Partial vacuum boron diffusion process
AssigneeMotorola, Inc.
InventorsDervin L. Flowers, Sylvia B. Thompson
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Abstract
A method is presented for the uniform and reproducible boron doping of many closely spaced silicon wafers in a single batch, wherein a particular process sequence and specified ranges of reactant gas compositions, flow rate and pressure are utilized. The method is illustrated for BCl.sub.3 as a boron source gas and H.sub.2 and O.sub.2 as an oxidant gas. Superior results are obtained when BCl.sub.3 and H.sub.2 O are present in the reaction chamber at pressures less than 10 Torr (1.3 kPa) and molar ratios are in a specific range close to but not equal to that necessary for stoichiometric production of B.sub.2 O.sub.3.
Claims15
A method for substantially uniformly and reproducibly boron doping a silicon body within a reaction chamber comprising the steps of:
- forming a protective layer on said silicon body to resist etching by gases present in said reaction chamber during subsequent steps;
- introducing a composite gas mixture which comprises a boron containing gas and a first oxidant gas of proportions differing from stoichiometric proportions for production of substantially pure boron oxide by a predetermined mole fraction .DELTA. in the range -3 to -0.03 or 0.06 to 6;
- forming a boron source layer on said silicon body by reacting said composite gas mixture in the presence of said silicon body;
- maintaining throughout the two preceeding steps a total gas pressure around said silicon body of less than 10 Torr (1.3 kPa);
- heating thereafter said silicon body and boron source layer in a controlled atmosphere to achieve a specified redistribution of boron and its incorporation within said silicon body to a desired depth.
A method for substantially uniformly and reproducibly boron doping a silicon body made up of at least two silicon wafers in a wafer holder in a reaction chamber by formation on said silicon wafers of a boron source layer formed by reacting a composite gas mixture in the presence of said silicon wafers, comprising the steps of:
- arranging said silicon wafers in said wafer holder in at least one group wherein major faces of adjacent wafers are separated by at least one millimeter;
- forming a protective layer on said silicon body to resist etching by gases present in said reaction chamber during subsequent steps;
- regulating proportions of said composite gas mixture which comprises a boron source gas and a first oxidant gas so that said composite gas mixture differs from stoichiometric proportions for production of substantially pure boron oxide by a predetermined mole fraction .DELTA. in the range -3 to -0.03 or 0.06 to 6, so as to form said boron source layer;
- maintaining throughout the preceeding step a total gas pressure around said silicon body of less than 10 Torr (1.3 kPa);
- heating thereafter said silicon wafers in a controlled atmosphere to achieve specified redistribution of boron and its incorporation within said silicon wafers to a desired depth.
Dependencies are inferred from the claim text.