View source for Specific Process Knowledge/Thin film deposition/Deposition of Gold

<center><span style="background:#87CEEB">4th Level - Comparison</span></center>
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Gold can be deposited by e-beam evaporation or sputtering. In the chart below you can compare the different deposition equipment.


== Adhesion of Au on Si ==
The adhesion of gold on Silicon or Silicon with native oxide is not very good. The Si substrate is often deposited an adhesion layer before the gold deposition. A few nm of Chromium or Titanium works well and they react with the Oxygen of Silicon oxide and present a metallic bond with gold. 5 nm to 10 nm thick of Cr or Ti is commonly used and it is important to deposit Cr or Ti and then immediately Au. If the vacuum chamber is opened in between, the surface of Cr or Ti will get oxidized and that will give a poor adhesion. If a gold layer needs to be deposited directly on Silicon, then native oxide has to be removed by deep in diluted HF and immediately load the evaporation chamber. And after the deposition, the wafer has to be heated op to get some Au-Si diffusion which improves the adhesion.  


{| border="1" cellspacing="0" cellpadding="4" 
 
|-style="background:silver; color:black"
! 
! E-beam evaporation ([[Specific Process Knowledge/Thin film deposition/Alcatel|Alcatel]])
! E-beam evaporation ([[Specific Process Knowledge/Thin film deposition/Wordentec|Wordentec]])
! Sputter ([[Specific Process Knowledge/Thin film deposition/Lesker|Lesker]])
! E-beam evaporation ([[Specific Process Knowledge/Thin film deposition/Physimeca|Physimeca]])  
! Sputter coater [[Specific Process Knowledge/Thin film deposition/Sputter coater#Sputter coater 03|(Sputter coater 03)]]
! Sputter coater [[Specific Process Knowledge/Thin film deposition/Sputter coater#Sputter coater 04|(Sputter coater 04)]]
|-style="background:WhiteSmoke; color:black"
! General description
| E-beam deposition of Au
| E-beam deposition of Au
| Sputter deposition of Au
| E-beam deposition of Au
| Sputter deposition of Au
| Sputter deposition of Au
|-
|-style="background:LightGrey; color:black"
! Pre-clean
|RF Ar clean
|RF Ar clean
|RF Ar clean

|
|
|
|-style="background:WhiteSmoke; color:black"
! Layer thickness
|10 Å to 5000Å* 
|10 Å to 5000Å*
|10 Å to
|10Å to about 3000Å*
|
|

|-
|-style="background:LightGrey; color:black"
! Deposition rate
|2 Å/s to 10 Å/s
|1 Å/s to 10 Å/s
|
|From 5 Å/s up to 10Å/s 
|Not measured
|Not measured

|-

|-style="background:WhiteSmoke; color:black"
! Batch size
|
*Up to 1x4" wafers
*smaller pieces
|
*24x2" wafers or 
*6x4" wafers or
*6x6" wafers
|
*Pieces or
*1x4" wafer or
*1x6" wafer
|
*1x 2" wafer or
*1x 4" wafers or
*Several smaller pieces 
|
*Several smaller samples
*1x4" wafer
|
*Several smaller samples
*1x4" wafer

|-

|-style="background:LightGrey; color:black"
!Allowed materials

|
* Silicon oxide 
* Silicon (oxy)nitride 
* Photoresist 
* PMMA 
* Mylar 
* SU-8 
* Metals 
|
* Silicon oxide 
* Silicon (oxy)nitride 
* Photoresist 
* PMMA 
* Mylar 
* SU-8 
* Metals 
|
* Silicon
* Silicon oxide 
* Silicon nitride
* Silicon (oxy)nitride 
* Photoresist 
* PMMA 
* Mylar 
* SU-8 
* Metals 
* Carbon
|
* III-V materials
* Silicon wafers 
* Quartz wafers 
* Pyrex wafers
|
* All samples allowed in the SEM Supra 1
|
* All samples allowed in the SEM Supra 2 or 3

|-style="background:WhiteSmoke; color:black"
! Comment
|
* For thicknesses above 200 nm permission is required
* An adhesion layer (of Cr or Ti) is recommended under Au.
|
* For thicknesses above 200 nm permission is required
* An adhesion layer (of Cr or Ti) is recommended under Au.
|
|

|
* Used for gold sputter coating of samples before SEM inspection
|
* Used for gold sputter coating of samples before SEM inspection
|-
|}


'''*'''  ''For thicknesses above 200 nm permission from ThinFilm group (thinfilm@danchip.dtu.dk) is required.''

== Studies of Au deposition processes in the Wordentec==
[[/Roughness of Au|Roughness of Au layers]] - ''Roughness of Au layers deposited with different equipment and settings''

===Wafer temperature===
The wafer temperature during e-beam deposition of 200 nm Au on six wafers has been measured using thermal labels on the backside of the wafers. The following results were obtained:
{| border="1" cellspacing="0" cellpadding="2"
! Wafer 
! Temperature [C]
|- 
|1
|48
|-
|2
|60
|-
|3
|65
|-
|4
|71
|-
|5
|71
|-
|6
|77
|-
|}
The temperatures are accurate within approximately +/- 3C and probably underestimating the actual wafer temperature slightly. It is observed that the wafer temperature increases with each wafer, thus if wafer temperature is of concern it is advised to reduce the number of wafers per run.


[[Image:section under construction.jpg|70px]]
== Thin Au layer deposition using Lesker==
For depositing very thin, down to 6nm continuous Au layers on Si/SiO<sub>2</sub> substrates. Works also with ALD deposited Al<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> as substrate.

Adhesion promoter: aminopropyltrimethoxysilane (APTMS).
Adhesion promoter deposition: 3h immersion in 95%IPA, 2.5% H<sub>2</sub>O, 2.5% APTMS.

''NOTE: the APTMS is time sensitive, so deposit it as close to the Au deposition as possible.''

Lesker deposition parameters:
{| border="1" cellspacing="0" cellpadding="2"
! Gun # 
! Power [W]
! Ramp rate [W/s]
! Pressure [mtorr]
! Atmosphere
! Deposition rate [nm/s]
|- 
|2
|300
|5
|3
|Ar
|1
|}

''NOTE: As a general rule, the lower the pressure and higher the power, the better.'' 

Film characteristics:
{| border="1" cellspacing="0" cellpadding="2"
! Thickness [nm]
! Roughness min [nm]
! Roughness max [nm]
|- 
|6
|0.25
|0.4
|- 
|10
|0.3
|0.5
|- 
|24
|0.3
|0.5
|}

''NOTE: After depositing 10layers of 10nm each, the roughness increased to 0.8nm RMS''

Work done by Johneph Sukham ([mailto:johsu@fotonik.dtu.dk?Subject=Thin Au deposition using Lesker click to email]) and Radu Malureanu ([mailto:rmal@dtu.dk?Subject=Thin Au deposition using Lesker click to email])