WO2002004692A2

WO2002004692A2 - Two-stage sputter deposition method

Info

Publication number: WO2002004692A2
Application number: PCT/US2001/041206
Authority: WO
Inventors: John C. Forster
Original assignee: Applied Materials, Inc.
Priority date: 2000-07-10
Filing date: 2001-06-29
Publication date: 2002-01-17
Also published as: WO2002004692A3

Abstract

A method and system for depositing a conductive layer on a substrate by serially providing, proximate to the substrate, first and second batches of conductive material, comprising electrically neutral atoms and electrically charge ions with a substantial majority of the conductive material associated with the first batch being electrically neutral atoms and a substantial majority of the conductive material associated with the second batch being electrically charged ions. A first portion of the conductive layer is formed on the substrate from the first batch. The first portion of the conductive layer is formed before the second batch of conductive material is present. Subsequent to formation of the first portion, a second portion of the conductive layer is formed from the second batch of conductive material.

Description

TWO-STAGE SPUTTER DEPOSITION METHOD AND SYSTEM FOR FABRICATING CONDUCTIVE LAYERS TO FORM CONTACTS WITH MINIMAL

RESISTANCE

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority from United States patent application number 09/013,823 entitled METHOD FOR FORMING TITANIUM SILICLDE LN SITU, which is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to deposition of conductive layers on patterned substrates. More particularly, this invention relates to sputter deposition of conductive layers employed to form contacts on patterned substrates. Formation of contacts in multi-level integrated circuits poses many challenges to the semiconductor industry as the drive to increase circuit density continues, due to the reduction in size of the circuit features. Formed by depositing conductive material in an opening on the surface of insulating material disposed between two spaced-apart conductive layers, the ever reducing feature size of contacts results in having to deposit conductive material in openings having high aspect ratios. The high aspect ratios of these openings frustrates deposition of conductive material that demonstrates satisfactory step coverage and gap fill, and often results in the conductive material presenting other deleterious characteristics that may adversely effect operation of the resulting electrical circuits.

A common technique for depositing the aforementioned conductive layers involves sputtering of atoms from a target, referred to as sputter deposition. During sputter deposition, a work piece, e.g., a semiconductor substrate, and a target are mounted within a processing chamber. A sputtering gas, such as argon, is flowed into the processing chamber while a DC power supply applies a negative voltage to the target, relative to the electrically grounded walls of the chamber. The negative target voltage excites the argon gas, positioned proximate to the target, into a plasma state forming argon ions. The argon ions are accelerated toward the target causing the same to emit, sputter, atoms. The atoms sputtered from the target travel toward the work piece at a differing of angles. To facilitate deposition of the sputtered atoms on the surface of the work piece, the target and work piece are placed in close proximity.

In a non-ionized sputtering process, a plasma occupies a relatively small region proximate to the target. Only a very small proportion, i.e., minority, of the sputtered atoms are ionized in the plasma. This results in a majority of the sputtered atoms maintaining a neutral charge. Control of the angular trajectories of the sputtered atoms is difficult, because the DC voltage applied to the substrate has little influence on the neutrally charged sputtered atoms. This frustrates formation of contacts in openings having high aspect ratios.

An ionized sputtering process is similar to the non-ionized sputtering process described above, but further includes a plasma generation system to form an additional plasma in the processing chamber. In this fashion, a plasma may be created between the target and the substrate that ionizes a majority of the sputtered atoms. A second power supply, typically generating RF power, is employed to bias the substrate, relative to the plasma. This facilitates control of the trajectory of the ionized sputtered material to impact the surface of the substrate along a path that is closely parallel to the normal to the surface. In this fashion, the characteristics of the layer disposed on features with high aspect ratios are greatly improved. However, drawbacks exist with respect to the ionized sputtering process. The ionized sputtering process may create contaminants that undermine formation of a conductive layer, which has been known to degrade the electrical characteristics of contacts by increasing the resistivity of the same.

In United States patent application number 5,707,498 to Ngan, which is assigned to the assignee of the present invention, a method is disclosed that avoids contamination of a conductive film by material sputtered from an induction coil. The method is a two- stage sputtering process in which a pasting process is performed with no RF power applied to the induction coil, during the first stage. During the pasting process, material is sputtered from a target disposed in the processing chamber that coats the induction coil. During a second stage, RF power is applied to the induction coil to create an inductively coupled plasma resulting in a desired film being formed on a semiconductor work piece. Were material sputtered from the induction coil, it is of no consequence, because it will be the same material that is sputtered from the target. The pasting process is repeated periodically, e.g., after formation of a conductive layer on a predetermined number of semiconductor work pieces, to reduce, or avoid, contamination from the induction coil.

What is needed, however, is a method and system for formation of high aspect ratio contacts having minimal resistance employing sputter deposition processes.

SUMMARY OF THE INVENTION

A method and system for depositing a conductive layer on a substrate features serially providing, proximate to the substrate, first and second batches of conductive material comprising atoms and ions, with a substantial portion of the conductive material associated with the first batch being atoms and a substantial portion of the conductive material associated with the second batch being ions. A first portion of the conductive layer is formed on the substrate from the first batch. The first portion of the conductive layer is formed before the second batch of conductive material is present. Subsequent to formation of the first portion, a second portion of the conductive layer is formed from the second batch of conductive material. To that end, a target is provided within a processing chamber and atoms are sputtered therefrom that move toward the surface of the substrate. The first and second batches of conductive material are formed from atoms sputtered from the target by intermittently generating a high-density plasma between the target and the substrate. This is achieved by having RF energy intermittently coupled, inductively, to the processing chamber. The high-density plasma is generated after the first portion of the conductive layer has reached a predetermined thickness. Typically, the substrate is biased with a voltage during deposition of the first and second portions. The target may be formed from any material suitable for depositing a conductive layer, including, aluminum, titanium, tungsten and tantalum. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic cross-sectional view of an exemplary processing chamber employed in accordance with the present invention;

Fig. 2 is flow diagram showing a method of depositing a conductive layer in the processing chamber shown above in Fig. 1, in accordance with the present invention;

Fig. 3 is simplified plan view of a processing environment in which the processing chamber shown above in Fig. 1 may be disposed;

Fig. 4 is a plan view of a gap in a substrate lined with a first portion of a conductive layer; and

Fig. 5 is a plan view showing the formation of the second portion of the conductive layer in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Fig. 1, an exemplary processing system 10 includes a housing 12. The housing 12 is typically formed from aluminum and defines a processing chamber 14 that has a sidewall 16, a cover 18, and a lower 20 wall, disposed opposite to the cover 18. A magnetron target assembly includes a target 22 and rotating magnets 24 and 26 that are positioned proximate to the cover 18. Specifically, the cover 18 is positioned between the target 22 and the magnets 24 and 26. A substrate support 28 is positioned within the chamber 14 opposite the target 22. In this manner, a semiconductor substrate 29, is disposed opposite to the target 22 when placed on the substrate support 28. A voltage source 30, typically a DC power supply, is in electrical communication with the target 22. A substrate voltage source is in electrical communication with the substrate support 28 that typically generates RF power, but may also generate a DC potential. Supplies of process gases 36 are selectively placed in fluid communication with the processing chamber 14 via flow valves 38. A coil 40 is disposed adjacent to the sidewall 16, inside the processing chamber 14, in a region located between the target 22 and the substrate support 28. The coil 40 is connected to a source of RF power 42 and electrically insulative spacers (not shown) are connected between the sidewall 16 and the coil 40. A pressure control system regulates the chamber pressure and includes a pump 44 in fluid communication with the processing chamber 14 via a multi-position gate valve 46. A conventional controller circuit 50 controls the operation of the processing system. The conventional controller circuit 50 is in electrical communication with the voltage source 30, the magnets 24 and 26, the sources of power 32 and 42, the pressure controller system, and the valves 38 and 46, and is discussed more fully below with respect to Figs. 1 and 4.

During operation, one of the process gases from the supplies 36 flows into the processing chamber 14 and the vacuum system exhausts gas from the processing chamber 14 to maintain the chamber pressure at a desired level, e.g., 0.1 to 50 milliTorr. The source of RF power 42 supplies a signal to the inductive coil 40 having a frequency in the range of 0.5 MHz to 100 MHz and a power level on the order of 1,500 watts. The substrate support 28 is biased, by the support source of voltage, with an appropriate voltage, e.g., a DC voltage in the range of -200 to 0 volts. In this manner, a substrate 29 disposed on the substrate holder 28 is biased. The target voltage source 30 supplies a negative DC voltage to the target 22 in the range of -600 to -100 volts, as measured from ground, at a power level in the range of 1,000 to 20,000 Watts. This excites process gas in close proximity to the target 22 into a plasma state by creating a plurality of radicals. An exemplary process gas is an inert gas such as argon. The negative voltage potential of the target 22 accelerates argon radicals toward the target 22 that causes emission, i.e., sputtering, of the material from which the target 22 is formed. A substantial majority of the sputtered material are atoms in a neutral state, i.e., a minority of the sputtered material is ionized. A substantial portion of the sputtered atoms travels into the coil region of the processing chamber 14 that is adjacent to the inductive coil 40. The RF signal supplied to the inductive coil 40 excites the sputtered atoms that enter the coil region into a high-density plasma, forming ions. The bias voltage on the substrate holder results in the trajectories of the ions being substantially parallel to a normal to the substrate 29 surface to form a film layer. In this manner, the step coverage of the film layer is greatly enhanced. It has been found, however, that the resistance of the contacts was undesirable when depositing a film in this manner on a patterned surface of a substrate having features with aspect ratios of 3:1 and greater. Specifically, it was found that the resistance associated with contacts was greatly increased. It is believed that the increase in resistivity results from re-sputtering of the material from the portion of the substrate 29 in which the gap is formed. In this example, the re-sputtering of the native oxide of the material from which the substrate 29 is formed, silicon oxide, causes large amounts of oxygen impurity to deposit in the gap. This extra oxygen reacts with the silicon in the gap forming silicon oxide, which is a good dielectric, e.g., increasing the overall resistance associated with a contact formed therein.

Referring to both Figs. 1 and 2, to minimize the resistance associated with the contact, the present method covers the substrate surface, particularly in regions thereof having features with high aspect ratios, with a conductive layer before introduction of the ionized sputtered material proximate to the substrate 29. This is achieved by serially providing, proximate to the substrate, first and second batches of conductive material, with a substantial majority of the conductive material associated with the first batch being atoms and a substantial majority of the conductive material associated with the second batch being ions. For purposes of the present invention, substantial majority is defined as nearly all. To that end, at step 60 argon gas flows into the processing chamber 14 with the vacuum system exhausting gas from the processing chamber 14 to maintain the chamber pressure to a desired level.

At step 62, conductive material is sputtered from the target by exciting the argon gas into a plasma state maintained in close proximity to the target 22. This is achieved by having the target voltage source 30 bias the target 22 with a negative DC voltage.

At step 64, the sputtered material moves toward the substrate 29, which comprises the first batch of material. The first batch of conductive material consists mostly of electrically neutral atoms. However, it is possible that a small portion of the sputtered material consists of electrically charged ions. It is said, therefore, that a substantial portion, i.e., almost all, of the sputtered material consists of electrically neutral atoms. This is achieved, at step 66, by maintaining, the inductive coil 40 in an unbiased state. To that end, the inductive coil may be very close to, if not at, ground potential, or the may float at an undefined potential, i.e., no biasing voltage is applied thereto. In this manner, a first portion of a conductive layer is formed on the substrate from the first batch of conductive material a substantial majority of which consists of atoms in a neutral state, i.e., a minority of the conductive material is ionized.

At step 68, it is determined whether the first portion has reached a predetermined thickness using techniques known in the art, e.g., timing the sputtering process and knowing the deposition rate of the sputtered material onto the substrate surface. Were it determined that the first portion had not reached a predetermined thickness, the process would continue from step 60.

Were it determined that the first portion had reached a predetermined thickness, then, at step 70, the source of RF power 42 would supply an RF signal to the inductive coil 40, creating a high-density plasma from sputtered atoms in the coil region of the processing chamber 14. In this manner, the second batch of conductive material is formed in which a substantial majority thereof consists of electrically charged ions. At step 72 process conditions are maintained, such as the bias voltage on the substrate holder, that results in the trajectories of the ions being substantially parallel to a normal to the substrate surface to form a second portion of the conductive layer. Typically, the second portion of the conductive layer is not formed until the first portion has reached a thickness in the range of 40 to 60Ainclusive with 5θAbeing preferred.

Referring to Figs. 1 and 3, in an exemplary embodiment, the conventional controller 50 may include a hard disk drive (not shown), a floppy disk drive (not shown) and a processor (not shown). The processor (not shown) may contain a single-board computer (SBC), analog and digital input/output boards, interface boards and stepper motor controller boards that may conform to the Versa Modular European (VME) standard that defines board, card cage, and connector dimensions and types. The VME standard also defines the bus structure as having a 16-bit data bus and a 24-bit address bus. The controller 50 operates on control software, which is a computer program stored in a computer-readable medium such as the memory 74. The computer program includes sets of instructions that dictate the timing, mixture of fluids, chamber pressure, chamber temperature, RF power levels, and other parameters of a particular process. The interface between a user and controller 50 may be via a visual display (not shown). To that end, two monitors 76 and 78 may be employed. One monitor 76 may be mounted in a clean room wall 80 having one or more processing systems 10 and 11. The remaining monitor 78 may be mounted behind the wall 80 for service personnel. The monitors 76 and 78 may simultaneously display the same information. Communication with the controller 50 may be achieved with a light pen associated with each of the monitors 76 and 78. For example, light pen 82 facilitates communication with the controller 50 through monitor 78, and light pen 84 facilitates communication with the controller 50 through monitor 80. A light sensor in the tip of the light pens 82 and 84 detects light emitted by CRT display in response to a user pointing the same to an area of the display screen. The touched area changes color, or a new menu or screen is displayed, confirming communication between the light pen and the display screen. Other devices, such as a keyboard, mouse, or other pointing or communication device, may be used instead of or in addition to the light pens 82 and 84 to allow the user to communicate with the system controller 50.

The process for depositing the film can be implemented using a computer program product that is executed by the system controller 50. The computer program code can be written in any conventional computer readable programming language: for example, 68000 assembly language, C, C++, Pascal, Fortran and the like. Suitable program code is entered into a single file, or multiple files, using a conventional text editor and stored or embodied in a computer-readable medium, such as a memory system of the computer. If the entered code text is in a high level language, the code is compiled, and the resultant compiler code is then linked with an object code of precompiled Windows® library routines. To execute the linked and, compiled object code the system user invokes the object code, causing the computer system to load the code in memory. The controller 50 then reads and executes the code to perform the tasks identified in the program. In an exemplary sputter deposition process, in situ formation of titanium suicide is achieved by resistively heating substrate support 28 to a temperature between 450°C and 750°C. The substrate support 28 additionally includes a throughway (not shown) that is connected to a supply of an inert gas, such as argon. A gas flow valve (not shown) regulates the flow of gas into the throughway. In the initial deposition step, non-ionized titanium is deposited to line the opening, or gap, where the contact is to be formed, discussed more fully below. This forms the first portion of the conductive layer being deposited. After formation of the first portion, ionized titanium atoms are deposited to form a second portion of the conductive layer. Both of these steps occur with the substrate temperature below the Ti-Si reaction temperature. After deposition of the ionized titanium, argon gas is introduced into the throughway (not shown) to raise the temperature of the substrate 20. This facilitates a reaction between titanium and silicon. At this stage, gettered contaminants are heated and become less stable and more volatile. Sputtering and formation of titanium ions are continued at elevated temperatures using backside substrate heating with argon in the presence of the high-density plasma to deposit titanium which ten forms titanium suicide. Heating of the substrate can continue without deposition to ensure that all of the titanium has been converted to titanium suicide.

Referring to both Figs. 1 and 4, during one exemplary process of titanium suicide formation, a first portion 90 of a conductive layer of titanium having a thickness ranging from 25Ato lOOAwas deposited to line the openings formed on the substrate 29. The first portion 90 was deposited or/and formed by sputtering titanium atoms from the target 22 without the presence of argon gas in the throughway, without an RF signal being applied to the inductive coil 40 and without biasing the substrate holder 28 with a voltage. After formation of the first portion 90, sputtering of titanium atoms from the target continued with RF power being supplied to the inductive coil 40 and the substrate holder 28 being bias to a negative DC voltage. However, no argon gas was present in the throughway. In this manner, a second portion 92 of the conductive layer was formed adjacent to the first portion 30 fill the gap with a layer of titanium, shown in Fig. 5. After formation of the second portion 92, argon gas was introduced into the throughway to heat the substrate to a temperature of about 580°C that initiated a reaction between the titanium and the silicon substrate to form titanium silicide. Sputtering of titanium ions was continued while heating with backside argon gas flowing into the throughway until the desired titanium silicide layer thickness was obtained, thereby completing the formulation a second portion 92 of the titanium silicide layer. This facilitated formation of a titanium silicide layer in a gap having an aspect ratio of 8:1 with superior step coverage, i.e., virtually no void being present, thereby greatly reducing the resistance of the resulting contact.

Although the invention has been described in terms of specific embodiments, one skilled in the art will recognize that various changes to the reaction conditions, i.e., temperature, pressure, film thickness and the like can be substituted and are meant to be included herein. In addition, other conductive materials may be employed in addition to those discussed above. Therefore, the scope of the invention should not be based upon the foregoing description. Rather, the scope of the invention should be determined based upon the claims recited herein, including the full scope of equivalents thereof.

Claims

WHAT IS CLAIMED IS:

1. A method of depositing a conductive layer on a substrate positioned in a semiconductor processing chamber, said method comprising: serially providing, within said processing chamber proximate to said substrate, first and second batches of conductive material comprising atoms and ions, with a substantial portion of the conductive material associated with said first batch being atoms and a substantial portion of the conductive material associated with said second batch being ions; and forming, on said substrate, a first portion of said conductive layer from said first batch, with said first portion of said conductive layer being formed before providing said second batch of conductive material.

2. The method as recited in claim 1 wherein serially providing first and second batches includes biasing said substrate with a voltage.

3. The method as recited in claim 1 wherein serially providing first and second batches includes providing a target of conductive material and sputtering a portion of said conductive material to create a plurality of dislodged conductive atoms, and creating a plasma.

4. The method as recited in claim 3 wherein creating said plasma occurs after said first portion has been formed.

5. The method as recited in claim 3 wherein creating said plasma occurs after said first portion has obtained a predetermined thickness.

6. The method as recited in claim 3 wherein creating said plasma includes inductive coupling RF energy into said chamber.

7. The method as recited in claim 3 wherein creating said plasma includes introducing an inert gas into said chamber and dissociating atoms associated with said inert gas.

8. The method as recited in claim 1 further including forming a second, portion of said conductive layer after forming of said first portion, with said second portion being formed from said second group of conductive atoms.

9. The method as recited in claim 1 wherein said substrate is formed from a semiconductor material and said conductive material of said first and second batches are selected from the set consisting of aluminum, titanium, tungsten, and tantalum.

10. The method as recited in claim 5 wherein said predetermined thickness is in the range of 40 to 60 Angstroms.

11. A method of depositing a conductive layer on a substrate positioned in a semiconductor processing chamber, said method comprising: providing, within said processing chamber proximate to said substrate, a first batch of conductive material; creating a plasma in said processing chamber to provide proximate to said substrate, a second batch of conductive material, with a substantial portion of the conductive material associated with said first batch consisting of atoms and a substantial portion of the conductive material associated with said second batch consisting of ions; biasing said substrate with a voltage; and forming, on said substrate, a first portion of said conductive layer from said first batch, with said first portion of said conductive layer being formed before providing said second batch of conductive material.

12. The method as recited in claim 11 further including providing, within said processing chamber, a target formed from conductive material and sputtering a portion of said conductive material to create a plurality of dislodged conductive atoms.

13. The method as recited in claim 12 wherein creating a plasma occurs after said first portion has obtained a predetermined thickness.

14. The method as recited in claim 13 further including forming a second, portion of said conductive layer after forming of said first portion, with said second portion being formed from said second batch of conductive material.

15. The method as recited in claim 14 wherein said substrate is formed from a semiconductor material and said conductive material of said first and second batches is selected from the set consisting of aluminum, titanium, tungsten, and tantalum.

16. The method as recited in claim 15 wherein said predetermined thickness is in the range of 40 to 60 Angstroms.

17. A system for processing a substrate in a processing chamber, said system comprising: means for serially providing, within said processing chamber proximate to said substrate, first and second batches of conductive material, with a substantial majority of the conductive material associated with said first batch consisting of atoms and a majority of the conductive material associated with said second batch consisting of ions; and means for forming, on said substrate, a first portion of said conductive layer from said first batch, with said first portion of said conductive layer being formed before providing said second batch of conductive material.

18. A processing system for a substrate, said system comprising: a body defining a processing chamber; a plasma generation system in electrical communication with said processing chamber; a holder, disposed within said processing chamber, to support said substrate; a conductive target positioned within said processing chamber, spaced- apart from said holder; a gas delivery system in fluid communication with said processing chamber; a temperature control system in thermal communication with said processing chamber; a pressure control system in fluid communication with said processing chamber; a source of voltage in electrical communication with said target and said holder; a controller in electrical communication with said plasma generation system, said gas delivery system, said temperature control system, said pressure control system and said source of voltage; and a memory in data communication with said controller, said memory comprising a computer-readable medium having a computer-readable program embodied therein, said computer-readable program including a first set of instructions for controlling said plasma generation system to serially provide, within said processing chamber, first and second batches of conductive material comprising of atoms and ions, with a substantial majority of the conductive material associated with said first batch being atoms and a substantial majority of the conductive material associated with said second group being ions, and a second set of instructions to maintain process conditions to form, on said substrate, a first portion of said conductive layer from said first batch before said second batch of conductive material is present in said processing chamber.

19. The system recited in claim 18 wherein said computer readable program includes an additional set of instructions for controlling said voltage source to bias said substrate with a voltage.

20. The system as recited in claim 18 wherein said first set of instructions includes an additional set of instructions for controlling said plasma generation system to sputter atoms from said target.

21. The system as recited in claim 18 wherein said first set of instructions includes an additional set of instructions for controlling said plasma generation system to form a plasma, between said target and said holder after said first portion has obtained a predetermined thickness.