Gas-admission element for CVD processes, and device
The invention relates to a method for depositing especially, crystalline layers onto especially, crystalline substrates. At least two process gases are led into a process chamber of a reactor separately from each other, through a gas inlet mechanism above a heated susceptor. The first process gas flows through a central line with a central outlet opening and the second process gas flows through a line which is peripheral thereto and which has a peripheral outlet opening that is formed by a gas-permeable gas outlet ring. Said gas outlet ring surrounds a ring-shaped pre-chamber. The invention provides that in order to avoid a parasitic deposition in the area of the peripheral outlet opening, the end section of the gas outlet ring that faces towards the susceptor or the radially outer section of the surface of the gas outlet mechanism surrounding the central outlet opening is cooled by the second process gas according to a truncated cone or revolution hyperboloid shape of a gas guiding surface formed by the pre-chamber back wall.
1. Gas-admission element for a device for depositing in particular crystalline layers on in particular layers on in particular crystalline substrates, by means of which two process gases can be introduced into a process chamber of a reactor separately from one another above a heatable susceptor, the gas-admission element having a central feed line with a central end-side outlet opening for a first process gas, and having a peripheral line which is peripheral with respect to the central feed line that flows a second process gas into an annular antechamber surrounded by a rotationally symmetrical gas-permeable gas-discharge ring, the second process gas emerges through the rotationally symmetrical gas permeable gas-discharge ring, the radial width of the annular antechamber decreases toward the free end of the rotationally symmetrical gas permeable gas-discharge ring, on account of a gas-guiding surface which does not run parallel to the central axis in longitudinal section, characterized by a frustoconical or rotationally hyperboloid-shaped gas-guiding surface, which is formed by the gas-guiding surface, for convective cooling of the portion of the rotationally symmetrical gas-permeable gas-discharge ring which is close to the susceptor, by means of the second process gas flowing along the gas-guiding surface.
2. Gas-admission element according to claim 1 , characterized in that the rotationally symmetrical gas-permeable gas-discharge ring consists of porous material and in particular is a quartz frit.
3. Gas-admission element according to claim 2 , characterized in that the gas-guiding surface is associated with an exchangeable part.
4. Gas-admission element according to claim 3 , characterized in that the gas-guiding surface links up with the peripheral line without there being a step.
5. Gas-admission element according to claim 4 , characterized in that the exchangeable part can be screwed to the feed line or can be connected to the feed line by way of a bayonet connection.
6. Gas-admission element according to claim 1 , wherein the rotationally symmetrical gas-permeable gas-discharge ring holds the pressure in the annular antechamber at a higher level than the process chamber pressure.
7. Gas-admission element according to claim 6 , wherein the rotationally symmetrical gas-permeable gas-discharge ring consists of porous material.
8. Gas-admission element according to claim 7 , wherein the rotationally symmetrical gas-permeable gas-discharge ring consists of a quartz frit.
9. Gas-admission element for a device for depositing in particular crystalline layers on in particular layers on in particular crystalline substrates, by means of which two process gases can be introduced into a process chamber of a reactor separately from one another above a heatable susceptor, the gas-admission element having a central line with a central end-side outlet opening for a first process gas, and having a peripheral line which is peripheral with respect to the central line that flows a second process gas into an annular antechamber surrounded by a rotationally symmetrical gas-permeable gas-discharge ring, the second process gas emerges through the rotationally symmetrical gas-permeable gas-discharge ring, the radial width of the annular antechamber decreases toward the free end of the rotationally symmetrical gas-permeable gas-discharge ring, on account of a gas-guiding surface which does not run parallel to the central line in longitudinal section, characterized by a frustoconical or rotationally hyperboloid-shaped gas-guiding surface, which is formed by the gas-guiding surface, for convective cooling of the portion of the rotationally symmetrical gas-permeable gas-discharge ring which is close to the susceptor, by means of the second process gas flowing along the gas-guiding surface; wherein the gas-guiding surface is associated with an exchangeable part.