Method for fabricating a vertical transistor
A method for fabricating a vertical transistor comprises steps: forming a plurality of first trenches in a substrate; sequentially epitaxially growing a first polarity layer and a channel layer inside the first trenches, and forming a first retard layer on the channel layer; etching the first retard layer and the channel layer along the direction vertical to the first trenches to form a plurality of pillars; respectively forming a gate on a first sidewall and a second sidewall of each pillar; removing the first retard layer on the pillar; and epitaxially growing a second polarity layer on the pillar. The present invention is characterized by using an epitaxial method to form the first polarity layer, the channel layer and the second polarity layer and has the advantage of uniform ion concentration distribution. Therefore, the present invention can fabricate a high-quality vertical transistor.
1. A method for fabricating a vertical transistor, comprising the steps of:
Step S1: defining at least one trench region and at least one insulation region in a substrate, and forming a first trench in each trench region;
Step S2: sequentially epitaxially growing a first polarity layer and a channel layer inside each first trench, and forming a first retard layer on the channel layer;
Step S3: etching the insulation region with the first retard layer being a mask until a top of the insulation region is lower than a top of the first polarity layer by an etch depth so as to form a connection portion connected with the first polarity layer, and defining a combination of the connection portion, the first polarity layer, the channel layer and the first retard layer which stack together as an integration layer, wherein the integration layer has two opposite side faces;
Step S4: forming a first insulation layer on each side face;
Step S5: forming a plurality of second trenches in the integration layers to form at least one pillar each having a first sidewall and a second sidewall, wherein the integration layer is etched until the channel layer is completely removed with the first polarity layer being preserved to form the second trenches, and wherein a lengthwise direction of the second trenches is vertical to that of the first trenches;
Step S6: respectively forming a gate on the first sidewall and the second sidewall;
Step S7: removing the first retard layer on the pillar; and
Step S8: epitaxially growing a second polarity layer on the pillar.
2. The method for fabricating a vertical transistor according to claim 1 , wherein Step S1 further comprises the steps of:
Step S1a: forming an extension layer on the substrate; and
Step S1b: etching the extension layer and the substrate to form the first trenches.
3. The method for fabricating a vertical transistor according to claim 2 , wherein the extension layer is made of an oxide.
4. The method for fabricating a vertical transistor according to claim 2 , wherein the extension layer is also completely removed in Step S3.
5. The method for fabricating a vertical transistor according to claim 1 , wherein between Step S3 and Step S4 is undertaken Step A1: using an ISSG (In Situ Steam Generation) technology to repair and flatten the two side faces.
6. The method for fabricating a vertical transistor according to claim 1 , wherein in Step S4, an insulating material is filled between two adjacent integration layers to form the first insulation layer.
7. The method for fabricating a vertical transistor according to claim 1 , wherein the trench regions and insulation regions are multiple and which are alternately arranged in the substrate, and wherein the first trenches are multiple and correspond to the trench regions, and the first trenches are parallel to each other, and wherein the integration layers are multiple and correspond to the trench regions.
8. The method for fabricating a vertical transistor according to claim 7 , wherein between Step S3 and Step S4 is undertaken Step A2: implanting a plurality of counter ions having a polarity opposite to that of a plurality of dope ions of the first polarity layer into regions of the substrate, which are between each two adjacent integration layers.
9. The method for fabricating a vertical transistor according to claim 7 , wherein between Step S5 and Step S6 is undertaken Step A3: forming a protection layer at the bottom of each second trench, and forming a second insulation layer on each of the first sidewalls and the second sidewalls.
10. The method for fabricating a vertical transistor according to claim 1 , wherein after Step S6 is undertaken Step A4: filling an insulating material into the second trench having the gates.
11. The method for fabricating a vertical transistor according to claim 1 , wherein between Step S7 and Step S8 is undertaken Step A5: forming a height adjusting layer between the channel layer and the second polarity layer.
12. The method for fabricating a vertical transistor according to claim 11 , wherein the height adjusting layer is made of a material identical to that of the channel layer or made of silicon.
13. The method for fabricating a vertical transistor according to claim 11 , wherein the height adjusting layer is formed by an epitaxial method.