JP4600427B2 - Thin film forming method and semiconductor device - Google Patents

Description

  The present invention relates to a thin film forming method for forming a thin film using a compound having a borazine skeleton as a raw material. Further, the present invention relates to a semiconductor device provided with a thin film formed by this thin film forming method as an insulating film.

  As the speed and integration of semiconductor devices increase, the problem of signal delay is becoming serious. The signal delay is expressed by the product of the wiring resistance and the capacitance between the wirings and between the layers. In order to minimize the signal delay, in addition to reducing the wiring resistance, the dielectric of the interlayer insulating film Lowering the rate is an effective means.

  Recently, as means for lowering the dielectric constant of an interlayer insulating film, interlayer insulation including a B—C—N bond is formed on the surface of an object to be processed by plasma CVD in an atmosphere containing a hydrocarbon-based gas, a borazine, and a plasma-based gas. A method of forming a film is disclosed. Further, it is also disclosed that the interlayer insulating film has a low dielectric constant (see, for example, JP 2000-058538 A (Patent Document 1)).

  However, in the above conventional method, a film having a low dielectric constant and a high mechanical strength can be formed by using borazine as a raw material. However, since no consideration is given to moisture resistance, the film absorbs water when left after film formation, and the dielectric There was a problem that the rate and mechanical strength could not be sustained. Further, there is a problem that the leakage current of the formed film is high and the insulation characteristics are not sufficient.

JP 2000-058538 A

  The present invention has been made in order to solve the above-described problems of the prior art, and the object thereof is to provide a film that can stably obtain a low dielectric constant and a high mechanical strength over a long period of time and that has an insulating property. It is providing the thin film formation method which can be manufactured.

The thin film forming method according to the present invention includes a step of introducing a compound having a borazine skeleton into the upper part of the substrate of the reaction vessel, a step of applying a negative charge to the power supply electrode that supports the substrate installed in the reaction vessel, High-frequency energy is oscillated by plasma generating means provided opposite to the feeding electrode through the substrate to generate plasma in the reaction vessel, and the reaction is performed while holding the borazine skeleton of the compound on the substrate. Of the reaction active state by the step of making the active state and the negative charge applied to the power supply electrode, the cation is selectively swept to the substrate, and the borazine skeleton of the reactive compound is converted into the substrate. And sequentially bonding to the upper film to increase the molecular weight and depositing on the substrate.

  A semiconductor device according to the present invention includes an insulating film formed by the above-described thin film forming method of the present invention on a substrate, and further includes a wiring.

  ADVANTAGE OF THE INVENTION According to this invention, the thin film which can maintain a low dielectric constant film and high mechanical strength stably over a long term can be provided. In addition, a low dielectric constant film and a thin film that can stably maintain a high mechanical strength over a long period of time can be formed. Further, the signal delay of the semiconductor device can be minimized, and high speed can be achieved.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing a schematic configuration of a plasma CVD apparatus (hereinafter referred to as a PCVD apparatus) in Embodiment 1 of the present invention. As shown in FIG. 1, a PCVD apparatus according to the present invention includes a reaction vessel 1 having a raw material inlet 5 for supplying a compound having a vacuum pump 4 and a borazine skeleton, a reaction vessel 1 installed inside the reaction vessel 1, and a substrate 8. A power supply electrode 7 that supports and applies a negative charge, and a plasma generation means 12 that is provided to face the power supply electrode 7 through the substrate 8 and generate plasma 11 inside the reaction vessel 1 are provided. In the PCVD apparatus according to the present invention, a compound having a borazine skeleton is introduced into the reaction vessel 1, and plasma is generated inside the reaction vessel 1 by the plasma generating means 12 provided facing the feeding electrode 7, whereby the compound is produced. When a negative charge is further applied to the power supply electrode 7, the excited compound is swept to the substrate side, and is sequentially bonded to have a high molecular weight and is deposited on the substrate 8.

  The plasma generator 12 can be composed of, for example, a high-frequency power source 22, a matching unit 32, and a coiled antenna 9. The high-frequency energy oscillated from the high-frequency power source 22 is adjusted by the matching unit 32, propagated into the reaction vessel 1 by the antenna 9, and can excite the raw material gas in the reaction vessel 1 to generate plasma. . A magnetic field can be generated by the coiled antenna 9 and resonated to increase the plasma density. Further, the plasma generation site can be changed by changing the shape of the antenna 9. Part of the above configuration may be omitted depending on the situation. Furthermore, it is preferable to provide the ground electrodes 102 and 103 for safety. The means for applying a negative charge to the power supply electrode 7 can be configured, for example, by connecting a DC power supply 10 to the power supply electrode 7. For safety, it is preferable to provide the ground electrode 101. The voltage of the DC power supply 10 is desirably 1500 V or less. This is because if the voltage exceeds 1500 V, the borazine skeleton of the film on the substrate 8 is destroyed and becomes a component that increases the dielectric constant such as boron nitride, thereby increasing the leakage current of the film and impairing the insulating characteristics.

  By configuring the PCVD apparatus as described above, the plasma generator 12 can uniformly apply desired plasma energy to the compound having a borazine skeleton introduced into the reaction vessel 1 from the raw material introduction port 5. The compound to which the plasma energy is applied becomes reactive while retaining the borazine skeleton, and the active species is sufficiently cross-linked by being attracted to the substrate 8 by a DC electric field applied to the feeding electrode 7 in the reactive state. Can be done. Since the plasma energy can be easily adjusted, the borazine skeleton is not decomposed more than necessary, and a desired structure can be maintained. Therefore, a film having a low dielectric constant, high mechanical strength, and moisture resistance can be obtained. Excellent characteristics can be imparted even over time. Furthermore, excessive decomposition generates boron nitride, which can suppress the increase in dielectric constant and the deterioration of the leakage current characteristics of the film.

  The frequency of the high frequency oscillated from the high frequency power source 22 can be exemplified by 13.56 MHz, for example, but can be arbitrarily set in the range of about 2 GHz to 4 kHz and the power of about 5 to 4000 W. When the power exceeds 4000 W, the frequency of decomposition of the compound having a borazine skeleton increases, and it becomes difficult to obtain a film having a desired borazine structure. More preferably, it is 10 W or more and 3000 W or less. RF (10 kHz to 1 GHz) or microwave (1 GHz to 10 GHz) may be used as the frequency of the applied high frequency. Any of the above may be mixed.

  The plasma generator 12 may be configured as shown in FIG. Plasma can be generated by propagating the microwave generated by the microwave generator 13 through the waveguide 14, propagating from the microwave introduction window 16 to the inside of the reaction vessel 1, and supplying it to the source gas. When a magnetic field is generated from the coil 15, the plasma density can be increased.

  Further, by providing the power supply electrode 7 with a heating device 61, the deposited film can be further cross-linked to increase the molecular weight, thereby improving the heat resistance. Heat-crosslinking is preferable because outgas generated from a film after film formation can be reduced and restrictions in a subsequent process can be reduced. Here, when the substrate 8 is heated, it is preferable that the source gas temperature and the substrate temperature can be controlled between room temperature and 450 ° C. When the source gas and the substrate temperature exceed 450 ° C., the time for obtaining a desired film thickness becomes extremely slow, and the film formation may not proceed. More preferably, it is 50 degreeC or more and 400 degrees C or less.

  The substrate temperature may be controlled by turning on / off the heating device 61, or a heating / cooling device 62 having a cooling function may be provided in place of the heating device 61 and set to a predetermined process temperature.

  Since the power supply electrode 7 on which the substrate 8 is installed may be a plasma source for inducing plasma, it may be constituted by a high-frequency power source 21 on which negative charges are superimposed and a matching unit 31 as shown in FIG. With the plasma on the substrate 8 side, the activation reaction directly above the substrate 8 can be controlled, and the film quality can be controlled. Examples of the high frequency oscillated from the high frequency power source 21 include 13.56 MHz, but RF (10 kHz to 1 GHz) or microwave (1 GHz to 10 GHz) may be used as the high frequency. Any of the above may be mixed. The power is preferably 3000 W or less. This is because if the power exceeds 3000 W, the borazine skeleton of the film on the substrate 8 is destroyed and becomes a component that increases the dielectric constant, such as boron nitride, increasing the leakage current of the film and impairing the insulating characteristics.

  As a means for introducing the compound having a borazine skeleton into the reaction vessel 1, the raw material gas may be introduced as it is from the raw material introduction port 5. Alternatively, a vaporization mechanism by heating or the like is separately provided and introduced in a gasified state. Also good. When the compound having a borazine skeleton is vaporized by heating the raw material storage container, the gas can be introduced using this vaporization pressure. Ar, He, nitrogen or other gas may be used as the carrier gas. The characteristics of the membrane can be controlled by mixing methane, ethane, ethylene, acetylene, ammonia or alkylamine compounds.

  The flow rate of the carrier gas is preferably about 100 to 1000 sccm, the flow rate of the gas having a borazine skeleton as a raw material is 1 to 300 sccm, and the flow rate of methane, ethane, ethylene, acetylene, ammonia or alkylamines to be added is 0 to 100 sccm. The degree is good. If the flow rate of the carrier gas is less than 100 sccm, the time for obtaining the desired film thickness becomes extremely slow, and the film formation may not proceed. On the other hand, if it exceeds 1000 sccm, the film thickness uniformity in the substrate surface tends to deteriorate. More preferably, it is 20 sccm or more and 800 sccm or less. When the flow rate of the source gas is less than 1 sccm, the time for obtaining a desired film thickness becomes extremely slow, and the film formation may not proceed. On the other hand, if it exceeds 300 sccm, the film has a low crosslink density, so that the mechanical strength is lowered. More preferably, it is 5 sccm or more and 200 sccm or less. When methane, ethane, ethylene, acetylene, ammonia, or alkylamine gas is added, the dielectric constant of the obtained film increases when it exceeds 100 sccm. More preferably, it is 5 sccm or more and 100 sccm or less.

  Moreover, it is preferable that the pressure inside the reaction container 1 is 0.01 Pa or more and 10 Pa or less. If it is less than 0.01 Pa, the frequency of decomposition of the compound having a borazine skeleton by plasma increases, and it is difficult to obtain a film having a desired borazine structure. Moreover, since it will become a film | membrane with a low crosslinking density when it exceeds 10 Pa, mechanical strength falls. More preferably, it is 5 Pa or more and 6.7 Pa or less. The pressure can be adjusted by a pressure regulator such as a vacuum pump or a gas flow rate.

  Further, a partition plate that can sweep ions on the substrate 8 and blocks radicals may be provided. This is because the radical component in the film absorbs moisture after film formation and affects the moisture resistance of the film, so that it can be prevented from being taken into the film.

  In the present embodiment, an example in which the feeding electrode 7 is arranged at the lower part of the reaction vessel 1 and the plasma generator 12 is arranged at the upper part is shown. However, the feeding electrode 7 and the plasma generator 12 may be arranged to face each other. For example, the structure upside down may be sufficient and you may comprise so that it may arrange | position to the side surface of the reaction container 1. FIG.

Embodiment 2. FIG.
Next, a film forming process using the PCVD apparatus in Embodiment 1 will be described. First, the substrate 8 is placed on the feeding electrode 7 and the inside of the reaction vessel 1 is evacuated. Next, a raw material gas, a carrier gas, and other gases as required are supplied into the reaction vessel 1 from the gas inlet 5. Further, the pressure in the reaction vessel 1 is evacuated by the vacuum pump 4 to maintain a predetermined process pressure. Further, the substrate 8 is set to a predetermined process temperature by the heating device 61 or the heating / cooling device 62.

  Further, when a high frequency is generated from the high frequency power source 22 and plasma is generated in the reaction vessel 1, the source gas and the carrier gas become ions and radicals in the reaction vessel 1. Among these ions, ions are attracted to an electrode having a potential opposite to that of their own charge and react repeatedly with collision. Here, when a negative charge is applied to the feeding electrode 7, cations can be selectively attracted to the feeding electrode 7 side to form a film, and the ratio of anions and radicals contributing to the film formation can be reduced.

  On the other hand, radicals are uniformly distributed in the plasma field, and can cause a reaction mainly composed of cations on the substrate 8 on the feeding electrode 7. Therefore, deposition of radicals on the substrate can be suppressed, and the amount of radicals in the formed film can be reduced.

  When borazine radicals remain in the film, B-hydroxyborazine is generated by reaction with oxygen or water. When this is opened to the air, it reacts with water to produce boroxine and ammonia, making it easier to break part of the membrane. That is, the film characteristics change with time and outgas is likely to occur. As described above, since the radical component in the film can be reduced in the thin film forming method according to the present invention, the formed film can suppress the reaction with water in the air. Therefore, it has good moisture resistance and can maintain stable characteristics over time. Specifically, the film by the conventional thin film formation method has maintained a dielectric constant of about 3.0 to 1.8 for several days, whereas the film by the thin film formation method according to the present invention has at least the dielectric constant. Can be maintained for several years. This low dielectric constant can be confirmed, for example, by measuring the dielectric constant by the same method as that immediately after forming a film stored for a certain period.

  Furthermore, since the film formed by the thin film forming method according to the present invention is less likely to contain overdecomposed substances such as boron nitride as compared with the film formed by the conventional thin film forming method, a lower dielectric constant can be realized. In addition, there is an advantage that the amount of outgas is reduced and no trouble occurs in the semiconductor device manufacturing process following the film formation.

  In the method for forming a thin film according to the present invention, the compound having a borazine skeleton used as a raw material may be any conventionally known appropriate compound without particular limitation as long as it has a borazine skeleton. A compound represented by the following chemical formula (1) is preferably used as a raw material from the viewpoint that a film with improved expansion coefficient, heat resistance, thermal conductivity, mechanical strength and the like can be produced.

  In the compound represented by the chemical formula (1), the substituents represented by R1 to R6 may be the same as or different from each other, and may be a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkenyl group, or an alkynyl group. Any of these can be used independently. However, not all of R1 to R6 are hydrogen atoms. In the case of all hydrogen, boron-hydrogen bonds or nitrogen-hydrogen bonds tend to remain in the film. Since these bonds have high hydrophilicity, there arises a problem that the hygroscopicity of the film increases, and the desired film may not be obtained. Further, in R1 to R6 of the compound (1), when the number of carbon atoms is larger than 4, the carbon atom content in the formed film increases, and the heat resistance and mechanical strength of the film may be deteriorated. More preferably, the carbon number is 1 or 2.

Embodiment 3 FIG.
Using the PCVD apparatus shown in the first embodiment, a film produced by the thin film forming method shown in the second embodiment is used as an insulating layer, and a copper wiring pattern is formed. A semiconductor device was manufactured. In the above semiconductor device, it was confirmed that the wiring delay can be reduced as compared with the case where the insulating layer is made of silicon oxide or silicon nitride. Furthermore, it was confirmed that there was no change in the signal speed after one month. In addition, it was confirmed that the signal gain performance can be improved when used as a passivation film of a HEMT (High Electron Mobility Transistor) using a gallium arsenide substrate which is one of high frequency devices.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not intended to be limited to this.

(Examples 1-3)
The following film formation was performed using the PCVD apparatus shown in FIG. Helium was used as a carrier gas, and the flow rate was set to 200 sccm. Further, B, B, B, N, N, N-hexamethylborazine gas as a raw material was introduced into the reaction vessel 1 in which the substrate 8 was placed through the heated raw material inlet 5 with a flow rate set to 10 sccm. The vapor temperature of B, B, B, N, N, N-hexamethylborazine gas was 150 ° C. Further, the temperature of the substrate 8 was heated to 300 ° C. by the heating device 61, and a DC electric field of −600 V to −200 V (Examples 1 to 3) was applied to the power supply electrode 7 that supports the substrate 8 by the DC power supply 10. Further, a high frequency of 13.56 MHz was incident at 1000 W from the antenna 9 to generate plasma 11, and an activated source gas was deposited to form a film. The pressure in the reaction vessel was maintained at 2 Pa.

(Comparative Example 1)
Film formation was performed without applying a DC electric field to the feeding electrode 7 (0 V). Other conditions are the same as those in Examples 1-3.

  In Examples 1 to 3 and Comparative Example 1, the input power from the high-frequency power source 22 was changed to 250 to 1500 W, and the dielectric constant change amount and 2 MV / cm electric field after being left for 96 hours in an atmosphere of 85 ° C. and 85% humidity. The leakage current values during application were measured, and the results are summarized in Table 1. Furthermore, the relationship between the leakage current value and the amount of change in dielectric constant is shown in FIG.

  It can be seen from Table 1 that when the input power from the high frequency power supply 22 is increased, the amount of change in dielectric constant corresponding to the amount of change over time can be reduced. However, it can also be seen that the leakage current value increases under conditions where the amount of change in dielectric constant can be reduced, leading to a decrease in the insulating properties of the film. Here, considering the relationship between the leakage current value and the amount of change in dielectric constant in FIG. 4, it can be seen that the amount of change in dielectric constant can be reduced by applying a DC electric field (Examples 1 to 3). Further, it can be seen that favorable conditions can be set in the range of applied voltage of −600 to −200 V and input power of 250 to 1500 W. In Examples 1 to 3, a dielectric constant change amount of 0.05 or less and a leak current value of 1.0E-9 A / cm or less can be achieved. Under suitable conditions, a more preferable change in dielectric constant of 0.02 or less and a leak current value of 1.0E-9 A / cm or less can be achieved. That is, it is possible to form a film having a small change over time (good moisture resistance) and excellent insulating characteristics.

It is a schematic diagram which shows schematic structure of the PCVD apparatus in Embodiment 1 of this invention. It is a schematic diagram which shows schematic structure of the PCVD apparatus in Embodiment 1 of this invention. It is a schematic diagram which shows schematic structure of the PCVD apparatus in Embodiment 1 of this invention. It is a characteristic view which shows the relationship between the leakage current value in Examples 1-3 of this invention and the comparative example 1, and a dielectric constant variation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Reaction container, 4 Vacuum pump, 5 Raw material inlet, 7 Feed electrode, 8 Substrate, 9 Antenna, 10 DC power supply, 11 Plasma, 12 Plasma generator, 13 Microwave generator, 14 Waveguide, 15 Coil, 16 Microwave introduction window, 21, 22 High frequency power supply, 31, 32 Matching device, 61 Heating device, 62 Heating / cooling device, 101-103: Ground electrode

Claims (5)

Introducing a compound having a borazine skeleton into the upper part of the substrate of the reaction vessel;
Applying a negative charge to a power supply electrode that supports a substrate placed in the reaction vessel;
High-frequency energy is oscillated by plasma generating means provided opposite to the feeding electrode through the substrate to generate plasma in the reaction vessel, and the reaction is performed while holding the borazine skeleton of the compound on the substrate. An active state process;
Among the reaction active states due to the negative charge applied to the power supply electrode, the cation is selectively swept to the substrate, and the borazine skeleton of the reaction active compound is sequentially bonded to the film on the substrate , A method of forming a thin film, comprising a step of increasing the molecular weight and depositing the polymer on the substrate. The thin film forming method according to claim 1, wherein the compound having a borazine skeleton is represented by the following chemical formula (1).

(Wherein R1 to R6 may be the same as or different from each other, each independently selected from a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkenyl group, or an alkynyl group, and R1 to R6) At least one of them is not a hydrogen atom) 2. The method of forming a thin film according to claim 1, wherein the film which is sequentially bonded to have a high molecular weight and is deposited on the substrate is heated and crosslinked. A film on the substrate is activated by plasma induction by a high-frequency power source connected to the power supply electrode, and a borazine skeleton that has been activated in a reactive state on the upper portion of the substrate is sequentially applied to the film activated by the plasma induction. The thin film forming method according to claim 1, wherein the thin film forming method is performed by increasing the molecular weight by bonding. A semiconductor device comprising: an insulating film formed by any one of the thin film forming methods according to claim 1; and a wiring.

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