WO2014197396A1

WO2014197396A1 - Gas deposition head for spatial ald

Info

Publication number: WO2014197396A1
Application number: PCT/US2014/040557
Authority: WO
Inventors: Michael J. Sershen; Laurent Lecordier
Original assignee: Ultratech, Inc.
Priority date: 2013-06-03
Filing date: 2014-06-02
Publication date: 2014-12-11

Abstract

An improved spatial ALD coating apparatus more uniformly applies deposition material layers to all regions of a substrate coating surface. The device is configured with the spatial position of precursor nozzles sites offset from one another such that each precursor nozzle site directs process gas onto a different region of substrate.

Description

GAS DEPOSITION HEAD FOR SPATIAL ALD

Cross Reference to Related U.S. Patent Applications

[0001] This application is related to commonly owned and co-pending U.S. Patent

Application serial number 13/273,417 filed October 12, 2011 by Sershen et al. entitled ALD Coating System, the entire disclosure of which is incorporated herein by reference for all purposes.

Background of the Invention

Field of the Invention

[0002] The present invention is a gas deposition head and method for applying gas deposition material layers onto a solid substrate. In particular an improved gas deposition head performs spatial Atomic Layer Deposition (ALD) with a more uniform deposition material layer thickness.

The Related Art

[0003] An example conventional gas deposition head is disclosed in related application US2012/0141676 filed on October 14, 2011 entitled ALD Coating System. The disclosed device includes a fixed gas manifold comprising a precursor orifice plate configured to direct process gases onto a coating surface. The precursor orifice plate includes a plurality of through orifices operating as gas deposition nozzles. The gas deposition nozzles are arranged in linear arrays and positioned opposed to a moving solid substrate in a manner that causes the gas deposition nozzles to direct process gases onto a desired coating surface of the solid substrate. The gas deposition nozzles emit a continuous flow of process gases onto the coating surface. The nozzles are oriented to direct the process gas at a normal incidence angle with respect to the coating surface. The substrate is supported on a substrate transport module which transports the coating surface past the precursor orifice plate at a substantially constant velocity. The substrate transport device and the gas deposition head are arranged to provide a substantially constant separation gap between outlets of the gas depiction nozzles and the coating surface.

[0004] Generally gas deposition nozzles are arranged in linear arrays of like nozzles with one linear array for each process gas. Each linear array is disposed across a transverse width of the coating surface. Accordingly as the coating surface is transported past the gas deposition head the entire coating surface is sequentially exposed to a plurality of process gases being emitted by the linear arrays of gas nozzles.

[0005] The deposition head includes a gas manifold configured to receive each of the plurality of process gases from a gas supply module and to feed appropriate process gases to each linear array of gas nozzles. Each linear array of nozzles is associated with a

longitudinal chamber which extends over the entire linear array of gas nozzles such that a process gas delivered into the longitudinal chamber exits the chamber through each gas nozzle in the associated linear array of gas nozzles. Additionally the gas nozzles are configured with a circular diameter sized to regulate the flow of process gas exiting the longitudinal chamber in order to more uniformly deliver a substantially similar exit gas flow rate from each gas nozzle in the linear array of gas nozzles.

[0006] Referring to Figure 1 a conventional orifice plate (1000) is shown schematically. The plate (1000) includes two unit cells (1010, 1020) positioned side-by-side along a velocity axis (V). Each unit cell is configured to deposit a single gas deposition material layer onto the coating surface as the coating surface is advanced past the unit cell along the velocity vector axis (V). The unit cells are configured for a conventional spatial ALD gas deposition process which comprises sequentially applying two ALD precursors or reactants to the coating surface such that the first precursor reacts with the coating surface to form a monolayer and the second precursor reacts with the monolayer to form a material deposition layer. In operation each unit cell applies one complete deposition layer with the first deposition lying being applied to the coating surface of the solid substrate and the second deposition layer being applied over the first deposition layer.

[0007] Each unit cell includes two linear arrays of precursor nozzles (1030, 1050) on the first unit cell (1010) and (1040, 1060) on the second unit cell (1020). Each cell has a first linear array of precursor nozzles (1030, 1040) for emitting a substantially continuous flow of a first precursor (A) and a second linear array of precursor nozzles (1050, 1060) for emitting a substantially continuous flow of a second precursor (B). All four linear arrays of gas nozzles include a plurality of substantially identical circular orifices disposed along a row axis (R). Each row of gas nozzles has a row length dimension (1065) and a center to center spacing defined by a pitch dimension (1070). In the conventional embodiment disclosed in related application US2012/0141676 each linear array of gas nozzles comprises a hole pattern and all the hole patterns are identically located along the row axis (R). More specifically each hole pattern is substantially identical and located at the same reference dimension (1075) with respect to a reference edge, e.g. the bottom edge of the unit cell. As a result same position gas nozzles in the cells (1010) and (1020) are collinear along linear axes (VI) and (V2).

[0008] One problem with the convention unit cell shown schematically in Figure 1 is that same position gas nozzles in each unit cell are collinear along a velocity axis (V).

Accordingly all four same position precursor nozzles emit precursor onto the same region of the coating surface as the coating surface is advance past the gas deposition head. As a result regions of the coating surface that fall directly under gas nozzle sites are directly under the precursor nozzle for each unit cell while other regions of the coating surface e.g. the region between adjacent nozzle sites are always more distal from a gas nozzle location.

[0009] Applicants have discovered the conventional gas deposition head of Figure 1 causes peak material coating thickness bands to occur along the velocity axis (V) at each of the gas nozzle sites. More specifically the position of peak material coating thickness band is coincident with the linear axes (VI) and (V2) and with each linear axis associated with gas nozzle sites of the linear arrays of the unit cells of Figure 1. In particular Example 1 below details deposition material thickness vs coating surface position for a substrate coated by the conventional gas deposition system disclosed in related application US2012/0141676 and shown schematically in Figure 1. The measurement reveal that pronounced material thickness peaks are formed along precursor nozzle sites and pronounced material thickness minimums are found midway between precursor nozzle locations.

[0010] As described in related application US2012/0141676 an ideal velocity for

transporting the coating surface past a unit cell allows complete saturation of the coating surface over a region of the coating surface that advances past a particular precursor nozzle during a dwell time (td). In this case the dwell time is dependent upon the width (w) of precursor nozzle assembly along the velocity vector axis (V) and the transport velocity of the coating surface. In particular:

Dwell Time: td= 2w/V

[0011] Where (td) is dwell time; (w) is the width of precursor exposure, e.g. the width of the precursor nozzle assembly; and (V) is the transport velocity. While the transport velocity is easily varied to determine an ideal velocity for complete saturation of the coating surface the width of precursor exposure for a given device is not that easily determined. Moreover, the width of precursor exposure depends in part on the separation gap between the nozzle outlet and the coating surface, the nozzle diameter and shape, the back pressure inside the longitudinal chamber feeding precursor gas through the gas nozzles as well as characteristics of the process gases such as vapor pressure, temperature, density, humidity and mass flow rate. In addition other factors that influence the width of precursor exposure at the coating surface in unknown ways include purge gas mass flow rate and pressure, exhaust vent flow rate and pressure local gas turbulence at the coating surface.

a. Without wishing to be limited to a single particular theory Applicants believe that the deposition layer thickness variations over the coating surface may be related to an insufficient residence or dwell time of precursor molecules at substrate coating surface in regions that are relatively distal from gas nozzle sites as compared with regions that are more proximate to gas nozzle sites. More specifically it is believed that precursor molecule residence time or dwell time may be greater on substrate surface regions that pass directly under or are more proximate to collinear gas nozzle sites positioned along axes that are parallel to the (V) axis such as (VI) and (V2) in Figure. Additionally it is believed that precursor molecule residence time or dwell time may be shorter on substrate surface areas that fall midway between or more distal from the collinear gas nozzle sites when the gas nozzles are positioned along axes that are parallel to the (V) axis such as (VI) and (V2) in Figure 1.

[0012] As will be detailed in Example 1 below Applicants have demonstrated that the conventional unit cells disclosed in related application US2012/0141676 produce bands of deposition material layer thickness peaks corresponding with the location of gas nozzle sites (e.g. along linear axes (VI) and (V2) and others in Figure 1. Moreover Example 1 below demonstrates that bands of deposition material layer thickness minimums corresponding with the midpoint between gas nozzle sites. Accordingly it is submitted that one explanation for the deposition thickness bands produced by the conventional deposition head disclosed in US2012/0141676 is that molecules of precursor (A) or precursor (B), and/or both precursors (A) and (B) have insufficient dwell time to complete saturation of the coating surface at coating surface locations that are midway or nearly midway between gas nozzle sites. [0013] Thus there is a need in the art for an improved ALD deposition head and deposition method capable of applying material deposition layers with a more uniform material layer thickness over the entire coating surface.

Summary of the Invention

[0014] In view of the forgoing it is an object of the present invention to provide an improved gas deposition head capable of applying a material deposition layer onto substrate using spatial ALD with a more uniform deposition coating thickens over the entire coating surface. Brief Description of the Drawings

[0015] The features of the present invention will best be understood from a detailed description of the invention and example embodiments thereof selected for the purposes of illustration and shown in the accompanying drawings in which:

[0016] Figure 1 depicts a schematic representation of a bottom view of a conventional precursor port arrangement for a gas deposition head having two unit cells.

[0017] Figure 2 depicts a schematic representation of a bottom view of a precursor port arrangement for a gas deposition head having two unit cells with the spatial position of each precursor port of one unit cell offset from the spatial position of precursor ports of the other unit cell according to the present invention.

[0018] Figure 3 depicts a first unit cell embodiment shown in isometric section view according to an aspect of the present invention.

[0019] Figure 4 depicts a second unit cell embodiment shown in isometric section view according to an aspect of the present invention.

[0020] Figure 5 depicts a schematic representation of a bottom view of a precursor port arrangement for a gas deposition head having "n" unit cells with the spatial position of each precursor port of each unit cell is offset from the spatial position of precursor ports of the other unit cells according to the present invention.

[0021] Figure 6 depicts a schematic representation of a bottom view of a precursor port arrangement for a gas deposition head having pairs of unit cells with the spatial position of each precursor port of one unit cell in each pair of unit cells is offset from the spatial position of precursor ports of the other unit cell in the pair according to the present invention.

[0022] Figure 7 depicts a third unit cell embodiment shown in isometric section view with each precursor nozzle assembly comprising a plurality of linear arrays of precursor nozzles according to the present invention.

[0023] Figure 8 depicts a schematic representation of a bottom view of a test apparatus used to apply material layers onto a silicon wafer substrate using an ALD process depicting a top view of the silicon wafer with peak coating thickness bands aligned with precursor nozzle sites when the precursor nozzle site are collinear in the velocity axis.

[0024] Item Number List

[0025] The following item numbers are used throughout, unless specifically indicated otherwise.

301 OB Exhaust vent 7040 Base wall

3010C Exhaust vent 7045 Longitudinal Chamber

3015A Purge gas nozzle assembly 7050 Linear array of precursor nozzles

3015B Purge gas nozzle assembly 7055 Linear array of precursor nozzles

3060 Base surface

3135 Side wall 8000 Silicon wafer substrate

3065 Coating surface 8005 Gas deposition head

3145 Separation gap 8010 Unit cell

4000 Unit cell 8015 Unit cell

4105A Exhaust vent 8020 Precursor nozzles

4105B Exhaust vent 8025 Precursor nozzles

4110A Precursor nozzle assembly 8030 Precursor nozzles

4110B Precursor nozzle assembly 8035 Precursor nozzles

4115A Purge nozzle assembly 8040 Purge nozzles

4115B Purge nozzle assembly 8045 Exhaust vents

4140 Separation gap 8050 Band of maximum material

thickness

4145 Separation gap 8055 Band of maximum material

thickness

4160 A Base wall 8060 Pitch dimension

4160B Base wall Rl Measurement axis

4165 Coating surface 9000 Plot of material thickness

4175 Separation gap 9010 Coating thickness

9020 Surface position

9030 Average material thickness

9040 Peak to Peak thickness variation

9050 Peak to peak pitch dimension

Description of Some Embodiments of the Invention

Overview

[0026] Embodiments of the present invention include novel gas deposition devices and methods designed to more uniformly equalize reactant or precursor molecule residence or dwell time over all regions of a substrate coating surface. In particular the present invention relates to an improved gas deposition head configured to direct process gases and or vapors onto a solid substrate coating surface wherein the process gases or vapors react with the coating surface to form a thin film material layer thereon. The deposition head comprises a gas manifold for distributing process gases to a precursor orifice plate. The gas manifold receives process gases from a gas supply module which may include gas bubbles and other gas delivery and modulating elements and feeds the process gasses to appropriate linear arrays of gas nozzles that pass through the precursor orifice plate. The gas manifold includes a substantially gas tight longitudinal chamber associated with each linear array of gas nozzles for receiving a process gas therein and the process gas received into longitudinal chamber exits therefrom through each nozzle of the linear array of gas nozzles. Moreover the longitudinal chamber and gas nozzles are configured to deliver a substantially uniform gas flow through each gas nozzle in the linear array of gas nozzles.

Precursor orifice plate

[0027] The precursor orifice plate is divided into a plurality of unit cells each independently operable to apply a single material deposition layer onto the coating surface. Each unit cell may include an associated exhaust module for removing process gases and reaction by product from the coating surface and directing the exhaust flow in an appropriate receptacle or exit port. Each unit cell directs a continuous flow of at least two precursor gases onto the coating surface in a manner that sequentially exposes the coating surface to a first precursor

(A) followed by a second precursor (B) in response to transporting the coating surface past the unit cell. Meanwhile the linear array of inter gas nozzles direct inert gas onto the coating surface between the linear arrays of precursor nozzles emitting precursor (A) and precursor

(B) onto coating surface to substantially isolate the dissimilar reactants from mixing with each other at the coating surface as well as to purge reaction by product and unreacted precursors from the coating surface. Each unit cell may also include one or more exhaust vents e.g. positioned between the linear arrays of precursor nozzles emitting precursor (A) and precursor (B) onto coating surface to substantially to remove gas from the coating surface to further prevent the dissimilar reactants from mixing with each other at the coating surface.

Substrate transport system

[0028] In a preferred embodiment the deposition head is fixedly supported on a frame disposed over a substrate transport device such as a web conveyer or the like which transports the substrate past the gas deposition head with the desired coating surface oriented to receive the process gas emitted from the gas nozzles thereon. In other embodiments either or both the substrate and the deposition head may be transported to create relative motion between the deposition head and the coating surface without deviating from the present invention. Preferably the gas exit point of each gas nozzle and the coating surface separated by a substantially uniform separation gap dimension to ensure that the width of the precursor gas footprint in the velocity axis direction is substantially constant for each linear array of gas nozzles. Preferably the substrate is coated at atmospheric pressure and ambient temperature. More specifically the present invention may include a coating chamber for housing the transport and the coating chamber may be purposely maintained slightly above or below atmospheric pressure during operation to control the coating environment the coating processes of the present invention are performed at substantially atmospheric pressure conditions and not at vacuum pressures. However the transport module may be housed in a vacuum chamber and the substrate coated may be carried out at vacuum pressures without deviating from the present invention.

Unit cell configuration

[0029] Preferably the gas deposition head of the present invention includes a plurality of substantially similar unit cells disposed side by side along a velocity axis (V) which defines the direction that the substrate is transported past the gas deposition head during coating. Each unit cell is configured to apply a single thin film material deposition layer onto the coating surface during a single pass of the coating surface across the unit cell. In one example embodiment of the present invention each unit cell includes two substantially identical linear arrays of precursor nozzles with each linear array of precursor nozzles directing a different precursor gas onto the same region of the coating surface at a

substantially normal incident angle such the region of the coating surface is sequentially exposed to a first precursor gas by the first linear array of precursor nozzles and then to a second precursor gas by the second linear array of precursor nozzles. Additionally each unit cell includes at least one and preferably two linear arrays of inert gas nozzles with each linear array of precursor nozzles disposed between a pair of linear arrays of precursor nozzles emitting dissimilar precursors. Each linear array of inert gas nozzles is configured to direct an inert or purge gas onto the coating surface at a substantially normal incidence angle between dissimilar precursor gas flows to prevent the dissimilar precursor gases from mixing at the coating surface. In other embodiments the purge gas can be introduced between dissimilar precursor gasses using other nozzle configurations without deviating from the present invention.

Unit cells spatially offset

[0030] The present invention more uniformly equalizes reactant or precursor molecule residence or dwell time at all regions of a substrate coating surface by offsetting the spatial position of unit cells such the linear arrays of precursor nozzles on each unit cell direct process gas onto a different region of the coating surface. In this manner each material layer that is applied by a unit cell is applied using precursor nozzles that direct the precursor gas onto a different region of the coating surface. While this technique does not affect the formation of peak martial thickness bands introduced by a single unit cell is does alter the spatial position of peak material thickness bands introduced by different unit cells which effectively reduces material thickness variation over the coatings surface.

[0031] In one example wherein the gas deposition head incudes two unit cells the linear arrays of precursor nozzles of a first or leading unit cell which deposits a first material deposition layer onto the coating surface are oriented such that each precursor nozzle of the leading unit cell direct precursor gas onto a first region of the coating surface while each precursor nozzle of a second or trailing leading unit cell directs precursor gas onto a second region of the coating surface which is spatially offset from the first region.

First example embodiment

[0032] Referring to Figure 2, a bottom view of an improved deposition head (2000) according to a first embodiment of the present invention is depicted schematically. The deposition head (2000) includes two unit cells (2005) and (2010). The unit cells are disposed side by side along a velocity axis (V). Each unit cell includes a first linear array of precursor gas nozzles (2015 and 2020) and a second linear array of precursor gas nozzles (2025 and 2030). Each nozzle in each first linear array of precursor nozzles (2015, 2020) emits a continuous flow of a first precursor gas or vapor (A) and each nozzle in each second linear array of precursor nozzles (2025, 2030) emits a continuous flow of a second precursor gas or vapor (B) out of each nozzle. A substrate to be coated is transported past the deposition head (2000) along the velocity axis (V) from left to right with its coatings surface facing the gas nozzle outlets. Accordingly a leading edge of the coating surface is sequentially advanced past the linear array (2015) then past the linear array (2025) followed by linear array (2020) and then linear array (2030). Preferably the separation gap separating each nozzle outlet and the coating surface is substantially uniform at each muzzle location. Additionally precursor nozzle outlets and coating surface are substantially opposed such that gas emitted from each nozzle impinges onto the substrate coating surface at a substantially normal indecent angle with respect to the coating surface. [0033] Relative motion is provided between the substrate and the deposition head. In a preferred embodiment the deposition head and substrate transport module are attached to a frame member and the substrate is advanced past the deposition head along the velocity vector axis (V). A row axis (R) is oriented perpendicular to the velocity vector axis (V). The substrate coating surface has a transverse width oriented along the row axis (R). Preferably each unit cell is constructed with an overall row dimension (2050) that is equal to or exceeds the transverse width dimension of the substrate coating surface.

[0034] In one example operating mode the substrate is advanced from left to right along the velocity vector axis (V) such that the first linear array of precursor nozzles (2015) emits precursor (A) onto the coating surface, across its entire transverse width. Upon impinging upon the substrate coating surface precursor (A) reacts with the substrate coating surface and forms a first monolayer onto the coating surface substantially covering the entire transverse width. As the substrate is further advanced from left to right along the velocity vector axis (V) the second linear array of precursor nozzles (2025) emits precursor (B) onto the first monolayer formed on the substrate coating surface and reacts therewith to complete the deposition of a first material deposition layer onto the coating surface. The composition of the first material deposition layer is dependent upon the composition of each of the precursors (A and B) and may be formed using different precursor combinations. In the same manner; as the substrate is further advanced from left to right along the velocity vector axis (V) it advances past the second unit cell (2010) which emits identical precursors (A and B) to react with the substrate coating surface and operates to deposit a second material deposition layer onto the substrate coating surface having the same material composition as the first material deposition layer.

[0035] As will be further detailed below, addition unit cells positioned side by side along the velocity vector axis (V) can be used to deposit additional material deposition layers of the same deposition material composition one above another onto the coating surface.

Alternately additional unit cells positioned side by side along the velocity vector axis (V) may include unit cells that emit different precursor gasses to apply different deposition material layers having a different material layer composition onto the coating surface without deviating from the present invention.

[0036] Referring to the first unit cell (2005) each linear array of precursor gas nozzles (2015) and (2025) comprises a plurality of gas nozzles disposed along a linear axis parallel with the row axis (R). Individual gas nozzles are disposed with a substantially uniform center to center pitch dimension (2035) with a row length dimension (2050). Additionally each gas nozzle in the first linear array (2015) is collinear a corresponding gas nozzle in the second linear array (2025) along a linear axis parallel with the velocity vector axis (V) as indicated by the dashed line (Zl).

[0037] Referring to the first unit cell (2010) each linear array of precursor gas nozzles (2020) and (2030) comprises a plurality of gas nozzles disposed along a linear axis parallel with the row axis (R). Individual gas nozzles are disposed with a substantially uniform center to center pitch dimension (2035) with a row length dimension (2050). Additionally each gas nozzle in the first linear array (2015) is collinear a corresponding gas nozzle in the second linear array (2025) along a linear axis parallel with the velocity vector axis (V) as indicated by the dashed line (Zl). However as indicated by an offset dimension (2040) separating the linear axes (Zl) and (Z2) the precursor gas nozzle position of each precursor gas nozzle of the second unit cell (2010) is offset from the precursor gas nozzle position of corresponding gas nozzles in the first unit cell by the offset dimension (2040). Accordingly each of the precursor gas nozzle sites of the first unit cell directs precursor gas onto a different region of the coating surface as compared to each of the precursor gas nozzle sites of the second unit cell.

Implementing the spatial offset

[0038] In one example embodiment the deposition head comprises two substantially identical unit cells (2005) and (2010). The precursor nozzle pattern on each unit cell is substantially identically oriented with respect to a reference edge e.g. the bottom edge shown in Figure 2. In particular each linear array of precursor gas nozzles (2015, 2025, 2020, 2030) is located at the same position along the row axis (R) with respect to the reference edge using reference dimension (2075). To achieve the desired offset dimension (2040) the (R) axis position of the second unit cell (2010) is shifted upward with respect to the (R) axis position of the first unit cell by the offset dimension (2040). The positional shift of the second unit cell is achievable assembling the unit cells into the precursor plate or the deposition head using a shim, stop, machined surface or the like in a well-known manner.

[0039] The offset dimension shown in figure 2 is obtainable using two different unit cell configurations. In one example embodiment the bottom edge of each unit cell is used as a reference edge to locate the precursor nozzle pattern of each unit cell. In this case the first unit cell has a first reference dimension (2075) and the second unit cell has a reference dimension that is increased by the desired offset dimension e.g. having a reference dimension of (2075 + 2040).

Precursor orifice plate for a unit cell

[0040] Referring now to Figures 3 and 4 two non-limiting example unit cell embodiments (3000) and (4000) are shown in isometric section views. In each embodiment the unit cell comprises two precursor nozzle assemblies emitting precursor (A) and precursor (B). The precursor nozzle assemblies are separated by a purge nozzle assembly emitting a purge gas (P). The purge gas is directed onto the coating surface in order to prevent dissimilar precursor gases from mixing during precursor reactions with the coating surface. An exhaust inlet separates each precursor nozzle assembly from each purge gas nozzle assembly in order to draw gases away from the coating surface for removal. Figures 3 and 4 each depict a coating surface (3065, 4065) advancing past the unit cell at a fixed velocity as indicated by the velocity vector (V). The base or bottom surface of each unit cell (3000) and (4000) is separated from the coating surface by a separation gap (3145) in Figure 3 and a separation gap (4145) in Figure 4. Each of the precursor and purge gas nozzle assemblies comprises a linear array of gas nozzles extending along the row axis (R) as described above.

[0041] Each precursor gas nozzle assembly as well as each purge gas nozzle assembly includes a longitudinal chamber extending along the row axis (R). Each longitudinal chamber is in fluid communication with the gas manifold portion of the deposition head and receives an appropriate process gas therein from the gas manifold. Each longitudinal chamber is bounded by sidewalls (e.g. 3135) in Figure 3 and (4135) in Figure 4 and a base wall (3160) in Figure 3 and (4160 A, 4160B) in Figure 4. Each gas nozzle in the linear arrays of precursor and purge gas nozzles passes through the corresponding base wall. Accordingly each longitudinal chamber is in fluid communication with the separation gap area, between the nozzle outlet and the coating surface, through each of the gas nozzles in each of the linear arrays gas nozzles. The size and shape of each gas nozzle is selected to control gas flow out from the longitudinal chamber and oriented to direct the gas flow onto the coating surface in a manner that delivers a substantially uniform gas distribution along the row axis (R) which extends along a transverse width of the coating surface. In a preferred embodiment each gas nozzle comprises a circular diameter sized to regulate the flow of precursor or purge gas exiting from corresponding longitudinal chambers. Preferably the unit cell delivers a substantially similar gas flow rate from each gas nozzle in a particular linear array as well as delivering process gas in a manner that substantially provided a uniform process gas impingement footprint across the full transverse width of the coating surface.

[0042] In one non-limiting example embodiment the linear arrays of precursor and purge gas nozzles are substantially identical comprising substantially identical circular through holes each having a diameter in the range of 0.0125-0.500 mm 0.0005 - 0.0200 inches) and preferably with each having a diameter in the range of 0.100 - 0.250 mm, (0.004 - 0.010 inches). Additionally each of the linear arrays is configured with a center to center spacing or pitch dimension in the range of 0.25 to 10 mm (0.010 to 0.4 inches) and more preferably about 3 mm (0.12 inches). However since the through hole diameter and pitch dimension is somewhat dependent on the desired coating materials and coating properties, other through hole, shapes and orifice areas as well as other center to center pitch dimensions that provide the desired coating results are usable without deviating from the present invention.

[0043] In further non-limiting example embodiments the linear arrays of purge gas nozzles may be configured with a different nozzle diameter and center to center pitch dimension. In still further non-limiting example embodiments the circular apertures of either or both of the precursor and purge gas nozzles may comprise one or more longitudinal slots extending along the row axis (R), one or more oval or other shaped orifices or other orifice patterns. In still further non-limiting example embodiments one or more or the linear arrays may comprise a non-constant center to center orifices spacing without deviating from the present invention. In another non-limiting example embodiment one or more or the linear arrays may comprise gas nozzles having different aperture areas depend upon the position of the aperture along the row axis (R). In a specific example a linear array of gas nozzles includes small area gas nozzle apertures near the center of the linear array and larger area gas nozzle apertures at distal ends of the linear array.

[0044] Referring to Figure 3 the base wall (3060) defines a uniform separation gap dimension (3145) to the coating surface for each of the precursor gas nozzles (A) and (B) and for each of the purge gas nozzles (P) as well as for each of the exhaust vents (301 OA, 3010B, 30 IOC). Referring to Figure 4 each precursor gas nozzle assembly (4110A, 4110B) have a separation gap (4140) each purge gas nozzles (P) has a separation gap (4175) and each exhaust vent has a separation gap (4145). Additionally each purge gas nozzle assembly includes side walls (4162) that extends toward the coating surface to mechanically prevent dissimilar precursors from mixing before being drawn away from the coating surface by the exhaust vents (4105 A, 4105B).

Unit cell deposition process

[0045] Referring to Figures 3 and 4 the deposition process of a unit cell is described below. As the leading edge of the coating surface is transported past a unit cell from left to right the first precursor nozzle assembly (3005 A, 4110A) the coating surface is contacted by precursor

(A) across its entire transverse width, i.e. the width of the coating surface along the row axis (R), for a duration equal to a dwell time that is consistent with obtaining complete saturation of coating surface as it passes under the first precursor nozzle assembly. In the case of Figure 3 the leading edge of the coating surface next advances past the exhaust vent (301 OA) which draws reaction by product, unreacted precursor and purge gas emitted from the purge gas nozzle assembly (3015 A) away from the coating surface and into an exhaust manifold, not shown. In the case of Figure 4 the exhaust vent (4105 A) is disposed on both sides of the precursor nozzle assembly (4110A) and therefore draws reaction byproduct and unreacted precursor from both sides of the precursor nozzle assembly (4110A) as well as purge gas emitted from the purge gas nozzle assembly (4115 A) as well as purge gas that may leak under the base wall from an adjacent unit cell.

[0046] As the leading edge of the coating surface is transported past the purge gas nozzle assembly (3015 A, 4115 A) the coating surface is contacted by an inert purge gas (e.g.

nitrogen) which purges the coating surface of any unreacted precursor (A) and or precursor

(B) emitted from either of the two precursor nozzle assemblies of the unit cell. As the leading edge of the coating surface is transported past the purge gas nozzle assembly (3015 A, 4115 A) it passes an exhaust vent (3010B or 4105B) which further draws reaction byproduct, unreacted precursor and purge gas away from the coating surface.

[0047] As the leading edge of the coating surface is transported past the second precursor nozzle assembly (3005B, 4110B) the coating surface is contacted by precursor (B) across its entire transverse width, i.e. the width along the row axis (R), for a duration equal to a dwell time that is consistent with complete saturation of coating surface as it passes under the first precursor nozzle assembly.

[0048] In the case of Figure 3 the leading edge of the coating surface advances past the exhaust vent (30 IOC) which draws reaction by product, unreacted precursor and purge gas emitted from the purge gas nozzle assembly (3015B) away from the coating surface and into an exhaust manifold, not shown. In the case of Figure 4 the exhaust vent (4105B) draws reaction by product, unreacted precursor from both sides of the second precursor nozzle assembly (4110B) as well as purge gas emitted from the purge gas nozzle assembly (4115B). Finally as the leading edge of the coating surface is transported past the purge gas nozzle assembly (3015B, 4115B) the coating surface is contacted by an inert purge gas (P) which purges the coating surface of any unreacted precursor (B) from the precursor nozzle assembly (3005B) and (4110B) and or precursor (A) which may have passed under the base wall from an adjacent unit cell.

[0049] Referring now to Figure 5 the Figure depicts a bottom view of a non-limiting exemplary gas deposition head (5000) comprising n unit cells. Each unit cell comprising two linear arrays of precursor nozzles (5010a, 5010b...501 On). Each linear array of precursor nozzles is substantially identical comprising a plurality of substantially identical circular gas orifices disposed along a row axis (R) with each linear array of circular gas nozzles having the same center to center pitch dimension (5020) and the same row length dimension (5030). The spatial position of the hole pattern along the (R) axis is established by a reference dimension (5035) e.g. measured from a reference edge (5040) or some other reference feature used to position the hole pattern.

[0050] According to the present invention the deposition head (5000) is configured with each unit cell having its hole pattern spatially shifted along the (R) axis compared to the other unit cells of the deposition head so each of unit cell directs precursor gas onto a different region of the coating surface. In particular the spatial position of the hole pattern (5010a) is a base position with the hole pattern located at reference dimension (5035) with respect to the reference edge (5040). For the second unit cell which included the hole pattern (5010b) the entire unit cell or the position of the hole pattern one the unit cell is spatially shifted (upward or downward) along the (R) axis by an offset dimension equal to (1/n) times the pitch dimension (5020) wherein (n) is the number of unit cells in the gas depiction head. The spatial shift is obtainable either by shifting the entire unit cell up or down or by constructing the unit cell using a different reference dimension (5035) to locate the hole pattern.

[0051] Similarly the spatial position of the hole pattern of each unit cell through hole pattern (501 On) is shifted in the same direction (upward or downward) by the same offset dimension equal to (1/n) times the pitch dimension (5020). Thus if (n) is 5 the position of the hole pattern on adjacent unit cells is spatial shifted by 1/5 of the pitch dimension (5020) as compare to the position of the hole pattern on adjacent unit cells on either side of it. Thus a deposition head (5000) comprising five unit cells directs precursor gas onto four different regions of the coating surface with each region of the coating surface being separated by a dimension equal to 1/5 times the pitch dimension (5020).

[0052] In one non-limiting example embodiment the deposition head (5000) is constructed from identical unit cells which are assembled together in a manner that offsets the location of adjacent unit cells along the (R) axis by (1/n) times the pitch dimension (5020) where (n) is the number of unit cells. Such an assembly technique may be accomplished by shimming the location of unit cells from a reference edge or by otherwise locating each unit cell at a desired position during assembly using well known mechanical assembly techniques.

[0053] In other embodiments the unit cells are not identical and the hole pattern location of each unit cell is different. In particular each cell is constructed by locating the hole pattern at a different reference dimension (5035). In particular the hole pattern of each unit cell is shifted along the (R) axis by (1/n) times the pitch dimension (5020) wherein (n) is the number of unit cells.

[0054] Referring now to Figure 6 a bottom view of a non-limiting exemplary gas deposition head (6000) comprising four unit cells grouped in pairs of two (6010) and (6015). Each unit cell comprising two linear arrays of precursor nozzles (6020, 6025, 6030, 6035). Each linear array of precursor nozzles is substantially identical and comprises a plurality of substantially identical circular gas nozzles disposed along a row axis (R) with each linear array of circular gas nozzles having the same center to center pitch dimension (6040) and the same row length dimension (6045). Additionally the spatial position of the hole pattern comprising the pair of linear arrays of gas nozzles along the (R) axis for each unit cell is established by a reference dimension (6050) measured from a reference edge such as the bottom edge (6055) of the unit cell. [0055] According to the present invention a first pair of unit cells (6010) includes two unit cells. The position of the hole pattern (6020) on the first unit cell is offset along the (R) axis as compared to the position of the hole pattern (6025) of the second unit cell in a manner that causes each unit cell to direct precursor gas onto a different region of the substrate coating surface during a coating cycle. In the present example, the offset dimension (6060) is equal to one half the pitch dimension (6040). Other offset dimensions (6060) are usable without deviating from the present invention.

[0056] Further according to the present invention a second pair of unit cells (6015) includes two unit cells which are substantially identically configured to the first pair of unit cells (6010). More specifically the hole pattern (6030) is located along the row axis (R) using the same reference position (6050) as the hole pattern (6020) and the hole pattern (6035) is offset along the row axis (R) from the hole patterns (6020) and (6030) by the offset dimension (6060) which is preferably equal to one half the pitch dimension (6040).

[0057] Accordingly the gas deposition head (6000) comprises four unit cells each operating to deposit a single deposition material layer onto the substrate coating surface each time the substrate is transported past the deposition head (6000). Moreover the gas deposition head (6000) is constructed with precursor nozzle positions offset from one unit cell to another such that precursor gas is directed onto the coating surface along two different linear axes each parallel to the velocity axis (V) and the two different linear axes are offset from one another by the offset dimension (6060) which is equal to one half the pitch dimension (6040).

[0058] Referring now to Figure 7 a further non-limiting example embodiment of the present invention comprises a unit cell (7000) shown in cutaway isometric section view. The unit cell (7000) includes two precursor nozzle assemblies (7005, 7010) and three purge gas nozzle assemblies (7015, 7020, and 7025). In addition two exhaust vents (7030, 7035) disposed on both sides of each the precursor nozzle assemblies draw process gas away from the coating surface. Thus the unit cell (7000) is configured like the unit cell (4000) shown in Figure 4 and described above however the unit cell (7000) includes two linear arrays of precursor nozzles in each precursor nozzle assembly with both linear arrays of precursor nozzles passing through the bottom wall (7040) of the same longitudinal chamber (7045).

[0059] Referring to the second precursor nozzle assembly (7010) two linear arrays of nozzles (7050, 7055) extend along the row axis (R). Each linear array (7040 and 7045) includes a plurality of nozzles passing through the bottom wall (7040). The nozzles are disposed along row axis with a hole pattern defined by a constant center to center hole center pitch dimension and an overall length equal to or exceeding the transverse width of the coating surface or other desired coating width. While the hole pattern of each linear array (7050) and (7055) is substantially identical, the spatial position of the two hole patterns are offset in the row axis dimension by an offset dimension. Thus each precursor nozzle in the linear array (7050) is spatially offset in along the row axis (R) from it corresponding precursor nozzle in the linear array (7055) by the offset dimension. Accordingly, each linear array of precursor nozzles (7050, 7055) directs precursor onto a different region of the coating surface. In the unit cell (7000), the first precursor nozzle assembly (7005) and the second precursor nozzle assembly (7010) are substantially identical except that the first precursor assembly emits precursor (A) and the second precursor assembly emits precursor (B). Accordingly the unit cell (7000) operates to deposit a single deposition material layer onto the coating surface but it does so by emitting precursor onto coating surface using two linear arrays of precursor nozzles for each precursor and the two linear arrays of precursor nozzle each direct the precursor gas onto a region of the coating surface. In further embodiments each precursor nozzle assembly (7005, 7010) may be configured with more than two linear arrays of precursor nozzles each having the same hole pattern but with each hole pattern offset along the row axis (R) in manner that prevents any of the hole patterns from directing precursor gas onto the same region of the coating surface.

[0060] Referring to Figure 8 a top view of a top view of a circular silicon wafer substrate (8000) is shown schematically on the right side of the figure next to a schematic bottom view of a two unit cell gas deposition head (8005) one the left side of the figure used to coat the wafer substrate (8000). The two unit cell gas deposition head (8005) with used to compare conventional unit cell performance with the performance of unit cells configured according to the present invention. The gas deposition head (8005) includes two unit cells (8010) and (8015). Each unit cell includes a first linear array of precursor gas nozzles (8020) and (8025) for emitting precursor (A) and a second linear array of precursor gas nozzles (8030) and (8035) for emitting precursor (B). Otherwise the unit cells include linear arrays of purge gas nozzles (8040) and exhaust vents (8045) substantially as shown in Figure 4 and described above. [0061] The two cell gas deposition head (8005) was used to apply material deposition layers onto the wafer substrate (8000). Each thickness measurement experiment comprised applying several hundred deposition material layers onto the wafer coating surface and measuring the resulting material thickness at a plurality of coating surface locations. The unit cells (8010) and (8015) were interchangeable with other unit cell configurations. In particular a convention unit cell having precursor ports arranged as shown in Figure 1 was compared with unit cells of the present invention arranged as shown in Figure 2. The resulting material thickness characteristics of each unit cell configuration were measured and compared and the results are presented below.

EXAMPLE 1 (Thickness uniformity evaluation of a conventional precursor port arrangement)

[0062] In a first evaluation of ALD coating thickness uniformity was measured for a wafer substrate coated using the conventional gas deposition head disclosed in related patent application US2012/0141676 and shown schematically in Figure 1. For this evaluation, a 150.0 mm diameter silicon wafer was ALD coated using two unit cells supported in test apparatus. The first precursor nozzle configuration test used two unit cells configured as shown in Figure 1 and described above with all nozzles co-aligned along the velocity axis (V) and with the center to center pitch dimension equal to 6.4 mm.

[0063] The test apparatus included the gas deposition head (8005) supported above a substantially closed process chamber. A substrate transport device and associated transport drive module, not shown, were housed within the process chamber. The transport device comprised a wafer support platform attached to a nut following a lead screw. The transport drive comprised a rotary stepper motor driving the lead screw at a substantially constant angular velocity under the control of a motor controller. Position sensing elements were used to detect and record the instantaneous position and velocity of the substrate.

[0064] The coating process included positioning and securing the wafer substrate onto the substrate transport device with the coating surface facing the gas deposition nozzles. Gas was fed to the longitudinal chambers above each linear array of gas nozzles and began to flow through the gas nozzles exiting the deposition head into the process chamber. The substrate transport was initially positioned to support a test wafer at a start position away from any influence of process gas exiting the gas nozzles. The transport device was initiated to advance the substrate past the two unit cells at a constant coating velocity. Each of the unit cells deposited a separate deposition material layer onto the entire substrate coating surface as the substrate was advanced past gas deposition head in one direction. Gas flow exiting the gas nozzles was then terminated while the substrate transport module moved the substrate back to the start position. In the present example the coating process was repeated approximately 160 times in order to build up a measurable coating thickness e.g. about 40θΑ. The coating process was carried out at substantially ambient temperature and atmospheric pressure. Each coating layer applied comprises aluminum oxide (A1₂0₃) which is formed using deionized (DI ) water as precursor A and trimethyl aluminum (TMA) as precursor B. In various cycles using various unit cell configurations the coating rate ranged from about 3- 20 A per coating pass.

[0065] The substrate was then removed and the deposition layer thickness was measured at various points across the coating surface. A Horiba Jobin-Yvon Uvisel spectroscopic ellipsometer was used to measure coating layer thickness at 400 points along a 120 mm segment along the row axis (R) shown in Figure 8 to achieve the thickness profiles shown in Figures 9 and 10. Thus the 400 measurements were approximately spaced 0.3 mm apart.

[0066] The coating thickness measurements clearly showed that the applied material layer thickness deposited by the conventional unit cell configuration (shown in Figure 1) was not uniformly thick over the coating surface when a large number of coating layers was applied. Instead the material thickness measurements show peak coating thickness bands

corresponding with the location of precursor nozzle sites. In particular as shown in Figure 8 by the linear axes (VI) and (Vs) peak material thickness bands are spatially coincident with each precursor nozzle site.

[0067] Specifically, the measurements reveal that a plurality of peak material thickness bands e.g. (8050, 8055) extend over the entire coating surface. As shown schematically in Figure 8, each peak material thickness band extends along a linear axis (e.g. (VI, VI) that is parallel to the velocity axis (V). Moreover the peak material thickness bands were found to have a center to center pitch dimension of 6.4 mm which matches the pitch dimension (8060) of the precursor orifice sites. Additionally the material thickness measurements further indicate that minimum material thickness bands extend parallel to the peak material thickness bands midway between the peak material thickness bands. [0068] Referring now to Figure 9 a graphical plot (9000) plots coating thickness (9010) vs coating surface position (9020) for the substrate (8000) shown in Figure 8. In particular the coating thickness plot represents material thickness measured along the row axis (R) at the center of the substrate along axis (Rl). An average material thickness (9030) is

approximately 40lA with a peak to peak thickness variation (9040) of approximately 387A or( +/- 89A at 1 sigma). Additionally peak maximum positions have center to center pitch dimension (9050) of 6.4 mm. As pointed out above, the position of the material thickness peaks is coincident with precursor gas nozzle sites in the two unit cells used to coat the substrate.

EXAMPLE 2 (Thickness uniformity evaluation of a novel precursor port arrangement)

[0069] In a second evaluation of ALD coating thickness uniformity was measured for a wafer substrate coated using the gas deposition head configured according to the present invention and specifically using two unit cells configured as shown in Figure 2. For this evaluation, a 150 mm diameter silicon wafer was ALD coated using two unit cells supported in test apparatus. The second precursor nozzle configuration test used two unit cells configured as shown in Figure 2 and described above with a first unit cell (2005) having its precursor nozzles co-aligned along the linear axis (Zl) and a second unit cell (2010) having its precursor nozzles co-aligned along the linear axis (72 ). Each linear array of precursor nozzles (2015, 2025, 2020, 2030) has the same center to center pitch dimension equal to 6.4 mm and the offset dimension (2040) is equal to one half the center to center pitch dimension (2035) of 3.2 mm.

[0070] The second evaluation was performed using the same test apparatus, the same precursors and the same ALD coating process as were used in the first evaluation process. After coating the wafer with approximately 160 coating cycles the substrate was removed and the deposition layer thickness was measured at various points across the coating surface as described above.

[0071] Specifically, the measurements reveal that a plurality of peak material thickness bands still extend over the entire coating surface with each peak material thickness band extending along a linear axis parallel to the velocity axis (V). However the peak to peak thickness variation is significantly improved as compared to the thickness measurements shown in Figure 9. Moreover in the second evaluation the peak material thickness bands were found to have a center to center pitch dimension of 3.2 mm which matches the offset dimension (2040) of the precursor orifice sites shown in Figure 2. Additionally the material thickness measurements further indicate that minimum material thickness bands extend parallel to the peak material thickness bands midway between the peak material thickness bands.

[0072] Referring now to Figure 10 a graphical plot (10000) plots coating thickness (10010) vs coating surface position (10020) for a substrate coated by the precursor nozzle

configuration shown in Figure 2. In particular the coating thickness plot represents material thickness measured along the row axis (R) at the center of the substrate e.g. along axis (Rl) shown in Figure 8. An average material thickness (10030) is approximately 144 +/-14A (1- sigma std.) with a peak to peak thickness variation (10040) of approximately 61 A.

Additionally material thickness peak maximum positions have center to center pitch dimension (10050) of 3.2 mm. As pointed out above, the position of the material thickness peaks is coincident with precursor gas nozzle sites both the two unit cells (2005) and (2010) shown in Figure 2.

[0073] Since the average coating thickness in the two samples measured is different, (401 A in Figure 9 vs 144A in Figure 10), a more accurate comparison is provided by determining the thickness standard deviation over the average thickness. In particular the coating layer thickness standard deviation is 22.2% for the thickness data shown in Figure 9 as compared with 9.8% for the thickness data shown in Figure 10.

[0074] The measurement data demonstrates that peak material thickness bands are associated with the precursor nozzle sites. Additionally the measurement data further demonstrates that peak material thickness band amplitude is reduced when precursor nozzle sites are offset by one half the pitch dimension of the precursor linear array configuration. In the view of the foregoing Applicants submit that offsetting unit cells by even smaller fractions of the pitch dimension will further reduce peak material thickness bands associated with precursor nozzle sites. Accordingly it is suggested that the precursor nozzle configuration shown in Figure 5 and described above provides and even more improved material layer thickness uniformity as compares to the performance of either of the conventional precursor nozzle configuration shown in Figure 1 or the precursor nozzle configuration of the present invention shown in Figure 2. [0075] It will also be recognized by those skilled in the art that, while the invention has been described above in terms of preferred embodiments, it is not limited thereto. Various features and aspects of the above described invention may be used individually or jointly. Further, although the invention has been described in the context of its implementation in a particular environment, and for particular applications e.g. Atomic layer deposition, those skilled in the art will recognize that its usefulness is not limited thereto and that the present invention can be beneficially utilized in any number of environments and implementations where it is desirable to avoid cumulative deposition material thickness build up associated with precursor nozzle site locations. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the invention as disclosed herein.

Claims

1. A gas deposition head for depositing material layers onto a solid substrate coating surface by atomic layer deposition comprising:

a first unit cell including two linear arrays of precursor nozzles arranged to sequentially direct two dissimilar precursor gases onto the coating surface during relative motion between the coating surface and the first unit cell;

a second unit cell including two linear arrays of precursor nozzles arranged to sequentially direct the same two dissimilar precursor gases onto the coating surface during relative motion between the coating surface and the first unit cell; wherein the two linear arrays of precursor nozzles of the first unit cell form a first spatial pattern of nozzle sites and the two linear arrays of precursor nozzles of the second unit cell form a second spatial pattern of nozzle sites; and,

wherein the second spatial pattern of nozzle sites is spatially offset with respect to the first spatial pattern of nozzles sites such that the first spatial pattern of nozzle sites and the second spatial pattern of nozzle sites direct precursor gas onto two different non-overlapping region of the coating surface.

2. The gas deposition head of claim 1 further comprising:

one or more additional unit cells each including two linear arrays of precursor nozzles arranged to sequentially direct two dissimilar precursor gases onto the coating surface during relative motion between the coating surface and the first unit cell;

wherein each additional linear array of precursor nozzles of the additional unit cells form additional spatial patterns of nozzle sites;

wherein each additional spatial pattern of nozzle sites is spatially offset with respect to the first spatial pattern of nozzles sites such that all of the spatial patterns of nozzles sites direct precursor gas onto a different non-overlapping region of the coating surface.

3. The gas deposition head of claim 2 wherein each unit cell is substantially identical and the first unit cell is located at a reference position and each of the second and additional unit cells is spatially offset with respect to the reference position of the first unit cell in a manner that shifts the nozzle patterns of each of the second and additional unit cells with respect to the first spatial pattern of nozzles sites such that all of the spatial patterns of nozzles sites direct precursor gas onto a different non- overlapping region of the coating surface.

The gas deposition head of claim 2 wherein each unit cell is configured with its spatial pattern of nozzle sites located at a reference dimension with respect to a reference edge of the unit cell and wherein each unit cell is configured with a different reference dimension.

A method for depositing material layers onto a solid substrate coating surface by atomic layer deposition comprising:

providing relative motion between the coating surface and a first unit cell including two linear arrays of precursor nozzles arranged to sequentially direct two dissimilar precursor gases onto the coating surface;

providing relative motion between the coating surface and a second unit cell including two linear arrays of precursor nozzles arranged to sequentially direct the same two dissimilar precursor gases onto the coating surface;

wherein the two linear arrays of precursor nozzles of the first unit cell form a first spatial pattern of nozzle sites and the two linear arrays of precursor nozzles of the second unit cell form a second spatial pattern of nozzle sites; and,

arranging the second spatial pattern of nozzle sites spatially offset with respect to the first spatial pattern of nozzles sites such that the first spatial pattern of nozzles sites and the second spatial pattern of nozzle sites direct precursor gas onto two different non-overlapping regions of the coating surface.

The method of claim 5 wherein the first and second unit cells are substantially identical and the step of arranging the second spatial pattern of nozzle sites spatially offset with respect to the first spatial pattern of nozzles comprise spatially offsetting the position of the second unit cell with respect to the position of the first unit cell by an offset dimension.

7. The method of claim 5 wherein the first and second unit cells are not substantially identical and the step of arranging the second spatial pattern of nozzle sites spatially offset with respect to the first spatial pattern of nozzles comprise spatially offsetting the position of the second spatial pattern of nozzle sites on second unit cell with respect to the position of the first spatial pattern of nozzle sites on first unit cell by an offset dimension.