Method to make a silicon layer being partly polycrystalline and partly monocrystalline

Claim 2

Method to make a silicon layer (6) on a monocrystalline semiconductor substrate (2) having a surface region (1) of relatively high impurity concentration and being covered with a masking layer (3) which has apertures exposing region (1), where the silicon layer (6) is monocrystalline in areas deposited over the exposed areas of region (1) and polycrystalline overlying masking layer (3) characterized in that a blanket layer (6) of polysilicon is deposited on the masked semiconductor substrate and subsequently irradiated with a laser radiation (14).

Claim 3

Method according to claim 1 wherein said substrate (2) and said region (1) are of opposite type conductivities.

Claim 4

Method according to claim 1 or 2 wherein said substrate (2) has an impurity concentration in the range from intrinsic value to about 1 x 10 15 atoms/cm 3 and wherein said region has an impurity concentration in the range from about 1 x 10 20 atoms/cm 3 to about 21 3 1.5 x 10 atoms/cm 3 .

Claim 5

Method according to claim 3 wherein a laser radiation is used having a wavelength of about 1.06 µm.

Claim 6

Method according to any one of claims 1 to 4 wherein a masking layer (3) consisting of silicon dioxide is used.

Claim 7

Method according to any one of claims 1 to 5 used to make a transistor wherein said region (1) serves as subcollector, a base dopant is introduced into one monocrystalline area (4) produced by the laser irradiation and into the area (7) of polycrystalline silicon surrounding area (4) and an emitter dopant is introduced into the upper portion (10) of area (4).

Claim 8

Method according to any one of claims 1 to 6 being applied to produce a filamentary transistor, wherein a semiconductor substrate (2) of relatively low impurity concentration is provided, a region (1) of relatively high impurity concentration is formed in substrate (2), a masking layer (3) is formed on saic substrate (2) and said region (1), said layer (3) being apertured at two locations above said region, a blanket layer (6) of polysilicon is deposited on layer (3) and the exposed areas of region (1), layer (6) is subjected to laser radiation (14) to convert said polysilicon deposited on the two exposed areas of region (1) into epitaxial monocrystalline silicon, the one area (4) of epitaxial monocrystalline silicon and area (7) of polycrystalline silicon surrounding area (4) are doped with an impurity effecting that area (4) and region (1) are of opposite type conductivities, the other area (5) of epitaxial monocrystalline silicon is doped with an impurity effecting that area (5) and region (1) are of the same conductivity type, the upper portion (10) of epitaxial monocrystalline area (4) is doped with an impurity effecting that portion (10) and area (4) are of opposite type conductivities and contacts (11, 12, 13) are made to areas (5) and (7) and to portion (10), respectively.

Claim 9

Method according to any one of claims 1 to 7 wherein prior to the laser irradiation, layer (6) is planarized e.g. by covering the structure with the polyimide layer and treating it by means of reactive ion etching.

Claim 10

Method according to any one of claims 1 to 8 wherein the undoped areas of polysilicon layer (6) are removed and replaced by oxide e.g. by means of chemical vapor deposition followed by a planarization step.