Device for plasma-chemical treatment of semiconductor wafers

FIELD: plasma-chemical treatment of wafers and integrated circuit manufacture.

SUBSTANCE: proposed device that can be used in photolithography for photoresist removal and radical etching of various semiconductor layers in integrated circuit manufacturing processes has activation chamber made in the form of insulating pipe with working gas admission branch; inductor made in the form of inductance coil wound on part of pipe outer surface length and connected to high-frequency generator; reaction chamber with gas evacuating pipe, shielding screens disposed at pipe base, and temperature-stabilized substrate holder mounted in chamber base. In addition device is provided with grounded shield made in the form of conducting nonmagnetic cylinder that has at least one notch along its generating line and is installed between inductor and pipe; shielding screens of device are made in the form of set of thin metal plates arranged in parallel at desired angle to substrate holder within cylindrical holder whose inner diameter is greater than maximal diameter of wafers being treated. Tilting angle, quantity, and parameters of wafers are chosen considering the transparency of gas flow screen and ability of each wafer to overlap another one maximum half its area. In addition substrate holder is spaced maximum four and minimum 0.6 of pipe inner diameter from last turn of inductance coil; coil turn number is chosen to ensure excitation of intensive discharge in vicinity of inductor depending on generator output voltage and on inner diameter of pipe using the following equation:

where n is inductance coil turn number; U is generator output voltage, V; Dp is inner diameter of pipe, mm.

EFFECT: enhanced speed and quality of wafer treatment; reduced cost due to reduced gas and power requirement for wafer treatment.

1 cl, 6 dwg, 1 tbl

 

The invention relates to the field of plasma-chemical processing of plates and can be used, in particular, photolithography is performed to remove the photoresist and radical etching of the various semiconductor layers in the technology of IP.

A device for plasma-chemical removal of the photoresist [1], comprising a reactor made of quartz tube, the length of which is wound the inductor connected to the RF generator. On one side of the pipe is introduced reaction gas, and on the opposite side - pumped. On this side is polictial for placement of the processed wafers coated with a film of photoresist.

The disadvantages of the known device lies in the low removal rate of the photoresist due to inefficient system activation gas. To obtain high speed and quality removal of the photoresist with the inefficient system activation gas necessary modes with high speed gas flow (0.5 to 10 m/s), pressure (150-1000) PA, the density of 1-10 W/cm3. If you increase the diameter of the plates (150, 200 mm or more) to get a reasonable uniformity of treatment it is necessary to increase the diameter of the cylindrical chamber. But when the chamber diameter exceeding 100 mm process becomes economically disadvantageous because of the high RA the moves of gas (more than 100 l/min), high power generator (>2 kW), resulting in large power consumption. In addition, since the plate is in contact with the plasma and subjected to intense bombardment by charged particles and UV radiation of the plasma, there is a high level of radiation damage to the treated surface. It is not possible to use the known device in the production technology of VLSI.

Known the closest to the technical essence and the achieved result is a device for plasma-chemical individual wafer handling [2]. The known device (figure 1) contains the activation chamber 1 made in the form of a tube of dielectric material with the nozzle inlet 2 of the working gas, the inductor is made in the form of an induction coil 3 wound on the outside of the pipe on the part of its length and connected to the RF generator 4, the reaction chamber 5 with a pipe pumping 6 gases. Between activation and reaction chambers has one or two metal screen that is made in the form of a disk with cylindrical holes. At the base of the reaction chamber has thermally stabilized polictial.

The disadvantages of the known devices are low removal rate of the photoresist, radiation damage of the workpiece, a large gas flow. is it due to the fact that in conditions corresponding to the characteristic modes of the plasma-chemical reactor at a pressure of 50-150 PA, in the inductor with a large number of turns is implemented capacitive phase of the discharge, characterized by a low degree of activation of the gas, since the vortex component of the electric field in the plasma is insufficient to excite the circular discharge. The known device is designed to handle wafers with a diameter of 100 mm With increasing size of the plates, which is currently in production of VLSI 150-300 mm, it is necessary to increase the diameter of the activation chamber. He must be at least equal to the diameter of the plates, as otherwise deteriorating the uniformity of processing. And in this case, the discharge device becomes less intense. For plates with a diameter of 100 mm, the removal rate of photoresist has a value of 0.5 µm/min and increasing the diameter of the plates is reduced.

In addition, the electrostatic voltage to the discharge applied from the coil, the coils of which serves a large (about 2 kV) voltage from the output circuit of the generator. Capacitive circuit RF current on polictial leads to the spread of the plasma towards the wafer and intensive bombardment plate charged particles. And this, in turn, leads to a change in Aramovich state boundary Si-SiO 2, the breakdown of thin oxide SiO2, the thickness of which at the present time in the manufacture of VLSI less than 100. All this leads to low quality processing.

The possibility of placing between activation and reaction chambers screens reduces the level of radiation damage, but only slightly. This is because the screens are flat disks with a diameter of 130 mm, thickness 3 mm, with 938 holes with a diameter of 2.5 mm with a pitch of 3.5 mm

The discharge is closed on the screens, capacitive field accelerates charged particles, and they slip through the hole with a diameter of 2.5 mm in the reaction chamber. In addition, two grids with the specified characteristics (diameter 2.5 mm, pitch 3.5 mm) does not cover the plate from the UV radiation of the discharge is concentrated in the vicinity of the nets, and, therefore, not excluded radiation damage to the surface due to the impact of high-energy UV-rays.

To increase the protective properties of the screens it is necessary to reduce the diameter of the holes and to increase the distance of their location. But this reduces the transparency grid for gas flow, which is Tog=0,35.

where sopen- the open part of the display area;

Se- the total area of the screen.

This leads to a reduction in the rate of removal of the photoresist.

the known device (with a low degree of activation gas and screens with low opacity) to ensure the speed of removal of the photoresist on the order of 1 μm/min, acceptable for individual processing, it is necessary to increase the gas flow rate to the value of the order of 5-10 l/min and equip installation of more productive, costly means of pumping, which leads to higher process.

The aim of the proposed invention is to improve the speed and quality of processing wafers, and the cheapening of the process by reducing gas consumption and reduce energy costs in the process.

This objective is achieved in that the device for plasma-chemical processing of semiconductor wafers, containing an activation chamber made in the form of a tube of dielectric material with the nozzle inlet working gas, the inductor is made in the form of coils wound on the outside of the pipe on the part of its length and connected to a RF generator, a reaction chamber with a pipe pumping gas, shielding grids located at the base of the pipe and thermally stabilized by podarkticules installed in the base of the chamber, is further provided with a grounded shield made in the form of a cylinder of conductive non-magnetic material having at least one slit along a generatrix of the cylinder, and established between the inductor and the pipe, and a screen grid in a device made in the form of a set of thin metal plates, is set parallel to each other at a given angle to polictial, in the cylindrical holder, inner diameter which is greater than the maximum diameter of the plates, the angle of inclination, the number and parameters of the plates is chosen from the condition of transparency grid for gas flow and overlapping plates of each other by more than half, in addition, polictial set from the last turn of the coil at a distance of not more than four and not less than 0.6 internal diameter of the pipe, and the number of turns of the coil is chosen from the condition of excitation of intensive discharge in the area of the inductor, depending on the output voltage of the generator and the internal diameter of the pipe, based on the ratio of:

where n is the number of turns of the coil inductance,

U is the output voltage of the generator. In,

Dp- internal diameter of pipe, mm

The introduction of a grounded cylindrical shield made of a conductive, nonmagnetic material allows screening of electrostatic or capacitive field generated by the surface charges distributed inter-turn capacitance of the inductor. This eliminates the stretching of the charged particles on the workpiece surface, which increases the efficiency of excitation of the discharge. And the presence of the dielectric gap (slit) to the generatrix of the screen eliminates the formation of a closed loop air relative to the positive RF vortex electric field of the inductor and does not prevent high-efficiency induction discharge in the activation chamber, reliable screening of the electrostatic field.

The location of podarkticules at a distance L from the bottom coil of the inductor due to the minimal impact of charged particles diffusing on the surface, and the number of turns of the coil is chosen from the condition of excitation of intensive discharge in the region of the inductor.

Screen grid, made in the form of a set of metal plates arranged parallel to each other at a given angle to polictial provide sufficient transparency grid for gas flow, which leads to the desired removal rate of the photoresist. The overlapping plates to each other is not more than half a minimal optical transparency to UV radiation while maintaining a high transparency for the gas flow, which prevents radiation damage of the processed wafers.

Thus, these signs are new, unknown in the prior art and is not explicitly follow from the prior art, and in the aggregate, provide positive impacts in obtaining high speed and quality, reduce energy costs and gas flow, which reduces the processing of semiconductor wafers.

Therefore, the proposed set of features relevant to the duty to regulate the conditions of patentability: novelty, “ “inventive step” and “industrial applicability”.

The essence of the proposed utility model is illustrated by drawings, which show:

figure 1 is a device for plasma-chemical individual wafer handling (prototype);

figure 2 - proposed device for plasma-chemical processing of semiconductor wafers;

figure 3 is a fragment of a shielding mesh in the prototype. View from above;

figure 4 is a shielding grid plates joined to the center;

figure 5 is a fragment of a section of screen grid when the upper edge of the plate coincides with the lower edge of the adjacent plate;

figure 6 is a fragment of a section of screen grid, when the overlapping of the plates is halved.

Device for plasma-chemical processing plates (figure 2) contains: activation chamber made in the form of a quartz tube 1, the top of which is a nozzle inlet working gas 2, the reaction chamber 3, a pipe pumping gas 4 whose base is perpendicular to the axis of the pipe has thermally stabilized polictial 5.

The excitation system of the gas discharge is a coil wound upon a portion of the length of the pipe and connected to a RF generator. Between the inductor and the pipe installed earthed screen 8, is made in the form of a cylinder made of copper and having cut the SAR is ü generatrix of the cylinder. The lower edge of the pipe between activation and reaction chambers equipped with two easily removable screen 9, is made in the form of a set of plane-parallel metal plates 10, is inserted into the cylindrical holder 11. Plates are mounted parallel to each other at an angle α to polictial so that they overlap, but not by more than half.

The removal rate of photoresist or speed isotropic etching of materials (for example, SiO2) is determined primarily by the concentration of the active components of the plasma in the treatment zone (atomic oxygen in the process of removing the photoresist; the radicals F - during the isotropic etching). For carrying out these processes at high speed and high quality it is necessary to implement a highly efficient activation of the gas and to exclude the influence of charged particles on the surface 12.

In the proposed device (figure 2) in the field coil 6 is excited N-rank (electrodeless ring discharge), the efficiency of activation gas which is substantially higher than in the “capacitive” phase induction discharge. N-category is supported by an alternating magnetic flux induces eddy electric field with intensity Eiin the discharge. Under the assumption of a uniform magnetic field for a coil of n turns, Diametro the D in accordance with the basic law of electromagnetic induction and Maxwell equation [3] you can obtain a simple estimate of the absolute magnitude of this field near the surface of the inductor:

where U is the voltage across the inductor,

Eivortex field near the surface,

ε - proteoids induction.

Experimental studies electrodeless ring discharge low pressure [4] show that for high-performance induction discharge at pressures of 0.1-1 Torr need the value of intensity of the vortex electric field

The diameter of the inductor is impractical to increase by more than 20 mm relative to the inner pipe diameter Dpin which is excited by the discharge,

Substituting the values of (2) and (3) in equation (1), we obtain:

where U is the output voltage of the generator, In,

Dp- internal diameter of pipe, mm

When reducing the number of turns of the vortex electric field increases, the discharge becomes more intense, but when n<1 occurs in a non-uniform excitation of the discharge, and consequently increases the uniformity and decreases the removal rate of photoresist (or isotropic etching). Taking this into account, we obtain:

Screen 8 installed between the inductor 6 and the tube 1, due to the presence of the dielectric gap (incision of vdol the forming does not form a closed loop relative to the RF vortex electric field of the inductor), does not prevent high-efficiency induction discharge in the activation chamber, securely shields the electrostatic field and eliminates the bombing of the processed surface of the charged particles. When this discharge is localized in the area of the inductor 6.

To achieve the minimum impact of charged particles diffusing on the surface, polictial placed at a distance L from the bottom coil of the inductor 6, defined by the ratio

3λ ≤ L≤ 20λ ,

where- the diffusion length of the ions and electrons in their ambipolar diffusion to the walls of the tubes;

Rpthe inner radius of the pipe.

This follows from the fact that at a distance of λ the concentration of charged particles is reduced by 2.7 times [5].

Thus, at a distance of 3λ the concentration of charged particles is reduced, which significantly reduces the impact on the treated surface. When L>3λ the effect increases, and when L=20λ the decrease is ~4· 103time.

The increase of L>20 λ leads to a significant reduction in the rate of the process, as this also reduces the concentration of active particles, although much more slowly than the concentration of charged particles.

Given that Rp=Dp/2, we get

0,6DpȦ L≤ 4Dp.

The choice of design and parameters of the shielding grids 9 determined by the maximum transparency Togfor gas flow and minimal transparency to UV radiation to avoid possible radiation damage:

where Sg- the area of the screen free for the transportation of gas flow to the plate 12,

Se- the area of the screen.

The maximum possible value of Kg maxfor a screen with holes, as in the prototype (figure 3):

Almostgmuch smaller, of the order of 0.35.

When using the screen in the form of a set of thin plane-parallel plates number of plates N is chosen so that Kgexceeds theoretically possible value for a planar mesh with holes, resulting in the screen does not reduce the speed of removal of photoresist and allows you to carry out the process at a much lower cost gas than in the known device.

The area of the screen that blocked for transportation of the gas stream (SC) set N plates of thickness d, installed in the cylindrical holder, inner diameter which is equal to Decan be approximated by rhombus (figure 4) with diagonals Deand N· d (SC=HD· De). Hence

The thickness of the plates is impractical to select more than 1 mm, So the number of plates N=0,17 De. When reducing the number of plates Togis increased, and, consequently, reduce the loss of active particles, but it is found experimentally that reducing the number of plates to less than 10 leads to an increase in non-uniformity of processing wafers with a diameter of >100 mm and a reduction in the rate of removal of the photoresist.

Thus, the number of plates is selected from the formula:

10≤ N≤ 0,17De,

where Dethe inner diameter of the cylindrical holder plates, mm When Deexceeds the maximum diameter of the plate Dnbecause otherwise there is a reduction of speed and uniformity of treatment by shading the perimeter of the plate.

The angle of the plates 10 is chosen such as to prevent UV radiation from the peripheral region of the plasma on the opposite edge of the plate.

where L is the distance from the bottom coil of the inductor to podarkticules;

Dpthe inner diameter of the pipe;

Dn- the maximum diameter of the plate.

With decreasing angle α plates 10 UV-radiation percribed is more effective but the reduction of the angle to less than 15° leads to a decrease in processing speed due to the dispersion of the gas stream. Therefore, the angle α choose from a condition:

In order to avoid ingress of UV radiation on the surface of the Central zone of the discharge, i.e. at normal incidence UV flux, it is necessary that the upper edge of the plate at least above the lower edge of the adjacent plate (figure 5). Then

Nd+Nl· cosα ≥ De,

therefore,

where l is the width of the plate 10.

It is impractical to implement the overlap of the plates 10 more than half (6), as it leads to reduction in the rate of removal of the photoresist.

So

Here

Thus, the width of the plate is selected from the formula:

where l, Demeasured in mm.

The device operates as follows. In the pipe 1 activation chamber through pipe 2 serves the working gas. The processed wafer 12 is placed on polictial 5. After switching on the RF generator 7 in a quartz tube in the area of the inductor occurs intensive inductive (electrodeless ring) discharge. The activated gas is dissolved, and ostranitsa in the direction of podarkticules, as charged particles, have much shorter lifetimes than the active particles (atomic oxygen or fluorine radicals), die on the pipe walls of the screen. The activated gas reaches the surface of the treated plate heated from podarkticules 5, and enter into chemical interaction with the surface. In the case of removal of the photoresist (operating gas - oxygen) under the action of atomic oxygen occurs disconnection of the polymer, which is a photoresist, the gap between end groups, their oxidation to CO, CO2H2O and removed from the surface of the plate.

In the case of isotropic etching materials working gas - fluoride compound, for example, CF4+O2(SF6, NF3). In the interaction of fluoride with the surface forms a volatile compound, such as SiF4which is removed through pipe pumping.

A specific example. The plasma-chemical device (figure 2) processing semiconductor wafers includes an activation chamber in the form of a quartz tube with an inner diameter of Dp=210 mm Processed silicon wafer with a diameter of 150 mm is installed on polictial 5 at a distance of L=300 mm from the bottom coil of the inductor with the number of turns n=2, having an inner diameter 226 mm Between the inductor and the pipe is the screen 8, is made of copper thickness is Noah 1 mm and having a slit along a generatrix of the cylinder. Between activation and reaction chambers are two screen 9, is made in the form of a set of N=19 aluminum plates 10 of thickness d=1 mm, width 1=10 mm, is inserted into the cylindrical holder, the inner diameter of Dp=152 mm Plates 10 are angled α =30° to polictial 5. The bottom screen can be deployed relative to the top in the vertical direction at 180° . The treatment was carried out in the plasma of oxygen, the temperature of podarkticules 5 was 250° C.

The proposed device for plasma-chemical processing of plates allows you to increase the process speed and quality of processing, to reduce the degradation of the electrophysical parameters of the structures and the breakdown of the thin gate oxide. This provides an increase in the percentage of yield of products by reducing marriage to control operations of the electrophysical parameters of structures formed on semiconductor wafers using plasma-chemical processing.

Currently, the company constructed a prototype of the proposed device for removing photoresist. The tests obtained positive results in the test report.

Sources of information taken into account

1. UK application No. 1461636, CL B3V, 1977.

2. The mouth of austo for plasmochemical individual wafer handling the Plasma-I”. Development of JSC “December”, SCM 3.240.254, , Voronezh.

3. Kalashnikov EG Electricity. - M.: Nauka, 1977. - 591 S.

4. Straub H.J. Ann. Phys. - 1958, Bd. 1, H.4-5. - S.281.

Device for plasma-chemical processing of semiconductor wafers, containing an activation chamber made in the form of a tube of dielectric material with the nozzle inlet working gas, the inductor is made in the form of coils wound on the outside of the pipe on the part of its length and connected to a RF generator, a reaction chamber with a pipe pumping gas, shielding grids located at the base of the pipe, and thermally stabilized by podarkticules installed in the base of the chamber, characterized in that it is further provided with a grounded shield made in the form of a cylinder of conductive non-magnetic material having at least one slit along a generatrix of the cylinder and installed between the inductor and the pipe, and a screen grid in a device made in the form of a set of thin metal plates arranged parallel to each other at a given angle to polictial in the cylindrical holder, inner diameter which is greater than the maximum diameter of the plates, the angle of inclination, the number and parameters of the plates is chosen from the condition of transparency grid for gas flow and overlap LastName each other no more than half, in addition, polictial set from the last turn of the coil at a distance of not more than four and not less than 0.6 internal diameter of the pipe, and the number of turns of the coil is chosen from the condition of excitation of intensive discharge in the area of the inductor, depending on the output voltage of the generator and the internal diameter of the pipe, based on the ratio of:where n is the number of turns of the coil inductance, U is the output voltage of the generator, In, Dp- internal diameter of pipe, mm



 

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18 cl

FIELD: electronics; semiconductor devices and methods for etching structures on their wafers.

SUBSTANCE: plasmochemical etching of material is conducted by way of acting on its surface with ion flow of plasma produced from plasma forming gas filling evacuated camber, electron beam being used to act upon plasma forming gas for plasma generation. Constant longitudinal magnetic field with flux density of 20-40 Gs is built on axis, plasma-generating gas pressure is maintained within chamber between 0.01 and 0.1 Pa, and electron beam at current density of 0.1-1 A/cm2 ensuring ignition of beam-plasma discharge is used. Etching condition (energy and ion current density) can be controlled ether by modulating electron beam with respect to speed or by varying potential of discharge collector.

EFFECT: enhanced etching efficiency (speed) and quality of etching structures on semiconductor material surface: high degree of etching anisotropy preventing etching under mask, minimized material structure radiation defects brought in during etching.

2 cl, 1 dwg

FIELD: physics; electricity.

SUBSTANCE: etching system contains plasma-generating facilities for plasma generating in vacuum chamber, high-frequency displacement voltage source, supplying high-frequency displacement voltage to electrode-substrate, floating electrode opposite to electrode-substrate in vacuum chamber and supported in floating condition by electric potential, solid material placed on the side of the floating electrode directed to electrode-substrate to form film layer protecting from etching, and control unit for periodic supply of high-frequency voltage to floating electrode. Etching method includes repetition, in specified sequence, of substrate etching stage by means of etching gas supplied to vacuum chamber, and film layer formation stage protecting substrate from etching by sputtering of solid material opposite to substrate.

EFFECT: high etching selectivity when using mask as well as production of anisotropic profile and great etching depth.

22 cl, 7 dwg

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