JPH0793382B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a semiconductor nonvolatile memory such as an EPROM (Erasabl).
The present invention relates to a method of manufacturing a semiconductor device such as an e Programmable Read Only Memory (electrically erasable and writable ROM), and particularly to a method of manufacturing a semiconductor device that improves the characteristics of a second gate oxide film on a floating gate electrode.

B. SUMMARY OF THE INVENTION The present invention is a method for manufacturing a semiconductor device such as a semiconductor non-volatile memory in which a second gate oxide film on a floating gate electrode is formed in an oxygen atmosphere at a temperature of 1100 ° C. to 1150 ° C. By performing the treatment in a nitrogen atmosphere containing oxygen at the time of rising to the temperature and at the time of decreasing from the temperature, it is possible to obtain good film quality of the second gate oxide film and improve the device characteristics.

C. Conventional Technology In general, research and development of a semiconductor device such as a semiconductor non-volatile memory having a floating gate electrode and a control electrode for storing an electric information signal is in progress.

Here, the operation of such a semiconductor device will be briefly described. The floating gate electrode formed on the oxide film between the source region and the drain region and in an electrically floating state is the second gate oxide on the upper side. Electrons can be accumulated and emitted according to the control voltage of the control electrode formed through the film. Then, a predetermined memory operation can be performed by associating the accumulation or emission state of the electrons with the writing / erasing operation of the information signal.

By the way, the floating gate electrode for storing and holding such an information signal is usually made of polycrystalline silicon, and the second gate oxide film on the upper part thereof is formed by thermally oxidizing the floating gate electrode. .

Here, the process of oxidizing such a floating gate electrode will be described with reference to FIG. 6. The wafer in which the polycrystalline silicon layer which will be the floating gate electrode is exposed is fed into an oxidation furnace to be oxidized. First, as shown in FIG. 6, first, the temperature is raised in a nitrogen atmosphere, and at time t ₁ , the oxidation treatment temperature T ₀ (= temperature of the oxidation furnace) is reached. This oxidation treatment temperature T ₀ is approximately 95
The temperature is 0 ° C., and the atmosphere is an oxygen atmosphere. next,
At time t ₂ , the oxidation process ends and the temperature drop period starts. The atmosphere at this time is a nitrogen atmosphere.

By such an oxidation treatment, an oxide film having a film thickness of about 400 Å is formed, and this is used as the second oxide film.

D. Problems to be Solved by the Invention Even in such a semiconductor nonvolatile memory, improvement in device characteristics is required, and one of them is improvement in memory retention characteristics and improvement in breakdown voltage.

However, when the second gate oxide film is formed by the conventional oxidation treatment as described above, there arises a problem that the memory retention characteristic cannot be improved due to the film quality. That is, when the floating gate electrode is oxidized by using the above-mentioned conditions, there is a drawback that a certain discharge or the like occurs from the floating gate electrode and the memory retention characteristic is impaired. In addition, there is also a problem that the breakdown voltage becomes low. Further, even in such a semiconductor device, there is a demand for miniaturization and high integration, and the amount of accumulated charges is also small. Therefore, if the problem of improvement of the memory retention characteristic is not solved, the miniaturization of elements will be sufficient. Difficult to do.

Therefore, in view of the above problems, it is an object of the present invention to provide a method for manufacturing a semiconductor device, which improves the film quality of the second gate oxide film and improves device characteristics.

E. Means for Solving the Problems The present invention provides a method of manufacturing a semiconductor device having a floating gate electrode and a control electrode for storing an electrical information signal, wherein the floating gate electrode and the control electrode are The oxide film between them is 1100 ° C to 1150 ° C in an oxygen atmosphere.
The semiconductor device manufacturing method is characterized in that the semiconductor device is formed at a temperature of 0 ° C., and is placed in a nitrogen atmosphere containing at least oxygen during a temperature rising period up to the oxidation process and a temperature down period from the oxidation process. Solve the point.

F. Action The oxide film between the floating gate electrode and the control electrode can be obtained by thermally oxidizing the floating gate electrode formed of a material such as polycrystalline silicon, but at the conventional oxidation treatment temperature. It is possible to improve the film quality of the oxide film (second gate oxide film) by thermally oxidizing it at a temperature of 1100 ° C to 1150 ° C, which is higher than a certain 950 ° C, and to improve breakdown voltage and memory retention characteristics. Become.
Further, since such a relatively high temperature heat treatment is performed,
During the temperature raising and lowering period, the atmosphere of nitrogen alone is not used, but a slight amount of oxygen is mixed to suppress the nitriding phenomenon on the wafer, and a high quality second gate oxide film is obtained from these synergistic effects. You can

G. Example A preferred example of the present invention will be described with reference to the drawings.

The method for manufacturing a semiconductor device according to the present embodiment is a method for manufacturing a semiconductor device such as a semiconductor nonvolatile memory having a floating gate electrode and a control electrode for storing / holding an information signal. The film quality of the second gate oxide film between the electrodes is improved to obtain good device characteristics.

First, the basic processing method will be described with reference to FIG. FIG. 1 is a time chart showing the temperature T of the wafer according to time t when the oxidation process is performed, and it is assumed that the floating gate electrode formed of, for example, polycrystalline silicon is exposed on the wafer.

The wafer mounted in the oxidation furnace at time t ₁ is left in the oxidation furnace until time t ₂ at which the wafer temperature reaches a fixed state. The initial temperature T ₁ of this oxidation furnace is a temperature of about 700 ° C to 900 ° C. Next, from time t ₂ to time t ₃ , the wafer is heated,
The temperature is raised to the oxidation treatment temperature T ₂ . During this temperature rising period, in order to prevent the nitriding phenomenon, etc., it is placed in a nitriding atmosphere containing at least oxygen. That is, by mixing a slight amount of oxygen, the production rate of silicon nitride is made lower than that of silicon oxide, and the nitriding phenomenon is effectively prevented. One example of the oxygen mixing ratio is N ₂
However, O ₂ can be set to about 10 cc.

When the oxidation treatment temperature T ₂ is reached, the surface of the floating gate electrode is oxidized, and the temperature T ₂ is
The temperature is 1100, which is higher than the conventional oxidation temperature of 950 ℃.
℃ to 1150 ℃. This is because such a temperature treatment improves memory retention characteristics, breakdown voltage, etc., as will be described later. If processing is performed at a temperature lower than these temperatures, the frequency of occurrence of asperities (protrusions) increases and the breakdown voltage and memory retention characteristics deteriorate. Conversely, if processing is performed at a temperature higher than these temperatures, Distortion on the wafer is considered to be a problem. In addition,
When the oxidation treatment temperature T ₂ is reached, the atmosphere in the oxidation furnace is made an oxygen atmosphere, and the oxygen atmosphere is maintained from time t ₃ to time t ₄ .

Also in the temperature decreasing period from time t ₄ to time t ₅ , the atmosphere is a nitrogen atmosphere containing a trace amount of oxygen as in the above temperature increasing period. Similarly, this is to prevent the nitriding phenomenon. Then, after returning the temperature of the oxidation furnace itself to the initial temperature T ₁ , time t ₆
Is taken out together with the wafer.

By such heat treatment, the quality of the second gate oxide film on the floating gate electrode becomes good, and the improvement of the memory characteristic and the withstand voltage can be realized.
Further, it is particularly advantageous when the element is miniaturized.

Here, an example of the structure of a semiconductor device manufactured based on such a method for manufacturing a semiconductor device will be briefly described with reference to FIG. 2, in which a field oxide film 16 is formed on a semiconductor substrate 13, A source region 15 and a drain region 14 are formed on the main surface of the substrate 13. A floating gate electrode 11 is formed on the source / drain regions 15 and 14 via the first gate oxide film 19, and a high quality film is formed by the above-described manufacturing method so as to cover the floating gate electrode 11. A second gate oxide film 1 is formed. The second gate oxide film 1 with this high quality film
A control electrode 12 is formed on the upper side, each region is covered with an insulating layer 17, and an Al wiring 18 is formed on the control electrode 18.

In the semiconductor device having such a structure, the second gate oxide film 1 functions as a dielectric layer for controlling the charge in the floating gate electrode 11 according to the potential of the control electrode 12. By setting 1 to be a good quality, it is possible to improve the memory retention characteristics of the entire semiconductor device and also to improve the breakdown voltage and the like.

As described above, depending on the method for manufacturing the semiconductor device of the present embodiment, it is possible to improve the film quality of the second gate oxide film on the floating gate electrode and improve the device characteristics. This can also be explained on the basis of the experimental results of experiments conducted under different temperature conditions as described below.

First, in the experiment, the temperature of the oxidation treatment was 950 ℃, 1000 ℃, 1050 ℃,
The temperature is 1100 ° C and 1150 ° C.
The horizontal axis represents each applied voltage (Stress Voltage; unit (V) volt), and the vertical axis represents the accumulated charge amount (normalized by the ratio of the initial charge amount and the remaining charge amount, Q / Q ₀ ). .

Here, the curves of each temperature are as follows: curve A at 950 ° C, curve B at 1000 ° C, curve C at 1050 ° C, curve D at 1100 ° C, curve E at 1150 ° C.
Then, it can be seen that increasing the temperature can maintain the amount of accumulated charge even when the applied voltage to the control electrode is increased, and the memory retention characteristic is improved.
Further, from the curves D and E, when the temperature is about 1100 to 1150 ° C, there is no discharge of electric charge even when the applied voltage is about 30 V, and good memory retention is achieved. Therefore, even when miniaturizing the element, etc. Would be able to hold the information signal.

The thickness of the second gate oxide film is constant at 400Å,
The formation conditions of the floating gate electrode are phosphorus predeposition, 820 ° C., ρs = 150Ω / □.

Next, the relationship between the oxidation temperature and the breakdown voltage will be described with reference to FIG.

FIG. 4 shows the relationship between each oxidation temperature (° C.) and breakdown voltage (MV / cm), and it is shown that each oxidation temperature affects the breakdown voltage value. That is, from the curve of FIG. 4, it can be seen from the temperature range of 1000 ° C. to 1050 ° C.
The pressure resistance value is higher in the temperature range of 50 ° C,
On the contrary, it is shown that the withstand voltage becomes lower at ° C. Therefore, as in the above process, the oxidation treatment temperature is set to 1100 ° C to 11 ° C.
It can be seen that the withstand voltage can be increased by setting the temperature in the range of 50 ° C.

Next, the impurity concentration of the floating gate electrode to be oxidized will be described with reference to FIG.

The floating gate electrode for forming the second gate oxide film is usually predeposited with phosphorus or the like to have a predetermined impurity concentration. However, the second gate oxide film is formed at the same time as the gate oxide film of the peripheral circuit, and by adjusting the impurity concentration to an appropriate value, a thicker oxide film can be formed and its quality can be improved. Can be improved.

In FIG. 5, the horizontal axis represents the applied voltage (V) to the control electrode, and the vertical axis represents the accumulated charge amount (normalized by the ratio of the initial charge amount and the remaining charge amount. Q / Q ₀ ). And the curve F is 750
C shows phosphorus predeposition conditions, and curve G shows 820 ° C phosphorus predeposition conditions.

From FIG. 5, it is shown that the curve G has a better charge storage characteristic, that is, the memory retention characteristic, and under the condition of phosphorus predeposition at 820 ° C. of the curve G,
Since it corresponds to approximately 1 × 10 ¹⁹ cm ³ in terms of Si crystal (100) 1 Ω-cm, for example, 820 ° C. or higher can be selected as the condition for phosphorus predeposition.

As described above, in the method of manufacturing a semiconductor device according to the present embodiment, the oxidation treatment temperature is set to 1100 ° C. to 1150 ° C. to improve the film quality of the second gate oxide film and improve the memory retention characteristics and the breakdown voltage. Can be planned. Further, at the same time, during the temperature rising period and the temperature lowering period, by mixing oxygen into the nitrogen atmosphere, the nitriding phenomenon can be suppressed and a good quality second gate oxide film can be formed. Further, a predetermined oxide film can be formed also depending on the impurity concentration of the floating gate electrode, and the improvement of the device characteristics described above is particularly advantageous for miniaturization of the element.

In addition, in the above-mentioned embodiment, the example of the EPROM having the floating gate electrode and the control electrode is exemplified, but the present invention is not limited to this, and another semiconductor device may be used.

H. Effects of the Invention According to the method for manufacturing a semiconductor device of the present invention, by the steps as described above, it is possible to mass-produce devices with excellent film quality of the second gate oxide film, and it is considered that the devices have excellent withstand voltage and memory retention characteristics. Become. Further, compared with the conventional process, only the condition of the oxidation treatment is different and no special process is added, which is advantageous when the device is further miniaturized.

[Brief description of drawings]

FIG. 1 is a time chart showing the temperature of a wafer in an example of the method for manufacturing a semiconductor device of the present invention, and FIG. 2 is a sectional view showing an example of a semiconductor device manufactured by the method of manufacturing a semiconductor device of the present invention. FIG. 4 is a characteristic diagram showing changes in accumulated charge amount with respect to applied voltage for each oxidation treatment temperature, FIG. 4 is a characteristic diagram showing relation between breakdown voltage and oxidation treatment temperature, and FIG. 5 is accumulation with applied voltage for each predeposition condition. It is a characteristic view which shows the change of the charge amount. Further, FIG. 6 is a time chart for explaining a conventional method for manufacturing a semiconductor device.

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor device having a floating gate electrode and a control electrode for storing information signals, wherein an oxide film between the floating gate electrode and the control electrode is 1100 ° C. in an oxygen atmosphere. A method for manufacturing a semiconductor device, which is formed at a temperature of 1150 ° C. to 1150 ° C., and is placed in a nitrogen atmosphere containing at least oxygen during a temperature rising period up to the oxidation process and a temperature down period after the oxidation process.