JPS63311767A - Semiconductor nonvolatile memory - Google Patents

Abstract

PURPOSE:To improve reliability by a method wherein an insulating film, where the highest voltage is applied and all the trap is charged up, such as an oxide film or the like is used as an interlaminar insulating film between a floating-gate electrode, a control gate and a selection gate. CONSTITUTION:A control gate electrode 7 is provided on an interlaminar insulating film 6 and the potential of a floating-gate 5 is controlled through the capacitance coupling. The interlaminar insulating film 6, which is applied with a bias once, is formed in such a manner that the voltage highest within the extent of voltage which does not break down the interlaminar insulating film 6, is applied to the control gate electrode 7 for tens of msec to a few seconds as a p-type conductor substrate 1, a source region 2, and a drain region 3 are kept at a ground level after the control gate electrode 7, other electrodes, and others are wired. Therefore, the insulating film 6 is improved in an insulating property and the ratio of ions once injected into the stray gate electrode 5 to those volatiled through the interlaminar insulating film 6 can be reduced. By these processes, the semiconductor nonvolatile memory can be improved in reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to semiconductor non-volatile memories such as EFROM-E'' FROM.

[Summary of the invention]

This invention is an EPROM-E" having a floating gate structure.
In semiconductor nonvolatile memories such as PROM, a voltage higher than the voltage applied during normal operation is applied once to the interlayer insulating film surrounding the floating gate electrode to charge up the traps of electrons and holes in the interlayer insulating film. However, by reducing the current flowing through the interlayer insulating film, the volatilization of electrons from the floating gate electrode is reduced, thereby increasing the reliability of the semiconductor nonvolatile memory.

[Conventional technology]

FIG. 2 shows a cross-sectional view of a conventional semiconductor nonvolatile memory.

An N-type source region 2 and an N-type drain region 3 are formed on the surface of a P-type semiconductor substrate 1. A gate insulating film 4 is formed by thermally oxidizing the substrate, and a floating gate electrode 5 usually made of polysilicon containing impurities such as phosphorus is formed on the gate insulating film 4. Furthermore, the surface of the floating gate electrode 5 is thermally oxidized to form an interlayer insulating film 16, and the control gate electrode 7 is provided thereon. A silicon dioxide film formed by CVD (chemical vapor deposition) is also used as the interlayer insulating film 16, and the operation of this semiconductor nonvolatile memory is determined by the charge in the floating gate electrode 5. When there are many electrons in the floating gate electrode 5, the threshold value as seen from the control gate electrode 7 becomes high, and on the other hand, when there are few electrons in the floating gate electrode 5, the threshold value as seen from the control gate electrode 7 becomes high. The threshold will be lower.

By maintaining one of these two states even when the power is turned off, it functions as a semiconductor nonvolatile memory.

[Problem that the invention seeks to solve]

In order for the semiconductor nonvolatile memory to maintain one of the two states for a long period of time, that is, to maintain electrons in the floating gate electrode 5 for a long period of time, the interlayer insulating film 16 is required to have high insulation properties. However, in the glabellar wA green membrane 16,
Usually, an oxide film formed by thermally oxidizing polysilicon containing a large amount of impurities such as phosphorus is used, so it is more prone to defects such as traps than a thermal oxide film on single crystal silicon, and has good characteristics. 1000-110 to get
Oxidation was carried out in a high temperature atmosphere of 0°C. On the other hand, as semiconductor integrated circuits become more highly integrated, lowering the temperature of the semiconductor manufacturing process has become an essential condition. However, 850-95
The oxide film on polysilicon formed at a temperature of about 0°C is
Does not have sufficient dielectric strength. Figure 3 shows the relationship between current density and electric field strength applied to the oxide film on polysilicon formed at different temperatures.As the oxidation temperature decreases, the current density-field strength curve shifts to the left and remains the same. The current increases relative to the electric field strength.

That is, the lower the oxidation temperature, the worse the film quality of the oxide film, which lowers the reliability of the semiconductor nonvolatile memory.

Further, in order to increase the degree of integration of semiconductor integrated circuits, it is required not only to reduce the planar size of each element but also to reduce the thickness thereof. Therefore, if the power supply voltage is constant (for example, 5V), it is absolutely 8! The electric field strength applied to the film increases in inverse proportion to the film thickness. That is, it can be said that there is a strong possibility that an insulating film that has met conventional requirements will no longer be able to meet the requirements associated with higher integration.

In addition to the above example, it is also possible to use a silicon dioxide film formed by a CVD method as the interlayer insulating film 16. Especially from dichlorosilane and nitrous oxide.
+ 2NgO→5iOz + 2Hc j! +2N
A CVD silicon dioxide film formed at 800 to 950° C. using the z reaction exhibits excellent insulating properties even when deposited on polysilicon. However, the excellent properties of the CVD silicon dioxide film are only exhibited when the underlying polysilicon is flat, and if the underlying polysilicon is not flat, has irregularities, or has etched edges. In some cases, the electrical properties of the CVD silicon dioxide film deteriorate significantly. FIG. 4 shows a comparison of the current density and electric field strength of CVD silicon dioxide films deposited on flat polysilicon and polysilicon with steps. It is clear that the characteristic curve a on polysilicon with steps is The characteristic curve is inferior to that of flat polysilicon. Therefore, in a semiconductor nonvolatile memory, the floating gate electrode 5
If the interlayer insulating film 16 between the floating gate electrode 5 and the control gate electrode 7 includes a stepped portion on the floating gate electrode 5, the characteristics of the interlayer insulating film 16 are not sufficient, and the electrons in the floating gate electrode 5 will pass through the interlayer insulating film 16. If it passes through, it will volatilize to the control gate electrode 7.

Normally, in an integrated semiconductor nonvolatile memory, the control gate electrode 7 is formed across a number of memory cells. 7 necessarily has a stepped portion at the end of the floating gate electrode 5, which poses a problem in terms of reliability.

Therefore, the present invention solves these conventional drawbacks and provides a highly reliable semiconductor nonvolatile memory that can be highly integrated without increasing the number of manufacturing steps.

[Means for solving problems]

In order to solve the above problems, the present invention provides an oxide film on polysilicon to which a voltage higher than that applied during normal operation is once applied, or a silicon dioxide film formed by CVD, as an interlayer insulating film around the floating gate electrode. film or silicon nitride film.

[Effect]

When a high voltage that does not cause electrostatic damage to the insulating film is once applied to the insulating film, the traps that already exist in the insulating film and the traps that are formed when current flows through the insulating film are filled with electrons ( Even if the voltage is applied again (charge-up), no current due to the trap will flow, so the current flowing will be extremely small. Figure 5 is 950℃
The current-voltage characteristics of the oxide film on polysilicon formed in
). It can be seen that the current-voltage characteristics are improved by applying a high voltage once. As a result, the characteristics of the interlayer insulating film are improved and the volatilization of electrons from the floating gate electrode is significantly reduced, making it possible to obtain a highly reliable semiconductor nonvolatile memory.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. 1st
The figure is a cross-sectional view schematically showing the structure of a semiconductor nonvolatile memory according to the present invention. An N-type source nods on the surface of a P-type semiconductor substrate l! Ii2 and drain region 3. A gate insulating film 4 is formed by thermally oxidizing the substrate, and a floating gate electrode 5 made of polysilicon containing impurities such as phosphorus is provided on the gate insulating film 4. Surrounding the floating gate electrode 5 is an interlayer insulating film 6 to which a bias is once applied.

The interlayer insulating film 6 may be formed by thermally oxidizing the floating gate electrode 5, or may be formed by depositing silicon dioxide using the CVD method. A control gate electrode 7 is provided on the interlayer insulating film 6, and controls the potential of the floating gate electrode 5 by capacitive coupling. To form the interlayer insulating film 6 once biased, the control gate voltage FfA? After wiring other electrodes, etc., the P-type semiconductor substrate 1. With the source region 2 and drain region 3 at ground level, a positive voltage as high as possible is applied to the control gate electrode 7 within a range that does not destroy the interlayer insulating film 6 for about several tens of m5ec to several seconds. This increases the insulation properties of the interlayer insulating film 6 and significantly reduces the rate at which electrons once injected into the floating gate electrode 5 evaporate through the interlayer insulating film 6, improving the reliability of the semiconductor nonvolatile memory. can be made higher.

FIG. 6 is a sectional view of a semiconductor nonvolatile memory showing a second embodiment of the present invention. An N-type source region 2, a drain region 3, and a gate insulating film 4 are formed on the surface of a P-type semiconductor substrate 1.
A floating gate electrode 5 made of polysilicon is provided on the gate insulating film 4. Around the floating gate electrode 5, a glabellar insulating film 6 to which a bias is once applied is provided, and further glabellar insulation 1f! A selection gate electrode 9 is provided on the control gate electrode 6 so as to span the control gate electrode 7, the floating gate electrode 5, and the semiconductor substrate 1. The characteristics and operation of the semiconductor nonvolatile memory having this structure are detailed in Japanese Patent Application Laid-open No. 58-64068, so they will not be described again here.

In this embodiment, a control gate electrode 7 and a selection gate electrode 9 are opposed to a floating gate electrode 5 with an interlayer insulating film 6 interposed therebetween. In particular, the selection gate electrode 9 forms a step at the end of the floating gate electrode 5. Furthermore, when reading information from this semiconductor nonvolatile memory, the control gate electrode 7 is at ground level, but the selection gate electrode 9 is normally biased to 5V. Therefore, when electrons are injected into the floating gate electrode 5 and it becomes negatively charged, there is a concern that the electrons will volatilize to the selection gate electrode 9. Since an insulating film is used, sufficient reliability can be obtained. FIG. 7 shows the dependence of the threshold voltage of the memory on the selection gate bias application time. This figure shows how a higher voltage than usual is applied to the selection gate electrode 9, and the electrons injected into the floating gate electrode 5 volatilize to the selection gate electrode 9 over time.

The characteristics of a memory that uses an oxide film as an interlayer insulating film once a bias is applied (curve e) has a smaller rate of decrease in threshold value than the characteristics of a memory that uses a normal oxide film (curve f). It can be seen that the retention characteristics are improved.

〔Effect of the invention〕

As described above, the present invention uses an insulating film such as an oxide film to which a high voltage is once applied as an interlayer insulating film between a floating gate electrode, a control gate electrode, and a selection gate electrode, and traps in the film are charged up. By using this, it is possible to provide a highly reliable semiconductor nonvolatile memory with extremely low volatilization of electrons from the floating gate electrode and excellent retention characteristics.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an embodiment of a semiconductor nonvolatile memory according to the present invention, FIG. 2 is a sectional view showing the structure of a conventional semiconductor nonvolatile memory, and FIG. 3 is an oxide film formed at different temperatures. Figure 4 is a diagram showing the dependence of current density on electric field strength in an oxide film formed on a step or flat surface.
FIG. 5 is a diagram showing the dependence of the current density on the electric field strength in each oxide film in order to compare the initial characteristics of the oxide film and the characteristics after bias application, and FIG. FIG. 7 is a cross-sectional view showing the structure of an embodiment of the present invention, and FIG. 7 is a diagram showing the dependence of the threshold voltage of the semiconductor nonvolatile memory on the selection gate bias application time. l... Semiconductor substrate 2... Source region 3... Drain region 4... Gate insulating film 5... Floating gate electrode 6... Interlayer insulating film 16 once biased...
・Interlayer insulating film 9...selection gate electrode and above Applicant: Seiko Electronic Industries Co., Ltd. Agent: Patent attorney Tsutomu Mogami (1 other person) Pass H'5
2. The thunder and cloudy arc of the 2nd picture of the drama was different from the previous one. Figure 7 Procedural amendment cap button 1986 Patent application No. 148249 No. 2, Name of the invention Semiconductor non-volatile memory 3, Person making the amendment 4, Agent ■ 104 2-6-21 Kyobashi, Chuo-ku, Tokyo, Seiko Seiko Co., Ltd. Mogami Patent Office 5, Subject of the amendment・(Direct Denou (V) Mr. Se mistakenly omitted (around 470)

Claims (2)

[Claims] (1) Source/drain regions of a second conductivity type different from the first conductivity type provided at intervals on the surface portion of the semiconductor substrate of the first conductivity type, and source/drain regions provided on the surface of the semiconductor substrate between the source/drain regions. a floating gate electrode provided on the gate insulating film, an interlayer insulating film provided around the floating gate electrode, and a control gate electrode provided on the interlayer insulating film. A semiconductor non-volatile memory comprising: a semiconductor non-volatile memory characterized in that the interlayer insulating film is charged up by applying a voltage higher than the voltage applied during normal operation to trap electrons and holes in the film; sexual memory. (2) source/drain regions of a second conductivity type different from the first conductivity type provided at intervals on the surface portion of the semiconductor substrate of the first conductivity type; and source/drain regions of a second conductivity type different from the first conductivity type provided on the surface of the semiconductor substrate between the source/drain regions; a floating gate electrode provided on the drain side on the gate insulating film;
an interlayer insulating film provided around the floating gate electrode;
A selection gate electrode provided across the interlayer insulating film on the floating gate electrode from the source side on the gate insulating film, and a control gate electrode provided on the floating gate electrode via the interlayer insulating film. A semiconductor nonvolatile memory characterized in that the interlayer insulating film is charged up by applying a voltage higher than the voltage applied during normal operation to trap electrons and holes in the film. memory.