JPH05218490A - Metal-semiconductor-metal photodetector and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide an MSM optical detector adapted for a silicon integrated circuit and suitable for application of short wavelengths. CONSTITUTION: There is provided a method of manufacturing an MSM optical detector having a silicon semiconductor surface layer, so as to form a comb-like metal electrode 10 having an about medium or high barrier height for silicon, for forming a Schottky barrier, and an electrode by using self-alignment metallization by a selective adhesion or selective reaction and etching in a method similar to a SALICIDE (self-alignment silicide) method. First, a surface of Si1 exposed to a substrate 2 is coated with a transparent oxide film, for example, silicon dioxide, silicon nitride, silicon oxynitride, etc., 12, and an interface between Si and an oxide indicates a low surface recoupling speed. Next, comb- shaped patterns are etched through an oxide film by lithography, and the Si surface is exposed in a shape of finger patterns. Next, an electrode of a metal or metal silicide is formed on the Si surface which is exposed by using self- alignment metallization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of semiconductor devices, and more particularly to an improved metal-semiconductor-metal (MSM) photodetector structure compatible with silicon VLSI and a method of manufacturing the same. is there.

[0002]

BACKGROUND OF THE INVENTION Metal-Semiconductor-Metal (MSM) photodetectors are a type of photodetector in which light is usually coupled into a semiconductor system and carriers generated by the light are deposited on the photoactive surface area of the semiconductor. A device that is trapped by an electric field between a set of comb Schottky contacts.

Specifically, MSM photodetectors consist of interdigitated (comb-shaped) metal-semiconductor-metal electrodes disposed on a photoactive semiconductor material on the surface of the device.
The operating principle is as follows. When a bias voltage is applied between the electrodes, radiation (ie, photons) from an infrared, visible, or ultraviolet source strikes the photoactive surface region of the semiconductor, causing a current flow between adjacent electrodes.
The electric current consists of electron-hole pairs generated when photons are absorbed by the semiconductor. The charge carriers generated by these lights are driven and collected by the electric field formed by the voltage between the electrodes. The Schottky barrier at the junction or interface between each electrode and the photoactive semiconductor surface
The current flow is limited to only the current flow produced by photons absorbed in the semiconductor. The most commonly used photoactive materials in MSM photodetectors are GaAs and GaInA.
s.

MSM device attributes include high sensitivity, high speed operation, and relative ease of manufacture. MSM photodetectors are made of silicon and various semiconductor materials including so-called Group III and V compound semiconductors and their alloys. The group III and V compound semiconductor materials are elements of groups III and V of the periodic table, for example, Ga, Al, In of group III, As and P of group V,
It is called in this way because it contains Sb and the like as its main component.
The most widely used group III and V for MSM photodetectors
Group compound semiconductor materials are GaAs and GaInAs.

A much more common type of semiconductor material is the infrared region of the electromagnetic spectrum, specifically 80
Designed to operate at wavelengths above 0 nm, II
It is a device made of a compound semiconductor material of group I and group V. Various examples of devices using such gallium and arsenic (Ga-As) are described in the following documents. M. Ito et al., "High-Speed Monolithically Integ
rated GaAs Photoreceiverusing a Metal-Semiconducto
r-Metal Photodiode ", Appl. Phys. Lett., Vol.47, No.1
1, pp.1129 ~ 1131,1985. D. L. Rogers
s), "Monolithic Integration of a 3-GHzDetector / Pr.
eamplifier Using a Refractory-Gate, Ion-Implanted
MESFETProcess ", IEEE Electron Device Lett., Vol.EDL
-7, No. 11, pp. 600-603, 1986. T. Sugeta et al., "Metal-
Semiconductor-Metal Photodetector for High-SpeedOp
toelectronic Circuits, Japan J. Appl. Phys., Vol.1
9, suppl.19-1, pp.459〜464,1980. O. Wada et al., "Very
High Speed GaInAs Metal-Semiconductor-Metal Photo
diodeIncorporating an AlInAs / GaInAs Graded Superla
ttice, Appl. Phys. Lett., Vol.54, No.1, pp.16-17,198
9 years. D. L. Rogers et al., "High Speed 1.3-micron
GaInAs Detectors Fabricated on GaAs Substrates ", IE
EE Electron Device Lett., Vol.9, No.10, pp.515〜517,1
988 years. C. S. Harder et al., "5.2-GHz Band
width Monolithic GaAs Opto-electronic Receiver ", I
EEE Electron Device Lett., Vol.9, No.4, pp.171〜173,1
988 years. W. Roth et al., "A Fast Large-Area Opto
electronic Detector ", IEEETrans. Electron Devices,
Vol.Ed-32, No.6, pp.1034-1036, 1985. M. Ito et al., "Low Dark Current GaAs Metal-Semiconductor-Met
al (MSM) Photodiodes Using WSix Contacts ", IEEE J.
Quantum Electronic, Vol.QE-22, No.7, p.1073-1077,198
6 years. L. Figueroa, W. Suleiman (S
layman), "A Novel Heterostructure Interdigital Pho
todetector (HIP) with Picosecond OpticalRespons
e ", IEEE Electron Device Lett., Vol.EDL-2, No.8, pp.2
08-210, 1981.

On the other hand, short wavelength (less than 850 nm) photodetectors are important because they can be widely used in computer environments. For example, in optical storage systems, short wavelengths are preferred because they can increase the recording density on the optical disc. Another possible application for short wavelength detectors is in fiber optic interconnections to replace expensive and bulky cables used in input / output devices such as printers, monitors and displays. In this application, the path lengths in the computer system are short, and thus long wavelength detectors are not absolutely necessary.

All of the above MSM photodetectors have been implemented in the form of discrete or integrated structures, but these have major drawbacks in incorporating them into the silicon-based technology currently practiced in the computer industry. There is. Disadvantages are the high cost due to the complicated process and the use of materials and processes that are not compatible with existing silicon VLSI manufacturing methods.

One of the particular drawbacks of GaAs MSM photodetectors is that they are difficult to incorporate in silicon integrated circuits. In comparison, silicon-based photodetector technology is more important because it can more fully meet the requirements for application in the above computer environment and can be incorporated into sufficiently mature CMOS or bipolar technology. There are advantages. This technique minimizes the cost increase of the photodetector, eliminating parasitic delays and costly assembly. Such an MSM photodetector has the advantages of easy integration, low capacitance and good responsiveness. For example, the M. Ito et al. (Appl. Phys. Lett., Vol.47, No.11, pp.1129〜1131,198
5 years).

The ultraviolet region of the spectrum, specifically 400
Silicon MSM photodetectors operating at wavelengths shorter than nm
Reported and described in the technical literature. For MSM photodetectors fabricated on bulk Si to avoid problems in short wavelength applications, see, for example, a recent paper, BW
Mullins et al., "A Simple High-Speed SiScho
ttky Photodiode ", IEEE Photonics Technol. Letts., V
ol.3, No.4, pp.360-362, 1991. For older silicon-based MSM technologies, see RJ Seymour, BK Garside, "Ultrafa
st SiliconInterdigital Photodiodes for Ultraviolet
Applications ", Can.J.Phys., Vol.63, pp.707 ~ 711,198
Listed in 5 years. In the former paper, the Schottky barrier is formed by Ni comb metal fingers on bulk Si, whereas in the latter paper, the metal is Au on n-type silicon-on-sapphire. The materials and processes used to make these devices are not compatible with the purpose of incorporating them into existing silicon VLSI technology.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an MSM photodetector that is suitable for silicon integrated circuits and suitable for short wavelength applications.

Another object of the present invention is to provide an MSM photodetector with improved photosensitivity and response speed.

Another object of the present invention is that long-wavelength light generates carriers deep inside the semiconductor that are not affected by the electric field of the comb-shaped surface electrode, so that the carriers are slow to be collected and the detector is It is to solve the problem of slowing the response to light.

Another object of the present invention is to provide a suitable silicon dioxide coating that protects and passivates the surface area of the photodetector between the comb electrodes to broaden the spectral sensitivity of the photoactive semiconductor surface area of the device. It is in.

[0014]

SUMMARY OF THE INVENTION The present invention forms a Schottky barrier in such a way that it has improved compatibility with silicon integrated circuits, is suitable for short wavelength applications, and can be used for other wavelengths. Using a metal or silicide for
It is directed to providing an MSM photodetector. In particular, the methods and products of the present invention include a semiconductor surface layer of silicon and a metal or silicide comb metal electrode having a moderate to high barrier to silicon so that a bias voltage can be applied between the electrodes. Schottky with
A metal-semiconductor-metal (MSM) photodetector having a barrier diode. These electrodes can be made using self-aligned metallization in a manner similar to the SALICIDE concept, by selective deposition or selective reaction and etching. SALIC
The IDE (self-aligned silicide) method is
It is based on the fact that the deposited metal coating adheres only to the exposed areas of the silicon surface that ultimately contact the silicon. Examples of such metals include thin films of tungsten (W) and titanium (Ti), which adhere only to silicon and not to protected or masked areas of the silicon surface. SALICIDE concept and titanium silicide (TiSi ₂ ) in silicon VLSI structure
For the implementation of the first Int by the 1st International VLSI Science and Technology Symposium (Proceedin-gsof the First Int
ernational Symposium on Very Large Scale Integrati
onScience and Technology), Vol.82-7, two papers published in 1982. The first paper, CM Osburn and others, "HighConductivityD
iffusions and Gate Regions Using Self-Aligned Sili
Cide Technology "discusses self-aligned silicide structures using conventional NMOS technology. Second paper, C.
Y. Ting et al., "The Use of Tisi2 in aSelf-Ali
gned Silicide Technology "discusses the formation and material properties of TiSi _2.

In a preferred method, at the beginning of the manufacturing process according to the invention, the exposed Si surface of the substrate is coated with a transparent oxide film so that the Si-oxide interface has a low surface recombination rate and a low interface state. The density is indicated so that the sensitivity of the resulting photodetector is increased and the operating speed is increased. The comb pattern is etched through the oxide film by a suitable lithographic technique to expose the Si surface in the pattern. Next, self-aligned metallization is used to form metal or metal silicide members on the exposed Si surface, spaced for optimal interdigital carrier transit time and photosensitivity, and well Form a comb silicide electrode with a rounded cross section.

Alternatively, as in the preferred fabrication technique, instead of utilizing metal deposition and reaction with the silicon surface to form the metal silicide, the metal silicide is sourced from the metal silicide source onto the Si surface. It can also be deposited directly and the resulting silicide film lithographically contoured to form the desired silicide electrode pattern.

In each case, the oxide is preferably a high quality transparent silicon dioxide film that protects and passivates the photoactive surface areas of the photodetector between the comb electrodes.
The interdigital capacitance is increased by the oxide, but tends to be reduced by using thin metal electrodes recessed from the silicon surface, which itself is a relatively thin layer, and this process and overall structure is Suitable for circuit technology.

Another feature of the invention is to adjust the thickness of the transparent oxide coating to function as an antireflective coating at the desired operating wavelength. For best performance, the film thickness should be an appropriate multiple of the operating wavelength λ. The film thickness T is given by T = (n + 0.25) λ / R. In the above formula, n is 0 or an integer, and R is the refractive index of the film.

Further, by adding Ge to form a SiGe layer, that is, a Si _1-x Ge _x (0 <x <1) layer, the spectral sensitivity of silicon in the photosensitive surface region can be broadened. For example, in one embodiment of the invention,
A layer of such an alloy of Si and Ge having a thickness of about 1 to 3 μm is epitaxially grown on the surface of the substrate, a thin layer of single crystal Si having a thickness of about 0.25 μm is coated thereon, and an oxide layer is coated thereon. Photosensitive Si-Ge
Form a high quality passivation layer on top of the layer. Photosensitive Si-
The composition of the Ge surface layer can be adjusted so that the germanium content is 0% Ge to 100% Ge as described above. Since the absorptance of Ge increases at long wavelengths, the photosensitivity of the Si-Ge layer can be extended from a wavelength of 850 nm to about 1.8 μm.

The addition of Ge to Si also has the advantage of increasing the speed of the device at short wavelengths, since it also reduces the penetration depth of photons impinging on this material. When Ge is not added, carriers generated far from the electric field on the surface do not occur when Ge is added. By adjusting the composition of Si and Ge, carrier generation is limited to very close to the surface of the device with the strongest electric field. This has the desired effect of increasing the detector's response speed to light. Thus, adjusting the composition of the material and the structure of the detector surface enhances the performance and stability of the photodetector and makes it easier to adapt the silicon MSM detector to standard silicon VLSI manufacturing processes. Become.

Another feature of the present invention is that the light generates carriers deep inside the semiconductor which are not affected by the electric field of the comb-shaped surface electrode, so that the carriers are collected slowly and the response of the detector to the light is high. The solution to the problem of slowing the device is to increase the sensitivity and speed of the device, which is associated with separating the semiconductor surface layer from the substrate with a barrier layer. The barrier layer may be 1) transparent and insulative, 2) absorptive and may recombine before the photocarriers are collected by the electric field, or 3) a layer in which this layer reflects light, for example , A dielectric mirror that can efficiently trap all incident light in the photoactive region, increase the number of carriers generated, and provide a more sensitive device. Since no carriers are generated far from the active surface area, the speed of the device is unaffected by previous measurements.

[0022]

1 is a plan view of the basic elements of an MSM photodetector structure according to the present invention. This structure basically consists of an electrode pattern of comb-shaped metal members or fingers 10 formed from two cooperating sets of metals or silicides in a silicon surface 11 (FIG. 2) by a self-aligned or selective method. The electrode metal is PtSi, TiSi ₂ , WSi
_{2, silicide} such as _{PdSi 2} , or W, Ti, Pt, P
It may be a metal such as d or Hf. The electrode material can also be selected to be transparent at the intended operating wavelength, for example such an electrode can be made of indium tin oxide (IT).
O). The most important property of this metal is that it has a moderate or high barrier height for Si,
Therefore, a sufficiently high bias voltage can be applied between the electrode elements 10. The interdigital space on the surface 11 is defined by silicon dioxide (SiO), silicon nitride (S
iN), a transparent film such as silicon oxynitride to ensure a low surface recombination rate necessary for high speed operation. The electrical contact pads 21, 22 are each connected to two sets of electrodes, which allow adjacent electrode elements or members 10 to be connected.
An electric potential is applied to a series of interdigital electric fields 20 as shown in FIG.

The preferred apparatus and fabrication method generally requires self-aligned metallization in a manner that meets the following criteria: 1. The comb-shaped electrode 10 is not short-circuited, and the interdigital space is made small so that the absorption length and size are about the same at the operating wavelength and the device performance is optimized. 2. The comb oxide or nitride coating 12 is transparent for most wavelengths, ensuring a low surface recombination rate. 3. The comb oxide or nitride coating 12 adjusts its thickness to act as an antireflection coating. 4. The reaction to form the silicide results in a well rounded (not sharp) cross section of the electrode in Si without the problems associated with dielectric breakdown. 5. The comb electrode 10 is a thin metal or silicide that is recessed lower than the Si surface 11 (FIG. 2). 6. As the metal and the silicide, those having a sufficiently high electron / hole barrier height with respect to Si are used. 7. The manufacturing process and structure are compatible with conventional silicon integrated circuit technology. 8. The photoactive region of the device is limited to the surface layers of conventional single crystal silicon substrates or only epitaxial layers grown on the surface of silicon substrates. 9. The composition and thickness of the epitaxial surface layer can be adjusted so that the amount of germanium in silicon contains silicon and germanium in a composition range in which the content of germanium varies from 0% to 10%.

More specifically, the steps of a particular manufacturing process are shown in flow chart form in FIG. Details of steps (a) to (h) are as follows. First, the crystal orientation (1
00), 125 mm in diameter, N type, 5 to 10 Ω · cm of a silicon wafer (FIG. 3A), which is thermally oxidized to have a thickness of about 250 on the surface of the silicon wafer.
A SiO ₂ film of nm is grown (FIG. 3 (b)). Lithographic techniques are used to create a pattern of comb fingers in a resist layer applied on the surface of the oxide. About 8 of exposed or unprotected oxide film thickness
After removing 0% by etching, the resist is completely stripped from the surface and the wafer is thoroughly cleaned. next,
The remaining oxide film having the comb-shaped pattern is immersed in a diluted HF aqueous solution for etching (FIG. 3C), and immediately thereafter, a platinum (Pt) film having a thickness of about 40 nm is deposited (FIG. 3).
(D)). By heating the wafer by strictly controlling the temperature, the time, and the gas atmosphere, the S in the comb pattern is reduced.
The Pt film contacting i is converted to PtSi (Fig. 3
(E)). The wafers were first exposed to 250 ° C in an inert gas containing no oxygen such as pure nitrogen or argon.
Heat for hours. Immediately thereafter, preferably 10% on the spot
20-in nitrogen or argon gas containing oxygen
A second heat treatment is performed at 375 to 550 ° C. for 30 minutes. The oxygen concentration in the gas atmosphere can be roughly changed over a wide range. The two temperature annealing step is crucial to the successful PtSi metallurgy necessary for good performance of the finished photodetector. At low temperatures, Pt
Completely converted to Pt ₂ Si and no oxygen is present,
The formation of harmful SiO ₂ is avoided. In the next high temperature anneal, if Pt is already bonded to Si, Pt ₂
The conversion of Si to PtSi easily progresses, and at the same time, since oxygen exists, a thin SiO ₂ film is formed on the PtSi surface. The oxide on PtSi is essential because it acts as a protective coating on the PtSi fingers during subsequent etching of unreacted Pt on the wafer surface. The unreacted free platinum is then selectively etched in an acid mixture containing HCL and HNO ₃ in a volume ratio of about 3: 1 (FIG. 3).
(F)). In the absence of an oxide film on the PtSi finger electrode, this acid mixture erodes PtSi, severely degrading the Schottky barrier diode (SBD) junction in the final device. The integrity of the PtSi metallurgy, which depends on the annealing and etching conditions, affects the leakage current of the SBD and thus the performance of the MSM photodetector. After etching the Pt film, an aluminum film (about 600 nm) is deposited on the wafer (FIG. 3 (g)), and a pattern is formed again by the lithographic technique to form an electrical contact pad to the comb-shaped electrode (FIG. 3). (H)).
The final oxide thickness of the finished device is approximately 150
nm so that the device surface has a desired antireflection property. A cross section of the resulting structure is shown in FIG. 4 before the contact pads are applied, but it will be appreciated that only two lithographic masking levels are required to form this. It will also be appreciated that this process has the following advantages. 1) Use PtSi (φ _n = 0.86V) to obtain high barrier and thus low dark current devices. 2) Use self-aligned silicide (SALICIDE) to minimize process complexity and obtain self-aligned structures. 3) Use a thermal oxidation passivation film in the active area of the device to reduce surface recombination. 4) Use a low temperature process after metal deposition so that it is easily compatible with current bipolar and CMOS processes.

The device geometries during each step of the preferred method of applying SALICIDE in manufacturing an MSM photodetector according to the present invention are shown in sequence in FIGS. This method can be carried out starting from the surface 11 of the silicon layer 1 on the substrate 2 in the following steps. 1. The exposed surface 11 of Si is coated with a thermally grown oxide, deposited oxide or oxynitride, shown as SiO ₂ in FIG. 6, so that the oxide-Si interface exhibits a low surface recombination rate. 2. The comb pattern 13 is etched through the oxide film 12 by standard lithographic techniques (FIG. 7). 3. As shown in FIG. 8, metal (for example, P
t) Attach 14 4. The unreacted Pt 14 on the oxide surface 12 is etched after annealing at high temperature to form PtSi 10, leaving the structure shown in FIG.

Alternatively, instead of depositing and etching the metal 14 as in the steps of FIGS. 8 and 9, FIG.
A selective attachment method as shown in FIGS. After performing the first three steps of the SALICID method described above to form the device shown in FIG. 12, a metal (eg, W or Ti) or metal silicide 15 is exposed on the silicon surface 11 of the patterned oxide 12. The portion is selectively reacted to form a comb-shaped silicide electrode as shown in FIG. Finally, separate metal contact pads are provided on the two sets of comb electrodes, thereby creating an electric field between the electrodes.

FIG. 14 is a cross-sectional perspective view of a completed MSM photodetector according to the present invention, and FIG. 15 is an enlarged view of a portion of the device of FIG. 14, showing the structure at the photoactive surface region 1.

Using any of the above methods, the oxide 12 protects and passivates the photoactive silicon surface area 1 of the photodetector between the comb electrodes 10 and is a high quality transparent silicon dioxide. Is preferred. The interdigital capacitance is also increased by the oxide, but also tends to be reduced by the use of thin metal electrodes recessed by the silicon surface, which itself overlies a relatively thin layer, and the overall process and structure is less than conventional silicon. Compatible with integrated circuit technology.

Further in accordance with the present invention, the thickness of the transparent oxide coating 12 can be adjusted to function as an antireflective coating at the intended operating wavelength. For example, if the operating wavelength is 600 nm and the refractive index of the coating is 1.5, the thickness T of the coating required to obtain the best performance is 100 nm,
500nm, 900nm, 1300nm, 1700nm
Etc., this value is T = 600 (n + 0.25) / 1.
5, (n = 1, 2, 3, 4, ...).

Another feature of the invention is that the addition of Ge to Si broadens the spectral sensitivity of silicon in the photoactive surface region. For example, as shown in FIG. 16, a Si—Ge alloy layer 13 having a thickness of about 1 to 3 μm is epitaxially grown on the surface of the substrate 2, and a thin film 14 of single crystal Si having a thickness of about 0.25 μm is coated thereon. The photoactive S after coating the oxide layer 12
A high quality passivation film can be formed on the i-Ge layer. The composition of the photoactive Si-Ge surface layer 13, i.e., _{Si 1-x Ge x (0} <x <1) can be adjusted so that the amount of germanium is 0 to 100%. Since the absorption coefficient of Ge at long wavelengths is larger than that of Si, Si-
The sensitivity of the Ge layer is 850 nm (about 20 to 30% Ge).
Can be extended to about 1.8 μm and beyond.

The addition of Ge to Si also has the advantage of increasing the speed of the device at short wavelengths, because the penetration depth of photons impinging on this material is reduced. By adjusting the Si-Ge composition, carrier generation is limited to very close to the surface of the device where the electric field is strongest.
This has the positive effect of increasing the response speed of the detector to light, since no carriers are generated which would otherwise occur at a distance from the surface electric field unless the composition is adjusted. Thus, by effectively adjusting the material composition and structure of the detector surface, the performance and stability of the photodetector is increased and the silicon MSM detector is easily integrated into standard silicon VLSI manufacturing methods. Become.

Next, the use of the barrier layer, which is another feature of the present invention, will be described to deal with the problem of the penetration depth of impinging photons.

As an example of application of the present invention, a VLSI compatible method such as that shown in FIG. 3 was used to produce several high bandwidths using self-aligned PtSi Schottky barrier metallurgy with SiO ₂ passivation layer. A Si MSM photodetector was manufactured. A PtSi Schottky barrier was manufactured by a self-alignment method using an N-type substrate having a resistivity of 2 to 15 Ω · cm. The line width was kept constant at 1 μm, and the finger interval was changed to 1 to 7 μm. These detectors are ideal for high speed applications with wavelengths longer than 700 nm, with finger spacing of 1.6 μm and total device area of 6375 μm ^2.
And if 50% of them are active, then at 630 nm excitation,
It shows a conventional Si spectrum response, and it was found that the measured cutoff frequency of 3 dB exceeds 1.1 GHz and the response exceeds 0.3 A / W.

Table I shows that the PtSi electrode has a void of 0.6-
It summarizes the important device geometric parameters of the seven comb MSM structure with a width of 6.6 μm and a constant electrode width of 1.4 μm.

[Table 1]

To optimize the design of the MSM photodetector,
The absorption depth, the interdigital space interval, and the depletion depth must be similar. The absorption depth of silicon increases from less than 500 nm at a wavelength of 400 nm to more than 10 μm at a wavelength of 850 nm. The absorption depth of silicon can be reduced at wavelengths longer than 850 nm by adding germanium in the range of 0-100% to silicon. In the manufactured device, the absorption depth of Si was about 3 μm at the wavelength of 630 nm selected for the purpose of measurement.

The electrical and optical properties of the manufactured devices were measured and tested, and various characteristics of these devices are shown in FIGS. FIG. 17 shows the DC characteristics of the MSM photodetector with different finger spacing. This characteristic curve is symmetrical and the dark current increases with total silicified area. The device with the smallest spacing has the highest dark current. There is no evidence of deep levels within the depletion region according to DLTS measurements. FIG. 18 shows the DC spectral response at a bias voltage of 4 V for a device with a finger spacing of 6 μm. This measurement is obtained using a scanning monochromator with a white light source. The maximum DC response at 633 nm is about 0.42 A / W. The DC responsiveness of the device with an electrode interval of 3.6 μm to the optical output at 633 nm when the bias voltage was changed was
It shows in FIG.

The time domain response was measured with a pulsed laser at wavelengths 532 nm and 630 nm. The pulse width and repetition rate are 2 picoseconds and 7 at 100 MHz, respectively.
It was 0.3 picoseconds at 6 MHz. FIG. 20 shows a typical impulse response. This result was obtained at a bias voltage of 5 V for a device manufactured on a substrate of 11 Ω · cm with a finger spacing of 1.6 μm. 630
An average power of 100 μW in nm was used. The corresponding frequency response is 1.1 GHz with a 3 dB electrical bandwidth.
In FIG. 21, the finger spacing is 1.6 on the substrate of 5 Ω · cm.
3 shows the relationship between the electrical bandwidth of 3 dB at 630 nm and the bias voltage for a device fabricated with μm. FIG. 22 shows
Wavelength 532nm of a Si MSM photodetector with a finger spacing of 2.6μm coupled to a transimpedance amplifier with a detector biased to 2.0V.
Shows the time domain response at.

Another feature of the present invention is that long wavelength light produces carriers deep inside the semiconductor which are unaffected by the electric field of the comb-shaped surface electrode, and thus the carriers are slow to be collected and the detector is Is to solve the problem of slowing the response to light. For this purpose, as shown in FIG. 23, for example, a photoactive semiconductor surface layer 1 having a thickness of about 1 to 3 μm is
It is separated from the silicon substrate 2 by the buried barrier layer 30. Its purpose is to electrically and optically insulate the photoactive layer 1 from the substrate 2. More specifically, the barrier layer is designed to perform one or several of the following functions. (1) Optically transparent and electrically insulating layer 31 (FIG. 24)
For example, silicon dioxide, silicon nitride, silicon oxynitride, glass, etc. (2) As the optically opaque or light-absorbing layer 32 (FIG. 25), for example, N-type or P-type Si doped with extremely high concentration and a doped Si-Ge alloy. (3) Optical reflection layer 33 composed of one or more thin films
As (FIG. 26), for example silicon dioxide or silicon nitride, this film effectively forms a dielectric mirror.

In the truncated structure in which the MSM device region of the surface 11 is separated from the lower substrate 2 by the barrier layer 30, the photoactive surface layer within the range of the influence of electron / hole pairs, that is, the electric field. Only the charge carriers generated in 1 (see FIG. 2) affect the photoresponse of the detector. By limiting the range of carriers or the passage to the active region 1, the optical response of the detector is significantly improved.

More specifically, as shown in FIG.
The barrier layer 31 separating the active region 1 of the MSM device from the support substrate 2 is made of silicon dioxide, silicon nitride, or the like.
It may be a material that is optically transparent but electrically insulating. In such a structure, photons absorbed in the photoactive surface region on the buried barrier are trapped by the electric field,
It therefore contributes to the response of the detector. Photons transmitted through the transparent barrier also generate photocarriers deep in the substrate. However, these carriers are blocked by the insulating barrier and therefore recombine before being trapped in the electric field, so they do not reach the surface and do not contribute to the photoresponse of the detector.

The buried oxide or nitride layer can be formed by oxygen or nitrogen ion implantation. Similar truncated structures can be formed on a silicon-on-insulator (SOI) substrate, which is well known in silicon IC technology. Other contemplated structures include heteroepitaxial structures formed by epitaxially growing a non-silicon material on a silicon substrate.

Alternatively, as shown in FIG. 25, the light absorbing barrier layer 32 embedded below the photoactive surface region 1 can also separate the MSM device on the surface 11 from the underlying substrate 2. Only the photons absorbed in the photoactive surface region are
Carriers can be generated that are trapped by the electric field and thus contribute to the photoresponse of the detector. The photons that reach the opaque barrier layer generate carriers that recombine rapidly before being collected by the electric field. Heavily doped N ⁺ or P ⁺ Si layers are examples of light absorbing layers formed by conventional ion implantation or epitaxial methods well known in the silicon IC industry. The doping of the silicon layer is
The lifetime of carriers (ie electrons and holes) must be very short and high enough so that recombination occurs before the carriers separate and are trapped in the electric field.

As shown in FIG. 18, the buried barrier layer 33, which is made of one or more thin films of a dielectric material such as silicon dioxide or silicon nitride, and which functions as a reflection medium for photons, is provided with a photoactive layer of MSM structure. It can also be provided between the surface region 1 and the substrate 2. This dielectric mirror reflects the penetrating photons back to the active area of the surface,
Therefore, the probability of absorption is increased, resulting in increased carrier generation and thus increased detector responsiveness.

The thickness of the dielectric mirror must be adjusted based on the operating wavelength of the detector. The barrier layer, which acts as a quarter-wave plate, acts as a buried mirror. The optical thickness of such layers is 0.25λ, 1.25λ,
Equal to 2.25λ, 3.25λ, etc. However, λ is the operating wavelength.

The feature of this barrier layer is that silicon-on-
It is demonstrated when forming an MSM photodetector on an insulator (SOI) substrate or a substrate having a heavily doped N ⁺ or P ⁺ buried layer.

The SOI layer can be formed by the SIMOX (separation by oxygen implantation) method or the ELO (extended lateral overgrowth) method. The SOI substrate is a thin oxide layer,
Alternatively, it consists of a thin layer of single crystal silicon separated from the silicon substrate by a similar insulating material such as silicon nitride or silicon oxynitride. The surface layer is a photoactive layer,
It is electrically isolated from the substrate. The performance of photodetectors in SOI substrates is much faster than similar devices made in conventional silicon substrates. SOI technology is a broad field of research and many different methods for forming SOI substrates are described in the literature. An example of these manufacturing methods is the 4th International SOI Technology and Device Symposium (the 4th
International Symposium on Silicon-On-InsulatorTec
hnologyand Devices), Electrochemical So
ciety Extended Abstracts, Vol. 90-1, Spring 1990, discussed in a paper published in Montreal, Canada. These methods include SIMOX (separation by oxygen implantation) method, ELO (epitaxial lateral overgrowth) method, Z
There are MR (zone melt recrystallization) method, DWB (direct wafer bonding) method, and BESOI (SOI bond and etchback) method.

The buried doping layer is formed by ion implantation or epitaxial growth. In either structure,
The desired thickness of the upper semiconductor layer 1 can be increased epitaxially and reduced by controlled etching.

Further, in the VLSI application example, LOCO is used.
Standard VLSI for S, shallow trench isolation, mesa isolation, etc.
The isolation technique allows the device to be electrically isolated.
Light impingement on the device can be controlled or limited by openings in the patterned metallization built into the device,
The device can be provided with a guard ring structure surrounding each electrode to reduce dark current.

[0049]

As described above, according to the present invention, it has good DC characteristics and high-speed AC response, which are suitable for wide use in the field of application of short wavelength such as optical interconnection. , S
There is provided an improved MSM photodetector and method of making the same that is widely used in chip and computer manufacturing for easy integration into iVLSI technology.

[Brief description of drawings]

FIG. 1 is a plan view of an MSM photodetector according to the present invention.

2 is a cross-sectional view of the MSM photodetector shown in FIG.

FIG. 3 shows PtSi electrode metallurgy and SiO according to the present invention.
₆ is a flowchart sequentially showing one process of manufacturing an MSM photodetector using ₂ .

4 is a cross-sectional view of a contact padless device manufactured by the process of FIG.

FIG. 5: M in the form of FIG. 4 according to the concept of SALICIDE
It is a figure which shows the shape of the device in the manufacturing process of a SM photodetector.

FIG. 6 is an M in the form of FIG. 4 based on the concept of SALICID.
It is a figure which shows the shape of the device in the manufacturing process of a SM photodetector.

FIG. 7: M in the form of FIG. 4 according to the concept of SALICIDE
It is a figure which shows the shape of the device in the manufacturing process of a SM photodetector.

FIG. 8: M in the form of FIG. 4 according to the concept of SALICIDE
It is a figure which shows the shape of the device in the manufacturing process of a SM photodetector.

FIG. 9: M in the form of FIG. 4 according to the concept of SALICIDE
It is a figure which shows the shape of the device in the manufacturing process of a SM photodetector.

FIG. 10: M in the form of FIG. 4, using an alternative metal deposition method.
It is a figure which shows the shape of the device in the manufacturing process of a SM photodetector.

FIG. 11: M in the form of FIG. 4, using an alternative metal deposition method.
It is a figure which shows the shape of the device in the manufacturing process of a SM photodetector.

FIG. 12: M in the form of FIG. 4, using an alternative metal deposition method.
It is a figure which shows the shape of the device in the manufacturing process of a SM photodetector.

FIG. 13: M in the form of FIG. 4, using an alternative metal deposition method.
It is a figure which shows the shape of the device in the manufacturing process of a SM photodetector.

FIG. 14 is a perspective view showing a cross section of a completed MSM photodetector according to the present invention.

FIG. 15 is an enlarged view of a portion of the device of FIG.

16 is a Si-Ge coating of a thin passivation layer of single crystal Si of an MSM photodetector as shown in FIG.
FIG. 3 is a perspective view showing a cross section of a portion including a photoactive region in the form of an alloy layer.

FIG. 17 is an M in which the finger interval is 3.6 to 6.6 μm.
It is a figure which shows the direct current | flow characteristic of an SM photodetector.

FIG. 18: Maximum DC response at 850 nm of 0.42 obtained using a scanning monochromator with a white light source.
FIG. 7 is a graph showing a DC spectrum response of a device having an A / W bias and a finger spacing of 6.6 μm at a bias voltage of 4V.

FIG. 19 is a graph showing the DC response at various voltages for a device with a finger spacing of 3.6 μm at 633 nm.

FIG. 20 shows a representative impulse response at a bias voltage of 5V for a device with a finger spacing of 1.6 μm at 630 nm.

FIG. 21: 1.1 GH formed on a 5 Ω · cm substrate
3 is a graph showing the relationship between the bias voltage and the 3 dB bandwidth at 530 nm for a 1.6 μm device, which exhibits a 3 dB bandwidth saturation at z.

FIG. 22. Finger spacing 2.6 obtained by wire bonding the device to a transimpedance amplifier.
FIG. 5 shows a typical impulse response of a μm device at 532 nm and a bias voltage of 2V.

FIG. 23 is a perspective view showing a partial cross section of an MSM photodetector having a barrier layer below the photoactive region, as shown in FIG.

FIG. 24 shows a cross section of an MSM photodetector as shown in FIG. 2 with a transparent barrier layer underneath a photoactive region of the kind shown in FIG. 23, showing the effect of the layer on the charge carriers generated by incident light. FIG.

FIG. 25 shows a cross section of an MSM photodetector as shown in FIG. 2 having an absorption barrier layer or a recombination barrier layer below a photoactive region of the kind shown in FIG. 23, showing the charge generated by incident light. It is a schematic diagram showing the action of the layer on the carrier.

FIG. 26 shows a cross section of an MSM photodetector as shown in FIG. 2 with a reflective barrier layer underneath a photoactive region of the kind shown in FIG. 23, showing the effect of the layer on the charge carriers generated by incident light. FIG.

Front Page Continuation (72) Inventor Jean-Mark Halbooth Echo Lane 53, Larchmont, NY 10538, USA (72) Inventor Subramanian Suricantes Swala Yell United States 10598, Yorktown Heights, NY, Cedar Road 3172 (72) Inventor Raj Vasant Joshi 10598 United States, Yorktown Heights, NY Pinebrook Court 1418 (72) Inventor Vijay Peasant United States 06877, Quincy, Ridgefield, Connecticut Close 9 (72) Inventor Michael Roy Schoerman 433 Valley Pond Road, Catona, NY 10536, USA

Claims (10)

[Claims] 1. A substrate having a surface semiconductor layer of silicon, and a plurality of comb-shaped metal members having a medium or high barrier height with respect to silicon formed by self-aligned metallization in the silicon layer. A metal / semiconductor / metal photodetector comprising a pair of electrodes. 2. The metal member is PtSi, TiSi ₂ , W
The photodetector according to claim 1, wherein the photodetector is made of a material selected from the group consisting of Si ₂ , PdSi ₂ , W, Ti, Pt, Pd, Hf, indium tin oxide (ITO), and combinations thereof. 3. An oxide layer deposited on the surface of the silicon layer between the comb-shaped metal members, wherein the oxide is SiO ₂ , Si ₃ N ₄ , silicon oxynitride or a combination thereof. The photodetector according to claim 1, wherein the photodetector is made of a material selected from the group consisting of: 4. The photodetector according to claim 1, wherein the silicon surface semiconductor layer contains germanium. 5. The plurality of comb-shaped metal members are formed in two sets of electrically insulated electrodes, and each pair of electrodes is formed so as to form an electric field between the electrodes. Carriers generated by light at a deep portion in the semiconductor layer, which is provided between the connected individual contact means and the silicon semiconductor layer and the substrate and is not affected by the electric field between the electrodes, are trapped by the electric field. Means for recombining before assembling, the photodetector of claim 1. 6. The photodetector according to claim 1, wherein the substrate is a silicon-on-insulator substrate. 7. A method of preparing a substrate having a semiconductor layer of silicon on a surface of the substrate, and self-aligned metallization within the silicon layer to provide a plurality of barrier heights of medium or high with respect to silicon. And a step of forming a pair of electrodes made of a comb-shaped metal member on the surface, and a method for manufacturing a metal / semiconductor / metal photodetector. 8. The metal member is PtSi, TiSi ₂ ,
_{WSi 2, PdSi 2, W,} Ti, Pt, Pd, Hf, characterized in that the indium tin oxide (ITO) and a material selected from the group consisting of The method of claim 7. 9. The step of providing the above-mentioned silicon semiconductor layer,
8. The method of claim 7, comprising epitaxially growing a layer of an alloy of Si _1-x Ge _x (0 <x <1) on the surface of the substrate. 10. The plurality of comb-shaped metal members are formed in two sets of electrically insulated electrodes, and further on the electrodes of each set so as to form an electric field between the members. The step of forming the contact pads, respectively, and the carriers generated by light at a deep portion in the semiconductor layer that is not affected by the electric field between the members between the silicon semiconductor layer and the substrate are collected by the electric field. Forming a layer of material to be recombined prior to forming.