Thin Contact Development for Silicon Detectors

agreementkittensSemiconductor

Nov 2, 2013 (3 years and 5 months ago)

307 views

Lawrence Berkeley National Laboratory

C.
Tindall,
P.
Denes
, S. E. Holland, N.
Palaio
,

D.
Contarato
, D.
Doering

Thin Contact Development for

Silicon Detectors

Lawrence Berkeley National Laboratory, Berkeley, CA 94720

1

D.E. Larson, D.W. Curtis, S.E. McBride, R.P. Lin
1


Space Sciences Laboratory, University of California Berkeley, Berkeley, CA 94720
-
7450

1
Also Physics Department, University of California, Berkeley, CA 94720
-
7300

Lawrence Berkeley National Laboratory

2

Thermco
/
Expertech

150mm furnaces

150 mm Lithography
tool

LBNL Microsystems Laboratory

LBNL Microsystems Laboratory


Class 10
Cleanroom

Lawrence Berkeley National Laboratory

Silicon Semiconductor Detectors

High purity
-

Si

(n
-
type)

200 to 300
m
m

SiO
2

n
+

contact

p
+

B
-

implant

Al Electrode

3

e
-

h
+

h
n

(high energy)

-
Absorbed in the


active volume.

h
n

(low energy)

-
Absorbed in the


contact.

Lawrence Berkeley National Laboratory

CCD Project

4

LBNL Engineering Group


200 fps CCDs for direct
detection of low
-
energy x
-
rays

Amplifiers every 10
columns, metal strapping of
poly, and custom IC readout

Lawrence Berkeley National Laboratory

MSL Processed Silicon Detector Wafer

5

Lawrence Berkeley National Laboratory

Instrument Size

WIND 3
-
D Plasma and Energetic

Particle Experiment

Suprathermal Electron Telescope

Element (STEREO
-
IMPACT)

(UC Berkeley Space Sciences Lab)

6

Lawrence Berkeley National Laboratory

In
-
Situ Doped Polysilicon

7

W127 A3

Detector Area =0.09 cm
2

Baseline Process


In
-
situ phosphorus doped polysilicon (ISDP).


It yields a thin (≤200
Å
), low leakage (~300
pA
/cm
2

@ ambient temp) contact.


Deposition temperature is >600
°
C so it can not be used on devices with metal.


In LBNL’s PIN diode and CCD processes it is deposited before the metal.

/cm
2
)

Lawrence Berkeley National Laboratory

Thin backside n
+

ohmic

contact development

The thin backside n
+

contact technology

developed at the MSL is an enabling

technology for

a)
Photodiodes for medical applications

b)
CCDs

c)
Charged
-
particle detectors in space

SIMS depth profile

ISDP


in
-
situ doped

polysilicon

8

Lawrence Berkeley National Laboratory

In
-
Situ Doped
Polysilicon

Contact

9

Energy lost by the
protons in the contact is
about 2.3
keV
.

Data taken by R. Campbell at

UC Berkeley’s Space Sciences
Laboratory

Lawrence Berkeley National Laboratory

In
-
Situ Doped
Polysilicon

Contact

10

Energy lost by electrons
in the 200
Å

doped
polysilicon window is
about 353
eV
.

Data taken by D. Larson at UC
Berkeley’s Space Sciences
Laboratory

Lawrence Berkeley National Laboratory

In
-
Situ Doped
Polysilicon

Contact

11

Spectrum obtained by illuminating a PIN diode to a mixed
55
Fe and
109
Cd
source. The detector has a 200
Å

in
-
situ doped polysilicon entrance contact.

Data taken by D. Curtis
at UC Berkeley’s Space
Sciences Laboratory.

Lawrence Berkeley National Laboratory

MSL detectors on NASA space missions


Mars Atmosphere and Volatile Evolution (MAVEN)


-

MAVEN will make definitive scientific measurements of present
-
day

atmospheric loss that will offer clues about the planet's history.


-


To date, the MSL has provided 36 thin window detectors for MAVEN.



16 detectors have been selected for flight as part of the Solar Energetic



Particle (SEP) Instrument.


-

Launch: late 2013.

Mock up of the SEP Instrument

Prototype Detector Stack

Lawrence Berkeley National Laboratory

MSL detectors on space missions



Charged particle detectors fabricated in the MSL by Craig
Tindall


CINEMA


Understanding space weather


Solid State Telescopes (two for ions, two for electrons per spacecraft)


104 detectors delivered, 80 used in flight


http://www.nasa.gov/mission_pages/themis/spacecraft/SST.html

THEMIS PIN Diode

Fabricated in the MSL

Lawrence Berkeley National Laboratory

MSL detectors on NASA space missions



THEMIS Update


Launched in 2007, all major science goals were achieved by 2009


MSL detectors on all five spacecraft are still returning science data.


ARTEMIS


extended mission to study the interaction of the moon


with the solar wind. Two THEMIS spacecraft diverted to the moon.


These two “ARTEMIS” spacecraft are now in lunar orbit.

Lawrence Berkeley National Laboratory



STEIN Detector (First Design)

15


Low Energy Threshold (1
-
2
keV
)


~1
keV

Energy Resolution


Sensitive to Electrons, Ions,
and Neutrals (But Can’t
Separate)


4 x 1 Pixel Array


Flight Heritage: STEREO
Mission STE Instrument


(
SupraThermal

Electrons)


(STE)



Silicon
Semiconductor Detector

Lawrence Berkeley National Laboratory

STEIN Instrument



Collimator



±

2000 V Field Separates
Electrons, Ions, and
Neutrals to ~20
keV




Particle Attenuator

(Blocks 99% of Particles)

Initial Version of the Instrument


Designed by Space Sciences Laboratory

Lawrence Berkeley National Laboratory

MSL detectors on an NSF space mission


Cubesat

for Ions, Neutrals and Magnetic Fields (CINEMA)


Mission consists of four “triple”
cubesats
, small satellites (10cm x 10cm x 30cm)
Two will be made by UC Berkeley’s Space Sciences Laboratory and two by Kyung
Hee

University in South Korea.


Each
cubesat

contains a magnetometer and a Suprathermal Electrons, Ions and
Neutrals (STEIN) instrument. STEIN contains a 30 pixel array of detectors with a
thin entrance window.


First spacecraft has been delivered. Launched: September 2012.

Cubesat

Mock
-
up

STEIN Detectors and Readout ASIC

Lawrence Berkeley National Laboratory

MSL detectors on NASA space missions


Solar Probe Plus (SPP)


Prototyping Phase


-

Mission to study the sun close
-
up. The closest approach


9.5 solar radii.


-

Prototype detectors for the Low Energy Telescope in the EPI
-
HI instrument




are being fabricated in the MSL.


-

Detectors with active volumes that are 10
m
m and 25
m
m thick are required.


-

Launch


2015.



675
m
m

SiO
2

p
+

B
-

implant

Al Electrode

Handle Wafer

Back Contact

Active
Layer


10
m
m

n
+

P
-

Implant

Lawrence Berkeley National Laboratory



Thin Silicon Alpha
Spectrum

19

Lawrence Berkeley National Laboratory

Other Thin Contact Techniques

-

Commercial
silicon detectors
(PIN diodes) are available with


contacts that are


≥500
Å thick. (ion implantation)

-

Reported leakage currents are roughly 20nA/cm
2
.

-

A 500
Å

contact transmits only about 65% of 280eV photons into


the active volume of the detector.


-
A thinner contact is needed to get high efficiency


at 280eV (C
-

K edge).

20

Lawrence Berkeley National Laboratory

Silicon
x
-
ray Transmission

21

Lawrence Berkeley National Laboratory

Thin Contact Fabrication Techniques

22


Technique


Thickness (
Å
)

Compatible

with metal?

%Transmission

at 280eV

Amorphous Si

≥300

Yes

≤77

In
-
situ doped

poly

200

No

84

Implant/Anneal

~1000

Yes

42

Implant/Laser

~700

Yes

54

MBE

≤100

Yes

≥92

Lawrence Berkeley National Laboratory

Implant/Low Temperature Anneal

23

-

ISDP is a very useful process for making thin contacts.


However:

a.) The deposition temperature ≥600
°
C so it




can’t be used on

devices with metal.



b.) Integration with the CCD process is complex.



c.) Integration with CMOS processes used to make




active pixel sensors is impossible.

-

For applications that do not require the thinnest contact we


developed a much simpler alternative


ion implantation and


low temperature annealing


that does not damage the metal.

-

Informally referred to as our “pizza process”.

Lawrence Berkeley National Laboratory

Implant/Low Temperature Anneal

24

-

Leakage current ranges from about 600
pA
/cm
2

to several nA/cm
2



at 100V bias and ambient temperature with this method.


-

The window thickness is about 1000
Å

of silicon.


-

Good uniformity. Used successfully with our largest CCD


16.59 cm
2
.

Our CCDs that utilize “pizza process”
contacts for soft x
-
ray detection.

Lawrence Berkeley National Laboratory

Implant/Low Temperature Anneal

25

SOI Imager (Active Pixel Sensor)

Guibilato
, et. al.
NIM A
650(2011) 184

Lawrence Berkeley National Laboratory

Implant/Low Temperature Anneal

26

After Thinning

Before Thinning

After the

“Pizza”

Process

SOI Imager
-
2 (Active Pixel Sensor)

Battaglia
, et. Al.
NIM
A 676 (2012) 50

Lawrence Berkeley National Laboratory

Implant/Laser Anneal

27

-

Gives only a nominal decrease in the window thickness from 1000
Å



to an estimated 700
Å
.

-

Requires a significant amount of stitching. Stitching only in one direction


works at some level. The yield is about 80%.

-

X
-
Y stitching doesn’t seem to give low enough leakage current, but our


testing of this is limited.

-

Bottom line


further testing needed to optimize the process. Most likely a


laser with a larger spot size would improve the result significantly.

Lawrence Berkeley National Laboratory

Chemical Etching/a
-
Si

28

-

Surface is chemically etched, then a 300
Å

thick layer of a
-
Si


is sputtered onto the surface. It is essentially a room


temperature process.

-

The defects on the surface form the contact. One obtains the


same contact properties with or without the a
-
Si.

-

The contact thickness has not been measured.

Lawrence Berkeley National Laboratory

-

Ideally a single monolayer of
electrically active dopant atoms
is desired.

-

The silicon capping layer is
required to form a stable contact.

Molecular Beam Epitaxy (MBE)

29

Contact Configuration

Incoming x
-
rays

Silicon cap layer

d
-
doping
layer

Silicon device

Front side
pattern/electronics


The Key:

-

This is a deposited contact, so


the beginning surface defect


density must be low in order


to obtain low leakage current.

Pioneering work on
d
-
doped contacts
was done by
Nikzad’s

group at JPL.

IEEE TED, 55, Dec. 2008

Lawrence Berkeley National Laboratory

Molecular Beam Epitaxy (MBE)

30

Load Lock

Buffer
Chamber

MBE Chamber

Base Pressure ~5x10
-
11

torr

e
-
beam gun

(silicon)

Sb or B

Knudsen Cell

Substrate

Lawrence Berkeley National Laboratory

Molecular Beam Epitaxy (MBE)

31

Deposition
Chamber

Load
-
Lock

Substrate
Preparation
Chamber

Typical

SVT Associates
Silicon MBE
System

Lawrence Berkeley National Laboratory

Thin Contact Fabrication Techniques

32

Technique

Advantages

Disadvantages

Amorphous Silicon

Room Temperature Process

Leakage

current varies
significantly from run to run,

n
-
type only.

Implant/Low

Temp Anneal

Low

temperature, low leakage,
simple process, high yield.

Relatively

thick contact.

Implant/
Laser Anneal

Patterned

side of the wafer is at
room temperature.

Leakage

current is somewhat
variable, thicker than optimal.

MBE

Low

temperature, low leakage,
ultimately thin contact.

Complex equipment and process.

In
-
situ doped poly.

Thin contact, low leakage.

Process

temperature too high for
metalized devices.

Implant/Flash

UV

Thin

contact, low leakage.

Process temperature too high,
expensive equipment.

Lawrence Berkeley National Laboratory

Silicon
x
-
ray Transmission

33

Implant/Low Temperature Anneal

“Pizza Process”

MBE

Lawrence Berkeley National Laboratory

Fine Pitch Germanium Strip Detector

34

Developed for time
-
resolved x
-
ray
absorption spectroscopy

J. Headspith, et al., Daresbury Lab

1024 strips, 50
m
m pitch, 5 mm length

1 mm thick detector

~ 30 pA / strip @ V
b

= 55 V, T >100 K

Lawrence Berkeley National Laboratory

Detector Group at LBNL

35


One of the first groups to develop lithium
-
drifted Si detectors (early
1960’s)


One of two groups that originally developed high
-
purity
Ge

crystal growth
(early 1970’s)


Fabrication technologies developed include: amorphous semiconductor
contact, implanted contact, and surface
passivation



Invented shaped
-
field point
-
contact
Ge

detector (1989)


Invented coplanar
-
grid technique for
CdZnTe
-
based detectors (1994)

Historical accomplishments with significant impact


on radiation detector technology:

Lawrence Berkeley National Laboratory

Summary

36

-

Thin contacts are needed for imaging soft x
-
rays.



-

The techniques of most interest appear to be:


1.) implant/low temperature anneal or “pizza” process


2.) Molecular Beam Epitaxy (MBE)


-

Germanium may be useful for higher energies. We have produced


strip detectors with 50
m
m pitch for use at light sources.


-

Thin contacts also have application in other fields of science,


for example
-

space science.