JP2005038937A - Method for manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To implant ions shallowly with high concentration by restraining the loss of the ions when the ions are implanted in a substrate. <P>SOLUTION: In an ion implanter, a natural oxide film formed on the substrate is eliminated first. After that in the ion implanter, ion implantation in the substrate is performed continuously. As a more concrete method of one, etching gas is supplied to the plasma room of the ion implanter and made a plasma, the substrate is irradiated with the plasma, and the natural oxide film is eliminated. After that, halogen gas is supplied to the plasma room of the same ion implanter continuously and made a plasma, and the inside of a guide tube is filled with the plasma. After that, ions which are to be implanted as dopant are supplied in the guide tube, and irradiation of the ions is performed on the substrate from the guide tube. During this period, the inside of the ion implanter is maintained at high vacuum. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ion implantation method and an ion implantation apparatus. Furthermore, specifically, it is suitable as an ion implantation method and an ion implantation apparatus used when an impurity is implanted into a substrate.
[0002]
[Prior art]
In recent years, with the miniaturization and high integration of semiconductor devices, pn junctions are required to have a shallow junction depth and a low resistance. That is, the pn junction layer is shallow and it is required to implant impurities at a high concentration.
[0003]
When forming a pn junction in a semiconductor substrate, Group III and Group V impurities are introduced into the semiconductor substrate. In general, an ion implantation method is used as a method for introducing the impurity. In the ion implantation method, generally, a permeable oxide film having a film thickness of about several nanometers is formed on a substrate, and ions are implanted as impurities through the permeable oxide film.
[0004]
FIG. 6 is a graph showing the relationship between the concentration of impurities implanted into the semiconductor substrate and the depth when ions are implanted into the semiconductor substrate by the ion implantation method. In FIG. 6, the vertical axis represents the impurity concentration (atoms / cc) in the semiconductor substrate, and the horizontal axis represents the depth (nm) from the surface of the semiconductor substrate.
[0005]
As shown in FIG. 6, when ions are implanted by ion implantation, the impurity concentration is the largest on the substrate surface. That is, most of the implanted ions are captured near the surface of the substrate. Therefore, as described above, when ions are implanted using a permeable oxide film in ion implantation, if the permeable oxide film is thick, most of the implanted ions are taken into the permeable oxide film. For this reason, a sufficient amount of ions may not be implanted into the semiconductor substrate. Therefore, in order to implant a sufficient amount of ions, it is necessary to sufficiently reduce the thickness of the permeable oxide film.
[0006]
Referring to FIG. 6, for example, in order to suppress the loss of impurities to 10% or less, the thickness of the permeable oxide film needs to be about 0.3 nm or less. However, it is very difficult to form a thin film having a thickness of 0.3 nm with the current thin film forming technology. When based on the current thin film formation technology, the thickness of the thin film is limited to about 1.5 nm. However, when ion implantation is performed at this thickness, the loss of impurities reaches 80%.
[0007]
Here, in order to ensure a sufficient impurity concentration, it is conceivable to increase the ion implantation amount or increase the implantation energy. However, this increases the junction depth, thereby achieving a shallow junction. I can't.
[0008]
Therefore, in order to ensure a sufficient impurity concentration, particularly in response to miniaturized semiconductor devices, it may be considered that ions are implanted without forming a permeable oxide film and with the surface of the semiconductor substrate exposed. Yes. In this case, before implanting ions, an excess film is removed from the surface of the semiconductor substrate in advance by wet or dry etching. Thereafter, ions are implanted while the surface of the semiconductor substrate is exposed. Here, if no excessive film is deposited on the surface of the semiconductor substrate, the implanted ions are surely taken into the semiconductor substrate, so that the loss of impurities is prevented and the impurity concentration is sufficiently increased. Can be high.
[0009]
[Problems to be solved by the invention]
However, even if the etching is performed immediately before the ion implantation as described above, the semiconductor substrate surface is exposed to the atmosphere due to the transportation of the semiconductor substrate or the like in the process from the completion of the etching to the ion implantation. Since the exposed semiconductor substrate has an active surface, when exposed to the atmosphere, it easily reacts with moisture in the atmosphere, and as a result, a natural oxide film is deposited on the surface of the semiconductor substrate.
[0010]
The thickness of the natural oxide film deposited in this manner is usually about 0.5 nm to 1.0 nm, although it varies depending on the exposure time to the atmosphere and the humidity. Therefore, even if a step of removing an excess film on the semiconductor substrate is provided before the ion implantation, if a natural oxide film is deposited, as shown in FIG. In other words, the loss of impurities increases.
[0011]
Accordingly, the present invention solves the above-described problems and provides an ion implantation method for implanting impurities at a high concentration in a semiconductor substrate, and an ion implantation apparatus used therefor.
[0012]
[Means for Solving the Problems]
An ion implantation method according to the present invention includes a natural oxide film removing step of removing a natural oxide film on a substrate in an ion implantation apparatus,
In the ion implantation apparatus, an ion implantation step of implanting ions into the substrate;
Is provided.
[0013]
The ion implantation apparatus according to the present invention is an ion implantation apparatus for implanting ions into a substrate,
A plasma chamber for converting the supplied gas into plasma;
An etching gas supply source for supplying an etching gas for removing a natural oxide film on the substrate into the plasma chamber;
A halogen gas supply source for supplying halogen gas to the plasma chamber;
An implantation ion source for supplying ions to be implanted into the substrate;
Connected to the plasma chamber and the ion supply source, into which plasma gas from the plasma chamber or ions from the ion supply source are introduced, and the introduced gas or the ions are introduced into the substrate A guide tube that irradiates
Is provided.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is omitted or simplified.
[0015]
Embodiment.
FIG. 1 is a schematic diagram for explaining an ion implantation apparatus 100 used in the embodiment of the present invention.
The ion implantation apparatus 100 is an apparatus for implanting ions as impurities into the substrate 200.
[0016]
As shown in FIG. 1, the ion implantation apparatus 100 is provided with an ion supply source 2 for supplying impurities to be implanted into the substrate. The ions supplied from the ion supply source 2 may be selected appropriately depending on the p-type or n-type case. The ion supply source 2 is connected to the guide tube 4.
[0017]
A plasma chamber 6 is connected to the guide tube 4 via a connecting tube 8. A filament 10 is provided in the plasma chamber 6. Further, one end of a supply pipe 12 is connected to the plasma chamber 6. The other end of the supply pipe 12 is divided into two directions. One side is provided with a CF ₄ supply source 14 for supplying CF ₄ as an etching gas in the plasma chamber 6 via a valve 16. In the plasma chamber 6, an Ar gas supply source 18 for supplying Ar gas is provided via a valve 20. A bias voltage 22 is applied between the guide tube 4 and the plasma chamber 6.
[0018]
A plate 24 is provided opposite to the side of the guide tube 4 opposite to the ion supply source 2 side. A substrate 200 is mounted on the plate 24 at the time of ion implantation. The plate 24 has a disk shape having a diameter larger than that of the substrate 200, and is capable of rotating around the center of the circle and reciprocating in the direction perpendicular to the disk. A bias voltage 26 is applied between the guide tube 4 and the plate 24. Furthermore, an ion current measuring ammeter 28 is connected to the plate 24.
[0019]
The ion implantation apparatus 100 configured as described above is similar to the ion implantation apparatus 100 conventionally used. However, a CF ₄ gas supply source 14 and an Ar gas supply source 18 are connected to the plasma chamber 6 of the ion implantation apparatus 100 in this embodiment via a supply pipe 12 and valves 16 and 20. Yes.
[0020]
As described above, in the ion implantation apparatus 100, the bias voltage 26 is applied between the guide tube 4 and the plate 24. Further, the bias voltage 26 can be changed to a desired magnitude as required. By this bias voltage 26, ions filled in the guide tube 4, CF ₄ , or the like are accelerated with a desired energy and irradiated onto the substrate 200 on the plate 24. This makes it possible to adjust the impurity implantation depth or the etching rate.
[0021]
In the plasma chamber 6, thermoelectrons generated by the filament 10 collide with gas molecules of the gas supplied into the plasma processing chamber 6. As a result, the gas molecules supplied to the plasma chamber 6 are electrically decomposed and ionized, and eventually enter a plasma state. In this way, the supplied gas is turned into plasma in the plasma chamber 6.
[0022]
Further, a CF ₄ supply source 14 and an Ar gas supply source 18 are connected to the plasma chamber 6 through a supply pipe 12 so that gas can be supplied. Further, the supply of CF ₄ gas and Ar gas can be switched by opening and closing valves 16 and 20 provided in the supply pipe 12.
[0023]
Further, the gas converted into plasma in the plasma chamber 6 is guided to the guide tube 4 side by a bias voltage 22 supplied between the plasma chamber 6 and the guide tube 4.
[0024]
FIG. 2 is a schematic cross-sectional view for explaining a substrate 200 into which ions are implanted by the ion implantation apparatus 100 in this embodiment.
In FIG. 2, a substrate 200 represents a part of a substrate for forming a CMOS transistor.
[0025]
As shown in FIG. 2, an STI (Shallow Trench Isolation) 32 is formed on the Si substrate 30. A gate electrode 36 is formed on the Si substrate 30 in a region separated by the STI 32 via a gate insulating film 34. In this embodiment, ions as impurities are implanted into a portion of the Si substrate 30 between the gate electrode 36 and the STI 32. A resist mask 40 is formed on the surface of the gate electrode 36 and the surface of the STI 32 in order to prevent damage due to ion implantation. A natural oxide film 42 is deposited on the ion implantation region 38 of the Si substrate 30.
[0026]
In the substrate 200, a portion of the gate insulating film 34 sandwiched between the gate electrode 36 and the Si substrate 30 is left, and an extra insulating film formed in another portion on the Si substrate 30 is dry-typed before ion implantation. Alternatively, it is removed once by wet etching. Therefore, a part of the surface of the Si substrate 30 is exposed immediately after the etching. However, the substrate 200 is exposed to the atmosphere when it is transported to a predetermined processing apparatus or the like used in each manufacturing process. For this reason, the substrate 200 before being attached to the ion implantation apparatus 100 is in a state where the natural oxide film 42 is deposited on the exposed portion of the Si substrate 30, that is, on the ion implantation region 38.
[0027]
In this embodiment, the substrate 200 with the natural oxide film 42 deposited as shown in FIG. 2 is processed in the ion implantation apparatus 100.
FIG. 3 is a flowchart for explaining an ion implantation method according to the embodiment of the present invention. 4 and 5 are schematic cross-sectional views for explaining the state of the substrate 200 in the process of ion implantation.
Hereinafter, the ion implantation method according to the embodiment of the present invention will be specifically described with reference to FIGS.
[0028]
First, the substrate 200 in the state shown in FIG. 2 is mounted on the plate 24 in the ion implantation apparatus 100 (step S2). Here, a transfer device (not shown) provided in the ion implantation apparatus 100 may be used. At this time, the entire interior of the ion implantation apparatus 100 is maintained at a high vacuum. Further, this high vacuum state is maintained until ion implantation is completed.
[0029]
Next, supply of CF ₄ gas into the plasma chamber 6 is started (step S4). Here, supplies by opening the valve 16, the CF ₄ gas supply source 14, through the supply pipe 12, into the plasma chamber 6, CF ₄ gas. At this time, the flow rate of the CF ₄ gas is 3 sccm to 5 sccm. When CF ₄ gas is supplied, in the plasma chamber 6, the heat electrons emitted from the filament 10, collide with the gas molecules of the supplied CF ₄ gas. As a result, the CF ₄ gas is electrically decomposed and ionized, and eventually enters a plasma state.
[0030]
The CF ₄ gas in a plasma state is guided and confined in the guide tube 4 through the connection tube 8 by the bias voltage 22 applied between the plasma chamber 6 and the guide tube 4.
[0031]
From this state, as shown in FIG. 4, the substrate 200 is irradiated with CF ₄ gas (step S6). The CF ₄ gas confined in the guide tube 4 is accelerated in the direction of the arrow 44 by the bias voltage 26 of about 100 V applied between the guide tube 4 and the plate 24, and is irradiated on the substrate 200. The natural oxide film 42 is etched. The substrate 200 and the plate 24 are arranged concentrically. During the CF ₄ gas irradiation, the plate 24 rotates and reciprocates so that the substrate 200 is uniformly irradiated with the CF ₄ gas. .
[0032]
During the CF ₄ gas irradiation, the ion current is measured by the ion current measuring ammeter 28. In this embodiment, the condition is that an ion current of about 200 mA can be acquired. Further, the bias voltage 26 applied as described above is suppressed to about 100 V in consideration of damage to the Si substrate 30. Therefore, the power that contributes to etching is 1 W / cm ² . Monitoring is performed so as to sufficiently remove the natural oxide film 42 having a thickness of about 1 nm from this power, etching time, and supply amount of CF ₄ gas.
[0033]
When the removal of the natural oxide film 42 is completed, the valve 16 is then closed, and the introduction of CF ₄ gas is stopped (step S8). Subsequently, the electrodes of the bias voltages 22 and 26 of the ion implantation apparatus 100 are changed (step S10). Here, as shown in FIG. 1, the guide tube 4 side is changed from the state in which both the bias voltages 22 and 26 are positive to the negative in the guide tube 4 side.
[0034]
Next, introduction of Ar gas is started (step S12). Here, Ar gas is supplied from the Ar gas supply source 18 into the plasma chamber 6 by opening the valve 20. The supplied Ar gas is turned into plasma by thermionic electrons in the same manner as described above, and electrons in the plasma are introduced into the guide tube 4 by the bias voltage 22. Here, the flow rate of Ar is 2 to 3 sccm, and the bias voltage 22 is 5 to 10V.
[0035]
Next, as shown in FIG. 5, supply of ions is started as an impurity to be implanted into the substrate 200 (step S14). Here, ions are supplied from the ion supply source 2 into the guide tube 4. The ions supplied into the guide tube 4 and the electrons introduced into the guide tube 4 from the plasma chamber 6 and accelerated by the bias voltage 26 are injected into the substrate 200 (step S16). As a result, the source / drain 46 is formed on the substrate 200. At the same time, the injected electrons neutralize the positive charge on the substrate 200 caused by ion implantation.
[0036]
As described above, according to this embodiment, when ion implantation for forming a shallow pn junction is performed, first, the natural oxide film 42 on the substrate 200 is removed in the ion implantation processing apparatus 100. As it is, ions can be implanted in the ion implantation apparatus 100 without moving the substrate 200. Further, the inside of the ion implantation apparatus 100 is maintained at a high vacuum. Therefore, even after the natural oxide film 42 of the substrate 200 is removed and the surface of the substrate 200 is exposed, the natural oxide film can be prevented from being deposited before the ion implantation. Therefore, impurity loss due to the deposition of the natural oxide film 42 can be suppressed during ion implantation for forming the pn junction. Thereby, ion implantation can be performed shallowly and at a high concentration, and a shallow junction and a low-resistance pn junction can be realized.
[0037]
Further, according to this embodiment, an etching gas such as CF ₄ can be supplied to a conventional ion implantation apparatus, and the natural oxide film can be removed only by changing the bias voltage. Therefore, a shallow junction and a low resistance pn junction can be realized without preparing a special device, and the productivity of the semiconductor device can be improved.
[0038]
In this embodiment, ion implantation for forming a pn junction has been described. However, the present invention is not limited to this, and can also be applied to the case where ions are implanted into another film in which a natural oxide film or the like is formed in a semiconductor device manufacturing process or the like. Also in this case, it is possible to perform ion implantation at a high concentration while suppressing loss of ions to be implanted.
[0039]
In this embodiment, the CF ₄ gas supply source 14 and the Ar gas supply source 18 are connected to the plasma chamber 6 through the supply pipe 12, and the valves 16 and 20 are opened / closed to open and close each gas. The case of controlling the supply has been described. However, in the present invention, the ion implantation apparatus is not limited to such a structure, and an etching gas such as CF ₄ and a halogen gas such as Ar can be switched and introduced into the plasma chamber 6. Other structures may be used.
[0040]
In this embodiment, the case where CF ₄ is used as the etching gas has been described. However, the present invention is not limited to this, and any other gas may be used as long as it is an etching gas that can remove the natural oxide film 42, such as CFH ₃ and CH ₂ F ₂ .
[0041]
In this embodiment, the case where CF ₄ gas is converted into plasma using the plasma chamber 6 of the existing ion implantation apparatus and the natural oxide film 42 is removed by plasma etching has been described. However, the method for removing the natural oxide film in the present invention is not limited to this method, and other etching gas or solution is supplied to the ion implantation apparatus, and the removal of the natural oxide film is performed in the same apparatus. It is also possible to perform ion implantation. Even if the removal method of the natural oxide film 42 is different, the deposition of the natural oxide film after the removal of the natural oxide film 42 can be prevented if it can be removed within the same ion implantation apparatus. It is shallow and ion implantation can be performed at a high concentration.
[0042]
In the embodiment, the case where Ar gas is turned into plasma and ions as impurities are implanted has been described. However, the present invention is not limited to this, and other halogen gas may be used instead of Ar gas.
[0043]
In this embodiment, the ampere meter 8 for measuring the ionic current is monitored to confirm that the natural oxide film 42 is completely removed from the etching power, CF ₄ gas injection amount, and the like. After confirmation, the case where switching from the removal of the natural oxide film to the ion implantation is performed by opening and closing the valves 16 and 20 has been described. However, the present invention is not limited to this. For example, a controller for measuring the removal state of the natural oxide film 42 from the measured ion current, bias voltage, etc., and automatically switching it is provided. There may be. In addition, a sensor that directly measures the film thickness or the like of the natural oxide film 42 may be provided on the substrate 200, and the film thickness may be observed and switched.
[0044]
In the present invention, the detailed structure of the ion implantation apparatus, the flow rate of gas used, the voltage, etc. are not limited to those described in this embodiment, and the object of the present invention can be achieved. If it is.
[0045]
In this embodiment, for example, the CF ₄ supply source 14 corresponds to the etching gas supply source of the present invention, and the Ar gas supply source 18 corresponds to the halogen gas supply source.
[0046]
Further, for example, in the embodiment, the natural oxide film removing process in the present invention is executed by executing steps S4 to S6, and the ion implantation process is executed by executing steps S12 to S16. Further, for example, the etching gas supply process of the present invention is executed by executing step S4, and the etching gas irradiation process is executed by executing step S6. Further, for example, the halogen gas supply process is executed by executing step S12, the ion supply process is executed by executing step S14, and the ion irradiation process is executed by executing step S16. .
[0047]
【The invention's effect】
As described above, according to the present invention, the natural oxide film can be removed in the ion implantation apparatus, and then ion implantation can be performed in the same apparatus. Therefore, it is possible to suppress the natural oxide film from being deposited on the substrate before the ion implantation, and it is possible to suppress the loss of impurities due to the natural oxide film during the ion implantation. Accordingly, the impurity can be implanted shallowly and at a high concentration, and the junction can be shallowed and the resistance can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view for explaining an ion implantation apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view for explaining the substrate in a state immediately before the ions are attached to the implantation apparatus in the embodiment of the present invention.
FIG. 3 is a flowchart for illustrating an ion implantation method according to the embodiment of the present invention.
FIG. 4 is a schematic cross-sectional view for explaining the state of the substrate in the ion implantation process in the embodiment of the present invention.
FIG. 5 is a schematic sectional view for explaining the state of the substrate in the ion implantation process in the embodiment of the present invention.
FIG. 6 is a graph showing the relationship between the concentration of impurities implanted into a semiconductor substrate and the depth when ions are implanted into the semiconductor substrate by an ion implantation method;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 Ion implantation apparatus 200 Substrate 2 Ion supply source 4 Guide tube 6 Plasma chamber 8 Connection tube 10 Filament 12 Supply tube 14 CF ₄ Gas supply source 16 Valve 18 Ar gas supply source 20 Valve 22 Bias voltage 24 Plate 26 Bias voltage 28 Ion current Ammeter for measurement 30 Si substrate 32 STI
34 Gate insulating film 36 Gate electrode 38 Ion implantation region 40 Resist mask 42 Natural oxide film 46 Source / drain

Claims (10)

In the ion implantation apparatus, a natural oxide film removing step for removing the natural oxide film on the substrate,
In the ion implantation apparatus, an ion implantation step of implanting ions into the substrate;
An ion implantation method comprising: The natural oxide film removing step includes
An etching gas supply step of supplying an etching gas to the plasma chamber of the ion implantation apparatus;
An etching gas irradiation step of irradiating the substrate with the etching gas plasmified in the plasma chamber;
The ion implantation method according to claim 1, comprising: The ion implantation method according to claim ₂ , wherein a gas containing CF ₄ , CFH ₃ , or CH ₂ F ₂ is used as the etching gas. The natural oxide film removing step includes
After the etching gas supply step,
An etching gas filling step of filling the plasmaized etching gas into a guide tube to which a predetermined bias voltage is applied in the ion implantation apparatus;
The ion implantation method according to claim 2, wherein the etching gas irradiation step is performed by irradiating the substrate with an etching gas from the guide tube. 5. The ion implantation method according to claim 4, wherein the etching gas irradiation step is performed by adjusting an etching energy by changing a voltage applied to the guide tube as necessary. 6. The ion implantation method according to claim 1, wherein the natural oxide film removing step includes a measuring step of measuring the etching gas irradiated in the etching gas irradiation step as an ion current. The ion implantation step includes
A halogen gas supply step of supplying a halogen gas to the plasma chamber of the ion implanter;
A halogen gas filling step of filling a halogen gas plasmified in the plasma chamber into a guide tube to which a predetermined voltage is applied in the ion implantation apparatus; and an ion supply step of supplying ions to the guide tube;
An ion irradiation step of irradiating ions to be implanted into the substrate from the halogen gas and a guide tube filled with the ions;
The ion implantation method according to claim 1, comprising: An ion implantation apparatus for implanting ions into a substrate,
A plasma chamber for converting the supplied gas into plasma;
An etching gas supply source for supplying an etching gas for removing a natural oxide film on the substrate into the plasma chamber;
A halogen gas supply source for supplying halogen gas to the plasma chamber;
An implantation ion source for supplying ions to be implanted into the substrate;
Connected to the plasma chamber and the ion supply source, into which plasma gas from the plasma chamber or ions from the ion supply source are introduced, and the introduced gas or the ions are introduced into the substrate A guide tube that irradiates
An ion implantation apparatus comprising: The ion implantation apparatus according to claim 8, further comprising a bias power source connected to the guide tube and variably applying a bias voltage. 10. The ion implantation apparatus according to claim 8, further comprising an ion current measurement ammeter capable of measuring the etching gas irradiated on the substrate as an ion current. 10.

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