GB2367561A

GB2367561A - Uniform deposition of material

Info

Publication number: GB2367561A
Application number: GB0118712A
Authority: GB
Inventors: Christian Hoepfner; Everett S Mcginley; Victor E Haven
Original assignee: Stratos Lightwave LLC
Current assignee: Stratos International Inc
Priority date: 2000-08-10
Filing date: 2001-08-01
Publication date: 2002-04-10
Also published as: GB0118712D0; DE10134806A1

Abstract

An apparatus 10 for uniform deposition of material onto a substrate 15 having an elongated vessel 12 of substantially uniform width and an opening at one end, a susceptor 14 for holding a substrate 15 mounted within the vessel 12, a porous diaphragm 32 having a non-uniform array of apertures 50 mounted across the opening 28, an antechamber 30 of predetermined volume adjacent the diaphragm 32, wherein the diaphragm 32 forms an interface between the antechamber 30 and an interior of the vessel 12, the antechamber 30 having a side wall substantially parallel to a wall of the vessel 12, and an inlet port 28 in the side wall of the antechamber 30 for inputting vapour gas into the antechamber 30 in a direction substantially perpendicular to the side wall and against a portion of the side wall opposite the inlet port 28, thereby causing turbulence within the antechamber 30. In a modification another diaphragm having a uniform distribution of apertures may also be used.

Description

SPECIFICATION TITLE VAPOR PHASE REACTOR HAVING VARIABLE FLOW DISTRIBUTION DIAPHRAM BACKGROUND OF THE INVENTION The present invention relates generally to gas reactor vessels for producing epi layers on a substrate. More particularly, the present invention relates to chemical vapor deposition (CVD), or metal organic chemical vapor deposition (MOCVD), of material onto a substrate using a reactor vessel having a porous diaphragm with a non uniform pattern of apertures.

Gas deposition is a process that is widely utilized in the production of semiconductor devices. A substrate, such as a planar wafer of silicon or other suitable material, is heated and exposed to gases that react with the substrate to deposit the desired materials onto the surface of the wafer. The deposited materials form epitaxial films that replicate the crystal lattice structure of the underlying substrate.

Several different reactive gas mixtures may be employed in succession to deposit layers of differing composition. Mixtures of hydrogen, silicon halides, and halides having a minor ingredient or dopant may be exposed to the wafer during heating. Upon contact with the heated wafer surface, the gases deposit a layer of silicon containing the desired dopant on the wafer surface. The process is repeated using different dopants to provide a multilayer semiconductor structure having several layers with different dopants. Similar processes may be employed with mixtures of trimethyl gallium and arsine to deposit layers of gallium arsenide.

The coated wafers are subjected to additional processes to form devices such as integrated circuits (ICs). The layers deposited on the wafer in the gas deposition process form the active elements of microscopic transistors and other semiconductor devices which are utilized in integrated circuits. The thickness, composition and quality of the deposited layers determine the characteristics of the resulting semiconductor devices. Accordingly, the gas deposition process must be capable of depositing films of uniform composition and thickness on each surface of a substrate. The requirements for uniformity have become progressively more stringent with the

use of larger wafers and the continuing reduction in the size of semiconductor devices fabricated from a coated substrate or wafer.

During the gas vapor deposition process, a substrate is placed on a platform or susceptor and heated by heat conduction, radiation, or similar known methods. The susceptor is typically located within an enclosed container during the gas or chemical vapor deposition process. A susceptor may support a plurality of substrates. A carrier gas, containing gaseous forms of atoms to be deposited on the substrate, is introduced into the container in the vicinity of the susceptor. The flow of the gas, determined by the geometry of the container and the susceptor, is generally constrained to flow parallel or perpendicular to the substrates. By a combination of transport and chemical reaction, the atoms of the deposition materials adhere at high temperature to the substrate surfaces, forming the desired deposition layer. This deposition technique has proven satisfactory in part. However, as higher volumes and quality of materials are being required, limits for this specific process are being reached.

The deposition technique has numerous problems. First, as the gas flows over the surfaces of the substrates and the susceptor, deposition of material onto the surface of the substrate changes the concentration of the deposition materials in the carrier gas.

Consequently, over the length of the susceptor, and indeed over the length of each substrate, a different rate of growth of the layer of material is found. A second problem is that, as the deposition material is depleted in the region of deposition, new deposition material must be transported across relatively long distances in a large reaction container. This transport deposition process limits the rate at which deposition can occur, and therefore, increases the cost of manufacture. A third problem is generally referred to as autodoping. In the autodoping process, impurity atoms from the highly doped substrate can be detached from the substrate surface and incorporated via the gas phase into the more lightly doped layer of material being deposited. Steps must be taken to minimize autodoping, such as deposition of an extra coating onto the back of the substrate. A final problem is particulate contamination. As chemical vapor deposition chambers become larger, the wall area of the chamber increases. Unwanted deposits that form upon these walls are sources for particulates that can be inadvertently incorporated into the deposition material. Finally, complicated gas flow dynamics within the reactor chamber can affect how material within the gas is

deposited on a substrate surface. This can affect to uniformity of desired layers being built up on a substrate surface.

All of these problems can affect the uniformity of the resulting layers of materials deposited upon a substrate. Accordingly, there is a need for increasing the growth rate uniformity of the deposited material onto a substrate over the entire area of the substrate.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved method and apparatus for chemical vapor deposition of material onto a substrate.

A further object of the present invention is to provide uniform layers and uniform concentration of materials onto a substrate surface.

Another object of the present invention is to provide variable flow concentration of gas to compensate for variable airflow patterns across a substrate within a reaction chamber.

These objects are achieved by the present invention which provides an apparatus for deposition of material onto a substrate having an elongated vessel of substantially uniform width and an opening at one end, a susceptor for holding a substrate mounted within the vessel, a porous diaphragm having a non-uniform array of apertures mounted across the opening, an antechamber of predetermined volume adjacent the diaphragm, wherein the diaphragm forms an interface between the antechamber and an interior of the vessel, the antechamber having a side wall substantially parallel to a wall of the vessel, and an inlet port in the side or top wall of the antechamber for inputting vapor gas into the antechamber in a direction substantially perpendicular to the side wall and against a portion of the side wall opposite the inlet port, thereby causing turbulence within the antechamber.

BRIEF DESCRIPTION OF THE FIGURES FIGURE 1 is a cross-sectional view of a basic vapor phase reactor configured in accordance with the present invention; FIG. 2 is a perspective view of a susceptor, wherein the flow of gas carrying deposition material across the susceptor is illustrated ;

FIG. 3 is a side view of the susceptor and gas flow shown in FIG. 2 ; FIG. 4 is a perspective view of gas flow through a porous diaphragm and onto a substrate surface in accordance with the present invention; FIG. 5a is another embodiment of a porous diaphragm configured in accordance with the present invention; FIG. 5b is an additional embodiment of a porous diaphragm configured in accordance with the present invention; FIG. 5c is a further embodiment of a porous diaphragm configured in accordance with the present invention; FIG. 5d is another embodiment of a porous diaphragm configured in accordance with the present invention; and FIG. 6 illustrate a data chart and line graph illustrating a non-uniform aperture distribution for a diaphragm configured in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, FIGURE 1 shows a chemical vapor deposition (CVD) reactor 10 configured in accordance with the present invention. The reactor 10 includes a cylindrical tube 12 that is typically made of quartz or stainless steel.

Located within the cylindrical tube 12 is reaction chamber 34. A susceptor or thermal absorber 14 is mounted on a rotatable support 16 within the reaction chamber 34. An upper cap or weldment 18 seals the top of the cylindrical tube 12. A base seals 20 seals the bottom of the cylindrical tube 12. The reactor 10 described herein is configured for OMVPE for GaAs/AlGaAs heterostructures, and the reactor 10 is suitable for deposition of similar materials as well. The illustrated reactor 10 is not the only configuration capable of using the present invention. Reactor 10 is shown for purposes of explanation and is only an example of one embodiment capable of incorporating the present invention. More specific descriptions of CVD reactors capable of incorporating the presenting invention can be found in U. S. Patent Nos.

4,997, 677 issued to Wang, et al. on March 5, 1991, and 5,871, 586, issued to Crawley et al. on February 16, 1999, both of which are hereby incorporated by reference.

A substrate 15 is placed on the surface 22 of the susceptor 14. The substrate 15 is heated to a desired temperature by the susceptor 14 itself or heating coils 24

proximate the susceptor 14. Heating may also be achieved by radiation or resistance heating. Vapor gas 26 carrying materials to be deposited upon a substrate 15 initially enters the reactor 10 via an input port 28. The input port 28 connects to a plenum-like antechamber 30. In other embodiments an input port 29 for vapor gas 26 can be on the top of the plenum-like antechamber 30. A diaphragm 32 is located between the antechamber 30 and the reactor chamber 34. Apertures in the diaphragm 32 cause the vapor gas 26 to be directed vertically downward towards the substrate 15, as shown by the gas flow arrows 36. Gas flow arrows 38 illustrate vertical laminar flow downward through the chamber 34 of the vapor gas 26. Gas flow arrows 40 illustrate the stagnation flow of the gas vapor 26 proximate the susceptor 14. A vacuum pump (not shown) causes the gas vapor 26 to be forced out through an output port 42 and exit the chamber 34.

FIG. 2 shows a schematic flow diagram of the gas vapor 26 passing over the surface 23 of the substrate 15. The vapor gas 26 flows first towards the center 44 of the surface 23, and then outward towards the outside edge 46 of the substrate 15.

FIG. 3 is a cross-sectional view of the flow path of the vapor gas 26 passing over the surface 23 of the substrate 15. The vapor gas 26 initially has a uniform velocity directed perpendicular to the substrate 15. As the vapor gas 26 approaches the substrate 15, the vapor gas 26 is directed away from the center axis 48 and towards the edge 46 of the substrate 15. Velocities are different due to the rotation and charge of the substrate.

At the center axis 48 on the surface 23 of the substrate 15, generally referred to as the stagnation point, there is theoretically no flow of vapor gas 26. The axially symmetric gas flow resulting from the uniform gas flow toward a surface is generally referred to as stagnation point flow. Due to the changing airflow at the center 44 of the substrate 15, uniform deposition of material is not achieved at the center of the substrate 15 in conventional deposition processes.

FIG. 4 illustrates a schematic flow diagram of the vapor gas 26. The vapor gas 26 is forced through apertures 50 in the diaphragm 32 and in a direction 33 initially perpendicular to the surface 23 of the substrate 15. Due to the relatively small size of the apertures 50, the velocity of the vapor gas 26 towards the substrate 15 is generally uniform among all of the apertures 50 as the vapor gas 26 passes towards the surface

23 of the substrate 15. However, turbulence and other complicated gas flow patterns within the antechamber 30 can affect the uniformity of gas flow passing through the apertures 50 of the diaphragm 50. Furthermore, laminar flow 38, stagnation flow 40, and other complicated gas flow patterns within the chamber 30 can affect the uniform distribution of deposition material from the gas 26 onto the surface 23 of the substrate 15.

As discussed in FIG. 3, upon striking the surface 23 of the substrate 15, the vapor gas 26 changes direction and flows in a direction 35 parallel to the surface 23 of the substrate 15. At the transition point at the center 44 of the substrate 15, or on other locations on the surface 23 of the substrate 15 where vapor gas 26 makes a change in direction, complicated flow dynamics can occur which affect the resultant uniform layer deposition on the substrate 15. Such gas flow dynamic can be very complicated and difficult to predict before testing the particular flow characteristic unique to a specific reactor or reactor model. As such, reactor diaphragms having uniform distribution or density of apertures do not compensate for such complicated and potentially unique flow characteristics of various CVD reactors.

In accordance with an apparatus of the present invention, the density of the apertures in a diaphragm of a CVA reactor are modified to be non-uniform in order to compensate for non-uniform flow of gas vapor on the surface of a substrate and other areas of the reactor. In one embodiment of the invention, the center of the diaphragm has a lower density of apertures than the remaining surface of the diaphragm. This decreased density of apertures in the center of the diaphragm compensates for stagnation or decreased gas flow at the stagnation point on the substrate. Furthermore, the density of apertures on other areas of the diaphragm may be modified in order to compensate for additional known and unknown factors affecting the uniformity of deposition on a substrate.

In accordance with the method of the present invention, deposition uniformity of material can be first measured using a diaphragm having a uniform distribution of apertures. A determination can then be made to check the resulting uniformity of the deposited layers using a uniform diaphragm in a specific reactor. Changes in the distribution of the apertures can then be made to correct or compensate for nonuniform layer distribution unique to a specific reactor or particular model of a reactor.

If necessary, the diameter of some or all of the apertures in the diaphragm may be modified in order to increase/decrease gas flow rate or to modify gas flow dynamics.

The apertures can be formed in the diaphragm by photo etching or other known processes in a specific deposition chamber.

FIG. 5a-5d illustrates four different diaphragms having different distributions of apertures. FIG. 5a illustrates a porous diaphragm 52 having apertures 54. Each of the apertures 54 are equal in diameter. Apertures 54 located near the center 56 of the diaphragm 52 are spaced further apart (lower density) than apertures 54 located further away from the center 56 of the diaphragm 52. Applicants have determined that a lower density concentration of apertures at the center 56 of a diaphragm 52 increase the deposition uniformity on a substrate.

FIG. 5b illustrates an embodiment of a diaphragm 60 wherein the apertures 62 proximate the edge 63 of the diaphragm 60 are smaller in diameter than apertures 64 closer to the center 66 of the diaphragm 60. This diaphragm 60 is another embodiment of the present invention illustrating both non-uniform distribution and non-uniform diameter of apertures on a single diaphragm 60 in order to increase uniform layer deposition on a substrate.

FIG. 5c illustrates a diaphragm 70 wherein the apertures 72 each have an equal diameter, but the distribution of the apertures 72 on the diaphragm is not uniform. More particularly, the concentration of apertures 72 is greatest near the edge 74 of the diaphragm 70, and lower than the concentration of apertures at the center of the diaphragm 70.

FIG. 5d illustrates another diaphragm configured in accordance with the present invention. Diaphragm 80 illustrates a high concentration or density of apertures 82. Close examination of the diaphragm 80 reveals that the concentration or density of apertures 82 is lower at the center of the diaphragm 80. The diameter of each of each of the apertures 82 is equal.

FIG. 6 shows a data chart 90 and a line graph 92 corresponding to the diaphragm 80 shown in FIG. 5d. Referring first to the data chart 90, the total number of holes contained within a specific radius from the center of the diaphragm 80 is set forth. For example, at 0.00 inches from the center of the diaphragm the total number of holes or apertures is one (1). At a radius of 0.31830 inches from the center of the

diaphragm, the total number of holes is 63 ; at a radius of 1. 01856 the total number of holes within that radius in 299.

Line graph 92 plots the data contained within data chart 90. As can be seen in line graph 92, the line graph is not linear. This non-linearity illustrates the nonuniform distribution or density of apertures on the diaphragm 80. The non-linearity can specifically be seen at 0.5 inches an less radius from the center of the diaphragm, which is indicated by label number 94.

The description of the foregoing embodiments and operating parameters has been undertaken for the purposes of illustration. The basic principles of the invention can be embodied in other designs or the same design with modifications operating under the same or different conditions without departing from the scope of the invention.

Claims

1. An apparatus for deposition of material onto a substrate, comprising: an elongated vessel of substantially uniform width and an opening at one end; a susceptor for holding a substrate mounted within the vessel; a porous diaphragm having a non-uniform array of apertures mounted across the opening; an antechamber of predetermined volume adjacent the diaphragm, wherein the diaphragm forms an interface between the antechamber and an interior of the vessel, the antechamber having a side wall substantially parallel to a wall of the vessel; and an inlet port in the wall of the antechamber for inputting vapour gas into the antechamber.

2. The apparatus of Claim 1, wherein the vessel forms a cylindrical tube.

3. The apparatus of Claim 1 or 2, wherein each of the apertures of the diaphragm are circular in configuration.

4. The apparatus of any of Claims 1 to 3, wherein each of the apertures of the diaphragm are substantially equal in diameter.

5. The apparatus of any of Claims 1 to 4, wherein the diaphragm is substantially circular in shape.

6. The apparatus of any of Claims 1 to 5, wherein the density of apertures per surface area of the diaphragm increases as the distance from a centre of the diaphragm increases.

7. The apparatus of any of Claims 1 to 6, wherein the density of apertures per surface area of the diaphragm is lower proximate a centre of the diaphragm than the density of apertures proximate the outer edge of the diaphragm.

8. The apparatus of any of Claims 1 to 5, wherein the density of apertures per surface area of the diaphragm decreases as distance from a centre of the diaphragm increases.

9. The apparatus of any of Claims 1 to 5, wherein the density of apertures per surface area of the diaphragm decreases at a predetermined rate from a centre of the diaphragm to a specific distance from the centre of the diaphragm, and from the specific distance to an edge of the diaphragm the density of apertures is uniform.

10. The apparatus of any of Claims 1 to 9, wherein the inlet port is in the side of the antechamber for inputting gas into the antechamber in a direction substantially perpendicular to the side wall and against a portion of the side wall opposite the inlet port, thereby causing turbulence within the antechamber.

11. The apparatus of any of Claims 1 to 9, wherein the inlet port is located in the top of the antechamber.

12. The apparatus of any of Claims 1 to 3, wherein diameters of a portion of the apertures in the diaphragm are unequal.

13. A chemical gas reactor for deposition of material onto a substrate, comprising: a susceptor for supporting a substrate; a substrate supported by the susceptor; an antechamber for receiving and directing a flow of gas carrying deposition material towards the substrate; a diaphragm positioned between the antechamber and the substrate, the diaphragm including a plurality of apertures for passing the gas from the antechamber in a direction substantially perpendicular to the substrate; and said plurality of apertures on the diaphragm having a non-uniform distribution over the surface of the diaphragm.

14. The reactor of Claim 13, wherein each of the apertures have substantially equal diameters.

15. The reactor of Claim 13, wherein a first portion of the apertures has a first diameter and a second portion of the apertures has a second diameter.

16. The reactor of any of Claims 13 to 15, wherein a first portion of apertures proximate a centre of the diaphragm has a first density per surface area of the diaphragm, and a second portion of apertures proximate an edge of the diaphragm has a second density per surface area of the diaphragm.

17. A method for deposition of material onto a substrate from a gas carrying the material within a chemical vapour deposition reactor (CVD), said CVD reactor including an antechamber, a reactor chamber, a susceptor for supporting a substrate within the reactor chamber, and a support for mounting a diaphragm between the antechamber and the reactor chamber, said method comprising the steps of: supporting a substrate on a susceptor within a reactor; placing a first diaphragm between the antechamber and the reactor chamber, the first diaphragm having a uniform distribution of apertures for passing gas therethrough carrying deposition materials to be deposited upon the substrate; heating the substrate to react with the gas; passing gas from the antechamber, through the first diaphragm, and into the reactor chamber and across the substrate, thereby forming deposition layers upon the substrate; determining resulting uniformity of layers deposited on the substrate using the first diaphragm having a uniform aperture distribution; and preparing a second diaphragm having a nonuniform distribution of apertures designed to

compensate for non-uniform layer deposition resulting from use of the first diaphragm.

18. The method of Claim 17, further comprising the steps of: supporting a second substrate on the susceptor within the reactor; and placing a second diaphragm between the antechamber and the reactor chamber, the first diaphragm having a non-uniform distribution of apertures designed to compensate for non-uniform layer deposition of the first diaphragm.

19. The method of Claim 18, further comprising the steps of: heating the substrate to react with the gas; and passing gas from the antechamber, through the first diaphragm, and into the reactor chamber and across the substrate, thereby forming deposition layers upon the substrate.

20. The method of any of Claims 17 to 19, wherein the second diaphragm is formed using photoetching.

21. The method of any of Claims 17 to 19, wherein the second diaphragm is formed using laser drilling.

22. The method of any of Claims 17 to 21, wherein density of apertures formed at a first portion of the second diaphragm located proximate the centre of the second diaphragm is different than the density

of apertures located in a second portion of the diaphragm proximate an outer perimeter of the second diaphragm.

23. An apparatus substantially as hereinbefore described and illustrated in the accompanying drawings.

24. A chemical gas reactor substantially as hereinbefore described and illustrated in the accompanying drawings.

25. A method substantially as hereinbefore described and illustrated in the accompanying drawings.