JP3507108B2 - Method of forming deposited film by bias sputtering method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deposited film forming method by a sputtering method adopted for forming a deposited film on a substrate such as a single crystal wafer in the manufacture of various semiconductor devices.

[0002]

2. Description of the Related Art As a method for forming a deposited film on a substrate such as a single crystal wafer, a sputtering method which can form the deposited film at a relatively low temperature is widely known. In the sputtering method, the inside of the vacuum vessel is generally 10 ⁻³ to 10 ⁻⁴ T.
By reducing the pressure to about orr and applying a DC voltage or an AC voltage to the target electrode holding the target material, plasma discharge is generated in the vacuum container, and cations in the plasma are accelerated and collide with the target material. Due to this impact, atoms constituting the target material are released from the target material and adhere and deposit on the substrate arranged in the vacuum container to form a deposited film. In recent years, among such sputtering methods, a so-called bias sputtering method has been studied in which a bias voltage is applied to a substrate or a target electrode and sputtering is performed in a state in which the energy of ions in the plasma incident on the substrate is controlled. In the bias sputtering method, the deposited film can be formed in a state in which the incident energy of ions to the substrate is controlled, so that the step coverage of the deposited film can be improved or the deposited film can be formed in a state in which the incident energy to the substrate is suppressed to a low level. And so on. As an example of a bias sputtering device that forms a deposited film with the incident energy to the substrate kept low,
U.S. Pat. No. 4,874,494 describes a device which uses a high frequency power supply having a frequency of 100 MHz or more. The bias sputtering device disclosed in the specification has the configuration shown in FIG.

In the bias sputtering apparatus shown in FIG. 10, a target electrode 702 is placed in a vacuum chamber 705.
The target material 701 held on the substrate and the silicon wafer (that is, the substrate) 703 placed on the substrate electrode 704 are arranged so as to face each other, and a permanent magnet 708 for magnetron discharge is provided on the back surface of the target electrode 702. Are arranged. A high frequency power source 709 is connected to the target electrode 702 via a matching circuit 710. Further, a DC power supply 706 is connected to the target electrode 702 via a filter 711 for cutting high frequencies. The substrate electrode 704 is grounded at a high frequency by a capacitor 712, and is connected to a DC power source 707 via a filter 711. Reference numeral 713 is a gas supply system, and 714 is an exhaust system. In this bias sputtering device, the plasma potential is V _p , the output voltage of the DC power supply 707 is V ₁ , and the output voltage of the DC power supply 706 is V ₂ , and V _p + |
Since the self-bias represented by V ₁ | or V _p + | V ₂ | can be controlled independently, | V ₁ | is increased to increase the acceleration voltage of ions to the target material and increase the sputtering rate. It is said that the film formation rate can be increased. Further, by using a high frequency power source of 100 MHz or more as the high frequency power source 709, plasma can be generated at a high density, and the width of the kinetic energy of ions can be set to 1
Since it can be suppressed to 1/10 or less as compared with the high frequency of 3.56 MHz, almost all the ions can be bombarded on the surface of the substrate 703 with a desired kinetic energy, and the substrate 703 is not damaged so much. It is said that a deposited film can be formed. Further, the US patent specification shows formation of a single crystal Al thin film on a silicon substrate.

International application WO 91/09161 discloses a bias sputtering apparatus similar to that disclosed in the above-mentioned US Pat. No. 4,874,494, which is used in an atmosphere inside a vacuum chamber. H ₂ O, CO, and CO ₂
It is described that the epitaxial film can be formed at a substrate temperature in the range of 400 ° C. to 700 ° C. by controlling the partial pressure of 1.0 × 10 ⁻⁸ Torr or less. Regarding lowering the substrate temperature, in order to solve the problem of thermal diffusion of doping atoms that occurs depending on the process temperature at the time of semiconductor device fabrication, and to respond to the sharpening of the dopant profile required for recent high-performance device fabrication. Is also widely required. However, regarding the formation of the epitaxial film using the sputtering method,
The fact that so-called sputtering gas, which causes sputtering, into the film and the densification of the film are raised as major problems, have not been sufficiently studied.

The present inventors have conducted diligent research in order to overcome this problem. The present inventors have filed the international application WO
An experiment for forming an epitaxial film of silicon on a silicon wafer was conducted based on the disclosure of Japanese Patent No. 91/09161. As a result, when the substrate temperature was set to about 400 ° C. or higher, a good epitaxial film could be formed relatively stably, but at a substrate temperature lower than 400 ° C.
A good epitaxial film could not be formed, resulting in poor semiconductor characteristics. That is, the substrate temperature is 400 ° C
The technique disclosed in the international application WO91 / 09161 is not sufficient for stably forming an epitaxial film with a lesser amount.

Further, in the international application WO91 / 09150, a sample to be processed is placed on a sample electrode in a vacuum container so that the voltage of the sample electrode is constant with respect to the plasma potential in the vacuum container. And applying a negative voltage to the sample electrode while controlling the negative voltage so that the energy distribution of the ions irradiated to the sample to be processed is in a desired state, and the ion irradiation is performed, and a positive voltage is applied to the sample electrode. A plasma processing method is described, which is characterized by repeating the steps of applying and irradiating a sample to be processed with electrons. Then, according to the plasma processing method, by controlling the ions in the vacuum container to a state in which energy dispersion is small, it is possible to perform plasma processing that causes less damage to the sample to be processed at high speed.
However, the plasma treatment described in this publication is specifically a plasma etching method or a plasma CVD method, and there is no mention of the sputtering method. Furthermore, there is no disclosure or suggestion regarding formation of an epitaxial film.

[0007]

SUMMARY OF THE INVENTION The present invention overcomes the above-mentioned problems and
It is a main object to provide a method for forming a deposited film capable of forming a high quality epitaxial film at a low temperature of less than 00 ° C. It is another object of the present invention to provide an improved method for forming a deposited film by bias sputtering, which makes it possible to form a deposited film at a low temperature while reducing ion damage to the substrate. Still another object of the present invention is a target electrode for holding a target material arranged in a vacuum container,
A plasma is generated by using high-frequency energy between a substrate electrode that holds a substrate for forming a deposited film that is arranged facing the target electrode, and the target material is sputtered, and the target electrode or the substrate is also formed. In a deposited film forming method by a bias sputtering method for applying a bias voltage to at least one of electrodes to form a deposited film composed of atoms sputtered on the substrate, the substrate is irradiated with ions in the plasma, Characterized in that the step of forming a deposited film on the substrate by sputtering the target material and the step of irradiating the substrate with ions in the plasma without sputtering the target material are alternately repeated. To provide a deposited film forming method by a bias sputtering method A.

[0008]

The structure and effects of the present invention are as follows. The deposited film forming method by the bias sputtering method provided by the present invention has the following structure. That is, plasma is generated by using high frequency energy between a target electrode that holds a target material that is placed in a vacuum container and a substrate electrode that holds a substrate for forming a deposited film that is placed facing the target electrode. And a target material is sputtered, and a bias voltage is applied to at least one of the target electrode and the substrate electrode to form a deposited film composed of sputtered atoms on the substrate by a bias sputtering method. In the method of forming a deposited film, the high frequency energy has a frequency of 50 MHz to 30.
It is supplied from a high frequency power source in the range of 0 MHz and the target
The ON / OFF control of the DC power supply connected to the
By irradiating the substrate with ions in the plasma, forming a deposited film on the substrate by sputtering the target material, and by sputtering the target material with the ions in the plasma without sputtering the target material. It is characterized by switching the irradiation process and repeating it alternately
It is a thing .

According to the deposited film forming method by the bias sputtering method of the present invention having the above-described structure, the deposited film forming step on the substrate and the ions to the atoms constituting the target material reaching the substrate or the deposited film By performing the irradiation step separately from the above step, it is possible to suppress mixing of sputtering gas such as Ar gas and Ne gas into the deposited film. In addition to this, irradiation of ions to the atoms constituting the target material reaching the substrate or the deposited film promotes the migration of atoms, so that high-quality epitaxial with excellent step coverage at a low temperature of less than 400 ° C. A deposited film can be formed. Further, since it becomes possible to form an epitaxial film at a low temperature of less than 400 ° C., when forming a laminated structure of deposited films, the interface state between the deposited films forming the laminated structure should be extremely favorable. The desired dopant profile can be achieved.

The present inventors have solved the above-mentioned problems, and
The experiment described below was conducted in order to provide a deposited film forming method capable of stably forming an epitaxial film at a low temperature of 00 ° C. or lower.

[0011]

[Experiment 1] Based on the disclosure content of International Patent Application No. WO91 / 09161 published under the Patent Cooperation Treaty mentioned above, formation of an epitaxial film of silicon on a silicon wafer was tried at various temperatures, and at low temperature. We examined the problems to be achieved.

The bias sputtering apparatus used here is shown in FIG. In the bias sputtering apparatus shown in FIG. 1, the target electrode 10 is placed in the vacuum chamber 101.
2 and the target material 112 held on the substrate electrode 105.
The silicon wafer (that is, the substrate) 104 placed on the substrate is disposed so as to face it, and the permanent magnet 103 for magnetron discharge is disposed on the back surface of the target electrode 102. A high frequency power supply 106 having a frequency of 100 MHz is connected to the target electrode 102 via a matching circuit 107. Further, a DC power supply 108 is provided to the target electrode 102 via a filter 111 for cutting high frequencies.
Are connected. The substrate electrode 105 is the capacitor 11
3 is grounded at a high frequency and is connected to the DC power supply 109 via the filter 110. Reference numeral 106 is a gas cylinder, 105 is a gas purifier, and 114 is a gas exhaust system. Reference numeral 115 denotes a load-lock chamber for loading a substrate, and the load-lock chamber is connected to the vacuum container 101 via a gate valve 116.

The vacuum container 101 is made of SUS316,
The inner wall is electropolished and the surface smoothness is R _max <0.
Finished to 1 μm. The gas exhaust system was constructed as follows. That is, a magnetic levitation type tandem turbo molecular pump was connected in series to a dry pump as an auxiliary pump. This exhaust system is an oil-free system, and the system is configured so that there is no impurity contamination in the vacuum container 101. Gas cylinder 10
6 to 5 N (purity 99.999%) of Ar gas was supplied to the gas purifier 105 (SAES GETS).
TERS S. p. A) PRF700IC-R64)
Was introduced into the vacuum vessel 101.

In this experiment, as a target material, an n-type FZ (100) 5 inch S having a P concentration of 1.8 × 10 ¹⁸ cm ^-3 was used.
Using an i-wafer, the substrate has a B concentration of 1.0 × 10 ¹⁵
A cm ^-3 p-type FZ (100) 4-inch wafer was used. In this experiment, a silicon film was formed on a silicon substrate, and the silicon film was subjected to crystal analysis by electron diffraction, resistance measurement by the four-point probe method, Ar by SIMS,
The C and O contents were measured and the reverse current density of the pn junction was measured.

In order to facilitate these measurements, the silicon substrate was patterned as shown in FIG. 2 and then used as a substrate. First, a thermal oxide film (SiO ₂ film) 202 having a film thickness of about 2000 Å was formed on a silicon substrate 201 by a resistance heating method (FIG. 2).

A resist 203 (OFPR: manufactured by Tokyo Ohka Co., Ltd.) having a thickness of 1 μm was formed on the SiO ₂ film 202 (FIG. 3). Then, the exposure, development and etching treatments which are usually used were carried out to remove the SiO ₂ film and the resist was peeled off to obtain a substrate for experiment (FIG. 4). The substrate thus obtained is washed by a usual method, and then the load lock chamber 1
Introduced in 15. When the pressure in the load lock chamber 115 is sufficiently reduced by an exhaust device (not shown), 1 × 1
Vacuum container 101 whose pressure is reduced to about 0 ^-10 Torr
The substrate 104 is carried in through the gate valve 116,
It was placed on the substrate electrode 105. The pressure inside the vacuum vessel 101 (background vacuum degree) when the substrate is heated to 300 ° C. by a heater (not shown) is 2.2 × 10 ⁻¹⁰ Torr.
Met.

Ar gas in the gas cylinder 106 was introduced into the vacuum container 101 via the gas purifier 105, and the pressure in the container was set to 10 mTorr. A power of 100 MHz and 30 W is applied from the high frequency power supply 106, a voltage of -30 V is applied from the direct current power supply 108, and a voltage of +15 V is applied from the direct current power supply 109 to generate plasma in the vacuum container 101, and the surface of the substrate is cleaned for 5 minutes. went. Then, the substrate temperature is in the range of 300 ° C to 500 ° C (3
00, 350, 400, 450 and 500 ° C.) to form a silicon film under the conditions shown in Table 1. By this film formation, a silicon film having a film thickness of about 1000 Å was obtained.

The obtained silicon film was evaluated by crystal analysis by electron diffraction, resistance measurement by the four-point probe method, Ar, C, O content measurement by SIMS, and reverse current density measurement of pn junction. . The obtained results are shown in Table 2 together with the background vacuum degree at the time of film formation.

From the experimental results shown in Table 2, the following was found. That is, (1) in the temperature range of 300 ° C. to 500 ° C., a single crystal film whose electron diffraction shows the Kikuchi line is obtained. (2) Regarding the resistivity showing the electrical characteristics and the reverse current density of the pn junction, which are the most important factors in the production of semiconductor devices, good values are obtained when the substrate temperature during film formation is 400 ° C. or higher. However, the substrate temperature is 4
If the temperature is lower than 00 ° C, good values cannot be obtained. (3)
When the substrate temperature is less than 400 ° C., the amount of oxygen and carbon mixed in the film is relatively stable, while the amount of argon mixed increases as the substrate temperature decreases. The adhesion coefficient of argon to the substrate is large when the substrate temperature is lower than 400 ° C. (4) It is considered that the deterioration of the resistivity and the reverse current density value of the pn junction at the substrate temperature of less than 400 ° C. is due to the incorporation of argon, which has a large adhesion coefficient to the substrate, into the film.

[0020]

[Experiment 2] In consideration of the results of Experiment 1 described above, a film forming method was studied in which the mixing of argon into the film could be suppressed even when forming a silicon film at a low temperature. When forming an epitaxial film, it is important to increase the energy of the atoms forming the epitaxial film so that migration on the substrate surface can be sufficiently taken. When the substrate temperature is high, atoms other than the atoms forming the epitaxial film (that is, atoms mixed into the epitaxial film) have a small adhesion coefficient to the substrate surface. Therefore, if the energy of the atoms forming the epitaxial film is increased. Migration will be sufficient.

On the other hand, when the substrate temperature is low, the sticking coefficient of the mixed atoms becomes large, and the mixed atoms adhering on the substrate hinder the migration of the atoms forming the epitaxial film, so that the energy of the atoms forming the epitaxial film is increased. A good epitaxial film cannot be formed only by increasing the value. The migration of atoms constituting the epitaxial film attached on the substrate is improved by irradiating the substrate with ions in plasma at appropriate energy (ion assist). In the film method, since it is assisted by argon ions and the atoms that make up the epitaxial film are simultaneously attached to the substrate, there is a possibility that the mixing of argon ions into the epitaxial film is promoted. An experiment on an assist method using argon ions was conducted.

In this experiment, the switch of the DC power supply 106 applied to the target electrode 102 is periodically turned on and off by using the sputtering apparatus of FIG. 1 used in the experiment 1.
Film formation was performed while changing F, and it was examined how the application of a DC voltage to the target electrode affects the film formation. Specifically, changes in the deposition rate of the deposited film with respect to time and changes in the amount of ions incident on the substrate with respect to time were measured. When the change in the deposition rate of the deposited film with respect to time was measured, n as a substrate with a B concentration of 1.0 × 10 ¹⁵ cm ⁻³ was used.
The type FZ (100) 5 inch Si wafer was used as it was, the switch of the DC power supply 108 was changed at intervals of 3 seconds, and the DC voltage applied to the target electrode 111 was changed to -200V, 0V and the substrate temperature. 30
Film formation was performed in the same manner as in Experiment 1 except that one point was set at 0 ° C. Table 3 shows the film forming conditions.

The deposition rate of the deposited film was measured by setting a film thickness meter near the Si substrate and calibrating the film thickness of the deposited film actually formed on the substrate. The obtained results are shown in FIG.

On the other hand, regarding the change in the amount of ions incident on the substrate, the substrate electrode 105 of the sputtering apparatus shown in FIG.
As an electrode, prepare an electrode with a 10 mm diameter hole in the center,
An ion collecting orifice of an ion detector PPM400 manufactured by Balzers, Inc. (ELA) was set in the hole, and the amount of ions incident on the substrate was measured by the ion detector. The film forming conditions here were the same as the above-described measurement of the change in the deposition rate of the deposited film except that the substrate was not placed on the substrate electrode. The obtained results are shown in FIG. The following has been found from FIGS. 5 and 6. That is, (1) by turning on and off the application of a voltage by the direct current power source connected to the high frequency power source side, it is possible to control the formation of the deposited film and the non-formation of the deposited film on the substrate. (2) The amount of ions incident on the substrate does not change due to ON-OFF control of voltage application by the DC power source connected to the high frequency power source side.

[0025]

[Experiment 3] In view of the results of Experiment 2 described above, when the voltage application by the DC power supply connected to the high frequency power supply side is ON-OFF controlled, the ion injection (ion assist) on the deposited film is continuously performed. At the same time, an epitaxial silicon film was formed by intermittently forming a deposited film on the substrate, and the characteristics of the obtained silicon film were measured.
In this experiment, a substrate similar to that used in Experiment 1 was prepared, and a film was formed using the sputtering apparatus shown in FIG.
The specific film forming condition is that the applied voltage of the DC power source 108 connected to the target electrode is -200 as in Experiment 2 described above.
The same operation as in Experiment 1 was performed except that V and 0 V were switched at 3 second intervals. For the obtained silicon film, crystal analysis by electron diffraction, resistance measurement by four-point probe method, S
The content measurement of Ar, C, O by IMS and the reverse current density measurement of the pn junction were performed. The results obtained are summarized in Table 4.

From the results shown in Table 4, the following was found. That is, (1) ON / OFF control of voltage application by a DC power source connected to the high frequency power source side allows ion injection (ion assist) on the deposited film to be continuously performed, and at the same time, the deposited film on the substrate. By forming the epitaxial silicon film which is intermittently formed, it is possible to suppress the mixing of argon into the silicon film to a low level even at a low temperature of less than 400 ° C. (2) From the comparison between the results shown in Table 2 and the results shown in Table 4, there is no great difference in the amount of carbon and oxygen mixed in the film formation at a low temperature of less than 400 ° C. Regarding the value of the pn junction reverse direction current, since Table 4 is much improved, the resistivity and the value of the pn junction reverse direction current are improved by suppressing the mixing of argon into the silicon film to a low level. To be done. (3) By applying ON / OFF control of voltage application by a DC power source connected to the high frequency power source side, ion injection (ion assist) is intermittently performed on the deposited film, and at the same time, the deposited film is formed on the substrate. According to the intermittent formation of the epitaxial silicon film, the deposited film having excellent electrical resistivity and reverse current density of the pn junction, which are the most important factors for semiconductor device fabrication, can be formed at a temperature of less than 400 ° C. It can be formed even at low temperatures.

[0027]

[Experiment 4] In view of the results of Experiment 3 described above, the relationship between the effective deposition film formation (deposition) time and the ion incidence (ion assist) time on the deposition film was examined.

[0028]

[Experiment 4-1] According to the method of Experiment 3, the time to turn on the voltage application by the DC power supply connected to the target electrode (deposition time) and the time to turn off the voltage (non-deposition time, time for only ion assist) The experiment was conducted for various times with 1: 1. In addition, the film forming conditions of this experiment are different except that the voltage application time by the DC power supply connected to the target electrode is variously changed, the film is formed until the film thickness of the deposited film is about 1000Å, and the substrate temperature is 300 ° C. The experimental conditions of Experiment 3 were the same. Here, the average deposition rate of the deposited film in the film forming step was about 1.3 Å / sec. Since the lattice constant of silicon crystal at 20 ° C is 5.43Å,
According to this average deposition rate, it is considered that about 1 atomic layer of silicon atoms is deposited per second. The obtained deposited film was evaluated by measuring the contents of argon, oxygen and carbon by SIMS. The results obtained are summarized in Table 5. Table 5
From the results shown in (1), when the film formation time is 4 seconds or less, that is, when the film formation is about 4 atomic layers or less, a preferable film having a low argon content is obtained. Was assumed to be N (Å / s) and the film formation time was T _d , and it was speculated that the relational expression T _d ≦ 5.43 / N might hold.

[0029]

[Experiment 4-2] In order to verify whether the relational expression obtained in Experiment 4-1 holds even when the deposition rates are different, film formation was performed while changing the deposition rate with the ion assist condition unchanged. Specifically, the same experiment as Experiment 4-1 was conducted by changing the value of the DC voltage applied to the target electrode to −100V and −300V. The film forming rates at this time were 0.9 Å / s and 1.8 Å / s, respectively. The obtained deposited film was evaluated by measuring the contents of argon, oxygen and carbon by SIMS. The obtained results are shown in Tables 6 and 7.
Shown in. According to Table 6, when the film forming rate is 0.9 Å / s, a preferable film having a small argon content was obtained when the film forming time was 6 seconds or less. In the case of 1.8 Å / s, a preferable film was obtained when the film formation time was 3 seconds or less. Therefore, the relational expression obtained in Experiment 4-1 was different when the film formation rate was different. It was confirmed that

[0030]

[Experiment 4-3] The time for turning on the voltage application by the DC power source connected to the target electrode (deposition time) was 3 seconds, and the time for performing only ion assist without film formation (non-deposition time) was 1 The film formation was performed by changing the time from 6 seconds to 6 seconds. Other film forming conditions were the same as in Experiment 4-1. The obtained deposited film was evaluated by measuring the contents of argon, oxygen and carbon by SIMS. The results obtained are summarized in Table 8.
The results shown in Table 8 show that when the ion assist time is set to 3 seconds or more, a preferable film having a low argon content can be obtained. Further, in this experiment, since the film formation time was set to 3 seconds, the ion assist time (a time during which only film formation is not performed and only ion assist is performed) is T _a , and the film formation time is T _d. , T _d ≦ T _a . It was also confirmed that this relational expression holds even when the value of the DC voltage applied to the target electrode is changed and the deposition rate of the film is changed.

[0031]

[Experiment 5] From the above experiment, in order to form an epitaxial film having good film characteristics at a low temperature, the film formation process and the non-film formation process (process only with ion assist) are alternately performed in a vacuum container at a certain cycle. It was understood that it was important to do. Therefore, in this experiment, in order to perform the film formation process and the non-film formation (ion assist) process with good controllability and form the epitaxial film, the frequency range of the high frequency power supply for generating plasma discharge should be set to any range. I examined whether it is preferable. The specific items to be examined are the following two points.
That is, (1) a high frequency in which the self-bias of the target electrode becomes small so that the film formation process and the non-film formation process (process only with ion assist) can be controlled depending on whether or not a DC voltage connected to the target electrode is applied. The power supply frequency and (2) the high frequency power supply frequency at which the energy dispersion value of the ions incident on the substrate for forming the epitaxial film becomes small.

In the experiment of the examination item (1), an apparatus provided with a voltmeter for monitoring the DC voltage of the self-bias induced on the target was used instead of the DC power source 108 of the sputtering apparatus shown in FIG. An n-type FZ (100) 5 inch Si wafer having a B concentration of 1.0 × 10 ¹⁵ cm ⁻³ was used as a substrate, and argon gas was used as a sputtering gas. A specific experiment is performed by measuring the self-bias of the target electrode with a voltmeter that monitors the DC voltage by forming a film while changing the frequencies of the signal generator and the amplifier that form the high frequency power supply 106 from 10 MHz to 400 MHz. It was Table 9 shows the film forming conditions.

FIG. 7 shows the relationship between the discharge frequency and the target electrode self-bias obtained in this experiment. From FIG. 7, when the discharge frequency is in the range of 50 MHz to 300 MHz, the self bias of the target electrode is | 25 | V.
It is understood that the following low values can be controlled. In this experiment, stable discharge could not be obtained when a high frequency of more than 300 MHz was used.

In the experiment of examination item (2), an electrode having a hole with a diameter of 10 mm was prepared in the center as the substrate electrode 105 of the sputtering apparatus shown in FIG. 1, and the hole was manufactured by Balzers (ELA). Ion detector P
An experiment was conducted in the same manner as the film forming condition of the examination item (1) except that the ion collecting orifice of PM400 was set and the ion energy could be measured by the ion detector. Table 10 shows the measured ion energy as the half-width of energy dispersion and together with the discharge frequency. From Table 10, in the frequency range of 50 MHz to 300 MHz, the energy dispersion value width of ions is 10 eV.
It is understood that the following small values are obtained. When forming an epitaxial film having high quality film characteristics, if the incident energy of the ions in the plasma to the surface of the deposited film is large, the ion damage to the film becomes large, which is not preferable. When the ion energy dispersion value width is small, the amount of relatively high-energy ions decreases, so the controllability is increased and the ion damage to the deposited film is decreased, and the film characteristics can be improved. It is desirable to set the frequency within the range of to 300 MHz.

The deposited film forming method by the bias sputtering method of the present invention obtained through the above Experiments 1 to 5 has the following constitution. That is, plasma is generated by using high frequency energy between a target electrode that holds a target material that is placed in a vacuum container and a substrate electrode that holds a substrate for forming a deposited film that is placed facing the target electrode. And a target material is sputtered, and a bias voltage is applied to at least one of the target electrode and the substrate electrode to form a deposited film composed of sputtered atoms on the substrate by a bias sputtering method. In the deposited film forming method, the step of irradiating the substrate with ions in the plasma, sputtering the target material to form a deposited film on the substrate, and performing the sputtering of the target material on the substrate The feature is that the process of irradiating ions in plasma is alternately repeated. A deposited film forming process according to the bias sputtering method with.

According to the deposited film forming method by the bias sputtering method of the present invention, the deposited film forming step on the substrate and the ion irradiating step to the atoms constituting the target material reaching the substrate or the deposited film are performed. By separately performing the above, it is possible to suppress mixing of sputtering gas such as Ar gas and Ne gas into the deposited film. In addition to this, irradiation of ions to the atoms constituting the target material reaching the substrate or the deposited film promotes the migration of atoms, so that high-quality epitaxial with excellent step coverage at a low temperature of less than 400 ° C. A deposited film can be formed. Further, since it becomes possible to form an epitaxial film at a low temperature of less than 400 ° C., when forming a laminated structure of deposited films, the interface state between the deposited films forming the laminated structure should be extremely favorable. The desired dopant profile can be achieved.

In the present invention, the high frequency voltage applied to the target electrode has a frequency of 50 MHz in order to switch between the film forming process and the non-film forming process (ion assist only) without stopping plasma discharge and with good controllability. ~ 30
The range of 0 MHz is preferable.

In the present invention, the steps of irradiating the substrate with ions in plasma and sputtering the target material to form a deposited film on the substrate, and the steps of sputtering the target material without exposing the substrate to the ions in the plasma Switching between the irradiation step and the irradiation step can be performed, for example, by ON / OFF controlling the switch of the DC power source connected to the target electrode, but it can also be performed by changing the value of the DC voltage to be applied.

In addition to the AC voltage, the DC voltage applied to the target electrode generally requires a voltage higher than -40V on the negative side in the case of a silicon film in order to cause sputtering. The DC voltage applied to the target electrode is preferably in the range of -100V to -500V.

The timing of switching between the film formation process and the non-film formation process (process only for ion assist) depends on the type and deposition rate of the deposited film to be formed. It is desirable to satisfy the formula. T _d ≦ 5.43 / N, and T _d ≦ T _a, where N: deposition rate (Å / s), T _d : film formation time,
T _a : Ion assist time (time when only ion assist is performed without forming a film).

When forming a film, the gas for sputtering introduced into the vacuum chamber is Ar gas, He,
Inert gases such as Ne, Xe and Rn can be mentioned. It is desirable to use a high-purity gas, but it is also possible to purify and use the gas using a gas purifier.

The target to be used can be appropriately selected according to the film to be formed, but for example, single crystal Si or polycrystalline S
A semiconductor such as i or Ge, or a metal such as Al or Mo can be used. Further, as a substrate for film formation,
Although a single crystal or polycrystal substrate can be used, it is desirable to use a single crystal substrate for forming an epitaxial film.

The substrate temperature during film formation is 250
The temperature can be appropriately selected within a range of up to 500 ° C, but the effect of the present invention becomes remarkable at a low temperature of 250 to 400 ° C. The pressure in the vacuum container at the time of film formation may be maintained within a range where discharge occurs, and in a preferred embodiment, 1 mTorr to
The range is 50 mTorr.

As a sputtering apparatus used for embodying the deposited film forming method of the present invention, for example, the bias sputtering apparatus shown in FIG. 1 can be cited. Other than this, any bias sputtering apparatus of the type that applies a DC voltage to the target electrode can be appropriately used.

In the present invention, the switching between the film forming process and the non-film forming process can be controlled by periodically changing the voltage value of the DC power source connected to the target electrode. Besides electrical control, electrical control can be used. Examples of electrical control include a method of generating a pulse signal using a computer and inputting the pulse signal to a DC power source via an amplifier. It goes without saying that the present invention is applicable to not only direct sputtering in which a sputtered target material is directly deposited on a substrate but also reactive sputtering in which a sputtered target material is reacted with a gas to be deposited.

[0046]

The present invention will be described in detail below with reference to specific examples, but the present invention is not limited to these examples.

[0047]

Example 1 The bipolar transistor shown in FIG. 9 was prepared according to the following procedure (see FIGS. 8 and 9).

(1) n on a p-type Si substrate having a resistivity of 4 Ωcm
^{The +} type buried region 52 was formed by a normal diffusion method. (2) Si substrate 51 using a CVD method that is usually used
N ⁻ -type region 5 having a film thickness of 1.2 μm on buried region 52 of
Formed 3. (3) The n ⁺ type region 54 is formed by a commonly used diffusion method. (4) After masking the n ⁻ type region 53, a groove for forming the element isolation region 55 is formed by etching by a commonly used RIE (reactive ion etching) method. Then, As ions were implanted into the bottom of the groove by an ordinary ion implantation method at a dose of 2 × 10 ¹³ cm ⁻² to form a channel stop region 56. After removing the masking, a SiO ₂ film for forming the element isolation region 55 is deposited to a film thickness of 2000 Å by a normal CVD method,
The element isolation region 55 was formed.

(5) Boron (B) as a p-type impurity at a dose of 8 × 10 ¹³ cm ^-2 by a normal ion implantation method through the SiO ₂ film for forming the element isolation region and the n ^- type region 5
3 to form a base region 57. Then, by a commonly used RIE method, a contact hole for forming the emitter 58 is formed, the base region 57 made of p ⁺ -type single crystal is exposed, and a substrate 104 for carrying out the deposited film forming method of the present invention is formed. did. (6) The substrate 104 thus obtained was washed by a usual method and then introduced into the load lock chamber 115 of the sputtering apparatus shown in FIG. Here target 1
N-type FZ with a P concentration of 1.8 × 10 ¹⁸ cm ^-3
A (100) 5 inch Si wafer was used. When the pressure in the load lock chamber 115 is sufficiently reduced by an exhaust device (not shown), the substrate 104 is loaded into the vacuum container 101, which has been reduced in pressure to about 1 × 10 ⁻¹⁰ Torr, through the gate valve 116, and It was placed on the electrode 105.
The pressure inside the vacuum vessel 101 (background vacuum degree) when the substrate is heated to 300 ° C. by a heater (not shown) is
It was 2.2 × 10 ⁻¹⁰ Torr. Gas cylinder 106
Ar (purity 99.999%) gas in the gas purifier 10
It was introduced into the vacuum container 101 through 5 and the pressure in the container was set to 10 mTorr. 100 from the high frequency power supply 106
DC power supply 10 while inputting power of MHz and 30W
A voltage of −30 V from 8 and a voltage of +15 V from a DC power source 109 were applied to generate plasma in the vacuum container 101, and the surface of the substrate was cleaned for 5 minutes. Then, a pulse generated by a microcomputer (not shown) was input to the DC power supply 108 via an amplifier to form a deposited film while controlling the voltage applied to the DC power supply 108. Specific film forming conditions are as shown in Table 11.

By such film formation, the film thickness is about 3000Å
The epitaxial silicon film 58 of was formed. The obtained silicon film is patterned to form a silicon emitter 58.
Was formed.

(7) After forming an insulating film 59 of SiO _{2 having a} film thickness of 0.5 μm by a normal plasma CVD method, a contact hole for forming a wiring electrode is formed and an aluminum film is deposited by a normal sputtering method. After letting
By patterning, the electrode wiring 60 was obtained. (8) An insulating film 61 made of SiO ₂ was deposited using a plasma CVD method, and an external extraction port was processed using a normal semiconductor process. A bipolar transistor was formed through these steps. In the bipolar transistor formed in this embodiment, the emitter 58 is formed by 300 times.
Since the diffusion of the dopant in the base region or the emitter region is suppressed to a very low level by performing the process at a low temperature of ℃ and the low temperature process in the subsequent process, h _fe shows a large and stable characteristic.

[0052]

[Embodiment 2] In this embodiment, a P type (B concentration: 1.
A 0 × 10 ¹⁵ doped silicon (100) FZ wafer was used, an epitaxial silicon film having a film thickness of 1000 Å was formed on the wafer, and the characteristics of the film were examined. In this embodiment, the wafer is used as the substrate,
A silicon film was formed in the same manner as in Example 1 except that the substrate temperature was 250 ° C. and the film thickness of the silicon film was 1000 Å.

With respect to the obtained silicon film, light etching (Wright) which is etching for revealing crystal defects is performed.
Etching method was used to observe the density of etch pits and the cross-sectional TEM was used to observe the defect density of stacking faults and dislocation defects. As a result, both the etch pit density and the defect density were 1.0 × 10 ^{7 to} 1.0 × 10 ⁸ pieces / cm ² , and it was confirmed that they had excellent crystallinity. Further, the van der Pauw method was used to measure the mobility of electrons and holes, and it was confirmed that these values were extremely close to the values of bulk silicon at room temperature. From this, it is understood that the deposited film forming method of the present invention can be applied to the production of various semiconductor devices.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

[Table 3]

[0057]

[Table 4]

[0058]

[Table 5]

[0059]

[Table 6]

[0060]

[Table 7]

[0061]

[Table 8]

[0062]

[Table 9]

[0063]

[Table 10]

[0064]

[Table 11]

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a bias sputtering apparatus that can be adopted to embody a deposited film forming method of the present invention.

FIG. 2 is a schematic diagram for explaining a substrate manufacturing process.

FIG. 3 is a schematic diagram for explaining a substrate manufacturing process.

FIG. 4 is a schematic diagram for explaining a substrate manufacturing process.

FIG. 5 is a graph showing the relationship between film formation time and deposition rate.

FIG. 6 is a graph showing the relationship between film formation time and substrate incident ion amount.

FIG. 7 is a graph showing the relationship between the discharge frequency and the bias potential induced in the target electrode.

FIG. 8 is a schematic diagram for explaining a manufacturing process of a bipolar transistor.

FIG. 9 is a schematic diagram for explaining a manufacturing process of a bipolar transistor.

FIG. 10 is a schematic diagram showing an example of a conventional bias sputtering apparatus.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A 63-26361 (JP, A) JP-A 2-138456 (JP, A) JP-A 5-263227 (JP, A) JP-A 62- 213129 (JP, A) JP 63-114965 (JP, A) JP 5-275358 (JP, A) JP-B 3-59986 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 14/00-14/58 H01L 21/203

Claims (8)

(57) [Claims] 1. High frequency energy is applied between a target electrode that holds a target material that is placed in a vacuum container and a substrate electrode that holds a substrate for forming a deposited film that is placed facing the target electrode. A bias that causes plasma to be generated using the target material and sputters the target material and applies a bias voltage to at least one of the target electrode and the substrate electrode to form a deposited film composed of atoms sputtered on the substrate. In the method for forming a deposited film by the sputtering method, the high frequency
Energy in the frequency range of 50MHz to 300MHz
It is supplied from a high frequency power source and connected to the target electrode.
A step of irradiating the substrate with ions in the plasma and performing sputtering of the target material to form a deposited film on the substrate by ON-OFF control of a direct current power supply, and without performing sputtering of the target material. Turn off the irradiating ions in said plasma to the substrate
A method of forming a deposited film by a bias sputtering method, characterized in that the method is repeated alternately. 2. The step of forming the deposited film and the step of irradiating the substrate with ions are performed by inputting a pulse signal generated by using a computer to a DC power source connected to the target electrode. The method for forming a deposited film by the bias sputtering method according to claim 1 , which is controlled. 3. The deposited film forming method according to claim 1 , wherein the DC voltage applied to the target electrode from the DC power source is in the range of −100V to −500V. 4. The inside of the vacuum container is 1 mTorr to 50 mT.
The method for forming a deposited film by the bias sputtering method according to claim 1, wherein the sputtering is performed while controlling the pressure within a range of orr. 5. The method for forming a deposited film by the bias sputtering method according to claim 1, wherein sputtering is performed while controlling the substrate in the range of 250 to 500 ° C. 6. The method for forming a deposited film by the bias sputtering method according to claim 5 , wherein the substrate is controlled to a temperature in the range of 250 to 350 ° C. for sputtering. 7. A deposited film forming method by a bias sputtering method according to claim 1, wherein a silicon film is formed. 8. The step of forming the deposited film and the step of irradiating the substrate with ions include N, a deposition rate of the deposited film, T _d , a time of forming the deposited film, and a time of irradiating the substrate with ions. Where T _a is the general formula T _d ≦ 5.43 / N, and T _d ≦ T _a
The deposited film forming method by the bias sputtering method according to claim 7 , wherein