Automatic ESC bias compensation when using pulsed DC bias

Abstract

Disclosed herein is a system for pulsed DC biasing and clamping a substrate. The system can include a plasma chamber having an ESC for supporting a substrate. An electrode is embedded in the ESC and is electrically coupled to a biasing and clamping circuit. The biasing and clamping circuit includes at least a shaped DC pulse voltage source and a clamping network. The clamping network includes a DC voltage source and a diode, and a resistor. The shaped DC pulse voltage source and the clamping network are connected in parallel. The biasing and clamping network automatically maintains a substantially constant clamping voltage, which is a voltage drop across the electrode and the substrate when the substrate is biased with pulsed DC voltage, leading to improved clamping of the substrate.

Description

BACKGROUND

Field

Embodiments of the present disclosure generally relate to a system used in semiconductor manufacturing. More specifically, embodiments of the present disclosure relate to a system for biasing and clamping a substrate.

Description of the Related Art

Ion bombardment is often used as a source of activation energy for chemical and physical processes in plasma etch and plasma enhanced chemical vapor deposition (PECVD) processes for processing a semiconductor substrate. High energy ions accelerated by plasma sheath are also highly directional and can be used for etching high aspect ratio features. Conventionally, a substrate may be biased using radio frequency (RF) power from an RF source. The RF source supplies an RF voltage to a first electrode embedded in an electrostatic chuck (ESC). The first electrode is capacitively coupled to the plasma of a processing system through a layer of ceramic, which is a part of the ESC. Non-linear, diode-like nature of the plasma sheath results in rectification of the applied RF field, such that a direct-current (DC) voltage drop, or self-bias, appears between the substrate and the plasma. This voltage drop determines the average energy of the ions accelerated towards the substrate.

The ESC secures the substrate disposed thereon by applying a fixed DC voltage to a second electrode embedded in the ESC to establish an electric field between the ESC and the substrate. The electric field induces opposite polarity charges to accumulate on the substrate and the second electrode, respectively. The electrostatic attractive force between the oppositely polarized charges pulls the substrate toward the ESC to secure the substrate. However, the electrostatic force can be affected by the RF bias power supplied to the first electrode in the ESC, leading to under or over clamping of the substrate. In addition, as large bias voltage become many kilovolts, the fluctuation of the self-bias voltage with respect to the fixed DC voltage can lead to an increase the risk of arcing or sudden de-clamping and breaking of the substrate. This is particularly a problem with very high bias power (kilovolts (kV) range) which is pulsing.

Therefore, an improved system for biasing and clamping a substrate is needed.

SUMMARY

Embodiments of the present disclosure generally relate to a system used in semiconductor manufacturing. More specifically, embodiments of the present disclosure relate to a system for pulsed DC biasing and clamping a substrate. In one embodiment, a system includes a plasma process chamber and a biasing and clamping circuit coupled to the plasma process chamber. The biasing and clamping circuit includes a first shaped DC pulse voltage source and a clamping network connected in parallel to the shaped DC pulse voltage source. The clamping network includes a DC voltage source and a diode.

In another embodiment, a system includes a plasma process chamber and a biasing and clamping circuit coupled to the plasma process chamber. The biasing and clamping circuit is configured to provide pulsed biasing voltage and constant clamping voltage to a substrate disposed in the plasma process chamber.

In another embodiment, a method includes pulsed DC biasing and clamping a substrate disposed on an electrostatic chuck disposed in a plasma process chamber. The substrate is clamped at a substantially constant voltage. The pulsed DC biasing and clamping the substrate includes providing a first voltage to the substrate, the first voltage being pulsed, and providing a second voltage to an electrode embedded in the electrostatic chuck. The substantially constant voltage is a difference between the first voltage and the second voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.

FIG. 1 is a schematic cross sectional view of a system for biasing and clamping a substrate.

FIG. 2 is a schematic circuit diagram of a biasing and clamping scheme for a process performed in the system of FIG. 1.

FIGS. 3A and 3B illustrate voltage waveforms by the circuit of FIG. 2.

FIGS. 4-7 are schematic circuit diagrams of a biasing and clamping scheme for a process performed in the system of FIG. 1.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

Embodiments of the present disclosure generally relate to a system used in semiconductor manufacturing. More specifically, embodiments of the present disclosure relate to a system for biasing and clamping a substrate. In one embodiment, the system includes a plasma chamber having an ESC for supporting a substrate. An electrode is embedded in the ESC and is electrically coupled to a biasing and clamping circuit. The biasing and clamping circuit includes at least a shaped DC pulse voltage source and a clamping network. The clamping network includes a DC voltage source and a diode. The shaped DC pulse voltage source and the clamping network are connected in parallel. The clamping network automatically maintains a substantially constant clamping voltage, which is a constant voltage drop across the electrode and the substrate when the substrate is biased with pulsed DC voltage, leading to improved clamping of the substrate.

FIG. 1 is a schematic cross sectional view of a system 102 for biasing and clamping a substrate. The system 102 includes a plasma process chamber 120 and a biasing and clamping circuit 108. In one embodiment, which can include or be combined with one or more embodiments described herein, as shown in FIG. 1, the plasma process chamber 120 is a reactive ion etch (RIE) plasma chamber. In some embodiments, the plasma process chamber 120 is PECVD chamber, a plasma enhanced physical vapor deposition (PEPVD) chamber, or a plasma enhanced atomic layer deposition (PEALD) chamber. In some embodiments, the plasma process chamber 120 is a plasma treatment chamber, or a plasma based ion implant chamber, for example a plasma doping (PLAD) chamber. Herein, the plasma process chamber 120 includes a plasma source 112, such as an inductively coupled plasma (ICP) source, electrically coupled to an RF power supply 190. In some embodiments, the plasma source 112 is a capacitively coupled plasma (CCP) source, such as a plasma electrode disposed in the processing volume facing the substrate support where the plasma electrode is electrically coupled to an RF power supply.

The plasma process chamber 120 includes a chamber body 175 and a chamber lid 180 defining a processing volume 170. One or more process gases are introduced into the processing volume 170 from a process gas source 185 via a nozzle 104. The plasma source 112, which is one or more inductive coils in one embodiment, is disposed over the chamber lid 180 outside of the processing volume 170. The plasma source 112 is electrically coupled to the RF power supply 190 via an RF matching circuit 195. The RF power supply 190 and the plasma source 112 are used to ignite and maintain a plasma using the processing gases and inductive energy in the processing volume 170. The processing volume 170 is fluidly coupled to one or more vacuum pumps 192, through a vacuum outlet 194, which maintain the processing volume 170 at sub-atmospheric conditions and evacuate processing, and/or other gases, therefrom. A substrate support assembly 100 is disposed in the processing volume 170. The substrate support assembly 100 includes an ESC 122 for supporting and securing a substrate 130. The ESC 122 is disposed on one or more layers 165.

In some embodiments, the one or more layers 165 include one or more fluid conduits (not shown) disposed therein that are fluidly coupled to, and in fluid communication with, a coolant source (not shown), such as a refrigerant source or water source having relatively high electrical resistance to control the temperature of the substrate support assembly 100. The ESC 122 is formed of a dielectric material, such as a bulk sintered ceramic material, such as a corrosion resistant metal oxide or metal nitride material, for example aluminum oxide (Al₂O₃), aluminum nitride (AlN), titanium oxide (TiO), titanium nitride (TiN), yttrium oxide (Y₂O₃), mixtures thereof, or combinations thereof. The ESC 122 includes an electrode 110 embedded therein. The electrode 110 is utilized for both biasing and clamping the substrate 130. The electrode 110 is formed of an electrically conductive material, such as one or more metal meshes, foils, plates, or combinations thereof.

The electrode 110 is electrically coupled to the biasing and clamping circuit 108. The biasing and clamping circuit 108 includes a shaped DC pulse voltage source 106 and a clamping network 160. The clamping network 160 automatically maintains a substantially constant clamping voltage, which is a constant voltage drop across the electrode 110 and the substrate 130 when the substrate 130 is biased with pulsed DC voltage by the shaped DC pulse voltage source 106, leading to improved clamping of the substrate. The biasing and clamping circuit 108 is described in detail in FIGS. 2, 4, 5, and 6.

The system 102 further includes a system controller 130. The system controller 130 includes a central processing unit (CPU) 132, a memory 134, and support circuits 136. The system controller 130 is used to control the process sequence used to process the substrate 130 including the substrate biasing and clamping described herein. The CPU 132 is a general purpose computer processor configured for use in an industrial setting for controlling the system 102 and sub-processors related thereto. The memory 134 includes random access memory, read only memory, floppy or hard disk drive, or other suitable forms of digital storage, local or remote. The support circuits 136 are coupled to the CPU 132 and include cache, clock circuits, input/output subsystems, power supplies, and the like, and combinations thereof. In some embodiments, the system controller 130 further includes one or more computer readable media (not shown).

Computer readable media includes any device, located either locally or remotely from the system controller 130, which is capable of storing information that is retrievable by a computing device. Examples of computer readable media useable with embodiments of the present disclosure include solid state memory, floppy disks, internal or external hard drives, and optical memory (CDs, DVDs, BR-D, etc). In one embodiment, which can include or be combined with one or more embodiments described herein, the computer readable media includes the memory 134. Software routines, when executed by the CPU 132, transform the CPU 132 into a specific purpose computer, herein the system controller 130, that controls the operation of the system 102, such that the processes are performed in accordance with embodiments of the disclosure. In some embodiments, the software routines are stored and/or executed by a second controller (not shown) that is located remotely from the system 102. In some embodiments, the processes described herein, or portions thereof, are performed by one or more application specific integrated circuits (ASIC) or other types of hardware implementations. In some embodiments, the processes described herein are performed by a combination of software routines, ASIC(s), and/or other types of hardware implementations. The software routines, which are stored within the memory, include program code that may be executed by the CPU 132 in order to perform various functionalities associated with the bias and clamping schemes and methods described herein.

FIG. 2 is a schematic circuit diagram of a biasing and clamping scheme for a process performed in the system 102 of FIG. 1. The circuit 200 shown in the circuit diagram is used to model the main aspects of the interaction of the biasing and clamping circuit 108 and the plasma process chamber 120. In practice, interaction of the biasing and clamping scheme described herein with the plasma in the processing volume 170 (as shown in FIG. 1) may be accompanied by complex physical phenomena.

As shown in FIG. 2, the circuit 200 includes components located within the plasma process chamber 120 and components located within the biasing and clamping circuit 108. The electrode 110 (as shown in FIG. 1), the dielectric material of the ESC 122 (as shown in FIG. 1), and the substrate 130 (as shown in FIG. 1) are represented in the circuit 200 by a capacitor 202. The plasma sheath 204 formed in the processing region 170 (as shown in FIG. 1) is represented in the circuit 200 by a 3-part circuit element including: a) a diode 206, which when conducting represents the plasma sheath collapse, b) a current source 208, which represents the ion current flowing in the presence of the plasma sheath, and c) a capacitor 210, which represents the plasma sheath for the main portion of the biasing and clamping cycle (˜90%), i.e., ion current phase, during which the ion acceleration and etching (or deposition) occur.

The biasing and clamping circuit 108, the electrode 110 (as shown in FIG. 1), and the external electrical conductor (such as an electrical cable) connecting the biasing and clamping circuit 108 and the electrode 110 together have some combined parasitic capacitance to ground, which is represented in the circuit 200 by a parasitic capacitor 212. The external electrical conductor may be a coaxial transmission line, which is represented in the circuit 200 by an inductor 215.

The biasing and clamping circuit 108 includes the shaped DC pulse voltage source 106 and the clamping network 160, as shown in FIG. 2. The shaped DC pulse voltage source 106 is connected between a node N3 and a ground node GND. A capacitor 218 is further connected between the node N3 and a node N1. The clamping network 160 includes at least a diode 216, a capacitor 222, a DC voltage source 214, and a resistor 220. The clamping network 160 is also connected between the node N1 and the ground node GND. The diode 216 and the resistor 220 are connected between the node N1 and a node N2, and the DC voltage source 214 and the capacitor 222 are connected between the node N2 and the ground node GND. The shaped DC pulse voltage source 106, or a pulsed bias generator, is used to establish a pulsed bias voltage waveform at the electrode 110 (as shown in FIG. 1). The DC voltage source 214 and the diode 216 are used to establish a substantially constant clamping voltage, which is a voltage difference across the capacitor 202 (e.g., across the electrode 110, the dielectric material of the ESC 122, and the substrate 130 (as shown in FIG. 1)).

FIG. 3A illustrates a first voltage waveform 302 and a second voltage waveform 304 using the circuit 200 of FIG. 2. Referring to FIGS. 2 and 3A, during operation of the system 102 (as shown in FIG. 1), the first voltage waveform 302 is the voltage at the substrate 130 (as shown in FIG. 1). The peak voltage of the first voltage waveform 302 is set to equal to the voltage on the surface of the substrate 130 (as shown in FIG. 1) from the plasma. The second voltage waveform 304 is the voltage at the electrode 110 (as shown in FIG. 1). With the diode 216, the second voltage waveform 304 automatically tracks the first voltage waveform 302. The presence of the diode 216 maintains a constant voltage difference between the first and second waveforms 302, 304. As shown in FIG. 3A, the first voltage waveform 302 and the second voltage waveform 304 have a constant difference, which is the constant clamping voltage across the electrode 110, the dielectric material of the ESC 122, and the substrate 130. In other words, the constant clamping voltage is the difference between the first voltage waveform 302 and the second voltage waveform 304.

For example, the shaped DC pulse voltage source 106 is set to provide pulses of DC voltage from 0 kV to −4 kV and the DC voltage source 214 is set to provide a constant DC voltage at −2 kV. When the first voltage waveform 302 is at 0 kV (i.e., a high state), the second voltage waveform 304 is at −2 kV because the diode 216 is conducting. A voltage drop of −2 kV is built up across the capacitor 218 (the voltage at the node N3 is 2 kV higher than that at node N1). When the first voltage waveform 302 is then changed from 0 kV to −4 kV (i.e., a low state), due to the voltage drop of 2 kV across the capacitor 218, the voltage at node N1, which is essentially the second voltage waveform 304, changes to −6 kV. The diode 216 is not conducting at this moment because the diode 216 is reverse-biased. When the first voltage waveform 302 changes back to 0 kV from −4 kV, the diode 216 is conducting again, setting the voltage waveform 304 at the electrode 110 back to −2 kV. Thus, bias compensation of the clamping voltage is automatically performed by the shaped DC pulse voltage source 106, the diode 216, and the DC voltage source 214. In some embodiments, the shaped DC pulse voltage source 106 can provide shaped DC pulses which have more complicated waveform than the voltage waveform 302 shown in FIG. 3A, and an example is shown in FIG. 3B.

FIG. 3B illustrates a first voltage waveform 306 and a second voltage waveform 308 using the circuit 200 of FIG. 2. Referring to FIGS. 2 and 3B, during operation of the system 102 (as shown in FIG. 1), the first voltage waveform 306 is the voltage at the substrate 130 (as shown in FIG. 1). The peak voltage of the first voltage waveform 306 is set to equal to the voltage on the surface of the substrate 130 (as shown in FIG. 1) from the plasma. The second voltage waveform 308 is the voltage at the electrode 110 (as shown in FIG. 1). With the diode 216, the second voltage waveform 308 automatically tracks the first voltage waveform 306. The presence of the diode 216 maintains a constant voltage difference between the first and second waveforms 306, 308. As shown in FIG. 3B, the first voltage waveform 306 and the second voltage waveform 308 have a constant difference, which is the constant clamping voltage across the electrode 110, the dielectric material of the ESC 122, and the substrate 130. In other words, the constant clamping voltage is the difference between the first voltage waveform 306 and the second voltage waveform 308.

FIGS. 4-7 are schematic circuit diagrams of a biasing and clamping scheme for a process performed in the system of FIG. 1. Circuits 400, 500, 600, and 700 include components in the plasma process chamber 120 and components in the biasing and clamping circuit 108. In some embodiments, the shaped DC pulse voltage source 106 outputs bursts of a plurality of short positive pulses rather than bursts of long negative pulses. In this case, over clamping between bursts can occur because the voltage waveform 302 (as shown in FIG. 3A) stops at the more negative voltage state. Then the substrate can get discharged by an ion current from the current source 208 (as shown in FIG. 2) and the voltage waveform 302 returns to 0 kV. However, the electrode 110 takes longer time to discharge compared to the substrate because of the RC time constant of the resistor 220 and the capacitors 202, 212, and 218. As a result, the voltage magnitude of the voltage waveform 304 remains high and over clamping of the substrate occurs. Circuits 500, 600, and 700 provide a solution to avoid long discharge time at the end of each burst of pulses. As shown in FIG. 5, the circuit 500 includes the biasing and clamping circuit 108 having a switch 502. At the end of each burst, the switch 502 is turned on to discharge the capacitors 218 and 212 in the circuit 500.

As shown in FIG. 6, the circuit 600 includes the biasing and clamping circuit 108 having a shaped DC pulse voltage source network 602 that is utilized to reduce over clamping between bursts. At the end of each burst, or between bursts of pulses, a second shaped DC pulse voltage source 603 turns on to pump the excess charge from the capacitors 202, 212, and 218 to the capacitor 604, so that the charge remained in the capacitors 202, 212, and 218 are just enough to maintain the predetermined clamping voltage at the electrode 110. As shown in FIG. 6, the diode 216 is connected between the node N4 and the node N5, and the DC voltage source 214 is connected between the node N4 and the ground node. The shaped DC pulse voltage source network 602 is connected between the node N4 and the node N5. The shaped DC pulse voltage source network 602 includes serially connected shaped DC pulse voltage source 603, diode 605, and an impedance (e.g., the capacitor 604 and the resistor 606).

Similarly, as shown in FIG. 7, the circuit 700 includes the biasing and clamping circuit 108 having a shaped DC pulse voltage source network 702 that is utilized to reduce over clamping between bursts. At the end of each burst, a second shaped DC pulse voltage source 703 turns on to discharge the excess charge stored in the capacitors 202, 212, and 218. Using one of the circuits 500, 600, and 700, the clamping voltage can remain constant during both burst on and burst off states. As shown in FIG. 7, the diode 216 is connected between the node N6 and the node N7, and the DC voltage source 214 is connected between the node N7 and the ground node. The shaped DC pulse voltage source network 702 is connected between the node N6 and the ground node. The shaped DC pulse voltage source network 702 includes the shaped DC pulse voltage source 703, a diode 704, a resistor 706, a DC voltage source 708, a resistor 710, and a capacitor 712. The shaped DC pulse voltage source 703, the diode 704, and the resistor 706 are connected between the node N6 and the node N7, and the DC voltage source 708, the resistor 710, and the capacitor 712 are connected between the node N7 and the ground node.

The biasing and clamping circuit automatically maintains a substantially constant clamping voltage on the substrate when the substrate is biased with pulsed DC voltage, leading to improved clamping of the substrate. The biasing and clamping circuit includes the DC voltage source, the diode, the capacitor, and the shaped DC pulse voltage source. The diode causes the voltage at the electrode to track the pulsed biasing voltage. As a result, the clamping voltage on the substrate is substantially constant.

While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A system, comprising: a plasma process chamber; anda biasing and clamping circuit coupled to the plasma process chamber, the biasing and clamping circuit comprising: a first shaped direct current (DC) pulse voltage source; anda clamping network connected in parallel to the first shaped DC pulse voltage source, the clamping network comprising: a second DC voltage source coupled to a ground node and coupled to a first node, wherein the second DC voltage source is further directly coupled in series to a second node;a diode directly coupled to the first node and directly coupled to the second node; anda resistor coupled to the first node and the second node and in parallel with the diode.

2. The system of claim 1, wherein the plasma process chamber comprises: a chamber body;a chamber lid, wherein the chamber body and the chamber lid define a processing volume; anda substrate support assembly disposed in the processing volume.

3. The system of claim 2, wherein the substrate support assembly comprises an electrostatic chuck, wherein the electrostatic chuck comprises a dielectric material and an electrode embedded in the dielectric material, wherein the first shaped DC pulse voltage source and the clamping network are connected to the electrode.

4. The system of claim 2, wherein the biasing and clamping circuit is configured to provide a pulsed biasing voltage and constant clamping voltage to a substrate disposed in the plasma process chamber.

5. The system of claim 1, wherein the biasing and clamping circuit further comprises a second shaped DC pulse voltage source.

6. The system of claim 1, wherein the biasing and clamping circuit further comprises a switch.

7. A system, comprising: a plasma process chamber; anda biasing and clamping circuit coupled to the plasma process chamber, the biasing and clamping circuit being configured to provide a pulsed biasing voltage and a constant clamping voltage to a substrate disposed in the plasma process chamber, wherein the biasing and clamping circuit comprises a clamping network comprising: a first direct-current (DC) voltage source coupled to a first node, wherein the first DC voltage source is further directly coupled in series to a second node;a first diode directly coupled to the second node;a first capacitor; anda first resistor coupled to the first node between the first diode and the first DC voltage source and in parallel with the first diode.

8. The system of claim 7, wherein the biasing and clamping circuit comprises: a first shaped DC pulse voltage source, and wherein the clamping network is connected in parallel to the first shaped DC pulse voltage source.

9. The system of claim 7, wherein the first diode is connected between the first node and a second node, and the first DC voltage source is connected between the first node and a ground node.

10. The system of claim 9, wherein the biasing and clamping circuit further comprises a first shaped DC pulse voltage source network, and wherein the first shaped DC pulse voltage source network is connected between the first node and the second node.

11. The system of claim 10, wherein the first shaped DC pulse voltage source network comprises a second shaped DC pulse voltage source, a second diode, and an impedance that are serially connected.

12. The system of claim 10, wherein the biasing and clamping circuit further comprises a second shaped DC pulse voltage source network, wherein the second shaped DC pulse voltage source network is connected between the first node and the ground node.

13. The system of claim 12, wherein the second shaped DC pulse voltage source network comprises a third shaped DC pulse voltage source, a third diode, a second resistor, a second direct-current voltage source, a third resistor, and a second capacitor, wherein the third shaped DC pulse voltage source, the third diode, and the second resistor are connected between the first node and the second node, and wherein the second direct-current voltage source, the third resistor, and the second capacitor are connected between the second node and the ground node.

14. A method, comprising: biasing and clamping, via a biasing and clamping circuit, a substrate disposed on an electrostatic chuck disposed in a plasma process chamber, the substrate being clamped at a substantially constant voltage, wherein biasing and clamping the substrate comprises: providing a first voltage to the substrate, the first voltage being pulsed; andproviding a second voltage to an electrode embedded in the electrostatic chuck, the substantially constant voltage is a difference between the first voltage and the second voltage, wherein the biasing and clamping circuit comprises a clamping network comprising: a DC voltage source coupled to a ground node and a first node, wherein the DC voltage source is further directly coupled in series to a second node;a diode directly coupled to the first node and directly coupled to the second node; anda resistor coupled to the first node and the second node and in parallel with the diode.

15. The method of claim 14, wherein biasing and clamping the substrate is performed by a first shaped DC pulse voltage source and the clamping network, and the first voltage is provided by the first shaped DC pulse voltage source.

16. The method of claim 15, wherein the diode is conducting when the first voltage is at a high state and the diode is in a reverse-bias mode when the first voltage is at a low state.

17. The method of claim 15, wherein the first voltage comprises bursts of negative pulses.

18. The method of claim 15, wherein the first voltage comprises bursts of positive pulses.

19. The method of claim 18, wherein the clamping network further comprises a switch, and the switch is turned on between the bursts of positive pulses.

20. The method of claim 18, wherein the clamping network further comprises a second shaped DC pulse voltage source, and the second shaped DC pulse voltage source is turned on between the bursts of positive pulses.