JPH03102835A - Semiconductor device and photoelectric converter using same - Google Patents

Abstract

PURPOSE:To improve a current amplification factor by providing at least a film formed on an emitter made of a material having wider forbidden band width than that of a material for forming the emitter and an electrode formed of polycrystalline semiconductor on the film. CONSTITUTION:P, etc., is ion implanted on an n-type substrate 1 to form an n<+> type buried region 2 having 1X10<15>-10<19>cm<-3> of impurity concentration, an n<+> type region 3 having 1X10<14>-10<19>cm<-3> of impurity concentration, and an n<+> type region 7 (1X10<17>-10<20>cm<-3> of impurity concentration). Then, an element isolating region 102 is formed in an active region, and a p<+> type region 5 and a p-type region 4 of a base region are formed. Thereafter, after an emitter contact is opened in an insulating film 101, P, etc.,-doped n<+> type region (5X10<17>-5X10<20>cm<-3> of impurity concentration) 6 is formed. Then, a thin tunnel insulating layer 30 is formed, polycrystalline Si is deposited, an n<+> type layer is formed by a thermal diffusing method, etc., and then patterned. Then, an insulting film 103 is deposited, a contact is opened, an AL-Si (1%) to become an electrode 200 is sputtered, then the AL-Si is patterned, an AL-Si electrode is eventually alloyed, and a passivation film is then formed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a semiconductor device and a photoelectric conversion device.

[Prior Art] As a conventional semiconductor device, for example, a piebora transistor (BP) having an MIS (metal-insulator-semiconductor) structure
T) was known.

FIG. 9 is a schematic cross-sectional view showing an example of a BPT with a conventional MIS structure.

Each component of the MIS structure BPT shown in FIG. 9 will be explained below.

1 is phosphorus (P), arsenic (As), antimony (s b
), or substrates doped with impurities such as boron (B), aluminum (Afl), gallium (G
This is a silicon substrate doped with impurities such as a) to make it p-type.

2 is an impurity concentration of 10'' to 10''cm-3
This is the n area as the embedding area.

3 has a low impurity concentration (1013~5 x 10 l7 cm
-3), which is the n region as part of the collector region.

4 is an impurity concentration of 10'5 to 10''cm-3
This is a p-type region as a base region.

5 is an impurity concentration of 1017 to 10"cm-3
This is the P+ region for lowering the base resistance.

Reference numeral 7 denotes an n region connecting the collector electrode and the buried layer 2 to reduce collector resistance.

30 is a thin insulating film for tunnel injection.

101, 102, and 103 are insulating films for separating electrodes, elements, and wirings.

200 is a wiring electrode formed of metal, silicide, or the like.

[Problems to be Solved by the Invention] However, the conventional MIS structure BPT has a collector current in the micro current region. There was a problem in that the ratio of the base current (1) to the base current (1)8 increased, and as a result, the electric amplification factor bri (=Ic/Ia) decreased. Furthermore, if the base current ratio increases significantly, more base current will flow than the collector current, and the current amplification factor will increase to 1.
In some cases, it was as follows.

In addition, even if the base current ratio does not increase that much, the base current flows together with the recombination current, so the current amplification factor changes depending on the collector current, and the stability of the current amplification factor is affected. There was also the issue of not ensuring that

Furthermore, the conventional MIS-structured BPT has a problem in that metals and insulators tend to react, resulting in poor reliability. In particular, when used for a long period of time, the base current tends to increase, which tends to cause deterioration of the current amplification factor.

[Means for Solving the Problems] A semiconductor device of the present invention includes a collector of a first conductivity type;
a base of a conductivity type; an emitter of a first conductivity type; a film formed on the emitter made of a material having a wider band gap than the material forming the emitter; a film formed of a semiconductor material on the film; It is characterized in that it has at least an electrode and;

In the above feature, it is desirable that the thickness of the emitter be thinner than the diffusion length of minority carriers injected from the base.

In the above feature, it is desirable that the electrode formed of the semiconductor material be an electrode formed of a polycrystalline semiconductor.

In the above feature, it is preferable that the insulating film is formed of a material in which the tunneling probability of carriers of the first conductivity type is greater than the tunneling probability of carriers of the second conductivity type.

In the above feature, it is desirable that the thickness of the film is such that the tunnel current of the film is larger than that of the collector NQ'IL determined by the base.

In the above feature, it is desirable that the material having a wider forbidden band width than the material forming the emitter is an insulator or a semiconductor.

A photoelectric conversion device of the present invention is characterized in that the semiconductor device of the present invention described above is used at least as a photoelectric conversion element.

[Function] According to the semiconductor device of the present invention, since the emitter region is provided under the insulating film for tunnel injection, a stable emitter-base junction can be provided in the semiconductor. Therefore, the current amplification factor does not decrease even in the micro current region, and the current amplification factor does not depend on the collector current.

Further, according to the present invention, since a semiconductor is used as the electrode, the reaction between the electrode and the insulating film can be suppressed, and therefore,
It becomes possible to dramatically improve reliability.

[Example] Hereinafter, examples of the present invention will be described, and the present invention will be explained in further detail.

(Example 1) An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a semiconductor device (MIS) according to an embodiment of the invention.
FIG. 2 is a schematic cross-sectional view showing the structure BPT.

In the figure, the same reference numerals as in FIG. 9 indicate the same components as in FIG. 9, respectively.

In addition, 6 has an impurity concentration of 10" to 10" cm
-' is an n+ region as an emitter region, and 8 is a polycrystalline silicon n0 electrode for stabilizing the insulating film 30.

In addition, FIG. 2 shows the A-A' of the semiconductor device shown in FIG.
This is an electric potential diagram in a cross section. The MIS structure BPT shown in FIG. 1 will be explained below.

In the MIS structure BPT shown in FIG. 1, electrons must pass through the insulating film due to the tunnel effect, but holes must be blocked.

Here, Tononel's probability is approximately expressed by the following equation.

7toc exp(-A-m””φ83/2)
-(1) where A is a constant, m8 is the effective mass of the carrier, and φ6 is the height of the barrier. In the case of the present invention, since the thickness of the insulating film and the electric field applied thereto are constant for electrons and holes, the probability of tunneling can be considered using equation (1).

In this example, Si was used as the semiconductor and Si02 was used as the insulating film. These φ and m1 are
As shown in Table 1.

Table 1 As can be seen from Table 1, both φ8 and m' are larger for holes, and therefore, it can be seen that holes have a smaller tunneling probability. However, this is the conventional MIS structure BP
The same is true for T, so the electron/hole injection difference is the same in principle.

The tunneling probability shown in equation (1) above is expressed by the thickness of the insulating film as follows: 7tcc exp (B (m”, φa)・t+)
-(1)'. However, B is the effective quality ffim"
The constant 1, which is determined by the barrier height φ, is the thickness of the insulating film.

Normally, in the case of an oxide film, when the film thickness is less than 50%, the tunnel current increases significantly. When φ8 becomes smaller, t1
can be used as a tunnel insulating film even in thick regions. Furthermore, as φ becomes smaller, the critical film thickness at which the tunnel current of the insulating film becomes dominant becomes larger.

In the present invention, the upper limit of the thickness of this insulating film is determined by the collector current of the BPT. That is, the collector current of the BPT, which is determined by the concentration and thickness of the base current, should not be determined by the thickness of the insulating film. B
If the thickness of the insulating film determines the rate of the PT collector current, the collector current will be determined by the thickness of the insulating film in the emitter, and the thickness of the insulating film must be controlled with high precision during the manufacturing process. This is because it will no longer be the case.

For example, if an oxide film is used as the insulating film, the
It is extremely difficult to accurately control the vicinity of people. As mentioned above, the lower the barrier height φB, the thicker the critical film thickness becomes, which is advantageous.

In the present invention, the emitter thickness W shown in FIG.
, and its concentration and the recombination speed So of minority carriers (holes) in the insulator and semiconductor are issues.

First, the constituent components of the BPT current will be described.

The collector current is approximately JC- (q-on-n+')/(Nil-Wl!)
{exp (vaz/kT) −t} (2) However, the electron diffusion distance is assumed to be longer than the base width. Note that N, is the base concentration, WB is the base width, and Dr1
is the diffusion distance of electrons, nl is the intrinsic carrier density of Si, V
S! is the base-emitter applied voltage.

In the present invention, it is desirable to design the collector current expressed by the above equation (2) to be larger than the tunnel current.

In addition, the base current is the recombination current of electrons injected from the emitter 'Jarac'(Q'On'n+2・Wl1)/(
2N1Ln')x (exp(Vat/kT)-1)
+++ (3) (However, L, 1 is the electron diffusion distance!!) and the hole current JBdlf injected from the base to the emitter, but JBdlff is the main component, and in normal BPT, It can be said that the base current is determined by this J Ildlff. In a BPT with an MIS structure like the present invention, JBdlff is J8dl tt"q (DIl/LP) [{SO-
(DIl/LP) tanh (tve/L.) }/
((Dp/Lp)-So・tanh (We/Lp)
)] (nt'/Nc) x exp ((VIIE-k
T) -1) -(4). However, N
, is the emitter concentration in the emitter, DP is the hole diffusion constant, LP is the hole diffusion distance, and So is the recombination rate at the Si02/Si interface.

Here, equation (4) is expressed as: the emitter thickness W, and the hole diffusion distance l! ! Using LP and recombination rate S, it can be expressed as follows.

■Case 1 If the hole diffusion distance is long and LP>WE, JBdI
ft is the same whether there is an insulating film or not, and can be expressed as follows.

JaaIer+-” (q-op/t.p) (n,
z /NE) (eXp(Vac/kT) -1)...
・(5) ■Case 2 When w,<Lp, the insulating film is affected and Jadr tt2- (Q'op/t.p) [
{(Dp 'we./ し.') -so}/ ((D
j/Lp) − (WE-So8,)}]X (n+”
/Nc) (exp(Vac/kT)-1) ++ (
6) ■Case 3 If W E < L p and S-O, Jadr
tt3・+(QJp'Wt/Lp2)ir++2/Nc
)x (exp(Vai/k cho)-1}
- (7)■Case 4 If Wε<Lp and S-■, JBdItt3- ”(QJp/Wc)In+2/Nz
)x (exp (Vac/kT) −1) −
(8) becomes.

Case 1 is a conventional general BPT that does not have an MIS structure.
This is the case. Case 4 is a case of BPT with high density and shallow emitter, MIS structure.

Case 3 is the case of the MIS structure BPT of the present invention. In fact, in this embodiment, a state close to Case 3 is realized. To realize Case 3, we set WE《LP, and furthermore, from equation (6), (DP/W!) (wz”/t.p') > s o
...It is necessary to satisfy the condition (9). When this condition is satisfied, JBd1ft becomes WE/LP times the BPT of case 1. In addition, for BPT in case 4, JBdlff is (WE /LP
) will be doubled. In this way, in this example, J lld
lff can be dramatically reduced. Therefore, the current amplification factor hrc can be dramatically increased.

In the conventional MIS structure BPT, Wl:=O and J! ldlff is not present, but another current component is present. In other words, since the insulating film is originally amorphous, it is not a perfect insulating film, and has a recombination level in the forbidden band. Therefore, in the emitter (metallic electrode) of the conventional MIS structure BPT, holes are Since they are majority carriers, the amount of injection is larger than in the case of the present invention, and the recombination current in the insulating film increases.On the other hand, the MIS structure BP of the present invention
At T, the holes injected into the emitter are minority carriers of the emitter and are expressed as n+2/Na H eXp (VaE/kT). These holes are much smaller than the base majority carrier N3 and do not pose a problem in a normal operating region. Further, in a large current region where recombination in the insulating film is small, the current is close to NB, but in this region, even in a conventional MIS structure BPT, the base current is smaller than the collector current and does not pose a problem.

FIG. 3 is a graph schematically showing the current/voltage characteristics of a transistor, where the horizontal axis represents the applied voltage between the base and emitter, and the vertical axis represents the base current I and the collector current ■. shows. In the M■S structure BPT of the present invention, the collector current and the base current are almost parallel, and hrE (given I c / I
a) is a constant value, but in the conventional MIS structure BPT, excess current flows in the micro current region. In the MIS structure BPT of the present invention, L P > W e and DP /we > S
o, the base current mainly becomes the recombination current shown by equation (3), and the current amplification factor hFE at that time is hrt-a- = 2 (Ln/Wa)'
- (10), and the upper limit of hPE is determined only by the base conditions.

FIG. 4 is a graph showing the relationship between impurity concentration, hole diffusion distance, and hole lifetime in the n0 region. The emitter depth is preferably at least about 1/5 of the hole diffusion distance. Further, although it depends on the method of forming the insulating film, S0 can definitely be made to satisfy the equation (9) by directly oxidizing Si. In addition,
The formation method at this time may be any method as long as it directly oxidizes Si.

In the present invention, in order to realize hFE determined by the above equation (10), as described above, the tunnel current is made larger than the collector current shown by the above equation (2), which is determined by the base condition. It is necessary to determine the thickness of the tunnel membrane. Further, variations in the thickness of the tunnel film are directly reflected in variations in the characteristics of the BPT. Since the base concentration and base width are much easier to control than the tunnel film thickness, the collector current can be stabilized. In addition, the base current is also determined by the emitter concentration, emitter depth, and base conditions, so the current amplification factor h
It is possible to obtain a BPT with a large rt and a small variation in the current amplification factor hrε.

Next, a manufacturing process for the semiconductor device shown in FIG. 1 will be described.

■By ion-implanting As, Sb, P, etc. into the p-type or n-type substrate 1 (impurity diffusion etc. may also be used), an n+ buried region 2 with an impurity concentration of 1×10'5 to 10 l9c is formed. did.

・■Impurity concentration t
An n-region 3 of 10'' to 10'' cm was formed.

(2) An n" region 7 (impurity concentration IXIO" to 10"cl3) was formed to reduce collector resistance.

(2) Element isolation regions 102 were created by selective oxidation, CVD, or the like.

(2) A p region 5 and a p region 4 as a base region were formed in the active region by ion implantation or the like.

■After opening an emitter contact in the insulating film 101,
n0 region doped with s, Sb, P, etc. (impurity concentration 5X
10'' to 5 x 10 20 am-3) 6 was formed by ion implantation or thermal diffusion.

(2) A thin tunnel insulating layer 30 was formed by oxidation at a low temperature of 500° C. to 650° C. or thermal oxidation using rapid thermal acceleration (RTA).

(2) Polycrystalline St was deposited by the LPCVD method, formed into an n0 layer by ion implantation or thermal diffusion, and then buttered.

(2) After depositing an insulating film 103 and annealing it, a contact opening was made.

[Phase] AL-Si (1%), which will become the electrode 200, was sputtered, and then AL-St was patterned.

■After alloying the ALSi electrode, we attached a patch base film and completed the MIS structure BPT.

As the tunnel insulating film in the present invention, a silicon oxide film is the simplest because it can be easily formed at a low temperature, but an insulating film such as a silicon nitride film or an alumina film may also be used.

Alternatively, an ultra-thin film such as SiC may be used to form a tunnel barrier structure. For example, compared to Si, SiC has a conduction band energy difference △EvJ: 90.53 eV, a valence electron f difference △Ec 40.55 eV, and a band gap E g
'F 2 - 2 e V, and SiC and Si
When both are n-type and are joined stepwise, the structure is different from that of a semiconductor/insulator junction.

FIG. 5 shows a band diagram of a junction between metal and n-type SiC.

A semiconductor junction of the same conductivity type by a semiconductor step heterojunction is as shown in FIG. 5, and ΔEv. ΔEC appears above and below, and a barrier called a notch is formed on the conductor side. on the other hand,
On the valence band side, a difference of ΔEc+ΔEv−ΔEf occurs.

Furthermore, when n-type Si, n-type SiC, and n-type Si are bonded together, a structure as shown in Figure 5(b) is obtained.Furthermore, when SiC is thinned, the SiC layer becomes depleted, as shown in Figure 5(C). It becomes similar to an insulator. Although the effect of the present invention can be obtained even with the structure shown in FIG. 5(b),
The structure shown in Figure (C) allows for a larger electron current. On the other hand, holes can be sufficiently blocked on the valence band side. In addition, in Fig. 5, S
Although an example using iC has been shown, it is clear that other wide bandgap materials may be used.

When the density of an IC sensor is increased, the two-dimensional current around the emitter becomes a problem because the planar dimensions become smaller. FIG. 6 shows a schematic cross-sectional view of the emitter periphery. In the case of the BPT of the present invention, as mentioned earlier, the diffusion current of holes into the emitter can be suppressed to an almost negligible level, so the base current is the recombination current of the current injected from the emitter. It becomes the main component. The longitudinal principal component of the base current is the same as equation (3), and the lateral force direction current is Jl! lraCX- (qJn/Ln) (n+2/
Na) {eXp(VILE/kT) -1)...(
11) It becomes. Furthermore, let the emitter area be Aε and the peripheral length!
．． If the emitter depth is W, hFE is approximately? rt = Ic/Ia # (AE-JC)/(AC・J, ■A+Lt41Ja
−. . 8)ξ{A!・(t/wa) 1 /fAE・(1/2) (Wa/Ln”)+L(・”i
(1/Ln))=hrz--x [{l/ (1+(
2LE・W1L,)/(AE・wa))]...(Eng.2
) becomes. Therefore, originally (2L,・WE−Ln)/AE・Wl1) < 1
...- (13) must be satisfied.

In the above equation (13), what can be considered in device design is W
, so Wt< 1/2 (AE/LE) (WB/Ln)
...It must be (14). Here, A,=1 μm, ? ．． = 1 μm, w,/Ln
= Q. 0 1, then from equation (14), WE (0
．． 005 μm. When miniaturizing the BPT of the present invention, W6 must be determined so as to satisfy equation (14).

Further, according to this example, the dark current was improved and the S/N ratio was significantly improved.

Although this embodiment has been described using polycrystalline Si as the electrode material, similar effects can be obtained using other semiconductor materials.

(Example 2) FIG. 7 is a schematic cross-sectional view showing a semiconductor device according to a second example of the present invention. In this embodiment, the emitter region 6
is formed on the base by epitaxial growth, and an insulating film for tunnel injection is formed thereon. With such a structure, in the above equation (14), W,=O
Therefore, the original h. ■It is possible to obtain a value close to 8.

(Example 3) FIG. 8 is a circuit diagram showing one example of a photoelectric conversion device according to the present invention, and is a solid-state imaging device disclosed in patent application (2) on December 21, 1988 by the present applicant. This figure shows a case where the BPT shown in Example 1 above is used in the apparatus. In FIG. 8, the BPT shown in Example 1 was used for the part shown by Tr. That is, in this example, an SIS type BPT was used as a photoelectric conversion element.

When the ERI7 sensor shown in FIG. 8 is used as a color camera, the optical information of the same photoelectric conversion element is read out multiple times. At this time, since the same element is read out multiple times, the ratio of the electrical output during the first readout and the second and subsequent readouts becomes a problem. If this value becomes small, correction is required.

If the ratio of the above-mentioned first and second readout outputs is defined as the non-destructive degree, the non-destructive degree is expressed by the following equation.

Non-destructiveness = (1:tot Xhrz)/(C:tot
Xt+ri: +CV) Here, Cta is T in Figure 8.
The total capacitance connected to the base of the photoelectric conversion element indicated by r is determined by the base-collector capacitance Cbe and 008. Further, Cv is the stray capacitance of the readout line represented by VL, . . . vLl. However, COX
may not exist depending on the circuit system. The degree of non-destruction can be easily improved by increasing the current amplification factor hFE. That is, by increasing hrt, the degree of non-destruction can be increased.

Here, for HD compatible area sensors, Ctot =
Since 10fF, Cv = 2.5pF, for example, in order to make the non-destructive degree 0.90 or more, hrt should be 2250
More than that is required. In order to obtain sufficient non-destructiveness, h,
8 seems to require 2000 or more.

On the other hand, conventionally, for example, in homozygous BPT, h
Since the FE was about 1000, it was not possible to obtain a sufficient degree of non-destruction. On the other hand, in the semiconductor device of the present invention, since h2E can be made sufficiently large, excellent nondestructiveness can be obtained.

Furthermore, the degree of non-destruction is preferably 0.98 or more. In that case, about 10,000 hFEs are required.

This value cannot be reached with conventional homojunction BPTs and is easily achieved with the transistors of the present invention.

Although the present embodiment shows the case of an area sensor, it is obvious that the present invention can also be applied to a line sensor.

[Effects of the Invention] As described above in detail, according to the semiconductor device of the present invention, it is possible to suppress an increase in the base current in the small current region of the collector current, and it is possible to suppress the increase in the base current over a wide region of the collector current. The current amplification factor can be maintained and the dependence of the current amplification factor on the collector current can be eliminated.

Further, the stability of the insulating film can be improved, and reliability can be significantly improved.

Further, according to the photoelectric conversion device of the present invention, the current amplification factor can be improved and the dependence of the current amplification factor on the collector current can be eliminated, so the linearity of the output with respect to the optical input can be maintained. It is possible to obtain a low dark current and a high signal/noise ratio (S/N ratio).

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a semiconductor device according to an embodiment of the present invention, FIG. 2 is a band diagram in the AA' cross section of the MIS structure BPT of this embodiment shown in FIG. 1, and FIG. is a graph schematically showing the current/voltage characteristics of a transistor, Fig. 4 is a graph showing the relationship between impurity concentration, hole diffusion distance, and hole life in the n0 region, and Fig. 5 (a) is a graph showing the relationship between the impurity concentration in the n0 region, the hole diffusion distance, and the hole lifetime. Figure 5(b) is a band diagram showing the junction between n-type Si and n-type SiC, and Figure 5(C) is a band diagram showing the junction between n-type Si, n-type SiC, and n-type Si. A band diagram showing a junction between n-type SiC and n-type Si, FIG. 6 is a schematic cross-sectional view of the emitter periphery of the semiconductor device shown in FIG. 1, and FIG. 7 shows a second embodiment of the present invention. FIG. 8 is a schematic cross-sectional view showing an example of a charging conversion device according to the present invention; FIG. 9 is a schematic cross-sectional view showing an example of a conventional Mis-structured BPT. . Thin insulation for channel implantation 101, 102, 3... Insulating film, 200... Wiring electrode. (Explanation of symbols) 1... N-type silicon substrate or p-type silicon substrate, 2... n0 region as a buried region, 3... n region as part of collector region, 4... base P-type region as a region, 6... N+ region as an emitter region, 5... P+ region for lowering base resistance, 7.
...00 region for lowering collector resistance, 8...Polycrystalline silicon n' electrode for stabilizing the insulating film 30 Fig. 2 Emitter base collector Fig. 3 Large current region VBE Fig. 6 Fig. 8 figure

Claims (1)

[Claims] (1) A collector of a first conductivity type; a base of a second conductivity type; an emitter of a first conductivity type; A semiconductor device (2) characterized in that it has at least a film formed on an emitter; and an electrode formed of a semiconductor material on the film. 3. The semiconductor device according to claim 1, wherein the electrode is thinner than a diffusion length. Claim 1 or 2, wherein the electrode formed of the semiconductor material is an electrode formed of a polycrystalline semiconductor. Semiconductor device according to (4) the insulating film,
4. The semiconductor device according to claim 1, wherein the semiconductor device is formed of a material in which a tunneling probability of carriers of the first conductivity type is larger than a tunneling probability of carriers of the second conductivity type. 5. The semiconductor device according to claim 1, wherein the film has a thickness such that a tunnel current of the film is larger than a collector current determined by the base. Claims 1 to 5, wherein the material having a wide forbidden band width is an insulator.
The semiconductor device (7) according to any one of claims 1 to 5, wherein the material having a wider forbidden band width than the material forming the emitter is a semiconductor.
Semiconductor device (8) A photoelectric conversion device characterized in that the semiconductor device according to any one of claims 1 to 7 is used at least as a photoelectric conversion element.