JP3210464B2 - Method for manufacturing semiconductor device - Google Patents

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 semiconductor device, and more particularly to an improvement in a step of flattening an interlayer insulating film provided between conductor layers.

[0002]

2. Description of the Related Art In a conventional integrated circuit manufacturing process, an interlayer insulating film made of a BPSG (boron phosphorus silicate glass) film or a PSG (phosphorus silicate glass) film is provided on a semiconductor substrate. Formed on a wiring made of polycrystalline silicon or high-melting-point metal silicide. The surface of this interlayer insulating film is flattened by, for example, a reflow method. That is, the interlayer insulating film is, for example, 900 ° C to 100 ° C.
It is fluidized and flattened by a high-temperature heat treatment at 0 ° C. Thereafter, a conductor layer is formed on the interlayer insulating film to form a wiring. This kind of interlayer insulating film plays an important role not only in insulating between conductor layers but also in mitigating unevenness of a base.
Therefore, when the flatness of the interlayer insulating film is poor, the step coverage of the wiring provided thereon deteriorates.

[0003]

In the conventional process of flattening an interlayer insulating film, a sufficient flat shape is obtained.
A heat treatment at a temperature of 900 ° C. or more, for example, for about 60 minutes was required. However, with the miniaturization of integrated circuits, especially in MOS LSI, a so-called shallow junction, in which an impurity diffusion layer in a substrate is thinned, is required.
For this reason, when a heat treatment at a high temperature for a long time is used, the impurity diffusion layer is extended, and it is becoming difficult to use such a heat treatment.

[0004] In response to the above requirements, various experiments were conducted.
However, when an attempt is made to flatten the interlayer insulating film by a low-temperature heat treatment, a longer process than in the past is required. For this reason, the extension of the impurity diffusion layer was not much different from the conventional one. Conversely, an experiment was also conducted on a high-temperature and short-time heat treatment.

FIG. 2 shows a semiconductor device applied to the above experiment. An impurity diffusion layer 12 in which, for example, boron is diffused is provided in the semiconductor substrate 11. A 0.8 μm-thick polycrystalline silicon 13 is provided on the semiconductor substrate 11, and a BPSG film 14 is provided on the entire surface thereof, for example. This BPSG film 14 is heat-treated in an atmosphere of N ₂ .

FIG. 3 shows the result of flattening the BPSG film 14 under various heat treatment conditions. The gradient (referred to as flow angle θ) at the step on the surface of the BPSG film 14 and the impurity diffusion layer 12 are shown. The extension amount, that is, the diffusion length ((Dt) ^1/2 3) shows the result of the measurement. In the same figure, the symbol ▽ indicates a 1000 ° C. process, and the symbol ９ indicates 950.
° C process, □ indicates 900 ° C process, Δ indicates 850 ° C
Process.

As is apparent from FIG. 3, the impurity diffusion layer 1
When the diffusion length of 2 is the same, the flow angle is the same, and it can be seen that there is no difference between the heat treatment for a short time at a high temperature and the heat treatment for a long time at a low temperature.

In order to suppress the extension of the impurity diffusion layer and obtain a sufficiently flattened shape, it is conceivable to increase the phosphorus concentration or the boron concentration in the PSG film and the BPSG film. However, in this case, the film itself becomes unstable, for example, the hygroscopicity of the film is increased, and the film is not practical.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to suppress the extension of an impurity diffusion layer by using an insulating film having fluidity to form a sufficient flattened shape. It is an object of the present invention to provide a method for manufacturing a semiconductor device which can be obtained.

[0010]

According to the present invention, in order to solve the above-mentioned problems, when an insulating film is formed on a main surface of a semiconductor substrate and then flattened by heat treatment, the insulating film has a sufficient fluidity. A first heat treatment step of rapidly heating the semiconductor substrate to a temperature having: a temperature of the semiconductor substrate from the temperature of the first heat treatment step to a temperature at which the insulating film has no fluidity in a steady state. A second heat treatment step;
A third heat treatment step of holding the semiconductor substrate at the temperature lowered in the heat treatment step for a predetermined time and planarizing the insulating film.

[0011]

According to the present invention, in the first heat treatment step, the semiconductor substrate is rapidly heated to a temperature at which the insulating film has sufficient fluidity, and in the second heat treatment step, the insulating film has fluidity in a steady state. Rapidly cools to no temperature. Due to the rapid temperature drop, the insulating film retains fluidity at high temperatures,
By maintaining this temperature in the third heat treatment step, the insulating film is flattened even at a relatively low temperature.
Accordingly, the extension of the impurity diffusion layer can be suppressed, and the insulating film can be sufficiently flattened.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. 4 to 6 show a manufacturing process of a dynamic RAM to which the present invention is applied.

Referring to FIG. 4, first, an element isolation region 22 is formed on a semiconductor substrate 21 made of silicon.
A capacitor insulating film is formed on a semiconductor substrate.
Subsequently, a capacitor electrode 24 is formed of polycrystalline silicon on the capacitor insulating film 23, and an interlayer insulating film 25 is formed on the surface of the capacitor electrode 24 by thermal oxidation. Thereafter, a gate insulating film 26 is formed in the transistor region on the semiconductor substrate 21, and the gate insulating film 2
6 and a gate electrode 27 made of polycrystalline silicon on the interlayer insulating film 25. Source and drain regions (not shown) as impurity diffusion layers are provided in the semiconductor substrate 21 corresponding to the transistor regions. The steps up to this point are the same as the steps for manufacturing a general MOS LSI.

Next, on the entire surface of the semiconductor substrate 21, for example, a phosphorus having a concentration of 4 wt% and a concentration of 4 w
A BPSG film 28 containing t% of boron is deposited to a thickness of 6000 Å by a commonly used normal pressure CVD method. The following heat treatment is performed on the BPSG film 28.

FIG. 1 shows a heat treatment step according to the present invention. As shown in the figure, in this heat treatment step, first, in a first heat treatment step TP1, the semiconductor substrate 21 is introduced into a diffusion furnace at a process temperature of 600 ° C.
The temperature is raised to 950 ° C. at a rate of 100 ° C./min in a nitrogen atmosphere. Next, in a second heat treatment step TP2,
When the process temperature reaches 950 ° C, start cooling down,
The temperature is decreased to, for example, 800 ° C. at a temperature decreasing rate of 70 ° C./min. Subsequently, in the third heat treatment step TP3, at 800 ° C.
At a temperature of 50 minutes. Generally, the above concentration of BPS
Unless the G film is kept at a temperature of 850 ° C. or more, the fluidity of the film which is practical as flattening does not occur. However, as in this example, the temperature of the BPSG film was rapidly raised to 950 ° C., and after a sufficient fluidity was reached, the BPSG film was rapidly cooled to 800 ° C.
When cooled to 800C, the fluidity is higher than when the BPSG film is heated to 800C, or when gradually cooled to 800C. Therefore, in the case of this embodiment,
Even at this temperature, the fluidity of the film is maintained and flattening proceeds.

Further, in the case of this embodiment, the flatness of the BPSG film after the heat treatment is 3 degrees in a nitrogen atmosphere at 900 ° C.
Although it is equivalent to the heat treatment for 0 minutes, the extension amount of the impurity diffusion layer in the semiconductor substrate is equivalent to the heat treatment at 900 ° C. for 8 minutes.

FIG. 5 shows the BPSG film 2 after the heat treatment step.
8, a contact hole 29 is formed in the BPSG film 28 as shown in FIG. After that, a wiring layer 30 made of, for example, molybdenum silicide is formed on the BPSG film 28 and in the contact hole 29. Next, for example, a BPSG film 31 is formed as a second interlayer insulating film on the entire surface, and is planarized. This flattening may use the heat treatment step shown in FIG. 1 described above. Thereafter, contact holes (not shown) are opened in the BPSG film 31, and Al wirings 32 and 33 are formed on the BPSG film 31. Finally, a final protective film 34 is formed on these entire surfaces, and a dynamic RAM is completed.

According to the above embodiment, in the first heat treatment step, the BPSG film 28 as the first interlayer insulating film is rapidly heated to a temperature having sufficient fluidity, and in the second heat treatment step, the BPSG film 28 is heated. However, in the steady state, the temperature rapidly decreased to a temperature at which the fluidity was not exhibited. Since the BPSG film 28 retains the fluidity at a high temperature due to the rapid temperature drop, flattening proceeds by maintaining this temperature in the third heat treatment step. Therefore, although the first and second heat treatment steps are performed at a high temperature, the processing is performed in a short time, so that the extension of the impurity diffusion layer in the semiconductor substrate can be suppressed.
In the third heat treatment step, the temperature is lower than usual, but since the BPSG film 28 has fluidity, the BPSG film 28 can be sufficiently flattened.

In the above embodiment, the pattern of the heat treatment step shown in FIG. 1 is merely an example, and there are other heat treatment patterns having the same effect. To find such a heat treatment pattern, the following experiment was conducted.

The configuration of the semiconductor substrate used in this experiment is the same as in FIG. That is, an impurity diffusion layer in which, for example, boron is diffused is provided in the semiconductor substrate. On this semiconductor substrate, a step of polycrystalline silicon having a height of 0.8 μm is formed. For example, a concentration of 4
A BPSG film containing wt% of phosphorus and boron having a concentration of 4 wt% is formed with a thickness of 0.8 μm by a normal atmospheric pressure CVD method.

In the first experiment, the following heat treatment was performed on the semiconductor substrate. The process temperature of the first heat treatment step is variously changed in the range of 850 ° C. to 1000 ° C.
In the heat treatment step, the temperature is reduced at a rate of 70 ° C./min.
The temperature was lowered to 0 ° C. Next, in a third heat treatment step,
This temperature was maintained for a predetermined time, and then the temperature was lowered to 600 ° C. The flow angle of the heat-treated BPSG film was measured as in the case shown in FIG.

FIG. 7 shows the result of the first experiment. As shown in the figure, the process temperature of the first heat treatment step is 90
It can be seen that when the temperature is 0 ° C. or lower, the flow angle is large. Therefore, it is understood that the process temperature of the first heat treatment step needs to be 900 ° C. or higher. However, 1
If the temperature is set to 100 ° C. or higher, it is not advisable to increase the extension amount of the impurity diffusion layer in the semiconductor substrate.

In the second experiment, the following heat treatment was performed on the semiconductor substrate. The process temperature in the first heat treatment step was kept constant at 950 ° C., and the temperature was lowered to 800 ° C. in the second heat treatment step by changing the cooling rate in the range of 20 ° C./min to 80 ° C./min. In the third heat treatment step, this temperature was maintained for a predetermined time, and subsequently, the temperature was lowered to 600 ° C.
The holding time in the third heat treatment step was determined so that the diffusion length of boron by the total heat treatment was the same as in the first experiment. The flow angle of the heat-treated BPSG film was measured as in the case shown in FIG.

FIG. 8 shows the result of the second experiment. It can be seen from the figure that the flow angle is large when the cooling rate is 30 ° C./min or less. Therefore, it can be seen that the cooling rate needs to be 30 ° C./min or more. Depending on the equipment used, this rate of temperature drop can be increased to about 1000 ° C./min.

In the third experiment, the following heat treatment was performed on the semiconductor substrate. The process temperature in the first heat treatment step was fixed at 950 ° C., and the rate of temperature decrease in the second heat treatment step was 70 ° C./min. Then, the holding temperature in the third heat treatment step was variously changed in the range of 650 ° C to 850 ° C.

FIG. 9 shows the result of the third experiment. As shown in the figure, the holding temperature in the second heat treatment step is 700 ° C.
In the following cases, it can be seen that the flow angle is large. Therefore, the holding temperature needs to be 700 ° C. or higher. However, when the holding temperature is 850 ° C. or higher, the diffusion length of the impurity is not much different from that of the conventional method.
A range from 00 ° C to 850 ° C is appropriate. When the holding temperature is 800 ° C., the holding time is suitably from 10 minutes to 120 minutes.

In the above embodiment, the BPSG film is used as the interlayer insulating film. However, another glass-based insulating film such as PSG, or a resin-based resin such as polyimide having fluidity similar to BPSG and PSG. It is also possible to use an insulating film.

In the first heat treatment step, the process is shifted to the second heat treatment step as soon as the semiconductor substrate reaches 950.degree. C., and the holding time is set to 0 second. As long as it is possible, the holding time can be set.

Further, the holding temperature in the third heat treatment step does not need to be constant as illustrated, for example, 8
After cooling down to 50 ° C at 70 ° C / min, 850 ° C
It is also possible to planarize while lowering the temperature up to 00 ° C. at a rate of 2 ° C./min.

The atmosphere at the time of the heat treatment is not limited to the above embodiment, and N ₂ , Ar, O ₂ ,
It is possible to use an atmosphere such as steam, POCl ₃ or the like. In addition, the present invention is not limited to the above-described embodiment, and does not change the gist of the present invention.
Needless to say, various modifications can be made.

[0031]

As described in detail above, according to the present invention, a sufficiently flattened shape can be obtained by suppressing the extension of the impurity diffusion layer by using the insulating film having fluidity. When applied to the manufacture of integrated circuits, it is possible to provide a method of manufacturing a semiconductor device capable of improving the yield and improving the reliability of the device.

[Brief description of the drawings]

FIG. 1, showing an embodiment of the present invention, is a view showing a heat treatment step.

FIG. 2 is a view for explaining a flow angle.

FIG. 3 is a characteristic diagram illustrating a relationship between a flow angle and a diffusion length of an impurity by a conventional heat treatment.

FIG. 4 is a sectional view showing a method for manufacturing a semiconductor device to which the present invention is applied;

FIG. 5 is a sectional view showing a manufacturing step following FIG. 4;

FIG. 6 is a sectional view showing a manufacturing step following FIG. 5;

FIG. 7 is a characteristic diagram illustrating a relationship between a flow angle and a process temperature according to the present invention.

FIG. 8 is a characteristic diagram for explaining the relationship between the flow angle and the cooling rate according to the present invention.

FIG. 9 is a characteristic diagram for explaining the relationship between the flow angle and the holding temperature according to the present invention.

[Explanation of symbols]

21: semiconductor substrate, 28: BPSG film, TP1: first heat treatment step, TP2: second heat treatment step, TP3: third
Heat treatment process.

Claims (8)

(57) [Claims] 1. A first heat treatment for rapidly heating a semiconductor substrate to a temperature at which the insulating film has sufficient fluidity when forming an insulating film on a main surface of the semiconductor substrate and then performing heat treatment for planarization. A second heat treatment step of rapidly lowering the temperature of the semiconductor substrate from the temperature of the first heat treatment step to a temperature at which the insulating film has no fluidity in a steady state; and a temperature decrease step of the second heat treatment step. A third heat treatment step of holding the semiconductor substrate at the set temperature for a predetermined time and planarizing the insulating film. 2. The method according to claim 1, wherein in the first heat treatment step, a heating temperature of the semiconductor substrate is 900 ° C. or more and 1100 ° C. or less. 3. The method according to claim 1, wherein in the first heat treatment step, a heating rate of the semiconductor substrate is 100 ° C./min or more. 4. The method of manufacturing a semiconductor device according to claim 1, wherein in the second heat treatment step, the temperature decreasing rate is 30 ° C./min or more and 1000 ° C./min or less. 5. The method according to claim 1, wherein, in the third heat treatment step, the temperature of the semiconductor substrate is maintained at 700 ° C. or higher and 850 ° C. or lower. 6. The method according to claim 1, wherein in the third heat treatment step, a holding time of the semiconductor substrate is set to be 10 minutes or more and 120 minutes or less. 7. The method according to claim 1, wherein the insulating film is made of silicate glass containing at least phosphorus among phosphorus and boron. 8. The method according to claim 1, wherein the insulating film is made of a resin.