TWI587348B - A machine for implanting ions in plasma immersion mode for a low-pressure method - Google Patents

Description

Machine for implanting ions in a plasma immersion mode in a low pressure process

The present invention relates to machines for implanting ions in a plasma immersion mode in a low pressure process.

The field of the invention resides in ion implantation machines that utilize plasma, in other words, ion implanters that operate in a plasma immersion mode.

As such, implanting ions in the substrate consists in immersing the substrate in the plasma and biasing the substrate at a negative voltage of tens of volts (V) to tens of kilovolts (kV) (typically less than 100 kV) to enable Accelerate the electric field of the plasma ions toward the substrate.

The depth of penetration of ions is determined by their acceleration energy. First, depending on the voltage applied to the substrate, the second is based on the respective nature of the ions and the substrate.

For reasons associated with physics, igniting and maintaining the plasma requires a relatively high pressure, typically 10 ^-3 mbar to 10 ^-1 mbar. This high pressure produces unwanted side effects. The substrate is where the unwanted redeposition and etching are. Moreover, gas consumption is directly dependent on the working pressure.

So try to reduce this pressure as much as possible. Nevertheless, this pressure reduction results in difficulty in igniting the plasma and its density is significantly reduced.

Today, the optimum operating pressure is based on the type of ionization source that produces and maintains the plasma: microwave source: 10 ^-2 mbar to 10 ^-1 mbar; and RF source: 10 ^-3 mbar to 10 ^-1 mbar.

Heat sources (heat sources with filaments) can reduce stress, but they are Contamination caused by evaporation.

The discharge source can also operate at lower pressures, but it damages the plasma density.

Thus, document US 2001/0046566 describes a machine for implanting ions in a plasma immersion mode, comprising: an enclosure connected to a pump device; a negatively biased substrate carrier disposed in the enclosure; and a plasma feed a device having a chamber provided with an ionization unit in the form of a generally cylindrical body extending between a start section and an end section opened into the enclosure; the chamber is provided with a gas delivery port; and the end section has an associated The drop of the body is lost.

The implanted machine is capable of producing plasma at a relatively high pressure and significantly reduces the aforementioned side effects.

Nonetheless, first of all, the grid that produces the drop loss is optimal for electromagnetic considerations, not the loss from the grid.

Second, the grid must be electrically conductive and therefore made of a metallic material, which can contaminate the plasma. The grid becomes in contact with the plasma for etching (chemical and ion etching). Metal contamination due to this etch is incompatible with certain applications such as microelectronics. Moreover, the phenomenon of unwanted redeposition occurring on the wall in contact with the plasma (i.e., the wall of the chamber) is significant.

Third, the metal grid attempts to block the electromagnetic field used to ignite the plasma in order to confine it to the chamber and prevent it from propagating into the enclosure that only accelerates the ions. An electrostatic field for accelerating ions is generated between the substrate and the grid, and It strongly applies an ion-tracking trajectory whereby a so-called "conformal" three-dimensional implant is prevented when the plasma is present around the substrate, which is obtainable via a Child Langmuir sheath.

Fourth, the chamber opens directly into the enclosure and is equally detrimental to the propagation of the plasma in the enclosed chamber.

Therefore, the object of the present invention is to improve the situation.

According to the present invention, an ion implantation apparatus includes: an enclosure connected to a pump device; a negative substrate carrier disposed inside the enclosure; and a plasma feeding device extending between the start segment and the end segment In the form of a generally cylindrical body, the device has a main chamber provided with an ionization unit; the main chamber is provided with a gas transfer port; and the last portion of the main chamber is provided with a drop loss device for generating a pressure drop about the body; Moreover, the plasma feed device also includes an auxiliary chamber configured to extend beyond the final segment in which the auxiliary chamber opens into the enclosure.

Preferably, the auxiliary chamber is provided with a second ionization unit.

Advantageously, the plasma feed device has a volume that is smaller than the volume of the enclosure.

In the first embodiment, the last segment is in the form of a partition into which a plurality of holes are inserted.

In the second embodiment, the last segment has an opening with a small area relative to any of the sections of the body placed between the start and end segments.

According to still further features of the invention, the first ionization unit has an excitation coil and a limit coil.

It is desirable that the shaft of the substrate carrier and the axis of the plasma feed device be two different axes.

In such an environment, the substrate carrier and the plasma feed device have an adjustable offset.

According to another advantageous point of the invention, the last segment is removable.

Optionally, the machine includes at least one additional plasma feed device.

Advantageously, the machine comprises: a voltage source having its anode connected to ground; a capacitor connected in parallel with the voltage source; and a switch connected between the cathode of the voltage source and the substrate carrier turntable.

Moreover, the substrate carrier turntable is rotatably movable about its axis.

Furthermore, the substrate carrier turntable has a dish shape, and a distance between the substrate carrier turntable and the plasma feeding device is greater than a diameter of the substrate carrier.

Preferably, the drop loss device is electrically insulated.

As shown in Figure 1, the vacuum enclosure ENV represents an ion implantation machine. In microelectronic applications, it is recommended to use an enclosure made of an aluminum alloy to limit contamination with metallic elements such as iron, chromium, nickel, cobalt, and the like. Also able Use a coating of tantalum or tantalum carbide.

The pump mechanism VAC is placed below the enclosure ENV.

The substrate carrier turntable PPS is in the form of a horizontal disk movable about a vertical axis AXT and receives the substrate SUB to be ion implanted. It is connected to the high voltage power supply HT through a high voltage electrical insulation jacket PET, which is also connected to the ground. The negative potential applied to the substrate carrier is usually in the range of several tens of volts to several tens of kilovolts.

Conventionally, the power supply consists of a simple direct current (DC) power source with its positive pole connected to ground. Nonetheless, the present invention can be applied regardless of the mechanism for applying a negative bias to the substrate in the implantation of the plasma immersion mode, and regardless of whether the bias voltage is constant or variable. In particular, if the substrate is insulated, the substrate tends to be positively charged.

Referring to Figure 2a, a first embodiment of a power supply HT is used to limit charge action. It contains a DC voltage source SOU whose anode is connected to ground. The branch connection connected in parallel with the source is formed by a capacitor CDS in series with a resistor RES connected to the cathode of the DC voltage source SOU. The substrate carrier turntable PPS is connected to a common point between the capacitor CDS and the resistor RES.

The capacitor CDS has a low value of capacitance so that the potential of the substrate gradually returns to a value close to zero during its discharge phase.

Even though the use of pulsed plasma can limit the charge action, problems still exist, especially if the potential of the substrate remains extremely negative during the method (when a high capacitance capacitor is used).

When using a low-capacitance capacitor, together with a plasma pulse of sufficient length The following phenomenon occurs: ̇ At the beginning of the pulse, the capacitor is charged, the potential of the substrate is set by the charging voltage, and the ions are accelerated toward the substrate by the above mechanism; 电压 the voltage across the terminals of the capacitor drops because the capacitor discharges to Inside the plasma; and 正 above a certain potential (herein referred to as the inversion potential), the positive charge accumulated on the insulating region generates an electric field, which becomes dominant and attracts the electrons of the plasma; thus the positive charge is Sexualize and eliminate the risk of arcing.

This neutralization is especially effective when the working pressure is low. If the average free path of the electrons is large, the electron flow reaching the surface for neutralizing the charge is also quite large.

Therefore, the conditions required to establish this mechanism are as follows: The capacitance of the tantalum capacitor CDS is small enough; the duration of the plasma pulse is long enough to reach the inversion potential before the accumulated charge on the surface generates an arc; and the tantalum is used for plasma The working pressure of the average free path of the electrons produced by the source is low enough to enable them to reach the substrate without the risk of colliding and regrouping with gas molecules and ions present inside the enclosure.

The function of the resistor RES is to limit the current when the capacitor CDS starts charging. Moreover, if the resistor has a resistance greater than the equivalent impedance of the plasma, it is also used to limit the recharging of the capacitor during the plasma pulse that is desired to be discharged.

For a typical plasma impedance equal to 100 kilo ohms (kΩ), the load resistance is preferably in the range of 200 kΩ to 2000 kΩ. Capacitor CDS The capacitance is the capacitance at which the discharge has almost completed at the end of the plasma pulse.

The parameters common to this mode are as follows: ̇ Plasma density is in the range of 10 ⁸ to 10 ¹⁰ /cm ³ per cubic centimeter (cm ³ ); ̇ plasma pulse duration is in the range of 15 microseconds (μs) to 500 μs ̇ The pulse repetition rate is in the range of 1 Hz to 3 kHz; ̇ working pressure is in the range of 2 × 10 ^-4 mbar to 5 × 10 ^-3 mbar; ̇ Gas used: N ₂ , BF ₃ , O ₂ , H ₂ , PH ₃ , AsH ₃ , or Ar; ̇ resistor RES has a resistance greater than 300kΩ; tantalum capacitor CDS has a capacitance of 500 picofarads (pF); and ̇ bias at -100V to -10000V In the scope.

Referring to Figure 2b, the second embodiment of the power supply HT2 also limits the charge action. This power supply contains a DC voltage source SOU whose anode is connected to ground. A capacitor CDD is connected in parallel with the voltage source. The switch SW is connected between the negative electrode of the DC voltage source SOU and the substrate carrier turntable PPS. The switch SW is made of metal oxide semiconductor (MOS) technology or by insulated gate bipolar transistor (IGBT) technology.

When the switch SW is turned on, the capacitor CDD is gradually charged in the nominal voltage of the DC voltage source SOU.

When the switch SW is turned off while the plasma is turned on, the current is drawn due to the equivalent capacitance of the machine and the capacitance of the plasma sheath. Machine equivalent capacitance The capacitance that constitutes all of the components of the machine, especially the cable, the insulating sleeve, the isolating transformer; and the capacitance formed between the substrate carrier and the enclosure.

The switch SW typically remains closed for 5 μs to 100 μs during phase implantation due to positive ions being attracted toward the substrate (this is a negative bias).

The capacitor has a large capacitance (typically in the range of 300 nanofarads (nF) to 1.5 microfarads (μF)) such that the voltage across its terminals does not drop during implantation.

After the implantation phase, the switch SW is turned on and the DC voltage source SOU again charges the capacitor CDD.

During this time, the equivalent capacitance of the machine is completely discharged into the plasma, and the substrate returns to the floating potential. As a result, the electrons in the plasma neutralize the insulating regions that have become positively charged substrates during implantation.

The neutralization phase during which the switch SW remains open typically lasts from 1 μs to 80 μs.

Once the neutralization phase is over, the plasma is extinguished during the extinguishing phase, thereby having the advantage of reducing plasma/surface interaction, reducing thermal budget, and minimizing particle generation. This extinguishing phase typically lasts from 20 [mu]s to 200 [mu]s during which the switch SW remains open.

The above cycle can then be repeated: ̇ implantation phase; ̇ neutralization phase; and ̇ extinction phase.

By using a second opening between the substrate carrier turntable PPS and the ground Turning off the discharge of the equivalent capacitance of the machine can shorten the neutralization stage. This second switch is turned off during the neutralization phase and during the extinguishing phase; it is turned on during the implantation phase.

Returning to Figure 1, the top of the enclosure ENV receives the plasma feed device AP. This device is in the form of a generally cylindrical body extending perpendicular to the vertical axis AXP between the beginning segment (at the top of the drawing) and the end segment (at the bottom of the drawing). The coupling flange BR enables the end section of the plasma feed device AP to be on the vacuum enclosure ENV. The beginning section has a transfer port ING for inserting a gas that generates plasma. This transfer port ING is at the center of the vertical axis AXP. The vertical axis AXP intersects the surface of the substrate carrier turntable PPS.

The plasma feed device AP is preferably made of alumina glass (usually misinterpreted as quartz) or alumina to limit contamination problems. The drop loss means for generating a pressure drop are provided, and in this embodiment, they are constituted by a partition CL which is penetrated by a plurality of through holes. The partition CL facilitates electrical insulation, preferably made of alumina glass, and is disposed between the beginning and end sections of the plasma feed device AP. By way of example, for a cylindrical body having a diameter of about 15 centimeters (cm), the apertures in the partition CL have a diameter on the order of a few millimeters (mm). In order to facilitate the maintenance operation, the partition CL can be removed.

The main chamber PR is defined by the space defined by the partition CL and the starting section. Thus the partition CL marks the last section of the main chamber. The main chamber PR is surrounded by the ionization unit from the outside, and the ionization unit first includes the radio frequency antenna ANT1, and the second is the limit coil BC1 if necessary. In this embodiment, the antenna ANT1 is composed of a plurality of electrical conductors such as copper tubes or copper strips.

Naturally, any type of plasma source can be used: a discharge source, an inductively coupled plasma (ICP) source, a spiral cone, a microwave source, or an electric arc. These sources must be capable of operating at low voltage levels that are low enough that the electric field generated between the turntable PPS and the grounded enclosure ENV does not present a risk of igniting the discharge plasma.

The drop loss between the body of the plasma feed device AP and the enclosure ENV enables the creation of a pressure difference between the two components, which is in the range of one to two levels of strength.

The auxiliary chamber AUX is defined by the space defined by the partition CL and the end segment.

Optionally, the auxiliary chamber AUX is also surrounded by a second ionization unit from the outside, the second ionization unit first comprises a limiting coil BC2, and the second is a radio frequency antenna ANT2.

It is also possible to provide a single limiting coil and a single antenna covering both the chambers PR and AUX of the plasma feeding device AP.

Any plasma-producing species can be implanted. Can start with a gas precursor such as N ₂ , O ₂ , H ₂ , He, Xe, Ar, BF ₃ , B ₂ H ₆ , AsH ₃ , PH ₃ , SiH ₄ , GeH ₄ , C ₂ H ₄ , SiF ₄ , GeF ₄ , AsF ₅ , CHF ₃ , SF ₆ , PF _5, and the like.

This configuration can greatly reduce interference with deposition and etching.

Typical parameters for plasma under the absence of the present invention are as follows: Helium gas flow rate: 10 standard cubic centimeters per minute (sccm) to 500 sccm under standard pressure and temperature conditions; ̇Vacuum enclosure internal pressure is 10 ^-3 mbar to 10 ^-1 mbar; and ̇ plasma density of 10 ⁹ /cm ³ to 10 ¹¹ /cm ³ .

The present invention greatly improves this situation because it can obtain the following values: helium gas flow rate: 0.5 sccm to 50 sccm; helium vacuum enclosure internal pressure: 10 ^-4 mbar to 10 ^-2 mbar grade; and tantalum plasma density of 10 ⁹ /cm ³ to 10 ¹¹ /cm ³ .

These results are obtained by the separator CL which introduces a considerable drop loss between the position where the plasma is generated (i.e., the main chamber PR) and the position where the plasma is used. In this way, the pressure in the vacuum enclosure ENV can be significantly reduced while preserving the pressure in the range of 10 ^-3 mbar to 10 ^-1 mbar in the main chamber. The pressure present in the main chamber can easily ignite the plasma. Under the effect of the electrostatic field applied by the ionization unit, the electrons of the plasma can then reach the vacuum enclosure ENV via the separator CL and enable the plasma to ignite and propagate therein.

This drop loss constitutes the essence of the present invention. It can be implemented in many ways.

Referring to Figure 3, a second embodiment of a plasma feed device as indicated by the indication can be seen.

The plasma feed device APB is still in the form of a generally cylindrical body extending between the beginning and end segments. The coupling flange BR still has the same function, that is, the end of the plasma feed device APB is fastened to the vacuum enclosure. As described above, the start section is provided with a transfer port INL for inserting gas. Conversely, the drop loss is not obtained via the perforated partition. In this embodiment, the body of the plasma feeding device APB constitutes the main chamber PR2. No longer has an auxiliary chamber, and it is the end point ST itself, the end point ST has a specific plasma feed The opening VS of the area of the middle section of the device APB that is much smaller.

Returning to Figure 1, the additional features of the implanter 1 enable more uniform implantation of large sized substrates.

As described above, the substrate SUB is positioned on the substrate carrier turntable PPS, which is generally dish-shaped and movable about its vertical axis AXT. With or without rotation, if the axis AXP of the plasma feed device ALP perpendicular to the substrate SUB is close to the axis AXT of the turntable PPS, the plasma diffusion is maximized along this axis, and the distribution gradient is related to the axis. . The dose implanted in the substrate SUB thus has a non-uniform distribution.

If the two axes AXT and AXP are offset, rotating the substrate carrier turntable PPS can move the substrate SUB relative to the axis AXP of the plasma source. The dose implanted in the substrate SUB then has a significantly improved uniform distribution.

The efficacy of this system has been verified on a silicon wafer having a diameter of 300 mm. For this, it has been found that BF ₃ is implanted at 500 volts (eV) and 10 ¹⁵ centimeters per square centimeter (cm ² ), and the final non-uniformity Sex is less than 1%.

Moreover, it is preferable that the distance between the substrate carrier turntable PPS and the plasma feeding device AP is larger than the diameter of the substrate carrier in the case of the dish shape.

Naturally, the present invention enables various plasma feed devices such as those described above to be implemented, the device then being attached to the enclosure ENV about the vertical axis AXT of the substrate carrier turntable PPS.

The plasma feed device is described above as being assembled to a vacuum enclosure. The invention may of course be applied if the device forms an integral part of the closure.

The embodiments of the invention described above were chosen because of their specific nature. Nonetheless, all of the embodiments covered by the present invention are not fully described. In particular, any of the illustrated mechanisms may be replaced by an equivalent mechanism without departing from the scope of the invention.

1‧‧‧ implanter

ENV‧‧‧ enclosure

VAC‧‧‧ pump mechanism

PPS‧‧‧Substrate carrier turntable

SUB‧‧‧ substrate

AXT‧‧‧ vertical axis

AXP‧‧‧ vertical axis

PET‧‧‧High-voltage electric insulation sleeve

HT‧‧‧Power supply

HT2‧‧‧Power supply

SOU‧‧‧DC voltage source SOU

CDS‧‧‧ capacitor

RES‧‧‧Resistors

CDD‧‧‧ capacitor

SW‧‧ switch

AP‧‧‧Purpose Feeder

APB‧‧‧Purpose Feeder

ALP‧‧‧Purpose Feeder

ING‧‧‧Transport

INL‧‧‧Transport

CL‧‧‧Baffle

PR‧‧‧Main room

PR2‧‧‧ main room

ANT1‧‧‧RF antenna

ANT2‧‧‧RF antenna

BC1‧‧‧Limited coil

BC2‧‧‧Limited coil

AUX‧‧‧Auxiliary Room

BR‧‧‧Coupling flange

ST‧‧‧end point

VS‧‧‧ openings

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail below with reference to the embodiments of the drawings, and the accompanying drawings in which: FIG. 1 is a cross-sectional view of an ion implantation machine; FIG. 2 is a circuit diagram for biasing a substrate carrier turntable, And in particular: Figure 2a is a first embodiment of the circuit; Figure 2b is a second embodiment of the circuit; and Figure 3 is a cross-sectional view of a second embodiment of the plasma feed device.

Elements appearing in more than one of the figures give each of them the same element symbol.

ENV‧‧‧ enclosure

VAC‧‧‧ pump mechanism

PPS‧‧‧Substrate carrier turntable

SUB‧‧‧ substrate

AXT‧‧‧ vertical axis

AXP‧‧‧ vertical axis

PET‧‧‧High-voltage electric insulation sleeve

HT‧‧‧Power supply

AP‧‧‧Purpose Feeder

ING‧‧‧Transport

CL‧‧‧Baffle

PR‧‧‧Main room

ANT1‧‧‧RF antenna

ANT2‧‧‧RF antenna

BC1‧‧‧Limited coil

BC2‧‧‧Limited coil

AUX‧‧‧Auxiliary Room

BR‧‧‧Coupling flange

Claims (15)

An ion implantation machine comprising: an enclosure (ENV) coupled to a pump device (VAC); a negative polarity (HT) substrate carrier (PPS) disposed within the enclosure (ENV); and a plasma The feeding device (AP) is in the form of a generally cylindrical body extending between a start section and an end section, the plasma feed device having a main chamber (PR, PR2) provided with a first ionization unit (BC1, ANT1) The main chamber (PR, PR2) is provided with a gas transfer port (ING, INL); and the last segment (CL) of the main chamber is provided with a drop loss device for generating a pressure related to the body (AP) The machine is characterized in that the plasma feed device (AP) also includes an auxiliary chamber (AUX) configured to extend beyond the last segment in which the auxiliary chamber opens to the enclosure (ENV) Inside. A machine according to the first aspect of the invention, wherein the auxiliary chamber (AUX) is provided with a second ionization unit (BC2, ANT2). A machine according to the first aspect of the invention, wherein the plasma feed device (AP) has a volume smaller than a volume of the enclosure (ENV). The machine of claim 2, wherein the plasma feed device (AP) has a volume smaller than a volume of the enclosure (ENV). The machine according to any one of claims 1 to 4, wherein the last segment is a shape of a partition (CL) penetrated by a plurality of holes formula. The machine of any one of clauses 1 to 4, wherein the last segment (ST) has any one of a section of the body (APB) placed between the start and end segments The area is a small area opening (VS). The machine according to any one of claims 1 to 4, wherein the first ionization unit has an excitation coil (ANT1) and a limiting coil (BC1). A machine according to any one of claims 1 to 4, wherein the substrate carrier (PPS) axis (AXT) and the plasma feed device (AP) axis (AXP) are two different axes. The machine of claim 8 wherein the substrate carrier (PPS) and the plasma feed device (AP) have an adjustable offset. The machine of any one of claims 1 to 4, wherein the last paragraph is removable. A machine according to any one of claims 1 to 4, wherein it comprises at least one additional plasma feed device. The machine according to any one of claims 1 to 4, wherein the machine comprises: a voltage source (SOU) having a positive electrode connected to the ground; a capacitor (CDD) connected in parallel with the voltage source (SOU); (SW), connected to the negative pole of the voltage source (SOU) and the Between the substrate carrier turntables (PPS). A machine according to any one of claims 1 to 4, wherein the substrate carrier turntable (PPS) is rotatably movable about its axis (AXT). The machine according to any one of claims 1 to 4, wherein the substrate carrier turntable (PPS) is in the shape of a dish, and a distance between the substrate carrier turntable and the plasma feeding device (AP) is greater than the substrate The diameter of the carrier. The machine of any one of claims 1 to 4, wherein the drop loss device (CL, VS) is electrically insulated.