Specific Process Knowledge/Thermal Process/Dope with Boron

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Dope with boron

The furnace A1 Boron Drive-in and Pre-dep can be used to pre-deposit silicon wafers with boron. The silicon wafers are positioned in a silicon carbide boat just next to wafers of boron nitride. Pre-deposit of boron is a diffusion process on the silicon wafers.

The concentration of boron in the wafer depends on the process temperature. The depth profile depends of the process time.

All this figures have been made at the time where there was a furnace only for Boron Pre-dep (furnace A2). The process was done at a temperature of 1125 ^oC and a flow of 5 slm N₂ and 0.2 slm of O₂.

• Boron profiles from SIMS
• 
  Pre-depostion for 1 hour at 1125 °C
• 
  Pre-depostion for 6 hour at 1125 °C
• 
  Pre-depostion for 16 hour at 1125 °C

• Boron diffusion depth vs. pre-deposition time
• 
• 

Boron pre-deposition

Results made by Filip Sandborg Olsen, Dec. 2015

Purpose

To study the uniformity across a wafer that has been boron doped using a pre-deposition process and a short wet oxidation to oxidize the boron phase layer in the Boron Predep and Drive-in furnace (A1) at DTU Nanolab.

Experimental setup

3 phosphorous doped device wafers (n-type) were used. In the furnace 3 RCA-cleaned wafers were placed in the center of the boat with Boron source wafers (also RCA cleaned) with the front side facing the source wafers. A pre-deposition process was made for one hour at 1125 °C, then the source wafers were removed and the device wafers oxidized in a wet oxidation process at 950 °C for half an hour. Finally the oxide was removed in BHF and one wafer was cut into small samples for SIMS measurements.

The experiment has been performed at 3 different pre-deposition times 30 min, 60 min and 90 min with and without a 30 min WET950 oxidation step. The results are resumed in the figures below.

Results

The samples for SIMS measurements corresponds to 5 different positions on the wafer.

Sample position on the wafer

SIMS Measurement at 5 different positions after pre-deposition of boron.The SIMS measurement shows a good uniformity across the wafer

SIMS Measurement for 3 different pre-deposition times 30 min, 60 min and 90 min with and without a 30 min WET950 oxidation step.