JPH1012816A - Manufacture of capacitance element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce dangling bonds on a dielectric film surface, by performing heat treatment at a temperature discharging the residual gas in a dielectric film after it is formed. SOLUTION: An element isolation insulating film 12 for isolating an element forming region is formed on the upper layer of a semiconductor substrate 11, and a first conducting layer 13 as a diffusion layer is formed in the element forming region. An insulating film 14 is formed on the semiconductor substrate 11, and a dielectric film 21 is formed on the semiconductor substrate 11, in such a manner that the insulating film 14 is covered with the film 21. It is heat-treated at a temperature discharging the residual gas in the dielectric film 21, and residual atoms and molecules which are unnecessary are made to leave. In order to reduce dangling bonds which are generated on the surface of the dielectric film 21, heat treatment is performed in an atmosphere containing the atoms to be buried in the dangling bonds generated in the dielectric film 21. Thereby the dangling bonds are substituted by the atoms and reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a capacitor.

[0002]

2. Description of the Related Art A capacitive element in a reaction apparatus has a dielectric film formed by chemical vapor deposition (hereinafter referred to as CVD, CV).
D is a silicon nitride (Si ₃ N ₄ ) film formed by a Chemical Vapor Deposition method. CVD
In general, source gases used for forming a silicon nitride film by a method include silane-based gases such as monosilane (SiH ₄ ) and dichlorosilane (SiH ₂ Cl ₂ ), and ammonia (NH ₃ ).

[0003]

SUMMARY OF THE INVENTION However, CVD
In the method, a substance containing an unnecessary atom (for example, hydrogen) in a film composition is used as a source gas, so that these unnecessary atoms are taken in and remain in the formed silicon nitride film. This is a problem caused by the upper limit of the temperature conditions during film formation by the CVD method. The film forming temperature conditions in the CVD method are set so as to suppress the generation of particles due to the CVD reaction in the film forming chamber and to make the reaction proceed at the substrate temperature of the processing surface. For this reason, decomposition and desorption of hydrogen contained in the source gas become insufficient and the hydrogen is taken in the silicon nitride film, and at the same time, there are many dangling bonds in which the bonds between atoms are incomplete. .

When such unnecessary residual atoms and dangling bonds are present in the dielectric film of the capacitor, they behave as so-called paths through which electrons leak.
The mobility of electrons increases, which causes a decrease in breakdown voltage and leakage current. In addition, the time-dependent dielectric breakdown evaluation (hereinafter referred to as TDDB evaluation, TDDB stands for Time Dependent Dielectric Breakdown)
(Abbreviation) significantly deteriorates the initial failure, thereby deteriorating the reliability of the capacitor. Further, a pinhole may be generated in the silicon nitride film. When such a silicon nitride film is used as the dielectric film of the MIS capacitor, a reduction in withstand voltage or a leak current is induced by the pinhole, and a reduction in charge storage performance is caused.

[0005]

SUMMARY OF THE INVENTION The present invention is a method of manufacturing a capacitive element for solving the above-mentioned problems. That is, in the method of manufacturing a capacitor in which a dielectric film is formed on a first conductive layer and then a second conductive layer is formed on the dielectric film, the dielectric film is formed and then left in the dielectric film. At a temperature at which a gas to be released is released, or in an atmosphere containing atoms filling the dangling bonds generated in the dielectric film, or at a temperature at which a gas remaining in the dielectric film is released and containing atoms filling the dangling bonds The problem is solved by performing heat treatment in an atmosphere.

In the above-described method for manufacturing a capacitor, a heat treatment is performed at a temperature at which gas remaining in the dielectric film is released after the formation of the dielectric film, so that the film composition present in the dielectric film is unnecessary. Residual atoms and molecules are released. Alternatively, since heat treatment is performed in an atmosphere containing atoms filling the dangling bonds generated in the dielectric film, the atoms in the atmosphere are bonded to the dangling bonds and the dangling bonds are eliminated. Alternatively, since the heat treatment is performed at a temperature at which gas remaining in the dielectric film is released and in an atmosphere containing atoms filling the dangling bonds, unnecessary atoms and molecules unnecessary in the film composition existing in the dielectric film are separated. The atoms in the atmosphere are bonded to the dangling bonds, and the dangling bonds are eliminated.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention is shown in FIG.
This will be described with reference to a manufacturing process diagram of FIG.

As shown in FIG. 1A, a semiconductor substrate 1
An element isolation insulating film 1 for isolating an element formation region is formed on the upper layer 1.
2 is formed, and the first conductive layer 13 is diffused in the element formation region.
It is formed of layers. Further, the insulating film 1 is formed on the semiconductor substrate 11.
4 are formed on the capacitor element forming region and the electrode forming region.
An opening 15 and an opening 16 are formed in the opening. And
The semiconductor substrate 11 is guided to cover the insulating film 13.
The conductor film 21 is formed. This dielectric film 21 is reduced, for example,
Silicon nitride (Si _ThreeN_Four) Equivalent to membrane
For example, it is formed to a thickness of 50 nm.

An example of film forming conditions by the above-mentioned low pressure CVD method will be described below. Source gas: monosilane (SiH ₄ ); 50 sccm, ammonia (NH ₃ ); 300 sccm, pressure of film formation atmosphere: 50 Pa, substrate temperature: 760 ° C. In addition, sccm represents a volume flow rate (cm ³ / min) in a standard state.

The dielectric film 21 made of a silicon nitride film formed under the above conditions contains SiH as a source gas.
Hydrogen contained in ₄ and NH ₃ remains. There are also many dangling bonds.

Next, as shown in FIG. 1B, the temperature of the dielectric film 21 formed on the semiconductor substrate 11 is changed under the following conditions by changing the temperature setting in the chamber of the low-pressure CVD apparatus. By performing a heat treatment, hydrogen in the dielectric film 21 is released.

An example of the above heat treatment conditions will be described below. Heat treatment atmosphere: nitrogen (N ₂ ); 10 slm, pressure of heat treatment atmosphere: normal pressure (101 kPa), substrate temperature: 900 ° C. Here, slm represents the volume flow rate (dm ³ / min) in the standard state. In order to further reduce dangling bonds generated on the surface of the dielectric film 21 made of silicon nitride, the above-described heat treatment is performed using an ammonia (NH ₃ ) atmosphere as an atmosphere containing atoms filling the dangling bonds generated in the dielectric film 21. You can go inside. In this case, the dangling bonds are reduced by being replaced by nitrogen atoms.
Therefore, it is preferable to perform heat treatment for releasing hydrogen and heat treatment for reducing dangling bonds.

Thereafter, as shown in FIG. 1 (3), the area for forming the capacitor element (opening) is formed by a usual lithography technique (for example, formation of a resist film by applying a resist, exposure, development, baking, etc.) and etching. Part 1
The dielectric film 21 is left only in 5), and the dielectric film 21 in other regions is removed. Next, the above resist film (not shown)
After the removal, a wiring layer is formed by a normal film forming technique. Then, the wiring layer is patterned by the same lithography technique and etching as described above, and a second conductive layer 31 serving as an upper electrode of the capacitor is formed on the remaining dielectric film 21, and a second electrode serving as a lower electrode of the capacitor is formed. An electrode 32 connected to the one conductive layer 13 is formed in the opening 16. As described above, the capacitive element 1 including the first conductive layer 13, the dielectric film 21, and the second conductive layer 31 is formed.

In the above manufacturing method, after the dielectric film 21 is formed, a heat treatment is performed in an atmosphere containing nitrogen (a nitrogen atmosphere in the above case) and at a temperature at which unnecessary atoms in the dielectric film 21 are released. , Hydrogen remaining in the dielectric film 21 is released. In addition, since the heat treatment is performed in an ammonia atmosphere, dangling bonds generated on the surface of the dielectric film 21 made of silicon nitride are replaced with nitrogen atoms in the heat treatment atmosphere, so that dangling bonds are reduced. In the heat treatment step, chlorine remaining in the dielectric film 21 formed by a CVD method using a source gas containing chlorine [eg, dichlorosilane (SiH ₂ Cl ₂ )] is also removed.

The heat treatment step in the manufacturing method of the present invention is intended to improve the film quality of the dielectric film 21, and is not limited to being performed by the dielectric film 21 film forming apparatus. Therefore, heat treatment can be performed by an apparatus different from the film formation. Further, the atmosphere of the heat treatment for releasing the gas in the dielectric film made of silicon nitride is not limited to the nitrogen atmosphere, and may be, for example, ammonia (NH ₃ ).
The atmosphere may be an atmosphere, a mixed gas atmosphere of an inert gas and a nitrogen gas, or a mixed gas atmosphere of an inert gas and ammonia. The atmosphere for the heat treatment for replacing dangling bonds on the surface of the dielectric film made of silicon nitride with nitrogen is not limited to an ammonia atmosphere. Dangling bonds generated on the surface of the body film 21 can be replaced by nitrogen atoms of ammonia. As described above, since the film quality of the dielectric film 21 is improved, the withstand voltage of the capacitive element 1 is improved, and the induction of leak current is reduced.

Next, the relationship between the charge accumulated in the dielectric film and the heat treatment temperature will be described with reference to FIG. In FIG. 2, the vertical axis indicates the electric charge accumulated in the dielectric film, and the horizontal axis indicates the heat treatment temperature. The electric charge accumulated in the dielectric film is obtained by forming a 20-nm-thick silicon nitride film by a CVD method on a diffusion layer formed on a silicon substrate, and then performing a heat treatment and then forming an electrode. The test was performed by applying a current of 1 mA.

As shown in FIG. 2, the charge accumulated in the dielectric film increases from around 760.degree. C., which is the film forming temperature of the dielectric film, and reaches a peak at 900.degree. When the heat treatment temperature was higher, the charge accumulated in the dielectric film was reduced. From this result, the heat treatment temperature was set at the dielectric film 2
It can be said that the film formation needs to be performed at a temperature higher than the film forming temperature of No. 1 and lower than about 1000 ° C.

FIG. 3 shows the relationship between the charge accumulated in the dielectric film and the heat treatment time. In FIG. 3, the vertical axis shows the charge accumulated in the dielectric film, and the horizontal axis shows the heat treatment time. The structure of the capacitor used for the measurement is the same as the measurement shown in FIG.

As shown in FIG. 3, when the heat treatment was performed at 800 ° C., the charge accumulated in the dielectric film increased as the heat treatment time increased. On the other hand, when the heat treatment is performed at 900 ° C., even if the heat treatment time is increased, the change in the charge accumulated in the dielectric film is small. from this result,
A long heat treatment time is required when the heat treatment temperature is low, but the heat treatment temperature is optimal (9 in this case).
In the case of (00 ° C.), about 20 to 30 minutes can be said to be sufficient.

Further, the effectiveness of performing a heat treatment on the dielectric film 21 was confirmed by TDDB evaluation. As a result, an improvement of one order or more was confirmed as compared with the conventional technology in which no heat treatment was performed, and high reliability could be obtained without deteriorating other capacitance characteristics, for example, a dielectric constant.

By performing the above heat treatment step,
Pinholes in dielectric film made of silicon nitride are reduced
It was confirmed. That is, when the heat treatment step is not performed
Has 108.33 pinholes / mm ^TwoWas
However, when a heat treatment (900 ° C., 30 minutes) process is performed
The number of pinholes is 59.78 / mm^TwoIt became. this
Of the dielectric film shrinks due to heat treatment.
This is due to a dense film. Thus, the heat treatment process
, The number of pinholes is reduced.

Further, in the heat treatment step, the film formation and the heat treatment are continuously performed in the same apparatus, thereby making it unnecessary to add heat treatment equipment. At the same time, the time for transporting the processing substrate can be saved, so that the throughput is improved. Furthermore, the throughput can be improved by using the heat treatment step also as a heat treatment step for impurity diffusion indispensable for forming a transistor element of a semiconductor device.

The above manufacturing method is a technique effective for all capacitive elements having a so-called MIM (Metal Insulator Metal) structure using a silicon nitride film formed by a plasma CVD method as a dielectric film.

[0024]

As described above, according to the present invention,
Since a heat treatment step is performed after forming the dielectric film by the CVD method, unnecessary gas in the dielectric film can be released, and dangling bonds on the surface of the dielectric film can be reduced. Therefore, the quality of the dielectric film is improved, so that the withstand voltage of the capacitive element can be improved and the leakage current can be reduced. In addition, since the dielectric film can be further thinned by improving the withstand voltage and the leak characteristics, a higher capacitance of the capacitor can be realized. Further, by increasing the thin film capacity, the area of the capacitor element can be reduced, and high integration can be realized. Further, since the working voltage of the capacitor can be further increased by improving the breakdown voltage and the leak characteristics, the circuit design margin is increased.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of an embodiment according to the present invention.

FIG. 2 is a diagram illustrating a relationship between electric charges accumulated in a dielectric film and a heat treatment temperature.

FIG. 3 is a diagram illustrating a relationship between charges accumulated in a dielectric film and a heat treatment time.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Capacitance element 13 1st conductive layer 21 Dielectric film 31 2nd conductive layer

Claims (9)

[Claims] 1. After forming a dielectric film on a first conductive layer,
In the method for manufacturing a capacitive element for forming a second conductive layer on the dielectric film, after forming the dielectric film, heat treatment is performed at a temperature at which gas remaining in the dielectric film is released. Manufacturing method of a capacitive element. 2. After forming a dielectric film on the first conductive layer,
In the method for manufacturing a capacitor in which a second conductive layer is formed on the dielectric film, after the formation of the dielectric film, a heat treatment is performed in an atmosphere containing atoms for filling dangling bonds generated in the dielectric film. A method for manufacturing a capacitive element, comprising: 3. After forming a dielectric film on the first conductive layer,
In the method of manufacturing a capacitive element for forming a second conductive layer on the dielectric film, after forming the dielectric film, at a temperature at which gas remaining in the dielectric film is released, and A method for producing a capacitive element, comprising: performing heat treatment in an atmosphere containing atoms for filling the generated dangling bonds. 4. The method for manufacturing a capacitor according to claim 1, wherein the heat treatment is performed simultaneously with a heat treatment in a process of manufacturing the transistor. 5. The method for manufacturing a capacitor according to claim 2, wherein the heat treatment is performed simultaneously with the heat treatment in a process of manufacturing the transistor. 6. The method for manufacturing a capacitor according to claim 3, wherein the heat treatment is performed simultaneously with a heat treatment in a process of manufacturing the transistor. 7. The method according to claim 1, wherein the heat treatment is performed continuously in the same chamber after forming the dielectric film. 8. The method for manufacturing a capacitive element according to claim 2, wherein the heat treatment is performed continuously in the same chamber after forming the dielectric film. 9. The method for manufacturing a capacitive element according to claim 3, wherein the heat treatment is performed continuously in the same chamber after forming the dielectric film.