WO2002071152A2

WO2002071152A2 - Method of controlling the thickness of layers of photoresist

Info

Publication number: WO2002071152A2
Application number: PCT/US2002/002268
Authority: WO
Inventors: Scott G. Bushman; Curtis W. Doss; Anthony J. Toprac
Original assignee: Advanced Micro Devices, Inc.
Priority date: 2001-02-23
Filing date: 2002-01-25
Publication date: 2002-09-12
Also published as: WO2002071152A3; AU2002240098A1

Abstract

In one illustrative embodiment, the present invention is directed to a method comprised of forming a first layer of photoresist above a first semiconducting substrate, sensing a thickness of the first layer of photoresist, and providing the sensed thickness of the first layer of photoresist to a controller (36). The method further comprises determining at least one parameter of a process used to form a second layer of photoresist above a second semiconducting substrate based upon the sensed thickness, and forming the second layer of photoresist using a process comprised of the determined at least one parameter.

Description

METHOD OF CONTROLLING THE THICKNESS OF LAYERS OF PHOTORESIST

TECHNICAL FIELD

The present invention is generally related to the field of semiconductor processing, and, more particularly, to a method of controlling the thickness of a layer of photoresist formed above a process layer.

BACKGROUND ART In general, semiconductor devices are manufactured by forming many process layers comprised of various materials above a semiconducting substrate, and, thereafter, removing selected portions of the layers, i.e., patterning the layers. This patterning may be accomplished using known photolithography and etching processes to define the various features of the device, e.g., the gate insulation layer, the gate electrode, sidewall spacers, metal lines and contacts, etc. This forming and patterning of the process layers is typically performed layer by layer as the individual layers are formed, although multiple layers may be patterned at any given time.

Photolithography is a common process used in patterning these various layers. Photolithography typically involves the use of a product known as photoresist. During the photolithography process, a feature that is desired to be formed in the underlying process layer is first formed in a layer of photoresist. Thereafter, the pattern in the layer of photoresist is transferred to the underlying process layer by performing one or more etching processes on the exposed portion of the process layer. There are positive and negative photoresist products currently available on the market. Negative photoresists produce a negative image of a pattern formed on a reticle, i.e., gaps or spaces in the reticle pattern appear as lines in the layer of photoresist. This occurs because exposure of the negative resist to a light source, i.e., through the reticle, makes the resist less soluble. Positive resists behave in an opposite manner. That is, with positive photoresists, exposure to a light source makes the resist more soluble which ultimately results in a resist pattern that is a reproduction of the reticle pattern.

In general, the photolithography process involves forming a layer of photoresist above a previously formed process layer, and exposing selected portions of the layer of photoresist to a light source to form a pattern in the photoresist that is desired to be formed in the underlying process layer. All of these steps are typically performed in well-known photolithography modules that include a section for depositing the photoresist on the wafer, e.g., a spin-coating station, a device for selectively exposing portions of the photoresist layer to a light source through a reticle, e.g., a stepper, and a section for rinsing and developing the photoresist layer after it has been selectively exposed to the light source. Thereafter, an etching process, such as a plasma etching process, is performed to remove portions of the underlying process layer that are not covered by the patterned layer of photoresist, i.e., the patterned layer of photoresist acts as a mask. After the etching process is complete, the patterned photoresist layer is removed so that additional process layers may be formed above the now patterned process layer. The purpose of the photoresist application step is to form a thin, uniform, defect-free film of photoresist above the substrate surface. A typical layer of photoresist may have a thickness varying from approximately .15-15 μm (1500-15,000 A), and it usually is required to have a uniformity of + .01 μm (±100 A). Typically, when resist types are switched, and/or target thicknesses of the layer of photoresist are changed, test wafers are run to determine the thickness of the photoresist produced by the system. All of these qualification processes are time consuming and generally contribute to less efficient semiconductor manufacturing operations.

The present invention is directed to a method of solving or at least reducing some or all of the aforementioned problems. DISCLOSURE OF INVENTION

In one illustrative embodiment, the present invention is directed to a method comprised of forming a first layer of photoresist above a process layer formed above a first semiconducting substrate, sensing a thickness of the first layer of photoresist, and providing the sensed thickness of the first layer of photoresist to a controller. The method further comprises determining, based upon the sensed thickness of the first layer of photoresist, at least one parameter of a process used to form a second layer of photoresist above a process layer formed above a second semiconducting substrate, and forming the second layer of photoresist using a process comprised of the determined at least one parameter.

BRIEF DESCRIPTION OF THE DRAWINGS The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

Figure 1 is a cross-sectional view of a process whereby a quantity of photoresist is positioned on a previously formed process layer;

Figure 2 is a cross-sectional view of a layer of photoresist formed by a spin-coating process; Figure 3 depicts one illustrative embodiment of a system that may be employed with the present invention; and

Figure 4 depicts one illustrative embodiment of the present invention in flowchart form. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

MODE(S) FOR CARRYING OUT THE INVENTION

Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The present invention will now be described with reference to Figures 1-4. Although the various regions and structures of a semiconductor device are depicted in the drawings as having very precise, sharp configurations and profiles, those skilled in the art recognize that, in reality, these regions and structures are not as precise as indicated in the drawings. Additionally, the relative sizes of the various features depicted in the drawings may be exaggerated or reduced as compared to the size of those feature sizes on fabricated devices. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present invention.

In general, the present invention is directed to a method of controlling the thickness of layers of photoresist. As will be readily apparent to those skilled in the art upon a complete reading of the present application, the present method is applicable to a variety of technologies, e.g., NMOS, PMOS, CMOS, etc., is readily applicable to a variety of devices, including, but not limited to, logic devices, memory devices, etc.

As shown in Figure 1, a wafer or semiconducting substrate 10 having a process layer 18 formed thereabove is positioned on a rotational element, such as a vacuum chuck 12. A vacuum may be applied, as indicated by arrow 14, to secure the substrate 10 to the vacuum chuck 12. The vacuum chuck 12 and the substrate 10 are capable of being rotated in the direction indicated by arrow 26. Photoresist from a source (not shown) is applied on the process layer 18 via a dispenser arm 20. As shown in Figure 1, a puddle of photoresist 21 is formed above the process layer 18. The substrate 10 may or may not be rotating at the time the puddle of photoresist 21 is deposited on the process layer 18. Thereafter, as shown in Figure 2, the substrate 10 is rotated such that the photoresist material is spread across the surface 19 of the process layer 18 and a layer of photoresist 23 is formed above the surface 19 of the process layer 18.

As will be recognized by those skilled in the art, the process layer 18 is meant to be illustrative only in that it may be comprised of any of a variety of materials, and there may be one or more intervening process layers between the process layer 18 and the substrate 10. For example, the process layer 18 may be comprised of an oxide, an oxynitride, a nitride, silicon dioxide, silicon nitride, a metal, polycrystalline silicon ("polysilicon"), or any other of a variety of materials used in semiconductor processing that may be patterned using photolithographic techniques. Moreover, the photoresist used with the present invention may be either a positive or negative type photoresist.

In the disclosed embodiment, the layer of photoresist 23 is formed by a spin-coating process. In many modern fabrication facilities, a spin-coating process involving a moving dispenser arm 20 is used to form layers of photoresist. In that process, the substrate 10 is rotated at a relatively low speed prior to the deposition of any photoresist material 21 on the process layer 18. As the photoresist material 21 is deposited on the substrate 10, the dispenser arm 20 moves in a more or less radially outward fashion, beginning at the center of the substrate 10 and moving outward. This technique is used to more evenly distribute the photoresist across the surface 19 of the process layer 18. Of course, as will be apparent to those skilled in the art upon reading the present application, the present invention is not limited to this particular spin-coating technique. For example, the present invention may also be used in processing techniques in which the dispenser arm 20 remains at the approximate center of the substrate 10. In that situation, the substrate 10 is initially rotated at a relatively low speed and photoresist material 21 is dispensed on the approximate center of the process layer 18. At that time, the rotational speed of the substrate is increased so as to disperse the photoresist. In yet another alternative embodiment, a static-type spin-coating process may be used in which the photoresist material 21 is deposited in the approximate center of a process layer 18 while the process layer 18, i.e., wafer 10, is stationary. Thereafter, the substrate 10 is rotated to disperse the photoresist evenly across the surface 19 of the process layer 18. If desired or required, a separate primer coating process may also be used prior to applying the photoresist above the process layer 18 in any of the above-described spin-coating methods. In general, the present invention is directed to sensing the thickness of a first layer of photoresist formed above a wafer, providing that sensed thickness to a controller, and using that sensed thickness for controlling one or more parameters of a photoresist application process used to form a second layer of photoresist above one or more subsequent wafers. Parameters such as the rotational speed of the wafer, the volume of photoresist dispensed, the dispenser pressure, acceleration, rate of the wafer, dispenser position, etc. may be varied if the determined thickness of the first layer of photoresist is outside of an acceptable thickness range. For example, if the determined thickness of the first layer of photoresist is less than desired, the rotational speed of the wafer 10 may be decreased, or the volume of photoresist dispersed through the dispenser arm 20 may be increased in the formation of a layer of photoresist above subsequently processed wafers. Conversely, if the layer of photoresist is thicker than desired, the rotational speed of the wafer may be increased, or the volume of photoresist may be decreased when forming photoresist layers on later processed wafers. Of course, the present invention may be used to control more than one parameter of the photoresist application process. For example, in a process recipe used to form layers of photoresist on subsequently processed wafers, both the rotational speed of the substrate 10 and the volume of photoresist applied may be varied or determined. Figure 3 depicts one illustrative embodiment of a system 30 that may be used with the present invention. As shown therein, a system 30 for processing wafers 32 is comprised of a photolithography tool 34, used for forming a layer of photoresist 23, a metrology tool 38, and an automatic process controller 36. The metrology tool 38 is used to measure or sense the thickness of a layer of photoresist 23 that is applied by the photolithography tool 34. The metrology tool 38 may be any type of device capable of measuring the thickness of the layer of photoresist 23, e.g., an Optiprobe manufactured by Thermawave, Inc. Moreover, the metrology tool 38 may be a stand-alone device or system, or it may be incorporated into the photolithography tool 34, or a system containing both. The photolithography tool 34 is used to form a layer of photoresist above the process layer 18. The photolithography tool 34 may be any tool useful for forming such layers of photoresist, e.g., a photolithography track manufactured by Tokyo Electron or ASML.

In one embodiment, the automatic process controller 36 interfaces with the metrology tool 38 to control, determine or vary one or more parameters of the process used to form a photoresist layer 23 on subsequent wafers. That is, the controller 36 may be used to control, determine or vary parameters such as the rotational speed of the substrate 10, the volume of the photoresist applied via the dispenser arm 20, the dispenser pressure, etc. In particular, the thickness of a first layer of photoresist is sensed by the metrology tool 38, via line 31, and that information is supplied to the controller 36, via line 33. Thereafter, the controller 36 determines, controls and/or varies one or more parameters of the process used to form a layer of photoresist on subsequently processed wafers 10. That is, the thickness of the first layer of photoresist 23 is fed forward to the controller 36, and one or more parameters of a process used to form a second layer of photoresist on a subsequent wafer are controlled based upon this determined thickness. For example, if the thickness of the first layer of photoresist is less than desired, the rotational speed of subsequently processed substrates 10 may be decreased. Conversely, if the thickness of the first layer of photoresist is greater than desired, the rotational speed of subsequently processed substrates 10 may be increased.

The present invention may be employed on a lot-by-lot basis and/or on a wafer-by-wafer basis. Moreover, the number of layers measured may be varied depending upon the desired degree of accuracy. In general, the more frequent the measurements, the more accurate will be the adjustment to the process used to form layers of photoresist on subsequently processed wafers.

In the illustrated embodiment, the automatic process controller 36 is a computer programmed with software to implement the functions described. However, as will be appreciated by those of ordinary skill in the art, a hardware controller (not shown) designed to implement the particular functions may also be used. Moreover, the functions of the controller described herein may be performed by one or more processing units that may or may not be geographically dispersed. Portions of the invention and corresponding detailed description are presented in terms of software, or algorithms and symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the ones by which those of ordinary skill in the art effectively convey the substance of their work to others of ordinary skill in the art. An algorithm, as the term is used here, and as it is used generally, is conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of optical, electrical, or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, or as is apparent from the discussion, terms such as "processing" or "computing" or "calculating" or "determining" or "displaying" or the like, refer to the actions and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical, electronic quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. An exemplary software system capable of being adapted to perform the functions of the automatic process controller 36, as described, is the ObjectSpace Catalyst system offered by KLA-Tencor, Inc. The KLA- Tencor Catalyst system uses Semiconductor Equipment and Materials International (SEMI) Computer Integrated Manufacturing (CIM) Framework compliant system technologies, and is based on the Advanced Process Control (APC) Framework. CIM (SEMI E81-0699 - Provisional Specification for CIM Framework Domain Architecture) and APC (SEMI E93-0999 - Provisional Specification for CIM Framework Advanced Process Control Component) specifications are publicly available from SEMI.

Referring to Figure 4, an illustrative embodiment of the present invention is depicted in flowchart form. As shown therein, the present invention comprises forming a first layer of photoresist above a process layer formed above a first semiconducting substrate, as set forth at block 40, sensing a thickness of the first layer of photoresist, as recited at block 42, and providing the sensed thickness of the first layer of photoresist to a controller, as set forth at block 44. The method further comprises determining at least one parameter of a process used to form a second layer of photoresist above a process layer formed above a second semiconducting substrate based upon the sensed thickness of the first layer of photoresist, as indicated at block 46, and forming the second layer of photoresist using a process comprised of the determined at least one parameter. The step of forming the layer of photoresist, as set forth at block 40, may be any type of process useful for forming such layers. For example, any of the spin-coating type processes described herein may be employed. Of course, the present invention should not be considered limited to those particular methods unless such methods are specifically recited in the appended claims. Sensing the thickness of the first layer of photoresist, as set forth at block 42, may be accomplished by any metrology tool capable of sensing or measuring such a thickness. As set forth previously, one illustrative sensor that may be used for this purpose is an Optiprobe manufactured by Thermawave, Inc. Moreover, although only one such metrology tool 38 is schematically depicted in the disclosed embodiment, more than one such tool may be used if desired or deemed necessary. For example, multiple metrology tools 38 may be positioned so as to provide multiple readings as to the thickness of the photoresist layer 23. In that case, the thickness described at block 42 may represent only one of the thicknesses sensed, or it may represent an average of all thicknesses sensed, etc. This sensed thickness is then provided to a controller, as described at block 44.

Next, as set forth at block 46, the present method involves determination of at least one parameter of a process used to form a second layer of photoresist on a subsequently processed wafer. Any of a variety of parameters of the process may be determined, varied or adjusted, e.g, the rotational speed of the second substrate, the volume of photoresist deposited on the process layer, the dispenser pressure, etc. As will be appreciated by those skilled in the art, the volume of photoresist applied may be controlled by adjusting the dispenser pressure. Additionally, the present invention may be used in situations where more than one parameter of the process used to form the second layer of photoresist on the subsequently processed wafers is varied or determined. That is, in the appropriate situations, both the rotational speed of the substrate and the volume of the photoresist dispensed may be determined or varied.

As set forth in block 46, the step of determining at least one parameter of a process used to form the second layer of photoresist based upon the sensed thickness of the first layer of photoresist may be performed by a variety of techniques. For example, a database may be developed that correlates the determined thickness of the first layer of photoresist to one or more corresponding parameters of the process used to form the second layer of photoresist. Alternatively, one or more parameters of the process used to form the second layer of photoresist may be calculated based upon the determined thickness of the first layer of photoresist. Other methodologies are also possible.

Lastly, as set forth at block 48, the present invention comprises forming the second layer of photoresist using a process comprised of at least one of the determined parameters. The present invention may be employed on either a lot-by-lot basis or on a wafer-by-wafer basis. Through use of the present invention, more uniform layers of photoresist may be formed, and they may be formed without excessive testing on non- production wafers, all of which results in a more efficient manufacturing operation.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.

Claims

1. A method, comprising: forming a first layer of photoresist above a process layer formed above a first semiconducting substrate; sensing a thickness of said first layer of photoresist; providing said sensed thickness of said first layer of photoresist to a controller (36) that determines, based upon said sensed thickness of said first layer of photoresist, at least one parameter of a process used to form a second layer of photoresist a second semiconducting substrate; and forming said second layer of photoresist using a process comprised of said determined at least one parameter.

2. The method of claim 1, wherein forming a first layer of photoresist above a first semiconducting substrate comprises spin-coating a first layer of photoresist above a first semiconducting substrate.

3. The method of claim 1. wherein sensing a thickness of said first layer of photoresist comprises measuring a thickness of said first layer of photoresist.

4. The method of claim 1, wherein sensing a thickness of said first layer of photoresist comprises sensing a thickness of said first layer of photoresist with an optical measurement tool.

5. The method of claim 1, wherein providing said sensed thickness of said first layer of photoresist to a controller (36) comprises providing said sensed thickness of said first layer of photoresist to a controller (36) resident on a photolithography tool (34).

6. The method of claim 1, wherein providing said sensed thickness of said first layer of photoresist to a controller (36) comprises providing said sensed thickness of said first layer of photoresist (36) to a stand-alone controller (36).

7. The method of claim 1, wherein said at least one parameter comprises at least one of a rotational speed of said second substrate, a rotational acceleration rate of said second substrate, a positioning of a dispenser nozzle, a volume of a photoresist material, and a dispenser pressure of a process used to form a second layer of photoresist above a second semiconducting substrate.

8. The method of claim 1, wherein forming said second layer of photoresist using a process comprised of said determined at least one parameter comprises spin-coating said second layer of photoresist using a process comprised of said determined at least one parameter.

9. A method, comprising: spin-coating a first layer of photoresist above a first semiconducting substrate; sensing a thickness of said first layer of photoresist; providing said sensed thickness of said first layer of photoresist to a controller (36) that determines, based upon said sensed thickness of said first layer of photoresist, at least one of a rotational speed of said substrate, a volume of a photoresist material, and a dispenser pressure of a process used to form a second layer of photoresist above a second semiconducting substrate; and spin-coating said second layer of photoresist using a process comprised of said at least one of said determined rotational speed of said substrate, a rotational acceleration rate of said second substrate, a positioning of a dispenser nozzle, a volume of a photoresist material, and a dispenser pressure.

10. The method of claim 9, wherein sensing a thickness of said first layer of photoresist comprises sensing a thickness of said first layer of photoresist with an optical measurement tool.

11. The method of claim 9, wherein providing said sensed thickness of said layer of photoresist to a controller (36) comprises providing said sensed thickness of said layer of photoresist to a controller (36) resident on a photolithography tool (34).

12. The method of claim 9, wherein providing said sensed thickness of said layer of photoresist to a controller (36) comprises providing said sensed thickness of said layer of photoresist to a stand-alone controller (36).

13. A method, comprising: spin-coating a first layer of photoresist above a first semiconducting substrate; sensing a thickness of said first layer of photoresist; providing said sensed thickness of said first layer of photoresist to a controller (36) that varies, at least one parameter of a process used to form a second layer of photoresist above a second semiconducting substrate based upon said sensed thickness of said first layer of photoresist; and spin-coating said second layer of photoresist using a process comprised of said varied at least one parameter.

14. The method of claim 13, wherein said at least one parameter comprises at least one of a rotational speed of said substrate, a rotational acceleration rate of said second substrate, a positioning of a dispenser nozzle, a volume of a photoresist material, and a dispenser pressure.

15. A system, comprising: a metrology tool (38) for sensing a thickness of a first layer of photoresist formed above a first semiconducting substrate; a controller (36) that determines at least one parameter of a process used to form a second layer of photoresist above a second semiconducting substrate based upon said sensed thickness of said first layer of photoresist; and a photolithography tool (34) for forming said second layer of photoresist using a process comprised of said determined parameter.