Epitaxial integrated E-dE solid state detector telescope

An epitaxial integrated E-dE solid state detector telescope comprising a dE detector produced on an epitaxial layer and a E detector produced on a high purity silicon layer, both of which are fabricated on a single silicon wafer having N-N.sup.+ -N type complex structure. Said dE and E detectors are electrically isolated by a very low resistive N.sup.+ type silicon layer, which is produced on the high purity N type silicon substrate by impurity diffusion technique and is buried under the epitaxial silicon layer. Electrodes of dE and E detectors are produced on both sides of the silicon wafer by means of evaporation of gold in a vacuum. Said electrodes are reverse biased and depletion layers which act as active regions of dE and E detectors are extended from outsides toward said buried layer, providing independent charge collections of carries produced by incident charged particles in dE and E detectors by said electrodes.

BACKGROUND OF THE INVENTION 
The present invention relates to a solid state detector telescope which is 
composed of a relatively thin dE detector and a thick E detector and is 
used for identifying charged particles and measuring incident energy of 
the particles. 
Heretofore, dE and E detectors used for this purpose are produced 
individually. For identifying heavy and low energy charged particles, a 
thin detector with a thickness less than 10 .mu.m is required as the dE 
detector of this solid state detector telescope. This thin detector has 
been produced from an epitaxial silicon wafer by etching off the highly 
doped substrate using a chemical preferential etching technique or 
electrochemical etching technique. However, this method has drawbacks that 
the dE detector suffers a degradation of thickness uniformity caused by 
etching irregularities and also the etching process itself is laborious. 
The purpose of the present invention is to eliminate said drawbacks, 
providing a new type of detector which integrates dE and E detectors in a 
single block. 
BRIEF SUMMARY OF INVENTION 
An object of the present invention is to provide an epitaxial integrated 
E-dE solid state detector telescope using an epitaxial crystal growth 
technique combined with an impurity diffusion technique whereby the thin 
dE detector is produced without employing a highly technical process of 
etching the substrate. 
The second object of the present invention is to provide an epitaxial 
integrated E-dE solid state detector telescope which has a thin dE 
detector with highly uniform thickness eliminating an additional 
non-uniformity which might appear caused by etching the substrate. 
The third object of the present invention is to provide an epitaxial 
integrated E-dE solid state detector telescope which is compact and rugged 
and is easy to handle because it is fabricated on a single semiconductor 
wafer. 
The fourth object of the present invention is to provide an epitaxial 
integrated E-dE solid state detector telescope which eliminates a 
separation of dE and E detectors whereby an unfavourable counting loss in 
the E detector caused by a scattering of charged particles in the dE 
detector is minimized. 
Other and further objects, features and advantages of the invention will 
appear more fully in the following description. 
P type materials may be used instead of N type, which is dealt with in the 
following description. 
Ion inplantation technique and epitaxial crystal growth technique may be 
used instead of an impurity diffusion technique for producing said very 
low resistive layer, which is buried by the epitaxial layer.

DETAILED DESCRIPTION 
Referring to the attached drawings, in FIG. 1, there is shown the solid 
state detector telescope composed of dE and E detectors produced 
individually for explaining the background of the present invention and in 
FIG. 2 to FIG. 5, there are shown the first embodiment of the present 
invention. 
In the FIG. 1, 1 and 2 are dE and E detectors placed in parallel on the 
same axis consisting the solid state detector telescope heretofore used. 
E.sub.i is the energy of incident particles and .DELTA.E and E are energy 
losses of particles in dE and E detectors respectively. If incident 
particles stop in the E detector consuming all of the energy, the energy 
of incident particles E.sub.i can be obtained by the following relation 
EQU E.sub.i =.DELTA.E+E 
Particles are also identified from energy losses .DELTA.E and E by using 
the standard particle identification formula of the form 
EQU (E+.DELTA.E).sup.4 -E.sup.4 =T/a 
where a is a constant proper to the particles, T is the thickness of the dE 
detector and .alpha. is a constant nearly equal to 1.73 for light ions. 
In order to obtain good results in identification of particles, it is 
necessary to determine the value of the constant a from energy losses 
.DELTA.E and E. It is easily seen from the above identification formula 
that the uniformity of thickness T of the dE detector should be very good 
for determining the constant a precisely. 
In the case of identification of heavy ions, it is necessary to use a thin 
dE detector with a thickness less than 10 .mu.m, because ranges of heavy 
ions are shorter than those of light ions. The thin dE silicon detector 
has been produced from epitaxial silicon wafer by etching off the highly 
doped substrate using a chemical preferential etching method or an 
electrochemical etching method. For obtaining a thin dE detector with a 
good thickness uniformity, a highly technical process by etching the 
substrate is required. Nevertheless, an additional irregularity of the 
thickness caused by etching is inevitable. 
FIG. 2(a) shows the first embodiment of the present invention in which 1 is 
the dE detector and 2 is the E detector of the integrated solid state 
detector telescope. A.sub.1 and A.sub.2 are the electrodes of dE and E 
detectors. N is a high purity N type silicon substrate. B is a heavily 
doped N.sup.+ type silicon layer which is produced by diffusion of impure 
Antimony into the above mentioned N type silicon substrate and has a very 
low resistivity. A slightly doped N type silicon layer is produced on the 
above mentioned very low resistive N.sup.+ type silicon layer by using 
the epitaxial crystal growth technique. Electrodes A.sub.1 and A.sub.2 are 
produced by evaporation of gold in a vacuum on both sides of the silicon 
wafer forming surface barrier rectifying contacts. The very low resistive 
silicon layer B acts as an electrical shield between dE and E detectors 
and is connected to the ground in usual applications. .DELTA.E and E are 
the signal outputs appearing on electrodes A.sub.1 and A.sub.2 of dE and E 
detectors corresponding to the energy losses of the incident charged 
particles in each detector. 
FIG. 2(b) shows the potential distribution in the epitaxial integrated E-dE 
solid state detector telescope of the present invention. .DELTA.V and V 
are voltages applied on the electrodes A.sub.1 and A.sub.2 in FIG. 2(a) 
respectively. These voltages have negative polarities and are reversely 
biasing dE and E detectors. Holes produced by incident charged particles 
are swept away into electrodes A.sub.1 and A.sub.2 from depletion layers 
of dE and E detectors by the fields of the potential shown in FIG. 2(b). 
On the other hand, electrons produced at the same time flow into the 
buried low resistive N.sup.+ type layer, which is connected to ground. 
Output signals .DELTA.E and E are derived from the flow of carriers, holes 
and electrons. 
In FIG. 3 are shown the geometry and the electrode configuration of one 
example of the present invention. The highly doped N.sup.+ type silicon 
layer has a thickness of 9 .mu.m and is very thin. The epitaxial N type 
silicon layer is polished with a slight slope as shown in the figure. The 
ohmic contact with the buried N.sup.+ type silicon layer is produced by 
evaporation of gold in vacuum on the edge of the buried layer appearing on 
the polished surface. 
The silicon wafer used here has a N-N.sup.+ -N type complex structure. The 
highly doped N.sup.+ type silicon layer is produced by diffusion of 
Antimony into a high purity N type silicon substrate. The N type silicon 
layer is produced on the N.sup.+ type silicon layer by means of epitaxial 
crystal growth. Electrodes A.sub.1 and A.sub.2 are produced by evaporation 
of gold in a vacuum on both sides of the silicon wafer, forming surface 
barrier rectifying contacts. 
FIG. 4 shows the profile of the spreading resistance of the epitaxial 
silicon wafer having N-N.sup.+ -N type complex structure one example of 
the present invention. The thicknesses of N.sup.+ and N type silicon 
layers are 9 .mu.m and 10 .mu.m respectively. In this example of the 
present invention, resistivities of N.sup.+ and N type silicon layers are 
estimated to be 0.015 .OMEGA.-cm and 40 .OMEGA.-cm respectively from FIG. 
4. The high purity N type silicon substrate is also estimated to have a 
resistivity of about 8k.OMEGA.-cm. 
FIG. 5 shows spectra of energy losses in dE and E detectors for .alpha. 
particles from .sup.241 Am. Energy resolutions of dE and E detectors are 
118 keV and 130 keV respectively. In this measurement, bias voltages of dE 
and E detectors are 15 V and 180 V respectively. This figure also shows 
(E+.DELTA.E) spectrum obtained by analog-summation of .DELTA.E and E 
signals. The energy loss of this (E+.DELTA.E) spectrum is 5.3 MeV and the 
energy resolution is 60 keV FWHM. The energy of particles from .sup.241 Am 
is 5.45 MeV, therefore the energy loss in the dead layer caused by the 
buried N.sup.+ type silicon layer is supposed to be 0.25 MeV. The 
thickness of the dead layer estimated from this value is less than 1 .mu.m 
and is much smaller than that of the buried N.sup.+ type silicon layer. 
This is due to the fact that most of the free carriers produced in the 
buried layer are swept away into dE and E depletion layers by diffusion of 
carrier in cooperation with the effect of built-in fields in the buried 
layer. 
The built-in potential difference V of two points in a semiconductor, where 
impurity concentrations are N.sub.max and N.sub.min, is expressed as 
follows 
EQU V=-(kT/q).multidot.ln(N.sub.min /N.sub.max) 
From this equation, the built-in potential differences in the buried layer 
are estimated to be 0.21 V and 0.32 V in the sides of dE and E detectors 
and the corresponding electric fields are about 700 V/cm and 530 V/cm 
respectively. As seen from the result, the built-in fields are so high 
that the dead layer is confined to a narrow portion of the buried layer 
where the impurity concentration has a flat top. 
As described in detail, the epitaxial integrated E-dE solid state detector 
telescope of the present invention has many advantages compared with the 
heretofore used one which is composed of dE and E detector produced 
individually. 
The first advantage is that fabrication of this epitaxial integrated E-dE 
solid state detector telescope is simple and easy, because this eliminates 
the highly technical process of etching the substrate, which is necessary 
for fabrication of the conventional epitaxial silicon detector. 
The second advantage is that the thickness uniformity of the dE detector 
does not suffer a degradation caused by etching and is very good. The 
third advantage is that the dead layer accompanied with the buried low 
resistive N.sup.+ type silicon layer, which is isolating the dE detector 
from the E detector electrically, is very thin because of the drift effect 
of carriers due to built-in fields. 
The fourth advantage is that the epitaxial integrated solid state detector 
telescope minimizes the separation of dE and E detectors. This is 
effective for reducing the counting loss of the E detector caused by a 
scattering of incident particles in the dE detector. 
The low resistive N.sup.+ type silicon layer shown in FIG. 3 and FIG. 4 
are produced by using the impurity diffusion technique. Fabrication of the 
low resistive N.sup.+ type silicon layer is also possible by using an 
epitaxial crystal growth technique and an ion implantation technique. 
The epitaxial integrated E-dE solid state detector telescope of the present 
invention may also be produced using a silicon wafer with a P-P.sup.+ -P 
type complex structure. This type of the epitaxial integrated E-dE solid 
state detector telescope is the second embodiment of the present 
invention. 
Electrodes A.sub.1 and A.sub.2 of FIG. 2 and FIG. 3, having rectifying 
characteristics, are surface barrier junctions produced by evaporation of 
gold in a vacuum on semiconductor surface Of course, other materials, 
having rectifying characteristics, are possible for producing the surface 
barrier junction. The semiconductor P-N junction instead of a surface 
barrier junction is also applicable as a rectifying junction. The 
epitaxial integrated E-dE solid state detector telescope having p-n 
junction type rectifying electrodes is the third embodiment of the present 
invention. 
The epitaxial integrated E-dE solid state detector telescope of the present 
invention is also produced by using the other semiconductor material such 
as germanium and gallium arsenide.