Inlet system for an MOCVD reactor

Abstract

The invention relates to a device for depositing especially crystalline layers on at least one especially crystalline substrate in a process chamber comprising a top and a vertically opposing heated bottom for receiving the substrates. A gas-admittance body forming vertically superimposed gas-admittance regions is used to separately introduce at least one first and one second gaseous starting material, said starting materials flowing through the process chamber with a carrier gas in the horizontal direction. The gas flow homogenises in an admittance region directly adjacent to the gas-admittance body, and the starting materials are at least partially decomposed, forming decomposition products which are deposited on the substrates in a growth region adjacent to the admittance region, under continuous depletion of the gas flow. An additional gas-admittance region of the gas-admittance body is essential for one of the two starting materials, in order to reduce the horizontal extension of the admittance region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is explained below with reference to accompanying drawings, in which:

FIG. 1 shows the cross section through one half of a rotationally symmetrical reactor in a broadly schematic representation,

FIG. 2 shows the radial variation in the growth rate, and

FIG. 3 shows the plan view of a substrate holder with altogether six substrate carriers, which are in each case loaded with seven substrates.

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiment shows a rotationally symmetrical reactor, in which the gases are introduced at the center and in which the gases are carried away in the region of the periphery. However, the invention also relates to those reactors which have the form of a tube, in which the gas is introduced at one end and the gas is discharged at the other end.

A significant component is a gas inlet member 5. This is located where the gas is introduced into the process chamber, that is to say at the center in the case of a process chamber 1 of a circular-symmetrical shape. The gas inlet member 5 has three gas inlet zones 6, 7, 8, disposed vertically one above the other. The three gas inlet zones are located between the ceiling 2 and the floor 3 of the process chamber 1.

In the exemplary embodiment, the floor 3 is actively heated by suitable means. The ceiling 2 is indirectly heated by the heated floor 3 by means of radiation and heat conduction. The heat for heating the floor 3 may be generated as infrared heat. However, it is also envisaged to generate the heat in the manner described by DE 100 43 601 A1, that is by high frequency.

In the case of the exemplary embodiment, the process gas flows through the process chamber 1 from the center to the periphery. For depositing III-V semiconductors, the V components are fed in as hydrides through the gas inlet zones 6, 8, which are directly neighboring the ceiling 2 and the floor 3, respectively. In particular, PH₃, AsH₃ or NH₃ is introduced through the gas inlet zones 6 and 8.

The metalorganic III component is introduced through the middle gas inlet zone 7, disposed between the outer gas inlet zones 6 and 8; in particular, TMG or TMI or an Al compound is introduced here.

An annular pressure barrier of a porous, gas-permeable material is designated by the reference numeral 11. The III component flows through this together with the carrier gas. The gas which passes through the outer gas inlet zones 6 and 8 is of a greater density and mass flow than the gas which flows into the process chamber 1 through the middle gas inlet zone 7. The gas inflows in the gas inlet zones 6, 8 can be set independently of the gas flow in the gas inlet zone 7.

Cross-pieces or separating elements by which the gases entering the process chamber through the gas inlet zones 6, 7, 8 are separated are designated by the reference numerals 12 and 13. Here, the representation is only schematic. It goes without saying that such gas conducting means as pipes or ducts that are capable of conducting the gases flowing through the gas inlet zones 6, 7, 8 separately from one another from a gas supply device to the reactor are provided.

In FIG. 2, the inlet zone is designated by EZ. Within this inlet zone, the reactive components entering the process chamber from the gas inlet zones 6 and 8 or 7 are mixed. This substantially takes place by diffusion. Adequate mixing is achieved by the limit of the inlet zone that is represented in FIG. 2 as a dashed line. By this limit, the flow profile in the process chamber has also been homogenized. The pyrolytically decomposable components, and in particular the hydride, which is decomposable with more difficulty and flows into the process chamber 1 through the gas inlet zones 6 and 8, have likewise been partially pyrolytically decomposed by this limit. However, the radial width of the inlet zone EZ is so small that adduct formation between the components is prevented to a sufficient extent.

The solid curve in FIG. 2 characterizes the growth rate in dependence on the radial distance from the center of the process chamber 1. The maximum 10 of the growth rate r lies shortly before the limit of the inlet zone EZ. In the region of the growing zone GZ adjoining the inlet zone EZ in the radially outward direction, the growth rate r falls as the radial distance R increases. This fall in the growth rate is compensated by the rotation about their own axis of the circular disk-shaped substrate carriers 9 represented in FIG. 3. The substrate carriers 9 may in this case be mounted on a gas cushion and—as described in DE 100 43 601 A1—be rotationally driven by means of gas jets. Also serving to make the layer thickness more uniform over the substrates 4 is the rotation of the entire substrate holder 3, which is formed by the floor of the process chamber 1, about the axis of the process chamber.

As can be gathered from FIG. 3, the individual substrate carriers 9 have a diameter which is great enough to accommodate seven 2″ substrates in extremely closely packed formation. Altogether, six substrate carriers are disposed around the center of the substrate holder 3 in a uniformly distributed manner.

The curve represented by a dashed-dotted line in FIG. 2 shows the variation in the growth rate r with respect to the radial distance R from the center of the process chamber 1 as it is in the prior art, in which a gas inlet member such as that described in DE 100 43 601 A1 is used. The additional gas inlet zone 8 for the V component has the effect that the maximum of the growth rate r shifts toward a smaller radial distance R.

It is provided that the vertical heights of the gas inlet zones 6 and 8 are each of the same size. The same amounts of gas per unit of time are also preferably intended to flow through these gas inlet zones 6 and 8. The heights of the gas inlet zones 6, 8 are less than the height of the middle gas inlet zone 7. In particular, the sum of the heights of the gas inlet zones 6 and 8 is less than the height of the middle inlet zone 7.

Model calculations in the case of a device of the prior art (DE 100 43 601 A1) have shown that the different densities and the great differences in the flow velocities of the gases entering the process chamber through the gas inlet zones produce an annular vortex underneath the ceiling in the region of the inlet zone EZ. It has been observed that a stream of gas with a gas which flows through an additional gas inlet zone 8 adjacent the ceiling 2 prevents this vortex. A flow profile that is symmetrical with respect to the horizontal center plane of the process chamber 1 is created in the region of the inlet zone EZ, homogenized into a parabolic flow profile up to the limit represented by the dashed line.

The ratios of the heights of gas inlet zone 6, gas inlet zone 7 and gas inlet zone 8 in relation to one another is preferably 4:15:4.

All disclosed features are (in themselves) pertinent to the invention. The disclosure content of the associated/accompanying priority documents (copy of the prior application) is also hereby incorporated in full in the disclosure of the application, including for the purpose of incorporating features of these documents in claims of the present application.

Claims

1. Device for depositing in particular crystalline layers on one or more in particular crystalline substrates in a process chamber, which has a ceiling and a heated floor, vertically opposite the ceiling, for receiving the substrates, with a gas inlet member, which forms gas inlet zones disposed vertically one above the other for introducing at least a first and a second gaseous starting material separately from one another, which starting materials flow in a horizontal direction together with a carrier gas through the process chamber, the first starting material being a hydride and the second starting material being a metalorganic compound, the stream of gas being homogenized and the starting materials at least partially pre-decomposed in an inlet zone directly adjacent the gas inlet member, the de-composition products of which starting materials are deposited on the substrates in a growing zone adjacent the inlet zone, while the stream of gas is steadily depleted, characterized by three gas inlet zones of the gas inlet member disposed vertically one above the other, the first starting material being introduced through a gas inlet zone neighboring the floor of the process chamber and a gas inlet zone neighboring the ceiling of the process chamber and the second starting material being introduced through a middle gas inlet zone between the one neighboring the floor and the one neighboring the ceiling, to reduce the horizontal extent of the inlet zone.

2. Method for depositing in particular crystalline layers on one or more in particular crystalline substrates in a process chamber, which has a ceiling and a heated floor, vertically opposite the ceiling, on which the substrates lie, in which method at least a first and a second gaseous starting material are introduced into the process chamber through gas inlet zones of a gas inlet member disposed vertically one above the other, which starting materials flow in a horizontal direction together with a carrier gas through the process chamber, the first starting material being a hydride and the second starting material being a metalorganic compound, the stream of gas being homogenized and the starting materials at least partially pre-decomposed in an inlet zone directly adjacent the gas inlet member, the decomposition products of which starting materials are deposited on the substrates in a growing zone adjacent the inlet zone, while the stream of gas is steadily depleted, characterized in that, to reduce the horizontal extent of the inlet zone, the first starting material is introduced through a gas inlet zone neighboring the floor of the process chamber and one neighboring the ceiling of the process chamber and the second starting material is introduced through a middle gas inlet zone between the one neighboring the floor and the one neighboring the ceiling.

3. Device according to claim 1, characterized in that the first starting material is AsH3, PH3 or an NH3.

4. Device according to claim 1, characterized in that the decomposition product of the first starting material is an element of the group V or VI and the decomposition product of the second starting material is an element of the group III or II.

5. Device according to claim 1, characterized in that at least one of the first and the second starting material is respectively introduced into the process chamber by means of a carrier gas through the gas inlet zone associated with it.

6. Device according to claim 1, characterized in that the first starting material is introduced into the process chamber in a concentration that is 100 to 5000 or 1000 to 5000 times higher than the second starting material.

7. Device according to claim 1, characterized in that the vertical height of the gas inlet zone neighboring the floor or the ceiling is less than the vertical height of the middle gas inlet zone.

8. Device according to claim 7, characterized in that the sum of the two heights of the gas inlet zones neighboring the floor and the ceiling is less than the height of the middle gas inlet zone.

9. Device according to claim 1, characterized in that the floor of the process chamber forming a substrate holder is heated from below.

10. Device according to claim 1, characterized in that the process chamber has an axial symmetry, the gas inlet member lying at the center.

11. Device according to claim 10, characterized in that the substrate holder is rotationally driven about the center of the process chamber.

12. Device according to claim 10, characterized by a multiplicity of circular disk-shaped substrate carriers, which are disposed next to one another in the circumferential direction on the substrate holder, are rotationally driven with respect to the substrate holder and carry one or more substrates.

13. Device according to claim 12, characterized in that each substrate carrier carries seven circular substrates and altogether six or more substrate carriers are associated with the substrate holder, located close to one another in uniform circumferential distribution.

14. Device according to claim 10, characterized in that the zone of the maximum growth rate lies radially within the annular growing zone in the marginal region of the inlet zones.

15. Device according to claim 14, characterized in that the diameter of the inlet zone is less than the radial extent of the growing zone.

16. Method according to claim 2, characterized in that the first starting material is one of AsH3, PH3 and NH3.

17. Method according to claim 2, wherein at least one of the first and the second starting material is respectively introduced into the process chamber by means of a carrier gas through the gas inlet zone associated with it.

18. Method according to claim 2, wherein the vertical height of the gas inlet zone neighboring the floor or the ceiling is less than the vertical height of the middle gas inlet zone.

19. Method according to claim 2, wherein the floor of the process chamber forming a substrate holder is heated from below.

20. Method according to claim 2, characterized in that the process chamber has an axial symmetry, the gas inlet member lying at the center.