Chemical vapor deposition method and apparatus

Abstract

The present disclosure relates to a method for chemical vapor deposition on a substrate, the method comprising a precursor step and a reactant step, the precursor step comprising chemisorbing a layer of precursor molecules onto a substrate (170), the reactant step comprising adding a species capable of reducing the precursor molecules to at least a portion of a surface of the substrate (170) whereby at least a portion of the reduced precursor molecules are deposited on the surface of the substrate (170), and during at least a portion of the reactant step, applying a positive bias to at least a portion of the surface of the substrate (170) by a voltage source (130), and the step of adding the reducing species comprises providing electrons as free particles by an electron source (150), whereby a closed electrical circuit is formed when the free electrons are transferred to the surface of the substrate (170) during the reactant step.

Description

Technical Field

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[0001] The present disclosure relates to chemical vapor deposition.

Background Art

[0002] Techniques for depositing thin films of materials on surfaces are used to form everything from the reflective layers of household mirrors to semiconductor devices such as processors. The desired thin films are often conductive or semiconductive.Chemical vapor deposition (CVD) is a technique for manufacturing thin films from gas molecules, and the molecules containing the atoms that form the thin film are called precursors.CVD is extremely important for the electronics industry, but it has limitations when it comes to pure metal thin films.The metal atoms in the precursor molecules are typically in a positive oxidation state, i.e., they lack electrons.Thus, the metal atoms are formally cations.In metal CVD, a molecular reducing agent that provides the missing electrons is required to deposit the metal film.However, many metals have a high reduction potential and are thus very difficult to reduce.Therefore, a strong reducing agent is required.Although some molecules with sufficiently high reducing power have been demonstrated, they are chemically complex to synthesize and difficult to use in CVD.

Summary of the Invention

[0003] In accordance with the above, there is a need for an improved deposition method that utilizes species containing atoms with a high reduction potential.

[0004] An object of the present invention is to improve the chemical vapor deposition of conductive and semiconductive materials.

[0005] This is achieved, according to this disclosure, by a method for chemical deposition onto a substrate, comprising a precursor step and a reactant step. At least a portion of the substrate surface is electronically connected to a voltage source. The precursor step includes chemically adsorbing a layer of precursor molecules onto the substrate. The reactant step includes adding a species capable of reducing the precursor molecules to at least a portion of the substrate surface. The method is characterized by applying a positive bias to at least a portion of the substrate surface by the voltage source during at least a portion of the reactant step, and the step of adding the reducing species includes transferring free electrons provided by an electron source connected to ground to at least a portion of the substrate surface, thereby forming a closed electrical circuit when the free electrons are transferred to the substrate surface during the reactant step. The term free electrons as used herein refers to electrons as free particles. The term substrate surface as used herein refers to the outermost layer of the substrate and any deposition material. The term closed circuit as used herein refers to the ability to continuously and substantially maintain a current through the substrate at a constant applied potential bias.

[0006] A positive bias attracts electrons toward a region of the substrate surface electrically connected to the voltage source. The resulting closed circuit prevents the accumulation of negative charge in the region of the substrate surface electronically connected to the voltage source. The positive bias attracts electrons to the electronically connected region of the substrate surface, and these electrons can reduce precursor molecules.

[0007] The use of free electrons to reduce precursor molecules eliminates the need to transport strong reducing agents to the surface. The use of free electrons to reduce precursor molecules may also eliminate the need to alter environmental conditions during deposition. By using free electrons to reduce precursor molecules primarily in connected regions of the surface, novel and / or improved techniques for fabricating semiconductor devices may become possible.

[0008] The electron source may be a plasma generator. Plasma generators are typically used in a vacuum chamber designed for chemical evaporation to provide a precursor. The widespread use of plasma generators in CVD setups makes this disclosure usable with minimal modifications in existing chemical evaporation systems.

[0009] This method is suitable for use with any precursor that can be chemically adsorbed onto a conductive substrate and then deposited onto the reduced substrate, at least a portion of which can be deposited. The precursor may be a metallocene molecule such as ferrocene, cobaltocene, nickerosene, or lutenocene.

[0010] To efficiently maintain the formation of film layers, the surface of the deposited material and the voltage source must remain electrically connected; therefore, the deposited material must be a conductor or semiconductor. Metallocenes are a group of molecules containing metal atoms in a positive oxidation state, such as ferrocene, cobaltocene, nickerosene, or ruthenocene. Reduction of at least some metallocenes on a conductive surface results in the deposition of metal atoms on the surface. At least some metallocenes are suitable for use as precursor molecules in this disclosure.

[0011] To reduce a multilayer of precursor molecules on a substrate surface, the method may be performed either by executing the precursor step and the reactant step simultaneously, or by cyclically executing the precursor step and the reactant step. However, for electrons to be attracted to a region on the substrate surface, the surface region must be electrically connected to a voltage source. Therefore, if the reduced precursor yields an insulating layer, the reduction of the precursor molecules will eventually stop. For the method to build layers continuously, the precursor molecules contain reducible atoms, and the solid material of the reduced atoms is at least semiconductive. As an example, precursor ferrocene may be reduced so that iron atoms in the precursor form a conductive iron film on the substrate. By taking advantage of the requirement for electrical connection between the substrate surface and the voltage source for efficient deposition, the position of layer growth can be controlled, for example, by using a substrate patterned with an insulating material created by a technique such as lithography. This disclosure may enable novel and improved methods for manufacturing integrated circuit components such as fins in fin field-effect transistors (FinFETs).

[0012] This disclosure relates to an apparatus for chemical deposition onto a substrate. The apparatus comprises a substrate holder, a substrate, a voltage source, and an electron source. The substrate holder is arranged to hold the substrate. At least a portion of the substrate surface contains chemically adsorbed precursor molecules. At least a portion of the substrate surface is electrically connected to the voltage source. The negative terminal of the voltage source may be grounded. The electron source may be grounded. The electron source is arranged to provide free electrons in the vicinity of the substrate. The apparatus is characterized in that a positive bias is applied to at least a portion of the substrate surface by the voltage source during operation. During operation, both the electron source and the positive substrate bias are active, and free electrons are transported to the substrate. The apparatus is arranged to create a closed circuit when the free electrons move onto the substrate.

[0013] The apparatus may include a vacuum deposition chamber. A substrate holder and the substrate are placed inside the vacuum deposition chamber. A voltage source and an electron source may be connected to the vacuum deposition chamber. The vacuum deposition chamber enables deposition in a low-pressure and controlled environment.

[0014] The apparatus may include a sublimation chamber equipped with a heater. The heater is positioned to hold and heat the precursor material. The sublimation chamber functions as a precursor vaporizer, providing precursor molecules into the gas phase. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 shows a schematic diagram of the apparatus for CVD. [Figure 2] Figure 2 schematically shows the apparatus for CVD in a vacuum chamber. [Figure 3A] Figures 3A and 3B schematically illustrate the two CVD methods. [Figure 3B] Figures 3A and 3B schematically illustrate the two CVD methods. [Modes for carrying out the invention]

[0016] Throughout the drawings, the same reference number refers to the same part, concept, and / or element. Therefore, anything stated with respect to a reference number in one drawing applies equally well to the same reference number in other drawings unless otherwise explicitly stated.

[0017] Figure 1 schematically shows a CVD apparatus 100 comprising a voltage source 130, a substrate holder 140, and an electron source 150. The substrate holder 140 is positioned to hold a substrate 170. At least a portion of the surface of the substrate 170 is conductive or semiconductive. At least a portion of the surface of the substrate 170 is electrically connected to the voltage source 130 when the substrate 170 is mounted in the substrate holder 140. The electron source 150 is grounded. The electron source 150 may be controlled by a grounding power supply 190. The voltage source 130 and the substrate 170 may be electrically connected via at least a portion of the substrate holder 140 positioned to form an electrical connection with the substrate 170.

[0018] The electron source 150 is positioned to provide free electrons in the vicinity of the substrate 170. The electron source 150 is, for example, a plasma generator, an electron flood gun, a field emission source, or a thermal ion source. The term "free electron" as used herein refers to an electron as a free particle. At least a portion of the surface of the substrate 170 is covered with chemiadsorbed precursor molecules. The precursor molecules on the surface of the substrate 170 include molecules that can be reduced by free electrons, such as ferrocene, thereby depositing at least a portion of the precursor molecules onto the surface of the substrate 170.

[0019] To ensure that a sufficient amount of free electrons provided by the electron source 150 reach the surface of the substrate 170, the voltage source 130 is configured to apply a positive potential relative to ground to at least a portion of the substrate 170 surface. In the region of the substrate 170 surface electronically connected to the voltage source 130, the applied potential reduces charge accumulation and attracts free electrons. During operation, a closed circuit is formed as a current flows through the substrate 170. If no new precursor molecules are added to the substrate 170 surface during operation, the number of precursor molecules on the substrate 170 surface that can be reduced can be depleted, thereby terminating the deposition process.

[0020] The apparatus 100 may include a precursor supply device that can continuously chemically adsorb a precursor onto the surface of the substrate 170 during operation. The apparatus 100 may also include a precursor supply device configured to perform a step of chemically adsorbing precursor molecules onto the surface of the substrate 170 before operating the apparatus 100 to perform a step of transporting electrons onto the surface of the substrate 170, thereby depositing multiple layers by circulating between steps.

[0021] Figure 2 shows apparatus 200 for CVD in a vacuum chamber.

[0022] In the illustrated example, the apparatus comprises a vacuum deposition chamber 110, a sublimation chamber 120, and a voltage source 130. The vacuum deposition chamber 110 is grounded. The vacuum deposition chamber 110 is configured to be connected to a pump. The vacuum deposition chamber 110 comprises a substrate holder 140, a plasma generator 250, a connection to the pump 111, and a connection to the sublimation chamber 120 112. The sublimation chamber 120 comprises a heater 160 and a connection to a gas line 121. The plasma generator 250 functions as an electron source 150. Both the connection between the chambers 112 and the connection between the sublimation chamber 120 and the gas line 121 are equipped with valves positioned to close their respective connections. The heater 160 is configured to hold and heat the precursor material. The substrate holder 140 is configured to hold the substrate 170 such that at least a portion of the substrate 170's surface is electrically connectable to the voltage source 130. The voltage source 130 is configured to apply a positive potential relative to ground to at least a portion of the surface of the substrate 170, which is electrically connected to the voltage source 130. The plasma generator 250 is grounded. The plasma generator 250 is configured to provide plasma within the plasma generation region 180. The plasma generator 250 may be controlled by the ground power supply 190. The substrate holder 140 is substantially located between the plasma generation region 180 and the connection 112 between the chamber. The plasma generation region 180 is substantially located between the connection 111 leading to the pump and the substrate holder 140. The distance between the plasma generation region 180 and the substrate holder 140 may be several centimeters.

[0023] Figures 3A and 3B schematically illustrate representative modes of two CVD processes 300A-B that include a precursor step 310, a reactant step 320, and a deposition step 330. The precursor step 310 includes chemisorbing precursor molecules onto the surface of the substrate 170. The reactant step 320 includes transporting free electrons to at least a portion of the surface of the substrate 170. The deposition step 330 includes electrons that reduce the precursor molecules at the surface of the substrate 170, and then at least a portion of the reduced precursor molecules is deposited onto the surface of the substrate 170. Unlike the user-controlled precursor step 310 and reactant step 320, the deposition step 330 represents the chemical reaction and resulting deposition at the surface of the substrate 170. Since the deposition step 330 is causally dependent on the precursor step 310 and the reactant step 320, the present disclosure may be described without the deposition step 330. The deposition step 330 is included to clarify a way in which the reactant step 320 does not necessarily deposit material onto the surface of the substrate 170.

[0024] Figure 3A illustrates a representative mode of method 300A, where the precursor step 310 and the reactant step 320 are initiated simultaneously, transporting precursor molecules and free electrons to the surface of the substrate 170, and are executed continuously and in parallel with the deposition step 330 until deposition stops by ending the precursor step 310 and / or the reactant step 320.

[0025] Figure 3B illustrates a typical mode of method 300B, in which the precursor step 310 and reactant step 320 are circulated, similar to the self-limiting steps circulated in atomic layer deposition (ALD). The precursor step 310 is performed until a sufficient amount of precursor molecules are chemically adsorbed onto the surface of the substrate 170. The addition of the precursor is stopped, for example, by closing a valve to the sublimation chamber 130 containing the vaporized precursor material. The reactant step 320 is performed until a sufficient amount of precursor molecules are reduced on the surface of the substrate 170, at which point the electron source 150 is turned off and / or the bias voltage on the surface of the substrate 170 is changed. The number of free electrons reaching the surface of the substrate 170 can be calculated based on the current flowing through the voltage source 130. Under normal operation, the deposition step 330 is performed substantially concurrently with the reactant step 320. However, if there are no readily reducible precursor molecules on the surface of the substrate 170, the deposition step 330 is not performed during the reactant step 320.

[0026] Returning to Figure 2, an example of a CVD deposition procedure utilizing this disclosure is described. The vacuum deposition chamber 110 is maintained at room temperature. First, the connection between the chambers 112 is closed. To deposit iron, ferrocene, a precursor material, is loaded into a heater 160 located in the sublimation chamber 120. To deposit cobalt, nickel, and ruthenium, cobaltocene, nickerosene, or ruthenocene may be used, respectively. A clean 10 × 10 mm substrate 170 containing a 50 nm Ag film on Si is placed on a substrate holder 140. The substrate holder 140 and the substrate 170 are located between the connector 112 to the sublimation chamber 120 and the plasma generation region 180. The substrate 170 is located several centimeters away from the plasma generation region 180. The substrate 170 and the voltage source 130 are connected by electrical leads, which bond to the Ag film on the substrate 170 at multiple points. The lead is joined to the substrate using at least a portion of the substrate holder 140, which is configured to be electrically connected to the substrate 170. The vacuum deposition chamber 110 is closed and pumped down. The connection between the chambers 112 is opened, thereby pumping both chambers down to 50 Pa (0.4 Torr). The connection between the sublimation chamber 120 and the gas line 121 is opened, and the sublimation chamber 120 is purged with 40 sccm of Ar gas for 2 hours. The connection to the gas line 121 is closed, and the chamber is pumped down to 50 Pa. The connection between the chambers 112 is closed. The heater 160 heats the precursor to the precursor sublimation temperature, 70°C for ferrocene. A voltage source applies a DC of +40V between the substrate 170 and ground, thereby giving the surface of the substrate 170 a positive bias. Simultaneously, the plasma generator 250 starts generating Ar plasma (70W, 40 sccm), and the connection between the chambers 112 is opened. When the ferrocene precursor molecules reach the surface of the substrate 170 and are reduced by electrons, Fe is deposited onto the substrate 170 surface. A film is deposited on the substrate surface with an average current of 300 mA passing through the substrate 170 for 60 seconds. Simultaneously, the Ar plasma is turned off and the connection between the chambers 112 is closed. The vacuum deposition chamber 110 is filled with nitrogen (gas inlet not shown), and the deposition is completed.

Claims

1. 1. A method (300A, B) for chemical vapor deposition onto a substrate, said method comprising: a precursor step (310); a reactant step (320), the precursor step (310) comprises chemisorbing a layer of precursor molecules onto the substrate (170), and the reactant step (320) comprises adding a surface species capable of reducing the precursor molecules to at least a portion of the substrate (170), whereby at least a portion of the chemisorbed precursor molecules are reduced and a film is deposited on the substrate (170) surface; applying a positive bias to at least a portion of the substrate (170) surface by a voltage source (130) during at least a portion of the reactant step (320); the step of adding (320) the reducing species includes providing electrons as free particles by an electron source (150); whereby, during the reactant (320) step, a closed electrical circuit is formed when the free electrons are transferred to the substrate (170) surface.

2. 10. The method of claim 1, wherein the precursor molecules comprise reducible atoms or molecules, and the solid material of reduced atoms or molecules is at least semiconductive.

3. 3. The method of claim 1 or 2, wherein the precursor molecule comprises a metallocene molecule, such as ferrocene, cobaltocene, nickelocene, or ruthenocene.

4. 4. The method of claim 1, wherein the precursor step (310) and the reactant step (320) are cycled by alternating between the precursor step (310) and the reactant step (320).

5. The method of any one of claims 1 to 4, wherein the substrate (170) is first patterned using lithography and / or etching techniques.

6. 6. The method of any one of claims 1 to 5, wherein the substrate (170) comprises a conductive substrate (170) masked with an insulating material leaving areas of the conductive substrate (170) exposed, thereby allowing deposition of material to occur only on the exposed conductive substrate (170) and a pattern of material to grow from the exposed substrate (170) areas.

7. A FET including a fin, wherein at least the fin of the FET is fabricated according to the method of claim 6.

8. An apparatus (100, 200) for chemical vapor deposition onto a substrate (170), said apparatus comprising: a substrate holder (140) for holding the substrate (170), the substrate holder being positioned such that precursor molecules are deposited on the substrate (170); a voltage source (130); a precursor molecule reducing species source positioned to provide reducing species capable of reducing the precursor molecules at the surface of the substrate (170); the precursor molecular reduced species source comprises an electron source (150), the electron source (150) positioned to provide free electrons in the vicinity of the substrate (170); the voltage source (130) is positioned to apply a positive bias to at least a portion of a surface of the substrate (170); whereby the free electrons form a closed electrical circuit when transferred to the surface of the substrate (170).

9. The apparatus of claim 8 , wherein the electron source (150) comprises a plasma generator (250).

10. 10. The apparatus of claim 8 or 9, comprising a precursor vaporizer (120, 160) arranged to provide precursor molecules in the gas phase.

11. The apparatus of any one of claims 8 to 10, comprising a vacuum chamber (110) configured to accommodate the substrate holder (140) and substrate (170) in a controlled low-pressure environment.

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