CN105891548A - Nanoscale optical subsurface damage detection method based on ion sputtering technology - Google Patents

Abstract

The invention discloses a nanoscale optical subsurface damage detection method based on ion sputtering technology. The method comprises steps: 1) ion beam sputtering is carried out on the surface of a detected optical element to form a slope groove, as density effects of materials are generated on an optical element subsurface damage area, the ion beam sputtering removal rate in the subsurface damage area with the dense material in the subsequent ion beam sputtering process is lower than that in other areas, and the subsurface damage of the detected optical element is exposed on the surface of the slope groove after ion beam sputtering, and a convex nano structure with the same structure as the original subsurface damage is generated; and 2) an atomic force microscope is used for measuring the convex nano structure in the slope groove to determine the subsurface damage depth information of the detected optical element. The method of the invention can measure the nanoscale damages on the optical element subsurface, the detection precision is high, and the subsurface damages can be exposed and observed conveniently.

Description

Nanoscale optics sub-surface damage detection method based on ion sputtering

Technical field

The present invention relates to sub-surface damage detection technique during optical element Ultra-precision Turning, be specifically related to one and spatter based on ion Penetrate the nanoscale optics sub-surface damage detection method of technology.

Background technology

The modern high performance optical system manufacture requirements to optical element, is not limited only to Nanosurface precision and super-smooth surface, with Time to the requirement of sub-surface quality also nearly close to physics limit, most typical is the system of high light optical element and lithographic objective Make.In laser nuclear fusion system, sub-surface damage is the principal element of induced optical part laser irradiation damage, in order to resist Power density is up to 10J/cm²The radiation of laser, needs to realize the region-wide processing close to zero damage of high light optical element.It addition, What the required precision of currently manufactured field was the highest is the processing of deep ultraviolet/extreme ultraviolet photolithographic object lens, needs unified face shape error Surface roughness to nanoscale all controls in sub-nanometer scale, sub-surface damage for sub-nano-precision surface generation extremely Close important.

Optical material generally is hard brittle material, is susceptible to brittle break under external force.According to active force in polishing process Difference, material removing method can be divided into the removal pattern in elastomeric domain, plastic region and fragility territory, and tradition polishing is main by mill Material realizes material plasticity territory and the removal in fragility territory with the mechanical function of workpiece material, easily produces stress raisers, and excessive Stress raisers can cause the generation of surface/sub-surface damage, be embodied in face crack, cut and sub-surface damage etc. Defect.The sub-surface damage produced for grinding and tradition polishing, researcher both domestic and external proposes HF pickling, magnetorheological The methods such as polishing are removed and are removed sub-surface damage.Additionally, due to sub-surface damage is generally covered by the deposit on surface, Relevant researcher also utilizes above-mentioned technology to effectively removes surface layer so that sub-surface damage is exposed, and successfully achieves The detection of sub-surface damage in tradition polishing process.

But, in the manufacture process of high-performance optical part, sub-surface damage presents the yardstick/thickness of microcosmic magnitude, and The multifarious feature of defect, said method has been difficult to meet damage accurately detection and the requirement of not damaged processing.On the one hand, adopt With the method strengthening chemical polishing, such as HF pickling, make use of the interaction removal of pickle or abrasive material and surfacing Material, has been avoided as much as denseization effect, but the sub-surface that the hydrolysis layer supervened not only can cover micro-scale has been damaged Wound, but also the performance of optical element can be affected；On the other hand, the polishing mode of contact, such as MRF, polishing All the time there is certain active force in granule and storeroom, inevitably results from the damage of micro-scale, and then the sub-surface of impact The removal of damage and detection.As can be seen here, said method is difficult to keep the original state of damage in the removal process of material, and And the most easily produce sub-surface damage and hydrolysis layer, it is difficult to realize not damaged processing and the micro-scale of fused quartz optical element Damage check.

Summary of the invention

The technical problem to be solved in the present invention: for the problems referred to above of prior art, it is provided that one can measure optical element Asia table The damage of face nanoscale, accuracy of detection is high, be easy to exposure sub-surface damage and the nanometer chi based on ion sputtering of observation Degree optics sub-surface damage detection method.

In order to solve above-mentioned technical problem, the technical solution used in the present invention is:

A kind of nanoscale optics sub-surface damage detection method based on ion sputtering, step includes:

1) surface to detected optical element carries out ion beam sputtering and forms slope groove, due to optical element sub-surface damage region The denseization effect of material can be produced, at the ion in the sub-surface damage region of follow-up ion beam sputtering process in which materials denseization Beam sputtering removal rate will be less than other regions so that the sub-surface damage of detected optical element is exposed to after ion beam sputtering The surface of slope groove also generates the protruding nanostructured identical with original sub-surface damage structure；Described denseization effect refers to optics Element is owing to being acted on by polishing force in polishing process, and the material in the sub-surface damage region of generation is compacted, and causes local The phenomenon that density increases；

2) utilize atomic force microscope that the protruding nanostructured in the groove of slope is measured, determine the sub-table of detected optical element Surface damage depth information.

Preferably, described step 1) detailed step include:

1.1) obtain the surface of detected optical element is carried out ion beam sputtering removal function R (x, y)；

1.2) calculate the surface to detected optical element and carry out the scan velocity V (X) of ion beam sputtering；

1.3) set and the surface of detected optical element is carried out the removal function R of ion beam sputtering (x, y), with scan velocity V (X) The surface of detected optical element is carried out ion beam sputtering and forms slope groove so that the sub-surface damage of detected optical element by Forming protruding nanostructured in the depth location that denseization effect is corresponding in the groove of slope, the degree of depth of described slope groove is H₁～H_N Between ramped shaped groove, wherein H₁～H_NSub-surface damage depth detection scope for detected optical element.

Preferably, described step 1.1) detailed step include:

1.1.1) testpieces of one block of material identical with detected optical element is taken；

1.1.2) utilize wavefront interferometer that the primary face shape of testpieces is measured；

1.1.3) set the time t of processing, use ion beam each appointment position on testpieces surface to carry out pinpointing bombardment time t；

1.1.4) again with wavefront interferometer, testpieces face shape after ion beam bombardment is measured；

1.1.5) the face shape that wavefront interferometer measurement before and after ion beam bombardment obtains carries out making difference process, obtain testpieces to correspondence time Between the material removal amount A of t (x, y), by described material removal amount A, (x, y) divided by time t, when obtaining detected optical element by unit In material removal amount constitute removal function R (x, y).

Preferably, described step 1.2) detailed step include:

1.2.1) divide the multiple etching points to be scanned of formation on slope based on equidistant l, obtain an X₁, some X₂..., some X_N, Wherein X₁Represent the starting point of ion beam sputtering, X₂Represent second etching point to be scanned of ion beam sputtering, X_NRepresent ion The terminal of beam sputtering, puts X₁Corresponding etching depth is the minima of the sub-surface damage depth detection scope of detected optical element H₁, put X_NCorresponding etching depth is the maximum H of the sub-surface damage depth detection scope of detected optical element_N；

1.2.2) according to remove function R (x, y), each to be scanned etching point material etch depth calculation in each etching to be scanned Point correspondence carries out the scan velocity V (X) of ion beam sputtering.

Preferably, described step 1.2.2) in calculate and carry out the scan velocity V (X) of ion beam sputtering in each etching point correspondence to be scanned Function expression such as formula (1) shown in；

$V\left(X\right)=\frac{(X_N-X_1)l{\∫}_{-\mathrm{\∞}}^{+\mathrm{\∞}}R(x,y=0)dx}{(H_N-H_1)X+H_1{X}_N-H_N{X}_1}---\left(1\right)$

In formula (1), V (X) represents the ion-beam scanning speed at etching point X to be scanned, X₁Represent rising of ion beam sputtering Initial point, X_NRepresenting the terminal of ion beam sputtering, l represents the spacing of equidistant division etching to be scanned point, H₁Represent that sub-surface is damaged Hinder the minima of depth detection scope, H_NRepresent sub-surface damage depth detection scope maximum, R (x, y) represent point (x, y) Material removal amount in the unit interval at place, (x, y) expression is left away in X direction except function centre distance respectively x, Y-direction are left away Except the point that function centre distance is y.

Preferably, described step 2) detailed step include:

2.1) in slope, mark the point to be measured of different etching depth；

2.2) utilize atomic force microscope that the point to be measured of labelling is carried out damage measurement, if some point to be measured can be observed To nanometer damaged structure, then show that corresponding depth areas to be measured exists sub-surface damage；If all points to be measured are the most not Observe damaged structure, then show that detected optical element does not exist sub-surface damage.

Present invention nanoscale based on ion sputtering optics sub-surface damage detection method has an advantage that

1, present invention physical sputtering based on ion beam effect removes surface layer material, belongs to non-contacting processing method, and itself is not Can produce sub-surface damage due to stress raisers, sputter procedure will not produce extra addition product simultaneously, it is possible to more accurate Really disclose the sub-surface damage being hidden under surface layer.

2, utilize the ion beam sputtering sensitivity characteristic to microcosmic material denseization phenomenon, the present invention propose based on ion sputtering Sub-surface damage detection method can measure the sub-surface damage of nanoscale, solve existing method at high-performance optical part Nanoscale sub-surface damage is difficult to the difficult problem detected by processing.

Accompanying drawing explanation

Fig. 1 is the basic procedure schematic diagram of embodiment of the present invention method.

Fig. 2 is the schematic diagram of embodiment of the present invention method intermediate ion beam sputtering processing slope groove.

Fig. 3 is the slope groove testing result utilizing ion beam sputtering to process in the embodiment of the present invention.

Fig. 4 is that in the embodiment of the present invention, detected optical element depth is the sub-surface quality microgram of 40nm.

Fig. 5 is that in the embodiment of the present invention, detected optical element depth is the sub-surface quality microgram of 60nm.

Fig. 6 is that in the embodiment of the present invention, detected optical element depth is the sub-surface quality microgram of 80nm.

Detailed description of the invention

As it is shown in figure 1, the present embodiment nanoscale based on ion sputtering optics sub-surface damage detection method step includes:

1) surface to detected optical element carries out ion beam sputtering and forms slope groove, due to optical element sub-surface damage region The denseization effect of material can be produced, at the ion in the sub-surface damage region of follow-up ion beam sputtering process in which materials denseization Beam sputtering removal rate will be less than other regions so that the sub-surface damage of detected optical element is exposed to after ion beam sputtering The surface of slope groove also generates the protruding nanostructured identical with original sub-surface damage structure；Denseization effect refers to optical element Owing to being acted on by polishing force in polishing process, the material in the sub-surface damage region of generation is compacted, and causes local density The phenomenon increased；In the present embodiment, the material of detected optical element is fused quartz, it is desirable to measuring thickness is 40nm to 80nm The sub-surface damage in region；

See Fig. 2, by the ion source 1 surface 5 emitting ions bundle 2 to detected optical element 4 in the present embodiment, to tested The surface 5 of photometry element 4 carries out ion beam sputtering, when finally the surface 5 at detected optical element 4 forms slope groove 3, The most shallow (the H of the left side degree of depth of slope groove 3₁), the deepest (H of the right side degree of depth_N)；

2) utilize atomic force microscope that the protruding nanostructured in the groove of slope is measured, determine the sub-table of detected optical element Surface damage depth information.In the present embodiment, the sub-surface damage of nanoscale refers to be hidden in the cut of below surface layer, crackle Etc. defect, and its width is less than 100 nanometers.

The basis of the present embodiment nanoscale based on ion sputtering optics sub-surface damage detection method is denseization effect, Denseization effect refer to optical element in polishing process owing to being acted on by polishing force, the material in the sub-surface damage region of generation Material is compacted, and causes the phenomenon that local density increases, and the denseization effect of material is not that ion beam sputtering produces, but optics Element produces along with sub-surface damage in the above course of processing, and ion beam sputtering material already present to optical element is thick Densification phenomenon is sensitive.Microcosmic material internal spatial organization, in addition to atom/molecule, there is also substantial amounts of space, by sufficiently large Action of compressive stress time, void space be very easy to is compressed so that local material denseization, the material of densified regions simultaneously Material density increases.Ion beam sputtering is very sensitive to the denseization effect of material, and it is main is characterized in that ion beam sputtering Material removal rate is inversely proportional to the density of local material, and denseization effect causes local density to increase so that the material of zones of different The material removal rate property of there are differences, and the biggest region removal rate of density is the least, specifically can be by function representation shown in formula (2) Formula is described；

$v(x,y)=\frac{3\mathrm{\ϵ}}{4{\mathrm{\π}}^2\sqrt{2\mathrm{\π}}{\mathrm{\βC}}_m}\frac{{\mathrm{JM}}_t}{{\mathrm{\ρ}}_t(x,y)N_A}\frac{1}{U_b(x,y)}\exp (-\frac{{\mathrm{\σ}}^2}{2{\mathrm{\α}}^2})---\left(2\right)$

In formula (2), v (x, (x, y) removal rate at place, (x, y) leave away in X direction except function centre distance is divided y) to represent point by expression Wei x, Y-direction not leave away except the point that function centre distance is y, ε be the gross energy that ion deposits at material surface, and β is vertical In the energy deposition width in ion incidence direction, C_mParameter for differential scattering；J is the beam current density of ion beam, M_tFor The molal weight of the basic component units of material, ρ_t(x y) is point (x, y) local material densities at place, N_AFor avogadros constant, U_b(x, is y) local binding energy, and σ is the average incident degree of depth of ion, and α is the energy deposition width along ion incidence direction.By Formula (2) understands, and the material (such as fused quartz and crystalline quartz) formed for same composition, at same ion sputtering condition (such as ion Energy, beam current density) effect under, point (x, y) place removal rate v (x, y) with point (x, y) local material densities ρ at place_t(x y) becomes anti- Proportionate relationship.Therefore, the surface to detected optical element carries out ion beam sputtering and forms slope groove so that detected optics unit The sub-surface damage region of part, as the densified regions of denseization effect, can be spattered due to ion beam during ion beam sputtering Penetrate taking-up speed less than other regions so that sub-surface damage is exposed to the table of detected optical element during ion beam sputtering Face also generates the protruding nanostructured identical with original sub-surface damage structure in the groove of slope；Then atomic force microscope pair is utilized The protruding nanostructured being exposed to optical surface measures, and just can obtain the sub-surface damage information of optical element.

In the present embodiment, step 1) detailed step include:

1.1) obtain the surface of detected optical element is carried out ion beam sputtering removal function R (x, y)；

1.2) calculate the surface to detected optical element and carry out the scan velocity V (X) of ion beam sputtering；

1.3) set and the surface of detected optical element is carried out the removal function R of ion beam sputtering (x, y), with scan velocity V (X) The surface of detected optical element is carried out ion beam sputtering and forms slope groove so that the sub-surface damage of detected optical element by Forming protruding nanostructured in the depth location that denseization effect is corresponding in the groove of slope, the degree of depth of slope groove is H₁～H_NBetween Ramped shaped groove, wherein H₁～H_NSub-surface damage depth detection scope for detected optical element.

In the present embodiment, step 1.1) detailed step include:

1.1.1) testpieces of one block of material identical with detected optical element is taken；

1.1.2) utilize wavefront interferometer that the primary face shape of testpieces is measured；

1.1.3) set the time t of processing, use ion beam each appointment position on testpieces surface to carry out pinpointing bombardment time t；

1.1.4) again with wavefront interferometer, testpieces face shape after ion beam bombardment is measured；

1.1.5) the face shape that wavefront interferometer measurement before and after ion beam bombardment obtains carries out making difference process, obtain testpieces to correspondence time Between the material removal amount A of t (x, y), by material removal amount A, (x, y) divided by time t, obtains detected optical element by the unit interval Material removal amount constitute removal function R (x, y), i.e. remove function R (x, y)=A (x, y)/t.

In the present embodiment, step 1.2) detailed step include:

1.2.1) divide the multiple etching points to be scanned of formation on slope based on equidistant l, obtain an X₁, some X₂..., some X_N, Wherein X₁Represent the starting point of ion beam sputtering, X₂Represent second etching point to be scanned of ion beam sputtering, X_NRepresent ion The terminal of beam sputtering, puts X₁Corresponding etching depth is the minima of the sub-surface damage depth detection scope of detected optical element H₁, put X_NCorresponding etching depth is the maximum H of the sub-surface damage depth detection scope of detected optical element_N；

1.2.2) according to remove function R (x, y), each to be scanned etching point material etch depth calculation in each etching to be scanned Point correspondence carries out the scan velocity V (X) of ion beam sputtering.

In the present embodiment, step 1.2.2) in calculate the scan velocity V (X) carrying out ion beam sputtering in each etching point correspondence to be scanned Function expression such as formula (1) shown in；

$V\left(X\right)=\frac{(X_N-X_1)l{\∫}_{-\mathrm{\∞}}^{+\mathrm{\∞}}R(x,y=0)dx}{(H_N-H_1)X+H_1{X}_N-H_N{X}_1}---\left(1\right)$

In formula (1), V (X) represents the ion-beam scanning speed at etching point X to be scanned, X₁Represent rising of ion beam sputtering Initial point, X_NRepresenting the terminal of ion beam sputtering, l represents the spacing of equidistant division etching to be scanned point, H₁Represent that sub-surface is damaged Hinder the minima of depth detection scope, H_NRepresent sub-surface damage depth detection scope maximum, R (x, y) represent point (x, y) Material removal amount in the unit interval at place, (x, y) expression is left away in X direction except function centre distance respectively x, Y-direction are left away Except the point that function centre distance is y.

In the present embodiment, step 2) detailed step include:

2.1) in slope, mark the point to be measured of different etching depth；

2.2) utilize atomic force microscope that the point to be measured of labelling is carried out damage measurement, if some point to be measured can be observed To nanometer damaged structure, then show that corresponding depth areas to be measured exists sub-surface damage；If all points to be measured are the most not Observe damaged structure, then show that detected optical element does not exist sub-surface damage.

See Fig. 3, the present embodiment has marked three to be measured some X altogether₁(11.5 ,-40.0), X₂(20.9 ,-60.0) and X₃(30.9, -80.0).Use atomic force microscope that the measurement result of labelling point is distinguished the most as shown in Figure 4, Figure 5 and Figure 6.Result from detection It is found that be the surface layer of more than 40nm in the degree of depth, do not observe the existence of material damage, as shown in Figure 4.But, When working depth increases to about 60nm, the microscopic appearance surface that detection obtains occurs in that small wire projection nanostructured, As it is shown in figure 5, show that exemplar exists sub-surface damage in this depth areas, the material surface denseization effect of injury region make from The etch rate of son bundle is less than other region, thus causes the generation of protruding nano wire.Along with the continuation of working depth increases, micro- The wire projection nanostructured seeing pattern will become more apparent, and as shown in Figure 6, demonstrates the existence of sub-surface damage further.On That states test result indicate that, uses the nanoscale optics sub-surface damage detection method of the present embodiment can effectively remove surface Layer, sub-surface damage is exposed, it is possible to auxiliary atom force microscope detects small sub-surface damage.

The above is only the preferred embodiment of the present invention, and protection scope of the present invention is not limited merely to above-described embodiment, all The technical scheme belonged under thinking of the present invention belongs to protection scope of the present invention.It should be pointed out that, for the art is common For technical staff, some improvements and modifications without departing from the principles of the present invention, these improvements and modifications also should be regarded as this The protection domain of invention.

Claims (6)

1. a nanoscale optics sub-surface damage detection method based on ion sputtering, it is characterised in that step includes:

1) surface to detected optical element carries out ion beam sputtering and forms slope groove, due to optical element sub-surface damage region The denseization effect of material can be produced, at the ion in the sub-surface damage region of follow-up ion beam sputtering process in which materials denseization Beam sputtering removal rate will be less than other regions so that the sub-surface damage of detected optical element is exposed to after ion beam sputtering The surface of slope groove also generates the protruding nanostructured identical with original sub-surface damage structure；Described denseization effect refers to optics Element is owing to being acted on by polishing force in polishing process, and the material in the sub-surface damage region of generation is compacted, and causes local The phenomenon that density increases；

2) utilize atomic force microscope that the protruding nanostructured in the groove of slope is measured, determine the sub-table of detected optical element Surface damage depth information.

Nanoscale optics sub-surface damage detection method based on ion sputtering the most according to claim 1, it is special Levy and be, described step 1) detailed step include:

1.1) obtain the surface of detected optical element is carried out ion beam sputtering removal function R (x, y)；

1.2) calculate the surface to detected optical element and carry out the scan velocity V (X) of ion beam sputtering；

1.3) set and the surface of detected optical element is carried out the removal function R of ion beam sputtering (x, y), with scan velocity V (X) The surface of detected optical element is carried out ion beam sputtering and forms slope groove so that the sub-surface damage of detected optical element by Forming protruding nanostructured in the depth location that denseization effect is corresponding in the groove of slope, the degree of depth of described slope groove is H₁～H_N Between ramped shaped groove, wherein H₁～H_NSub-surface damage depth detection scope for detected optical element.

Nanoscale optics sub-surface damage detection method based on ion sputtering the most according to claim 2, it is special Levy and be, described step 1.1) detailed step include:

1.1.1) testpieces of one block of material identical with detected optical element is taken；

1.1.2) utilize wavefront interferometer that the primary face shape of testpieces is measured；

1.1.3) set the time t of processing, use ion beam each appointment position on testpieces surface to carry out pinpointing bombardment time t；

1.1.4) again with wavefront interferometer, testpieces face shape after ion beam bombardment is measured；

1.1.5) the face shape that wavefront interferometer measurement before and after ion beam bombardment obtains carries out making difference process, obtain testpieces to correspondence time Between the material removal amount A of t (x, y), by described material removal amount A, (x, y) divided by time t, when obtaining detected optical element by unit In material removal amount constitute removal function R (x, y).

Nanoscale optics sub-surface damage detection method based on ion sputtering the most according to claim 3, it is special Levy and be, described step 1.2) detailed step include:

1.2.1) divide the multiple etching points to be scanned of formation on slope based on equidistant l, obtain an X₁, some X₂..., some X_N, Wherein X₁Represent the starting point of ion beam sputtering, X₂Represent second etching point to be scanned of ion beam sputtering, X_NRepresent ion The terminal of beam sputtering, puts X₁Corresponding etching depth is the minima of the sub-surface damage depth detection scope of detected optical element H₁, put X_NCorresponding etching depth is the maximum H of the sub-surface damage depth detection scope of detected optical element_N；

1.2.2) according to remove function R (x, y), each to be scanned etching point material etch depth calculation in each etching to be scanned Point correspondence carries out the scan velocity V (X) of ion beam sputtering.

Nanoscale optics sub-surface damage detection method based on ion sputtering the most according to claim 4, it is special Levy and be, described step 1.2.2) in calculate the scan velocity V (X) carrying out ion beam sputtering in each etching point correspondence to be scanned Function expression such as formula (1) shown in；

$V\left(X\right)=\frac{(X_N-X_1)l{\∫}_{-\mathrm{\∞}}^{+\mathrm{\∞}}R(x,y=0)dx}{(H_N-H_1)X+H_1{X}_N-H_N{X}_1}---\left(1\right)$

In formula (1), V (X) represents the ion-beam scanning speed at etching point X to be scanned, X₁Represent rising of ion beam sputtering Initial point, X_NRepresenting the terminal of ion beam sputtering, l represents the spacing of equidistant division etching to be scanned point, H₁Represent that sub-surface is damaged Hinder the minima of depth detection scope, H_NRepresent sub-surface damage depth detection scope maximum, R (x, y) represent point (x, y) Material removal amount in the unit interval at place, (x, y) expression is left away in X direction except function centre distance respectively x, Y-direction are left away Except the point that function centre distance is y.

6. according to the nanoscale optics sub-surface damage based on ion sputtering described in any one in Claims 1 to 5 Detection method, it is characterised in that described step 2) detailed step include:

2.1) in slope, mark the point to be measured of different etching depth；

2.2) utilize atomic force microscope that the point to be measured of labelling is carried out damage measurement, if some point to be measured can be observed To nanometer damaged structure, then show that corresponding depth areas to be measured exists sub-surface damage；If all points to be measured are the most not Observe damaged structure, then show that detected optical element does not exist sub-surface damage.