GB2082879A

GB2082879A - Improvements in or relating to furnaces for producing semiconductor materials

Info

Publication number: GB2082879A
Application number: GB8027107A
Authority: GB
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1980-08-20
Filing date: 1980-08-20
Publication date: 1982-03-10

Abstract

A furnace for producing semiconductor materials comprises an R.F. coil 14 surrounding a reactor 20. The reactor is water cooled (e.g. by a water cooling jacket 12) and contains an annular graphite susceptor 10 spaced from the walls thereof which is adapted to induce radiant heat into a substrate 24 located inside the susceptor. <IMAGE>

Description

SPECIFICATION Improvements in or relating to furnaces for producing semiconductor materials This invention relates to furnaces, for producing semiconductor materials particularly, but not exclusively for the epitaxial growth of thin layers of semiconductor material on a semiconductor substrate, such as silicon layers on a silicon substrate.

It is difficult to produce very thin silicon epitaxial layers that are uniform both in doping concentration and in thickness on-to a silicon substrate that is already heavily doped with arsenic due to the effects of autodoping. Also bowing of the substrate can take place during epitaxy because of differential heating across the substrate. This can result in the production of slip lines across the crystalline substrate plane and can be a serious problem especially on larger substrates in the region of 75 to 100 cms in diameter.

It is an object of the present invention therefore to provide a furnace which will reduce the effects of auto-doping and improve the uniformity of thin epitaxial layers. A further object of the invention is to reduce teomperature differentials across the substrate and to maintain the substrate at a substantially constant temperature.

According to the present invention a furnace for producing semiconductor materials comprises an RF coil surrounding a reactor, the reactor including cooling means and a hollow susceptor located inside the reactor and spaced from the walls thereof and adapted to induce radiant heating of a substrate positioned within the hollow susceptor.

The temperature of the substrate may be measured by an optical pyrometer and thermocouple system and is preferably controlled by the supply of RF power to the coil around the reactor.

The susceptor is preferably made of graphite and is preferably annular in shape.

An embodiment of the invention will now be .described by way of example only with reference to the accompanying drawings in which: Figure 1 is a longitudinal cross section of a furnace for producing semiconductor materials in accordance with the invention, and Figure 2 is a cross-sectional view perpendicular to the longitudinal axis of the furnace along line 2-2 in Figure 1.

The furnace comprises an annular glass reactor 20 mounted horizontally which incorporates an annular water cooling jacket 12, a gas inlet duct 32 and an exhaust duct 34. Surrounding the reactor 20 is a R.F. coil 14. Located inside the reactor 20 is an annular graphite susceptor 10 with its outer walls spaced from the inner walls 26 of the reactor 20.

A quartz slice holder 22 is located in the centre of the susceptor 10 which is adapted to support a silicon substrate 24 on which the silicon slices are to be grown, and the reactor gases. typically hydrogen and silane are passed down the centre of the susceptor. The slice holder 22 is supported on a quartz carrier 30 which rests on the inside walls 26 of the glass reactor 20, the quartz carrier also supporting the susceptor 10 in position.

The R.F. coil 14 induces heat into the susceptor 10. R.F. induced radiant heating has the advantage that the heated susceptor 10 has a uniform distribution of heat and the growth cycle time is relatively short. Radiant heating reduces the effects of autodoping and improves slice temperature uniformity resulting in thickness and doping improvements. The cooling jacket reactor system also enables the deposition of high purity layers but eliminates deposition on the inside walls 26 of the glass reactor 20.

Since the substrate 24 and susceptor 10 are not in intimate contact, the thermal gradient is eliminated as is the diffusion of impurities incorporated within the graphite susceptor 10 into the silicon substrate 24 and subsequently into the epitaxial layer. The bowing of substrates during epitaxy caused by differential heating can produce slip lines and is a serious yield problem especially on larger substrates of, for example, 75 to 100 cms in diameter. The furnace according to the present invention substantially reduces this possibility since the slice is uniformly heated and therefore doping and thickness uniformity is achieved.

A further use for the furnace is in the epitaxial growth of compound semiconductors by the well known "Alkyl or Organo-metallic Process". The method is very similar to silicon epitaxy and substitution of the apparatus by the annular susceptor and R.F. heating would have similar advantages over the present system of growth to those in the growth of silicon slices.

In experiments, silicon epitaxial growth was conducted using different flow rates of reactor gases, in this case hydrogen, silane and phosphine or diborane. The layers exhibiting good quality surfaces were profiled to determine the epilayer doping concentration and layer thickness, and the results confirmed that the furnace can produce layers with good quality surfaces, flat doping profiles. Transmission electron microscope examination confirmed that good quality single crystal epitaxial silicon had been deposited.

In a typical method of epitaxiaily growing an n-type silicon layer on a silicon substrate, firstly a new susceptor 10 is placed in the furnace with a thoroughly cleaned quartz carrier 30 and a slice holder 22 carrying a silicon substrate 24. The substrate is then given an atomically clean surface by gas polishing for a few minutes by passing a mixture of hydrogen chloride gas and hydrogen through the surface at around 1 2000C. The RF power required to achieve this temperature is approximately 30 KW at a frequency of 350 KHz.

An n-type layer is now grown by passing hydrogen (as a carrier gas), silane (as the silicon source) and phosphine (as a doping gas) through the furnace at around 1 1000C for approximately one minute producing a layer approximately 0.5 ,"m thick.

A p-type layer is grown in a similar manner but the phosphine is replaced by a flow of diborane.

Claims

1. A furnace for producing semiconductor materials comprising an RF coil surrounding a reactor, the reactor including cooling means and a hollow susceptor located inside the reactor and spaced from the walls thereof and adapted to induce radiant heating of a substrate positioned within the hollow susceptor.

2. A furnace as claimed in claim 1 in which the temperature of the substrate is measured by an optical pyrometer and thermocouple system and is controlled by the supply of RF power to the coil around the reactor.

3. A furnace as claimed in claim 1 or claim 2 in which the susceptor is made of graphite and is annular in shape.

4. A furnace for producing semiconductor materials constructed and adapted to operate substantially as hereinbefore described with reference to the accompanying drawings.