oxide film is formed at 450 ° C., which is a relatively low temperature, the program operation before and after the baking process is performed. It can be seen that the Vth difference (ΔVth) is improved by about 0.03V.

According to the present invention, in forming a blocking oxide film constituting a flash memory element, by applying a temperature condition high enough to obtain a crystallized blocking oxide film to improve the film quality of the blocking oxide film, the impurity content in the blocking oxide film is improved. Leakage current can be minimized to minimize, and program and erase operation characteristics can be improved. In addition, the HTS characteristics may be improved to provide a flash memory device having improved reliability.

In the above, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications and changes by those skilled in the art within the spirit and scope of the present invention. This is possible.

Claims (10)

Forming a tunneling oxide film on the semiconductor substrate; Forming a charge storage layer on the tunneling oxide layer; Forming a blocking oxide film crystallized on the charge storage layer under a first temperature condition; And forming a gate electrode on the blocking oxide film. The method of claim 1, The first temperature is selected in the range of 500 to 1000 ° C. The method of claim 1, And said blocking oxide film has a thickness of 150 to 250 GPa. The method of claim 1, The blocking oxide film is made of at least one material selected from the group consisting of Al ₂ O ₃ , SiO ₂ , HfO ₂ , ZrO ₂ , LaO, LaAlO, LaHfO and HfAlO. The method of claim 1, The blocking oxide film is formed by a PVD, ALD or CVD method. The method of claim 1, And forming the crystallized blocking oxide film, and then annealing the crystallized blocking oxide film under a second temperature higher than the first temperature. The method of claim 6, And said second temperature is selected in the range of 950-1200 [deg.] C. The method of claim 1, And the tunneling oxide film is formed of a silicon oxide film. The method of claim 1, And the charge storage layer comprises a silicon nitride film, a metal oxide film, a metal nitride film, or a combination thereof. The method of claim 1, And the gate electrode is formed of at least one material selected from the group consisting of TaN, TiN, W, WN, HfN, and tungsten silicide.

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