Semiconductor: Solid-source Diffusion

In summary: According to the data sheet, a 60-min predeposition at 925°C should yield a sheet resistance of 10 Ω/sq. and a junction depth of approx. xj = 1.3 μm. My calculations show that the sheet resistance is only 1.3 Ω/sq. when the junction depth is <0.19 μm. This does not seem reasonable, so I'm not sure where I'm going wrong.
  • #1
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Homework Statement



You use the solid diffusion source wafers PH-950 from St. Gobain (see data sheet on TSquare, Diffusion Chapter) to form phosphorous-doped resistors in a p-type wafer with a background doping concentration of 1015 cm-3. According to the data sheet, a 60-min predeposition at 925°C should yield a sheet resistance of 10 Ω/sq. and a junction depth of approx. xj = 1.3 μm.

(a) Verify these numbers by calculating (and plotting) the doping profile ND(x), the junction
depth xj, and the sheet resistance. Assume that the surface concentration reaches the solid
solubility at the pre-deposition temperature.

(b) What thickness must a masking oxide have to locally prevent P-diffusion?

Homework Equations



[tex]C(x,t)=C_serf\left\frac{x}{2\sqrt{Dt}}\right[/tex]

[tex]D=D_0^{-E_a/kT}+D_0_-^{-E_a_-/kT}+D_0_--^{-E_a_--/kT}[/tex]

The Attempt at a Solution


See attached

Briefly, I'm trying to plot concentration as a function of x, so I solved for D and plugged everything into the equation for C(x,t), with t=3600s. However, that returns an answer that the concentration > 0 only when the depth is < 0.19um. As the manufactuer claims a junction depth of 1.3um, I assume I did something very, very wrong.
 

Attachments

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  • #2
1.3 micron sounds awfully deep for those parameters. Are you sure you have the manufacturers specs right? Maybe the 1.3 micron Xj is after a subsequent drive-in? I think you did the calculations correctly for what you were given
 
  • #3
Oh, dear. The manufacturer's specs are stated in the problem, and I checked it on the graphs the manufacturer gives out. Sounds unreasonable, but that's what they say, and I can't imagine they'd get away with such an egregious error. I must be making a mistake somewhere...

To clarify, the wafers have a background doping concentration of 1015 cm-3. (I lost formatting when I copied and pasted.) Either way, though, I'm still getting a ridiculously small junction depth.
 

Related to Semiconductor: Solid-source Diffusion

1. What is solid-source diffusion in semiconductors?

Solid-source diffusion is a process used in the fabrication of semiconductors, where a solid material is used as the source of dopant atoms to introduce impurities into a semiconductor material. This method is commonly used to create regions of different conductivity within the semiconductor material, such as creating p-n junctions in diodes and transistors.

2. How does solid-source diffusion work?

In solid-source diffusion, the semiconductor material is placed in contact with a solid source of dopant atoms, such as a layer of phosphorous or boron. The material is then heated to high temperatures, causing the dopant atoms to diffuse into the semiconductor material. The resulting impurities alter the electrical properties of the semiconductor, allowing for the creation of different types of electronic components.

3. What are the advantages of solid-source diffusion?

Solid-source diffusion offers several advantages in the fabrication of semiconductors. It is a relatively simple and cost-effective process, requiring only a few steps and readily available materials. It also allows for precise control of the doping concentration and depth, resulting in consistent and reliable electronic components.

4. What are the limitations of solid-source diffusion?

One limitation of solid-source diffusion is that it is only suitable for creating shallow doping profiles in the semiconductor material. This means that it is not suitable for creating more complex electronic components, such as high-frequency devices, which require more precise control of the doping profile. Additionally, the diffusion process can introduce defects in the semiconductor material, affecting its overall performance.

5. How does solid-source diffusion compare to other doping methods?

Solid-source diffusion is one of the oldest and most widely used methods for introducing impurities into semiconductors. It is a relatively simple and cost-effective method, but it does have limitations in terms of the depth and complexity of the doping profile that can be achieved. Other doping methods, such as ion implantation and chemical vapor deposition, offer more precise control over the doping profile, making them better suited for certain applications.

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