JP5731841B2 - Method for forming silicon nitride film - Google Patents

Description

  The present invention relates to a method for forming a silicon nitride film using a plasma CVD apparatus.

  In the manufacture of various electronic devices such as silicon semiconductors, silicon nitride films are used to suppress light reflection for the purpose of preventing the diffusion of atoms between thin films and the entry of atmospheric components such as moisture and oxygen. For the purpose, silicon nitride films having a high refractive index are widely used.

In general, it is known that a silicon nitride film has a lower carbon atomic ratio, a higher refractive index, and a higher barrier property and etching resistance of atoms and atmospheric components, as it is closer to the composition of Si ₃ N ₄ .

  By the way, as a method for forming a silicon nitride film, a method is known in which a mixed gas of dichlorosilane and ammonia is supplied to a film formation target substrate heated to 700 ° C. or higher by a plasma enhanced chemical vapor deposition method. It has been.

  In the case of forming a silicon nitride film on a substrate on which a pattern circuit with metal wiring or the like is formed, a plasma enhanced chemical vapor deposition method using a mixed gas of monosilane and ammonia and a forming temperature of about 400 ° C. is used. The forming method used is known (Patent Document 1).

Japanese Patent No. 33421633

  However, when the silicon nitride film is formed by the method described in Patent Document 1, when the formation temperature is lowered to 400 ° C. or lower, the hygroscopicity of the formed silicon nitride film increases rapidly and is likely to change over time. There was a problem.

  Thus, when a silicon nitride film is formed on a substrate on which a pattern circuit with metal wiring or the like is formed, it is desirable that the film forming temperature be a low temperature environment of 300 ° C. or lower, more preferably 200 ° C. or lower. However, it has been difficult to form a silicon nitride film that is stable at such temperatures.

  There is also a method using organic silane and ammonia instead of monosilane, but the film formed by this method is a carbonitride film (SiCN), and if the adjustment of the carbon content in the film cannot be optimized, the hygroscopic property is obtained. There was a problem that it was extremely high.

  The present invention has been made in view of the above circumstances. When forming a silicon nitride film using a plasma CVD apparatus, silicon having excellent film characteristics in a low temperature environment (preferably a forming temperature of 300 ° C. or lower). An object of the present invention is to provide a silicon nitride film forming method capable of forming a nitride film.

To solve this problem,
The invention according to claim 1 uses a plasma CVD apparatus provided with a capacitively coupled plasma source constituted by parallel plate electrodes as plasma generating means , using a source gas serving as a silicon source and a source gas serving as a nitrogen source. A method of forming a silicon nitride film having a refractive index of 1.85 or more by forming a mixed gas into a plasma in a vacuum environment, wherein tetramethyldisilazane is used as the silicon source, and the forming pressure is 1 to 100 Pa. The power density for generating plasma is in the range of 4 to 5 W / cm ² , and the mixing ratio of the tetramethyldisilazane and the source gas serving as the nitrogen source is 1: 100 to 1 in terms of flow rate. : A method of forming a silicon nitride film, characterized in that the range is 1000.

  The invention according to claim 2 is the method for forming a silicon nitride film according to claim 1, wherein the formation temperature is 300 ° C. or lower.

The invention according to claim 3 is the method for forming a silicon nitride film according to claim 1 or 2 , wherein nitrogen gas is used as the source gas serving as the nitrogen source .

  According to the method for forming a silicon nitride film of the present invention, when a silicon nitride film is formed using a plasma CVD apparatus, a silicon nitride film having excellent film characteristics can be formed at a forming temperature of 300 ° C. or lower. Furthermore, a silicon nitride film having a refractive index of 1.85 or more can be formed by optimizing the film formation conditions.

It is a schematic block diagram which shows the example of the plasma CVD apparatus used for the formation method of the silicon nitride film which is one Embodiment of this invention. It is a figure which shows the result of the test 1 of this invention, and is a graph which shows the condition dependence of the silicon nitride film formed using hexamethyldisilazane as a silicon source. It is a figure which shows the result of the test 2 of this invention, and is a graph which shows the condition dependence of the silicon nitride film formed using tetramethyldisilazane as a silicon source. It is a figure which shows the result of the test 3 of this invention, and is a graph which shows the condition dependence of the silicon nitride film formed at the formation temperature of 200 degreeC, using tetramethyldisilazane as a silicon source. It is a figure which shows the result of the test 4 of this invention, and is a graph which shows the condition dependence of the silicon nitride film formed at the formation temperature of 300 degreeC, using tetramethyldisilazane as a silicon source. It is a figure which shows the result of the test 5 of this invention, and shows the infrared absorption spectrum immediately after film-forming and after 100-hour progress of the silicon nitride film formed on the film-forming conditions of high refractive index.

  Hereinafter, a silicon nitride film forming method according to an embodiment to which the present invention is applied will be described in detail with reference to the drawings together with a plasma CVD apparatus for carrying out the silicon nitride film forming method. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

  The silicon nitride film forming method of this embodiment is a method of forming a silicon nitride film by using a plasma CVD apparatus to turn a film forming gas into a plasma in a vacuum environment. FIG. 1 shows an example of a plasma CVD apparatus used in the silicon nitride film forming method of this embodiment.

As shown in FIG. 1, the plasma CVD apparatus 1 includes a parallel plate type plasma generating means (not shown) that generates plasma by applying high-frequency power, and a silicon nitride film or the like is formed on the substrate in a plasma atmosphere. A chamber 2 for forming a thin film, a first introduction pipe 3 for feeding a raw material gas containing tetramethyldisilazane serving as a silicon source constituting the film forming gas into the chamber 2, and nitrogen constituting the film forming gas It is generally configured by a second introduction pipe 4 for sending nitrogen gas (N ₂ ) as a source into the chamber 2 and an exhaust pipe 6 provided with an exhaust pump 5 for exhausting the gas in the chamber 2.

The film-forming gas is a mixed gas of a source gas that becomes a silicon source and a source gas that becomes a nitrogen source.
Here, the silicon nitride film forming method of the present embodiment is characterized by using tetramethyldisilazane ((CH ₃ ) ₂ H—Si—NH—Si— (CH ₃ ) ₂ H) as a silicon source. . As a result, a silicon nitride film having excellent film characteristics can be formed at a formation temperature of 300 ° C. or lower.

As the raw material gas as a nitrogen source that although the nitrogen gas (N _2), is not limited to this, it is possible to use a general source of nitrogen such as ammonia gas (NH _3).
When nitrogen gas is used as the nitrogen source, it is preferable because a silicon nitride film having a high refractive index is easily obtained.

  In forming a silicon nitride film by the plasma CVD apparatus 1 shown in FIG. 1, first, a substrate such as a silicon substrate is placed in the chamber 2. Next, a raw material gas containing tetramethyldisilazane at a predetermined flow rate from the first introduction pipe 3 through the mass flow meter 7, and a nitrogen gas at a predetermined flow rate from the second introduction pipe 4 through the mass flow meter 8, respectively. Introduce into chamber 2. Next, after confirming that the inside of the chamber 2 is stabilized at a predetermined flow rate, temperature and pressure, the plasma generating means is operated to form a silicon nitride film on the substrate by plasma CVD reaction. The gas in the chamber 2 is sucked by the exhaust pump 5 and discharged from the exhaust pipe 6.

  Here, since the raw material gas containing tetramethyldisilazane as a silicon source is a liquefied gas having a low vapor pressure, tetramethyldisilazane is preferably supplied by tetramethyldisilazane alone by a forced vaporizer, The gas may be bubbled and supplied with helium gas.

  Moreover, the mixed gas (film-forming gas) introduced into the chamber 2 has a flow rate ratio of 1: 100 to 1: 1000 as a mixing ratio of a source gas containing tetramethyldisilazane and a source gas serving as a nitrogen source. It is preferable to be in the range.

If the flow rate ratio is less than 1: 100, the nitrogen concentration in the formed film becomes low, which is not preferable. On the other hand, when the flow rate ratio exceeds 1: 1000, the film formation rate is remarkably reduced, which is not preferable.
On the other hand, when the flow rate ratio is within the above range, it is preferable because a film that does not change with time can be formed by applying a high deposition rate condition.

  The formation temperature (film formation temperature) is not particularly limited, but it is possible to achieve film formation in a low temperature environment by using tetramethyldisilazane as a silicon source. Specifically, a silicon nitride film having excellent film characteristics such as barrier properties and etching resistance can be formed even when the formation temperature is 300 ° C. or lower or 200 ° C. or lower.

The forming pressure is preferably stabilized in the range of 1 to 100 Pa. When the forming pressure is less than 1 Pa, the discharge voltage is remarkably increased and abnormal discharge is likely to occur, which is not preferable. On the other hand, if the forming pressure exceeds 100 Pa, the carbon concentration in the film increases and the refractive index is lowered, which is not preferable.
On the other hand, when the formation pressure is within the above range, it is preferable because excellent film characteristics can be obtained while ensuring controllability of plasma discharge.

The plasma generating means, for example, using a capacitively coupled plasma source configured by a flat row plate electrodes, applying a power density in the range of 4~5W / cm ^2.
The applied power is preferably a high frequency band such as 13.56 MHz, and a low frequency of several hundred kHz to 2 MHz may be combined with this.
Note that the method of applying high-frequency power is not limited to the capacitive coupling type, and other methods such as an inductive coupling type can also be used.

  In the method for forming a silicon nitride film of the present embodiment, the film forming gas is a mixed gas of tetramethyldisilazane and nitrogen gas, and the mixing ratio of tetramethyldisilazane and nitrogen gas is 1: 100 to 1: Even when the silicon nitride film is formed at a forming temperature of 300 ° C. or lower by adjusting the film forming conditions so that the forming pressure is in the range of 1 to 100 Pa, the refractive index is 1 It is possible to form a silicon nitride film having a thickness of .85 or more and high etching resistance and gas barrier properties. For the measurement of the refractive index, a general measuring apparatus (for example, an ellipsometer manufactured by SOPRA) can be used.

  As described above, according to the method for forming a silicon nitride film of this embodiment, when forming a silicon nitride film using a plasma CVD apparatus, tetramethyldisilazane is used as a silicon source, so that it is 300 ° C. or lower. A silicon nitride film having excellent film characteristics can be formed at the formation temperature.

  Further, the film forming gas is a mixed gas of tetramethyldisilazane and nitrogen gas, the mixing ratio of tetramethyldisilazane and nitrogen gas is in the range of 1: 100 to 1: 1000 in flow rate ratio, and the forming pressure is By optimizing the film formation conditions so as to be in the range of 1 to 100 Pa, a silicon nitride film having a refractive index of 1.85 or more can be formed at a formation temperature of 300 ° C. or less.

Specific examples are shown below.
[Test 1]
Using a plasma CVD apparatus (Precision 5000, DxL, electrode area: 123 cm ² ) manufactured by Applied Materials, a silicon nitride film was formed using a mixed gas of hexamethyldisilazane (HMDS) and nitrogen gas as a film forming gas.

  The formation conditions (film formation conditions) were a hexamethyldisilazane flow rate of 1 sccm, a film formation temperature of 200 ° C., a pressure of 0.5 Torr, and a distance between electrodes of 7.6 mm. The flow rate of nitrogen gas was changed in the range of 250 to 350 sccm, and the discharge power was changed in the range of 400 to 600 W. The relationship between the refractive index of the formed silicon nitride film, the nitrogen gas flow rate, and the discharge power is shown in FIG.

  As shown in FIG. 2, the silicon nitride film formed using hexamethyldisilazane (HMDS) as the silicon source has a maximum refractive index of 1.82 and a refractive index of 1.85 or more. It was confirmed that it would not be.

  Moreover, as shown in FIG. 2, although the refractive index increase tendency can be confirmed on the high flow rate side and the low discharge power side of the nitrogen gas flow rate, if the nitrogen gas flow rate is increased too much, the pressure cannot be kept low, which is not preferable. On the other hand, if the discharge power is too low, the thickness of the film formed on the substrate becomes non-uniform, which is not preferable.

[Test 2]
A silicon nitride film was formed under the same conditions as in Test 1 except that the silicon source of the film formation gas was changed from hexamethyldisilazane (HMDS) to tetramethyldisilazane (TMDS), and film formation was evaluated. FIG. 3 shows the relationship between the refractive index of the formed silicon nitride film, the nitrogen gas flow rate, and the discharge power.

As shown in FIG. 3, the silicon nitride film formed using tetramethyldisilazane (TMDS) as the silicon source was confirmed to have a maximum refractive index of 1.90 obtained in this condition range. As for the discharge power, the refractive index is 1.85 or more when the power density (discharge power / electrode area) is 4 to 5 W / cm ² , and a decrease in the refractive index is observed under lower and higher conditions. It was.

By the way, the molecular structures of hexamethyldisilazane (HMDS) and tetramethyldisilazane (TMDS) are as follows.
_{Hexamethyldisilazane: (CH 3) 3 -Si-} NH-Si- (CH 3) 3
_{Tetramethyldisilazane: (CH 3) 2 H-} Si-NH-Si- (CH 3) 2 H

Table 1 shows the intramolecular binding energy (unit: kJ / mol) of hexamethyldisilazane (HMDS) and tetramethyldisilazane (TMDS).

As shown in Table 1, there is no significant difference in bond dissociation energy between hexamethyldisilazane (HMDS) and tetramethyldisilazane (TMDS). On the other hand, regarding the molecular structure, tetramethyldisilazane is gasified as methane (CH ₄ ), in which a hydrogen atom (H) bonded to a silicon atom (Si) and a methyl group (—CH ₃ ) are adjacent to each other. . For this reason, it is considered that the composition of the silicon nitride film formed using tetramethyldisilazane (TMDS) as the silicon source has a low carbon component and a high refractive index.

  From the same effect, it is considered advantageous to use a lower methylated silazane as a silicon source when forming a silicon nitride film having a high refractive index. However, a disilazane compound having a lower methylation than tetramethyldisilazane has a problem that the stability of the material itself is low and a polymerization reaction is caused in a room temperature storage state, so that it cannot be used stably.

[Test 3]
A gas mixture of tetramethyldisilazane (TMDS) and nitrogen gas was used as the film forming gas. As formation conditions (film formation conditions), the flow rate of nitrogen gas was fixed at 300 sccm, the film formation temperature was 200 ° C., and the distance between the electrodes was fixed at 7.6 mm. Then, the discharge power is changed to 400 to 600 W, the forming pressure is set to 1 to 1.5 Torr, and the flow rate of tetramethyldisilazane (TMDS) is changed in the range of 1 to 3 sccm as variable factors, and the dependency on the condition of the formed silicon nitride film Sex was evaluated. FIG. 4 shows the measurement results.

  As shown in FIG. 4, it was confirmed that the maximum refractive index obtained in this condition range was 1.83, and the refractive index was not 1.85 or more. From this result, it was found that even when hexamethyldisilazane (HMDS) was used as the silicon source, a silicon nitride film having a high refractive index was not formed unless the film formation conditions were optimized.

[Test 4]
A silicon nitride film was formed under the same conditions as in Test 3 except that the formation temperature was changed to 300 ° C., and the film formation was evaluated. FIG. 5 shows the evaluation results of the condition dependency of the formed silicon nitride film.

As shown in FIG. 5, it was confirmed that the silicon nitride film formed at the formation temperature of 300 ° C. has a maximum refractive index of 2.07 obtained in this condition range.
Further, it was confirmed that the silicon nitride film formed in this test had a high refractive index as a whole as compared with the silicon nitride film formed at a formation temperature of 200 ° C. (Test 3).

[Test 5]
Comparison was made when nitrogen gas and ammonia were used as the nitrogen source. Table 2 shows the film forming conditions and the refractive index of the obtained silicon nitride film. When ammonia was used as the nitrogen source, nitrogen gas was used as the carrier gas (see Table 2).

  As shown in Table 2, it was confirmed that the refractive index was relatively higher when nitrogen was used than when ammonia was used as the nitrogen source. Therefore, in order to form a silicon nitride film having a high refractive index, it is desirable to use nitrogen gas as the nitrogen source.

[Test 6]
The silicon nitride film formed using tetramethyldisilazane (TMDS) as the silicon source was checked for changes with time.

First, the conditions for forming a high refractive index silicon nitride film are as follows: the flow rate of tetramethyldisilazane (TMDS) is 1 sccm, the flow rate of nitrogen gas is 300 sccm, the deposition temperature is 200 ° C., the distance between the electrodes is 7.6 mm, and the discharge is performed. The power was 540 W and the forming pressure was 0.5 Torr.
On the other hand, the formation conditions of the low refractive index silicon nitride film are as follows: the flow rate of tetramethyldisilazane (TMDS) is 5 sccm, the flow rate of nitrogen gas is 750 sccm, the deposition temperature is 200 ° C., and the distance between the electrodes is 7. The discharge power was 500 W and the forming pressure was 3 Torr.

  Next, with respect to the formed silicon nitride film, the refractive index and the infrared absorption spectrum were measured immediately after the film formation and after being stored in the atmosphere for 100 hours after the film formation. Table 3 shows the measurement results of the refractive index of each silicon nitride film. FIG. 6 shows infrared absorption spectra of a silicon nitride film formed under a high refractive index film formation condition immediately after film formation and after 100 hours have elapsed.

  As shown in Table 3, it was found that no change in refractive index with time was observed in the silicon nitride films formed under the respective film forming conditions having a high refractive index and a low refractive index.

  As shown in FIG. 6, in a silicon nitride film formed under a film formation condition with a high refractive index, it appears when moisture absorption occurs both in the infrared absorption spectrum immediately after film formation and after 100 hours after film formation. It was confirmed that no absorption attributed to Si-OH was observed. Therefore, it was confirmed that the silicon nitride film formed by the silicon nitride film forming method of the present invention has a film quality that does not change with time.

  As described above, according to the method of forming a silicon nitride film of the present invention, it was confirmed that a silicon nitride film having a refractive index of 1.85 or more, high resistance, and high barrier properties can be formed.

DESCRIPTION OF SYMBOLS 1 ... Plasma CVD apparatus 2 ... Chamber 3 ... 1st introduction pipe 4 ... 2nd introduction pipe 5 ... Exhaust pump 6 ... Exhaust pipe 7 ... Mass flow meter 8 ....・ Mass flow meter

Claims (3)

Using a plasma CVD apparatus equipped with a capacitively coupled plasma source composed of parallel plate electrodes as plasma generating means , a mixed gas of a source gas serving as a silicon source and a source gas serving as a nitrogen source is plasmad in a vacuum environment. A method of forming a silicon nitride film having a refractive index of 1.85 or more,
Tetramethyldisilazane is used as the silicon source,
The forming pressure is in the range of 1 to 100 Pa,
The power density of power for generating plasma is in the range of 4 to 5 W / cm ² ,
A method for forming a silicon nitride film, wherein a mixing ratio of the tetramethyldisilazane and the source gas serving as the nitrogen source is in a range of 1: 100 to 1: 1000 in flow rate ratio.   The method for forming a silicon nitride film according to claim 1, wherein the formation temperature is 300 ° C. or lower.   3. The method of forming a silicon nitride film according to claim 1, wherein nitrogen gas is used as a source gas serving as the nitrogen source.

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