WO2008113571A1

WO2008113571A1 - Gas distribution system

Info

Publication number: WO2008113571A1
Application number: PCT/EP2008/002196
Authority: WO
Inventors: Andreas Pflug; Michael Siemers; Bernd Szyszka; Michael Geisler
Original assignee: Leybold Optics Gmbh; Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2007-03-20
Filing date: 2008-03-19
Publication date: 2008-09-25
Also published as: TW200900528A; WO2008113571A9

Abstract

The invention relates to a gas distribution system comprising at least three plates, the first having a common gas supply line, the third an array of gas outlet nozzles and the second plate between situated between said first and third plates. The third plate contains at least one conduit system that interconnects the gas supply line and the outlet nozzles, a sub-region of said system, accounting for at least 60% of the total surface of the system, being located in the central plate in a non-overlapping manner and/or or one plane. At least 60% of the branching points of the conduit system are binary branching points.

Description

description

Gas distribution system

The invention relates to a gas distribution system according to the preamble of the independent claims.

Parallel-plate plasma reactors are used in particular in the field of photovoltaics for the purpose of depositing amorphous or microcrystalline silicon layers in a SiH ₄ -H ₂ plasma. In the dissertation by T. Repmann, "Stacked solar cells made of amorphous and microcrystalline silicon" describes such a parallel plate reactor, here it turns out that over the entire coating surface consistent electrical quality of the solar cell can only be achieved if sufficient homogeneity of a -Si / Dc-Si layer is given both in terms of the layer thickness and the morphology.

To achieve a sufficient layer homogeneity, the gas inlet is designed in the form of a gas shower, which is integrated in the form of a regular array of gas inlet nozzles in one of the two electrode plates.

Also in other coating technologies such as e.g. large-area PVD coating, such gas distribution systems are helpful if the homogeneity of the coating critical and thus the homogeneity of the gas pressure distribution over the substrate surface is a critical process variable.

In the patent EP1 1 18693B1 of White et al. is a "hanging gas distribution" described, this consists of two horizontally arranged plates, which include a narrow cavity. In the upper plate is centrally located a central gas supply, while the lower plate, which is attached by means of flexible sheets to the upper plate, having an array of gas outlet openings. Due to the transverse conductance value, the gas pressure distribution in the cavity adjusts in such a way that sufficient homogeneity of the outflow through the gas outlet nozzles takes place in a limited process window. Such an arrangement becomes critical as soon as high gas flows are used or a low pressure in the process chamber - e.g. As in PVD processes - prevails, so that builds up in the cavity of the gas inlet system, a significant pressure gradient.

With this background, US Pat. No. 6,502530B1 to Turlot et al. a concept for a gas shower consisting of a plate with an array of gas outlet nozzles and a described common gas supply, in which it is ensured by a channel arrangement that the Strömungsleitwert between the common gas supply line and each gas outlet nozzle is approximately equal. This is achieved with a duct system between gas supply and gas outlet nozzles, which is designed either as a binary or quaternary branch tree. The first case described allows the construction of one-dimensional gas lances, ie for a two-dimensional array of gas outlet nozzles one would have to create a large number of these binary branching trees and combine them with another binary channel system.

The known quaternary branching system uses quadruple branches each. The channels in different levels of branching run partially overlapping, so that this concept is structurally relatively complex to implement.

The object of the invention is to provide a gas distribution can be avoided with the disadvantages of the prior art.

The achievement of the object of the invention succeeds with the features of the independent claims.

The gas distribution system according to the invention has at least three, preferably solid plates, of which the first has a gas supply line, the third has a preferably two-dimensional arrangement of gas outlet nozzles. The second plate is disposed between the first and the third, wherein the second plate includes at least one channel system which interconnects gas supply and outlet nozzles. According to the invention, a subregion of the channel system with at least 60% of the total area of the channel system is arranged in the middle plate, preferably non-overlapping and preferably in one plane, and that at least 60% of the branching points of the channel system are binary branch points.

A branch point of the channel system is defined as a position in the channel system in which the gas can flow from a volume into more than one volume. For example, at a binary branch point, the gas may flow in two volumes.

It is preferred if the non-overlapping and / or lying in a plane portion of the channel system has at least 70%, 80%, 90% or 95% share of the total area of the channel system. It is further preferred if at least 70%, 80%, 90% or 95% of the branch points of the channel system are binary branch points. An embodiment of the invention is preferred with a common gas supply line and / or a regular array of gas outlet nozzles, wherein the channel system connects the common gas supply line with the gas outlet nozzles in such a way that the flow conductance values of each connection are equal within the manufacturing tolerances. The connections between gas supply line and gas outlet openings are realized by channels milled within a rectangular, solid plate, which preferably have a rectangular cross-section. The channel system is realized in one plane and / or the channel system contains only binary branches. The plate is clamped vacuum-tight between two further rectangular plates. In the latter, the openings for gas supply and -austrittsöffnungen be realized through holes whose longitudinal axes are preferably perpendicular to the aforementioned channels within the middle plate.

If the channel system is arranged in non-overlapping and / or a single two-dimensional plane, this simplifies its technical realization considerably.

In a preferred embodiment, only three superimposed or successively arranged metal plates are provided, of which the middle contains a preferably milled channel system, while the two outer plates contain the common gas inlet or the grid of the gas outlet nozzles in the form of circular holes.

According to a further aspect of the invention, this relates to a plasma reactor comprising two parallel plates which are connected to an electrical power supply. At least one of the two plates in this case contains a gas distributor which contains at least one channel system which connects gas supply line and outlet nozzles with one another. According to the invention, a subregion of the channel system with at least 60% of the total area of the channel system is arranged in the middle plate, preferably non-overlapping and preferably in one plane, and that at least 60% of the branching points of the channel system are binary branch points.

It is preferred if the plasma reactor consists of two parallel plates and / or the channel system or the partial area connects the common gas supply line with the gas outlet nozzles in such a way that the flow conductance values of each connection are equal within the manufacturing tolerances and / or has exclusively binary branch points.

Further embodiments and advantages of the invention will become apparent independently of the patent claims in the following description with reference to drawings. Show it

Figure 1: an illustration of the design rule for the milling pattern of a two-dimensional, binary gas distributor system.

Figure 2: exemplary embodiments for the connection of a plurality of gas distributors of the third order by U-shaped channels in order to provide non-square surfaces with a uniform grid of gas outlet nozzles can.

FIG. 3: Exemplary embodiments using two gas flow regulators for a gas distributor system

Figure 4: Calculated H ₂ pressure distribution along the dashed line in the left graph.

In Figure 1 a - d, a rule for the construction of the Fräsmuster is illustrated. The arrow indicates the position of the common gas supply line.

The realization according to the invention of a uniform flow conductance value of all duct connections is illustrated by the following concept: on a rectangular plate with the dimensions L _X + 2U, L _Y + 2V, in the first step a horizontal line of length L _x / 2 and two vertical lines of length are formed L _γ / 2 an H - shape drawn centrally on the rectangular plate. The parameters U and V specify horizontal and vertical edges in which no gas outlet nozzles are provided. The H-shape has four ends which have a distance L _x / 2 in the horizontal direction and a distance L _γ / 2 from each other in the vertical direction. In a next step, in each case an H-shape is drawn in the middle of each end point of the previous H-shape with dimensions halved relative to the previous H-shape, ie L _x / 4 in horizontal and L _γ / 4 in vertical direction. This results in now 16 endpoints, which are arranged in a regular grid with horizontal distance Lχ / 4 and vertical distance L _γ / 4. This process is repeated iteratively with the newly created endpoints and further H - shapes, again in each case halved dimensions, until the raster resulting from the endpoints has the desired density.

Each line now represents the central axis of a channel to be milled. The channel width D must be smaller than half the grid spacing of the end points of the last iteration step. It now results, for example by complete induction, that the flow conductance values from the middle of the first H-shape to the end points of the H-shapes of the last iteration stage are equal within the production tolerances. The basic form of the gas distributor according to the invention is characterized in that, in the two-dimensional arrangement of the gas outlet nozzles, the number of columns and rows is 2 ^{M in} each case, wherein M corresponds to the number of iteration stages in the design. An approximately square plate can be coated with this concept with a grid of gas outlet nozzles, in which the vertical and vertical distances between adjacent nozzles are approximately equal. For rectangular panels, where length and width are widely different, this concept would require a corresponding distortion between horizontal and vertical spacing of adjacent nozzles.

In order to avoid strongly distorted arrangements of gas outlet nozzles, an embodiment of the invention provides for connecting two channel networks of order M through a further, U-shaped channel, as shown in FIG.

As a result, rectangular areas with a ratio of 2: 1 or 4: 1 between length and width can be provided with a uniform nozzle grid. By the combination of several different gas distributor arrangements shown in FIG. 3, further ratios of length to width can be realized. However, this requires at least two independent mass flow controllers. Figure 3 shows a rectangle with a length to width ratio of 2/3 (left graph) and 4/5 (right graph), which is coated with a uniform grid of gas outlet nozzles.

The gas distributors described can be used, for example, in a plasma reactor consisting of two parallel or three plates, which are connected to an electrical power supply, wherein at least one of the two plates contains a gas distributor.

a)

The gas distributor can have a channel system which connects the gas supply line and outlet nozzles with one another such that the flow conductance between the gas supply line and each gas outlet nozzle is equal within the production tolerances, and it is provided that the channel system does not overlap between the gas supply line and the gas outlet nozzles in the middle plate is constructed in a single plane and contains only binary branches. b)

Furthermore, gas distributors can consist of 2 ^M linearly arranged, binary, two-dimensional gas distributors according to a), wherein the 2 ^M gas supply lines of the 2 ^M gas distributors are fed by means of a binary, one-dimensional gas distributor.

c)

Further, the gas distributor may consist of several independent mass flow controllers according to a) or b), wherein a corresponding number of gas distributors are combined with each other.

A simulation calculation of the gas flow of H ₂ by a binary gas distributor system of order 3 with 64 gas outlet openings with area dimensions of 300 * 375 mm ² shows that the gas distribution system according to the invention behaves particularly advantageous compared to manufacturing tolerances in the production of the channel system.

The thickness of the plate containing the channel system is 5 mm, the channel cross section is 5x5 mm ² . At the gas outlet openings cylindrical end nozzles are assumed with 3 mm in diameter and 10 mm in length. The width is varied for the vertical channel which adjoins the center piece on the right, in order to be able to read the effect of manufacturing tolerances on the outflow homogeneity of the gas distributor.

The simulation of the pressure distribution was firstly done with the Direct Simulation Monte Carlo method (see A. Pflug et al., Parallel DSMC Gasflow Simulation of an In-Line Coater for Reactive Sputtering) and secondly with the help of analytical semiempirical formulas performed for the Strömungsleitwerte the channel sections. The semiempirical model calculates the gas pressure in individual test volumes V ₁ , which are respectively arranged at the branch points and in the center of the gas distributor.

The temporal pressure development can be described approximately in the semiempirical model with the following differential equation, which corresponds to a time derivation of the ideal gas equation:

v _J ^ r = ^kTF ₁ -p _J s _PJ + Σ (p _k ^-P _J ) s _jk . (D

^Ol k ≠ i

In this case, F _{1 is} the optional gas inlet in volume j and S _{PJ is} an absorbency of an optional pump in volume / For the flow conductance between the volumes j and k, first the Knudsen formula (see M. Wutz, H. Adam, W. Walcher, K. Jousten: Handbook Vacuum Technology, 7. erw. Edition, 2000) for gas flow through tubes with a round cross-section:, "} ( ² )

In the flow through a tube with an isotropic gas inlet before the tube opening has been shown (see A. Pflug, Simulation of reactive magnetron sputtering, Dissertation Uni Giessen, 2006) that in addition to conductance according to Knudsen each Einströmleitleit

jk orissa = A ^ (3)

must take into account, so that in Eq. (1) the harmonic mean of both guiding values must be used:

¹ ' ₊ (4)

^ Jk "jk knudsen" -> jk orifice

With the in Eq. (2) - (4), both the guide values of the individual pipe sections and the guide values of the nozzles with D = 3 mm and L = 10 mm were calculated.

FIG. 4 shows the simulation calculations carried out with both methods for the symmetrical case as well as for the case where the width of the vertical channel adjoining the centerpiece on the right has been reduced by 20%. This results in an increased admission pressure on the gas supply side of this channel and consequently an increased pressure difference across this channel, whereby according to Eq. (2) the effect of the reduced flow coefficient is partially compensated.

On the gas supply side of a channel with a reduced cross-section, an increased pre-pressure, the resulting from the reduced channel cross-section reduced Strömungsleitwert is therefore partially compensated by the increased pressure difference across this channel. The solid and dashed curves represent the DSMC calculations in the symmetric and asymmetric case, the black and gray symbols representing the simplified semiempirical calculations.

It can be seen that when the channel cross-section is reduced by 20%, the outflow at the end nozzles only varies by ± 7.8%. It follows that a good homogeneity of the outflow can be realized even with relatively generous manufacturing tolerances with the gas distribution system according to the invention.

Claims

claims

A gas distribution system having at least three plates, the first having a common gas supply line, the third having an arrangement of gas outlet nozzles, and the second plate between the first and the third, wherein the third plate includes at least one channel system, which gas supply and outlet nozzles interconnected, characterized in that a portion of the channel system with at least 60% share of the total area of the channel system in the middle plate, non-overlapping and / or arranged in a plane and that at least 60% of the branch points of the channel system are binary branch points.

2. Gas distribution system according to claim 1, characterized in that the Strömungsleitwert between the gas supply line and each gas outlet nozzle is equal within the manufacturing tolerances.

3. Gas distribution system according to claim 1 or 2, characterized in that in the sub-area only binary branch points are provided.

4. Gas distributor system according to one of the preceding claims, characterized in that the subregion of the channel system with dimensions L _x + U, L _γ + UM orders H-shaped elements, wherein an H-shaped element of the first order is arranged centrally and horizontal and vertical dimensions of L _x / 2 and Lγ / 2 and at the ends of the H-shaped elements of order N further H-shaped elements of the order Λ / + 1 are connected centrally, their horizontal and vertical dimensions relative to the H-shaped Elements of order N are halved.

5. Gas distribution system according to one of the preceding claims, characterized in that the gas supply line and the gas outlet nozzles in the form of, preferably cylindrical holes are realized.

6. Gas distributor, characterized by 2 ^M linearly arranged gas distributor systems according to one of the preceding claims, wherein the 2 ^M gas supply lines of the 2 ^M gas distributor are fed by means of a binary, one-dimensional gas distributor.

7. Gas distributor arrangement, characterized by a plurality of independent mass flow controllers, wherein a corresponding number of gas distributor systems or gas distributor are combined according to at least one of the preceding claims. Plasma reactor comprising at least two parallel plates, which are connected to an electrical power supply, characterized in that at least one of the two plates includes a gas distributor at least one channel system, the gas supply and outlet nozzles interconnected, wherein a portion of the channel system with at least 60% share of the Total area of the channel system is non-overlapping and / or arranged in a plane and that at least 60% of the branch points of the channel system are binary branch points.